Quaternary Nonglacial Geology : Conterminous US

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U 1980 1989

The Geology of North America Volume K-2

QuaternaryNonglacial Geology: Conterminous U.S.

Edited by Roger B. Morrison Morrison and Associates 13150 West Ninth Avenue Golden, Colorado 80401

t234oo051o(0

1991

931,041090035 9303 6 FDR 4ASTE TDR U ,rWRSITYOF NEVADAS LAS VEIM WI-li LBRARY 6-, Acknowledgment

Publication of this volume, one of the synthesis volumes of The Decade of North American Geology Project series, has been made possible by members and friends of the Geological Society of America, corporations, and government agencies through contributions to the Decade of North American Geology fund of the Geological Society of America Foundation. Following is a list of individuals, corporations, and government agencies giving and/or pledging more than $50,000 in support of the DNAG Project:

Amoco Production Company Pennzoil Exploration and ARCO Exploration Company Production Company Chevron Corporation Phillips Petroleum Company Cities Service Oi and Gas Company Sbell Oil Company Diamond Shamrock Exploration Caswell Saver Corporation Standard Oil Production Company Oryx Energy Company (formerly Exxon Production Research Company Sun Exploration and Production Getty Oil Company Company Gulf Oil Exploration and Production Superior Oil Company Company Tenneco Oil Company Paul V. Hoovler Texaco, Inc. Kencon Minerals Company Union Oil Company of California Kerr McGee Corporation Union Pacific Corporation and Marathon Oil Company its operating companim Maxus Energy Corporation Union Pacific ReOOuMcs company McMoRan 0i and Gas Company Union Pacific Railroad Mobil Oi Corporation Company Occidental Petroleum Corporation Upland Ilndusuries Corporation US. Department of Energy

Data *1991 by The Geological Society of America, Inc= Lxary of Congress Catalogtng-ln-Publication All rights reserved. Quaternary nonglacial geology : conterminous US. / edited by Roger B. Mo-rison. p. an. - (The Geology of North America; v. K-2) materials aubject to thiso pyoty and included . Includes bibliographical references and index. n30J110 yslume may bpoboxcoped fixr thedoncoorndrcial ISBN 0-8137-5215-9 in ientiUicoreductiionalsed adv'ainCcM'L 1. Geology, Stratigraphic-Quaternary. Z Geology-United States. L Morrison, Roger B (Roger Barron), 1914- . H.Series. DAp ht is not caimed on any material prepared, QE696.Q336 1991 arc sovernmntereiployees within thescope oftheir b 551.7'9'0973-dc2O 91-23046 aP bployment. Published by The Geological Society of America. In= 3300 Penrose Place, P.O. Box 9140, Boulder. Colorado g3030

Printed in USA.

Cover Photo: East bluff of the Walker River viewed from middle of Weber the Eetza Alloformation (130-350 ka) in Lake Lahontan's northern aubbasins. gravel Damn At least two million yeams of Lake Lahontan lacutrine and subaerial history Below another unconformity is 6 to 10 m of darker gray, chiefly lacustrine are ahown here in about 42 m of atrata in the Walker Like basin, the aouthern and sand (the upper pre-Eetza unit of Morrison and Davis, 1984b, p. 24, which most of Lake Lahontan's aubbasirs The top 6 i (light gray and light yellowish contains the I Ma Glass Mountain G tephra layerý Beneath a marked erosional gray) are lacustrine gravel and sand of the middle member of the Sehoo Allofor unconformity and extending to below the modem flood plain of the Walker River mation (about 13 ka) unoonformably overlying eolian and slopewash sand bear is 20+ m oftan-gray alluvial gravel and and intercalated with many palemols--a ing the Wyemaha Geosol (35-130 ka). Beneath another unconformity is 9 to unit considerably older than the Lovelock Alloformation in the northern basins. 10 m of medium to pale gray lazustrine gravel, aand, and salt equivalent to parts of Photo by R. B. Morrison.

10 9 8 7 6 5 4 3 2 1

ii .4

iv Contents

K.Ar dauing of Quaternary olcanwc rocks ...... 49 P. L. Damon

Fission-track dating ...... 53 C. W. Naescv and N. D. Namser

Conventionaluranium-serles and uranium-trenddating ...... 55 B.J. Szabo and J. N. Rosholt

Paleomagneticdating ...... 60 J. C. ddicoast

Th7emo/-inescence dating ...... 61 S. L Forman and M. N. Machette

Amino aid geochronology of foil mollusks ...... 65 D. L. Muhs

4. Quaternaryvolcanism in the western conterminous United States ...... 75 R. G. Luedke and R. L. Smith

5. Quaternarytephrochronology ...... 93 A. M. Sama-Wojcicki and J. 0. Davis

6. Tephrochronologiccorrelation of upper Neogene sediments along the Pacific margin, conterminous United States ...... 117 A. M. Sarna-Wojcicki, K. R. Lajoie, C. E. Meyer, D. P. Adam, and H. J. Rieck

REGIONAL CHAPTERS

7. Quaternarygeology of the Pacific margin ...... 141 W. R. DuprE, R. B. Morrison, H. E. Clifton, K. R. Lajoie, D. J. Ponti, C. L Powell II, S. A. Mathieson, A. M. Sarna-Wojcicki, E. L. Leithold, W. R. Lettis, P. F. McDowell, T. K. Rockwell, J. R. Unruh, and R. S. Yeats

Imtroducion ...... 141 W. RLDupre and H. E.CMifton

Quaternarycoas andshatow-mrine facies sequenc= Northern Ca/ifornia and die Pac#1c Northwest ...... 143 H. E. Clifton and E. L Leithold

Quaernary.gmradgwkp and geomorphic surfaces of de Wruilamerte Valley. Oregon...... 156 P. F. McDowdl

Qaernarygeolov of the Great Vaet. Californu ...... 164 W. f. Leuti and J. R. Unruh

Quaternarygeology of te So-them CaliforniaCoast Ranges ...... 176 W. R. Duprh

Quaterniaygeology of the Ventura and Los Angeles basm Cahjbnia ...... 185 R.I Yeats and T. K. Rockweil The Geology of North America Vol. K-2. Quaternarv Nonglactal Geology. Conterminous US. The Geologicai Society of Amenca. 1991

Chapter 3 Dating methods applicableto the Quaternary

John N. Rosholt* US GeologicalSurvey. MS 963. Box 25046. Denver FederalCenter. Denver. Colorado 80225 Steven M. Colman US Geological Survey. Woods Hole. Massachuseas 02543 Minze Stuiver Departmentof GeologicalSciences and Quaternarv Research Center. Universuty of Washington, Seattle, Washington 98195 Paul E. Damon Departmentof Geosciences. Universaty of Arizona. Tucson. Arizona 85721 Charles W. Naeser. Nancy D. Naeser, Barney J. Szabo. and Daniel R. Muhs US GeologicalSurvey, MS 424, Box 25046. Denver FederalCenter. Denver, Colorado 80225 Joseph C. Liddicoat Universigv of Ca'fornia,Santa Cruz California95064 Steven L Fornan Institute of Arctic and Alpine Research and Departmentof Geological Sciences. University of Colorado.Boulder, Colorado 80309 Michael N. Machette and Kenneth L Pierce U.S GeologicalSurvey, MS 913. Box 25046, Denver Federal Center.Denver. Colorado 80225

SUMMARY OF QUATERNARY ments and should not be considered definitive; the entries for DATING METHODS applicability, age range, and optimum resolution are particularly interpretive. Details concerning assumptions, analytical tech Steven M. Colman and Kenneth L Pierce niques, uncertainties, and interpretations should be obtained from specialized references using the key references in Plate 2 as a INTRODUCTION AND COMPILATION OF guide. The dating methods described range from well-known and QUATERNARY DATING METHODS established techniques to experimental procedures whose results are subject to considerable interpretation. A wide variety of dating methods are used in Quaternary Key references included on Plate 2 are intended as an entry research. and each method has many applications and limitations. into the vast literature on dating methods-, space prohibits a more Because of this variety, we cannot discuss the applications and complete listing. We have emphasized recent review papers and limitations of all methods here. The more versatile and widely notable examples of applications as sources of additional refer used methods, including 14C, K/Ar, fission-track, U-series, pa ences and information. Dating methods discussed in other leomagnetism, thermoluminescence, and amino acid dating are sections of this chapter are indicated by asterisks in the summary treated more comprehensively in this chapter than other methods table. The first five references are reviews or edited volumes that that are shown on the summary chart. The summary chart is discuss Quaternary dating methods in general; references 6-11 provided here to give an overview of dating work and research are edited volumes that focus on individual methods or closely for the Quaternary. related methods. In the interest of brevity and clarity, we have not This summary consists mainly of a table (Plate 2) that is cited individual papers in these edited volumes. Some dating modified and updated from Colnan and Pierce (1977, Plate I, methods are based on fundamental geological principles, such as ref. 66). The table isintended as an overview and concise guide to stratigraphy, for which references are deemed unnecessary here. Quaternary dating methods. It contains many subjective judg- For the purpose of our discussion and summary table, it is useful to classify dating methods, which can be done in a variety of ways. Perhaps the simplest classification is one that groups methods that share similar assumptions, procedures, or applica- Rmholt. J. N., Columan. S. M.. Stuivcr. M, Damto. P. F-, Naeser, C. W. Naeser. N. D., Szabo. t. N. and S. J. Mubs. D. . Liddicoa. J. C. Fommn. S. L. Machet. Pierce, K. L.. 1991. Dating methods applicable to the Quaternary, in Mo'rison, R. B.. ed. Quaternary nonglacial geology-. Conterminous US. Boulder, Colorado. Geological Society of Amenca. The Geology of North America v. K-2.

45 J.N. Rosholt and Others S46

TABLE 1. CLASSIFICATION OF QUATERNARY DATING METHODS*

Numerical-age------...... Calibrated Age------.--...... Relative-age ------Correlated-age-

Sidereal Isotopic Radlogenic Chemical and Geomorphic Correlation Biochemical

Historical records 14C Uranium-trend Amino acid Sol profile Stratigraphy racemization development Dendrochronology K-Ar and Thermoluminescence Obsidian Rock 3 0 and mineral Tephrochronology 9Ar-4 Ar hydration weathering

Varve Uranium- Electron-spin Tephra Rock varnish Paleomagnetism Chronology series resonance hydration

Fission 101pb5Uchenometry Progressive land- Fossils and track form modification artifacts Other cosmo- Sol chemistry Rate of deposition Stable isotopes genic isotopes Rate of deformation Astronomical correlation

Geomorphic position Tectites and mlcrotectites *Oashed line Indicates the type of result most commonly produced by the methods below it dotted line Indicates the type of result less commonly produced by the methods below ft. tMethods above this line routinely produce numerical ages; methods below the line are more experimental and Involve nonradloactive processes or processes whose effects on age estimates are not well established. tions. Accordingly, we have grouped dating methods into six (quote from Taylor [1987] which also contains other relevant categories (Plate 2; Table 1, lower part of header): sidereal references). The relatively large sample size (one pound of car (annual), isotopic, radiogenic, chemical and biological, geomor bon) needed at that time may explain the reluctance of the ar phic, and correlation methods. Dating methods may also be class cheologists present at the meeting to commit themselves to the ified by the type of result they produce (Plate 2, Table I, upper combustion of precious museum materials. The 40 years of prog header); numerical-age (quantitative estimate on a ratio scale), ress in radiocarbon dating technology is best illustrated by calibrated-rate (numerical-age based on the rate of a process rate comparing the above required sample size to the 0.05-mg C that has been calibrated by another dating method), relative-age sample (Nelson and others, 1986) recently used for a radiocarbon (chronologic order, in some cases induding some measure of age determination by accelerator mass spectrometry. magnitudes of age differences), and correlated-age (correlated to During the last decade, two major improvements were independently dated deposits or to standard stratigraphic made. A major breakthrough has been the above-mentioned di sections). rect detection of 14C in mg samples through accelerator mass RADIOCARBON DATING spectrometry. In addition, the conventional decay counting tech nique can now deliver an enhanced level of exactness (Stuiver, M'nze &uiver 1978) that has resulted in a high precision radiocarbon age termi nology. It is especially INTRODUCTION the latter improvement that is important for radiocarbon timescale calibration. An early interest in radiocarbon dating of geological samples The cosmic ray-produced 14C isotope is used for a wide was expressed by Richard Foster Flint when attending a lecture array of scientific investigations. The technique is used in many given by W. F. Libby at the 1948 Viking Fund Supper Confer discilirs, and requires of the radiocarbon "expert" a truly inter ence in New York. At the conclusion of Libby's remarks, the disciplinary mode of thinking. Applications can be found in cos audience remained mute until Flint commented, "Well, if you mic ray and solar physics (paleochanges in cosmic ray flux and people are not interested in this, I am .... If you don't want solar surface conditions [Stuiver and Quay, 1980]), oceanog anything dated, I am for it, and would like to send some material" raphy (the mixing and circulation of water masses [Stuiver and Dating Methods Applicable to the Quaerna4 47

others. 1983b]), climatology (long-term changes in carbon exchange with its environment. In other words, samples should reservoir properties related to the Holocene-Wisconsin climate not receive, between the moment of formation and the moment change (Andree and others. 1986b]), environmental chemistry of sampling, an admixture of carbonaceous material having a 14 14 (fossil fuel dilution of atmospheric CO 2 [Stuiver and Quay, specific C content different from that of the original sample. 198 1] and particulate carbon and methane in the atmosphere The user can reduce the influence of contamination by selec [Currie and others, 1983; Levin, 1985]), glaciology (ice core tive sampling; for instance, collect samples far below the surface stratigraphy (Andree and others, 1986a]), archeology (chronome where root contamination is usually less. Remaining rootlets try). geology (geochronometry as, for instance applied to earth should be removed before drying the sample. Part of the labora quake frequency research (Sieh. 1984]), hydrology (groundwater tory procedure is oriented toward reducing the influence of con dating (Monk, 1980]), and geophysics (earth geomagnetic field taminants. Organic materials are acidified to remove carbonates, change deduced from long-term atmospheric 14C change (Stem and an alkali treatment is given to appropriate samples for the berg and Damon, 19831). removal of humic materials. The majority of geological applications is directed toward In addition to the above in situ contamination, foreign mate the determination of time. Because 14C disappears fairly rapidly rials can also be introduced during sampling and transport, or from the geological scene through radioactive decay, the applica during storage and handling of the sample in the laboratory. ble timespan is relatively short. With a half life of 5,570 yr, the These additions can usually be entirely avoided by following amount of 14C in a sample is reduced by a factor 2 every 5,570 proper procedures. However, for in situ contamination, the best yr. For 10 half lives, or 55,700 yr, the reduction is a factor 210 = possible procedures, although minimizing the effects, do not nec 1024. For the maximum ages of about 75,000 yr determined so essarily remove all contaminants. far. the amount of 14C in a sample is only 1/10,000 of its original The influence of specific levels of modem contamination is level. Clearly the timespan limitations of the radiocarbon method largest for the older samples. As mentioned, a sample in the result from the obvious statistical truth that measurement error mid-50,000-yr range contains only 1/1,000 of its original activ becomes infinitely large when the activity to be measured ap ity. The addition of a similar minute amount of modern contami proaches zero. nation will double its 14C content, and reduce the sample age by As with all measuring devices, there are technical factors one half life or 5,570 yr. For the 75,000-yr sample, contamina that limit the precision and accuracy with which an age can be tion levels of only one part in 10,000 will have a similar impact. determined. Major limitations are also imposed by the degree to This should be a warning against attaching too much significance which the basic assumptions of the 14C dating method are cor to very old dates. But even the forewarned user should realize that rect. Whereas improvement of the technique can still lead to the existence of samples with 75,000-yr-old radiocarbon ages further progress, the limitations imposed by the basic assumptions implies an upper limit of 14 C contamination of I part in 10,000. provide much greater obstacles. For instance, with high-precision Thus it must be possible to collect "similar" samples (samples dating it is now possible to date a sample with a radiocarbon age containing less than I part in 10,000 14C contamination) in the error of ±15 yr. After converting the radiocarbon age to a cal 50,000 to 60,000 yr range. These samples would then yield relia endar year age, however, there can occasionally be an uncertainty ble ages because the low level of 14C contamination would be of centuries in the calibrated age. negligible. A conventional radiocarbon age can be calculated from the Contamination with older materials (e.g., graphite) is usu measured 14C activity by using the conventional radiocarbon half ally of lesser import than contamination with younger materials 14 life (5,568 yr) and by assuming constancy of atmospheric C because the relative change in 14C activity induced by the con level in the past (Stuiver and Polach, 1977). The calculation also taminants is often greater for the younger additions. For instance, 13 corrects for isotope fractionation by using the C isotope as an a 10-mg-C-old (lacking 14C) addition to a I-g-C sample reduces indicator of possible enrichment or depletion of sample 14C dur the sample 14C activity by I percent for all samples of any age. ing its formation. The primary function of the laboratory is to This one percent 14C dilution results in an 80-yr-older radiocar 4 measure the remaining 1 C activity of the sample and to deter bon age, because 14 C decays with a constant rate of approxi mine the uncertainty (standard deviation) in the measurement. mately I percent per 80 yr. A 10-mg addition of younger material This information is then converted into a conventional radiocar to a large sample also has relatively little influence when the bon age ± a standard age error. sample is very young (after all, adding material of the same age would not change the age of the contaminated sample), but usu CONTAMINATION ally has drastic consequences for the age of an old sample. For instance, a 37,000-yr-old sample retains about I percent of its Given the age supplied by the laboratory, the user has to original 14C activity. Doubling this activity by adding to a 1-g C decide whether the number given provides relevant information. sample another 10 mg C of modem material (defined as mateial A major concern will be adherence to another assumption: The of zero age or 100 percent 14 14 C activity) reduces the age of the remaining sample C should be representative of its original contaminated material to 31,400 yr. activity, which implies a dosed system with respect to carbon A detailed discussion of the contamination-induced change A

48 .8N. Roshoft and Others

in radiocarbon ages is given by Grootes (1983) and Bradley librium with the atmosphere to 2,500 yr for lakes with important (1985). groundwater bicarbonate contributions (Stuiver, 1975). . Given the amount and activity of the contamination, the A weakness in the above approach is the assumption of a "new" radiocarbon age can be very precisely calculated. In actual constant past reservoir deficiency. Variable lake levels and practice, however, the influence of contamination can often only bicarbonate concentrations may well cause a variable reservoir be evaluated in general terms such as, "the charcoal sample was deficiency. Here again, accelerator mass spectrometry provides a very well preserved and a visual inspection indicated an absence breakthrough because it is now possible to measure at various of rootlets:" therefore, the chances of retaining contaminants after depths the age differences between plant macrofossils (in equilib pretreatment are small. rium with the atmosphere), lake carbonate, and gyttja. The first The nonhomogenous dispersal of contaminating material study of this kind has been made for the sediments of a small has become important now that mg C samples are measured. For closed basin of the Lobsingensee, Switzerland (Andree and oth instance, consider a lake core with 5 percent graphite contamina ers, 1986c). tion. Combustion of a large sample would produce an age 400 yr too old. But a mg C sample selected randomly could well be a THE RADIOCARBON AGE ERROR graphite particle and result in an infinite age. However, here the small-sample approach can also be used to eliminate the influence Most analytical facilities outside the radiocarbon commu of graphite (or coal) contamination by selecting macrofossils (e.g., nity estimate an error (one standard deviation) in a measurement leaves) that were originally in 14C equilibrium with the by assessing the data obtained for repeat analyses of identical atmosphere. samples. The histogram of repeat analyses gives the precision of measurement Repeat analyses are only made for a limited RESERVOIR EFFECTS number of samples because it is not cost effective to make multi ple measurements of each sample. Thus the precision obtained for a limited number of analyses is used for an error estimate of all A radiocarbon age is calculated with the aid of an equation sample measurements. in which the ratio of the measured sample 14C activity to pre The error in precision is not the only error in a measure 4 sumed initial 1 C activity is the important parameter. The initial ment. A laboratory can be quite reproducible in its repeat mea activity used in the equation is that measured for the laboratory surements, yet be off in accuracy through a systematic deviation oxalic acid standard. The oxalic acid 14C has been calibrated from the true value. Systematic errors are usually evaluated against the 14C activity of a 19-century wood sample. Thus the through interlaboratory comparisons of results obtained for the initial activity used for the calculation of a conventional radiocar same sample. bon age is tied to atmospheric 14C activity because, after correc Contributing to the radiocarbon age error is the statistical tion for isotope fractionation, the wood reflects atmospheric 14C uncertainty in a radioactivity measurement. Radioactive disinte leveL gration varies randomly about a mean value, and measured count The 14 C content of nonatmospheric carbon reservoirs (e.g., rates of the same sample form a Poisson probability curve. Even oceans or lakes) may differ from the atmospheric value. Thus, a the laboratory with the most sophisticated instrumentation so-called reservoir correction has to be applied to account for the cannot escape the realities of Poisson counting statistics. Thus the age differences between reservoirs. As these reservoirs usually Poisson error in the count rates, when converted into radiocarbon have a lower specific 14C activity (activity per gram C) than that years, provides a minimum age error. of atmospheric carbon dioxide, the conventional radiocarbon Unfortunately, the radiocarbon community has traditionally ages have to be reduced. been satisfied with reporting age errors based on counting statis The reservoir correction for the surface mixed layer of the tics alone. It is now dear that this was an unwise choice. Interlab midlatitude ocean is approximately 300 radiocarbon yr. A con oratory comparisons of results obtained for the same samples ventional radiocarbon age would therefore be 300 yr too old for show substantial underreporting of the radiocarbon age errors samples properly corrected for isotope fractionation (for details, (The International Study Group, 1982; Stuiver, 1982). In order see Stuiver and Polach, 1977). For oceanic regions where upwell to arrive at a realistic estimate of the precision error, as well as ing of older waters reduces surface water 14C activities even possible systematic errors, the recipient of a radiocarbon age more, the reservoir correction is still larger. The largest correction should request from the supplier information on interlaboratorY is for Antarctic coastal regions, where shells of the last century comparison and reproducibility measurements. may have conventional radiocarbon ages of 1,000 to 1,300 yr (Stuiver and others, 1983a). TIME-SCALE CALIBRATION The ages of the top of the sediment (or, to be more precise, a few cm below the top to avoid the influence of nuclear bomb 14C) As previously mentioned, a radiocarbon age is derived from of lake cores reflect the reservoir deficiency of those lakes. These a comparison of present-day remaining 14C activity to an atmo may range from a few hundred years for lakes approaching equi- spheric 14C level which is assumed to have been constant during DatingMethods Applicable to the Quaterna4 49

14 did change, it is the past. As atmospheric C levels, however, o gqjent that a radiocarbon age is only an approximation of the ,,.tual age in calendar years. For a conversion of a radiocarbon curve is needed 4,g to1 more realistic calendar date, a calibration age ,Ahere radiocarbon ages of wood samples are plotted versus ,n calendar years. Such calibration curves are obtained by deter independ a mining the radiocarbon ages of wood samples dated ently by dendrochrOnological means. e0 The construction of a calibration curve from radiocarbon 0I C ages with limited precision is not a simple matter. Not only e- ,hould the standard error in the determination be as small as in that possible. but the calculation of this error has to be realistic L 1 should account for all variability encountered in the laboratory N procedures. Proof of accuracy has to come from a comparison of results obtained in two or more laboratories. High-precision calibration curves covering the last 4.500 yr 4000 3500 3C00 2500 "I1.00 now available. The internationally recommended 4.500-yr are RAO.IGCR8ON AGE (YWS 9P) curve (Stuiver and Era, 1986) was obtained by combining the data of the Seattle and Belfast radiocarbon laboratories (Stuiver Figure 1.The ranges, in calendar years, obtained from the calibration of radiocarbon ages up to 4,000 yr B.P. and Pearson. 1986; Pearson and Stuiver. 1986). The comparison of the Seattle and Belfast data demonstrate systematic differences oi only a few radiocarbon years and age differences for contem poraneous samples that can be fully explained by the precisions and Seattle laboratory. The above high quoted by the Belfast of cal years. Multiple intercepts are responsible for the wiggly curve has. on average, a radiocarbon-age error of ± 12 precision nature of the individual cal age uncertainty. ,r IStuiver and Pearson, 1986) for bi-decadal wood samples. For the above example (zero error in the sample 14C deter curves are given in the special 1986 Additional calibration mination), 50 percent of the ages show an age range larger than isue of Radiocarbonon age calibration. Dendrochronologically expected from the uncertainty in the calibration curve alone. This dated wood currently available covers nearly the last 10,000 yr, increases to 72 percent for an age determination with an 80-yr thousand years is possible using varve and an extension by a few error (i.e., the oldest and youngest cal ages derived from a specific chronologies (Stuiver and others 1986). Detailed age calibration 72 percent of the further back in time is not yet possible. radiocarbon age differ by more than 160 yr in cases). Unfortunately, the benefits of high-precision dating (with Although the availability of a precise calibration curve re radiocarbon-age error circa 15 yr for 6-g C samples) appear to be margin of error in cahlbrated AD/BC dates, a duces the partly, but not always, negated by the conversion process. substantial uncertainty remains, because a given radiocarbon age may correspond to several AD/BC dates. A continuous spectrum 14 Iseven possible when C levels in the atmosphere decline at the K-AR DATING OF QUATERNARY %tmerate as 14C declines through radioactive decay. All samples VOLCANIC ROCKS formed during such an interval will have the same radiocarbon content at the end of the interval, and thus yield identical radio PaulE. Damon carbon ages. Such a major disaster area for radiocarbon calibra tion occurs between 420 BC and 750 BC where radiocarbon ages INTRODUCTION are nearly all in a narrow 2,430 to 2,470-yr-BP band. The wiggly nature of the calibration curve causes a radio There are two basic methods of isotopic dating that make carbon date to be converted in a range (or ranges) of calibrated use of the radioactive decay of 40K to 40Ar. These are the conven ,cal) AD/BC (or cal BP where 0 BP equals 1950 AD ages), even tional K-Ar method and the 4°Ar/ 39 Ar method. In the conven if the radiocarbon-age determination could be made without tional method, the K content of the sample is usually measured error. Figure I is the graphic representation of these ranges en by flame photometry or atomic absorption spectrometry, and the ,-ountered when converting ideal (zero error) radiocarbon ages radiogenic 4°Ar by mass spectrometric isotope dilution. In the Into calibrated ages. The baseline ranges of up to a few decades 40Ar/ 39 Ar method, 39 K is first converted to 39Ar by an n, p are due to the uncertainty in the calibration curve, whereas the reaction in a nuclear reactor, and the argon isotope ratios are larger deviations are obtained when the conversion process is determined by mass spectrometry. The 4 0Ar/ 39 Ar method has influenced by the wiggles. A large vertical Figure 1 spike repre the advantage of allowing both isotopes to be released from sim 'ints a radiocarbon age that, after conversion, gives a wide range ilar K sites in minerals by incremental heating. This yields a -v

50 J. N. Rosholt and Others

TABLE 2. EFFECT OF CONTAMINATION BY 70 MICROGRAMS OF A PRECAMBRIAN FELDSPAR (1.5 Ga) CONTAINING 4.00 X 104 MOLES/GRAM RADIOOENIC 4OAr ON A 30-ka FELDSPAR

Weight K 4OAr Radlogenic 'mAr Atmospheric 4Ar Almospheric K-Ar Date (g) (%) -12x 10 mole .12x 10mole (%) (ka)

Uncontaminated 12.600 9.48 6.36 20.6 76.4 30.7 a 1.6

Contaminated 12.600 9.48 9.16 20.6 69.2 44.2 * 1.6

spectrum of 4oAr/ 39Ar ratios as a function of the temperature of failure to apply the correction would result in a 19 percent error incremental release. Even though argon may have been lost from in the radiogenic 4oAr measurement. mineral sites in which argon was less tightly held, plateaus are There will be an error in the atmospheric air correction if the frequently obtained at higher temperatures for tightly held argon, atmospheric Ar has been fractionated prior to measurement For and the plateau data yields a better value of the time since the example, atmospheric Ar entering a rapidly cooling volcanic rock sample began retaining argon by correcting partial argon loss. may not fully equilibrate. As a result of equipartition of energy, The 4°Ar/ 39Ar method is particularly useful for dating geologi the average velocity of 36Ar is 5.4 percent greater than 4oAr and cally old samples where there is a high probability of resetting of will equilibrate faster. The effect of nonequilibration would be a the K-Ar clock by argon loss during subsequent thermal events. reduction in apparent age as a result of over correction for atmo Thermal resetting is much less probable and relatively easily rec spheric Ar. It will be shown later that this effect can be minimized ognized in Quaternary volcanic rocks, but other problems must by using ground-mass crystallites rather than phenocrysts in the be overcome. Several books and many papers have been written K-Ar dating of Quaternary volcanic rocks. on the subject of K-Ar dating. A summary of both methods with The effect of contamination by extraneous older materials many references is available in Faure (1986). can be very severe, as shown in Table 2. Large xenocrysts that Three major problems are encountered in the dating of Qua may contain inherited radiogenic 4OAr must be removed and ternary volcanic rocks: (1) The correction for the atmospheric extreme care taken to avoid contamination during sample argon is very large and subject to error due to isotope fractiona preparation. tion resulting from incomplete equilibration (Krummenacher, Radiogenic OAs4 is released from rocks heated by magma, 1970), (2) samples are more easily biased by extraneous older and argon is soluble in the magma and minerals. At the low Ar materials (e.g., see Fig. 8-7 of Dalrymple and Lanphere, 1969), pressures likely to occur in magma chambers of volcanic flows. (3) amounts of excess radiogenic argon that would be negligible Henry's Law will hold (Damon, 1970): for older samples may seriously affect the apparent age of Qua ternary volcanic rocks (for review see Chapter 8 of Dalrymple 4°Ar£ = Sp (1) and Lanphere, 1969). Argon has three stable isotopes, which compose nearly I where 4OArE = moles/g of dissolved radiogenic 4oAr, S 2 percent by volume of the Earth's atmosphere. The isotopic moles/g dissolved at I bar, and p = the partial pressure of argon. abundance of the three isotopes according to Nier (1950) is: 36Ar For example, S for albite at 10001C is 3.9 x 10-9 moles/g. If the (0.337%), 38Ar (0.0630%), and 4oAr (99.60%). In the conventional partial pressure of 4oAr in the magma reached .001 bar, the albite method, measurement of 4oAr and 36 Ar is made by isotope dilu would dissolve 3.9 x 10-12 m/g of 4oAr. This amount would tion in which the diluent is very pure 38 Ar. The concentration of prohibit a meaningful date for a Quaternary volcanic rock. For 4oAr and 36Ar is measured relative to the known amount of 38As tunately, upon extrusion, the excess 4oAr will tend to escape, but diluent. Atmospheric oAr4 must be subtracted from the measured the mineral will also tend to equilibrate with atmospheric argof). sample 40Ar to obtain radiogenic 40Ar. 36At is used as a measure Again, as will be shown, the smaller the mineral, the more rapid of the atmospheric componentL The atomic ratio of 4oAr to 36At the equilibration. in air is 295.5 but, as a result of instrumental fractionation, the ratio measured when pure air argon is introduced into a mass EQUILIBRATION OF ARGON AT ELEVATED spectrometer may not be exactly 295.5. A fractionation correc TEMPERATURES tion must be determined by repeated, precise measurement of air argon samples. As an example, consider a Quaternary sample A good approximation to diffusion in minerals can be ob argon measurement comprising 95 percent air and 5 percent tained by use of the concept of an escape constant, Ad (Damon. radiogenic 4oAr. If the fractionation correction is 1 percent, a 1970): I Dating Methods Applicable to the Quaternar. 51 TABLE 3. TIME FOR 99 PERCENT LOSS OF EXCESS 4OArs AT 1,050' C*

r, (cm) 0.142 0.071 0.027 0.006 0.001

t 1 month 1 week I day 1 hour 2 minutes 4 *Do a 1.18 x 10- cm2/sec and E a 26 Kcal/mole.

TABLE 4. TIME FOR 99 PERCENT LOSS OF EXCESS 4OAr,*

T 20" C 50"C 100" C 2000 C 3000 C 400 C t(yr) 1 1.22x 101 1.93 x 10 B.44 x 10 5.08 x 103 41 1.4

T 515*C 590* C 7150 C 1,030" C 1.1000 C t I month 1 week I day 1 hour 35 minutes

"r, a 0.005 cm; diffusion parameters are those of Table 2.

gD Ad- - (2) t, 4OArd(o) is the initial concentration before eruption, t is the time after eruption, and g in Equation 2 is (2.405 2). Because the where g is a geometry factor, D is the diffusion coefficient, and X square of the radius (rb)and temperature (T) enter into the expo is the pertinent diffusion dimension. e.g., the radius of a sphere or nential of Equation 4, the rate of loss is critically dependent upon the thickness of thin slab of large area. D is related to temperature crystal size (Table 3) and temperature (Table 4). At magmatic by-the Arrhenius equation: temperatures, ground mass plagiodase microlites would lose 99 percent of excess radiogenic argon within minutes, whereas phe D = D, exp (-E/RT) (3) nocrysts would retain much of their excess radiogenic argon dur ing the cooling process. This effect would tend to yield where E is the activation energy for diffusion, R is the Boltzmann anomalously old ages. On the other hand, the phenocrysts will constanL and T is the temperature in degrees Kelvin. also not equilibrate completely, resulting in fractionation of at At magmatic temperatures in the magma chamber before 36 mospheric argon. The excess Ar, when multiplied by the air eruption, argon will rapidly equilibrate, and the argon content of ratio, will tend to produce anomalously young ages. Thus, ages the mineral will be the excess `mAr supported by the partial which are too young or too old may result, depending on which pressure of 4OAr in the magma chamber (Equation 1). effect is dominate in each particular case. Upon extrusion, the lava with its contained minerals will Groundmass plagiodase microlites lose their excess argon tend to approach equilibrium with the atmosphere. The excess rapidly and equilibrate rapidly with air. Consequently, they tend 4OAr will escape and atmospheric Ar will enter. For the dating of to yield consistent ages if not reset by subsequent thermal events. Quaternary rocks, we require a dose approximation to equilib 4 36 It should be emphasized that a temperature of 100*C sustained rium, i.e., a OAr/ Ar ratio of 295.5. For example, consider a for a sufficiently long time could cause a significant error in the small plagioclase crystal in the melt with Do = 1.18 x 2 age of plagiodase microlites. From Table 5, it can be seen that a 10-4 cm /sec and E = 26 Kcal/mole (Laughlin, 1969), and ap 0 temperature of 100 C sustained for 60,000 yr would result in a proximate its geometry as that of a cylinder whose length is great 15 percent loss of argon from the microlites. compared to its radius rc. According to Jost (1960), the escape of excess `mAr for losses greater than 30 percent closely approxi COMPARISON OF THEORY WITH PRACTICE mates an exponcatial relationship. '°Ar 5(o)(4 Theory then suggests that for young samples that have not 4OA91) - 24052 exp(--dt) (4) been deeply buried or otherwise thermally reset, plagioclase mi 0 crolites are better K-Ar docks than phenocrysts that may not where `mArE(t) is the average concentration of ' ArE after a time have completely lost excess argon or equilibrated with air. Our 52 J. N. Roshoft and Others

TABLE 5. PERCENT 4OAr LOSS AT 1000 C* Percent loss 15 30 45 60 75 90

t(yr) 6 6.0x 104 1.7x 103 4.5 x 106 1.1x10 2x106 3.9x 104

*DIffusion parameters of Table 2, r, = 0.005 cm.

TABLE 6. WORST CASE EXAMPLES FOR K.Ar DISCORDANCY BETWEEN PLAGIOCLASE MICROUTE CONCENTRATES AND PHENOCRYSTS Sample No. Type K 'OArrd 'OAr., K-Ar Date (%) (10"12 mlg) (%) (Ma)

UAKA-6-65 Microlite 0.652 3.59 88.4 2.43 * 0.32 UAKA-6.65 Phenocryst 0.190 3.14 39.2 9.52 * 0.81 UAKA-65-365 MicroUte 0.992 10.82 37.2 6.28 * 0.15 UAKA-85-365 Phenocryst 0.318 1.88 89.3 3.41 * 0.24 UAKA-85-367 Mlcrolite 0.762 8.301 40.6 6.27 a 0.16 UAKA-65-367 Phenocryst 0.135 0.962 79.6 4.10 * 0.24 UAKA-85-378 Microlfte 1.202 1.032 83.1 0.49 * 0.035 UAKA-85-378 Phenocryst 0.162 0.271 95.6 0.967* 0.158

experience has confirmed theoretical expectations. Dates on mi It is important to sample the Quaternary rock to be dated in crolite concentrates yield reasonable results consistent with stra such a way as to minimize error. The quickly quenched parts of a tigraphy, whereas K-Ar dates on phenocrysts are often discord flow may not have been purged of excess argon or equilibrated ant. This is true not only for plagioclase; biotite and hornblende with air. The rubbly bottom of a flow may contain extraneous phenocrysts also frequently yield discordant ages for Quaternary older material, and vuggy samples may contain exorbitant rocks. However, sanidine phenocrysts usually give concordant amounts of air. We prefer to sample the massive interior of the dates. flow; it has few vesicles and has cooled relatively slowly, allowing Table 6 shows the worst cases that we have observed during time to purge excess 4OAr. Typically, air corrections are usually years of dating young rocks. Sample UAKA-6-65 was one of the also much lower for samples from the interior of the flow. earliest and the most extreme examples of the not infrequent In preparing the Quaternary volcanic rock sample, pheno discordance between K-Ar dates on plagioclase microlites and crysts, xenocrysts, and xenoliths should be removed before phenocrysts from the same pre rock and, fortunately, alerted us to the paring the microlite concentrate. Glass, clay, and ferromagnesians problem. Phenocrysts from this sample are very large, up to 2 cm, should be removed from the sieve-classified fraction transucent and semiprfect. (e.g., This sample had not completely < 100>150) by the usual heavy-liquid and magnetic-separation equilibrated with air nor lost all of its excess 4OAr. However, the methods. Carbonate, if present, and residual dominant effect glass should be re was the large amount of excess 4oAr. This also moved by washing in dilute acids. occurred for sample UAKA-85-378. The dominant effect in samlpes UAKA-85-365 and UAKA-85-367 seems to be incom CONCLUSIONS plete equilibration with air, leading to over correction. An added factor in favor of dating the microlites is the much The fundamental limitation in K-Ar dating of Quaternary higher K content of the more sodic microlites compared to the volcanic rocks is not our inability to measure argon precisely. more calcic phenocrysts. This results in a higher radiogenic 4OAr Rather, it is intrinsic to several basic assumptions of the method content and, typically, a lower air correction. Sample UAKA-6 which are not always met. Specifically, the sample to be dated 65 is atypical because of its extremely high 4 excess OAr content must have no excess 4oAr or extraneous 4oAr from contamination that results in a relatively low percent air correction. and it must have equilibrated with atmospheric argon. In addi- Dating Methods Applicable to the Quaernar5y 53 tion. the atmospheric correction should not be prohibitively high. irradiating the sample in a nuclear reactor to induce fission of These limitations can be minimized by careful sampling, careful 235U with a known dose of thermal neutrons. Early development sample preparation, and by dating groundmass feldspar concen of the fission-track method is reviewed by Fleischer and others trates rather than phenocrysts. Because of their small size, micro (1975) and Naeser (1979). lites lose excess 4°Ar and equilibrate with atmospheric argon Two major factors determine whether or not a sample can much more rapidly than phenocrysts. Guided by this strategy, we be dated by the fission-track method. First, the sample must have had gratifying success in dating volcanic rocks even as contain a mineral or glass of appropriate uranium content. In young as Wisconsin. But, in the words of Bobby Burns, the Quaternary samples, there must be enough uranium that a statis Scottish bard, "The best laid plans of mice and men gang oft tically significant number of tracks can be counted in a reasonable aglae." time. Second, tracks must completely retained once they are formed, or the calculated age will be anomalously young. Heating FISSION-TRACK DATING can cause partial to complete fading (annealing) of the spontane ous tracks. The fission track is stable in most non-opaque miner Charles W. Naeser and Nancy D. Naeser als at temperatures of 50MC or less, but fission tracks in natural glasses can be affected at much lower temperatures (Seward, INTRODUCTION 1979; Naeser and others, 1980). Several Quaternary studies have made use of track fading, for example, to determine rates of Fission-track dating has been applied to many problems in landform development (e.g., Zeitler and others, 1982: Naeser and Quaternary geology. Most studies involve dating of volcanic ash others, 1983; Coates and Naeser, 1984). layers or determining rates of landform development. Examples In the Quaternary studies, only zircon and glass are rou of such studies are given below. To a more limited extent, the tinely used for fission-track dating, and they require two different method has been used in archaeological studies (for example, laboratory procedures. The external detector method (Naeser, Fleischer and others, 1965b; Bigazzi and Bonadonna, 1973; 1976, 1979) is used to date single crystals of zircon because the Wagner, 1978; Gleadow, 1980). uranium distribution is inhomogeneous in individual zircon grains. In contrast, glass is usually dated by the population meth THEORY AND METHODS od (Naeser, 1976, 1979); because all of the glass from a single source has a similar uranium concentration, it is possible to de A fission track is a zone of intense damage formed when a termine the spontaneous and induced track densities from differ "fissionfragment passes through a solid. When an atom of 23BU ent splits of the same sample. (The reader is referred to Naeser fissions, the nucleus breaks up into two lighter nuclei, one averag and Naeser (1984] for a more detailed discussion of the theory ing about 90 atomic mass units and the other about 135 atomic and methodology of fission-track dating.) mass units, with the liberation of about 200 MeV of energy. The two highly charged nuclei recoil in opposite directions and dis ADVANTAGES AND LIMITATIONS rupt the electron balance of the atoms in the host mineral or glass along their path. This disruption of electron charge in turn causes One advantage that fission-track dating has over most other the mutual repulsion of positively charged ions and the displace methods is that sample contamination often can be readily recog ment of the ions from their normal crystallographic positions in nized and, therefore, minimized. In conventional radiocarbon and the host. The result is a zone of damage defining the fission track K-Ar dating, bulk samples must be analyzed. Contamination of (Fleischer and others, 1975). The new track is tens of angstroms a sample with older or younger carbon can result in an erroneous in diameter and about 10 to 20 pim in length. radiocarbon age, and a few older detrital grains can have a signif A track in its natural state can only be observed with a icant effect on a K-Ar age (Damon, this chapter; Naeser and transmission electron microscope, but a suitable chemical etchant others, 1981). Fission-track dating is a grain-specific method in can enlarge the damage zone so that it can be observed with an which individual grains are scanned and counted. In the case of optical microscope at intermediate magnifications (x200-500). zircon dating, an age is obtained on each grain that is counted. Common etchants used to develop tracks include nitric acid (for Therefore, older detrital grains often can be recognized and dis apatite), hydrofluoric acid (mica and glass), concentrated basic carded from the age calculation. solutions (sphene), and alkali fluxes (zircon) (Fleischer and oth A major limitation of fission-track dating of Quaternary ers, 1975; Gleadow and others, 1976). samples is that very young samples (< 100,000 yr) usually have a Because 23SU fissions spontaneously at a constant rate, the very low spontaneous track density. This requires tedious exami age of a mineral or glass can be calculated from the number of nation of large numbers of mineral grains or glass shards and spontaneous fission tracks and the amount of uranium that it produces ages with large analytical uncertainties. Naeser and oth contains. The relative abundance of 23SU and 235 U is constant in ers (1982) noted one glass sample in which they did not see any nature, and thus the easiest and most accurate way to determine spontaneous tracks after scanning thousands of shards. However, the amount of uranium is to create a new set of fission tracks by even though the analytical uncertainty is large for very young 54 J. N. Rosholt and Others samples, some such results can solve significant geological with the Lava Creek Tuff. These ages matched the ages in the problems. source region and confirmed the geochemical evidence of Izet Zircons, although preferable to glass, are not present in all and others (1970, 1972) that there were three Peadette ashes samples. In tephras, their presence depends on the chemistry of rather than just one. the parent magma. Acidic tephras are more likely to yield usable In another study, fission-track dating has demonstrated that zircons than basic tephras. Zircons that are extremely fine grained a tephra is considerably older than had been inferred from radio (<75 pm) cannot be dated by the fission-track method, and this carbon dating of associated organic matter. The Salmon Springs is often the case in tephra sampled a long distance from the vent. Drift at its type locality, at Salmon Springs, Washington, consists Natural glasses have been extensively dated because of the of two drift sheets separated by about 1.5 m of peat, silt, and widespread occurrences of tephra and obsidian in Quaternary volcanic ash (Lake Tapps tephra) (Crandell and others, 1958; rocks. The dating of natural glasses presents special problems. Easterbrook and others, 1981). The peat grades downward with The greatest of these is the ease with which glass can lose spon decreasing organic content into about one meter of silt, which in taneous tracks by annealing (Fleischer and others, 1965a; Stoner turn grades into the volcanic ash (D. I. Easterbrook, personal and Wagner, 1969; MacDougall, 1976; and Seward, 1979). Hy communication, 1980). The peat was radiocarbon dated at drated glass shards, which are found in most tephra beds, are 71,500*•o yr BP by the enrichment method (Stuiver and others, particularly susceptible to annealing (Lakatos and Miller. 1972). 1978), and the drift sheets were thus considered early Wisconsin Work by Naeser and others (1 980) has shown that both hydrated in age. Fission-track dating of this ash and a correlative ash at and nonhydrated glass can lose tracks at ambient surface temper Auburn. Washington, along with paleomagnetic and tephrochron atures over periods of geologic time. In a study of 14 tephras from ological evidence, shows that the Lake Tapps tephra is ca. upper Cenozoic (<30 Ma) deposits of the western United States, 860,000 yr old, and thus the Salmon Springs Drift is an order of only one glass had a fission-track age that was concordant with magnitude older than indicated by the radiocarbon date (Easter the fission-track age of coexisting zircon. All other samples had brook and others, 1981). ages that were significantly younger than the zircon ages. Seward (1979) showed that 60 percent of the glass fission-track ages of Landscape evoludon Quaternary tephras studied in New Zealand were significantly younger than the fission-track ages of the coexisting zircons. Several studies have used fission-track dating to determine rates of landform developmenL An example is a study in the APPLICATIONS Powder River Basin, Wyoming, that involved dating of clinker formed by natural burning of coal beds. Tephrochronology The burning of the coal occurs when the coal beds are exposed to atmospheric oxygen. In the Rochelle Hills, coal beds The major contribution of fission-track dating to Quater are exposed as east-flowing streams cut headward through the nary studies has been in the field of tephrochronology. Fission west-dipping coal. This headward erosion lowers the water table tracks have proved to be the most suitable method for dating in the coal, allowing it to burn. If the heat from the burning coal tephras, particularly those older than the maximum limit of anneals the spontaneous tracks in the detrital zircons, then the radiocarbon dating, which for most analyses is 40 to 50 ka. zircons record the time when the clinker cooled after the burn. The following two studies illustrate the use of fission-track Coates and Naesr (1984) dated zircons separated from the dating in tephrochronology. Volcanic ash beds of the Pearlette clinker capping the mesa north of Little Thunder Creek, Wyo family occur in Pleistocene deposits of western North America ming. This study showed that the ages of zircons in the clinker (Ozett and others, 1970, 1972). Before 1970, the Pearlette ash was become progressively younger from east to west. Zircons from considered to be the product of a single eruption, and it was used eastern end of the mesa give ages of ca. 700,000 yr, while zircons as an isochronous time marker for many midcontinent Quater at the western edge of clinker development do not contain any nary deposits. Izet and others (1970, 1972) reported consistent spontaneous fission tracks, indicating an age of <80,000 yr for chemical differences among three subsets of the Pealette ash that burn. The results of this study show that during the last samples. They suggested that the three subsets could be correlated 700,000 yr, the burn front at Little Thunder Creek has migrated geochemically with three major ash-flow deposits originating in westward about 8 kin, and that there has been about 200 m of the region of Yellowstone National Park, Wyoming. The three downcutting of the eastern edge of the escarpment ash-flow deposits were dated at 2.02 ± 0.08 Ma (Huckleberry Another example of using fission-track dating to study Ridge Tuff), 1.27 ± 0.10 Ma (Mesa Falls Tuff), and 0.616 ± landscape evolution is the use of apatite ages to determine the 0.008 Ma (Lava Creek Tuff) by the K-Ar method (J. D. Obra uplift and erosion (cooling) history of a mountain block. Apatite dovich, personal communication, 1973). Naeser and others will not retain fission tracks if it is held at temperatures in excess (1973) dated zircons from two of the three subsets of Pearlette of' 1050C (for heating of 108 yr duration) to 1500C (105 yr). tephra and obtained ages of 1.9 ± 0.1 Ma for ash correlated with When a rock containing apatite cools during an uplift/erosion the Huckleberry Ridge Tuff and 0.6 ± 0.1 Ma for ash correlated cycle, the apatite in that rock vill begin to record fission tracks.

t Dating Methods Applicable to the Quaternar. 55

tive daughter nuclides will become established-that is, all mea Therefore, apatite fission-track ages provide information on the sured parent-to-daughter activity ratios are unity. However, uplift history of a mountain block. several geochemical processes can cause isotopic and elemental Naeser and others (1983) used apatite ages to determine an fractionation resulting in states of disequilibria. Conventional uplift/erosion rate of the Wasatch Mountains northeast of Salt dating is based on the measurement of the extent Lake City, Utah. They separated and dated apatite from the uranium-series to which the state of secular equilibrium is approached in a dosed Precambrian rocks of the Farmington Canyon Complex. Apatite after the initial disturbance. In contrast, uranium-trend fission-track ages as young as 5 Ma were found at the base of the system dating is based on the measurement and modeling required to mountains near the Wasatch Fault, indicating that these rocks determine the extent and maintenance of disequilibria in an open had been at a temperature in excess of --120'C prior to 5 Ma. system after sedimentation. The data indicate further that the latest episode of uplift in this segment of the Wasatch Mountains began about 10 Ma and has CONVENTIONAL URANIUM-SERIES DATING continued to the present with an average uplift rate of 0.4 mm/yr, and that these rocks have been cooling at a rate of about The conditions for reliable conventional U-series dating are 12°C/m.y. that the material remained a dosed system through geologic time respect to the nuclides of interest, and that the material is SUMMARY with pure, reasonably uniform, and was not subject to recrystallization processes that could produce subsequent mobilization of Fission-track dating has widespread application in Quater or other daughter products. nary studies. The major contribution has been in the field of The most commonly utilized methods for Quaternary de tephrochronology, where fission-track dating has been used to rely on the measurements of disequilibria between 230Th date tephra horizons in Quaternary deposits and thereby date posits and 234U (23Th deficiency method), between 231Pa and 235U Quaternary events. The method has also been used to study the (231pa deficiency method), and 234U and 238U (234U excess rates of landform development and to determine rates of tectonic method). Deficiencies of 23°h and 231Pa in secondary minerals processes and how those rates relate to the overall development difference between the aqueous mobility of of the landscape. are due to the marked uranium relative to thorium and protactinium. Uranium is readily source rocks, then transported and re CONVENTIONAL URANIUM-SERIES AND leached from weathered deposited, whereas 23h and 23tPa are extremely insoluble, and URANIUM-TREND DATING trace amounts dissolved from source rocks are effectively re during transport. Materials R J. Szabo and A. N. Rosholt moved from solution by adsorption datable by the 23°Th and 231Pa deficiency methods are either (I) geologically derived, such as various forms of carbonates, INTRODUCTION sulfates, phosphates, opal, and young volcanic rocks, or (2) bio corals, mollusks, bones, and peat deposits. Climatic fluctuation was the dominating condition during genic in origin, such as The upper (oldest) limit of 230Th deficiency dating is about 360 the Quaternary. It resulted in expansion and recession of pluvial limit of 23 1Pa deficiency dating (used mainly as a lakes, glaciation and deglaciation, large glacio-eustatic sea-level ka the upper complementary method to 23Th dating) is about 180 ka. changes affecting both stable and uplifting coastlines, and land Natural waters and secondary minerals generally contain scape evolution. The alternating periods of higher versus lower relative to 23sU because the alpha recoiling precipitation and temperature influenced rock weathering, alluvi excess 234U (Fleischer, 1980) associated with the process of 238U radioactive ation, and soil evolution; also, climatic changes enhanced the to 234U (Fig. 1) displaces the 234U atoms to more leacha mobility of elements in soil profiles and formation of associated decay than those of 23 8U atoms, which occupy the original secondary minerals. Many of these secondary deposits and some ble sites crystal lattice positions. The excess 234U is then the measure of young volcanic rocks are potentially datable by conventional 4 8 the age of the material, provided that the initial 23 U/23 U activ U-series dating, and the time of deposition of some Quaternary be ascertained. The 234U excess method has been sediments can be estimated by uranium-trend dating, both tech ity ratio can corals, speleothems, and calcitic veins. The range niques of dating provide the opportunity for deciphering the tim used for dating 100,000 and ing of some of the complex Quatemary events. for practical dating by this method is between about 5 232 the age calculations and general The natural radioactive series of 23mU, 23 U, and Th 1.5 m.y. Equations used for by Ivanovich (1982) and Lally produce numerous daughter products of varying chemical prop chemical procedures are described erties and half lives (Fig. 2). Both the parents and their daughter (1982). elements are common trace constituents in nearly all geologic Secondary carbonates materials. If any of these materials containing the parent isotopes or remain undisturbed for a period of about 2 my., a state of secular Inorganic (predominantly calcite) and organic (aragonite components in most equilibrium between parents and all of their respective radioac- calcite) carbonate deposits are common 56 J. N. Roshok and Others

n2 Th serie =' U series 238U 2 UU (4.47 Go) (244 ka) (0.704 Go) 2t Pa (32.5 ko) (1.17 m in) W-'Th 2 30 Th 23 Th 2M Th 231 Th U7 Th (2.41 d) (75.2 ko) (14.0 Go) (1.91 a) (25.6 h) Ia(18.2 d) =7 Ac a (6.13 hr) a (21 .8 a)

2 2 2eRa 222 R =4 RR n23Ra (1.60 ka) (5.75 a) (3.64 d) (11.4 d)

t 0t8 t spb pb' "st Pb (stable) (stable) (stable)

Figure 2. Decay series of naturally occurring uranium and thorium nuclides.

depositional environments, and they display a variety of textures veins occurring in ash-flow tufts at Yucca Mountain, and Nevada, structures. Most of the dense, pure carbonates are suitable for suggests episodic fluid movements and fracture filling during the reliable U-series dating. past 400,000 yr (Szabo and Kyser. 1985). Speleothems (carbonates precipitated in caves) are usually Travertines (dense and dean varieties of spring-deposited good material for U-series dating. Results are utilized in various carbonates) are also suitable for U-series dating. They often occur ways. Ages can establish the local cave chronology and rates of as extensive horizontal or sloping layers, mounds, or steep drap deposition (Thompson and others, 1975). Speleothem growth in ings. Travertines may cap fluvial terrace deposits, thus providing an ard climate may indicate pluvial periods, and lack of growth limiting ages for periods of deposition and terrace cutting may indicate dry climatic conditions (Harmon and Curl, 1978). (Schwartz and Gascoyne, 1984). Extensive erosion during the The absence of speleothem growth in alpine caves indicates peri Pleistocene developed pediments in central Montana. Dating ods of prolonged cold, preventing the movement of ground water travertines associated with one pediment surface indicates that the (Harmon and others, 1977 and Lively, 1983). Combinations of surface is older than about 320,000 yr (Szabo and speleothem Lindsey, dating with stable isotopic analyses are used in pa 1986). Evidence for paleospring activities is represented by trav leoclimatic studies in both temperate and glacial zones (Mills, this ertine deposits in Grand Canyon National Park. Arizona dated at volume: Schwartz and others, 1976; Thompson and others, 1976: about 170, 110, and 80 ka (Szabo and others, 1986). Harmon and others, 1978a, and Harmon and others, 1978b). The porous variety of spring-deposited calcium carbonate Calcitic veins are dense, low-temperature precipitates from (calcareous tufa), usually contains detrital materials, and their calcium carbonate-saturated ground water that fill or line frac open structure permits secondary mobilization or addition of the tures. Some of these veins provide a continuous record for the U-series nuclides. Separation and analysis of both the acid-soluble past 2 m.y., and they can be dated reliably by the 230Tn defi carbonates and acid-insoluble residues of carefully selected sam ciency and 234U excess methods (Winograd and Doty, 1980). ples may yield useful limiting dates for various Quaternary proc Reduced deuterium contents in fluid inclusions of U-series-dated esses (Szabo and others, 198 1a). calcitic veins from the southern Great Basin indicate major uplift Clean and dense parts of lacustrine carbonates may yield of the Sierra Nevada during the Quaternary (Winograd and oth reasonable dates by U-series analysis (Kaufman and Broecker, ers, 1985). Dates on calcitic veins in the Amargosa Desert. 1965). Lacustrine carbonates, however, usually contain various Nevada. indicate a lowering of the paleo-ground-water table at amounts of datdtai materials, thus requiring large age corrections that area by about 0.04 m/ 1000 yr, probably due to an increase due to initial 23Th contamination (Kaufman, 1971). in aridity during the Pleistocene (Winograd and Szabo, 1985), Secondary carbonate, concretions, rinds, and components and these dates provide other implications for the climatic record that may be either pedogenic or nonpedogenic and are referred to (Winograd and others, 1988). Uranium-series dating of calcitic as caliches or calcretes are potentially datable by U-series meth- Dating Methods Applicable to the Quaterna7 57

ods. These deposits usually contain large amounts of detrital Mollusks. abundant in many marine, fluvial and lacustrine residues. therefore, extensive age corrections are required for the sediments, are potentially datable by U-series methods. Unlike uranium and thorium derived from the noncarbonate fraction. corals, however, major amounts of uranium enter the molluscan Selected dense calcretes from the Nevada Test Site region yielded shells after the death of the animals, and they often remain sus useful limiting ages for recent faulting (Knauss. 1981; Szabo and ceptible to gradual or episodic post-depositional assimilation of others, 198 la). By multiple analysis of both the carbonate and the uranium so that some pre-Pleistocene samples give erroneous detrital fractions of caliche cement samples, Ku and others (1979) finite dates (Kaufman and others, 1971). Furthermore. shells may determined periods of carbonate cementation in alluvial deposits be subject to recoil gain of 231Pa, 230Th, and 23U (Szabo and of the Mohave Desert, California. Rosholt. 1969); to partial loss of 23Th and/or 231pa (Szabo and Carbonate-rinds, nodules, and rhizocretions are pedogenic Gard, 1975: and Szabo and others, 198 1b); and to initial 23OTh or ground-water-precipitated carbonates that coat rock surfaces. contamination, as determined by measured 232Th (Osmond and form in sediments, or form root-like structures. If dense and others, 1970). In the absence of other U-series datable materials, relatively clean, these materials can be successfully dated by U and in conjunction with other correlative techniques, mollusk series methods. Carbonate-rinds on boulders from fan deposits dates generally are only approximate, usually minimum, ages for near Arco, Idaho, have been dated. Rind carbonates accumulated depositional events (Szabo and Rosholt, 1969; Szabo and between about 10,000 and 100.000 yr ago, and apparently re Vedder, 1971; Bradley and Addicott, 1968-redated by Szabo, mained a closed system with respect to uranium and thorium 1980a, Wehmiller and others, 1977; and Mixon and others, migration (Szabo and Rosholt, 1982). Carbonate-rind dates indi 1982). Fossil echinoids from California also show open-system cate an age of about 200.000 yr for the Yermo fan deposit at conditions similar to mollusks (Muhs and Kennedy, 1985). Calico. California (Bischoff and others. 1981). Corals have consistently yielded reliable age results, pro Secondarydeposits other than carbonates vided they are composed of unrecrystallized aragonite and are free of void-filling contaminants. Coral flourishes in the tropics, Detritus-free evaporites may yield useful U-series dates for but certain solitary species occur even in temperate regions. Up the time of sedimentation. Dates on bulk salt samples (mostly to the present, only four California and one Oregon Pacific coast halite, trona, and gaylusite) in Searles Lake, California, have been localities yielded enough coral material for U-series dating. The reported recently (Peng and others, 1978; and Bischoff and oth California localities are: Nestor Terrace, San Diego (Ku and ers, 1985), where the lake sediment consists of sequences of mud Kern, 1974); Cayucos, San Luis Obispo County;, San Nicolas (pluvial) and salt (arid) layers. Results indicate semidry and in Island (listed in Ku and Kern, 1974); and San Clemente Island termediate climate with moderate salinities during the period (Muhs and Szabo, 1982). The Oregon coral is from the Whiskey from about 200 to 300 ka, followed by a generally wet climate Run Terrace, Bandon (Kennedy and others, 1982). The dating and greater water depth with low salinities during about the last results of corals have been applied for calculating local uplift rates 100,000 yr. and for calibrating amino-acid ratios from mollusks, which in Under favorable conditions, other evaporites such as sulfates turn were used for regional correlations and relative dating are also datable. Anhydrite samples from Stanton's Cave, Grand (Wehmiller and others, 1977; Kennedy and others, 1982; and Canyon National Park, Arizona, yielded apparently reliable U Muhs. 1985). series dates between 16 and 59 ka (Rosholt and others, 1987a). Over 55 fossil corals have been dated from marine deposits Dating of gypsum spring deposits near Carlsbad, New Mexico, (some in place) along the southeastern U.S. Atlantic Coastal was attempted (Szabo and others, 1980), but the results show that Plain (Szabo, 1985). Ages of these corals have been used for these surface-exposed samples contain detrital contaminants, and paleoclimatic reconstruction (Cronin and others, 1981) and for did not remain an ideal closed system with respect to uranium lithostratigraphic and biostratigraphic differentiation (Colqu and daughter elements. houn, this volume; Mixon and others, 1982 and McCartan and Knauss (1981) reported that some pure secondary silica, others, 1982). Fossiliferous deposits along the northern part of the opal deposits, contain uranium, but negligible amounts of tho Atlantic Coastal Plain contain scarce corals; dated fragments rium, and that the samples appear to constitute a closed system from the Pleistocene Sankasty Sand, southeastern Massachusetts, with respect to uranium isotopes and their respective radioactive indicate a last interglacial age (about 130,000 yr) for the deposi daughters. Laminated opal from the Yucca.Mountain region, tion of this marine unit (Oldale and others, 1982). Of the con Nevada (Szabo and O'Malley, 1985), and opal-filling fractures in terminous United States, reef-building corals occur only in ash-flow tuffs of Yucca Mountain, Nevada (Szabo and Kyser, southern Florida. Dates from fossil corals from the Pleistocene 1985), have been dated but there is at present no independent age Key Largo Limestone and reef deposits of the Bahamas indicate control to test the reliability of the results. In theory, clean sec that reef formation occurred about 135 ka in the southern Florida ondary accumulations of iron and manganese hydroxides and area, while sea level was several meters above its present level oxides can be dated by U-series. Desert varnishes, dark coatings (Osmond and others, 1965; Neumann and Moore, 1975; and of ferromangenese oxides on exposed rock surfaces in arid cli Harmon and others, 1978b). mate regions, have been proposed as suitable materials for dating 58 J. N. Rosholt and Others

(Knauss and Ku, 1980), but again, no independent age control is tween deposits. Results of many studies of U-series disequilibria as yet available. indicate that uranium commonly exhibits open-system behavior Fossil bones take up uranium after the death of the animal, in many near-surface deposits (Ivanovich and Harmon, 1982). and do so presumbly until all active organic matter within the Because materials suitable for dosed-system dating often are lack bone has decomposed. Comparison of U-series and 14C dates of ing in Quaternary deposits, an open-system dating method is bones younger than 30,000 yr indicates that most secondary ura needed. The model for uranium-trend dating was developed by nium assimilation occurs within a few thousand years after burial, Rosholt (1985) and applied to a variety of Quaternary deposits, but in some cases the progressive uranium uptake by these fossils including alluvium, eolian sediments, glacial deposits, zeolitized can be considerably longer (Szabo. 1980b). Some of the older volcanic ash, and marine terrace deposits (Muls and others, U-series-dated bone samples from alluvial deposits of Colorado 1989). This open-system, empirical model requires a calibration (Szabo, 1980b), from the middle unit of the Riverbank alluvium based on deposits of known age; results of such calibrations are near Sacramento, California (Hansen and Begg, 1970), and from included in Rc,," :'!t and others (1985b). gypsum deposits, Carlsbad, New Mexico (Szabo and others, For U-trend dating of sediments, the distribution of 1980), have provided useful, although probably minimum-age uranium-series members during and after sedimentation must estimates for the deposition of sediments containing the fossils. have been controlled by their open-system behavior. Sediments Severe weathering can cause uranium loss, resulting in U-series and soils are penetrated continuously or episodically with ground ages that are older than the actual burial age of the bone (Bada water or soil water that contains at least small amounts of dis and others, 1984). Other materials, such as wood (Szabo, 1972), solved uranium, some of which may include exchange of locally peat (Vogel and Kronfeld, 1980; Zielinski and others, 1986), and leached and/or adsorbed uranium. As this waterborne uranium organic matter adhering to sand (Szabo, 1982) have been at decays, it produces a trail of radioactive daughter products that tempted for U-series dating, but most of these studies resulted in are readily adsorbed in solid matrix materials such as day and minimum-age estimates only, due to the open-system behavior of silt. If the trail of daughter products, 234 U and 230Th, is distrib uranium. uted through the deposit in a consistent pattern, then uranium trend dating is possible. The large number of geochemical Volanic rocks variables in an open system precludes the definition of a rigorous mathematical model for uranium migration. Instead, an empirical Young volcanic rocks can be dated by U-series methods in model is used to define the parameters that can reasonably ex certain favorable circumstances. The requirements are: (1) that plain the patterns of isotopic distribution. This model requires secular equilibrium was maintained between 238U, 234U, 230 and independent time calibration with known-age deposits and care Th during the process of partial melting and during uprising ful evaluation of the stratigraphic relationships of the deposits to and eruption of the magma, (2) that no contamination occurred by be dated, however, they do not have to occur in the same geo remelting of the older crust, and (3) that the volcanic rock re graphic area as the calibration deposits (Rosholt and others, mained a chemically closed system after solidification. During 1985b). crystallization of the volcanic rocks, all individual mineral phases Analyses of the abundances of 238U, 234U, 23 and 232Th are assumed to have 2 232 the same 'DTh/ Th activity ratios, but in a single sample do not establish a meaningful time-related their 238U/ 232Th would differ according to the relative partition relationship of isotopic distribution in an open-system environ coefficients of uranium and thorium in the different mineral ment. However, analyses of several samples, each of which has phases. In all mineral phases, the 23°Th then approaches reestab only slightly different physical properties and only slightly differ lishment of radioactive equilibrium relative to the amount of ent chemical compositions within a unit, may provide a consist uranium in that particular phase. In an ideal case, 230 a plot of ent pattern in the distribution of these isotopes (Rosholt, 1985). Th/ 232Th against 23SU/ 232Th defines a line, the slope of Analyses of 5 to 8 samples per unit from several alluvial, collu which will vary as a function of time (Harmon and Rosholt, vial, glacial, and eolian deposits have shown that these types of 1982), This method has been utilized to date rhyolites from deposits, ranging from clay-silt to gravel units, have isotopic dis Mono Crater, California (Taddeucci and others, 1967), and Long tributions that appear to fit an open-system model (Rosholt and Valley, California (Baranowski and Harmon, 1978). others, 1985a and 1985b). To obtain a U-trend date, several samples are collected from a vertical section of each separate URANIUM-TREND DATING stratigraphic unit. The number of samples required to establish a reliable linear trend in the data depends on the variation in ratios For successful conventional uranium-series dating, a closed of uranium and thorium that define the trend line. system is required to exist throughout the history of a sample, It is preferable to collect samples from a channel cut through meaning that there has been no postdepositional migration of deposits exposed in a trench wall or a relatively fresh, well 23SU or of its daughter products, 24U and 230Th. In contrast, "exposed outcrop; existence of soil development is not a necessary open-system dating techniques require no such restrictions on requirement, nor is sampling of the entire stratigraphic unit al postdepositional migration of these radioisotopes within and be- ways necessary. Pebbles and other larger fragments are removed Dating Methods Applicable to the Quaternao,. 59

unpublished data). The deposits include alluvium, colluvium, Co lian sand, and gypsum. some of the alluvial deposits now have well-developed carbonate horizons. The U-trend dates for two of these middle Pleistocene calcretes appear to be too young, based on geologic considerations, because of the effect of late stages of carbonate accumulation. The remaining deposits give reasonable ages based on stratigraphic relationships. Uranium-trend system . 2 ti ! -I atics of deposits in New Mexico and in Nevada indicate that Sr resolution of chronology is better for calcareous deposits than for M1-4 noncalcareous deposits such as glacial till and loess. However, very strong calcium carbonate development, such as in calcretes, tends to yield ages closer to the mean age of carbonate enrich ment rather than the ages of deposition of the host sediments. Alluvial deposits. which tend to be more poorly sorted and of mixed mineralogy, usually yield a better spread of the data on the uranium-trend plot than do eolian, quartz-rich sand deposits. Studies of unconsoldiated Quaternary deposits in Grand -0.2 -0.6 -04 - .2 0 0.2 0.4 Canyon National Park along the Colorado River near Nanko weep Creek and in the vicinity of Basalt Canyon and Tanner Figure 3. Uranium-trend plot of alluvium (160 ka) at Charlie Brown Creek reveal a history of relatively young downcutting and depo Quarry, Shoshone. California. All samples are plotted in terms of activity sition in the lowest 100 m of the canyon (Patton this volume; ratios: zero coordinates represent radioactive equilibrium in isotopic ra Macbette and others, 1986). This interpretation is based on U tios (reproduced from Rosholt and others, 1985a). trend ages of the deposits and on the stratigraphic relations be tween deposits. Ages were obtained on Pleistocene deposits that form prominent terraces from 20 m to 50 m above the present river level; four ages were determined, ranging from 40 *24 ka to by sieving and the remaining less-than-2-mm size fraction is pul 150 * 30 ka, with increasing age for higher level terraces. A verized to less-than-0.2-mm size, homogenized, and retained for rockfall debris 60 m above the river on the Nankoweep delta analysis. Chemical procedures used for separating uranium and was dated at 210 ± 25 ka. Farther from the river, alluvial deposits thorium for alpha spectrometry measurements are those de in high valleys (400 to 500 m above the river) at Chuar Valley scribed by Rosholt (1984 and 1985). For defining uranium-trend and Surprise Valley were dated at 300 * 100 ka and 250+ 30 ka, slopes, the results of these analyses are plotted in the form of respectively (Rosholt and others, 1986). 8 8 238 (23U=238U)/23 U against (23 U=230Th)/ U. Ideally, this In Fisher Valley, Utah (Colman and others, 1986), U-trend yields a linear relationship, as shown in Figure 3, in which the ages were reported on basin-fill sediments. A Lava Creek Ash slope is a function of the age of the deposit based on the horizon was dated at 530 ± 70 ka, ages of 240 ± 35 ka and 210 calibration. ±40 ha were obtained for the top of the basin-fill sediments; and 9 ± 11 ka was obtained for Holocene eolian sand. These results Applicationsfordating Quaternarydeposits for the oldest and youngest units are in fair agreement with ages determined by tephrachronology (610 kh) and radiocarbon (8 In a report for the Nevada Test Site (Rosholt and others. and 9 ka) methods, respectively (Patton and others, this volume). 1985a), 31 of 37 depositional units analyzed were datable by the In the San Joaquin Valley, the U-trend method was used to U-trend method. These results have median age estimates that determine ages on sediments ranging from about 30 to 600 ka indicate four separate time frames of deposition during the late (J. N. Rosholt, unpublished data); these included Pleistocene and middle Pleistocene in this geographic area: 40 ± 15 ka, 170 + deposits of the upper and lower members of the Modesto Forma 40 ka, 270 ± 50 ka, and 440 ± 60 ka. The results are reasonably tion, the upper and middle units of the Riverbank Formation, and consistent with other dates (Swadley and others, 1984) and with the upper unit of the Turlock Lake Formation. Of 13 deposi estimates based on geomorphic evidence. Analyses of deposits tional units analyzed, 5 were not datable because the U-trend from a trench near Beatty, Nevada, suggest that a sequence of method does not appear to work for soils with missing horizons several fluvial deposits was laid down by the Amargosa River at or for soils that have developed in parent materials of more than the base of the Beatty scarp during the last 500,000 yr (Rosholt one age. On the California coast, marine terrace deposits near and others, 1988). Deposition of silts, sands, and gravel were San Pedro were dated by U-trend method at 1 5 0 ksa, 230 ± dated at 75 ± 10ka, 155 ± 30 ka, and 500 ± 100ka. 60 ka, and >700 ha (Muhs and others, 1989). These dates Nine units from deposits in New Mexico have yielded ages are in agreement with conventional U-series and amino acid age ranging from about 20 ka to about 700 ha (Rosholt and others, determinations. 60 J. N. Roshoki and Others

DISCUSSION A reversal of polarity is easy to conceptualize as a strati graphic marker because it occurs simultaneously around the A variety of middle and late Pleistocene depositional, ero world. Four boundaries are well known for the Quaternary, and sional, climatic, and volcanic events can be dated, and rates of their age is established primarily by K/Ar dating of volcanic change can be determined, by applying U-series methods. To rocks: termination of the Olduvai Normal Subchron (1.67 Ma), obtain reliable results, however, one needs to find the high limits of the Jaramillo Normal Subchron (0.97 Ma and 0.90 Ma), quality, homogenous samples that have formed in a short period and onset of the Brunhes Normal Chron (0.73 Ma: Mankinen in relation to their age and represent a discrete geologic event. and Dalrymple, 1979). Additional reversals have been encoun Unfortunately, nature rarely provides such ideal samples; there tered and dated in Quaternary volcanic rocks, and they likewise fore. investigators have devised different correction techniques to serve as distinct horizons wherever identified. The best data are account for the presence of impurities. The dosed-system condi for the Cobb Mountain Normal Subchron in California (1.19 ± tion (no migration or addition of nuclides) is always required in 0.2 Ma: Mankinen and others, 1978), the Emperor Reversed conventional U-series dating, but it is seldom ascertained. Be Subchron in Idaho (0.46 ± 0.05 Ma; Ryan, 1972; Champion and cause of uranium mobility, often the uptake of uranium is dated, others, 1981), and the Laschamp Reversed Subchron in France not the deposit itself, and in these cases dates should be inter (Bonhommet and Zahringer, 1969) that is assigned the age of preted as minimum-age estimates. about 0.04 Ma (Heller and Peterson, 1982). Another brief rever Uranium-trend dating results show that it is a suitable me sal is the Blake Reversed Subchron at about 0.12 Ma (Denham thod of estimating the age of some Quaternary deposits. The most and others. 1977) that was discovered in cored sediment from the reliable ages appear to be in the time range of 60,000 to 600,000 Blake Plateau in the western North Atlantic (Smith and Foster, yr, which, at best, may be accurate within ± 10 percent for a 1969), but is not found in all sections believed to span that deposit whose samples provide a linear pattern of isotopic varia interval. The same applies to several other short episodes of re tion. The U-trend ages have large relative errors near the lower versed polarity in the Brunhes Normal Chron that are not (10 ka) and upper (800 ka) limits of the method: deposits universally recognized for a variety of reasons; examples are the younger than 20 ka have errors near or greater than ± 100 Gothenburg in Sweden (M6rner and others, 1971) and Biwa in percent, and deposits older than 600 ka have errors greater than ± Japan (Kawai and others, 1972). As a result, they are not in all 20 percent. compilations of the reversal time scale, including the one adapted Conventional U-series and U-trend dating have yielded use for the Decade of North American Geology (Palmer, 1983). ful results for various Quaternary dating problems. Due to the If the magnetostratigraphy is complete to the base of the imperfections, the reliability and accuracy of the dates are not Quaternary (as in a core of lacustrine or deep-sea sediment), uniform, however. Therefore it is a good practice to test the dating the stratigraphy using only the reversal time scale can be dating results against the stratigraphic constraints of the particular done with a high level of confidence. However, where there are geologic application. hiatuses in the section, a safe assumption is that rocks possessing reversed polarity acquired that magnetization before 0.73 Ma. A PALEOMAGNETIC DATING similar rationale cannot be used for rocks of normal polarity because they might be remagnetized by the present (normal) field. Joseph C. Liddicoat Fortunately, field and laboratory (demagnetization) experiments can usually establish whether the magnetization is primary or Two characteristics of the Earth's magnetic field have appli secondary in origin. In a section where the polarity is normal cation for dating strangraphy-reversals of polarity and system exclusively, improvement of the dating beyond assignment to the atic changes in the paleomagnetic vector. The benefits and Brunhes Normal Chron is left to correlating secular variation of limitations of each are controlled by several factors, and among the palcomagnetic field. It is a subject that has received consider them is the time interval. Whereas the reversal time scale (Har able attention in recent years both in stratigraphic studies and in land and others, 1982) covers all of the Quaternary (and investigations of the dynamics of the Earth's cor beyond), records of short- and long-term behavior (called secular Because secular variation is the result of a complex interac variation) of the field apply only to the post-Wisconsin and Hol tion between the dipole and non-dipole fields, it is highly variable ocene. Also restricting are the location and areal extent of the when considered worldwide. Still, where systematic changes in study, there are no bounds on magnetostratigraphic studies, but declination, inclination, and intensity are calibrated by radiomet secular variation is confined mainly to regions several thousand ric dates, the curves are potentially useful for correlating and kilometers across. In this discussion, we will not deal with the dating stratigraphy on a regional scale. Among the places where specifics of paleomagnctism or the Earth's magnetic field, which successful application has been mad, iming wet lake sediments are in McElhinny (1973) and Merrill and McElhinny (1983), but are the midwestern United States, Canada. Great Britain, Europe, will highlight those elements that bear on stratigraphic correlation and Australia. The curves for those and additional regions are in and dating. Creer and others (1983). Dating Methods Applicable to the Quayerna6 61

Changes in the paleomagnetic vector and field strength are THERMOLUMINESCENCE DATING also preserved as thermal remanent magnetization in baked clay at archeological sites. Because of the very good age control on Steven L. Forman and MichadN. Machette samples (usually by radiocarbon) and stringent requirements on archeomagnetic data, reliable curves for much of the Holocene INTRODUCTION are available for the southwestern United States. Britain. Europe. the Middle East, and Australia (Wolfman, 1983). The curves not The development of thermoluminescence (TL) dating tech only have utility in stratigraphic studies, but help to confirm the niques during the past two decades came about through TL stud secular variation measured in lake sediments as recorded by the ies of pottery from archaeological sites (Flemming, 1979; Aitken, process of detrital remanent magnetization. 1974, 1985). During the past ten years these techniques have The value of detailed curves of secular variation would be been applied successfully to dating of Quaternary sediments (see enhanced if there is a large departure from typical field behavior review articles by Dreimanis and others, 1978; Wintle and Hunt that does not constitute a reversal; such directions are called an ley, 1982; Singhvi and Mejdahl, 1985). The basic principles of excursion (Cox and others. 1975). In practice. excursions are the technique for dating Quaternary sediment are similar to those difficult to locate in the stratigraphic record because they have a used in dating archaeologic materials. However, heating of pot duration of only a few thousand years at most. A case in point is tery removes any TL signal that may have accumulated in the the Moho Lake Excursion (Denham and Cox, 1971; Liddicoat minerals, whereas in sediments the inherited TL in minerals is and Coe, 1979) that occurred about 26 ka (Liddicoat and others, assumed to be zeroed by exposure to sunlight (light bleaching) 1982) in exposed dry lake sediments in east-central California. prior to deposition. This important difference in zeroing mecha Within the structural basin containing pluvial Lake Russell (of nisms prompted development of new laboratory procedures for which Moho Lake is the remnant), the excursion can be posi dating sediments (i.e.. see Wintle and Huntley, 1980). For TL tively traced over a distance of 20 km using a distinctive tephra dating of sediments, environments of deposition are evaluated in layer as a marker (Denham, 1974). Only recently, and after terms of their effectiveness in removing previously acquired TL several unsuccessful attempts at other localities (Verosub, 1982), from minerals. Samples are taken from sediment that has not was the excursion discovered in sediment from another pluvial been exposed to sunlight since it was deposited. lake. The closest one, Lake Lahontan in southwestern Nevada, is As a dating technique, TL does not depend on presence of 200 km away (Liddicoat and others, 1982), and the other, organic or volcanic materials, and it has the distinct advantage of Summer Lake, is 300 km farther to the north in southern Oregon directly dating many kinds of sediment. More importantly, it can (Negrini and others, 1984). In each instance, it was not the excur provide age determinations at dose intervals and at significant sion that was first identified, but the associated tephra layer or positions in a stratigraphic section. The TL method can be ap another one close in age (Davis, 1985). Thus, the utility of an plied to sediments ranging from younger than 100 ka to possibly excursion alone as a method for placing an age on stratigraphy in as old as 500 ka. Because of its wide applicability, TL is an a large geographical area (such as the Great Basin of the western extremely important new dating technique for Quaternary depos United States) remains to be demonstrated. Other excursions in its. This brief review explains the method, discusses the types of the Pleistocene have been reported, but they have not been veri materials that can be dated, and discusses some of the problems fied at multiple sites (Banerjee and others, 1979;, Verosub, 1982) involved in different applications of the method. Extensive litera and as yet do not warrant serious consideration as stratigraphic ture on TL dating is reviewed in Aitken (1985), PACT volumes markers. 3, 6, and 9 (Journal of the European Study Group on Physical Rock-magnetic information, such as susceptibility, and other Chemical, and Mathematical Techniques Applies to Archaeology laboratory experiments designed to identify the physical proper and in Nuclear Tracks and Radiation Measurements (1985, v. 10, ties and composition of the carrier of magnetization are akin to nos. 1, 2, 4-6). These sources give more complete reference list records of secular variation in wet lake sediment. The approach is ings dedicated to this subject. relatively quick and circumvents the problems associated with paleomagnetic studies of cores in which there might be errors in THERMOLUMINESCENCE DATING OF GEOLOGIC orientation or there has been disturbance to the sediment during MATERIAL recovery and subsequent sampling. The early work in North America began in the Midwest (Banerjee, 1981) and followed a Thermoluminescence dating of minerals was first attempted successful application of the technique in Great Britain (Blom by Daniels and others (1953). They measured TL signals from endal and others, 1979). Rock-magnetic studies are thus be some common minerals, but production of reliable age determi coming an important pa.t of detailed investigatons of wet lake nations was difficult. McDougall (1968) summarized much of the sediments, and complement the other methods for dating and early research on thermoluminescence of geologic materials. The correlating stratigraphy within late Pleistocene and Holocene potential of dating unheated sediment by TL was first recognized lakes or in a drainage basin (Thompson and others, 1975; 1980). by Morozov (1968) and later described by Shelkoplyas (1971), 62 J. N. Roshot and Others wh6 obtained ages for sediments in the Soviet Union. In assessing 4 the early Soviet TL dating, Wintle and Huntley (1982) concluded that the obtained TL dates may be in correct chronologic se E0 quence but that they may be in error by a factor of 2 to 10. Bothner and Johnson (1969) reported TL studies from four deep 3 sea cores rich in nannofossils. They found that the naturally in 0, duced TL. thought to be characteristic of foraminiferal calcite (Johnson and Blanchard, 1%7), increased down-core to a pla teau (saturation) value. Huntley and Johnson (1976) reported a 2 similar increase in equivalent dose with depth in a core of radiolarian-rich sediment. These studies led to Wintle and Hunt ley's (1979) recognition that the TL in these marine sediments Cn was from detrital grains that adhere to the nannofossils, rather -J 1 than the nannofossils themselves. Following this fundamental dis z covery there has been increased interest in and application of thermoluminescence to dating of mineral sediments. -J Two new dating techniques related to thermoluminescence I-- are electron-spin resonance (ESR) (Hennig and Griin, 1983) and 0 optical dating (Huntley and others. 1985). ESR dating is based on 0 100 200 300 400 500 direct measurement of radiation-induced paramagnetic electrons TEMPERATURE, "C (during progressive heating) that have been trapped in crystal defects through geologic time. Figure 4. Natural TL glow curve and laboratory TL glow curve caused The technique has been applied to apatite and to organic and by an additional 360 gray of radation. Material is a fine-grained poly inorganic carbonate, and research is underway using silicate min mineralic sediment. Samples were preheated at 150 0C for 16 hours prior erals. Optical dating involves photo-stimulated luminescence, to glowing to enhance the TL signal above 2000C. rather than heat stimulation (thermoluminescence). Electrons ac cumulated in traps through geological time are freed by laser light, thus transferring electrons to luminescence centers, which transmit visible light.

FUNDAMENTALS OF THERMOLUMINESCENCE brated source of beta or gamma rays. Assuming that the labora DATING tory irradiation simulates natural conditions and that TL does not decay more in nature (under long-term conditions) than in the The TL signal emitted by mineral grains is acquired by laboratory (short-term conditions), the equivalent dose (ED) can exposure to ionizing radiation. The radiation causes electrons to be determined. Equivalent dose is the amount of laboratory radia be displaced from outer electron shells and trapped in crystal tion that produces a TL response "equivalent" to that of the defects. In most environments, the contribution from cosmic rays natural sediment. is small. especially at depths of more than 10 cm in sediment. Three methods have been developed to assess ED (Fig. 5). Therefore the causative radiation in sediment is almost entirely I. Regeneration method (Wintle and Pr6szydska. 1983). alpha, beta, and gamma particles that are released during the The natural TL in sediment is measured and then aliquots of the decay of radioactive nuclei of 40K, 238 U, and 232Th contained in sediment are bleached in the laboratory to their experimentally the sediment. In order to obtain a reliable date from a given determined pre-depositional TL level. These aliquots then are sample of mineral sediment, its electron traps initially must have re-exposed to increasing doses of radiation, and the level of natu been emptied by exposure to light, and these traps subsequently ral TL is matched to the regenerated TL curve. ED is determined must have accumulated and retained a post-deposition TL signal. as shown on Figure SA. This method is used predominantly on The TL signal is quantified by measuring the light emitted as a sediments that have been zeroed (light bleached) of TL prior to sample is heated continuously from about 250 to 5000C at a rate their deposition. These sediments are mainly wind-transported of about 5*C/sec in an oxygen-free atmosphere (see Fig. 4). materials, such as loess and eolian sand. Minerals such as feldspar, quartz, and calcium carbonate have 2. Total bleach method (Singhvi and others, 1982). diagnostic TL-response (glow) curves at different temperature Without prior laboratory bleaching, the natural sediment is irra ranges. diated at progressive levels, and the rate of TL acquisition is To evaluate the amount of radiation received by the sample defined by a sloping line shown in Figure 5B. ED is the intercept in its geologic environment, the sample's sensitivity to radiation of this sloping fine with the TL level induced by total fight bleach must be determined. This sensitivity is assessed in the laboratory ing (horizontal dashed line). This method commonly is applied to by measurement of the TL response to irradiation from a cali- eolian sediments to check for sensitivity changes relative to the Dating Methods Applicable to the Quaternav. 63

regeneration method and to ascertain if the growth in the TL A. Regeneration method signal is linear with increasing radiation. 3. Partialbleach method (Wintle and Huntley, 1980). Z ED is defined by the intersection of two sloping lines, as shown in NAT Figure 5C: (I) the regression line defined by nT resulting from zU I-- progressive does of laboratory radiation on natural sediment. and I (2) the regression line determined from partially light-bleached w INAT sediment that previously has been exposed to progressive doses of NAT, LBt* 02 laboratory radiation. A level of partial bleaching that has been determined experimentally on the basis of the sediment's envi ronment of deposition is applied. This technique commonly is used for water-lain sediments (alluvial, lacustrine, and debris-flow "I- ED--- deposits) that may not have been fully light bleached prior to deposition (i.e., the inherited TL signal is only partially zeroed). DOSE (INCREASING-) Depending on the type of material being analyzed, TL is measured on specific grain sizes and (or) mineral fractions. Most workers prefer the 3 to I 1 pm micrometer fraction of polyminer B. Total-bleacn method alic materials or the 100 to 300 pm fraction of quartz or feldspar grains. The radiation contributed by alpha, beta, and gamma Z NAT 'D2 particles is assessed most easily for these minerals and grain sizes. Ns The 3 tollIpm grains are exposed to the full effect of alpha, beta, and gamma radiation, whereas the 100 to 300 tim grains are 0U +.01 incompletely penetrated by alpha and beta particles. However, U-J there will be no apparent effect from alpha particles and there I-z will be a reduced contribution of TL from beta particles if the outer surface of the grains are removed by acid etching. The effect of beta radiation in large mineral grains is not well understood, but it does depend on grain size (Mejdahl, 1979). Additionally, T I - radiation generated internally may be an important contribution in the larger grains. DOSE (INCREASING - Wintle (1973) showed that sediments that were stored after irradiation had lost TL compared with those samples measured shortly after irradiation. This loss of TL was termed "anomalous fading" because the observed stability of the TL signal is much less than that predicted from kinetic considerations. The phenom "NA 2 enon is not present in all minerals, although feldspars-especialiy 7 those of volcanic origin-seem to be particularly susceptible to fading (Wintle. 1973; 1977). If corrections are not made for anomalous fading, then both the ED and the iL age will be 0 z underestimated. Lamothe (1984), Berger (1984, 1985a), and IAT. 02 +LBp Templer (1985) developed procedures to circumvent the effects of anomalous fading. Once an acceptable value of ED has been determined, the I- sample's age is calculated from the following relation:

T Equivalent Dose (ED) DOSE (INCREASING -- ) Dose Rate (DR) Figure 5. Three methods used to determine equivalent dose (ED) in TL dating of sediment: A) regeneration method, B) total Wea ch method, and where DR is the annual dobe rate (grays/yr) in the material's C) partial bleach method. Abbreviations indicate the foollowing: NAT, natural environment. DR is calculated from the types and natural TL of sediment; LB, light-bleach procedure peilormied on sedi mert (LBp. partial bleach. LBt, total bleach) and D, a Sditional amounts of radioactive elements in the sample and their rates of mental doses of radiation to sediment (D1 , D2. DI2). Modified from production of gamma. beta, and alpha particles. The gamma Singhvi and Mejdahl (1985). component can be measured directly by placing field dosimeters 64 J. N. Rosholt and Others

in the sediment (for as much as a year), by using a gamma rily from feldspar, which did not exhibit anomalous fading. Four spectrometer, or by elemental analysis of the sediment. The alpha determinations on loess yielded an average TL age of 86 * 8 ka. and beta contributicins usually are determined by measuring the which is consistent with geologic constraints on the tephra's age. alpha activity of the uranium and thorium decay chains and the Significant advances have been made on TL dating of water total potassium content of the sample. Alpha particles are 5 to 20 laid sediments. Mineral grains transported by and deposited in percent as effective as beta and gamma particles in producing TL water are exposed to a less intense and more restricted spectrum because of localized saturation in the alpha track (Zimmerman. of light than are mineral grains deposited in eolian sediments. 1972). The calculated dose rate (DR) commonly is corrected for Huntley (1985) summarized methods for dating incompletely absorption of alpha, beta. and gamma radiation by water in the light-bleached sediments of marine, fluvial, and lacustrine sedi sediment. This correction factor is the greatest potential source of ments. Berger's ( 1984, 1985a) TL studies of glacial-lacustrine silt error in a TL age determination for sediment because of possible units showed that those sediments were incompletely bleached variations in pore-water content during and after burial (i.e.. as a prior to deposition. He also showed that in rapidly deposited result of periodic drying and wetting). An additional problem water-lain sediments from British Columbia, Canada, feldspars may be caused by disequilibrium of the uranium-decay chain, were bleached preferentially over quartz. Also, the pre especially if a significant amount of radon has diffused through depositional (inherited) TL signal of glacial silt was not signifi the sediment. For example, uranium-series disequilibrium occurs candy reset before deposition in lakes, but mudflow silts were during deposition of deep-sea sediments and cave speleothems, sufficiently bleached to be dated. By using an artificial light spec and analysis of these materials requires using a model of time trum that simulated attenuated light bleaching in the lacustrine dependent dose rates (Wintle. 1978; Wintle and Huntley, 1980). environment, Berger (1984) obtained TL ages of 36 and 66 ka for Post-depositional weathering, accumulations of secondary miner the glacial-lacustrine silt units, in agreement with age controls als in soils (silica, calcium carbonate, and clay), and ground-water based on regional stratigraphic correlations. movement also can change the amounts and types of radioactive A similar procedure of partial light bleaching was used to elements in the sampled material. date sediments of the St. Pierre interstade in southern Quebec (Lamothe, 1984). Sediments of the interstade exhibited signifi APPLICATION OF THERMOLUMINESCENCE cant anomalous fading, but delayed measurement of the post TO DATING irradiation TL signal minimized the fading;, the determined TL age of 61.1 ±9.2 ka is consistent with the enrichment radiocar bon age for the unit TL dates for lacustrine silt units related to the Only recently has TL been used as in Quaternary studies in past three major lake cycles in the Bonneville Basin in Utah were -North America. Much of the pioneering work on TL dating of used to establish a local history of faulting (McCalpin, 1986). In sediment was on the loesses of Europe (i.e., Wintle and others, this study, the moisture history of the sediment was reconstructed 1984). Loesses and loess-like deposits are widespread, they have and its effects on dose rate (DR) were considered in the age paleoclimatic significance, and they have been difficult to date by determinations. The TL ages of 13 to 138 ka are compatible with methods other than radiocarbon. Eolian sediments are ideal for accepted ages of the lacustrine units that are based on amino acid TL dating because they satisfy the basic criterion of exposure to racemization ratios from shells, soil development, and the re sunlight during deposition. gional history of the Bonneville basin. In the United States, the preliminary studies by Johnson and The TL technique also has proven useful in dating soils. others (1984) on loess from southern Mississippi indicate that the Huntley and others (1983) reported TL ages for buried soils from TL signal may have been accumulated linearly during the past two late Holocene archaeological sites in British Columbia. The 130,000 yr. TL ages from the Peoria Loess (late Wisconsin, latest A horizons yielded ages that agreed with radiocarbon dates from Pleistocene) are in agreement with radiocarbon ages from the the soil parent material. Wintle and Catt (1985) studied a surface same deposits. Similar results (but having considerable scatter soil and two buried soils developed in Holocene deposits; they and showing chronologic reversals) were obtained from the Peo determined that the degree of light bleaching in a soil is related ria Loess in Iowa (Norton and Bradford, 1985). However, three chiefly to the depth and degree of pedoturbation (mixing). In of their TL ages, from the older Farmdale Loess and Loveland these soils, surface A horizons commonly are zeroed, and TL in Loess, are in conflict with ages inferred from stratigraphic and the upper part of B horizons may be partly zeroed, depending on climatic relations. The significance of the TL dates from the older the extent and depth of mixing. The upper horizons of a buried loesses is difficult to evaluate because there are only a few anal soil in loess yielded apparent TL ages of 4.6 ± 0.4 ka and 7.4 ± yses and the basic laboratory data were not presented. 0.7 km, in general agreement with a radiocarbon age from the Wintle and W:stgate (1986) made a detailed study of the same material. However, the lower part of the soil yielded 7L mineralogy and thermoluminscence properties of loess inter ages that were younger than expected, indicating that weathering bedded with the Old Crow tephra (volcanic ash) near Fairbanks, may affect TL acquisition in the loess. Alaska. The TL signal in the fine fraction of the loess was prima- iT has been applied to the dating of soluble minerals that Dating Methods Applicable to the Quaternar6 65 accumulate in sediments. The precipitation and crystallization of AMINO ACID GEOCHRONOLOGY OF soluble minerals, such as calcium carbonate, gypsum, and halite, FOSSIL MOLLUSKS sets the TL clock of each individual crystal into motion (Zeller and others, 1955). TL has been applied with limited success to D. R. Muhs the dating of calcite stalagmites (Wintle, 1978; Hennig and oth ers. 1980: Debenham and Aitken. 1984). Recently, the TL prop INTRODUCTION erties of pedogenic calcium carbonate were studied from calcic soils of known age in the Rio Grande Valley of New Mexico In the last two decades, considerable progress has been (May and Machette, 1984). The TL signal increased systemati made in using ratios of the protein amino acids in fossils, such as cally in soils ranging in age from about 15 ka to at least 400 ka. shell and bone, to estimate the fossil's relative or numerical age. but the processes of TL acquisition and dose rate history of these The basis of amino acid geochronology is the observation that the soils are complex and still poorly understood. Nonetheless, the protein of living organisms contains only amino acids of the L method is potentially useful for dating secondary precipitates in configuration. Upon the death of an organism, amino acids of the soils and sediments. L configuration convert to amino acids with D configuration, a Significant advances in the analytical techniques of TL now process referred to as racemization. Racemization is a reversible permit the dating of volcanic ashes (Berger and Huntley, 1983; reaction that results in increased D/L ratios in a fossil through Berger, 1985b). Due to the high temperatures involved in the time until a D/L equilibrium ratio (1.00 to 1.30, depending on eruption and deposition of volcanic ash, the ash is emplaced the amino acid) is reached. Thus, in a simplified view, a higher without inherited TL. The glass fraction from ash exhibits negli D/L ratio in a fossil indicates a relatively greater age. gible anomalous fading and it may retain a stable TL signal for as Several lines of evidence suggest that amino acid ratios do much as 500 ka. not increase linearly over time; in other words, they do not follow simple, first-order reversible kinetics. Analyses of reasonably SUMMARY well-dated deep-sea sediments (Wehmiller and Hare, 1971; King and Neville, 1977) indicate that foraminifera experience a rapid In North America, the application of TL dating to geologic linear change at first, followed by a much slower linear rate of materials has gained popularity since Wintle and Huntley's change, with an uncertain area in between (Fig. 6). Fossil mol (1979) study of deep marine sediments. TL has been applied to a lusks have been thought to follow similar, nonlinear kinetic variety of terrestrial deposits; during the past five years, intensive pathways, but sufficient data to prove this are still lacking (Weh research on TL dating of eolian and water-laid sediments has miller, 1982). Pyrolysis experiments at elevated temperatures on produced new techniques that provide near-routine dating capa modern mollusks dearly indicate that nonlinear kinetics are fol bilities. Recently, research has expanded to chemical precipitates, lowed in the racemization reaction. However, some pyrolysis volcanic ashes, and buried soils; preliminary results from these experiments indicate that the break in slope may occur at higher studies are promising. However, since the TL technique is still in D/L ratios than is indicated by analyses of deep-sea foraminifera its infancy, it should be considered experimental and should be (Masters and Bada, 1977; Kriausakul and Mitterer, 1978). In any applied judiciously. The measurement of TL and the processes of case, it is generally agreed that the causes of the change in rate of TL acquisition by natural materials are complex and not fully racemization are related to two factors: (I) racemization occurs at understood at present. Additionally, the mechanisms of bleaching strikingly different rates depending on the position of the amino by sunlight are not understood, including the physical mecha acid in the peptide chain (internal, terminal, or free) and (2) the nisms for different levels of bleaching. Significant problems re changing abundances of different molecular weight components main in determining past dose rates, particularly where diagenetic in the fossils (Wehmiller, 1984a). processes have changed initial concentrations of radioactive Amino acid geochronology has been used in the US. in a elements. wide variety of contexts in Quaternary stratigraphy, tectonics, Although the TL technique has restrictions and limitations paleoclimate, sea-level history, and archaeology. This section will (as do most dating techniques), the greatest asset of thermolumi only highlight some recent results on mollusks in the contermi nescence is that it directly dates a wide variety of types and ages nous U.S. More detailed reviews are found in Williams and of sediment. Thus, the method can provide detailed chronologic Smith (1977), Hare and others (1980), Wehmiller (1982, 1984a), information about past geologic events that cannot be dated by Miller (1985), and Bada (1985). other methods. Study of deposits with independent dating control and dear stratigraphic relations may result in refinement of the FACTORS AFFECTING AMINO ACID RATIOS method and may provide important information related to the effect of light bleaching in different sedimentary environments, Several variables are known to affect amino acid racemiza the mobility of radioactive elements, and the moisture history of tion rates and/or observed ratios in fossils including temperature sediments. (both the mean annual temperature and the amplitude of the .1 66 J. N. Roshoft and Others

difference in rates of racemization between species of the same 1.0F genus. Miller and Hare (1980) also report significant differences Q) i 9" C-, 15: in amino acid ratios between different genera of nonmarine mol 0) 0.9 F lusks. Apparently, however, there are also reversals of this gener 0.8 alization in the later stages of diagenesis: in some older deposits, I- amino acid ratios of a given genus are greater than those of 0.7 another genus, whereas the opposite relationship holds for the C 0.6 U same two genera in younger deposits (Lajoie and others, 1980). 0.5 These investigators also found that there are differences in rates of 0.4 racemization among different amino acids in the same genus, n 0.3 V:0 with proline being most rapid and valine the slowest. Brigham 0.2 of a single species 0.1 "irst linear portion (1983) conducted experiments with valves from a single deposit in order to investigate intrashell variability. 0 100 200 300 400 500 600 Her results indicate that amino acid ratios did not vary signifi AGE (KA) candy between five anatomically different shell parts; however, results from the central or hinge parts of valves had less variability Figure 6: Possible pathways of racemization based on extrapolation of about their mean values. She also found that the absolute concen deep-sea foraminifera kinetics to higher temperatures, derived from data trations of various amino acids did vary significantly between in Webmiller and Belknap (1978). Particularly uncertain areas are indi shell parts. cated by dashed lines. In addition to natural sources of variability in amino acid ratios, there are also differences in reported amino acid ratios due to the type of laboratory analysis used. At present, there are four analytical methods in routine use, three using gas chromatograph ic (GC) techniques (Kvenvolden and others, 1972; Frank and others, 1977; Hoopes and others, 1978) and one using annual temperature cycle), genus. type of amino acid, and diage ion-exchange liquid chromatography (LC) (Hare, 1975). The LC netic processes (Wehmiller, 1982). Temperature history is one of method is most commonly used, but the only amino acid ratio the most critical factors, because higher temperatures greatly in obtained is D-alloisoleucine/L-isoleucine. The GC methods are crease racemization rates. However, because of repeated climatic more expensive and are less commonly used, but yield D/L ratios changes, it generally is difficult to estimate diagenetic temperature for several amino acids, including alanine, valine, leucine, proline, histories. Webmiller (1982) gives a method for estimating what aspartic acid. glutamic acid, and phenylalanine. Unfortunately, he calls the Effective Quaternary Temperature (EQT) of a sample alloisoleucine and isoleucine are usually not well resolved on GC from paleoclimatic data. The EQT is defined as the integrated systems, so it is often not possible to compare results from GC kinetic effect of all temperatures to which a sample has been and LC systems. Most investigators report amino acid ratios of exposed during its burial history. Refinement of EQTs for various total extractions, i.e., those including both protein-bound amino localities by Wehmiller's method will be an important advance acids and those freed by natural hydrolysis. However, the pool of ment in amino acid studies. free amino acids contains amino acids from terminal positions An important and often overlooked factor is the effect of where the rate of racemnization is high (Kriausakul and Mitterer. burial depth on temperature. Wehmiller (1977) found that aver 1978), so some investigators analyze separate extractions of free age racemization rate constants varied by more than four times amino acids as well as total extractions. In cold regions such as within a depth interval of 1.5 m in a Holocene shell midden in arctic North America, amino acid ratios in the free fraction are California, due to differences in the amplitude of the annual useful because the overall rate of racemization is low (Nelson, temperature cycle. Similar results have been reported by McCoy 1982; Miller, 1985). Interlaboratory comparisons indicate that (1987) in the Great Basin. Often, information about depth of there are differences in results on control samples (Wehmiller, sampling is not given in amino acid studies, but it is clear from 1984b). Coefficients of variation range from 3 to 18 percent, Wehmiller and McCoy's data that depth of burial has a consider depending on the amino acid and are best for alanine, glutamic able effect on amino acid ratios in shells from the same deposit. acid, and aspartic acid and worst for isoleucine, proline, and The rate of racemization is not constant among different valine. Instrumental rather than wet-chemical preparation proce genera or among different amino acids in the same molluskan dures are apparently responsible for most of the variability. genus. Lajoie and others (1980) have reported a large number of amino acid ratios for different, co-existing genera of west coast AMINOSTRATIGRAPHY AND RELATIVE AGES marine mollusks from the same stratigraphic unit. Their data indicate that some genera racemize much more quickly than The simplest application of amino acid ratios in geochrono others (as much as 40 to 50 percent), but there is no significant logical studies is relative age determination and lateral correla- DatingMethods Applicable to the Quaternai6 67 tion, or aminostratigraphy (Miller and Hare, 1980). The main and Belknap (1982), Wehmiller (1982), and Hearty and others assumption in this approach is that the localities studied have had (1986), who combined local aminostratigraphic data with re similar temperature histories. Stratigraphic units that have mol gional temperature gradients to develop regional amino acid lusks with amino acid ratios that cluster around a certain value isochrons. The idea is based on the assumption that, while paleo can be identified as aminozones (Nelson, 1982). temperatures along a north-south trending coastline may have The aminostratigraphic approach has been used with con differed from those of the present, regional temperature gradients siderable success on the west coast of the U.S. by Wehmiller and have always been in the same direction. Thus. in deposits of others (1977), Lajoie and others (1979), and Kennedy and others similar age, one should expect to find systematically lower D/L (1982). Similarity of D/L leucine ratios in fossil bivalves allows ratios in fossils as one moves north into cooler latitudes. Kennedy correlation of discontinuous exposures of the lowest emergent and others (1982) used this approach for lateral terrace correla marine terrace in southern California. At other localities on the tion on the Pacific coast of the US. (Fig. 7). They plotted D/L west coast, small but significant differences in D/L ratios between ratios in fossil Saxidomus as a function of latitude and connected the lowest terraces and terraces 10 to 30 m higher indicate two geographically proximal points into isochrons. Age control for distinct high stands of sea that are closely spaced in time, such as Pleistocene deposits was provided by U-series ages of coral at a high stands of- 120 ka versus high stands of - 105 ka or -80 ka. few localities. Their correlations are supported by faunal aspects: Such results were obtained for terrace pairs in California near San terraces thought to be 80 to 105 kyr old are characterized by Diego, Santa Barbara, and Point Afilo Neuvo, and on Whidbey cool-water faunas, whereas terraces thought to be - 120 kyr old Island, Washington. Similar results were obtained for low are characterized by warm-water faunas. elevation terrace pairs on the southern California Channel Islands A similar latitudinal gradient approach to aminostratigraphy by Mubs (1983, 1985). Wehmiller and others (1977) and Lajoie was developed for U.S. Atlantic coast marine deposits by Weh and others (1979) found unusually low D/L ratios in fossils miller and Belknap (1982). They generated latitudinal isochron collected from low terraces near Goleta and Ventura, California, plots of D/L leucine ratios in fossil Mercenariaand their results and Cape Blanco, Oregon. These terrae are estimated to be on indicate at least six major periods of marine sedimentation. Thus, the order of 30,000 to 50,000 yr old rather than 80,000 to their data suggest more depositional episodes than the biostrati 120,000 yr old as is the case with low terraces found elsewhere graphic criteria of Cronin (1980) and the multiple criteria of on the Pacific coast of North America. The significance of these McCartan and others (1982). One interpretation of these conflict results is two fold: (1) the time-honored concept that the lowest ing results is that amino acid ratios may be more sensitive age emergent terrace along the Pacific coast is everywhere equivalent indicators than biostratigraphic or other criteria. For some in age is dearly in error, and (2) significantly higher uplift rates localities, however, uranium-series age estimates conflict with ame implied for localities where young terraces are found. amino acid results (Wehmiller and Belknap, 1982, Szabo, 1985). The major aminostratigraphic studies in the U.S. using Wehmiller and Belknap (1982) suggest that the problem may be freshwater mollusks have been conducted by W. D. McCoy and related to uranium-series-dated samples that have relatively low co-workers in the Great Basin. In the Lake Bonneville Basin, 230 Th/232Th ratios. Correction for the samples with low McCoy (1987) and Scott and others (1983) recognize four major 23°Th/ 2 32Th ratios does not eliminate the conflict, however aminozones related to major lake cycles. The oldest deposit is (Szabo, 1985). Also, Wehmiller and Belknap (1982) used differ >600 ka, and the youngest is - 11 to 30 ka. In the Lahontan ent uranium-series age estimates of corals to calibrate their iso Basin, McCoy (1981) recognizes five major lake cycles and has chrons; thus the issue of agreement versus disagreement of distinguished three of them with amino acid ratios. Comparing uranium-series and amino acid age estimates depends on which amino acid ratios in shells from the last two major lake cycles in deposits are selected for age comparison and which dated depos the Bonneville and Lahontan basins, McCoy (1981) suggests the its are used for calibration. cycles can be correlated. In the midcontinent of the US., terrestrial gastropods in NUMERICAL AGES FROM KINETIC MODELS glacial tills or sediment associated with till appear to be suitable for aminostratigraphic correlation. Miller and others (1987) ana An important goal #f amino acid geochronology is the de lyzed terrestrial gastropods from glaciated parts of Indiana and velopment of numerical ages from amino acid ratios. Such age found four distinct aminozones ranging in age from late Wiscon estimates require not only knowledge of sample temperature his sin (-20 ka) to >730 ka. Midcontinent tills, loesses, and other tory but also an understanding of racemization kinetics. Some sediments have considerable potential for aminostratigraphy be studies have assumed that racemization follows simple linear ki cause terrestrial gastropods are common there. netics and numerical ages have been generated using independent AMINOSTRATIGRAPHY USING LATITUDINAL age control on one or more deposits for calibration. For example, TEMPERATURE GRADIENTS Mitterer (1975) assumed an age of- 124 ka for the Coffee Mill Hammock Formation in Florida and used this age estimate and A refinement to the aminostratigraphic approach used some radiocarbon-dated Holocene deposits as calibration points above was presented by Kennedy and others (1982), Wehmiller to generate linear kinetic model ages for four older units. Al- 1.

68 J N. Roshoft and Others

U.Ur

0) ~120 ka\ 0 C 0.4 I- U --80 ka Fauna:

_J 0.2 o warm a neutral * cold

48" 4WO 32 LATITUDE Washington I Oregon I California

Figure 7. Latitudinal isochron plots of D/L ratios (leucine) in Saxidomus from the Pacific coeas of the US. from marine tera of the last interglacial complex. Modified from Kennedy and others (1982).

though his age estimates seemed to be reasonable based on sim histories similar to -12(hka samples. On San Nicolas Island. ilar dates derived from other coastlines and the deep-sea record, California, nonlinear kinetic model age estimates calculated for his results were criticized by Wehmiller and Belknap (1978), who the same terraces by Wehmiller and Belknap (1978) and Muhs showed that Mitterer's age estimates would require temperature (1985) disagree significantly. The problem may be related to the histories that were incompatible with available paleoclimatic fact that different genera, differing numbers of samples, and dif data. They showed that a nonlinear kinetic model made more ferent amino acids were analyzed in the two studies, but the reasonable assumptions about temperature history for the results imply that nonlinear kinetic modeling as presented by area, and recalculated ages for the Florida units based on Wehmiller and others (1977) is perhaps not universally applica Mitterer's amino acid ratios and their nonlinear model. The new ble. An alternative approach that has been used by some workers age estimates are significantly older than Mitterer's original is to calculate numerical ages based on linear kinetics, but to treat determinations. these as minimum-age estimates (Masters and Bada, 1977; Kar In colder regions where the rate of racemnization is low, even row and Dada, 1980; Muhs, 1985). Whereas the analysis pre old deposits may have D/L ratios that fall on the first linear sented by Webmiller and Belknap (1978) argues convincingly portion of the racemization pathway of Figure 6. In such situa against linear kinetics applied to numerical age estimates, prob tions, it is probably reasonable to calculate numerical ages assu ably there are still too few calibration points to define accurately ming linear kinetics, and the main uncertainty remaining is a racemization pathway for mollusks. temperature history;, where this is the case, alternative numerical ages can be calculated using a variety of temperature history ADVANTAGES OF AMINO ACID models. Nelson and Van Arsdale (1986) used such an approach GEOCHRONOLOGY for fossil gastropods found in alluvium in central Utah and used the derived ages to determine fault slip rates. A similar approach Several factors make amino acid geochronology a particu was used by Miller (1985) to develop a chronology for marine lady useful technique in Quaternary studies. One advantage is deposition in Arctic Canada. that mollusks suitable for such work are common in Quaternary Nonlinear kinetic models for amino acid racemization have deposits. A second advantage is that very small sample sizes are been developed by a number of investigators. Using the assump required, normally only 100 to 400 mg (Miller and Hare, 1980), tion that foraminifera provide a reasonable analog to mollusks but sometimes as little as 5 mg (Wehmiller, 1984a). This gives the and extrapolating foraminifera racemization pathways to higher investigator the possibility of analyzing the same shell for both temperatures, nonlinear kinetic models have been used to gener amino acid ratios and accelerator 14C dating. In addition, because ate numerical age estimates for marine mollusks on both the east individual shells can be analyzed, amino acid ratios can identify and west coasts of the US. by Wehmiller and others (1977), mixed populations, or deposits that contain shells of more than Wehmiller and Belknap (1978, 1982), Lajoie and others (1979), one age. Evidence for reworking of shells into younger deposits Belknap and Wehmilier (1980), We&l'• (1981), Muhs and based on amino acid ratios has been documented by Nelson Rosholt (1984), and Muhs (1983, 1985). Calibration for most of (1982). Finally, in most environments. racemization rates are low these studies was from deposits with coral that have U-series enough that amino acid ratios can be used for relative age deter ages of -120 ka. In all studies, an assumption was made that minations of shells that are well beyond the range of radiocarbon marine fossils older than - 120 ha have experienced temperature dating. a.

Dating Methods Applicable to the Quaternary 69

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of amino acid racemization to geochronology and geothermometry. Origins Winde. A. G. Shackleton. N. J., and Lautridou. J. P.. 1984. Thermolumincscence of Life. v. 8. p. 91-144. dating of periods o loess deposition and soil formation in Normandy. Na Winograd. 1. J. and Doty. G. C.. 1980. Paleohydrology of the southern Great ture, v. 310, p. 491-493. Basin with special reference to water table fluctuations beneath the Nevada Wolfman. D, 1983. Archaeomagnetism of baked clays, in Creer. K. M, Tu Test Site during the late?) Pleistocene: U.S. Geological Survey Open-File cholka. P., and Barton. C. E. eds.. Geomagnetism of baked clays and recent Report 80-569.91 p. sediments: Amsterdam. Elsevier. p. 76-196. 1982, Winograd. 1. J.. and Szabo. B. J_ 1985. Water-table decline in the south-central Zeider. P. K, Johnson. N. M.. Naeser. C. W, and TahirkhliL R..A.K. Great Basin during the Quaternary period. Implications for toxic-waste dis Fission-track evidence for Quaternary uplift of the Nanga Parbat region. posal: US. Geological Survey Open-File Report 85-697. 18Ip. Pakistan: Nature. v. 298, p. 255-257. by Winograd. I. J_ Szabo. B. J., Coplen. T. B, Riggs, A. C.. and Kolesar. P. T, 1985. Zeller. F. J.. Wray. J. L, and Daniels. F, 1955, Thermoluminescence induced in Great Basin ground wa presure and by crystallization: Journal of Chemical Physics. v. 23. Two-million-year record of deuterium depletion 9 ters: Science. v. 227. p. 519-522. p.2187-218 . Winograd, L J, Szabo. B. J., Coplen, T. B. and Riggs. A. C, 1988, A 250,000 Zielinski. R. A.. Bush. C. A.. and Rosholt. J. N, 1986, Uranium-series disequilib year climatic record from Great Basin vein calcite; implications for Milanko rium in a young surficial uranium deposit, northeastern Washington: vitch theory: Science, v. 242. p. 1275-1280. Applied Geochemistry. v. i, p.503-51i. of alpha- and Wintle, A. G. 1973, Anomalous fading of thermoluminescence in mineral sam Zimmerman. D. W.. 1972. Relative thermoluminescence effects 14, p. 81-92. pies: Nature, v. 245. p. 143-144. beta-radiation: Radiation Effects, v. . 1977. Detailed study ofa thermoluminescence mineral exhibiting anomal ous fading- Journal of Luminescence, v. 15. p.385-393. MANUSCRIPT ACCEPTED BY THE SOCIETY JUNE 10, 1987 A therm olum inescenceS,1978. study of som e Q uaternary calcite; Potential ACKNOWLEDGMENTS and problems: Canadian Journal of Earth Sciences. v. 15, p. 1977-1986. Laboratory is sup Wintle. A. G.. and Catt. J, 1985, Thermoluminescence dating of soils developed Radiocarbon research at Stuiver's Quaternary Isotope Grants ATM-8318665 and in late Devensian oess at Pegwell Bay. Kent: Journal of Soil Science. v. 36. ported through National Science Foundation (NSF) p. 2'93-298. EAR-S115994. Winde. A. G.. and Huntley, D. H., 1979. Thermoluminescence dating of deep sea The K-Ar dating research of Damon was supported by NSF Gram EAR 0 - 7 12. ocean core: Nature, v. 279. p. 7 1 7811535 and the State of Arizona during development of the described metho Dr. Muhammad Shafiqullah has been a . 1980. Thermoluminescence dating of ocean sediment: Canadian Journal dology and its theoretical rationale. of Earth Sciences, v. 17. p. 348-360. diligent and effective collaborator in this research. . 1982. Thermoluminescence dating of sediments: Quaternary Science Re Forman's research on thermoluminescence was supported by NSF Grant views. v. I. p. 31-53. DPP-M303425. Forman and Machette thank A. G. Wintle for sharing her exten Wintle, A. G.. and Prdszyaska, H. 1983. TL-dating of loess in Germany and sive knowledge of thermoluminescence dating, and G. H. Miller, J. T. Andrews, Poland: PACT. v. 9, p.547-554. D. S. Fullerton, and K. L Pierce for comments on early versions of the thermo Wintle, A. 0, and Westgate, J. A., 1986, Thermoluminescence properties of loess luminescence section of this chapter. in relation to the age of Old Crow Tephra in Alaska. Geology, v. 14, Muhs thanks G. H. Miller, A. R. Nelson, and B. J. Szabo for helpful com p. 594-597. ments on early versions of the amino acid geochronology section of this section.

NOTES ADDED IN PROOF ADDITIONAL REFERENCES Addition to setion by.&M. Colman and K. L Pierce A derivative paper concerning classification and terminology for dating meth Quaternary events by luminescence. in Easterbrook, ods was published in 1987 (Colman and others, 1987). Maor advances in Berger. G. W. 1988, Dating L., ed, Dating Quaternary sediments: Geological Society of America research into dating methods have occurred between 1986 and the time of publi D. Special Paper 227, p. 13-50. cation of this volume. Some of the recem advances in dating methods have been K. Land Birkeland. P. W, 1987. Suggested terminology published in recent collections of papers by Easterbrook ( 1989), Rutter and others Colman. S. M, Pierce. p. 314-319. (1989), and Townsend and others (1988). for Quaternary dating methods: Quaternary Research. v. 28, Easterbrook. D. L (edAt 1989, Dating Quaternary Sediments: Geological Society 227. 165 p. Addition to section by C. W. Naeser and N. D. Naeser of America Special Paper Forman, S. L. 1989. Applications and limitations of thermoluminescence to date 1. p. 47-59. An important recent advancement in application of fission track dating to Quaternary sediments: Quaternary Internationad, v. M.LW., 1985. Optical Quaternary tephra is development of the isothermal plateau method fr Correcting Huntley. D. W. Godfrey-Smith, D. L and Thewalt. thermally lowered fission-track ages on hydrated glass shards (Westgate, 1988& dating of sediments: Nature, v. 313, p. 105-107. Thermoluminescence dating of l0 in 1989). This method has produced glass ages that are concordant with zircon Rendell, H_ and Townsend, P. D, 1988, 39 v. 7, p. 251-255. fission-track, K-Ar. 4°Ar/ Ar, and thermoluminescence ages on coexisting min bess profile in Pakistan: Quaternary Science Reviews. Applied Quaternary erals from rocks ranging from Quaternary to Cretaceous (Westgate, 1988, 1989). Rutter, N, Bdrigham-Grette. J., and Catto. N. (eds.), 1989. Geology: Quaternary International, v. 1, 166 p. Addition to sectdon by . L Forman and M. N. Machette Townsend. P. D., and 9 others (eds.), 1988, Thermoluminescence and Electron Spin-Resonance Dating: Quaternary Science Reviews. v. 7. p. 245-536. Since 1986 when this chapter was completed there have been some signifi plateau fissiou-track age of the late Pleistocene cant advances in luminescence dating. Thermoluminescence dating of buried soils, Westgate, J. A., 1988. Isothermal tephmr Alaska. Geophysical Research Letters. v. 15, p. 376-379. loess and eolian sand has yidded ages U agreement with a radiocarbon chronol Old Crow ogy (Berger, 1988: Forman. 1989). The temporal limitations of the method , 1989, Isothermal plateau fission-track age of hydrated glass shards from v. 95, p. 226-234. remain uncertain but apparently accurate ages of ca. 100 ka have been reported silicic tephra beds. Earth and Planetary Science Letters. (Forman. 1989), The more energy sensitive analysis provided by optical stimu (Huntley and others. 1985). lated luminescence may be a better geochronometer Printed in U.S.A. 74 J. N. Roshol tand Others

of amino acid racemization to geochronology and geothermometry Origins Winde. A. G.. Shackleton. N. J. and Lautrduo. J. P.. 1984. Thermoluminescence and soi formation in Normandy. Na. of Life, v. 8. p. 91-144. dating of periods of loess deposition Winograd. L J.. and Dory, G. C. 1980, Paleohydrology of the southern Great ture, v. 310. p. 491-493. days. in Creer. K. M, Tu Basin with special reference to water table fluctuations beneath the Nevada Wolfman. D. 1983. Archaeomagnetism of baked Test Site during the laue?) Pleistocen. US. Geological Survey Open-File cholka. P, and Barton, C. E.. eds. Geomagnetism of baked clays and recent Report 80-569. 91 p. sediments: Amsterdam. Elsevier. p. 76-196. C. W, and Tahirkheli. R.A.K.. 1982, Winograd. L J_ and Szabo. B. J. 1985. Water-table decline in the south-central Zeiter. P. K. Johnson. N. M. Naeser, Nanga Parbat region. Great Basin during the Quaternary period; Implications for toxic-waste dis Fusion-track evidence for Quaternary uplift of the posal: US. Geological Survey Open-File Report 85-697. 18 p. Pakistan: Nature, v. 298. p. 255-257. induced by Winograd. L J.. Szabo. B. J, Coplen. T. B. Riggs. A. C. and Kolesar, P. T. 1985. Zeller. L- J.. Wray, J. L, and Daniels. F., 1955, Thermoluminescence crystallization: Journal of Chemical Physics. v. 23, Two-million-year record of deuterium depletion in Great Basin ground wa pressure and by ters: Science, v. 227. p.519-522. p. 2187-2189. Uranium-series disequilib Winograd, 1. J.. Szabo. B. J. Coplen. T. B. and Riggs, A. C. 1988, A 250,000 ZielinskiL R. A.. Bush. C. A., and Rosholt. J. N, 1986. for Milanko rium in a young surficial uranium deposit, northeastern Washington: year dimatic record from Great Basin vein calcite: implications 3 vitch theory Science, v. 242. p. 1275-1280. Applied Geodchmistry, v. 1,pi 50 -51I. thermoluminescence effects of alpha- and Wintle. A. G, 1973, Anomalous fading of thermoluminescence in mineral sam Zimmerman. D. W. 1972. Relative p. pics Nature. v. 245, p. 143-144. beta-radiation: Radiation Effects, v. 14, 81-92. . 1977. Detailed study ofa thermoluminescence mineral exhibiting anomal ous fading: Journal of Luminescence. v. 15. p. 385-393. MANuscawr ACCEPTED BYTHE SOCIETY JUNE 10, 1987 of some Quaternary calcite: Potential . 1978, A thermoluminescence study ACKNOWLEDGMENTS and problems: Canadian Journal of Earth Sciences. v. 15. p. 1977-1986. is sup Winde. A. G., and Catt. J, 1985. Thermoluminescence dating of soils developed Radiocarbon research at Stuiver's Quaternary Isotope Laboratory and in late Devensian loess at Pegwell Bay. Kent: Journal of Soil Science. v. 36, ported through National Science Foundation (NSF) Grants ATM-8318665 p. 293-298. EAR4 115994. Grant EAR Winde. A. G, and Huntley, D. H1. 1979. Thermoluminescence dating of deep sea The K-Ar dating research of Damon was supported by NSF described metho ocean core Natur v. 279, p. 710-712. 7811535 and the State of Arizona during development of the Dr. Muhammad Shafilqullah has been a . 1980. Thermoluminescence dating of ocean sediment: Canadian Journal dology and its theoretical rationale. of Earth Scienes. v. 17. p. 348-360. diligent and effective collaborator in this research. Forman's research on thermoluminescence was supported by NSF Grant - 1982. Thermoluminescence dating of sediments: Quaternary Science Re views. v. I. p. 31-53. DPP4303425. Forman and Mache'te thank A. G. Winde for sharing her exten and G. H. Miller. J. T. Andrews. Wintle. A. G, and Pr6szyfiska. H. 1983. TL-dating of bess in Germany and sive knowledge of thermoluminescence dating, early versions of the thermo Poland: PACT, v. 9, p. 547-554. D. S. Fullerton. and K. L Pierce for comments on chapter. Wintle. A. G., and Westgate, J. A.. 1986k Tbermoluminescence properties of bess luminescence section of this com in relation to the age of Old Crow Tephra in Alaska- Geology, v. 14, Muhs thanks G. H. Miller, A. R. Nelson, and B. J. Szabo for helpful p. 594-597. ments on early versions of the amino aciid geochronology section of this section.

NOTES ADDED IN PROOF REFERENCES Addition o section by I M. Colman and K. L Pierce ADDmONAL A derivative paper concerning dassilication and terminology for dating meth Quaternary events by luminescence, in Easterbrook. published in 1987 (Colman and othes 1987). Major advances in Berger. G. W. 1988. Dating ods was Geological Society of America research into dating methods have occurred between 1986 and the time of publi D. J.. ad.- Dating Quaternary sediments: Special Paper 227, p. 13-50. cation of this volume. Some of the recent advances in dating methods have been W, 1987. Suggested terminology published in recent collections of papers by Easterbrook (1989). Rutter and others Colman. S. M_ Piercek K. L and Birkeland. P. methods: Quaternary Research. v. 28, p.314-319. (1989). and Townsend and others (1988). for Quaternary dating Eastebrook. D. L (ed.). 1989, Dating Quaternary Sediments: Geological Society p. Addition s seion by C W.Noaese and N. D. Noeser of America Special Pawer 227.165 Forman, S. L- 1989, Applications and limitations of thermoluminescence to date An important recent advancement in application of fmsion track dating to Quaternary sediments: Quaternary International, v. I. p. 47-59. Quaternary tephra is development of the isothermal plateau method for Correcting Huntley. D. W.. Godfrey-Smith, D. I. and Tbewalt. M.LW, 1985, Optical thermally lowered fission-track age on hydrated glass shards (Westgate, 1988. dating of sediments: Nature. v. 313. p. 105-107. dating of a 10 m 1989). This method has produced glass ages that are concordant with zircon Rendell. H. and Townsend. P. D. 1988. Thermoluminescence fission-track. K-Ar, "0Ar/-9Ar. and thermoluminescence ages on coexisting min toes profile in Pakistan: Quaternary Science Reviews. v. 7, p. 251-255. erals from rocks ranging from Quaternary to Cretaceous (Westgate. 1988. 1989). Rutter, N, Brigham-Grette. J., and Catto, N. (eds.). 1989. Applied Quaternary Geology. Quaternary International. v. I, 166 p. Addition to section by £ L Formanand M. N. Mache Townsend. P. D., and 9 others (eds.), 1988. Thermoluminescence and Electron Reviews. v. 7, p. 245-536. Since 1986 when this chapter was completed there have been.rome signifi Spin-Resonance Dating: Quaternary Science fission-track age of the late Pleistocene cant advances in luminescence dating. Thermoluminescence dating of buried soils. Westgate. J. A. 1988, Isothermal plateau v. 15, p. 376-379. loess and colian sand has yielded ages in agreement with a radiocarbon chronol Old Crow tephra, Alaska- Geophysical Research Letters. glass shards from ogy (Berger. 1988: Forman. 1989). The temporal limitations of the method -, 1989, Isothermal plateau fission-track ages of hydrated remain uncertain but apparently accurate ages of ca. 100 ka have been reported slicic tephra beds: Earth and Planetary Science Letters. v. 95, p. 226-234. (Forman, 1989). The more energy sensitive analysis provided by optical stimu abetter geochronomet (Huntley and othem 1985). lated luminescence may be Printed in US.A. Report of Investigations No. 180 Geomorphic Processes and Rates of Retreat Affecting the Caprock Escarpment, Texas Panhandle

Thomas C. Gustavson and William W. Simpkins

"I. "-i

Sw-- .o4#- - y. IN'

__ Bureau of Economic Geology

1989 ..-' ,2 -W.. L. Fisher, Director The University of Texas at Austin Austin, Texas 78713

'7'ý IZ

NI - - Report of Investigations No. 180

Geomorphic Processes and Rates of Retreat

- Affecting the Caprock Escarpment, Texas Panhandle

Thomas C. Gustavson and William W. Simpkins*

Bureau of Economic Geology 1989 W. L. Fisher, Director The University of Texas at Austin Austin, Texas 78713

*Department of Geology and Geophysics University of Wisconsin Madison, Wisconsin 53705 CONTENTS Abstract ...... 1 Introduction ...... 2 G eologic Setting ...... 3 Structural Development ...... 3 Stratigraphy ...... 4 Regional Hydrology ...... 5 Geomorphology and Physiography ...... 5 C lim ate ...... 5 R unoff ...... 8 Relation of Dissolution-Induced Subsidence to the Caprock Escarpment ...... 10 Stratigraphy beneath the High Plains, Caprock Escarpment, and Rolling Plains ...... 10 Structure on the Tubb Interval ...... 10 Salt Thickness ...... 13 Structure on the Alibates Formation ...... 13 Middle Tertiary Erosional Surface ...... 13 Relation of Post-Ogallala Lake Basins to the Caprock Escarpment ...... 18 Fracture Systems and Landform Development ...... 18 Systematic and Nonsystematic Fractures ...... 18 Clastic Dikes ...... 19 Ground-Water Flow beneath the Caprock Escarpment ...... 20 Conceptual Model of Ground-Water Flow beneath the Caprock Escarpm ent ...... 22 Numerical Model of Ground-Water Flow beneath the Caprock Escarpment ...... 24 M odeling Results ...... 25 Surface Processes Causing Scarp Retreat ...... 27 Surface Runoff ...... 27 Drainage Developm ent ...... 27 Thresholds for Sediment Movement ...... 28 Spring Sapping and Seepage Erosion ...... 29 Rockfalls ...... 31 Rotational Slum ping ...... 31 Piping ...... 34 Stages in the Physiographic Development of the Eastern Caprock Escarpment ...... 35 Rates of Retreat of the Caprock Escarpment ...... 38 Rates of Interstratal Salt Dissolution along the Caprock Escarpment ...... 38 Procedure for Calculating Salt Dissolution Rates ...... 38 Salt Dissolution Rates ...... 39 Surface Erosion Rates ...... 41 Effect of Diminished Spring Discharge on Geomorphic Processes ...... 42 Summary and Conclusions ...... 44 Acknowledgments ...... 45 R eferences ...... 45

nli Figures 1. Location of the study area in the eastern Texas Panhandle ...... 2 2. Major structural elements, Texas Panhandle and surrounding area ...... 3 3. Stratigraphic nomenclature of Permian and younger strata, Texas Panhandle ...... 4 4. Topography along the Caprock Escarpment ...... 6 5. Views of the Eastern Caprock Escarpment in Palo Duro Canyon State Park ...... 7 6. Three-day total rainfall distribution, June 24-26, 1965, along the Eastern Caprock Escarpment ...... 8 7. Intensity-duration profiles of four storms along the Caprock Escarpment ...... 9 8. Regional stratigraphic cross section illustrating zones of section lost owing to dissolution of salt and collapse of overlying strata beneath the 11 Southern High Plains, Caprock Escarpment, and Rolling Plains ...... 9. Structure-contour map of the top of the middle Permian Tubb interval ...... 12 10. Net-thickness map of salt in the Permian upper Clear Fork Group and San Andres, Seven Rivers, and Salado Formations ...... 14 11. Net-thickness map of salt in the Salado and Seven Rivers Formations ...... 15 12. Structure-contour map of the top of the Upper Permian Alibates Formation ...... 16 13. Structure-contour map of the base of the High Plains aquifer (Ogallala Formation) ...... 17 14. Head map of the unconfined aquifers in the Palo Duro Basin ...... 20 15. Potentiometric-surface map of lower Dockum Group ground water ...... 21 16. Map of physiographic units, major streams, and brine emission areas in the study area ...... 22 17. Conceptual model of ground-water flow and its impact on Permian bedded salt beneath the High Plains Caprock Escarpment and Rolling Plains ...... 23 18. Finite-element mesh design based on cross section shown in figure 8 ...... 24 19. Steady-state hydraulic heads and recharge/discharge rates computed by ground-water flow model ...... 26 20. Plot of maximum rainfall intensity versus percent of erosion pins showing erosion at the Buffalo Lake National Wildlife Refuge station ...... 29 21. Area of spring sapping at the head of Red Canyon, Palo Duro Canyon State Park ...... 30 22. Detail of the spring discharge area illustrated in figure 21 ...... 30 23. Rockfall consisting of blocks of massive channel sandstones, Upper Triassic Dockum Group at the head of Tub Springs Draw, Palo Duro Canyon State Park ...... 31 24. a. Fracture in caprock caliche of the Miocene-Pliocene Ogallala Formation at Fortress Cliff, Palo Duro Canyon State Park ...... 32 b. Fracture in sandstone of the Upper Triassic Dockum Group in Tub Springs Draw ...... 32 25. Distribution of rotational slumps and landslides in Palo Duro Canyon, Palo Duro Canyon State Park ...... -...... 33 26. Three segments of rotational slumps exposed along the northeastern side of Palo Duro Canyon ...... 34 27. Entrance to a large pipe in Caprock Canyons State Park ...... 35 28. Outlet for a large pipe in Palo Duro Canyon State Park ...... 35 29. Stages in development of drainage at the Caprock Escarpment ...... 36 30. Drainage basins and gauging stations in the Rolling Plains ...... 40 Tables 1. Rainfall intensity-duration-frequency relationships, Amarillo, Texas, 1904-1951 ...... 9 2. Hydrostratigraphic units and hydraulic conductivities used in the ground-water flow model ...... -...... 25 3. Erosion-pin measurements made on eroded canyon slopes following storm on M ay 26, 1978 ...... 28 4. Record of intense storms at Buffalo Lake National Wildlife Refuge ...... 28 5. Dissolved chloride loads for streams, calculated salt volumes, and salt dissolution rates for selected drainage basins, Texas Panhandle ...... 39 6. Spring discharge rates, Eastern Caprock Escarpment, Texas Panhandle ...... 43

iv Abstract

The interaction of geomorphic and ground-water processes has produced the Caprock Escarpment that bounds the eastern margin of the Southern High Plains in the Texas Panhandle. Spring sapping, slumping, and piping at the surface and salt dissolution in the subsurface are some of the many erosional processes affecting the escarpment. Substantial thicknesses of bedded Permian salt (halite) have been dissolved from the Salado, Seven Rivers, San Andres, and Glorieta Formations beneath the Caprock Escarpment and the Rolling Plains, east of the escarpment. Dissolution of salt from the Salado and Seven Rivers Formations beneath the Caprock Escarpment has resulted in subsidence and development of a regional dip reversal in the overlying Alibates Formation. Although most dissolution has taken place beneath the Caprock Escarpment and Rolling Plains, dissolution and subsidence extend westward beyond the escarpment to beneath the Southern High Plains. Dissolution-induced subsidence apparently accounts for as much as 75 m (250 ft) of Caprock Escarpment relief. Complex fracture systems along the escarpment have developed in part because of subsidence. Permian and Triassic strata contain systematic and nonsystematic fractures, extension fractures, and, locally, clastic dikes. The Ogallala Formation contains systematic fractures in basal calcretes and silcretes and, locally, clastic dikes. Of these, the nonsystematic fractures, extension fractures, and clastic dikes probably result from salt dissolution and subsidence. Ground-water leakage downward toward the salt-bearing zones is most likely enhanced by fractures. Conceptual and numerical models of ground-water flow beneath the Caprock Escarpment suggest that low-salinity ground water flows downward from the Ogallala and Dockum aquifers to dissolve Permian salt. Brines flow eastward through permeable anhydrites, dolomites, and dissolution breccias beneath the Rolling Plains to discharge as springs in topographic lows. Dissolution is active along the Caprock Escarpment; during a 15-yr period it resulted in the loss of over 15 million m 3 (525 million ft3) of salt from the study area. Westward expansion of the active dis solution zone along the Caprock Escarpment and beneath the Rolling Plains occurs at a mean rate of 0.02 km/1,0OO yr (0.013 mi/1,000 yr). Surface erosion on the hillslopes of the Caprock Escarpment occurs by sheetflooding, slope wash, rill wash, rockfalls, spring sapping, piping, and rotational slumping. Fluvial erosion dominates in canyon bottoms. Sheetflooding, slope wash, and rill wash resulting from runoff from episodic, high-intensity rainfall events have modified the upper margin of the escarpment. Runoff from these same events scours canyons and their tributaries. Sapping below areas of spring discharge in strata of the Dockum Group and Ogallala Formation helps to remove sediment and contributes to the development of rockfalls. Numerous rotational slumps and landslides have substantially accelerated slope degradation in Palo Duro Canyon. Large pipes commonly develop along the slip planes of these slumps. Scarp retreat rates based on surface erosion rates were examined and compared with the subsurface salt dissolution rates. Scarp retreat rates based on projected former positions of the Caprock Escarpment are probably maximum rates that range from 0.06 km/1,000 yr (0.038 mi/1,000 yr) to 0.19 kin/1,000 yr (0.119 mi/1,000 yr). Short-term erosion rates based on semiannual measurement of erosion pins and stream headcuts range from 0.01 to 0.03 km/1,000 yr (0.006 to 0.019 mi/1,000 yr). The mean horizontal dissolution rate for salt in the study region is 0.02 km/yr (0.013 mi/yr). Because the Caprock Escarpment parallels and overlies the zone of salt dissolution, the retreat rates of these two features are comparable and appear to converge in the range of 0.01 to 0.20 km/1,000 yr (0.006 to 0.12 mi/1,000 yr). Discharge from many springs along the Caprock Escarpment has decreased as much as an order of magnitude over the last 50 yr as a result of widespread exploitation of the Ogallala aquifer for irrigation. Because of this trend, associated erosional processes such as spring sapping, slumping, rockfalls, and stream discharge have most likely decreased as well, thus slowing the westward retreat of the Caprock Escarpment.

Keywords: Caprock Escarpment, fractures, geomorphic processes, ground-water flow systems, Rolling Plains, salt dissolution, scarp retreat rates, Southern High Plains, Texas Panhandle

1 10X°

10w

FIGURE 1. Location of the study area in the eastern Texas Panhandle. Major physiographic divisions of eastern New Mexico, the Texas Panhandle, and the Oklahoma panhandle are shown. Letters A through J locate Department of Energy stratigraphic and hydrologic test wells: (A) DOE-Gruy Federal Rex White No. 1; (B) DOE-Gruy Federal Grabbe No. 1; (C) Stone and Webster Engineering Corporation (SWEC) Sawyer No. 1; (D) SWEC Mansfield No. 1; (E) SWEC No. 1; (F) SWEC Detten G. Freimel No. 1; (G) SWEC Zeeck No. 1; (H) SWEC J. Freimel No. 1; (I) SWEC Harman No. 1; (J) SWEC Holtzclaw No. 1.

Introduction The Southern High Plains of eastern New Mexico spring sapping, seepage erosion, and northwestern and slumping) and Texas is bounded by a high escarp that both the position of the escarpment and the pro ment on its western, northern, and eastern sides (fig. 1) cesses that cause retreat are affected and by interaction merges to the south with the Edwards Plateau. with ground-water systems. On the basis of literature Field observations from 1978 to 1986 indicate that review, Gustavson (1983) and Osterkamp and erosion and retreat of the others escarpment were most active (1987) concluded that geomorphic processes related to along the eastern margin of the Southern High Plains, ground-water discharge, such the Eastern Caprock as springs and seeps, Escarpment. Previous studies dominate landform development on suggest that several geomorphic the southern Great processes affect scarp Plains. Zones of active salt (primarily halite) retreat (for example, salt dissolution, dis subsidence, solution lie beneath the escarpment (Gustavson and

2 M Basement structural high

FIGURE 2. Major structural elements, Texas Panhandle and surrounding area (modified from Nicholson, 1960). Limits of Permian bedded salts are closely associated with the structural margins of the Palo Duro Basin. Structurally high areas are most likely to be affected by salt dissolution.

and Fogg, 1982; Gustavson and occur. Integrating the results of previous work by others, 1980; Simpkins (1980, 1981, 1983), Gustavson Finley, 1985; Gustavson, 1986a), and exposed strata are Finley and Gustavson and others (1980, 1981, 1982), Simpkins and Fogg fractured and deformed as a result of dissolution and and others, 1980; (1982), Gustavson and Finley (1985), and Simpkins induced subsidence (Gustavson concluded that ground and Goldstein and Collins, 1984). Gustavson (1987), we have Collins, 1983, 1984; play a significant role in scarp retreat of a major physio water processes To understand the development and that rates of westward scarp retreat are similar to graphic feature such as the Caprock Escarpment, it is of the salt dis geo the rate of westward advancement necessary to analyze both surface and subsurface solution zone. morphic processes as well as the stratigraphic, hydro logic, and structural framework of the region. The study area, which includes approximately 210 km Geologic Setting (131 mi) of the Caprock Escarpment in the Texas Structural Development Panhandle (fig. 1), was chosen because the escarpment roughly parallels the interstratal dissolution The Caprock Escarpment in this region overlies a zone of of the Palo Duro Basin. The Palo Duro Basin is Upper Permian salt and because spring flanks of bedded bounded by the Amarillo Uplift trend on the northeast sapping is active in many valleys in this region. Uplift on the south the major geomorphic and by the Matador Arch-Roosevelt In this report, we describe west the Palo Duro Basin is bounded by development of the Caprock Escarp (fig. 2). To the processes affecting the Pedernal and Sierra Grande Uplifts. These positive ment, their interaction, and the rates at which they

3 structural elements resulted from faulting and uplift PALO DURO the Paleozoic, perhaps as early as the initiated during BASIN late Cambrian. AGE During the Pennsylvanian and early Permian, tec West and central the Amarillo Uplift and the tonic movement along lackwalter I Tatoka Formation Arch controlled sedimentation and facies dis QUATERNARY Draw _rDoue ZLs Formttion Matador L Tue Formation tribution in the Palo Duro Basin (Dutton and others, Formation uplift during the Triassic formed elanco Formation Cila Canyon lake laa 1979). Epeirogenic Formation the terrestrial basin that contains the Dockum Group TERTIARY Ogallolo - (fig. 3) (McGowen and others, 1979). By Cretaceous time the region had subsided to below sea level. Epeirogenic CRETACEOUS_imet Edwards,o~n_ movements continued into the Tertiary and elevated Dockum Group Cretaceous marine strata in the study area to more TRIASSIC than 940 m (3,100 ft) above sea level (Eifler, 1968; Gable and Hatton, 1983; Budnik, 1984). Nontectonic deformation, expressed as regional sub sidence induced by extensive dissolution of Permian has occurred beneath the entire study area Dewey Lake bedded salt, Formation (Gustavson and others, 1980, 1982; Johnson, 1981; Boyd and Murphy, 1984; Gustavson and Budnik, 1985; Alibates Formation Gustavson and Finley, 1985; Reeves, 1985; DeConto *:-:.::*:-:~::'Salado Formation::.: and Murphy, 1986; Gustavson, 1986a, 1986b; Reeves X: X.* and Temple, 1986). Several of the lacustrine basins on * Tonsill Formation z the High Plains may have formed in part from dissolu 41) Yates Formation 0. Tertiary or tion-induced subsidence during the late - 0 Quaternary (Baker, 1915; Gustavson and Budnik, 1985; !;D Gustavson and Finley, 1985; Reeves, 1985; Reeves and Temple, 1986). Other interpretations suggest that disso n..n lution beneath the High Plains occurred during the a. Triassic and could not have affected Tertiary or Quater a Queen and nary lacustrine basins (DeConto and Murphy, 1986). "C Grayburg Formations In addition to causing surface subsidence, dissolu tion has resulted in the widespread development of extension fractures in strata above zones of salt disso lution. These fractures commonly occur in Permian mudstones and locally in mudstones of the Triassic Dockum Group. Extension fractures are recognized by their filling of fibrous gypsum (var. satin spar), in which the elongate crystals are oriented primarily ver tically .(Gustavson and others, 1981; Goldstein and Glorieta Collins, 1984; Machel, 1985). tLa. Sandstone

Stratigraphy *..-.:.:.:.:..-.:.:...... :..-.:.:.:.:.:.:.:.:.:.:..... In the eastern Texas Panhandle, episodes of deposi "0"""" ...... tion on shallow marine shelves alternated with periods Glowrieto:::-**:: 0 of erosion during the early Paleozoic. Terrigenous clastics, informally called granite wash, were derived from the Matador Arch and Amarillo Uplift during the S•) :6 ~:i:i::.::::::::ClearCimarron Forkanhydrite "sali: •a and deposited as Wi C Tubb Interval W Pennsylvanian and Early Permian 4 fan deltas (Handford and Dutton, 1980). Marine sedi 3: 0 mentation during the Late Pennsylvanian and Early Permian was dominated by shelf-margin carbonates, while the deeper parts of the basin were being filled by Red Cove Formation fine-grained terrigenous clastic sediments. During the middle and Late Permian, a wide, low-relief marine shelf developed, and salt, anhydrite, dolomite, lime I Salt-bearing units OA 6071 stone, and red beds were deposited (Presley, 1979a, 1979b, 1980a, 1980b; McGillis and Presley, 1981; FIGURE 3. Stratigraphic nomenclature of Permian and Hovorka and others, 1985; Fracasso and Hovorka, younger strata. Texas Panhandle. Principal salt units are 1987). shaded (modified from Johnson, 1976).

4 Post-Permian stratigraphic units are well repre Geomorphology and Physiography sented in the study area. Fluvial, deltaic, and lacus The study area includes parts of two major physio trine sandstones and mudstones of the Triassic graphic regions-the Southern High Plains to the west Dockum Group unconformably overlie Permian strata and the Rolling Plains to the east-and the Caprock (McGowen and others, 1979). Although Jurassic rocks Escarpment, which separates the two regions (fig. 1). are not preserved in the study area, the Lower The Southern High Plains is characterized by a flat, Cretaceous Edwards Limestone unconformably over low-relief surface partly covered with small playa lake lies the Dockum Group. During the Late Cretaceous basins. Drainage of the High Plains is mostly internal and early Tertiary, extensive erosion exposed both into these lake basins. Widely separated draws with "Triassic and Lower Cretaceous strata. Fluvial and very narrow drainage basins slope to the east and eolian sediments of the Neogene Ogallala Formation southeast. Adjacent draws do not share common overlie the Tertiary erosional surface (Seni, 1980; drainage divides but rather are separated by broad Winkler, 1984, 1985; Gustavson and Holliday, 1985; interfluves containing numerous playa lake basins. Gustavson and Winkler, 1988). Locally, Pliocene Relief along the Caprock Escarpment locally exceeds lacustrine sediments of the Blanco Formation and Cita 305 m (1,000 ft) near the mouth of Palo Duro Canyon. Canyon lake beds overlie the Ogallala Formation. The The western, or upper, topographic limit of the Caprock Quaternary Blackwater Draw Formation, which is Escarpment is clearly defined as a sharp eastward composed primarily of eolian sediments, overlies the facing break in slope (fig. 4). The eastern limit of the Ogallala Formation and Pliocene lacustrine forma escarpment occurs where the eastward slope is dimin tions (Gustavson and Holliday, 1985; Machenberg and ished at the western edge of the Rolling Plains. Locally, others, 1985). Lacustrine sediments of the Tule For however, the Caprock Escarpment extends downward mation are interbedded with the Blackwater Draw without interruption to the floor of the Palo Duro Formation. Thick, widespread Quaternary eolian, Canyon. In Randall, Armstrong, and northern Briscoe fluvial, and lacustrine deposits, composed of sediments Counties the escarpment is steep and relatively narrow. eroded from the Caprock Escarpment, overlie Triassic Escarpment width in these areas is approximately and Permian strata on the Rolling Plains at the foot of 5 km (3.1 mi). In Motley, Floyd, and southern Briscoe the Caprock Escarpment (Caran and others, 1985). Counties the escarpment is less steep but is as much as 16 km (10 mi) wide. In all areas the terrain of the escarpment is highly dissected and characterized by Regional Hydrology numerous short, steep canyons; tributaries in the head Studies of the hydrology of the Palo Duro Basin waters of the canyons near the top of the escarpment indicate that the lower (Wolfcampian) brine aquifer is are arranged in a partly centripetal pattern (pectinate separated from aquifers in the overlying Ogallala For drainage of Higgins, 1982). Relief of the escarpment is mation and Dockum Group by an aquitard composed of supported by resistant calcretes and silicified zones of upper Permian evaporites and salt-cemented terrige the Ogallala Formation and resistant sandstones of the nous clastics. Regional flow of the Wolfcampian Dockum Group and Permian Quartermaster Formation aquifer is toward the northeast (Smith and others, (fig. 5). The escarpment parallels and overlies the 1983). Ground-water movement through the evaporite western margin of the zone of active salt dissolution aquitard is minimal; flow is to the east and southeast (Gustavson and others, 1981; Gustavson and Finley, (Dutton, 1983; Orr, 1983; Kreitler and others, 1985). 1985). Ground-water flow in the unconfined Ogallala aquifer The Rolling Plains, which were developed primarily and in the Dockum aquifer is also toward the east and on easily eroded Permian strata of the Quartermaster southeast (Dutton and Simpkins, 1986; Nativ, 1988). A and Whitehorse Formations (Bath, 1980; Gustavson model of ground-water flow along a west-to-east cross and others, 1981; Simpkins and Gustavson, 1987), are section across the Caprock Escarpment suggests that locally highly dissected. In most upland areas, how leakage of fresh water from the Ogallala Formation is ever, topography is rolling, hence the name Rolling downward into the salt dissolution zone and eastward Plains. Drainage in the Rolling Plains tends to parallel beneath the Rolling Plains (Simpkins and Fogg, 1982). the margins of subsurface salt units undergoing dissolu Sodium chloride ground waters from the salt dissolu tion, and karst features resulting from dissolution tion zone beneath the Southern High Plains have "'C induced subsidence are common (Simpkins and others, ages of less than 16,200 ± 3,500 yr and 23,500 ± 1,000 yr 1981; Gustavson and others, 1982; Gustavson and and salinities of 95,000 to 68,000 ppm (Dutton, 1987). Finley, 1985). Numerous fresh-water springs, which mark discharge points of the Ogallala and Dockum aquifers, are Climate present along the Caprock Escarpment at the base of area is continental semiarid to the Ogallala Formation and to a lesser extent at the Climate in the study subhumid (45 to 55 cm [18 to 22 inches] mean annual base of Dockum Group sandstones (fig. 4) (Brune, 1981). varies from halite dis precipitation), although annual precipitation Springs discharging brines derived of Commerce, areas east of the escarpment widely (Orton, 1964; U.S. Department solution occur in several 75 percent of the annual of Engineers, 1975; Richter and 1978a, 1978b). Approximately (U.S. Army Corps the end of March and the Kreitler, 1986). precipitation occurs between

5 EXPLANATION N d-- ,-"' Drainage divide

A Gouging station ,P Spring

0 30 mi | I I z o 40km Contour interval 400 ft

0A6611

between the FIGURE 4. Topography along the Caprock Escarpment. The escarpment is approximately defined by the area the Southern High Plains and the Rolling Plains occur to the west and east. respectively. 2,600- and 3,000-ft contours; that of springs are from Brune (1981). The drainage divide marked by the Caprock Escarpment separates areas Locations lake basins of the contribute runoff to the escarpment and Rolling Plains from areas that contribute runoff mostly to playa Southern High Plains.

6 (a) L

(b)

FIGURE 5. Views of the Eastern Caprock Escarpment in Palo Duro Canyon State Park (fig. 25). Topography of the escarpment varies from (a) steep cliffs at Fortress Cliff to (b) deeply dissected slopes. Relief at Fortress Cliff, including the vertical cliff and the steep talus apron, is approximately 100 m. The vertical cliff (a) is supported by the upper Tertiary Ogallala Formation, and Triassic Dockum Group strata underlie the toe of the talus apron. Relief along the dissected slope in (b) is approximately 200 m from the floor of the canyon to the skyline: the Upper Permian Quartermaster Formation is exposed in the foreground, and Ogallala and Dockum strata are exposed in deeply dissected terrain of the middle ground.

7 0.2_ o

10Omi QA6662 0 1*0kmn

FIGURE 6. Three-day total rainfall distribution, June 24-26, 1965, along the Eastern Caprock Escarpment. Daily station totals are not for the same time periods. Contours are in inches (modified from Finley and Gustavson, 1980).

beginning of October. Annual pan evaporation is Runoff approximately 158 cm (62 inches) (Kier and others, 1977). Rapid temperature changes and large ranges in Runoff from precipitation occurs when the infil daily and annual temperature are characteristic tration capacity of surface soils is exceeded (Young, (Orton, 1964). 1972). Infiltration capacity is largely a function of Erosional processes on the Caprock Escarpment are antecedent moisture and textural composition of the dominated by high-intensity, short-duration rainfall soil. In the High Plains along the Eastern Caprock and clayey from convective storms during the spring and summer Escarpment, soils are primarily sandy (Finley and Gustavson, 1980). Thunderstorms in the loams of the Acuff, Amarillo, Mansker, and Pullman Texas Panhandle commonly yield heavy rainfalls that series. These soils are moderately to poorly permeable, in flash floods, especially in the canyons that cut and infiltration rates range from 0.5 to 5 cm/hr (0.2 to result Soil into the Caprock Escarpment. Figure 6 illustrates a 2 inches/hr) (U.S. Department of Agriculture, series of intense rainfall events resulting in local Conservation Service, 1972, 1977a, 1977b, 1977c). precipitation depths of 12.5 to 22 cm (5 to 8.7 inches) Surface soils on the escarpment belong to the Quinlan along the Caprock Escarpment. These and other data Burson-Obaro association and are shallow, permeable, suggest that the Caprock Escarpment may cause and subject to moderate to very rapid runoff. Triassic orographic uplift of moisture-laden tropical maritime and Permian bedrock, primarily sandstone and mud air flowing from the southeast sufficient to encourage stone, is exposed over much of the Caprock Escarp rocks are low except thunderstorm development along the escarpment. ment: infiltration rates of these

8 Palo Duro Canyon State Park Polo Ouro Canyon State Park August 9, e76 July 1,1978 1.99 inches (50.6 mm) total rainfall 1.15inches (29.2 mm) total rainfall

I-,

-I

1401

1201 P State Park (Caprock gouge) Caprock Canyons State Park (Ouitaque gouge) Caprock Canyons June 8,1979 April 19,1979 400 600 2.47 inches (62.S mai) total rainfall 2A9 inches (63.2mm) iotal rainfall

so 3.001 so E 1 S160 I 1 I

200' '40. 40

lo01 204 20' L1,t. I I I I I ii- ; flrftrhfll fl ...... r , ] , : . . . . " ' ' * A6700 1300 1400 1500 l700 1110eoo190 120011'V Teime(hours) Time (thws)

the Caprock Escarpment (modified from Finley and FIGURE 7. Intensity-duration profiles of four storms along Gustavson, 1980).

TABLE 1. Rainfall intensity-duration-frequency escarp along fractures. Along the upper part of the relationships, Amarillo, Texas, 1904-1951 (modified ment, sediments of the Ogallala Formation are from U.S. Department of Commerce, 1955, and exposed, and infiltration rates of this material prob Finley and Gustavson, 1980). ably vary from low in well-cemented sections to high in sections of poorly cemented sand or gravel. Return intensity can also affect runoff. In very Rainfall period (yr) 2 5 10 25 50 100 intense storms, runoff may occur before the moisture part of the soil profile has been capacity of the lower Duration Rainfall intensitys reached by infiltration (Linsley and others, 1949). The soils and bedrock with moderate to low combination of 5 nmn 4.50 6.00 6.90 8.00 9.00 9.60 intense rainfall yields high runoff infiltration rates and 15 min 3.00 4.10 4.90 5.50 6.10 6.90 Plains and along the Caprock Escarp rates on the High 30 min 2.10 2.90 3.50 4.00 4.50 5.00 intensity-duration-frequency data from ment. Rainfall 60 min 1.30 1.80 2.20 2.50 2.90 3.40 1), illustrate that high-intensity Amarillo, Texas (table 2 hr 0.78 1.10 1.33 1.50 1.75 2.00 often on the High Plains. High rainfall events occur 6 hr 0.33 0.47 0.56 0.68 0.76 0.85 precipitation events are also common along intensity 12 hr 0.19 0.27 0.32 0.39 0.44 0.48 (fig. 7), where peak intensities the Caprock Escarpment 24 hr 0.11 0.15 0.18 0.23 0.25 0.27 have exceeded 12.5 cm/hr (5 inches/hr) and intensities of 2.5 cm/hr (1 inch/hr) are typical (Finley and "*Intensityexpressed in inches/hr (1 inch/hr = 25.4 mm/hr). Gustavson, 1980).

9 Relation of Dissolution-Induced Subsidence to the Caprock Escarpment To test the hypothesis that dissolution of Permian ness across the section. These relations indicate that salt and subsidence of overlying strata have affected Permian strata beneath the Rolling Plains were not the position and rate of retreat of the Caprock Escarp substantially affected by differential basin subsidence ment, we must establish the likelihood that salt was and that within the study area these strata do not thin once present where it is now absent beneath and to the much toward the eastern margin of the Palo Duro east of the escarpment. In addition, structures attrib Basin. Salt beds of the upper San Andres Formation, uted to dissolution-induced subsidence must be differ however, thin considerably between wells 6 and 7 entiated from tectonic structures. Several lines of (fig. 8), but nonsalt units do not. The significant evidence suggest that dissolution has truncated or decrease in the westward dip of strata above the thinned salt beds that currently underlie the Southern remaining San Andres salt beds is interpreted as High Plains, the Caprock Escarpment, and the Rolling evidence of removal of section through dissolution and Plains. subsidence of overlying strata. Similarly, changes in Seven logs indicates that thicknesses of salt beds of the San Andres, (1) Interpretation of geophysical are accompanied by where structural collapse of overlying beds has Rivers, and Salado Formations sequences radical changes in the dip of overlying units between occurred, abrupt loss of subjacent salt and 4, salt dissolution wells 8 and 9, wells 4 and 5, and wells 3 between wells probably resulted from relations also indicate facies change (Johnson, 1976; respectively (fig. 8). These rather than from Salado, Seven Rivers, and San Andres Gustavson and others, 1980, 1982; Gustavson and dissolution of Finley, 1985; Gustavson, 1986a, 1986b; McGookey and salts and subsidence of overlying strata. Furthermore, a stepwise pattern of dissolution in others, 1988). figure 8 illustrates which stratigraphically higher salts are first dissolved (2) Brecciated zones, fractures with slickensides, in areas closer to the escarpment. This pattern, in extension fractures, and insoluble residues composed of conjunction with structural changes, suggests dissolu mudstone, anhydrite, and dolomite overlie the upper tion by ground water; it is not a relict facies pattern. A most salts in core from wells A through I (fig. 1), facies change in the upper Clear Fork Group from salt indicating that dissolution has occurred beneath both and anhydrite to clastic sediments, however, occurs the Southern High Plains and the Rolling Plains. between wells 10 and 11 (fig. 8). Consequently, only (3) Permian outcrops throughout most of the Rolling minor salt thinning is due to dissolution there. Plains and the Palo Duro Canyon contain folds, sys In the study area approximately 30 m (100 ft) of salt tems of extension fractures, and, locally, breccia beds has been dissolved from the Salado Formation beneath interpreted to have resulted from dissolution of salt and the Southern High Plains and approximately 45 m collapse of overlying beds (Gustavson and others, 1980; (150 ft) from the Seven Rivers Formation beneath the Goldstein, 1982; Collins, 1984; Goldstein and Collins, Caprock Escarpment. Consequently, as much as 75 m 1984; Machel, 1985; and Gustavson, 1986b). (250 ft) of the relief of the Caprock Escarpment can be (4) High chloride concentrations in many streams attributed to dissolution and subsidence. Approxi draining the Rolling Plains indicate that salt dissolu mately 130 m (425 ft) of salt has been dissolved from the tion is active beneath most of the Rolling Plains and San Andres Formation beneath the western Rolling along most of the Eastern Caprock Escarpment (U.S. Plains and approximately 35 m (115 ft) from the Clear Geological Survey, 1969-1983). Fork Group beneath the central Rolling Plains. If the entire salt section was originally present as far east as Childress County, as is suggested by the continuity in Stratigraphy beneath the thickness of nonsalt strata, then as much as 240 m High Plains, Caprock Escarpment, (790 ft) of salt has been dissolved in that area. and Rolling Plains Regional stratigraphic relations along the eastern Structure on margin of the Palo Duro Basin are shown in figure 8. the Tubb Interval Permian salt thins along the eastern margin of the Palo Duro Basin primarily as a result of salt disso The Tubb interval, an informal subsurface strati lution and, to a lesser extent, facies change or deposi graphic unit of the Clear Fork Group, underlies all .the tional thinning toward the basin margin. Nonsalt units salt-bearing formations that have been affected by such as the Alibates Formation, anhydrite/gypsum dissolution. Therefore, we conclude that structure on and dolomite strata within the San Andres/Blaine the Tubb interval (fig. 9) has not been influenced by Formation, and anhydrite within the upper Clear Fork dissolution and subsidence but is rather the result of Formation thin only slightly to the east (fig. 8). Clastic tectonic movement. The map in figure 9 illustrates a strata of the Tubb interval maintain the same thick- nearly uniform dip of approximately 7 m/km (35 ft/mi)

10 A9 A East HARMON CO CASTRO CO SWISHER CO BRISCOE CO HALL CO CHILDRESS CO I I i

ft m

Lower Pease River Group i--a

Upper Clear Fork Group

r"11/

ME Salt J Anhytdrite

Dolomite

FF Salt dissolution

LATRueA!51Eve, .-- of I[•IUM, cross section illustrating zones of section lost owing to dissolution of salt and collapse FIGURE 8. Regional stratigraphic A-A' is located in overlying strata beneath the Southern High Plains, Caprock Escarpment, and Rolling Plains. Section figures 9 through 13 and 16.

• ...... level•O EXPLANATION

,• Coprock Escarpment 0 DOE stratigraphic test well location 0 Well location Datum* sea level 30mi I B I n I 40km Contour interval 200 ft

-/`•C LL

OA6612

FIGURE 9. Structure-contour map of the top of the middle Permian Tubb interval shows that major structural elements of the study area are unaffected by salt dissolution (modified from Budnik, 1984). A-A' locates cross section shown in figure 8.

12 the northeastern flank of the Palo western margin of the Rolling Plains. West of the to the southwest over escarpment and beneath the Southern High Plains, the Duro Basin. Major structural elements are the Bush to the southwest at the Alibates Formation dips regionally Dome and Amarillo Uplift, north of Amarillo, Regional dip reversal positives, the 2 to 3 m/kkm (10 to 15 ft/mi). Donley County and Armstrong County of the Caprock Escarpment and and the Matador occurs along the trend Plaska structure in Hall County, zone where, owing to dissolution, salts of limit of the study area. In the overlies the Arch, near the southern Salado, Seven Rivers, and San Andres Formations of Carson County the Tubb inter the southwestern corner rapidly thin (figs. 10 and 11). The floor of a large closed val differs only slightly in elevation from the Bush County lies as the structural basin in southwestern Carson Dome and dips to the southwest. Comparison of of the adjacent limit of much as 300 m (1,000 ft) below the crest outline of the upper physiographic, or western, and 12). Thus, the change contours on Bush Dome (compare figs. 9 the Caprock Escarpment with structure to northeastward to form relation between in dip from southwestward the Tubb surface fails to reveal any beneath the Caprock Escarpment from tectonic movement a broad anticline regional structure resulting has resulted from dissolution of salts of the Salado Caprock Escarpment in the study and position of the and Seven Rivers Formations and subsidence of over area. lying strata. The axial trace of the broad anticline on the Salt Thickness Alibates Formation crosses the western limit of the Cumulative thickness of salt units of the Salado, Caprock Escarpment in several areas and locally Seven Rivers, San Andres, and Clear Fork Formations underlies the Southern High Plains and the western decreases from west to east, but the most abrupt thick margin of the Rolling Plains (fig. 12). In conjunction ness changes occur beneath the Caprock Escarpment with the aforementioned thinning of salt beds of the and the western part of the Rolling Plains (fig. 10). Salt Salado and Seven Rivers Formations west of the thinning is attributed primarily to dissolution. The Caprock Escarpment, this relationship provides zone of abrupt thinning of the Salado and Seven Rivers further evidence that dissolution of Permian bedded Formations also closely coincides with the Caprock salts locally precedes the westward retreat of the Escarpment and the western margin of the Rolling Caprock Escarpment. Plains, indicating that interstratal salt dissolution has strongly affected and perhaps continues to affect the Middle Tertiary retreat of the escarpment (fig. 11) (for additional discus sion of dissolution of the Salado and Seven Rivers Erosional Surface Murphy, 1984, and DeConto and salts, see Boyd and unconformity separates Triassic Murphy, 1986). An extensive strata from the overlying Miocene-Pliocene Ogallala dissolution also appears to have occurred west Salt Formation (figs. 3 and 8). Although much of this sur of the escarpment. For example, Salado salts thin be has Plains face (fig. 13) in other parts of the Texas Panhandle neath the eastern margin of the Southern High of dissolution headwaters of been extensively deformed because near the Tule Draw and west of the and others, 1980; relationship suggests induced subsidence (Gustavson Pease River tributaries. This and Budnik, 1985; Gustavson and Finley, locally, dissolution precedes the southwest Gustavson that, at least 1985), the middle Tertiary erosional surface in the backwasting of the escarpment. Additional evi ward study area appears to be only locally modified by dence of dissolution beneath the Southern High Plains DOE-Gruy Federal Rex White subsidence. comes from core from the paleoslope of the erosional surface is to and Webster Engineering Corpora The regional No. 1 and the Stone Aligned groups of V-shaped contours Harman No. 1 wells in Randall and the southeast. tion (SWEC) point upslope and probably mark broad paleovalleys Swisher Counties, respectively (fig. 1), which contain to that contained streams that drained the erosion surface insoluble residues and extension fractures related the regional Rivers salts. before Ogallala deposition. Although dissolution of both Salado and Seven southeast, beneath Grabbe No. 1 and paleoslope of this surface is to the Cores from the DOE-Gruy Federal in southwestern Carson Swisher County (fig. 1) the Caprock Escarpment and the SWEC Zeeck No. 1 wells in the northeast. Such slope and extension fractures County, slope is locally to also contain insoluble residues Palo Duro Canyon, in the canyon of Salado Formation salts. changes occur along related to dissolution of Mulberry Creek, in central and northwestern parts of Briscoe County, and in southwestern Motley County. Structure on the These areas overlie areas where salt thins abruptly, Alibates Formation and where the Alibates Formation maintains a north easterly dip beneath the Southern High Plains. Such Structure on the Permian Alibates Formation changes in slope direction support our interpretation (fig. 12), which overlies the salt-bearing interval, is and subsidence locally preceded Tubb that dissolution markedly different from the structure on the Caprock Escarpment retreat. interval (fig. 9) near the Caprock Escarpment and the

13 EXPLANATION N

Caprock Escarpment DO E stratigraphic test well location e Well location 0 30mi [ . I i . i 0 4 Okm Contour interval lOOft

L!aNLEY OINS RT

6 I a

*a a

OA6613 FIGURE 10. Net-thickness map of salt in the Permian upper Clear Fork Group and San Andres, Seven Rivers, and Salado Formations. A-A' locates cross section shown in figure 8.

14 I CARSON EXPLANATION

liz Caprock Escarpment

0 wellOOE locationstratigraphic test

0 Well location 0 3Omi I i , , a . e 0 40km 0 Contour interval lOOft | a

RANDALL~

OA6614

FIGURE 11. Net-thickness map of salt in the Salado and Seven Rivers Formations. Salt thickness of the Seven Rivers Formation is shown where no overlying Salado salt exists. A-A' locates cross section shown in figure 8.

15 EXPLANATION Coprock Escarpment * Well location 0 DOE stratigrophic test well location & Outcrop location •o Axial trace of fold

0 30mi I i . i I 0 40km Contour interval lOOft Datum sea level

FIGURE 12. Structure-contour map of the top of the Upper Permian Alibates Formation. A-A' locates cross section shown in figure 8.

16 Erosional limit of Ogallala Formation

0 30mi | i I . I 0 40km Contour interval 100 ft Datum sea level

-~ - -QA6616

FIGURE 13. Structure-contour map of the base of the High Plains aquifer (Ogallala Formation) (modified from Knowles and others, 1982). The Miocene-Pliocene Ogallala Formation was deposited on the middle Tertiary erosional surface; therefore, this figure also represents a paleotopographic map of the unconformity between the base of the Ogallala and underlying Permian, Triassic, and Cretaceous Systems. A-A' locates cross section shown in figure 8.

17 Relation of Post-Ogallala Lake Basins to the Caprock Escarpment large breached lake basins can be recog (2) lacustrine sediments near Canyon, Texas; (3) the Several Formation nized along the Caprock Escarpment, including basins Cita beds in Palo Duro Canyon; (4) the Tule containing (1) the Quaternary Tule Formation in the in Swisher and Briscoe Counties; and (5) the Blanco of the Double Mountain Fork of the Brazos Formation in the White River-Running Water Draw headwaters and River and along Tule Draw, (2) the Pliocene Blanco valley (Gustavson and Budnik, 1985; Gustavson 1986a, 1988). Most of the large - Formation along Yellowhouse Draw and along the Finley, 1985; Gustavson, contain White River, (3) the Pliocene Cita beds in Palo Duro alkaline lake basins south of Lubbock that salt Canyon (Prairie Dog Town Fork of the Red River), and Quaternary strata are underlain by areas of thin (4) unnamed lacustrine sediments in Mulberry Creek and structural lows on horizons above the salt; these and Tierra Blanca Creek at Canyon, Texas (Evans and basins probably formed at least in part by dissolution Meade, 1944; Eifler, 1967,1968; Schultz, 1977,1986). All and subsidence (Reeves and Temple, 1986). Contrary to of these former lake basins, except the basins along the these studies, DeConto and Murphy (1986) suggested Brazos and White Rivers, occur in the study area that dissolution beneath the High Plains occurred (fig. 1). during the Triassic and therefore development of sur Breached lake basins along the escarpment deter face geomorphic features is unrelated to Cenozoic mine where major streams intersect the escarpment dissolution and subsidence. Although most of the afore and, therefore, the morphology of the scarp. All major mentioned studies demonstrate that areas of thin salt reentrants along the escarpment (the valleys of and structural lows in units overlying the salts occur Mulberry Creek, the Prairie Dog Town Fork of the Red beneath these lake basins, the full extent of most River, Tule Creek, White River, Yellowhouse Draw, and basins cannot be attributed to dissolution and subsi the Double Mountain Fork of the Brazos River) contain dence. Eolian deflation most likely contributed to their remnants of former lake basins at or near the Caprock formation (Evans and Meade, 1944), as is suggested by Escarpment. the presence of dunes along the eastern, or lee, side of Many of the larger lake basins on the surface of the most of the larger lakes on the High Plains surface. Southern High Plains and the breached lake basins Dissolution of soil carbonate, including the Caprock along the margin of the High Plains have been attrib caliche, also may have played a role in lake basin uted wholly or partly to subsidence over areas of salt development (Osterkamp and Wood, 1987; Wood and dissolution during Pliocene and Quaternary time. For Osterkamp, 1987). example, because Triassic strata are deformed, the Tule The relation between reentrants in the escarpment lacustrine basin in Swisher and Briscoe Counties and and lacustrine basins that formed partly because of the remnants of the lake basin in Mulberry Creek salt dissolution suggests that the position of the valley were thought to have resulted from subsidence reentrants is, in part, structurally controlled. Clearly, following dissolution of Permian salts (Evans and retreat of the escarpment by backwasting and head Meade, 1944). On the basis of subsurface stratigraphic ward extension of streams was also accelerated where and structural data, the following basins are thought to the escarpment extends into the preserved catchment have developed partly from dissolution and subsidence: areas of Cenozoic lake basins because of an increased (1) the Rita Blanca Formation near Channing, Texas; source of runoff.

Fracture Systems and Landform Development Several types of fractures have influenced landform of the Salt Fork and Double Mountain Fork of the development along the Caprock Escarpment. These Brazos River have north-south, northwest-southeast, include both tectonically induced systematic fractures and northeast-southwest orientations. Although he did and nonsystematic fractures that apparently resulted not describe regional fracture orientations, Reeves from vertical extension over zones of salt dissolution. (1971) inferred that these streams may have responded Clastic dikes also commonly occur in lower Ogallala to the "Earth's regmatic fracture pattern." Linear Formation, Dockum Group, and Dewey Lake Forma valley segments of the Middle and North Pease Rivers tion strata. and the Prairie Dog Town Fork of the Red River have been attributed to the influence of fractures formed by Systematic and Nonsystematic the dissolution of salt, gypsum, and possibly dolomite and the subsequent collapse of overlying strata (U.S. Fractures Army Corps of Engineers, 1975). Lineament trends Development of linear segments of streams and recognized from Landsat images, including linear other landforms in the Rolling Plains may be related to segments of streams, topographic elements, and tonal adjustment to fractures. Linear segments of the valleys anomalies, are similar to orientations of joints exposed

18 of veins, overall to subsurface struc swell, and sometimes form a network in the Caprock Escarpment and dikes are wedge shaped, being widest near 1981). On the basis the clastic tural trends (Finley and Gustavson, ends and narrowing with depth. They may physiographic features their upper of these observations, linear extend vertically for as much as 30 m (100 ft). In the were interpreted to be structurally controlled. and overlying fis Mulberry Creek valley, the Ogallala Karst landforms, primarily dolines and open are deformed so that the as a result of salt lacustrine sediments sures, developed on the Rolling Plains sediments strike N 800 W and dip 320 S, an collapse (Gustavson and lacustrine dissolution and associated orientation that coincides with that of most of the others, 1982). Orientations of fissures and the long axes of strata exposed in this joint sys clastic dikes. Deformation of dolines are similar to trends of regional valley was attributed by Evans and Meade (1944) to of systematic vertical tems. Zones or concentrations subsidence due to salt dissolution. Our regional subsur joints, which result from horizontal extension, intersect 13) also indicate that the Escarp face maps (figs. 9 through Permian and Triassic strata in the Caprock salt dissolution extends beneath the of 5 joints per zone of active ment, having an average concentration Mulberry Creek valley and that the deformation meter for sandstone beds 3 m (10 ft) thick (Goldstein, due to dissolution-induced Collins, 1984; exposed there is most likely 1982; Collins, 1983, 1984; Goldstein and The attenuated wedge shape of these depressions, minor subsidence. Collins and Luneau, 1986). Synclinal clastic dikes suggests that they formed from horizontal faults, and extension fractures filled with gypsum stress directions being strata extension, their principal (var. satin spar) are common in upper Permian axis of the subsidence basin these struc perpendicular to the exposed near the base of the escarpment; 12). The postulated genetic relation between locally subsidence over dissolu (fig. tures probably resulted from occurring tensional fractures (clastic dikes) and folding depressions trend parallel to tion zones. The synclinal from dissolution-induced subsidence is consistent with systematic joints. Similarity in orientation among deformation due to joint our interpretation of regional synclinal depressions, dolines, fissures, and along the Caprock Escarpment. flow and dissolu dissolution systems suggests that ground-water Several open fractures, partly filled with sediments tion were more pronounced along zones of systematic surface of the Rolling Plains, were strongly washed in from the fractures, and, as result, systematic fractures by Gustavson and others (1982) and morphology of subsi described influence the distribution and Gustavson (1986b). The fractures occur on the flanks of dence structures. formed in Hall County above an area nonsystematic ver large dolines that Along the Caprock Escarpment, of extensive salt dissolution. In 8 yr (between 1978 and tical joints are typically curved, have no preferred opened several times, only to be against sys 1986) these features orientation, and are commonly truncated by loose surface sediment washed in therefore postdate filled each time tematic joints. Nonsystematic joints during subsequent rainfalls or when farmers cultivated systematic joints (Goldstein, 1982). Nonsystematic the fractures. Wallner fields crossed by joints, which locally display convex-upward The presence of clastic dikes deep in the Ogallala lines indicating upward propagation of the fracture, and Dewey Lake Formations in the Mulberry Creek were attributed to subsidence induced by salt dissolu water has been important or bed valley indicates that ground tion (Goldstein and Collins, 1984). Horizontal near-surface sediments downward into the filled with fibrous in moving ding-plane extensional fractures Ogallala Formation and as deep as the Permian Dewey gypsum occur in Permian strata throughout the region dissolution-induced subsidence areas Lake Formation. If and have also been attributed to subsidence over that were later filled with 1984). The resulted in open fractures of salt dissolution (Goldstein and Collins, sediment, then the same fractures were Caprock Escarp near-surface highly fractured strata exposed in the probably open conduits for enhanced leakage to strata ment probably enhance downward leakage of ground the salt-bearing Permian System. weathering as deep as water as well as chemical and mechanical Fractures and clastic dikes probably have enhanced of these rocks. the leakage of low-salinity ground water downward toward Permian strata and the dissolution zone. Fur Clastic Dikes thermore, both nonsystematic fractures and clastic Along the northern flank of Mulberry Creek valley dikes appear to result from dissolution-induced sub (fig. 4) numerous clastic dikes occur locally in the sidence. Thus, a feedback system is created by which Ogallala Formation and in the underlying Permian ground-water flow through sediments and along frac Dewey Lake Formation. Their orientations range from tures leads to interstratal salt dissolution. Resulting N 800 W to S 40° W. Clastic dikes in the Ogallala subsidence causes additional fracturing or the opening Formation are filled with sediment that appears to of existing fractures, which in turn allows the flow of have washed down from the overlying Quaternary more water toward the dissolution zone. Blackwater Draw Formation. Although they pinch,

19 0 .5 3C i zi .

FIGURE 14. Head map of the unconfined aquifers in the Palo Duro Basin (modified from Bassett and others. 1981). West of the Caprock Escarpment, this surface corresponds to the Ogallala aquifer. Note the steep hydraulic gradient along the Eastern Caprock Escarpment.

Ground-Water Flow beneath the Caprock Escarpment Aquifers underlying the Southern High Plains, Steep vertical hydraulic gradients imposed by the Rolling Plains, and particularly the Caprock Escarp boundary condition of the Caprock Escarpment create ment are strongly influenced by topography (Bassett potential for downward leakage from the Ogallala and and others, 1981; Dutton and Orr, 1986; Dutton and Dockum aquifers. Throughout the study area the Simpkins, 1986). Hydraulic-head and potentiometric potentiometric surface of the evaporite aquitard lies far surface maps (figs. 14 and 15) illustrate the steep below both the water-table elevation of unconfined hydraulic gradient and the strong potential for down surface aquifers and the potentiometric surface of the ward leakage of ground water beneath the Caprock lower Dockum aquifer, indicating a strong potential for Escarpment. The potentiometric surface of the lower downward leakage of ground waters to the San Andres Dockum Group aquifer lies below the base of the Formation. Ogallala Formation (Fink, 1963), indicating an overall Potentiometric-surface data in figures 14 and 15 indi potential for downward leakage from the Ogallala cate that springs are likely to develop at the boundary aquifer to the lower Dockum Group aquifer (fig. 15). of the Caprock Escarpment, where flow encounters

20 34'

ss~jo

o 0 ...... ata fro-w

-'I• EXPLANATION"..',j •, ----,,-,-.- , -T i + ,+

N TEXEPANASO / C, tu itra: 5it 7.m

+ 6+08

o 550 7 00km 11"•' ol*t FIURa 1 o iec surface -DCoprockEscarpment o inferred subcrop limit (from Granotd, 1981) /Approximate altitude of hydraulic head in ./*e Regional ground-woter-basin divide inferred ,• the Lower Dockum aquifer. Sea level datum. fro oetoeti ufc

Potentiometric gradient steepens at the Eastern Caprock Escarpment.

21 Okohm

SBrine amieii= a

0 30 km o. .. ..

FIGURE 16. Map of physiographic units, major streams, and brine emission areas (U.S. Army Corps of Engineers, 1975) in the study area. Brine emission areas XI and XV occur in outcrops of strata equivalent to the Seven Rivers Formation. Brine emission areas V, VII, IX, XIII, and XIV occur in outcrops of strata equivalent to the San Andres Formation. A-A' locates figures 8 and 17 (Simpkins and Fogg, 1982, their fig. 91).

layers of low hydraulic conductivity and the path of Conceptual Model of Ground-Water least resistance is to discharge at the boundary. Numer beneath the ous springs are, in fact, present along the Caprock Flow Escarpment above strata of low hydraulic conductiv Caprock Escarpment ity, such as Dockum mudstones. This in turn suggests that spring sapping and seepage erosion contribute to Hypothetical flow paths of low-salinity ground water backwasting of the Caprock Escarpment. Sapping and through the dissolution zones in Permian bedded salt seepage erosion are discussed on p. 29. are shown in the conceptual model in figure 17. The Discharge from this flow system occurs to the east, model illustrates how the hydraulic-head distribution where saline springs in the Rolling Plains discharge a imposed by the escarpment boundary could be the mixture of both locally derived and deeper ground major force behind ground-water flow to salts in the waters, as evidenced by geochemical and isotopic data subsurface and to springs along the escarpment, where (Richter and Kreitler, 1986). Large areas of saline zones of low hydraulic conductivity exist. Low-salinity discharge have developed in topographically low parts ground water moves downward to discharge as springs of outcrop belts of the Salado, Seven Rivers, and San along the escarpment and laterally to the relatively Andres Formations (compare figs. 8 and 16). shallow updip elements of Permian bedded salt. Per-

22 0O W Wd. IL z Zz 4 in,4. 4 W 4i8 14- ZJ ~12 x:% J &'* "-I.-W I I I I !I I CHILDRESS CO. BRISCOE CO. HALL CO. I

EXPLANATION

Caprock Sondstone/ Mudstone Escarpment EEDi l Alluvium riw---TI 13, -1 ! "s' - -- Oolomite [• Anhydnite (locally converted to gypsum) MSolt

$Salt dissolution

0 t0 20 km o 10 mi

Town Fork, Red RIver

bedded salt beneath the High Plains, 17. Conceptual model of ground-water flow and its impact on Permian FIGURE 1980). Inferred flow paths are indicated by arrows. Caprock Escarpment, and Rolling Plains (from Gustavson and others, Stratigraphic units are identified in figure 8. Datum sea level. Ecs!

W•rtW.tf East ft m 3600- '1100

32000

800

2600 H

O700 2200

2600 EXPLANATION

1800- Ogallala aquifer

1600500Dolomite banhydnte a~uifer

2400 1PNTN300

km 0 10 20 U( 00 20mt 10i 15 20m 00200 0

400

200 Datum: Se" level Af n

FIGURE 18. Finite-element mesh design based on cross section shown in figure 8. Upper surface is the water table. Lower surface is drawn at upper stratigraphic limit of salt-bearing units (from Simpkins and Fogg, 1982. their fig. 93).

mian salt is readily dissolved as it comes into contact are particularly important because they provide the with low-salinity ground water, and the resulting drive by which low-salinity ground water reaches brines flow eastward through highly transmissive Permian salt-bearing units and by which brines from dolomite and anhydrite/gypsum beds to discharge into salt dissolution zones are discharged to the surface at topographically low areas. saline springs in the Rolling Plains region (fig. 16). In the numerical model, the prescribed hydraulic head boundary conditions are imposed on the upper, Numerical Model of Ground-Water left, and right boundaries. The upper boundary is the Flow beneath water table (Knowles and others, 1982). The lower boundary is a no-flow boundary (upper stratigraphic the Caprock Escarpment limit of salt beds), and thus it is assumed that any Numerical simulations were conducted by Simpkins upward leakage from the deeper units occurs at a and Fogg (1982) to evaluate the importance of topog negligible rate compared with the flow rate in the raphy, hydraulic head, permeability, and boundary modeled area. conditions in the hydrologic system. Their model, Ground-water flow was simulated using the com which is summarized here, simulated ground-water puter program FLUMP, which employs a finite-ele flow in two dimensions and was based on the same ment, mixed explicit-implicit numerical scheme for stratigraphic cross section as that used in the concep solving linear and nonlinear subsurface-water-flow tual ground-water flow model (fig. 17) in this report. problems (Neuman and Narasimhan, 1977). The finite Their numerical model was oriented vertically to take element mesh (fig. 18) was designed to accommodate advantage of the detailed stratigraphic framework the heterogeneities of the local stratigraphic system provided by well data and to enable examination of and to provide greater accuracy near the Caprock vertical hydraulic-head gradients. Vertical gradients Escarpment, where hydraulic gradients are steepest.

24 TABLE 2. Hydrostratigraphic units and hydraulic conductivities used in the ground-water flow model (from Simpkins and Fogg, 1982) (1 ft/day = 0.3 m/day).

Hydraulic conductivity (ft/day) Hydrostratigraphic unit Kh Kv Source Ogallala (sand and gravel) 26.7 26.7 Both values from Myers, 1969

Dockum (sand, silt, clay) 2.7 2.7 Both values from Myers, 1969 Quartermaster/Cloud Chief 0.27 0.00027* Kh value from P. R. Stevens, 1980 (mudstone) personal communication, Whitehorse (sandstone) 3.0 3.0 Both values from Freeze and Cherry, 1979

Blaine and San Andres 10.0 10.0 Both values from U.S. Army cycle 4 in shallow sub Corps of Engineers, personal crops (dolomite/ communication, 1980 anhydrite) Flowerpot (mudstone) 0.27 0.00027* Kh value from P. &. Stevens, personal communication, 1980

*Values were not estimated from field or laboratory tests but are based on the fact that these units are horizontally stratified mudstones containing small amounts of sand, thus indicating large Kh/Kv (horizontal and vertical conductivity) values.

Hydraulic conductivities (K) of the various strati puted by the numerical model using the values of K graphic units were compiled from several sources listed in table 2 are shown in figure 19. Unfortunately, are estimates of a range of K data ground-water flow lines cannot be drawn perpendicular (table 2). Most values of from pumping tests. Where data were unavailable, K to the hydraulic-head contours in figure 19 because was estimated either by extrapolation from other data anisotropy and the extreme vertical exaggeration of the for units of similar lithology or by selection of a cross section. The effects of vertical exaggeration value" from the literature (such as from Freeze are greatest at the escarpment, where the vertical "typical sub and Cherry, 1979). Vertical K values (Kv) of the Upper (downward) gradient computed by the model is Permian mudstones (table 2) are not from field or stantial; however, in figure 19, head contours seem to laboratory tests; rather, their calculation is based on indicate only horizontal flow. Our interpretation of the the observation that these units are horizontally strati results is therefore based on node-to-node hydraulic fied mudstones containing small amounts of sand. heads and ground-water fluxes printed in the model Key uncertainties that may be important in inter output listing. preting the results of the model are (1) Kv values in the According to Simpkins and Fogg (1982) the numer vicinity of the Caprock Escarpment that control the ical model supports the conceptual model of salt of low-salinity water introduced to dissolution by indicating (1) downward flow of fresh rate and amount salt Permian salt beds in the subsurface and (2) Kv and Kh ground water from the Ogallala aquifer into the (horizontal hydraulic conductivity) values for the dolo bearing strata beneath the Caprock Escarpment; and Kv values for other units east (2) eastward movement of the resultant brine through mite/anhydrite units San of the Caprock Escarpment that govern where the high transmissive dolomite/anhydrite beds of the waters discharge and to what extent topog Andres Formation; and (3) discharge of the brine into salinity of the raphy affects the ground-water flow system. saline springs in topographically low areas Rolling Plains. The numerical model also suggests that Modeling Results nearly all ground-water discharge from the system can bedding and Several simulations were made by Simpkins and be accounted for by horizontal flow along Fogg (1982) to calibrate the model and to determine its by vertical (upward) discharge through saline springs. sensitivity to hydraulic conductivity (K) variations. Discharge along the right-hand prescribed head bound Hydraulic heads and recharge/discharge rates com- ary is negligible (fig. 19).

25 cast

EXPLANATION [/ Ogallala aquifer (

Dolom ite/anhydrite aquifer

Scale

(b)

m3/d 113dRecharge -ischrge- -ORecharge r. DOischarge --W

0 .•'4"-s

-e ...... i~ "a

o -4

-8 -2

FIGURE 19. steady-state hydraulic heads and recharge/discharge rates computed by ground-water flow model (from Simpkins and Fogg, 1982). (a) Flow fines cannot be assumed to be orthogonal to the head contours because of anisotropic K values and because the vertical scale exaggeration is approximately 104 to 1. (b) The recharge/discharge rates shown are regional averages of rates computed at groups of nodes and thus reflect only major recharge and discharge areas. Flow rates through the sides of the model are on the order of 10""MS/day, which are minute compared with the rates illustrated.

26 Surface Processes Causing Scarp Retreat National Wildlife spring sapping, seepage erosion, Creek within the Buffalo Lake Fluvial erosion, Randall County (fig. 13). This drainage basin wasting are important erosional processes all Refuge, and mass is morphologically similar to drainage basins on the along the escarpment. However, in Palo Duro Canyon, Caprock Escarpment, and it is developed in the and especially in the northern part of the canyon in the same rotational slumping Ogallala and Blackwater Draw Formations, Palo Duro Canyon State Park, drainage basins along the plays a major role in scarp retreat. strata underlying small crest of the escarpment. The Buffalo Lake National Wildlife Refuge study basin, located 48 kmn (30 mi) west Surface Runoff of the escarpment, and drainage basins within the results pre Caprock Escarpment are subject to the same weather Rainfall near the Caprock Escarpment believe that geo Single storms with conditions. For these reasons we dominantly from convective storms. the Buffalo Lake site are com inches) generally morphic processes at precipitation in excess of 6 cm (2.4 that are shaping drainage basins once every 24 months in the Amarillo parable to processes occur at least the upper part of the Caprock Escarpment. intensities of 2.5 cm/hr (1 inch/hr) of area, and rainfall Instrumentation for data collection at the Buffalo or more account for more than 8 percent of the hourly air- and 1980). Lake site included a recording rain gauge, rainfall for the region (Finley and Gustavson, soil-moisture inches) ground-temperature-recording probes, A 24-hour rainfall of approximately 25 cm (10 lines of marked During especially probes, several groups of erosion pins, occurs about once every 19 yr. within the capacity of the soil, as gravel clasts, and markers set into headcuts heavy rainfalls the infiltration floor of the canyon. Weather data at of certain playa lake basins, is channel at the well as the capacity Lake were collected continuously from January overland discharge from the playas Buffalo exceeded, and 1977 to November 1987. Erosion pins and headcut mark occurs locally. severe storms. the effects of ers were measured biannually or after During field studies we observed long profile of the Plains. Rainwater that Before the first storm (in 1978), the several sheetfloods on the High sections, and detailed topog Plains moves to the rim of canyon, topographic cross falls on the Southern High headcut areas were surveyed. as sheetfloods. Sheet wash raphy of the Caprock Escarpment drainage basin at the Buffalo Lake site received when waters from heavy rains and The and rill wash occur 7.1 cm (2.8 inches) of rain during a 3.2-hr storm on May sheetfloods flow down the walls of the canyons (Bath, was 6.4 cm/hr Runoff, 26, 1978; maximum intensity of rainfall 1980; Simpkins and Gustavson, 1985, 1987). Intense rainfall removes stored (2.5 inches/hr) over a 30-min period. concentrated in the floors of canyons, storm rapidly exceeded the infiltration floor, and, as discharge during the sediment, erodes the channel of soils on the High Plains surface, and large sediment eroded from the canyon floor capacity wanes, deposits volumes of water were directed into the headwaters of and walls. rim. Sheetflooding on that contributes the canyon and over the canyon The area of the High Plains surface indicated by drift lines of is small. A drainage the High Plains surface was runoff to the Caprock Escarpment plant debris 6 to 8 cm (2.4 to 3 inches) high on cacti and divide exists between the Caprock Escarpment and the (2 to 30) because fenceposts. Erosion pins on the low-sloping first playa lake basins west of the escarpment no change or 1 to playa lake High Plains surface showed either of the distribution of internally drained of net deposition. Gullied slopes The surface that 2 mm (0.04 to 0.08 inch) basins on the High Plains surface. sand of the Quaternary is a narrow (340 and 270) in very fine normally contributes runoff, therefore, the top of the canyon Pullman Blackwater Draw Formation at band of terrain containing silty and clayey 6.2 cm (2.4 inches) by rill wash of the top of were eroded as much as and Amarillo series soils that lies just west Gully floors in the Ogallala of the escarp and sheet wash (table 3). the escarpment. Along many segments Formation were scoured to bedrock in some cases, and ment this band is usually less than I km (0.6 mi) wide gravel were wide. small fans of pebble- to cobble-sized and rarely more than 2 to 3 km (1.3 to 1.9 mi) floor. Sheet wash and rill wash runoff to deposited on the canyon Although the area potentially contributing resulted in an average erosion of and slope erosion on the canyon slopes the escarpment is small, sheetflood inch) in all slope classes; a maximum of slope degradation. Sur 2.2 cm (0.9 are important to canyon and (2.4 inches) was recorded. In addition, an aver only when the infiltration 6.2 cm face runoff, however, occurs age of 41 percent of pebble- to cobble-sized clasts were exceeded. capacity of the soil is moved by sheet wash from lines of painted clasts. Large volumes of pebble- to boulder-sized sediment Drainage Development were deposited on the canyon floor, and large volumes sediment were carried (1983) and Simpkins and of mostly sand- and pebble-sized Finley and Gustavson deposited on the valley floor of the geomorphic effects of out of the canyon and Gustavson (1985) described Blanca Creek. return interval storms (May 26, 1978, and Tierra two 10-year of the 1978 storm, bedrock surfaces in the 10, 1984) on a small, instrumentally monitored As a result June canyon were scoured of loose sediment. Between 1978 drainage basin that is a tributary of Tierra Blanca 27 two storms caused the most erosion in the canyon, TABLE 3. Erosion-pin measurements made on erosion-pin readings. on May 26, according to field observations and eroded canyon slopes following storm from the June 10, 1984, storm in Finley and Gustavson, 1980). Inclusion of data 1978 (modified from base helped us to identify the effect of Storm duration was 3.1 hr (25.4 mm= I inch). the climate data intense rainfall on erosion. Figure 20 is a plot of the maximum 30-min rainfall intensity (most intense storm Average Net erosion (mm) per measurement period) versus the percent of erosion Slope vegetative Number erosion (Simpkins and Gustavson, 1987). Min. pins showing class cover (%) of pins Average Max. All rainfall event intensities lasted for at least 30 min, a 0-90 22 8 24 59 6 few slightly longer. An exponential relationship is 6 27 54 9 indicated, and field evidence suggests that a critical 10-190 11 with 15 21 19 62 3 geomorphic threshold is crossed during storms 20-290 6.0 cm (2.4 inches) 30-39° 14 9 17 60 6 rainfall amounts of approximately 10 1 - 51 and intensities greater than 6.0 cm/hr (2.4 inches/hr). 420 in rainfall 520 5 1 - 19 Scatter in the data is related to variation frequency during a period and to availability of erodi ble sediment. The somewhat anomalous value for the 1978 storm may be partly due to the location of erosion on the drainage divides in the and these pins that were set high and 1984, more loose sediment accumulated, erodible Pleistocene loess (Blackwater Draw Forma bedrock surfaces assumed their pre-1978 appearance. of down in the tributary canyon. The large on canyon slopes tion) instead Alluvium and colluvium accumulated volume of sediment moved during this event strongly and on the canyon floor as a result of small rainfalls. availability of loose sediment affected (9.3 cm [3.7 suggests that the On June 10, 1984, intense rainfall the amount of erosion. inches]) during a 4-hr period again caused significant scour and deposition of sediment in the tributary can yon of Tierra Blanca Creek. A maximum 30-min pre Thresholds for Sediment Movement was cipitation intensity of 6.9 cm/hr (2.7 inches/hr) sediment movement in the tributary can Canyon, Texas, Fire Study of attained during that storm. The yon at Buffalo Lake National Wildlife Refuge after Station recorded 11.7 cm (4.6 inches), and the Amarillo rainfall suggests that sediment is 12.5 cm episodes of intense National Weather Service office recorded stored in a stepwise manner. Three Effects of transported and (4.9 inches) of precipitation on June 10, 1984. incremental steps are related to attainment of critical thc 1984 storm were similar to those of the May 26, intensity. Minor rainfall events (1983). thresholds in rainfall 1978, storm discussed by Finley and Gustavson than 6.0 cm/hr [2.4 inches/hr]) (step 1) move preceded by rela (less The 1978 and 1984 storms were both sediments down hillslopes and lower alluvial surfaces; tively dry periods in the short-term climatic record, is stored there until an intense Rainfall most of that sediment although, overall, 1984 was wetter than 1978. event occurs. Intense rainfalls (greater than and intensity) rainfall of similar magnitude (total amount 6.0 cm/hr [2.4 inches/hr]) (step 2) generally cause ero- occurred between these two events (table 4), yet these

TABLE 4. Record of intense storms at Buffalo Lake National Wildlife Refuge during the course of this study. These data were used to construct the plot in figure 20 (25.4 mm = 1 inch).

Total 30-min maximum Percentage of precipitation Period intensity pins showing (MM) (hr) (mm/hr) erosion Date 91.0 71.0 3.1 64.0 05/26/78 20.0 30.8 10/29/79 12.8 3.5 1.95 47.6 42.3 06/21/80 26.0 32.7 20.2 2.1 36.0 08/05/80 76.8 53.8 08/16-17/81 82.0 4.5 5.3 18.0 30.8 10/15/81 27.2 42.3 52.0 1.5 52.0 07/20/82 24.8 17.3 09/07/82 15.0 2.7 1.2 35.6 28.0 10/07/82 18.6 37.0 20.8 0.5 38.4 09/10/83 69.0 66.0 06/10/84 93.4 4.0

28 Spring Sapping and Seepage Erosion In addition to the interstratal dissolution of bedded r a 0.82 Intercept u 17.1 salt, spring sapping and seepage erosion are ground Standard error a 0.27 water-related geomorphic processes active along bases Slope * L02 1954 of cliff faces and in the headwaters of streams draining the Caprock Escarpment. Sapping and seepage erosion in these areas have apparently had a marked effect on headward erosion of stream valleys. CL Higgins (1982, 1983) recently described spring sapping as a process by which larger drainage systems T are developed. Although spring sapping is commonly 00 understood to influence development of gullies and smaller streams, especially in semiarid climates, its a! contribution to larger drainage systems has been reported only rarely (Higgins, 1982). Active sapping in large drainage systems or valleys has not been observed, except in Nebraska (Gerster, 1976) and some 20 40 ec 100 southwestern states (Gregory, 1917), but it has been Maximum 30-min rainfall intensity (mm/hr) inferred from ground observations in Egypt (Peel, 1941) GA 66O and from spacecraft images of Mars (Higgins, 1982). extending FIGURE 20. Plot of maximum rainfall intensity versus Spring sapping and seepage erosion are percent of erosion pins showing erosion at the Buffalo the stream network that drains the approximately Lake National Wildlife Refuge station (modified from 210-kin (130-mi) length of the Eastern Caprock Escarp Simpkins and Gustavson, 1987, their fig. 37). Correlation ment in the study area. Field observations in Luttrell coefficient is 0.82. Although based on only two data points Canyon, Tub Springs Canyon, Capitol Peak Canyon, (1978,1984) a critical geomorphic threshold seems to occur Red Canyon, and Timber Canyon (all tributaries of when rainfall intensity values exceed 60 mm/hr, depend Palo Duro Canyon) and interpretation of aerial photo ing on sediment availability. Plotted values are provided graphs of other areas along the escarpment indicate in table 4. that sapping and seepage erosion are active beneath thick (3 m to 7 m [10 ft to 23 ftD, coarse fluvial sandstone beds of the Triassic Dockum Group and beneath basal sand and gravel of the Ogallala For sion on hillslopes, erosion and deposition on the can mation (fig. 21). Seepage discharge from the base of yon bottom, and deposition in Tierra Blanca Creek. these sandstones carries away particles of underlying to the canyon floor by smaller mudstones, which are continually wet, and promotes Large boulders carried (fig. 22). Even on vertical faces, tributary canyons act as sediment traps for finer weathering and erosion material moving down the thalweg or tributar a continuous supply of water encourages the growth of grained in the mechan ies. Step 3 represents a storm capable of removing plants, and root growth probably aids Tierra Blanca Creek and its tributary ical breakdown of the mudstones. On some exposures, sediment along min No storm of this magnitude, however, was crusts of gypsum and calcite are deposited as canyons. of crusts recorded during the study period. In this model of eralized ground water evaporates. Formation sediment is constantly created by may also encourage the disintegration of Dockum sediment transport, displacement weathering and disaggregation and is transported strata by interstitial growth and bedrock down canyon walls by small rainfall events. Intense by evaporite precipitation. have a significant erosional impact only Discharge records from springs and seeps in these rainfall events is prob when they occur periodically, thereby allowing enough canyons are unavailable. Discharge, however, for loose sediment to be created, stored, and ably perennial, at least near the headwaters of the time is the High Plains ultimately eroded. High-intensity rainfalls may not canyons, because the water source A few seeps are ephemeral transport sediment, as this model predicts, if most aquifer, not local recharge. removed by an earlier storm and apparently related to local recharge. Cottonwood, stored sediment was at the (Simpkins and Gustavson, 1987). horsetail rush, and leopard frogs can be found similarities in soils, bedrock, and spring sites, all of which require a nearly continuous Because of the become the processes and rates of erosion supply of water. Nonetheless, these streams scarp morphology, discharge is affecting the upper part of the Caprock Escarpment, ephemeral in their lower reaches because which is developed in the Ogallala and Blackwater absorbed into alluvium. sandstone beds of the Dockum Group Draw Formations, are probably similar to the processes The resistant and rates that Finley and Gustavson (1983) and and carbonate-cemented or silicified sands and gravels (1985) observed at Buffalo of the basal Ogallala Formation also support pouroffs Simpkins and Gustavson present Lake canyon. (waterfalls). Plunge pools are commonly

29 FIGURE 21. Area of spring sapping at the head of Red Canyon, Palo Duro Canyon State Park. Efflorescence is primarily gypsum. Discharge is through a Lower Triassic Dockum Group sandstone in contact with an underlying mudstone. Figure stands on blocks of sandstone that are part of a rockfall. Erosion of mudstone is beginning to undercut the overlying sandstone block. See figure 25 for location.

a A

FIGURE 22. Detail of the spring discharge area illustrated in figure 21. Plants have rooted in the discharge zone, and roots probably help to disaggregate rocks at the contact between Dockum sandstone and mudstone.

30 FIGURE 23. Rockfall consisting of blocks of massive channel sandstones, Upper Triassic Dockum Group at the head of Tub Springs Draw, Palo Duro Canyon State Park. Spring sapping between lower Dockum Group sandstone and underlying mudstone (obscured by at the contact to rockfall) probably caused this rockfall. Spring discharge is active here and continues undercut Dockum sandstones. See figure 25 for location.

beneath the pouroffs. Stream discharge from canyon Rotational Slumping segments above the elevation of spring sapping appears to be important in preventing the area of Substantial parts of the Eastern Caprock Escarp sapping from being blocked or covered by rockfall ment have been affected by rotational slumping. Slump debris. Stream discharge over the pouroffs moves ing (Varnes, 1958) is particularly evident in Palo Duro alluvium downstream in the process of creating the Canyon State Park, where more than 100 slumps are plunge pool, thereby removing material that might preserved (fig. 25), and is common throughout the otherwise eventually cover the rock face undergoing northern half of Palo Duro Canyon (fig. 1). The largest sapping. area of slumping occurs at the foot of Fortress Cliff, along the eastern slope of Palo Duro Canyon. Here, at Rockfalls least 40 separate slumps can be recognized. Individual slumps vary markedly in size, but the largest in tributaries of Palo Duro Can rotational Sapping observed apparently continuous slump blocks in Palo Duro Can yon has undercut one or more of the thick Dockum sand m (1,800 ft) in width. rockfalls of yon exceed 550 stones or basal Ogallala calcretes, causing the terrain along the escarpment that is Canyon and Much of the sandstone beds. In Luttrell Springs by lacustrine mudstones of the Triassic of fresh rockfall scars and underlain Red Canyon the appearance Dockum Group has been subjected to slumping. Coher the jumble of large and small fragments suggest that composed of Dockum sandstone and block ent rotated blocks, rockfalls have occurred recently (fig. 23). A large of the Ogallala Formation, commonly x 7 m x 15 m lithified units of Dockum sandstone (approximately 3 m dip steeply toward the canyon walls (fig. 26). The best [10 ft x 23 ft x 50 ft]) separated from the main body of however, occur high up on the canyon fell into Tub preserved blocks, a Dockum sandstone bed in 1977 and Slump blocks in these areas have moved rela to rockfalls con slopes. Springs Canyon. Processes leading tively short distances and are not severely broken up. tinue in Palo Duro Canyon and its tributary canyons, the most recent slumps because in These are apparently as evidenced by tension cracks that developed nearest undisturbed Dockum and Ogallala of underlying sup they occur Dockum sandstones due to removal strata. Disruption and deformation of slump blocks port, commonly by spring sapping (fig. 24).

31 (a) Formation at Fortress FIGURE 24a. Fracture in caprock caliche of the Miocene-Pliocene Ogallala Cliff, Palo Duro Canyon State Park-an incipient rockfall.

(b)

in sandstone of the Upper Triassic Dockum Group in Tub Springs Draw. FIGURE 24b. Fracture mudstone is 5 to 10 cm (2 to 4 inches pwide and apparently has formed as the underlying Fracture 25 for location. erodes and undercuts the sandstone by means of spring sapping. See figure

32 N Rotational slump

Landslide debris (Ls)

'4 0 Spring sapping 0 Imi 0I I . I I .j

FIGURE 25. Distribution of rotational slumps and landslides in Palo Duro Canyon, Palo Duro Canyon State Park. Areas of spring sapping occur where springs discharge from the base of the Ogallala Formation or from the base of permeable sandstones in the Dockum Group. Base from U.S. Geological Survey 7.5-minute (topographic) series, Fortress Cliff Quadrangle.

33 I

FIGURE 26. Three segments of rotational slumps (I-Ill) are exposed along the northeastern side of Palo Duro Canyon (viewer facing north). The three planes of rotation exposed here are in lower Dockum Group smectitic mudstones. Relief on the slumped mass is approximately 12 m. See figure 25 for location. Dashed lines mark bases of slump blocks.

Piping Piping is the process whereby water percolating increase downslope. Near the canyon floor, blocks of erodes narrow tunnels or pipes by resistant Dockum sandstones and, to a lesser extent, through the subsoil soluble or granular soil material. Examples calcretes of the Ogallala Formation are widely dis removing small-scale piping occur in many persed, and slumped Dockum mudstones are severely of both large- and the Caprock Escarpment. Large pipes com disturbed. In some areas only chaotically arranged areas along at the contact between rotational slump resistant blocks of Ogallala and Dockum strata monly occur strata. Large slump blocks remain, capping hills of relatively undisturbed Per blocks and undisturbed have a back-tilted upper surface where precipi mian red beds. These are apparently the eroded rem typically are ponded. Precipitation and nants of substantially older mass movements. tation and sediment slump blocks partly drain along The lower part of the rotational plane of most runoff ponded behind of rotation, and water movement along these slumps appears to have been either partly within or at surfaces numerous large pipes. The pipes, some the upper contact of the relatively impermeable and surfaces erodes features, begin as sinks or incompetent lacustrine mudstones of the Dockum times called pseudokarst as much as 10 m (30 ft) in diameter Group. The Dockum mudstones contain expansive closed depressions downward into single or complex passage smectitic clays (Bath, 1980), which probably also that drain as much as a meter or more in diameter (fig. 27). provide lubrication along the lower part of the slip ways pipes are large caverns at the eroded surface. The mudstones, which are effective aquitards, The exits of these blocks and may be as much as 4 m (13 ft) also cause ground waters to saturate overlying Dockum bases of slump (fig. 28). Small-scale piping occurs to a lesser sandstones; as saturation increases, pore pressure high sediments within a few meters of the increases and the strength of the rock mass is reduced. extent in Ogallala pipes are narrow and short, In this sense, ground water has affected the retreat of edge of the canyon. These a few meters in length. They are the escarpment by facilitating slumping. Where rarely exceeding erosion and transport of surface sedi Dockum lacustrine mudstones are absent, slumping is usually related to fractures in well-cemented calcrete. only a minor process. ment through

34 FIGURE 27. Entrance to a large pipe in Caprock Canyons FIGURE 28. Outlet for a large pipe in Palo Duro Canyon pipe developed in thin-bedded Permian State Park. Approximately 3 x 5 m (10 x 17 ft), this pipe is State Park. The at and sandstones that were subjected to 50 to located on the southwestern side of Palo Duro Canyon mudstones Quarter 100 m (165 to 330 ft) of subsidence induced by dissolution the contact between Permian mudstone of the salt. Most of the pipe has collapsed. leaving a master Group and a large mass of debris from a rotational of Permian are appar 15-m- (50-ft-) long segment as a natural bridge on which slump. Several sinks exposed along the skyline the figure is standing. ent entrances to the pipe.

Stages in the Physiographic Development of the Eastern Caprock Escarpment the instrumentally monitored tributary canyon of on most of the Eastern Cap Drainage developing Tierra Blanca Creek. Therefore, the processes that is characterized by short, steep rock Escarpment created the 'drainages shown in figure 29 are probably headwater tributaries arranged in a canyons with similar to those operating at the monitored canyon. (fig. 29). Higgins (1982) considered centripetal pattern Processes of erosion by surface runoff and spring pattern to be indicative of spring the centripetal sapping that are active at the Caprock Escarpment These canyons are developed in the same sapping. appear to have resulted in a characteristic morphology as Luttrell Springs, Tub Springs, stratigraphic units that evolves through time. Segments of the Caprock and Capitol Peak Canyons and are morpho and Red Escarpment shown in figure 29 illustrate postulated similar (fig. 25). We can infer, therefore, that logically successive stages in the development of landforms that sapping and pouroffs observed in the areas of spring characterize a substantial part of the Caprock Escarp present near the heads of canyons in field are also ment. In the initial stages (fig. 29a), drainage segments along the scarp. The presence of pouroffs many places are predominantly subparallel, and areas of converging along the scarp was confirmed by inter and springs or partly centripetal drainage along the western mar of aerial photographs. Furthermore, the pretation gin of the scarp are poorly developed. Divides between of these canyons are developed in the same headwaters areas of incipient centripetal drainage in the heads of strata and exposed to the same climatic conditions as

35 (a)

Index contour interval 50 ft EDOEMON LAKE QUADRANGLE (b)

Index contour interval I00 ft 0 0.5 1Imi

6 ikm OA6608A

at the Caprock Escarpment. FIGURE 29. Maps (a) through 4d) represent postulated stages in development of drainage (b) and (c) Intermediate (a) Early stage in development of partly centripetal drainage ipectinate drainage of Higgins. 1982).

36 DICK MOORE CANYON QUADRANGLE (c)

Index contour interval 100ft COLLETT SPRINGS QUADRANGLE I / (d)Drainage' divide

Index contour interval 50 ft 0 0.5 Imi

0 1krn OA6608 6 stages in drainage development. (d) A late stage in drainage development, where divides between areas of centripetal drainage are well established and in some instances have been separated from the Caprock Escarpment.

37 the Southern High Plains are preserved here (fig. 29c). canyons are absent. The upper margin of the escarp Erosion rates on divides are lower than those in the ment is cut by a profusion of small stream heads; on headwaters of canyons because ground-water flow con topographic maps the scarp appears to be crenulated, verges at the heads of the canyons, thus reducing but regionally it is straight. Progressive drainage devel ground-water flow to divides and also reducing the opment leads to well-defined areas of radial drainage effects of spring sapping and seepage erosion along at the heads of steep, relatively straight canyons divides. Divides become elongate and, with further (fig. 29b). Ground-water flow converges at areas of erosion, are reduced in width to the point of detachment radial drainage at heads of canyons, and the resulting from the High Plains. The last stage of development increase in spring and seep discharge accelerates head occurs when segments of divides are separated from the ward erosion of the canyon. The margin of the escarp High Plains surface (fig. 29d). As divides between ment is highly crenulated, and divides between areas of canyons are separated from the escarpment, the radial drainage are forming. Continued headward ero sequence of evolving landforms is reestablished. sion extends the area of radial drainage westward, and large divides (upland areas) consisting of remnants of

Rates of Retreat of the Caprock Escarpment 9 yr of data for the Salt Fork of the Red River, 5 yr of Estimating the rates at which a major physio data for the Prairie Dog Town Fork of the Red River, 5 yr graphic feature such as the Eastern Caprock Escarp of data for the Pease River, and 6 yr of data for the ment of the Southern High Plains has retreated during of the Wichita River. Horizontal dissolution the North Fork geologic time is at best difficult. Nevertheless, rates for the 15 drainage basins in the eastern Texas following discussion of erosion rates reviews published calculated by Gustavson and others (1980) on Panhandle surface erosion rates and offers new information varied by more than three orders of magnitude. To scarp-retreat rates based on rates of salt dissolution. some of the variability seen in earlier calcula affected avoid Both surface and subsurface processes have tions, we analyzed solute discharge only from down escarpment retreat. Because the Caprock Escarpment stream gauging stations near the Oklahoma-Texas closely parallels the western edge of the zone of active border, using 8 to 14 yr of water quality data (fig. 4). dissolution, both features may be retreating westward at comparable rates. If this parallelism is not merely Procedure for Calculating coincidental, then the rates of westward interstratal Salt Dissolution Rates reflect rates of scarp retreat. salt dissolution Data used to calculate horizontal rates of salt dissolution (table 5) were taken from Water Resources Mean of Interstratal for Texas (U.S. Geological Survey, 1969-1983). Rates chloride solute load, expressed in tons, was obtained by Salt Dissolution along the Caprock dividing the total chloride load by the number of years Escarpment of record. Richter and Kreitler (1986) have shown that in the study area brines encountered in springs and test The average annual solute discharge of streams holes were mostly derived from salt dissolution. They draining the study area was 1,376,304 t (1,513,934 recognized that salt dissolution brines typically have tons) between 1969 and 1983, including approximate molar Na/C1 ratios near 1 and Br/C1 and I/Cl weight ly 919,455 t (1,011,400 tons) of dissolved halite and ratios less than 4 x 10' and 1 x 10", respectively. These 456,818 t (502,5M tons) of dissolved gypsum (U.S. values are significantly different from Na/Cl, Br/Cl Geological Survey, 1969-1983). Dissolution of gypsum and I/Cl ratios of deep-basin brines. Therefore, we appears to be primarily a surface or near-surface phe assume that all chloride came from dissolved bedded nomenon occurring on outcrop faces and along joint Permian salt, although we recognize that ground water planes (Gustavson and others, 1982), whereas dissolu contains approximately 30 ppm of chloride in the tion of salt is an interstratal process occurring beneath Ogallala aquifer and locally as much as 25,000 ppm of the Caprock Escarpment and Rolling Plains at depths chloride in the Dockum aquifer. Since NaCl is 60.66 as great as 300 m (1,000 ft) (fig. 8). percent by weight chloride, tons of chloride were Discussions of salt dissolution rates are presented divided by 0.6066 to obtain tons of NaCL Tons of NaO by Swenson (1974) for a part of the headwaters of the were converted to kilograms by multiplying by 900 Salt Fork of the Brazos River and by Gustavson and kg/ton. The mean volume of salt undergoing dissolu. others (1980) for all the gauged streams draining the tion annually was obtained by dividing the mass in eastern Texas Panhandle from the Canadian River on kilograms of salt being transported from the eastern to the Brazos River on the south. Previous Panhandle by the density of the salt (0.0022 the north Texas3 estimates of dissolution rates were based on only 3 to kg/cm ). 9 yr of discharge data, including, in the study area, 38 TABLE 5. Dissolved chloride loads for streams, calculated salt volumes, and salt dis solution rates for selected drainage basins, Texas Panhandle. Total Mean Cross Years dissolved dissolved Volume of sectional of chloride chloride NaCI NaCI area of salt Drainage 3 (cm) basin data (tons)* (tons/yr) (tons/yr) (cm /yr) 7.0371 x 109 Salt Fork of 15 129,500 8,633 14,232 5.8222 x 109 Red River 137.56 x 109 Prairie Dog 14 6,595,000 471,071 776,576 317.69 x 109 Fork of Red River 130.73 x 109 Pease River 14 1,755,700 125,400 206,726 85.57 x 10' 54.77 x 10' 0.7273 x 10' North Fork of 8 649,200 81,213 133,882 Wichita River 463.85 x 10P 276.47 x 10W Combined 8-15 9,129,300 687,317 1,131,416 drainage basins Mean horizontal Maximum annual Minimum annual rate of rate of rate of dissolution dissolution dissolution (cm/yr) (cm/yr) (cm/yr) 0.21 Salt Fork of 0.82 1.69 Red River 1.35 Prairie Dog 2.33 3.97 Town Fork of Red River 0.37 Pease River 0.65 1.06 60.12 North Fork of 75.31 90.60 Wichita River Combined 1.68 drainage basins

* U.S. Geological Survey (1969-1983); values in English units.

Salt Dissolution Rates The area of the salt surface undergoing dissolution from salt-thickness maps of all four salt Dissolution rates determined for this report differ was estimated same (Salado, Seven Rivers, San Andres, only slightly from dissolution rates for the bearing formations and others Glorieta Formations) (fig. 30). Each line was drainage basins determined by Gustavson and others (1980) calcu segmented in lengths of equal thickness of salt, and, (1980). For example, Gustavson and a map wheel, the length of each thickness seg lated a dissolution rate of 2.59 cm/yr (1.02 inches/yr) using Fork of ment was measured and multiplied by the average for the drainage basin of the Prairie Dog Town salt along the line to obtain the cross the Red River for the years 1969 to 1977, whereas the thickness of the same area for sectional area of salt. Salt thicknesses along the line dissolution rate that we calculated for were interpreted from geophysical logs. The total cross 1969 to 1982 is 2.33 cm/yr (0.92 inch/yr). Current 0.82 cm/yr (0.32 inch/yr) sectional area of salt in the study area is the sum of the dissolution rates range from crossing a given for the Salt Fork of the Red River to 75.31 cm/yr area along each of the contours mean drainage basin. (29.6 inches/yr) for the North Wichita River. The study area The horizontal rate of dissolution is the mean interstratal dissolution rate for salts in the discharged per year divided by the total is 1.68 cm/yr (0.66 inch/yr), close to the 2.33-cm/yr volume of salt of area of salt in the drainage basin (0.92- inch/yr) dissolution rate for the drainage basin cross-sectional largest (table 5). Maximum and minimum rates were deter the Prairie Dog Town Fork of the Red River, the mined by taking the highest and lowest annual drainage basin in the study area. chloride loads for the years of data available and These dissolution rates are conservative estimates performing the same calculations (table 5). because they are based only on solute loads carried by

39 EXPLANATION

5)' Drainage divide •~ Escarpment p 220 Thickness ofunderlyifl saltunit .g,- Boundary of beginning sall dissolutof SALT lM•T Limit of salt unit undergoing dissatluion 1O.Ae Stream gouge stotion

for the basins and gauging stations in the Rolling Plains. Salt thicknesses are shown FIGURE 30. Drainage northern limits Rivers, upper and lower San Andrea, and Glorieta Formations at the eastern and Salado, Seven 1980, their fig. 29). of the next stratigraphically higher salt unit (from Gustavson and others, 40 surface waters. No data on solute load or discharge are deposited along Holmes Creek at the foot of the available for ground water discharging out of this escarpment, to the present, (2) from about 620,000 yr region, although numerical simulations suggest that ago, after deposition of the Seymour Formation, to the ground-water discharge on the Rolling Plains could present, and (3) from about 3,000,000 to 5,000,000 yr account for all flow out of the system. Furthermore, ago, from the end of deposition of the Ogallala For these dissolution rates are determined for a climate mation, to the present (Gustavson and others, 1981; that was probably both warmer and drier than the Simpkins and Baumgardner, 1982). In addition, semi Quaternary glacial episodes (Caran, 1984); both dis annual measurements of erosion pins and headcuts in charge and solute load were presumably higher during streams draining the escarpment at selected sites glacial periods. Although spring discharge has record short-term erosion and deposition rates decreased substantially since the onset of irrigation on (Simpkins and Gustavson, 1987). the High Plains, no corresponding decrease in stream Holmes Creek in Briscoe County, Texas, has head discharge is evident. This probably results from the waters in the Caprock Escarpment and has incised its fact that most gauging stations on streams draining valley approximately 12.5 m (41 ft) during the last 8,010 the escarpment lie approximately 60 to 100 km (40 to + 110 to 9,360 ± 170 radiocarbon yr. The 12.5-m 60 mi) east of the escarpment, and any change in deep incision equals the difference in elevation between spring discharge along the escarpment is likely to be the dated horizon (Harrison and Killen, 1978) and the masked by surface runoff. present stream floor. If the longitudinal profile of the If the alignment between the Caprock Escarpment stream has not changed substantially over the last and zones of salt dissolution and subsidence (figs. 10 7,900 to 9,500 yr, an incision of 12.5 m (41 ft) would have through 12) is not coincidental, then the rate of regional been accompanied by approximately 1.1 km (0.7 mi) of mean dissolution of Permian bedded salt should be scarp retreat. This is equivalent to a retreat rate similar to the rate of scarp retreat, at least during the ranging from 0.12 to 0.14 km/1,000 yr (0.08 to 0.09 late Quaternary. mi/1,000 yr). Because 12.5 m is the maximum incision that could have occurred within 7,900 to 9,500 yr, the retreat rate is also a maximum estimate. The Seymour Formation comprises sediments Surface Erosion Rates thought to have been derived from the Ogallala The following discussion of estimates of long-term Formation at a time when the Caprock Escarpment erosion rates for the Caprock Escarpment presupposes was just west of the present western limit of the a series of critical assumptions, each of which could Seymour deposits (Meinzer and Slaughter, 1971). The strongly affect the magnitude of the estimated rates. presence of Lava Creek B Ash (Izett and Wilcox, 1982) For example, effects of climatic cycles are not con in the upper part of the Seymour indicates that most of sidered here because the number, duration, and inten the silts, sands, and gravels were deposited more than sity of cyclic climatic changes in the region are 620,000 yr ago. If the eastern limit of the Ogallala unknown. Rainfall and stream and spring discharge Formation (Caprock Escarpment) was immediately probably varied in the past with climatic cycles, thus west of the Seymour Formation at the time of its affecting erosion rates. Furthermore, the original east deposition, then the scarp has retreated approximately ward extent of the High Plains and Ogallala Forma 114 km (71 mi) since the end of Seymour deposition tion is assumed to have been approximately 320 km (Simpkins and Baumgardner, 1982). An escarpment (200 mi) east of the present Caprock Escarpment on the retreat rate of 114 km in 620,000 yr is equivalent basis of projections of the High Plains surface to a maximum rate of approximately 0.18 km/1,000 yr (according to Gustavson and others [1981], who (0.11 mi/1,000 yr). reviewed the various published projections of the High Lava Creek B Ash is also exposed along Duck Creek Plains surface). in Kent County, Texas, approximately 45 km (28.1 mi) Salt dissolution and subsidence were active during southeast of the Caprock Escarpment. Although the deposition of lower Ogallala sediments (Schultz, 1977), context in which the ash was deposited is unknown, and the extensive deformation of Permian and younger deposition was on the Rolling Plains; thus, the Caprock strata in the Rolling Plains indicates that these Escarpment lay to the west of the ash bed. In this case, processes were probably active throughout the late assuming that the escarpment was immediately west of Tertiary and Quaternary. Ogallala sediments that the ash when it was deposited, *the maximum scarp originally overlaid the Rolling Plains were also at least retreat rate was approximately 0.07 km/1,000 yr (0.04 partly water saturated, and therefore spring sapping mi/1,000 yr). and seepage erosion occurred along dissected margins Several authors have estimated the former eastern of the Ogallala much as they do today. Consequently, most extent of the Ogallala Formation (Harris, 1970; processes affecting the Caprock Escarpment during the Byrd, 1971; Meinzer and Slaughter, 1971; Thomas, late Tertiary and Quaternary were probably similar to 1972; Gustavson and others, 1980; Osterkamp and processes operating today. Wood, 1984), and on the basis of these projections the Three time periods were examined to analyze the Caprock Escarpment seems to have retreated as much westerly retreat of the Caprock Escarpment: (1) from as 320 km (200 mi) since deposition of the Ogallala about 9,500 yr ago, when a Holocene terrace was Formation ended. Gustavson and others (1980, 1981)

41 for slopes of approximately 300 that ranged from 0.4 to approxi stated that the end of Ogallala deposition was 0.6 cm/yr (0.16 to 0.24 inch/yr). These vertical erosion mately 3 Ma ago; however, Schultz (1977) and Winkler probably correspond to a horizontal slope retreat have ended as rates (1985) suggested that deposition may rate of 1 cm/yr, or 0.01 km/1,000 yr (0.4 inch/yr, or early as 5 Ma ago. Clearly, timing of the end of yr). Retreat rates of headcuts along but the 0.006 mi/1,000 Ogallala deposition is not well constrained, stream thalwegs ranged from 0.8 to 1.7 cm/yr (0.3 to 3-Ma age estimated by Gustavson and others (1981) is 0.7 inch/yr). the probably too young. To complicate matters further, Rates of scarp retreat calculated from estimates of upper eolian part of the Ogallala and the Ogallala position of the Caprock Escarpment range Plains the former caliche caprock in the present area of the High to 0.18 km/1,000 yr (0.04 to 0.11 mi/1,000 yr). time that the from 0.06 - could have been deposited at the same Retreat rates based on short-term measurements of undergoing ero eastern margin of the Ogallala was slope erosion and headcut retreat are about 0.01 to 0.02 sion. Nevertheless, if we estimate that Ogallala deposi to 0.012 mi/1,000 yr). Subsurface of km/1,000 yr (0.006 tion ended 5 Ma ago, we can say that the rate dissolution rates are minimum rates and has been interstratal Caprock Escarpment retreat since then average nearly 0.02 km/1,000 yr (0.013 mi/1,000 yr). approximately 0.06 km/1,000 yr (0.4 mi/1,000 yr). though escarpment retreat rates calculated by headcuts Even Measurements of erosion pins and stream these different methods exhibit some variation, these were made at least biannually since 1978 at selected only by one order of magnitude. This and rates differ sites along the Caprock Escarpment (Simpkins suggests that westward scarp retreat and westward Gustavson, 1987). These sites, however, were chosen of the dissolution zone throughout the late Erosion expansion because they appeared to be actively eroding. Cenozoic was about 0.01 to 0.20 km/1,000 yr (0.006 to rates were monitored on a variety of slopes, vegetative 0.12 mi/1,000 yr). cover, and substrate textures. Analyses of these data have yielded, for example, mean vertical erosion rates

Effect of Diminished Spring Discharge on Geomorphic Processes Group aquifer. However, because pumping the Ogallala The discharge of most springs from the base of the aquifer decreases the vertical head gradient between Ogallala Formation or from the base of sandstones of the Ogallala and lower Dockum and because the the Dockum Group along the Eastern Caprock Escarp Ogallala is the source of recharge to the Dockum ment has decreased substantially during the last 50 yr (Dutton and Simpkins, 1986), we speculate that leakage (fig. 4, table 6). From 1900 to 1978, spring discharge and hence recharge to the lower Dockum aquifer have decreased as much as 98 to 100 percent, averaging a also decreased. Consequently, spring discharge from drop in discharge of 86 percent. Only two springs the Dockum aquifer at the Caprock Escarpment has (Roaring Springs and Wolf Springs) increased dis probably decreased since irrigation was introduced in charge. All measurements were made at about the same the Southern High Plains. time of year, and therefore the possibility of discharge Sapping and other geomorphic processes associ variation due to seasonal climatic fluctuations was ated with spring discharge along the Caprock Escarp minimized. Ground-water pumpage has substantially ment are demonstrably important in scarp retreat. reduced the saturated thickness of the Ogallala aquifer However, with pumping of large volumes of water since the beginning of this century, when irrigation from the Ogallala aquifer, spring discharge has began in the Southern High Plains (Knowles and decreased to a trickle in most areas. With continued others, 1982). Consequently, decreases in spring dis mining of this aquifer, spring discharge may cease and charge probably resulted from ground-water pumpage the rate of scarp retreat will be reduced. Partly coun (Brune, 1981; Gustavson, 1983). terbalancing these effects are land-use practices in the Although diminished discharge is clearly estab region, including cultivation, overgrazing, and road lished for springs emitting ground water from the building, which have probably exacerbated erosion Ogallala aquifer, no comparable data are available for (Machenberg, 1986). springs emitting ground water from the lower Dockum

42 TABLE 6. Spring discharge rates, Eastern Caprock Escarpment, Texas Panhandle (from Brune, 1981). Figure 4 shows distribution of springs along the Eastern Caprock Escarpment (1 liter = 0.26 gal).

Discharge Discharge (U.s) County Spring name (L/s) Potter Cedar Springs 0.79 (1937) dry (1978) Tecovas Springs 32.00 (1881) 2.50 (1978) Randall CCC Springs 0.38 (1937) 0.05 (1978) Armstrong Salt Fork Springs 8.80 (1940) 0.65 (1978) Baker Springs 0.31 (1940) seep (1978) Pleasant Springs 9.50 (1940) 1.20 (1978) Country Road Springs 0.19 (1940) dry (1978) Harrell Springs 0.63 (1940) dry (1978) Dripping Springs 0.95 (1940) seep (1978) Luttrell Springs 0.44 (1940) seep (1978) Dry Creek Springs 0.63 (1940) seep (1978) Donley Dunbar Springs 19.00 (1968) 13.00 (1978) Cottonwood Springs 15.00 (1968) 7.50 (1978) Luttrell Springs 14.00 (1968) 1.30 (1978) Chamberlain Springs 13.00 (1968) 1.60 (1978) Eagle Springs 11.00 (1968) seep (1978) Buck Springs 0.32 (1943) dry (1978) Parker Springs 0.32 (1932) seep (1978) Highway Springs 0.13 (1943) seep (1978) Browder Springs 12.00 (1968) 0.09 (1978) Broome Springs 1.60 (1943) seep (1943) Indian Springs 0.83 (1943) 0.20 (1978) Bitter Creek Springs 50.00 (1968) 3.70 (1978) West Bitter Creek Springs 10.00 (1967) 0.52 (1978) Sandy Springs 3.80 (1968) dry (1978) Swisher Rogers Springs 0.32 (1943) seep (1978) Briscoe Deer Springs 19.00 (1946) 1.30 (1978) Turkey Springs 25.00 (1946) 2.50 (1978) Cedar Springs 16.00 (1946) 1.00 (1978) Martin Springs 0.95 (1969) 0.12 (1978) Gyp Springs 6.70 (1969) 0.12 (1978) Haynes Springs 2.50 (1969) 0.35 (1978) Las Lenguas Springs 19.00 (1967) 1.90 (1978) Floyd Blue Hole Springs 14.00 (1968) dry (1978) Bain Springs 6.70 (1938) dry (1978) Motley Ballard Springs 0.95 (1938) 0.85 (1978) Willow Springs 1.50 (1938) 0.95 (1979) Mott Camp Springs 0.63 (1938) dry (1978) Burleson Springs 8.80 (1938) dry (1978) Roaring Springs 31.00 (1938) 40.00 (1978) Wolf Springs 1.90 (1938) 7.10 (1978)

43 Summary and Conclusions

is main transmissive units in topographically low areas of the The Caprock Escarpment developed and Plains. Saline springs occur in outcrops of the near-surface Rolling tained by the interaction of surface and Seven Rivers and San Andres Formations. erosional processes, such as slumping, spring sapping, convective storms supply most of the flow, rockfalls, High-intensity piping, sheetflood, sheet wash, channel rainfall to the High Plains surface. Sheetfloods trans and the subsurface processes of salt dissolution and on the eastern margin of the for port rainwater that falls subsidence. Ground water provides the impetus to the Caprock Escarpment, and sheet dissolution. High Plains slumping, spring sapping, piping, and salt wash and rill wash scour the escarpment surface. Sheet logs, core, and out Interpretation of geophysical floods with flow depths of as much as 10 cm (4 inches) crops indicates that a cumulative thickness of as much effect on the High Plains surface. dissolved have little erosional as 230 m (750 ft) of bedded Permian salt has and erosion rates were monitored in a deeply Caprock Escarp Climate from beneath the Rolling Plains and incised tributary of Tierra Blanca Creek, a stream that loads in local streams ment. Furthermore, high solute is developed in the same strata as the upper part of indicate that dissolution is an active process and that is subject to the same 3 the Caprock Escarpment and as much as 15,000,000 m (525,000,000 ftW) of salt was as the escarpment. As a result of a streams weather conditions carried out of the study area by surface on May 28, 1978, which yielded 7.1 cm (2.8 resulting from storm between 1969 and 1983. Subsidence inches) of rain in 3.2 hr, slopes in the Blackwater Draw dissolution is locally expressed along the escarpment the upper units of the filled and Ogallala Formations, as clastic dikes, minor folds, extension fractures were eroded an average of 2.2 cm (0.87 in the regional escarpment, with fibrous gypsum, and a change sheet wash and rill wash. A storm of similar Formation to an inch) by southwesterly dip of the Alibates intensity on June 10, 1984, resulted in comparable easterly or northeasterly dip beneath the escarpment. of erosion and weather data collected Caprock erosion. Analyses Dissolution-induced subsidence beneath the since 1979 suggest that erosion and much as 75 m (250 ft) continuously Escarpment may account for as transportation of sediment from first-order streams in of escarpment relief. Dissolution and subsidence locally occur in a series of incre and the Caprock Escarpment extend westward from the Caprock Escarpment steps. The three-step process involves (1) rain High Plains, as mental occur locally beneath the Southern fall events of intensities less than approximately evidenced by thinning of Salado and Seven Rivers salts that move sediment on slopes in this 6.0 cm/hr (2.4 inches/hr) and by deformation of the Alibates Formation surfaces of first-order streams, although Prairie Dog and alluvial region. The valleys of Mulberry Creek, is stored locally; (2) intense rainfalls Creek, the White the sediment Town Fork of the Red River, Tule (more than 6.0 cm/hr (2.4 inches/hrD that result in River, and Double Mountain Fork of the Brazos River erosion and accretion on the floor lacus erosion of hillslopes, (all reentrants along the escarpment) contain streams, and deposition of sediment in the basins that prob of first-order trine sediments in small structural valleys of second-order streams; (3) storms capable of ably formed by salt dissolution and subsidence. of second-order streams. Storms water eroding the channels Downward leakage of low-salinity ground of step 3 magnitude, however, were not recorded during from the High Plains aquifer to underlying Permian the study period. steep head salt is partly controlled by fractures and Spring sapping occurs primarily on the floors and Stream seg gradients at the Caprock Escarpment. slopes of canyons below outcrops of basal sands and ments and subsidence basins on the Rolling Plains Ogallala Formation and below fluvial that gravels of the tend to parallel fracture orientations, suggesting of the Dockum Group. It undermines resis Clastic dikes sandstones dissolution was enhanced along fractures. tant overlying sandstones and initiates rockfalls. Mass deep within the Ogallala Formation are filled with sedi contributes to escarpment retreat; at least 100 Draw wasting ment washed in from the overlying Blackwater slumps are recognizable in the Palo Duro Can through open large Formation, indicating ground-water flow yon. The lower part of the planes of rotation of many fractures. of these features are within or at the upper contact of The interpretation that low-salinity ground water in the Dockum Group. Smectitic to the lacustrine mudstones moves downward from the High Plains aquifer these mudstones probably provided lubrication model that clays in salt beds is also supported by a numerical fot the movement of slump blocks. Along the slip simulates two-dimensional ground-water flow through planes of these slump blocks, large pipes have devel strata that underlie the High Plains, Caprock Escarp of sediments by slumping 1982). oped. Physical disruption ment, and Rolling Plains (Simpkins and Fogg, has accelerated erosion on the escarpment slopes. The model illustrates (1) downward flow of fresh, low Escarpment overlies and is roughly into The Caprock salinity ground water from the Ogallala aquifer parallel to the western edge of the salt dissolution zone, the salt dissolution zone at the Caprock Escarpment; suggesting that the rate of retreat of the Caprock brines through (2) eastward movement of the resultant Escarpment and the rate of westerly advance of the salt transmissive dolomite/anhydrite beds of the Seven zone are similar. Rates of salt dissolution discharge dissolution Rivers and San Andres Formations; and (3) and scarp retreat have been calculated by several of the brines into saline springs at outcrops of those 44 0.01 to 0.20 km/1,000 yr (0.006 on projected former positions of the Caprock Escarp methods and range from ment range from 0.06 to 0.18 km/1,000 yr (0.04 to to 0.13 mi/1,000 yr). An average dissolution rate was yr). salt dis 0.11 mi/1,000 obtained by dividing the annual volume of in the Caprock Escarpment has region by the Spring discharge charged by streams draining the study decreased substantially in the past 50 yr. Springs that cross-sectional area of underlying salts. The rate of 10 L/s (2.2 gal/s) now yr formerly discharged nearly retreat is approximately 0.2 cm/yr, or 0.02 km/1,000 gal/s). Reduction in spring a min discharge barely 1 L/s (0.2 (0.8 inch/yr, or 0.013 mi/1,000 yr)-probably has coincided with and is apparently the not consider the salt that discharge imum rate because we did of extensive pumping of the Ogallala aquifer for means other than stream result may leave the study area by irrigation water. Reduction of spring discharge is likely discharge. The rate of scarp retreat derived from long of spring sapping as a is approximately to reduce the effectiveness term monitoring of hillslope erosion process in the erosion of the Caprock Escarpment. 0.01 km/1,000 yr (0.006 mi/1,000 yr) under current climatic conditions. Average scarp retreat rates based Acknowledgments Figures for this report were prepared by Annie by the U.S. Department of This research was funded Kubert-Kearns under the supervision of Richard L. Energy Salt Repository Project Office under contract Dottie Johnson and and C. W. Dillon. Word processing was by no. DE-AC97-83WM46651, T. C. Gustavson was by Susan Lloyd under the supervision The conclusions of the typesetting Kreitler, principal investigators. of Lucille C. Harrell and Susann Doenges. Vance authors are not necessarily endorsed or approved by Raney, and Robert W. and Holliday, Waite Osterkamp, Jay the Department of Energy. Ann D. Hoadley the report. Technical data. Baumgardner, Jr., reviewed Julieann Mahler helped compile dissolution-rate Hentz. Their comments and his help in editing was by Tucker Special thanks go to Graham Fogg for appreciated. Duran Dodson edited and of flow beneath the criticisms are implementing the numerical model Jamie S. Haynes designed this publication; Lana Caprock Escarpment. Dieterich coordinated its production.

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Geology Geological Circular 79-1, p. 50-56. and hydrochemistry of Nativ, R., 1988, Hydrogeology - 1980a, Upper Permian salt-bearing stratigraphic Plains, Texas the Ogallala aquifer, Southern High units, in Gustavson, T. C., and others, Geology and Mexico: The Univer Panhandle and Eastern New geohydrology of the Palo Duro Basin, Texas Pan Economic Geology sity of Texas at Austin, Bureau of handle, a report on the progress of nuclear waste 64 p. Report of Investigations No. 177, isolation feasibility studies (1979): The University Geology Neuman, S. P., and Narasimhan, T. N., 1977, Mixed of Texas at Austin, Bureau of Economic explicit-implicit iterative finite-element scheme for Geological Circular 80-7, p. 12-23. Theory: International diffusion-type problems: I., - 1980b, Salt depth and thickness studies, in Methods Engineering, v. 11, Journal of Numerical Gustavson, T. C., and others, Geology and geohy p. 309-323. drology of the Palo Duro Basin, a report on the Nicholson, J. H., 1960, Geology of the Texas Pan progress of nuclear waste isolation feasibility handle, in Aspects of the geology of Texas, a studies (1979): The University of Texas at Austin, symposium: Austin, University of Texas Publication Bureau of Economic Geology Geological Circular 6017, p. 51-64. 80-7, p. 33-40. to Orr, E. D., 1983, An application of geostatistics Reeves, C. C., Jr., 1971, Appendix A, in Allen, B. L, determine regional ground-water flow in the San and others, Environmental impact analysis-salt Andres Formation, West Texas and eastern New retention structures, upper Brazos River Basin, Mexico, in Gustavson, T. C., and others, Geology Texas: Texas Tech University, Water Resources and geohydrology of the Palo Duro Basin, Texas Center, WRC-71-3, p. A1-A34. progress of nuclear waste Panhandle, a report on the S1985, Nuclear-waste repository impaired by effects studies (1982): The University of isolation feasibility of subsurface salt dissolution (abs): Geological Bureau of Economic Geology Texas at Austin, Society of America Abstracts with Programs, v. 17, Geological Circular 83-4, p. 102-108. p. 697. The climate of Texas and adjacent Orton, R. B., 1964, C. C., Jr., and Temple, J. M., 1986, Permian salt Washington, D.C., U.S. Department of Reeves, Gulf waters: dissolution, alkaline lake basins, and nuclear-waste Weather Bureau, 195 p. Commerce, storage, Southern High Plains, Texas and New Osterkamp, W. R., Fenton, M. M., Gustavson, T. C., Mexico: Geology, v. 14, p. 939-942. Hadley, R. F., Holliday, V. T., Morrison, R. B., and 48 Richter, B. C., and Kreitler, C. W., 1986, Geochemistry Geology and geohydrology of the Palo Duro Basin, a of salt-spring and shallow subsurface brines in the report on the progress of nuclear waste isolation Rolling Plains of Texas and southwestern Okla feasibility studies (1982): The University of Texas homa: The University of Texas at Austin, Bureau of at Austin, Bureau of Economic Geology Geological Economic Geology Report of Investigations No. 155, Circular 83-4, p. 94-96. 47 p. Swenson, F. A., 1974, Rates of salt solution in the Schultz, G. E., 1977, Field conference on late Cenozoic Permian Basin: U.S. Geological Survey Journal of biostratigraphy of the Texas Panhandle and adja Research, v. 2, p. 253-257. cent Oklahoma: West Texas State University, Thomas, Kilgore Research Center, Department R. G., 1972, The geomorphic evolution of the of Geology Pecos River and Anthropology Special Publication No. 1, 160 p. system: Baylor University, Baylor Geological Studies Bulletin, no. 22,31 p. . 1986, Biostratigraphy and volcanic ash deposits of U.S. Army Corps of Engineers, 1975, Red River chloride the Tule Formation, Briscoe County, Texas, in remote-sensing Gustavson, T. C., ed., Geomorphology and Quater study, final report for NASA SR/T nary stratigraphy of project no. W-13,557: Tulsa District, Tulsa, Okla the Rolling Plains, Texas homa, Panhandle: The University Geology Section, Foundation and Materials of Texas at Austin, Branch, 8 Bureau of Economic Geology Guidebook 22, p. 82-84. p. U.S. Department Seni, S. J., 1980, Sand-body geometry and depositional of Agriculture, Soil Conservation Service, 1972, Mansker soil series. systems, Ogallala Formation, Texas: The University of Texas at Austin, Bureau of Economic Geology - 1977a, Acuff soil series. Report of Investigations No. 105, 36 p. - 1977b, Amarillo soil series. Simpkins, W. W., and Baumgardner, R. W., Jr., 1982, Pullman soil series. Stream incision S1977c, and scarp retreat rates based on U.S. Department of Commerce, volcanic ash data from the Seymour Formation, in 1955, Rainfall inten sity-duration-frequency curves for selected stations Gustavson, T. C., and others, Geology and geohydrol in the United States, Hawaiian Islands and Puerto ogy of the Palo Duro Basin, Texas Panhandle, a Rico: Washington, report on the progress of nuclear waste isolation D.C., U.S. Weather Bureau Technical Paper 25, 53 p. feasibility studies (1981): The University of Texas at Austin, Bureau of Economic Geology Geological - 1978a, Local climatological data, annual sum Circular 82-7, p. 160-163. mary with comparative data, 1978, Lubbock, Texas: Asheville, North Carolina, National Climate Center, Simpkins, W. W., and Fogg, G. E., 1982, Preliminary 4 p. modeling of ground-water flow near salt dissolution zones, Texas Panhandle, in Gustavson, T. C., and - 1978b, Local climatological data, annual sum others, Geology and geohydrology of the Palo Duro mary with comparative data, 1978, Amarillo, Texas: Basin, a report on the progress of nuclear waste Asheville, North Carolina, National Climate Center, isolation feasibility studies (1981): The University of 4 p. Texas at Austin, Bureau of Economic Geology U.S. Geological Survey, 1969-1983, Water resources for Geological Circular 82-7, p. 130-137. Texas, part II: surface water quality. Simpkins, W. W., and Gustavson, T. C., 1985, Late Varnes, D. J., 1958, Landslide types and processes: Pleistocene and Holocene channel aggradation, National Research Council, Highway Research Tierra Blanca Creek, Southern High Plains, Texas Board, Special Report No. 29, p. 20-47. Panhandle (abs): Geological Society of America Winkler, D. A., 1984, Biostratigraphy of the Ogallala Abstracts with Programs, v. 17, p. 192. Group (Miocene), Southern High Plains, Texas (abs): . 1987, Erosion rates and processes in subhumid and Geological Society of America Abstracts with semiarid climates, Texas Panhandle: statistical Programs, v. 16, p. 698. evaluation of field data: The University of Texas at - 1985, Stratigraphy, vertebrate paleontology, and Austin, Bureau of Economic Geology Report of Inves depositional history of the Ogallala Group in Blanco tigations No. 162, 54 p. and Yellowhouse Canyons, Northwestern Texas: Simpkins, W. W., Gustavson, T. C., Alhades, A. B., and The University of Texas at Austin, Ph.D. disserta Hoadley, A. D., 1981, Impact of evaporite dissolution tion, 243 p. and collapse on highways and other cultural Wood, W. W., and Osterkamp, W. R.. 1987, Playa-lake features in the Texas Panhandle and eastern New basins in the Southern High Plains of Texas and Mexico: The University of Texas at Austin, Bureau New Mexico: Part II, a hydrologic model and mass of Economic Geology Geological Circular 81-4, 23 p. balance arguments for their development: Geo Smith, D. A., Bassett, R. L., and Roberts, M. P., 1983, logical Society of America Bulletin, v. 99, p. 224-230. Potentiometric surface of the Wolfcampian aquifer, Young, A., 1972. Slopes: New York, Longman Group Palo Duro Basin, in Gustavson, T. C., and others, Limited, 288 p.

49 110 (codI,4 4A/ZZ)

IMPACT OF TIME AND CLIMATE ON QUATERNARY SOILS

IN THE YUCCA MOUNTAIN AREA

OF THE NEVADA TEST SITE

by

Emily Mahealani Taylor

B.S., University of California, Berkeley, 1980

A thesis submitted to the

Faculty of the Graduate School of the

University of Colorado in partial fulfillment

of the requirements for the degree of

Master of Science

Department of Geological Sciences

1986

-43031/0-90/t- To the GRADUATE SCHOOL OF THE UNIVERSITY OF COLORADO:

Student's Name: Emily Hahealani Taylor

Degree: H. S. Discipline: Quaternary Geology and Soils

Thesis Title: Impact of Time and Climate on Ouaternary Soils in the

Yucca Mountain Area of the Nevada Test Site

The final copy of this thesis has been examined by the undersigned, and we find that both the content and the form meet acceptable presentation standards of scholarly work in the above discipline.

"Chairperson

Committee member

ate I °i liii

Taylor, Emily Mahealani (M.S., Geology)

Impact of time and climate on Quaternary soils in the Yucca

SMountain area of the Nevada Test Site r• Thesis directed by Professor Peter W. Birkeland I

The influences of time and climate were studied on a

Quaternary chronosequence in the Yucca Mountain area of the Nevada

Test Site. The soils are formed in alluvium derived from ish-flow

tuffs and eolian dust. Both secondary CaCO 3 and opaline SiO2 appear

initially as coatings on the underside of clasts and over time form

indurated horizons. The maximum amounts of CaCO 3 , opaline SiO2 , and

usually clay occur in the same horizon. In these horizons, opaline

SiO2 is more abundant than CaCO 3 and clay. There is little change

* in the soil-clay mineralogy over time. Vesicular A (Av) horizons.

have not formed on Holocene deposits, but are common on Pleistocene

deposits. There is no relationship between the thickness of the Av r and the age of the underlying depositt Regression statistics suggest that quantified field

properties and secondary clay, silt, CaCO3 , and opaline Si02

accumulate at a logarithmic rate. However, owing to the effects of

erosion, and eolian additions, these secondary properties may be

better ixpressed by linear rates. It is likely that erosion results

in long-term accumulation rates less than the measured accumulation

rates. Average accumulation rates are higher for the Holocene

soils. This relationship suggests that the translocation of eolian

material was not limited by Holocene precipitation. iv The modern climate and two climatic models of the last g!a:ial maximum were used to generate soil water balances and to calzulate evapotranspiration (ET p). The Papadakis method was used to calculate ETp. These calculations suggest that translocation of dissolved and solid material in Holocene soils can be attributed

chiefly to high-precipitation storm events.

There are several different trends in CaCO3 accumulation in the Holocene soils, and in older soils that have experienced at least one major climatic change. These trends suggest that changes in temperature and (or) seasonality of the precipitation dominated

the climatic change associated with the Holocene-Pleistocene

boundary. Comparison of actual Holocene soil CaCO3 profiles with those generated by a computer suggest that this climatic change was gradual. ACKNOWLEDGMENTS

This work has been funded by the U.S. Geological Survey, Branches of Central and Western Regional Geology, which provided a stipend, office space, field support and lab facilities from the summer of 1983 to the present. The support Is from the Tectonics of the Southern Great Basin project and this work began under the encouragement of Michael Carr, our fearless leader, and seen to completion by Ken Fox who took over as project chief in February of 1985.

The lab work was completed only because of the patience of Don Cheney at the Central Regional Geology Soil and Sediment Laboratory, who not only spent a great deal of time on my samples, but also allowed me to spend months in his lab. Some lab work was also completed at the University of Colorado Soils Laboratory and INSTAAR with the help of Rolf kthl.

The guidance and support from faculty and friends at the University of Colorado made it all possible. A special thanks to Dr. Peter W. Birkeland who made suggestions, read and reread (the one "GOOD1" comment on the final draft was next to a paragraph he had written), and humored me on through the years. His encouragement and faith kept me on track. Dr. Nel'Caine's statistical coaching and text review was also very helpful. vi

My cronies and colleagues at work who criticized my hallway

ramblings were also a great help; they include Will Carr, Jennifer

Harden, Michael Machette, Dan Muhs, Steve Personius, Ken Pierce,

Marith Reheis, and Dub Swadley. Ralph Shroba's guidance in the

field, text reviews, and dietary suggestions were indispensable.

Heather Huckins field assistancC and Mercury-survival-tips make the

long stints in Nevada both productive and enjoyable.

My parents and family who have kept faith can not be forgotten. Finally, thanks to Ross Jacobson who has provided moral support and kindness throughout this entire ordeal. Vii

CONTENTS

CHAPTER

I. INTRODUCTION AND METHOD OF STUDY ...... 1

Introduction ......

Statement of Problem ...... 1

Objectives ...... *...... 3

Strategy ...... 4

Location of Study Area ...... 6

Methods of Field Work and Soil Description ...... 6

Locating Study Area ...... 6...... 6

Description and Sampling 7...... 7

Pedogenic Silica ...... 8

Index of Soil Development ...... 9

Micromorphology ...... 9

Statistical Methods ......

II. ENVIRONMENTAL SETTING, PAST AND PRESENT ...... 11

Geologic Setting and Chronology ...... 11

Quaternary Stratigraphy ...... 11

Ages of Deposits ...... •0.0...... 17

Geomorphic Setting ......

Terrace Formation--Tectonic vs Climatic ...... 17

Ground Wdter Setting ...... 21

Modern Climate ...... 22 viii Paleoclimate in the NTS Region ...... 25

Packrat Midden Evidence ...... 25 Pluvial Lake Evidence ...... 26

Summary of the Glacial Climate Models ...... 27

III. MAJOR PEDOLOGICAL CHANGES WITH TIME ...... 29 Morphology ...... 29

Pedogenic Opaline Silica ...... 29

Car mnate and Opaline Silica ......

Vesicular A Horizons ...... 33

Profile Index Values ...... 34

Accumulations of Carbonate, Clay, Silt, and Opaline Silica ...... 42

,Method to Calculate Rates of Accumulation ...... 43

Rates of Accumulation of Carbonate, Clay, Silt, and Opaline Silica ...... 3 Depth Functions of Significant Soil Properties ...... 49

Primary and Secondary Minerals Identified by X-ray Diffraction .....

IV. USING SOIL DATA TO ASSESS PALEOCLIMATE ...... 65 Soil Water Balance and Leaching Index o...... 65 Carbonate Translocation .S...... ** ...... 75

Computer Generated Model for Carbonate Translocation ...... 80 Pedogenic Silica Morphology as a Climatic Indicator .. 83 V. SUMMARY, CONCLUSIONS, AND FUTURE STUDIES ...... s...... 85 REFERENCES ...... 92 ix

APPENDICES

A Soil Field descriptions for the Yucca Wash and F Fortymile Wash Area, Nevada Test Site ...... 104

B Soil profile index values ...... 1 tCLaboratory Methods--particle size distribution (PSD), bulk density, percent carbonate, gypsum and soluble salts, percent organic carbon and loss on ignition (LOI), pH, silica, clay mineralogy ...... 161

D Effects on the particle size distribution and clay mineralogy after the removal of opaline silica ...... 165

E Laboratory procedure for measuring pedogenic opaline silica using a spectrophotometer ...... 170

F Laboratory Analyses--particle size, bulk density, carbonate, gypsum, soluble salts, organic carbon, oxidizable organic matter, loss on ignition, pH, and silica by weight ...... 179

G Representative Dates for the Quaternary deposits, NTS .. 192

H Horizon weights of carbonate, clay, silt, and opaline silica ...... 201

I Soil parameters used to model calcic soil development .. 200

J Use of pollen, spores, and opal phytoliths from three different aged deposits as paleoclimatic indicators .... 193 mu -- _____

X

TABLES

Table area, I Quaternary stratigraphy of the Yucca Mountain NTS

2 Temperature, precipitation and potential evapotrans piration data for the Holocene (present) and two models for the last glacial maximum ...... 23 silica 3 General characteristics of pedogenic opaline stages ...... for the study 4 Comparison of soil profile index values area with those for Las Cruces, New Mexico ...... 42 2 clay, 5 Correlation coefficients (r ) for carbonate, silt, and opaline silica ...... 46 2 age, log age, 6 Correlation coefficients (r ) for linear K, carbonate, clay, and opaline silica for A, B and 50 and C horizons and all horizons combined ......

7 Clay minerals identified and their diagnostic -features ...... 57 opaline silica ...... 61 8 X-ray diffraction classification of potential 9 Comparison of methods to calculate data .... 67 evapotranspiration using Beatty, Nevada weather

I - U w-

FIGURES

Figure

I Location of study area

2 Map of Quaternary deposits, Tertiary bedrock, and trench locations in the study area

3 Generalized cross section showing the stratigraphic relationships of Quaternary fluvial deposits along Yucca Wash and Fortymile Wash ...... *...18

4 Profiles of terrace deposits along Yucca Wash and Fortymile Wash .... o...... 20

5 livariate regression analyses of significant property profile index values vs time ...... 36

6 Bivariate regression analyses of soil profile index values vs time ...... 38

7 Soil profile index values vs elevation ...... 41

8 Profile sum of horizon weights vs age of carbonate, clay, silt, and opaline silica on soils developed on stratigraphic units Qic, Q2b, Q2c, and QTa ...... 44

9 Average rates of accumulation of pedogenic carbonate, clay, silt, and opaline silica based on profile weight sums on stratigraphic units Qic, Q2b, Q2c, and QTa ...... 45

10 Depth plots of pedogenic clay, CaCO 3 , and opaline SiO2 in soils developed on unit Qic *...... 51

11 Depth plots of pedogenic clay, CaCO3 , and opaline SiO2 in soils developed on unit Q2b ...... 52

12 Depth plots of pedogenic clay, CaCO 3 , and opaline SiO2 in soils developed on unit Q2c ...... 54

13 Depth plots of pedogenic clay, CaCO 3 , and opaline SiO2 in soils developed on unit QTa ...... 55

14 Representative XRD traces of toberuorite and mixed layer clays: Untreated, glycolated and heated traces ...... 58 U.U

xii

15 Representative XRD trace of Opal-CT ...... 62

16 Relative abundance of clay minerals on soils formed on deposits Q~c, Q2b, Q2c, and QTa ...... 6

17 Soil water budget for Beatty, Nevada, which is assumed to approximate the Holocene climate ...... 69

18 Soil water budget for the glacial maximum climate- Spaulding model ...... *71

19 Soil water budget for the glacial maximum climate- Mifflin and Wheat model ...... 73

20 Percent carbonate vs depth for soils formed on deposits Qic and Q2b ...... 76

21 Percent carbonate vs depth for soils formed on deposits Q2c and QTa ...... 73

22 Modeled carbonate accumulation for 30,000 yrs of glacial climate with either an abrupt or gradual change to the Holocene climate for 10,000 yrs for the low and high ends of the elevation transect ...... 77 CHAPTER I

INTRODUCTION AND METHOD OF STUDY

Introduction

Statement of Problem

A high-level nuclear waste site has been proposed for Yucca

Mountain on the Nevada Test Site (NTS) (Fig. 1). This waste is the by-product of commercial enterprises and nuclear weapons production. Estimates vary from 1,000 to 100,000 yrs for the duration that this material remains hazardous (Winograd, 1981). To assure prolonged integrity of any nuclear-waste repository, long term environmental stability of that site needs to be considered, as well as the Impact of future climatic change.

This study addresses the problem of characterizing past climatic variability near the proposed nuclear-waste repository site at Yucca Mountain. Climatic changes are considered to be caused by variation in net global solar-energy input, a consequence of the precession of Earth's orbit and the obliquity and eccentricity of its axial position (Imbrie and Imbrie, 1980). Major global climatic change occurs at regular frequencies of 10,000 to 100,000 yrs

(Shackleton and Opdyke, 1973). The Holocene Epoch is the most recent in a long series of relatively brief (7,000-20,000 yrs) interglacials, that punctuate much longer (90,000-150,000 yrs) 2

IILA

.~\ @80Area

4~\ .mIVA * ~~FIST

CR-TE SIT

ou- I~ .... /PV .44 11 11 %.11.6

It

Figure 1. Location of study area. 3 periods of glaciations. A permanent repository for nuclear waste must be able to withstand the effects of a major climatic change. A climatic change that results in greater effective moisture may cause percolating water to move within the zone of waste material during the time that the material is still hazardous.

Objectives

The objectives of this study are twofold, (1) to document the effects of time and climate on soil developement, and (2) to use soil data to characterize long-term, past climatic variability in the study area. Paleoclimatic reconstructions span the last 2 Ma, emphasizing the last 45,000 yrs because the age control and botanical evidence is best understood during this time. This study

is part of a larger study of the paleoclimate of the NTS area. For example, other workers are studying past ground water levels and

rates of recharge (Winograd, 1981; Winograd and Doty, 1980),

regional lake and playa chronologies (L. V. Benson, U.S. Geological plant macro Survey, oral communication, 1985), and radiocarbon-dated R. and microfossils from ancient packrat middens (Spaulding, 1983, 1985). One S. Thompson, U.S. Geological Survey, oral communication, climates of the assumptions common to all these studies is that past yrs. approximate the climates that may occur in the next 100,000 4 Strategy

Soil-geomorphic research can provide data useful for

interpreting relative and absolute dating of alluvial deposits,

stratigraphic correlation, and paleoclimate. To apply pedologic

data to this goal, I use the state-factor approach developed by

Jenny (1941, 1980) which defines the independent factors of soil

formation as climate, biota, parent material, relief, and time. To

understand the impact of a single factor on the development of

soils, all other factors must either be held constant, or any

variation in one of the factors must have little impact on the

single factor that is being studied. The assumption then is made

that soil development is chiefly dependent.on the single varying factor. In this study two factors have varied--climate and time.

When all factors are held constant except time, the soil sequence is defined as a chronosequence. When all factors are held constant except climate, the soil sequence is defined as a climosequence.

The study area is particularly suitable for soil-paleoclimatic interpretations because the factors can be identified, key ones can be considered constant, and all pedogenic processes occur well above the present or former ground water table.

Five groups of different aged geomorphic deposits were studied along an elevation transect of 400 m of relief, from 1082 to

1483 m (Fig. 2). Present-day annual precipitation nearly doubles along the transect. For any group of deposits'of the same approximate age, one can observe or predict the depth relationships of most soil properties. Soil properties that are much deeper than anticipated suggest climatic change. These properties can be IF 5 I L

Explanation

z ale

a 0 F: Gib .. j

a a 0a 6 U a D 02c C 4 £ S U

a ai z GT U a U 4 77-7i7 Tert ". Vote mlev ASnl:ani RD' U

1 .9 0 -Road I . s , . A • _ _ * • alges 1016s6ters

it IE N

bedrock, and Figure 2. Map of Quaternary deposits, Tertiary trench locations in the study area. 6 compared to possible climate-models for the glacial maximums. The

primary evidence and discussion for the effects of climatic change

and time on soil development are based on physical and chemical soil properties.

Location of Study Area

The study area is along Yucca Wash and Fortymile Wash on the

east side of Yucca Mountain near the southwest corner of NTS (Fig.

1). This area is in the Basin and Range Province of western North

America (Fenneman, 1931), on the southeastern margin of the Great

Basin (Morrison, 1965). With respect to the flora, the site is located on the boundary of the Mojave Desert to the south and the

Great Basin Desert to the north (Cronquist and others, 1972).

The Quaternary deposits at the upper end of the elevation transect are along Yucca Wash (YW) just northeast of Yucca

Mountain. The transect follows Yucca Wash southeastward to its confluence with Fortymile Wash (FW), and proceeds due south to the road crossing across Fortymile Wash. The total transect distance is just over 13 km.

Methods of Field Work and Soil Description

Locating Study Area

The selection of the study area was accomplished with the use of air photos and preliminary surficial geologic maps by D. L.

Hoover (U.S. Geological Survey, written communication, 1983). The primary study site was then selected and mapped. Stratigraphic units are defined on the basis of landscape position, surface - Umm

7

pavement, desert morphology, degree of packing and sorting of desert

varnish, and soil-profile development.

Description and Sampling the soil Twenty trenches were excavated by backhoe through parent material. The into unconsolidated material similar to the CaCO and opaline difference being that in some cases translocated 3

in the soil profile, and not in the SiO2 are present at depths which is comparable to unconsolidated alluvium in the modern washes buried soils were the parent material (Appendix A). Frequently, Trenches were located encountered at depths in the soil exposures. with the stability on stable parts of terrace or fan surfaces, and the preservation of measured by the integrity of the pavement

the B horizon. and Soil profiles were described according to methods

Staff (1951) and Birkeland terminology outlined by the Soil Survey for horizons that have all (1984). I use the horizon descriptor Cuk material with the the characteristics of unconsolidated parent texture is from laboratory exception of translocated CaCO3 . Soil and silica cement were particle-size data after the carbonate is after Gile and others (1979 removed. Calcic horizon terminology Machette, 1985). Greater than and 1981; Bachman and Hachette, 1977; fraction is detectable in the 0.20 percent carbonate in the <2 mm

field by 10% HC1. to eight peds were Two to three kg bulk samples, and three were sieved and the gravel collected for each horizon. Bulk samples in the laboratory. percent determined on a weight basis a Measurements were checked with field estimates to make sure that gravel in bouldery deposits was not underestimated. If the precent gravel was thought to have been underestimated, the value was corrected with the field observations.

Pedogenic Silica

Silica-cemented horizons or duripans were identified in the field by first soaking air-dried samples in water, followed by soaking in 10Z HCU overnight. Cementation and brittleness are preserved when the predominant cementing agent is silica. Duripans in the study area also have a characteristic pinkish-yellow color,

7.5YR 7/4-6 (dry) and 7.5YR 5-6/6 (moist) Munsell colors, and are extremely hard when dry.

Because of the presence of silica, allophane was suspected. Allophane is a noncrystalline-clay weathering product of volcanic glass and associated with duripan formation. A field test

(Fieldes and Perrott, 1966) that determines the presence of amorphous allophane by measuring the change in pH with the addition of NaF, was unsuccessful. A simple, laboratory method, independent of pH (Wada and Kakuto, 1985) was not much more successful. Thirty to 50 mg of air-dried soil (<2mm) is placed on a white spot plate, and 0.4 ml of 0.02Z toluidine blue solution is added. If the color of the supernatant remains blue after 15 seconds, it suggests the presence of allophane and imogolite. A larger sample, 50-100 mg, is used for coarse-textured soil. The samples frequently remained blue in horizons that contained opaline SiO2 cement as well as the eolian vesicular A horizons. 9 Index of Soil Development

SOil field properties were quantified according to Harden

(1982), and Harden and Taylor (1983) (Appendix B). The soil

development indices were programmed and calculated with the "LOTUS

1-2-3" spreadsheet on an IBM-PC computer (Nelson and Taylor, 1985a and 1985b).

Micromorphology

Oriented samples of soil peds and gravel were collected.

Samples were stained with blue epoxy so that amorphous material

could be more easily recognized. Thin sections were cut perpendicular to the soil surface.

Statistical Methods

Statistical techniques used in this study include (1) descriptive statistics that characterize the sample population, (2) bivariate regression and correlation (r 2 ) analysis of individual properties with time or climate as the dependent variable, and (3) multiple and stepwise regression analyses to test possible predictive models of groups'of soil properties with a single soil property as the dependent variable (Till. 1974; Davis, 1973).

The null hypothesis (H.) for regression analysis is to test whether there is a significant relationship between time or climate, and the independent soil properties. Ho - no apsociation. When

Fcalculated > Fcritical or tcalculated > tcritical, at the 5% significance level, Ho is rejected and the cciclusion is made that there is a significant relationship. Significance is the level of El

10

properties could probability that the described relationship between that the occur randomly. Thus at 5% there is a 1:20 chance is a measure of the relationship is random. The standard error of the standard error of accuracy of prediction. It is an estimate between the residuals, or the estimate of the standard error variable about the measured and predicted values of the dependent or the standard deviation regression line. The standard error of B, of or the standard deviation regression line. The standard error B, the regression, is used due to sampling variability in the slope of Residual analysis was to generate the 95Z confidence intervals. All statistics were used to check multiple regression assumptions. statistical package. done on an IBM-PC computer with the "STATPRO' -Uii inull i l

CHAPTER 11

ENVIRONMENTAL SETTING, PAST AND PRESENT

Geologic Setting and Chronology

Yucca Wash originates in an area composed exclusively'of

Tertiary volcanic rocks (Christiansen and Lipman, 1965; Lipman and

McKay, 1965). The alluvium in Yucca Wash is derived from these

welded and nonwelded ash-flow tuffs. The alluvium in Fortymile Wash

is also derived from similar siliceous volcanic rocks with a small

component of basalt. Carbonate and opaline SiO2 -rich eolian dust

have been added to these alluvial deposits over time.

Quaternary Stratigraphy

The Quaternary stratigraphic nomenclature used on NTS (Table

1) was modified from that initially described by Bull (1974; Ku and

others, 1979; McFadden, 1982) in the Vidal Junction area,

California, about 320 km south of NTS. Deposits at Vidal Junction

were differentiated mainly on the basis of soil properties.

However, the identification of units at NTS is based primarily on

geomorphic features# and to a lesser extent on soil properties

(Hoover and others, 1981; Swadley, 1983). The main features include

preservation of bar-and-swale topography, elevation above modern and washes, packing and sorting of desert pavement, desert varnish, horizon. the presence or absence, and thickness of the vesicular A 12

Table 1. Quaternary stratigraphy of the Yucca Mountain area, NTS. Modified from Hoover and others (1981; Szabo and others, 1981; and Swadley and Hoover, 1983); soil properties are those of this study. Textures are for the <2 mm fraction and pertain to all soil horizons. Pleistocene deposits have age estimates based on U Trend dating. Some of the age estimates may be minimum ages. Holocene deposits on the most part have inferred ages. See Appendix G for information on the origin of assigned ages. Units can be combined (e.g. Qla/Qlb) in areas where they cannot be differentiated at a given map scale and (or) where a unit is mantled by a thin, patchy unit.

Stratigraphic Units Key Properties and Diagnostic Criteria Unit Estimated for Recognition Designation Age

Latest Holocene Qla historic Fluvial gravel and finer grained over bank deposits on and adjacent to the floors of active washes. No pedogenic alteration. Typically <2 m thick.

Late Holocene Qlb <140 yrs Fluvial gravel, sheetwash, or debris flows on steep slopes. Fluvial deposits form a terrace 0.5-2 m above active channels; bar-and-swale topography preserved. Thought to date from major episode of arroyo incision considered to have taken place 140 yrs ago (Bryan, 1925). No desert pavement has developed. Soils have a thin A; Cox, Cuk and (or) Cu; stage I CaCO3 (commonly contains reworked gravel with stage II CaCO3 coats); texture S, LS or SL. Usually <2 m thick.

Qle Eolian sand in active modern dunes in areas away from mountain fronts. No pedogenic alteration; texture S or LS. Locally as much as 50 m thick; typically <10 m thick. F

13

Table 1 continued. Quaternary stratigraphy of the Yucca mountain Area, NTS.

Sttatigraphic Units Key Properties and Diagnostic Criteria Unit EstimatecI. for Recognition Designation Age

Qls 3.3-7 ka Slope wash or sand sheets. composed primarily of reworked eolian sand and <25 percent gravel; deposited as much as 10 km from mountain fronts. Commonly dissected near active channels. Soils and pavement are similar to those of unit Qic, except texture is most commonly S. Usually <2 m thick.

Middle to Early Holocene or Late Pleistocene Qlc -10 ka Primarily terraces formed in fluvial gravel; may include fans, colluvium, or sheetwash. Fluvial deposits form a terrace 1-2 m above active channels. Lacks bar-and-swale topography. Incipient desert pavement development and little or no varnish development. Soils have an A; IOYR

Bw, BkJ, Btj and (or) Bqj; stage I-II CaCO3 and

(or) stage I SiO2 ; texture S, LS, or SL. Commonly <2 m thick.

Late Pleistocene Q2a 30-47 ka Mostly sandy slope wash derived in part from eolian sediment. Commonly contains <25 percent gravel. Typically caps older deposits and is locally covered by Holocene deposits. Usually lacks topographic expression. Soils have an Av;

Bt and (or) Bk; stage I CaCO3 ; texture SL, L, or C. Usually <1.5 m thick. mu K 14

Table I continued. Quaternary stratigraphy of the Yucca Mountain Area, NTS.

Stratigraphic Units Key Properties and Diagnostic Criteria Unit EstimatedF for Recognition Designation Age

Middle Pleistocene Q2b 145-160 ka Fluvial gravel that forms strath terraces, or debris flow fans. Fluvial deposits form a terrace 5-12 m above active channels. Typically very poorly sorted with large boulders up to 1 m in diameter; commonly contains fluvial sedimentary features. Desert pavement Is well sorted, tightly packed and darkly varnished. Soils have an Av; IOYR to 7.SYR Bw, Bt, Bqm, and

(or) Bk; stage 1-1I CaCO 3 and (or) stage Il-III SiO2; texture S, LS or SL. Commonly <2 m thick.

Q2c 270-430 ka Fluvial gravel or debris flows on steep slopes. Fluvial deposits form a terrace 10-21 m above active channels. Desert pavement is well sorted, tightly packed with continuous varnish. Soils have an Av; 7.5YR. Bt, Bqm, B/K and (or) Kqm;

stage III-IV CaCO3 (K horizon <1 m thick) and

(or) stage III SiO2 ; texture S to L. Usually <65 m thick.

Q2e <738 ka Eolian sand in inactive dunes and sand ramps at and adjacent to hill and mountain fronts. Desert pavement is well sorted, tightly packed, and darkly varnish. Soils have an Av; Bk, Bkq, B/K

and (or) K; stage III-IV CaCO 3 and (or) stage

Ill-IV Si0 2 ; texture LS, SL, or L. Usually <20 m thick. 15

Table I continued. Quaternary stratigraphy of the Yucca Mountain Area, NTS.

Stratigraphic Unit d Key Properties and Diagnostic Criteria Unit Estimate for Recognition Designation Age

Q2s <738 ka Slope wash or sand sheets (tabular bodies of sandy slopewash) down slope from sand ramps. Generally lacks desert pavement. Soils have an

Av; Bk, Bkq, B/K and (or) K; stage III-IV CaCO3 and (or) stage III-IV S102; texture LS, SL or L. Usually <2 m thick.

Early Pleistocene QTa 1.1-2.0 my Alluvial fans; usually extremely eroded and overlain by a veneer or mantle of younger deposits. Commonly deposits are adjacent to hills and mountain fronts, 20-30 m above active channels. Lacks depositional form; erosional modification results in ballena or accordant, rounded ridges. Large boulders up to I m in diameter may be scattered on the surface. Desert pavement is well-sorted, tightly packed and has continuous dark varnish; commonly contains opaline S102 platelets from the underlying soil. Soils have an A or Av; 7.5YR Bt, Bqm, B/K,

Kqm, and (or) Kmq; stage Ill-IV CaCO3 (K horizon

>1 m thick) and stage III-IV SiO 2. Commonly <20 m thick. 16

The assigned ages for these mapping units are based almost exclusively upon U-trend analyses on soil samples (Rosholt, 1980)

(Appendix G).

Several depositional facies are recognized in these deposits. Fluvial deposits are poorly to moderately well sorted and poorly to well bedded; gravel clasts are angular to subrounded.

Debris flows are poorly sorted, and poorly stratified to massive.

Clasts are matrix supported and are angular to subrounded. Eolian sand and loess are moderately to well sorted, respectively.

Sheetwash is moderately well sorted and may have thin bedding.

Features of desert pavement help distinguish some units.

Pavement packing tends to change from none to dense with time, sorting increases from poor to well, and varnish changes from none to dull black to shiny purplish-black. Desert pavement features are a useful relative age indicator because they clearly change with time. However, thin layers of eolian and sheetwashed fine-grained deposits tend to blanket most gravelly deposits In the study area, and thus may not preserve the desert pavements.

The expression of. fluvial bar-and-swale features become more subdued with time. The obliteration of these features is due primarily to burial by eolian or sheetwash deposits, and (or) to erosion. With time, the surface becomes smoother.

"Topographic form of terraces also change in a gross way.

Deposits younger than QTa have a good terrace expression. However, erosional modification results in ballenas or accordant, rounded 17 ridges (Peterson, 1981) that are typical of the QTa unit. These topographic forms represent a distinctive late stage of piedmont dissection.

Ages of Deposits

The ages assigned to the stratigraphic units on NTS and the surrounding area are based primarily on U-trend dating of deposits exposed in trenches excavated to study Quaternary faults (Hoover and others, 1981; Szabo and others, 1981; Swadley and Hoover, 1983)

(Appendix G). Other techniques used are the age of assumed channel incision, 1 4 C, and correlation to ash geochronologies. The

Quaternary stratigraphy used in the Yucca Mountain area (Table 1) was a product of the above tectonic studies.

Geomorphic Setting

Terrace Formation--Tectonic vs Climatic

The Quaternary landscape in the study area was formed by three major geomorphic processes; (1) fluvial erosion and deposition, (2) eolian erosion and deposition, and (3) hillslope processes. Major influences on these processes are tectonism (basin subsidence and (or) mountain front uplift) and climate. Of most interest here are the fluvial terraces.

The terraces studied are fill terraces (Fig. 3). Although the overall net effect of fluvial activity has been one of downcutting, these were interrupted by periods of aggradation.

Subsequent downcutting resulted in fill terraces. E OTa Fortymile Wash Yucca Wash 30

25. 02c OTa o 20 02c a0 C 02b 0 1. 02b /1 0 00 4 I le Olb Olb Olc.

Figure 3. Generalized cross section showing the strattgraphic relationships of Quaternary In height of terrace surfaces above fluvial deposits along Yucca Wash and Fortymile Wash. Variability ZZ the modern wash Is defined with the vertical bars. 19

A recent to be of tectonic origin. The terraces do not seem that faulting has of Yucca Mountain suggests study on the west side U.S. W. Whitney and R. R. Shroba, occurred in the Holocene (J. there has not communication, 1985). However Geological Survey, oral Quaternary fluvial faulting of any of the been any evidence for longitudinal study area.' In addition, terrace deposits in the Wash (Fig. along Yucca Wash and Fortymile profiles of the terraces tectonism to downstream, do not require 4), although they diverge have been Finally, if the terraces explain this relationship. of the uplifts in the upper reaches influenced by tectonic than fill terraces. might be expected rather drainages, cut terraces in the presence of fill terraces Climatic change may explain propose a model and Bull and Schick (1979) the area. Bull (1979) change. If the arid areas during climatic for fluvial behavior in the aridity and higher temperatures, climate changes to greater responds by are such that the stream basin characteristics decreases as on, sediment availability aggrading. As time goes erosion of the valley runoff increases, and erosion exposes bedrock, therefore could general, each terrace, fill takes place. In the formation of a change. In this case, represent a climatic with the early interglacials. terrace could be correlative models for the region. There have been few paleohydrologic may be correlative. units in the study area that the depositional my, with most of the one for the last 3.2 Smith (1984) has proposed The four most in Searles Lake, California. data taken from a core Regime 1 (0 - -10 ka) are of interest here. recent climatic regimes by both dry and (V10 - 130 ka) was characterized was dry. Regime Ii 14 I'se- 4,

-0 QTa B a S 3e0" 4 a S lose S...... 02b S S a a 4 a S-Oic 211- U 0 a U B lloo. a e S 0 U log. a U S lose. a S S 5 a B

I a al v 0

a V a a U V a D1l6e.04 down stream s ,e ii II is kIlemetoge

Figure 4. Profiles of terrace deposits along Yucca Wash Locations (YW) and Fortymile Wash (FW). of soil trenches are Indicated by dots and numbers. Ili 21

levels support a wet cycles, but long intervals of high lake (130 - "310 ka) was similar to relatively wet interval. Regime III Regime IV (310 - 570 ka) was a but drier than Regime II. Finally,

long dry period. deposits in the area Correlation can be made of some of the Unit Qlc could correlate with the climatic model of Smith (1984). I, and that would follow the with the transition from Regime II to may correlate to. Bull and Schick (1979) model. Other deposits Unit Q2b is a strath terrace changes from one regime to another. Therefore, deposits of Q2c age deposit inset into the older Q2c. of incision of Fortymile place a minimum age on the major time with the transition from Regime Wash. Unit Q2b could be correlated stabilization of unit Q2c III to II at 130 ka, and likewise the from Regime IV to III at would be correlative with the transition are very tentative and do not 310 ka. These latter correlations the fluvial response to follow the Bull (1979) model. Obviously the threshold model proposed by climatic change is not simple, as formation. Schumm (1977) may also explain terrace

Ground Water Setting

NTS area originates in Most ground water flow through the these include Pahute Mesa (35 km volcanic highlands to the north; N). The remainder of the ground NW) and Timber Mountain (15 km as underflow in the regional lower water flow enters from the east Doty, Thordarson, 1975; Winograd and carbonate aquifer (Winograd and the the eastern part of NTS are to 1980). Flow directions beneath the until the water surfaces at south and west from the highlands, - --

22

extensive network of active springs at Ash Meadows in the Amargosa

Desert (45 km SE). Evidence exists for somewhat greater spring

activity during the last glacial maximum. Fossil tufa deposits area occur as high as 40 m above present ground water level in this

(Winograd and Doty, 1980). All pedogenic processes in the Yucca

Mountain area are well above the ground water table of the area

which is from 490 to 610 m below the surface today.

Modern Climate

Southern Nevada is arid to semiarid. Because average annual there is precipitation in much of this area is less than 150 mm and

greater than 10X perennial plant cover, it is actually a semiarid only 24 km desert (Houghton and others, 1975). Beatty, Nevada is the due west of the study area. It is at the same elevation as m), and is lowest soil-trench elevation in the study transect (1083

0 as an at the same latitude (37 54-N) (Fig. 1) It is used here area. The estimate of the climate of the lower end of the study and the mean mean annual precipitation (HAP) at Beatty is 117 mm, upper end of annual temperature (MAT) is 15.3°C (Table 2). At the precipitation is the transect, which lies 400 m above the lower end, is assumed to increase by 70% to about 200 mm. This assumption data from stations based on (1) vegetation change, (2) precipitation similar elevations in southern and south-central Nevada that are at equation relating and latitudes, and (3) Quiring.s (1983) regression

MAP and elevation on NTS:

y - 1.36x - 0.51 Equation (2.1)

where y - MAP in inches and x - elevation in feet. Table 2: Temperature, precipitation and potential evapotranspiration data for the Holocene (Present) and two models for the last glacial maximum. Precipitation is divided into the low and high ends of the elevation transect, representing a 70% increase.

I/ U.S. Department of Commerce Weather Bureau, Beatty, :. ada, elevation 1087 m, latitude 36054'N. 2/ U.S. Department of Commerce Weather Bureau, Pahrump, Nevada, elevation 717 m, latitude 36 0 12'N. 3/ Thornthwaite (1848) and Van Hylckama (1959). T/ Blaney and Criddle (1962) - K coefficient from reach 3, Culler and others, 1982, p. 32. 5/ Papadakis (1965) - Mean monthly maximum and minimum temperature used to calculate saturation vapor pressure and dew point according to Linsley and others, (1975, p. 35). Sat Vapor Pressure a 33.8639 (0.00738 T0C + 0.8072)8 - 0.000019 11.8 T0C +481 + 0.001316 6/ Pan evaporation summed for growing season (April-October), with total for entire year in parentheses (Farnsworth and others, 1982, p. 1). Smu

24

CLIMATE HOLOCENE(PRESENT) preci~pitatiJon Pan ET mont:h Tamperat~urek'C) (CZ3 Mean Monthly (cmt) Evp aq I/ a i lo,, high (CSJ T1/ B &C jA/P1 , 5.53 -6.71 -1.5----8 -S.39 J 4.8 12.4 -2.9 1.80 3.07 7.54 1.17 2.36 6.23 F 6.6 14.6 -1.3 1.78 3.02 14.44 2.74 2.83 8.42 14 9.8 18.7 1.1 1.27 2.16 15.14 5.35 4.89 11.18 A 14.2 23.3 5.0 1.27 2.16 9.06 10.19 15.01 m 18.4 28.1 8.8 0.84 .1.43 26.52 29.52 13.42 14.72 20.62 J 23.3 33.5 13.1 0.31 0.52 31.64 17.45 16.13 25.61 J 27.1 37.5 16.7 0.46 0.78 27.07 15.17 14.76 23.90 A 25.9 36.2 15.5 0.51 0.86 20.63 10.39 12.17 19.68 S 22.2. 32.5 11.9 0.46 0.78 13.34 5.62 8.52 12.62 0 15.8 25.2 6.4 0.76 1.30 6.53 2.22 3.11 8.35 N 9.7 18.5 0.8 0.91 1.55 5.38 0.91 2.39 5.79 D 5.7 13.5 -2.2 1.32 2.25 avg or sum 163.86-6/ 84.21 93.65 162.80 15.3 24.5 6.1 11.68 19.86 (203.28)

uodel CLIMATE DURING GLACLAL KhIITJlM - Spaulding 4.98 0.00 0.00 2.32 J -2.2 5.5 -2.9 2.44 4.14 6.79 0.00 0.00 2.76 F -0.4 7.6 -1.3 2.40 4.08 13.00 1.28 0.29 4.02 1M 2.8 11.7 1.1 1.72 2.92 13.63 3.73 1.10 5.52 A 7.2 16.3 5.0 1.72 2.92 23.87 6.73 3.22 7.70 14 11.4 21.1 8.8 1.13 1.92 26.57 9.92 5.85 10.99 J 16.3 26.5 13.1 0.15 0.26 28.48 12.58 7.23 13.87 J 20.1 30.5 16.7 0.23 0.39 24.36 11.03 6.39 12.88 A 18.9 29.2 15.5 0.25 0.43 18.57 7.71 4.63 10.51 S 15.2 25.5 11.9 0.23 0.39 12.01 4.07 2.24 6.35 0 8.8 18.2 6.4 1.03 1.75 2.10 5.88 1.02 0.30 4.00 N 2.7 11.5 0.8 1.23 4.84 0.00 0.00 2.53 D -1.3 6.5 -2.2 1.78 3.31 avg or sum 31.25 83.45 8.3 17.5 6.1 14.31 24.32 (182.96)147.47 58.07 and Vheat model CLIMATE DURING GlACIAL MAXDIMU - Mitffln 5.15 4.48 0.00 0.00 3.07 J -0.2 7.5 -2.9 3.03 5.08 6.11 0.40 0.16 3.61 F 1.6 9.6 -1.3 2.99 11.70 1.82 0.50 5.11 H 4.8 13.7 1.1 2.13 3.63 3.63 12.27 4.22 1.40 6.92 A 9.2 18.3 5.0 2.13 21.48 7.33 3.78 9.52 13.4 23.1 8.8 1.41 2.39 m 10.70 6.56 13.40 28.5 13.1 .0.51 0.87 23.91 J 18.3 13.62 7.95 16.82 32.5 16.7 0.77 1.31 25.63 j 22.1 11.93 7.06 15.65 31.2 15.5 0.85 1.45 21.92 A 20.9 8.33 5.24 12.81 27.5 11.9 0.77 1.31 16.71 S 17.2 4.51 2.75 7.91 6.4 1.28 2.18 10.81 0 10.8 20.2 0.53 5.07 1.54 2.61 5.29 1.47 N 4.7 13.5 0.8 3.33 3.77 4.36 0.15 0.07 D 0.7 8.5 -2.2 2.22 avg or sum 132.73 64.48 35.96 103.22 10.3 19.5 6.1 19.63 33.37 (164.67) 25

tn addition to the orographic influence on precipitation,

types result two basic storm types exist in the area. The two storm and (2) in precipitation derived from (1) winter. cyclonic activity, As will be intense summer convection (Houghton and others, 1975). some of shown later, the seasonality of precipitation will influence

the soil property vs depth relationships.

No long term temperature data exist for the Yucca Mountain communication, area. D. L. Hoover (U.S. Geological Survey, written 0 in MAT in the 1984) however estimates that there is a 3 C difference that, 400 m elevation change. He bases this on the relationship (2.2) x - 7.48 - 0.004081y for MAT Equation

where x - MAT in OF and y - elevation in feet.

Paleoclimate in the NTS Region

the A large number of data sources exist to reconstruct two sources of paleoclimate in the American Southwest. There are in the study area, paleoclimatic information of particular interest to the formation of packrat middens and inferred climates condusive

pluvial lakes.

Packrat Midden Evidence microfossils Paleoenvironmental data from analyses of plant perhaps the most remains in packrat (Neotoma sp.) middens provide and nature of climatic detailed information concerning the timing (Van Devender and changes on the NTS during the late Quaternary Plants sensitive to Spaulding, 1979; Spaulding, 1983 and 1985). to moist habitats are frigid temperatures and those restricted 26 missing in the plant microfossil record from 45-10 ka (Spaulding,

1985). Juniper and pinyon pine and Joshua tree were present at lower altitudes in the NTS area. These data suggest milder, wetter winters and cooler, drier summers relative to the present during the last glacial maximum (18 ka). Following the last glacial maximum

Spaulding (1985) infers a warming trend from 16-10 ka. After 11-10 ka, the conditions like the present prevailed and Juniper and pinyon pine woodland are not present. Elements of desert scrub were present by 15 ka at elevations as high as 990 m Spaulding (1982).

The vegetation change was transitional, implying a transitional climatic change from late Pleistocene to Holocene.

Based on evidence from packrat middens, climatic conditions in the Yucca Mountain area during the glacial maximum (18 ka), compared to the present climate, probably had (1) a HAT decrease of

0 6-7 0 C, (2) drier summers with a temperature decrease of 7-8 C, and

(3) winter precipitation up to 70% greater than present. In all the

following discussions this climatic change is referred to as the

Spaulding climatic model for the glacial maximum (Table 2).

Pluvial Lake Evidence

The pluvial lake chronologies in the southwestern United

States suggest that the effective moisture of the late glacial and

early Hoiocene was much greater than the effective moisture in the

modern climate. High lake stands are recorded at 14-11 ka in lakes

in both glacial and nonglaciated drainages (Morrison, 1965; Benson, The 1978; LaJoie and Robinson, 1982; Wells and others, 1984). ka is disappearance of Juniper and pinyon pine woodland at 11-10 m

27

coincident with the lowering of Lake Mojave from a high stand

between 15.5 and 10.5 ka (Wells and others, 1984).

Although the effective moisture was greater, there is little

evidence in the northern Mojave Desert for increased annual day playas precipitation during the late Wisconsin (18 ka). Present north contained ephemeral lakes or marshes during the full-glacial and Wheat of latitude 360 N (Mifflin and Wheat, 1979). Mifflin 0 greater, and (1979) propose that the MAT was 5 C lower, the MAP 69% to in the the evaporation 10% less than today. This is referred maximum following discussions as the Mifflin and Wheat glacial

climatic model (Table 2).

The reduction of full-glacial summer precipitation in the to the NTS area, relative to that of today, can be attributed the Gulf of dependence of summer precipitation on oceanic air from

Mexico. Global cooling weakened these subtropical high-pressure air to very systems and restricted the influence of the oceanic precipitation southern regions (Houghton and others, 1975). Summer lacking if summer also depends upon local convective uplift which is

temperature is low.

Summary of the Glacial Climate Models desert In the southern Basin and Range and northern Mojave began about 45 regions, the onset of the last major glacial climate about 24 ka, based ka (Spaulding, 1985). The~late Wisconsin began the pollen and lake on dates from Searles Lake (Smith, 1979), and Benson, 1978), and at 18 record from Lake Lahontan (Mehringer, 1967; in the western United ka is thought to have been a full glacial 28

11 ka was the maximum The period from 25 to States (CLXLAP, 1976). filling of playa lakes, glaciers, intermittent development of alpine evidence for vegetation. Physical and expansion of upland last reconstructions for the paleoclimatic and paleoenvironmental and a 100% increase 0 C temperature decrease glacial vary from a 2-3 0 decrease and less a 7-11 C temperature in precipitation, to 1983; Thompson, (Spaulding and others, precipitation than today decrease in the ka, there was a significant 1984). At about 11 that mark the and changes in the vegetation, pluvial lake levels, Devender and in the southwest (Van end of the late Wisconsin until the plant communities persisted Spaulding, 1979) Transitional 1983). ka) (Spaulding and others, early Holocene (7.8 29

CHAPTER III

TIME MAJOR PEDOLOGICAL CHANGES WITH

Morphology

colluvium and eolian sand Soils that are formed in alluvium, or latest Pliocene(?) age near of Holocene to early Pleistocene by distinctive trends in the Yucca Mountain are characterized SiO that clay, CaCO3 , and opaline 2 accumulation of secondary the surficial deposits. correspond with the ages of

Pedogenic Opaline Silica in the study opaline Si0 2 is common Cementation by pedogenic Si0 is common in soils containing area. Accumulation of opaline 2 ash, from pyroclastic rock or volcanic readily weatherable glass soluble area. Eolian influx of readily such as those in the study tends to weather a likely source. Class silica-rich dust is also weathering composition, rich in bases, rapidly and if it is of mafic to amorphous rapid rate. The glass alters can liberate silica at a and opaline S02 SiO2 or semi-crystalline allophane, imogolite

(Bleeke and Parfitt, 1984). cemented used for silica and (or) In general, two terms are (Soil for pedogenic accumulations layers: (1) duripan, specifically (2) silcrete for geologic-pedologic Survey Staff, 1975), and 1983). Both 1983; Nettleton and Peterson, occurrences (Summerfield, 30

and (or) indurated product of surficial terms are applied to an and (or) formed by the cementation near-surface silicification, or soil. The unconsolidated sediments, replacement of bedrock, by low temperature physio-chemical silicification is produced of pedogenic not exclusively the product processes. Silcretes are horizons laterally into petrocalcic weathering. A few grade arbitrary lower 1983). Silcrete has an (Summerfield, 1982 and 1982 and 1983), so by weight (Snmmerfield, limit of 85% opaline SiO2 are not pedogenic horizon. Silcretes it would be a very unusual limits on the Duripans have no specified present in the study, area. of cementation by , they vary in the degree content of opaline SiO2

accessory cements, chiefly CaCO 3 . SiO2 and commonly contain produces a unique morphology Because silica accumulation in this study of development recognized that varies with age, stages morphology, 3). On the basis of horizon have been defined (Table as duripans of the morphology would qualify those with stages III-IV p. 41). (Soil Survey Staff, 1975, Soil Conservation Service 31

opaline Table 3. General characteristics of pedogenic silica stages. coatings <2 mm Stage I White, yellow, or pinkish scale-like clasts. Found in some thick on the undersides of gravel at depths on older soils on Qlc deposits, may occur deposits.

features 2-4 mm long Stage II Stalactitic or pendant-like the undersides of extending downward from a coat on deposits, may gravel clasts. Found in soils on Q2b occur at depths on older deposits.

Stage III Opaline SiO cemented horizon, extremely hard when or a weak solution of dry. Peds ao not slake in water hue is probably due to HCl. The characteristic 7.5YR Found in soils on clay particles in the silica cement. accumulations Q2c and QTa deposits, and maximum Q2b, CaCO tend to form in horizons of maximum 3 field stage III appears accumulation. Frequently in the accumulation of CaCO 3 to be forming above the maximum CaCO masks the because the whiteness of the 3 precipitated opaline SiO2 . laminar, indurated IV Stage III morphology along with Stage mm thick, in the upper opaline SiO2 platelets, 4-10 is below maximum part. Maximum CaCO3 accumulation calcareous ooids are opaline SOi induration. Commonly in soils on Q2c precipitatea above platelets. Found (infrequently and thin) and QTa deposits.

Carbonate and Opaline Silica CaCO and opaline At the NTS, soils accumulate secondary 3 surficial trends with increasing ages of the SiO2 in distinctive alluvium less than 3(?) ka (Qib) deposits. Soils formed in gravelly or opaline S1O2 . Soils formed contain little or no secondary CaCO3 30 (Qic) and sandy colluvium about in gravelly alluvium 3-20(?) ka has horizon about 20-50 cm thick that 40 ka (Q2a) commonly have a Bk opaline of CaCO (stage I) and (or) thin, discontinuous coatings 3 I-II). undersides of stones (stage S102 scales and pendants on the have a about 140-160 ka (Q2b) may Soils formed in gravelly alluvium 32

(duripan, stage III) about 50 cm opaline SiO2 -cemented Btqm horizon Bk/K (stage II-III) thick chat overlies or engulfs a CaCO 3-enriched

opaline SiO2 in the horizon about 50-70 cm thick. The secondary matrix cement and as duripan typically occurs as finely disseminated CaCO in the coatings and pendants on stones. The secondary 3 as coatings on stones and underlying Bk/K horizon typically occurs in the Bk-layers, and as as bridges between some of the stones

in the CaCO3 coatings and finely disseminated matrix cement alluvium about 300-400 indurated K-lenses. Soils formed in gravelly Kqm horizon (stage ka (Q2c) commonly have a opaline SiO2-indurated a Bk/K horizon (stage 11-11) III) about 50 cm thick that overlies which is >1 Ma (QTa), about 40-50 cm thick. The oldest alluvium, 100 cm thick. Commonly, the has soils with a Kqm horizon more than of platelets, 0.5-1 cm thick, upper part of the Kqm horizon consists IV), and it may be overlain cemented by laminar opaline SiO2 (stage as 10 cm thick (stage II1). by layers of CaCO3 ooids as much dust and the Carbonate is primarily derived from airborne weathering of the parent material, opaline SiO2 from in-place dust may also be a likely although the addition of silica-rich source, NTS area differs from that The CaCO 3 morphology in the Las Cruces area, New Mexico, described by Gile and others for the climates, soil parent materials, although both areas have similar airborne dust (Gile and others, and accumulation rates of modern NTS CaCO is less abundant in the 1979). In addition, secondary 3 These age in the Las Cruces area. area than in deposits of similar CaCO may result from differences in the amount of secondary 3 33

and the amount of differences in the seasonality of precipitation

Cruces area, most secondary opaline Si0 2 . Unlike the Las the cool, winter months precipitation in the NTS area occurs during CaCO being more at soil moisture temperatures that result in 3 tends to translocate soluble (Table 2). Infiltrating soil moisture

wetting zone, where it forms lenses rather CaCO 3 to the base of the area. Thin-section than discrete K horizons as in the Las Cruces opaline SiO has studies of soils in the NTS area indicate that 2 soils. This relationship replaced CaCO3 in some of the older in the NTS soils is favored suggests that opaline SiO2 accumulation over that of CaCO3 .

Vesicular A Horizons not formed on Well developed vesicular A horizons (Av) have in the Yucca Mountain the coarse gravelly Holocene deposits (Qic) are typically between 5 area. On the Pleistocene deposits the Av's between the thickness and 10 cm thick and there is no relationship deposit. Eolian of the Av horizon and the age of the underlying only on deposits that have silts and fine sands appear to accumulate by the addition of fine been previously plugged or partly plugged McFadden and others material into the coarse alluvium. Although of Av's in the Mojave (1984) have described the ubiquitous nature flows, it appears in this desert on Holocene deposits and volcanic of the young deposits, area that due to the coarseness of most deeper into the available eolian fines are either translocated is also possible that the deposit or lost by wind erosion. It has been less abundant during eolian material that forms Av horizons . ---

34

the Holocene, although this contradicts many of the current ideas on

sediment availability associated with the Holocene-Peistocene

climatic change (Bull. 1979).

Profile Index Values

Field properties of soilb (Appendix A) can be quantified by

assigning points for developmental increases in soil properties in

comparison to those of the parent material (Harden, 1982; Harden and

Taylor, 1983) (Appendix B). Ten field properties are quantified and

normalized for each horizon, including two properties that reflect

CaCO 3 buildup in soils formed in arid environments. The ten

properties are rubification (increasing (redder) color hue and (or)

chroma), melanization (decreasing (darkening) color value), color

paling (decreasing (yellower) color hue and (or) chroma), color

lightening (increasing (whitening) color value), total texture

(includes texture and wet consistence), clay films, structure, dry

consistence, moist consistence, and pH. Unlike the Harden (1982)

definition, values for pH were quantified based on the absolute

difference in comparison to the parent material. Moist consistence

was usually not determined in this study, therefore it was not

included in the index calculations.

Soil profile indices were initially calculated two different

ways; using all soil properties and (1) rubification and

melanization, or (2) color paling and lightening properties. Both

ways to calculate the soil profile index include eight properties.

I have called the first way to calculate the profile index value

rub-mel, and the second pale-light. Rub-mel was developed for a -I

35

xeric soil moisture regime, and pale-light for an arid soil moisture

regime. According to Harden and Taylor (1983) complete profiles are

calculated using either one of the two methods, not combinations for

a given profile. Profile indices are calculated using either

rubification and melanization, (rub-mel) or color paling and color

lightening (pale-light).

Parent material values used to calculate the indices vary

with the kind of material. For alluvium they are IOYR 6/2 (dry) and

lOYR 4/2 (moist), sand, loose, and non-sticky and non-plastic. In

contrast, for the eolian sand and reworked gravels the values are

IOYR 6/3 (dry) and IOYR 4/3 (moist), sandy loam, soft, and non

sticky and non-plastic.

Of the ten possible independent properties all were

significant with log age at the 5Z level, except melanization

(r2.O.01) and color paling (r 2-O.O1) (N-20, r 2 critical-O.18) (Fig.

5). The properties most significant in the profile index

calculation have the highest r 2 values. They are dry consistence 2 (r 2 .0.48), color lightening (r 2 .0.45), rubification (r .0.40), and

structure (r 2 .0.37), and are referred to as the four best properties

(Fig. 5). The profile index values using the four best properties

did not improve the relationship between soil development and time 2 over that using all eight properties with the highest r values

(Fig. 6).

Significant trends are apparent when profile index values

(Appendix B) are plotted as a function of age (Fig. 6). Profile

index values have been calculated using rub-mel and pale-light soil

properties (Fig. 6). It makes no difference in the index values vs m A B ,=S S =25.91"-43.8 p. D 4 4 - , 4 2 3 6 6 9 C

3.6

low awe low age

-i aaw C .=0 ASS3D

,1a'X~*6. 1.9 SS.-5S.? .

time. Figure 5.Bivariate regression analyses of significant property,profile index values vs tightening, (C) 95Z confidence Interval surrounds regression line. (A) dry consistence, '(B) color rubtfication, (D) structure, (E) texture. (F) clay films. E - F . VAO 25."3,t A=.S.x-22.0.5 . P .

N+i t

-. 9 . 4.L 5's 6. . A.9 3.0 . a

Ike" age

5 Figure continued. Bivarlate regression analyses of significant property profile index values vs time. 95% confidence Interval surrounds regression line. (A) dry consistence, (B) color lightening, (C) rubification, (D) structure, (E) texture, (F) clay films...... 1. I ...... / J I Ill inl l l u i i n~ n ,...... S...

A B 4.2 W= A. A1K-.-2. 14 w11.4.?x-30.2S 2 ii. 3S. 4.5 44 I. p-u%- no a p.3.-DiwbO p C: I [-27 * 4.

2 - C U .--- I W. 3 6.4 .0 3., 4.2 5.3 4.4 low ago . aOg ame

C D

7Z 0 3 VwO13.94-34.301"V ._=, , as• .. eu-ewi u.

w*-~ 30 a 56 I- its

N . l " -AT I-! .4 , - a..a W. A 4.2 5.3 4.4 3so" 4.w 5.3 6.4 too AN&. | og Aoe.

Figure 6. Bivariate regresaion analyses of soil profile index values vs time. 95% confidence interval limits are above and below the regression line. (A) Rub--mel, all soil properties including rubification and melanization. (B) Pale-light, all soil properties including color lightening and color paling. (C and D) Soil properties for rub-,mel and pale-light climatic regime are quantified to an arbitrary maximum depth of 300 cm. (E) Rub-light, all soil properties including rubification and color lightening. (F) Best four properties are dry consistence, color lightening, rubtfication, and structure. I-) F E as tau"1has-45.44 p p U. U. 7 3X2 I U 62 I I C 2 '4 C K 2.6 3.1 4.2 5. •3 4• 2.0 . 4,.2- 51.3 &.4 low age saw &No

95% Figure 6 continued. Bivariate regression analyses of soil profile Index values vs time. Rub-mel, all soil properties confidence Interval limits are above and below the regression line. (A) properties including color lightening including rubification and melanization. (B) Pale-light, all soil climatic regime are quantified and color paling. (C and D) Soil properties for rub-mel and pale-light including rubification and to an arbitrary maximum depth of 300 cm. (E) Rub-light, all soil properties lightening, rubification, and color lightening. (F) Best four properties are dry consistence, color structure. - I______

40

time if the rub-mel (r 2=0.65) or pale-light (r 2 .0.65) properties are

for *the -measured profile thickness, or are for an arbitrary depth of

300 cm for the rub-mel (r 2 .0.63) or pale-light (r 2 .0.61) properties

(Fig. 6).

Because melanization and color paling did not have

significant correlations with time, the profile index was calculated

using rubification and color lightening. When all soil properties

are included with rubification and color lightening the profile

index value is called rub-light. The rub-light profile index values.

vs time increases the r 2 value to 0.71 (Fig. 6).

The increase in the individual profile property values with

time (Fig. 5) can be explained by aridic climatic pedogenesis

models. Rubification increases both because of the increasing

redness of Bt horizons and the accumulation of opaline SiO2, as the

latter results in colors redder than the parent material.

Lightening increase with time because A horizons do not get darker,

and CaCO3 and opaline SiO2 accumulating horizons are lighter than

the parent material. Dry consistence gets harder over time as clay

and cementing agents accumulate and indurate horizons. Structure

changes from unconsolidated parent material. Texture, wet

consistence, structure, and clay films represent pedogenic

accumulations of clay.

There may be a subtle influence of local climate on profile

index values. Unit Qic shows little change with elevation, but weak

trends are discernable for units Q2b, Q2c, and QTa with the increase

in QTa being much greater than that of the younger units when only

the four best properties are used (Fig. 7). IIH -

41

68 . Q T & )Ta P C•2c :2b 34 e 21OT L7 1C x X 116 w 14 623 1173 1293 £393 1£5! 13 elevation. fe ters

U - QTr B ightIub- -OTa Go I. P K, -Q2c 2hL b 02b

lb £&&20 IC S29' Lb L 1.

x LU LU

le 63 I173 1 29-83 13293 1J51 3 elevation. ve tegs

U U tou" Le==t QT& C .. QTa Pag' 02c "Q2b

22, 1L O S0£ ale 2

i - - £L73 L283 £393 L503 1062 elevation. notevs

Figure 7. Soil index values vs elevation. The index value plots between the number and letter of each stratigraphic unit. (A) Pale-light field properties including color paling and color lightening. (B) Rub-light properties Including rubification and color lightening. (C) Index calculated using four best properties: dry consistence, rubification, color lightening, and structure. t . 42

comparable to ?rofile index values for the study area are

soil chronosequence index values from the Las Cruces, New Mexico index values are (Harden and Taylor, 1983) (Table 4). Comparative properties. The older best when they are based on the four best values probably because soils in the Las Cruces area have greater Las greater for deposits of a given age at CaCO3 accumulation is

Cruces than at NTS.

values for Table 4. Comparison of soil profile index the study area and Las Cruces, New Mexico. INDEX VALUES Best AGE This Study Las Four Properties -This Study-- Las Cruces Rub- Pale- This Las log Cruces Pale- 3 4 light 2 light, Study Cruces Age - Age - light, <5 2.18 150 yrs -- <5 <5 5-41 9-33 4-35 4.00 10 ka 4-20 ka 6-21 9-32 22-26 23-39 24-31 5.18 150 ka 120 ka 23-38 29-41 1-56 30-54 29-95 5.48 300 ka 290 ka 26-42 31-49 >43 49-83 >110 6.18 1.5 my >500 ka 27-64 38-74 color lightening 1 all properties including color paling and color lightening 2 all properties including rubification and 3 dry consistence, structure, color lightening, rubification 4 dry consistence, structure, color lightening, color paling

and Opaline Silica Accumulations of Carbonate, Clay, Silt,

soils can be evaluated The influence of age and climate on

of pedogenic CaCO 3 , clay, silt, based on trends in the accumulation 1979 and 1981; McFadden, 1982; and opaline SiO2 (Gile and others, pedogenic constituents can be Machette, 1985). The amounts of these amount in the soil parent determined by deducing the initial

material from that in the present soil. -Im

43

Method to Calculate Rates of Accumulation when expressed on a ,rends in soil constituents are best

of all constituents can be mass basis. Secondary accumulation cm2 area for the <2mm computed in gm in a vertical column of 1 to equation 3.1. fraction, for each horizon according

Equation (3.1)

P ([(ZP)(BD)present - (%p)(BD)pMjthickness)(%(2mm)

- bulk density, and PMH parent where P - pedogenic property, BD

material. the horizon values through The profile sum is calculated by summing accumulation are computed by the profile (Fig. 8), and rates of average profile sum for a unit dividing the estimated age into the 2 3 the average gm/cm /10 yr rate (Fig. 9). Predicted profile sums are number, and multiplied by the for a given unit converted to a yearly profile sums are used to check the soil age (Appendix H). Predicted

age assignment for a given unit.

Silt, and Opaline Si, Rates of Accumulation of CaCO 3 , Clay, silt, and opaline profile sums suggest that CaCO 3 , clay, r 2 values were a logarithmic rate (Fig. 8). All Sio 2 accumulated at model was used (Table 5). highest when the log age regression may be a function of the erosion However, these logarithmic rates and the complete volume of and soil .loss on the older surfaces, The long term rates in these constituents may not be measured. on eolian additions is fact, for properties dependent primarily rate. probably better expressed as a linear • A B 2 0 0 AA W--=0. 30M-2

AICa-- 3 .- N:32 t

3.4 -2. _ _5'.33.__4 4.2_ .low Ago leow age

C D

48 .36pg-20.6an 72 3.45-7

- P2=0. 37 .. -2 8 46

6-1 64 6a , 616

-A . 3 -36 2.4..A.. 4.2 .3 6. 4 low ago I OW aO

Figure 8. Profile sum of horizon weights vs age for pedogenic CaCO (A), clay (B), silt and opaline Sig (D) 3 on soils developed on stratigraphic units Qic (104"O), Q2b (105. 88), Q2c (IO1'0A) and QTa (IO6"18. 45

0.45

0.4

0.35

0.3 0 C 0

02

0.15

0.1

0.00

VIC (1o ku) Q26 (,150 ke) 02c (3M k) are (I. my)

= Coo03 Cm Cy

Figure 9. Average rates of accumulation of pedogenic CaCO 3, clay, silt, and opaline S10, (profile sums divided by age) based on profile weight sums, on soils developed on stratigraptic units 9Ic, Q2b, Q2c and QTa. -U

46

for CaCO , clay, Table 5. Correlation coefficients (r2) 3 linear age and log age. silt, and opaline Si2 2 profile sums vs. level is 0.42, and at 1% Critical value for r at a 5% probability is 0.54.

linear age log age 0.44 CaC0 3 0.39 Clay 0.12 0.38 Silt 0.02 0.37 0.46 S10 2 0.23

clay, and silt at a Holocene soils (Qic) accumulate CaCO3 ,

For example, CaCO 3 higher average rate than the older soils. 2 3 rate of 0.04 gm/cm /10 yr accumulation decreases from an average 2 /103yr in the older soils during the Holocene to 0.01-0.03 gm/cm rates on the Qlc deposits are (Fig. 9). Clay and silt accumulation deposits. Deposits Q2b and considerably higher than on the older long term average rates of Q2c are the best estimates of silt, and opaline SiO2 . The gently accumulation of CaCO 3 , clay, of long term erosion. The low rolling topography of QTa is a result are a result of the erosion rates for all four properties on QTa The loss of soil results which has formed the ballena topography. (Appendix H). in calculated low accumulation rates CaCO , clay, silt, and There are several sources for the 3 and in soils. One source is weathering opaline SiO2 accumulations in place. Pedogenic opaline (or) translocation of a constituent source is way as may some clays. A second Sio 2 forms this of as ions in solution (in the case atmospheric additions, either ) (Gile (clay, silt, and some CaCO 3 Ca++) or as solid dust particles

and others, 1979). 47

, clay, silt, and opaline SiO2 A generalized model for CaCO3 During the rates vary with climate. accumulation rates is that rapid because yrs duration) rates are interglacials (7,000-20,000 playa vegetation cover, and exposed increased aridity, decreased Greater to increased airborne transport. surfaces, all contribute resulting in has better access to it, areas are exposed and wind and In contrast increased vegetation greater accumulation rates. of glacial climates (100,000-150,000 more effective precipitation of in comparatively slow rates yrs duration) could result precipitation factor is having sufficient accumulation. Yet another into the soil. For example, to move atmospheric materials during CaCO in the Mojave Desert accumulation rates of pedogenic 3 or by Hachette (1985) as climate the Holocene are characterized that soils may be accumulating precipitation-limited, suggesting of the lack in the late Pleistocene because material slower now than soil via soil to move material into the of sufficient precipitation is less during glacial climates there water movement. Therefore to translocate but greater precipitation available eolian material, interglacLal climates insufficient the material, and during the available eolian dust. precipitation to translocate or different. be the same in both climates, Accumulation rates could in the study area are extremely Rates of CaCO 3 accumulation the Vidal by Hachette (1985) for low compared to rates calculated of the study a climate similar to that Junction area, which has unit in the with age of stratigraphic area. The rates also vary actually range in However, if the Qlc soils study area (Fig. 9). rates may be too these reputed Holocene age for 5 to 40 ka, then mm

high. If an age of 5,000 yrs is assumed, the rate for CaCO3 2 3 age of 40,000 accumulation would be 0.08 gm/cm /10 yr, and if an 2 /10 3 yr. Both yrs is assumed, the rate would decrease to 0.01 gm/cm case, the rates fall within the range of long term rates. In either change at the decrease in precipitation associated with the climatic

Holocene-Pleistocene boundary was not enough to significantly In fact, decrease the already extremely low rate of CaCO3 influx. and pre similar rates of carbonate accumulation during the Holocene result of Holocene may suggest that the climatic change was the

decreased temperatures and not precipitation. way Rates of accumulation of clay and silt respond the same

on the Qic deposit. If Qic is as CaCO3 to changes in age assessment remain higher than estimated to be between 5-40 ka, the rates still (Fig. 9). For the long term rates calculated on the older deposits 2 /10 3 rates is between 0.7-0.09 gm/cm clay the range of accumulations 2 3 yr on the Qic deposit. yr, and for silt between 0.8-0.1 gm/cm /10 and for silt The long term rate for clay is 0.08-0.07 gm/cm2/103 yr, precipitation since the 0.13-0.06 gm/cm 2/103 yr. This suggests that and that clay and stabilization of Qlc is not a limiting factor, the Holocene than silt are not being accumulated slower during accumulation data during glacial climates. This supports the CaCO3 significantly decrease that the climatic change was not enough to

rates of accumulation. relatively Rates of accumulation of opaline SOi2 remain yr. There is little or constant over time at about 0.08 gm/cm2/103 soils on the Qic deposits. no opaline SLO2 to be measured for 49

Machette (1985) proposes that it is reasonable to use average profile CaCO 3 content of relic soils between about 100,000 and 150,000 yrs old to estimate the ages of still older calcic soils in the same chronosequence. Soils in this age range have experienced a number on glacial-interglacial climatic cycles. Age estimates of soils younger than 100,000 yrs may also be made, but they may be less precise. In this study, no unit consistently best estimated tne age.

In the study area a number of different rates for a given property were used to calculate an estimated profile sum (Appendix

H). The difference between the estimated sum and the actual profile sum was calculated. The amount of time to account for the difference was then computed. For example, for deposit Q2c the

2 average profile sum is 6.80 gm/cm , but the estimated profile sum is

3.0 gm/cm2 (0.01 gm/cm2 /10 3 yr, the long term rate, X 300,000

2 3 yrs). At a rate of 0.01 gm/cm /10 yr it would take 380,000 yrs to

2 accumulate the difference (6.80-3.0-3.80 gm/cm ). This discrepancy is either (1) an age error of 100%, (2) accumulation rates are off by one half for that age range, this may be accounted for by erosion on deposits that the long term rates are calculated from or (3) represents additions of about two times the potential CaCO3 on the

Q2c deposits used in this example.

Depth Functions of Significant Soil Properties

Soil properties that commonly exhibit change with time and of these (or) climate include clay, CaCO 3, and opaline S1O2* Host the properties are also strongly influenced by vertical position in MMMMMý

50 soil profile, as illustrated for some properties of soils in the

Yucca Mountain area (Figs. 10-13).

Soils exhibit increases in clay, CaCO3 , and opaline Sio2 over time. Pedogenic change can be better examined by converting these properties to horizon weights. Pedogenic clay clearly

increases with time, although CaCO3 and opaline SiO2 have higher correlation coefficients with the age of the deposit (Table 6). With the exception of soils formed on deposits of Q2c age, clay, CaCO , and opaline 3 SiO2 maximums occur in the same horizon (Figs. 10-13). On Q2c deposits the maximum occurrence of pedogenic clay is immediately above the maximum occurrence of pedogenic CaCO3 and opaline SiO 2 . In nearly all soils formed in all deposits, the maximum CaCO and 3 opaline Si0 2 occur in the same horizon, and there is more opaline Si02 than CaCO3 .

Table 2 6. Correlation coefficients (r ) for linear age, log age, CaC0 , clay, 3 and opaline SO12 for A, B and K, and C horizons, and all horizons combined. No significant •paline SiO was measured on A and C 2 horizons. Critical values for r• at the 5X probability level are 0.35 for A horizons, 0.18 for B and K horizons combined, 0.37 for C horizons, and 0.14 for all horizons combined.

A B & K A B & K A B & K A B & K C all C all C all C all linear log age CaCO3 Clay age

CaCO3 .55 .49 .43 .42 .58 .43 .42 .26

Clay .21 .44 .18 .42 .40 .55 .11 .37 .49 .34 .30 .58 Opaline - .52 - .47 - .75 - .85 S10 . 2 ...... I

51

%clay day CACn3

1 5 10 0 2 0 0.1 1

I t I

FW-4 2 2 2

0 20 0.5 1 E -II I1 F'W-¶7

II .1 o0 .1 I

I

E

ir-

Figure 10. Depth plots of pedogenic clay, CaCOa opaline SIO in soils and 2 developed on unit QIc. Lines on Ehe far right represent major horizon and depositional for boundaries: solid lines are A-I or K-C horizons, dashed lines are for depositional boundaries. 52

% cly clay CaC3O SO2 l0 20 0 5 0 0.5 1 o s lO

10 20 0 0.51 0 5 lO 2 21 1 I

yW-21 2 2 ji 1111.

0 a n0 5 0 0.5 1 0 5 10

jI~t a 1 2.

Figure 11. Depth plots of pedogenic clay, CaCO and opaline SiO2 in soils developed on unit Q2b. Lines on Lhe far right represent major horizon and depositional boundaries: solid lines are for A-B or K-C horizons, dashed lines are for depositional boundaries, and dashed lfnes with x's are for buried soils. 53

gM/nCr 2

% clay lay CaCO3 S22 S20 0 5 0 0.5 1

Ii VW-12 2 27 2 2 05 k~l.0

20 0a 0 a o.s I

Et I

3 YW-14 2 2 2

0 5 10 20 0 0.5 I 0 5 10

E

VW-20 2

Figure 11 continued. Depth plots of pedogenic clay, CaCO3 , and opallne SiO2 In soils developed on unit Q2b. Lines on the far right represent major horizon and depositional boundaries: solid lines are for A-B or K-C horizons, dashed lines are for depositional boundaries, and dashed lines with x's are for buried soils. 54

2 9'Twiwn % Cay Ca0O03 S-02 0 20 40 0 $ 20 0 £ 10 E 2 2 FW-s

0 20 40 0 0 - 0

A I 2 FW-i8 I[

f 20 40 0 S a S I. E

i7 2 2 YW-8

YW-16

0 20 40 0 5

1 11 2A

2 2 YW-1!

Figure 12. Depth plots of pedogenic clay, opaline St0 In soils CaCO•. and 2 developed on unit Q2c. Lines on &he represent major horizon far right and depositional boundaries: solid for A-B or K-C lines are horizons, dashed lines are for depositional boundaries, and dashed lines with x's are for buried soils. ... L _

55

% clay day CaCO3 20 40 0 10 20 0 5 10 0 10 20 0 i 1 2 2 2 2 FW-19

Fw-s

£

w T .1 T I

YW-2

20 40 ID 20 0 5 10 0 10 20 Cl i I I 2 2 22 YW-22

Figure 13. Depth plots of pedogenic clay, CaCO , and opaline Si0 2 In soils developed on unit QTa. Lines on Rhe far right represent major horizon and depositional boundaries: solid lines are for A-B or K-C horizons, dashed lines are for depositional boundaries, and dashed lines with x's are for buried soils. 56

Diffraction primary and Secondary Minerals Identified by X-ray

orthoclase), Quartz, feldspars (primarily plagioclase and

sand and silt are the dominant minerals in the parent material dominate the clay fraction. These minerals as well as dolomite X-ray diffraction fraction. Quartz is the dominant peak in most in the soils: (XRD) traces. The following clays were identified of minerals, and tobermorite, weathered mica, a mixed layer group for amorphous kaolinite (Table 7). There is also XRD evidence silica.

a hydrated calcium Tobermorite [Ca 5 (Si 6 0 1 8H2 )*4H 2 01 is

nature (Taylor, 1950; silicate found in cement, and rarely occurs in structure similar to Heller and Taylor, 1951). It has a 2:1 layer Hamid, 1980), with that of vermiculite (Megaw and Kelsey, 1956; composition. minor variations in structure due to the chemical 0 when untreated, which Tobermorite displays a sharp peak at 11.6A 0 14). Although it is always shifts to 10.4A when glycolated0 (Fig 300 0 C and collapse at reported to shift to 9.35A when heated to soil samples (Reheis, 1984) 800 0 C (Taylor, 1959), in these and other and when pedogenic it is completely destroyed by heat treatment, (Appendix D). It has cation opaline SiO2 is chemically removed between those of exchange and selectivity properties intemediate and Roy, 1983). Wollastonite clay minerals and zeolites (Komarneni destruction of tobermorite at is the stable phase resulting from the o0c.

of intense Tobermorite is usually found in zones McConnell, 1954; Harvey and hydrothermal alteration (Heddle, 1880; Diagnostic Features Table 7. Clay Minerals Identified and their

Clay Mineral Air Dry 0 Silica Probable Source Clyeolated 30& C 500°C Removed

parent material s 10.6 d _ d d Tobermorite 11.3-11.42/ and pedogenic (002) nc nc ne pedogenic -weathered 10.2-10.3 mr-w, b nc _ Mica (001) nc peak nc pedogenic Layer 10.5-12.0 b nc Mixed (s) (001) intensifies nc d nc parent material Kaolinite 7.1-7.3 s-w, b nc (001)

spike; w, weak spike; b, broad or I/ Intensity of Peak: s, strong or sharp spike; m, moderate spread out. 2/ All values are in A.o 3/ d, peak disappeared 4/ nc, no change in peak intensity or width. Noun

58

Tobermorite 1 1.4A

Untreated

Mixed Layer 4.46A A.

10 Is 20

I Mixed Layer Glycolated

300 C

500 C

29 5 10

.0 I A 1'? 10 7.0 6.0

Representative XRD traces of toberuorlte and Figure 14. and heated traces. mixed-layer clays: untreated, glycolated, U______

59

Beck, 1960; Gross and others, 1967: Webb, 1971; Kusachi and others,

1984). It has also been reported in contact metamorphic limestones

(Eakle, 1917). In some cases it is completely replaced by

calcite. In all cases tobermorite is of secondary origin. Reheis

(1984) reported the presence of tobermorite in Montana soils, that

it was pedogenic in origin, and that the amount increased with age. 0 Tobermorite with an 11A primary peak has been synthesized

hydrothermally and at low temperatures from many different starting

materials such as mixtures of lime or portland cement with either

quartz or amorphous silica (Heller and Taylor, 1951; Mitsuda, 1970;

Snell, 1975; Mitsuda and Taylor, 1978; Komarneni and Roy, 1983).

It is difficult to know whether the source of the

tobermorite is from the parent material (Harvey and Beck, 1960), or

formed in place. In the soils studied, tobermorite tends to be most

abundant in two places: (1) at the surface where eolian materials

are abundant, and (2) at depth in horizons with the greatest amount

of secondary opaline SiO2 and CaCO 3 in older soils developed on

deposits Q2c and QTa. The origin of tobermorite at the surface

seems to be from the eolian materials, but that at depth could be

eolian material. pedogenic and formed in place or translocated 0

Weathered mica has a poorly defined broad peak (10.0 A) and

is not effected by glycolation. (Appendix D). Upon heat treatment

the peak intensifies.

Mixed-layer illite-montmorillonite clays are recognized by 0 distinct shoulders on diffraction peaks at about 10.5 or 12 A,

suggesting incipient, poorly developed intergrades of layer-lattice of the clays (Vanden Heuvel, 1966). The intensity and consistency -E______

60 0 high order (004) 4.5A peak, and low-20 angle background levels,

reflects random interstratification common in a weathering

environment (Jones, 1983). Because of the complete collapse of

smectitic layers at 500 0 C, this treatment produces a sharp, well 0 defined peak at 10.2A (Figs. 14). These mixed-layer clay minerals

are common in volcanic parent materials in southwestern Nevada

(Jones, 1983). 0 Kaolinite (7.2 A) in the study area is poorly crystalline,

with a low height to width ratio (Appendix D). Because the same

peak appears in most samples including unweathered alluvium, it is

likely that it is derived from the parent material. 0 0 0 Palygorskite (10.7A and 5.4A) and sepiolite (12.3A and 0 2.68A) were never identified even though they are abundant in calcic

soils in the southwestern U.S. (Vanden Heuvel, 1966; Gardner, 1972;

Bachman and Machette, 1977; Hay and Higgins, 1980; Jones, 1983).

Most of the above workers attribute the formation of palygorskite

and sepiolite to the alteration of detrital mixed-layer illite

montmorillonite. The one speculation that can be made for the

absence of these Mg-rich silicate clay minerals is that Ca-rich

silicates (tobermorite) may form preferentially in this environment.

Amorphous silica can be identified on the XRD traces (Table

8, Figure 15). Jones and Segnit (1971, 1972) have subdivided

hydrous silica opaline S10 2 (poorly crystalline naturally occurring

with >1% water) into three classes based on XRD and the amount of

disorder of crystal stacking. In order of increasing amorphous with state they are Opal-C, Opal-CT, and Opal-A. Each is associated

a unique environment of formation (Jones and Segnit, 1971). Table B. X-ray Diffraction Classification of Opaline Silica (Jones and Segnit, 1971).

Source in Temperature 0 Classification of Formation Environment of Formation Soil Environment IMD Peaks (A)

OpaL-C high lava flows, parent 4.0, 2.5, and 2.8 material

Opal-CT low silica associated with secondary primarily 4.3, 4.1, 3.9, and 2.5 (most common) clays, biogenic skeletons, pedogenic definition and spacing Is volcanic ash, and infrequently variable based on order, gem-quality opal. water content, and age.

Opal-A low gem-quality opal, biogenic parent diffuse peak centered at skeletons, material and volcanic material 4.1 ash, silica gels, and some ane pedogenic silica associated with clays. dmm

62

Opal-C

Jones & Signet

1971 Opal-CT

I Opal-A a a -J 50 40 30 20 29

Opal-CT

I I 1I 25 20 17 29

Figure 15. Representative XRD trace of Opal-CT vs the three opal classes of Jones and Signet (1971). . -------

63

Diffractograms of several of the mixed-layer illite

smectite-dominated soils do have broad, but sharply spiked peaks 0 centered between 4.1-4.3A, suggesting the presence of Opal-CT

(Figure 15). Peaks are not effected by heat treatment, but are

absent after pedogenic silica is removed.

The clay mineralogy and relative abundance is strongly

related to the climate, but also changes with the time and with

depth in the profile (Birkeland, 1974 and 1984). Time-related

changes in clay mineralogy are related to the stability of the

various clays in the local soil environment, however Birkeland (1974

and 1984) believed that the clay minerals of soils developed in low

clay parent material change little with time. The uniformity of the

clay minerals present in the study area suggest the latter, that

there has been little change in either environment or in the

mineralogy over time. However, the relative abundances increase

with time (Fig. 16). Figure 16. Relative abudance of clay minerals on the soils formed on deposits Qlc, Q2b, Q2c, and QTa. Width of bars equals approximate abundance.

Qc Q2b Q2c QTa --Increasing Age Surface Horizons (A, Av)

Tobermorite Weathered Mica Mixed Layer

Kaollnite ...... ______

Opaline SiO2

Subsurface Horizons (Bt, Bq, Bk, K)

Tobermorite Weathered Mica

Mixed Layer II__ __III__

Kaolinite ___II__ ___

Opaline SIO2

a' CHAPTER IV

USING SOIL DATA TO ASSESS PALEOCLIMATE

Soil Water Balance and Leaching Index

The relationship between soils and climate can be - 1-proximated by evaluating soil water balance and leaching indices (Arkley, 1963, 1967). If the available water-holding capacity (AWC)

of a soil is known, the amount of water that will potentially percolate through each soil horizon or depth increment can be

calculated. Sometimes the word recharge is used by pedologists instead of percolation, but to clearly distinguish between the hydrologic application of recharge, I use percolation. Knowing the frequency of wettings per year, and assuming (a) that downward movement of water takes place only when field capacity for that part of the soil has been reached, and (b) that moisture is removed from the soil by evapotranspiration until the permanent wilting point is reached, one can construct curves depicting water movement (Arkley, 1963; Birkeland, 1984). In order to forecast soil water movement it is necessary to know the precipitation (P) and approximate potential evapotranspiration (ET p). ETp is the amount of water lost by evaporation and vegetative transpiration as long as sufficient soil moisture is available (Thornthwalte, 1948). 66

Water balance calculations predict the status of soil moisture .3n a mean annual basis. Critical to this study are those months when water is stored in various depths in the soil at moisture values above permanent wilting point; this happens when P

is greater than ETp . This water is available for plant growth, weathering reactions, and if the water is moving, it can translocate dissolved or solid material within the soil. In contrast, water is lost from the soil system when P

(Table 9). All are based on empirical formulas. Of the Penman (1956) and Ritchie (1982, Williams, 1984) methods to calculate ETp, the latter is recommended by the Soil Conservation Service; these were estimated from data in similar climatic regions, because of the lack of necessary data. The methods were selected because they

compare favorably with lysimeter measurements in arid regions (Stanhill, 1961; Omar, 1968; McGuinness and Bordne, 1972; Farnsworth and others, 1982).

Pan evaporation data for the growing season only (Apr-Oct) from Pahrump, Nevada, about 30 km south of Yucca Mountain, are used here as a reasonable approximation of ET p Pan evaporation data come closest to the lysimeter-derived measurements of 150-200 cm from similar arid regions. Nevada currently has only four stations that measure pan evaporation, and Pahrump (203 cm/yr) is the nearest such station to NTS. Longer term pan evaporation records exist for Boulder City, adjacent tq Lake Head, but because of its proximity to i

67

Table 9. Comparison of methods to calculate potential evapotranspiration using Beatty Nevada 2)" weather information (Table

-Method and Calculated Annual Liaitations Variables

1) Thornthwaite (1948) - 84 cm latitude Underestimates in an arid mean monthly temperature (T) environment by as much as 150%. day length factor

2) Blaney & Criddle (1962) - 94 cm latitude Underestimates in an arid mean monthly T environment, and vegetation % daytime hours factor must estimated for vegetation consumptive use nonirrigated soil. coefficient

3) Penman (1956) - -100 cm mean monthly T Limited number of solar radiation mean monthly min T stations, and a large amount of daily solar radiation error in wind movement data due wind movement (mi/day) to variability in height of monitoring stations.

-4) Ritchie (1972), Williams (1984) - -100 cm mean monthly maximum and Same as Penman, and data are not and minimum T available for most areas daily solar radiation and albedo soil cover and biomass indices

5) Kohler and others (1955) - 127 cm mean monthly T Data are not always available. mean water surface T wind movement (mi/day) pan evaporation

6) Pan Evaporation for the growing season only (Apr-Oct) - 164 cm cm of water loss Data are sparse, may overestimate amount due to the influence of wind, and assumes no ET during cold months.

7) Papadakis (1965) - 163 cm saturation vapor pressure May overestimate amount and dew point that can be derived respectively from the mean monthly maximum and minimum T 68 the lake, the pan evaporation values are extremely high compared to

lystmecer-derived measurements from areas similar to NTS. The

average monthly long term values for pan evaporation from Pahrump

was summed for the growing season only, April to October (164 cm),

because it is assumed that little or no evapotranspiration occurs

during the winter months. The Papadakis method for estimating ETp

is used in this study because it best approximated the pan

evaporation data summed for the growing season only from Pahrump.

Water budget plots for several different climatic models for

the study area indicate significant soil-moisture differences

between glacial and interglacial climates. The data for Beatty

(Table 2) is used to approximate the Holocene climate (Fig. 17) and

two different models for climates during the last glacial maximum

are presented (Figs. 18 and 19). The climatic models for the

glacial maximum are (1) Spaulding's (1983 and 1985) with a decrease

in HAT of 70C, an increase HAP of 35%, and a decrease in summer

precipitation of 50% and (2), Mifflin and Wheats' (1976) with a

decrease in MAT of 50 C, an increase of MAP of 68% and, a decrease in

evaporation of 10% (Table 2). These three climatic conditions were

evaluated at the low end of the elevation transect, and again at the

high end where the modern climate has 70% greater MAP than at the

low end of the elevation transect (Quiring, 1983).

When the Papadakis method is used to estimate ETp, the

Holocene climate (Beatty) shows that ET >p and no soil water percolation occurs in the soil when monthly climate data are used

(Fig. 17). Translocation of dissolved and solid material within the soil can be attributed to periodic high-precipitation storm Figure 17. Soil water budget for Beatty, Nevada, which is assumed to approximate the Holocene climate. A and B are comparisons of four methods to calculate ET including pan evaporation (+), Thornthwaite (A), Blaney and Criddle (*), and Papadakis (x) at the lower end (A) and higher end (B) of the elevation transect. C and D are the Papadakis method only at the lower (C) and upper (D) ends of the transect. Temperature is plotted as (9) and precipitation as (0). Oc con

0 B 0

0 lx 00

3.4 o t %. 40mmeal"

34 40 00

10t

350 c CI . jiS 4 00

% a 0 0 a - .4t month I

t i model.watte A0 and6X) v 8 Olaney are Soil wa,ter bud get fo rthe glslaci l .ttmaximlum C1 ration.ate--Spauldting, (+.• ) ornth of) (A) Bansey includinlg pan evapoato Th~thelva~tio 18 eod toclculate ET (A) and higher end (B) f the elevato Tran ue andCOU~F Criddle ig5~ofure (s), and pfpadakis (tc) at the Yower end upper (D) ends at the lower (C) and Papadakis method only C and D are the as (0)- is plotted as (o) and precipitation * a Z * * ~cc g g I I

* S 0 33

3 I I

- - .J 4 F 7 ? ? I I .. . . .

I.

3 U 3 I

b.

C.

a.

a climate-iMifflin and Wheat model. A and B Figure 19. Soil water budget for the glacial maximum pan evaporation (+), Thornthwaite (a ), are comparisons of four methods to calculate ET including lover end (A) and higher end (B) of the elevation Blaney and Criddle (0), and Papadakis (x) at tle at the lower (C) and upper (D) ends of the transect. transect. C and D are the Papadakis method only Temperature is plotted as (e) and precipitation as (0). OC m

so..

a-

fonth l"outh

CIm a. so.

a.

so. is

'S

a 5.

.60

-a. F U i J a s 0 0 J F U * U J J J ~ month m

1 75 events. This is true for both ends of the elevation transect. In

contrast, if'the Thornthwaite or Blaney-Criddle methods of

calculating ETp had been used, soil water percolation would have

been predicted during one or more winter months (Fig. 17).

The two glacial climatic models give very similar water balance plots (Figs. 18 and 19). Soil water balance calculations of

the glacial maximum climate using the Papadakis method of

calculating ETp predict that soil water percolation can occur only

at the upper end of the elevation transect during January and

February (Figs. 18 and 19). It is concluded that translocation

could occur during these months in addition to both winter and

summer high precipitation storm events. The other models for

calculating ETp predict even longer periods of soil water

percolation as well as greater amounts.

Both soil water balance calculations of the glacial maximum predict soil water percolation during the cooler winter months at

the upper end of the elevation transect, and not at the lower end.

On similar aged deposits there should be a response to the increased

available moisture on the dissolved and solid material that is

translocated in the soils.

Carbonate Translocation

When moisture is available for translocation, soluble salts and CaCO3 move downward and precipitate at a depth approximated by the wetting front (Arkley, 1963; McFadden and Tinsley, 1985). The percentage of CaCO 3 decreases with elevation in the Holocene soils

(Qlc, Fig. 20), thus following the suggested difference in leaching % CaCO 3 % CaCO3 0 1 2 0 0 2 3 4

E E

100 C.) 100 "0 -C "a)

200 200

Figure to 20. Percent CaC03 vs depth 6 are In order of lowest for soils formed on deposits to highest soil profile Qlc (A) and Q2h (B). elevation up the transect. Numbers 1

-rJ I

77

with elevation. The Qic soil at the lowest elevation in the

transect has over 2% CaCO 3 accumulation at 9-60 cm, whereas at

greater elevations on the transect, the CaCO 3 accumulation is much

less ((0.3%). In addition the depth at which the maximum CaCO 3

occurs in each profile, is deeper with higher elevation. Therefore,

with increasing precipitation the CaCO 3 decreases in amount and the

depth of maximum accumulation increases. The increase in frequency

and amount of precipitation in the modern climate at the upper end

of the transect is sufficient to translocate the CaCO3 , but

insufficient at the lower end.

If the climate in the past has been similar to the Holocene,

CaCO3 accumulation should occur at similar depths along the transect

in the older soils. Significant variations in the CaCO3 depths

observed in older soils should reflect differences in amounts of

effective moisture.

The CaCO 3 in the soils formed on Q2b deposits does not have

the predicted response. Generally CaCO 3 increases rather than

decreases in amount, and increases to depth of maximum accumulation

with increasing elevation (Fig. 20). The CaCO3 in soils formed on

Q2c deposits has a similar response with some reversals, however the

two highest soils are nearly at the same elevation (Fig. 21).

Although, generally the soils at lower elevations have far less

CaCO 3 (1-2%) than the soils at higher elevations (18-23%), and the

depth to maximum accumulation increases with elevation. The soils

formed on QTa deposits do not show an obvious trends with increasing

elevation (precipitation) (Fig. 21). Irrespective of elevation,

detectable CaCO 3 first occurs at a depth of 10 to 30 cm. This could ______-J

% CaCO 3 % CaCO 3

0 . 10 20 0 10 20 30 0 0 . 1 I 1 | | 1 .1.. ..i . . .. •I. .

Ii: E -4 100- E 100 -"i .... C. SI a 0) 1-) i. I 10 i.! 200- I.I (:5 I, . 200 - Q2c I' QTa r-J (300 ka) a (1.5 Ma)

1?

Figure 21. Percent CaCO vs depth for soils formed on deposits Q2c (A) and QTa (B). Numbers I to 5 are in order of lowest to highest soil profile elevation up the transect.

-J a

79

be due to the influence of a greater number of climatic changes, and

the erosion on the QTa deposits. Soils of extreme age tend to

reflect the leaching of occasional wet years.

During the modern climate storm events tend to flush the

soil system and translocate any available CaCO3 (Fig. 20). In

comparison, soils that have been exposed to one or more glacial

events are "more efficient at accumulating CaCO3 ". This

accumulation effect could be due to two climatic influences. First,

based on the soil water budgets during the glacial maximum (Figs. 18

and 19) predictable soil water percolation occurs using monthly

climate data at the upper end of the transect. The constant wetting

and drying may be more efficient at precipitating CaCO 3 . Secondly,

effective precipitation could have actually been less during glacial

climatic conditions than during the Holocene, and as a result

moisture was not available to translocate soluble CaCO3 deeper. In

the both cases the regional climatic change associated with the

Holocene-Pleistocene boundary would not be associated with changes

in precipitation, but primarily changes in temperature. Without

changing the amount of precipitation during the glacial maximum,

CaCO 3 can be translocated deeper by simply increasing the

temperature of available moisture and thus the solubility of

CaCO3 . This temperature increase of the available moisture may

represent increased precipitation during the warmer summer months.

Some pre-Holocene soil profiles have a bimodal distribution

of CaCO3 (Figs. 20 and 21). The bimodal nature of soil can be

explained by climatic change, much the same way McFadden (1982)

did. The deeper accumulation represent periods of greater 80 leaching. In contrast, the shallower accumulation is similar enough to that of the Qic soils to suggest an origin during the Holocene.

Computer Generated Model for Carbonate Translocation

Computer models can be generated to approximate CaCO 3 distribution in the soils of NTS. Basically they follow those of McFadden and Tinsley (1985). Climate can be related directly to the change in soil moisture throughout the year. The calculation of soil water movement (Arkley 1963, 1967) is based on the concept that the net excess of P over ETp for those months in which P>ETp

represents the total moisture available to wet the soil, but this is surely a simplification of natural conditions. This value, defined as the leaching index, may be calculated two different ways. In one method the excess of P over ET during the months in which P>ET is summed. In the other method the average P for the wettest month is used if the maximum P for a given month is greater than the summed difference of P>ET p. For arid and semiarid regions the second

method gives a higher leaching index than does the first.method. Both the Spaulding and Mifflin and Wheat climatic models along the Fortymile Wash and Yucca Wash transect have a leaching index less than the average January precipitation, and thus the second method

is appropriate. The latter value is used in the computer model.

The computer-generated compartment model for CaCO3 translocation generates "synthetic" distributions showing the translocation of CaCO3 as a function of soil depth, time, and climate (Mayer and others, 1985). Different scenarios can be simulated, including abrupt or gradual changes In climate. The 81 variables utilized in the model are the leaching index value, calcic-dust influx, parent material CaCO3 content, and partial pressure of soil (PCO ), 2 texture, initial water content, and soil

temperature (Appendix I). Various parameters were used In the model. Fresh alluvium is the parent material. The following parameters were used: a

CaCO3 dust flux of 2 3 0.lgm/cm /10 yrs, no parent material carbonate, the PCO at the surface 2 of 10-3.5, increasing to 1072o5 at the maximum rooting depth, and decreasing with depth to 10-3o4 , a sand texture, an initial moisture content of 0.02% with a permanent wilting point of 0.018%, and a soil temperature at the surface of

16.5 0C which levels off to 19.3 °C at 50 cm. (Appendix I). The calculated precipitation for the two extremes along the transect were used for the Holocene climate, and the glacial maximum climate used is the model proposed by Spaulding (Table 2). The program was run for 30,000 yrs of glacial climate, followed by 10,000 yrs of Holocene climate. Two climatic scenarios were considered for the Pleistocene-Holocene climatic change, abrupt and gradual (Fig. 10).

The abrupt climatic change model predicts a bimodal CaCO3 distribution, whereas the gradual climatic change model does not (Fig. 22). The CaCO translocation 3 modeled is compared to data from soils on Q2b deposits because they have experienced at least one glacial'climate. At the low end of the transect there is a bimodal distribution of CaCO 3 , in contrast at higher elevations the distribution is gradual (Fig. 20). So which climatic model Is most closely predicting the expected distribution: the abrupt model for the-lower elevations and the trend climatic model for the higher 82

Abrupt Gradual

%CaCO3

0OW 0

%CaCO3 %CaCO3

high V.

Figure 22. Hodeled CaCO accumulation for 30.000 yrs glacial climate with either an of agrupt (A and C) or gradual (B and change to the Holocene for 10,000 D) yrs for the low (A and B) and high (C and D) ends of the elevation transect. 83 elevations? Based on the CaCO 3 translocation on Qlc (Fig. 8A),

CaCO 3 is not being moved out of the soil at lower elevations. The

bimodal distribution in the lower soils is considered to be a

function of the Bolocene climate, and the best long term prediction

is that climatic change is gradual, not abrupt.

Pedogenic Silica Morphology as a Climatic Indicator

Duripans are silica-cemented pedogenic horizons which form

whenever silica is released by mineral weathering and not

subsequently combined with secondary clay minerals or leached from the soil profile.

The chemistry and morphology of duripans are different in

areas of arid and subhumid climates (Summerfield, 1983; Chadwick,

1985). In subhumid climates duripans contain Fe and Al as accessory

cements along with oriented clays and high concentrations of

resistant TiO2 compared to more soluble cations. They also have

prismatic structure. Colloform features and glaebules dominate the

micromorphology of subhumid duripans (Brewer, 1964). The matrix

silica is well crystallized quartz rather than opaline silica.

The micromorphology of arid-soil silica concentrations are

characterized by length-slow chalcedony in vughs or voids. The

secondary fill is microquartz and megaquartz. These void fills are diagnostic of silicification at a high a pH (Folk and Pittman,

1971). Some argue the formation of silica in arid climates is related to the replacement of carbonates (West, 1973; Jacka, 1974;

Milner, 1976). Claebules of clay are absent or inherited. The primary fabric is floating, and the secondary fabric is grain and -- I

84

(or) macrix supported (Brewer, 1964). Opaline silica is the primary

-3atrix component. The structure associated with the maximum duripan

development is massive to platy.

Silica cemented horizons in the study area have no

characteristics associated with duripans formed in subhumid

climates. There is a lack of evidence for deep weathering in the

profile. CaCO 3 is the accessory cement with little or no secondary

clay accumulation. In the absence of effective precipitation or

drainage to remove newly-dissolved silica, it is precipitated

elsewhere within the calcrete horizon, or CaCO3 preferentially

precipitates after opaline silica bonds adjacent soil grains without

necessarily plugging intervening pore spaces (Chadwick, 1985). The

complimentary solubility relationship with respect to pH between

calcite and quartz is a highly alkaline environment (>pH 9). This

suggests that localized zones could develop across a pH gradient in

which calcite and silica were simultaneously precipitating. This

kind of model implies contemporaneous calcrete and duripan

development as a function of local variations in pH related to

topography and soil-moisture conditions. CHAPTER V

SUMMARY, CONCLUSIONS, AND FUTURE STUDIES

A high level nuclear waste site has been proposed In the Yucca Mountain area of the Nevada Test Site. A permanent repository for nuclear waste must be able to withstand the effects of a major climatic change. A climatic change that results In greater effective moisture may cause percolating water to move within the zone of waste material during the time that the material is still hazardous. The objectives of this study are to document the effects of time and climate on the soil development and to use soil data to characterize long-term past climatic variability. Five groups of different-aged deposits were studied along an elevation transect of 400 m, from 1082 to 1483 m (Fig. 2). Present day annual precipitation nearly doubles along the transect from 120 to 200 mm (Table 2).

No definitive evidence exists regarding any climatic or tectonic influences on the formation of the terraces In the study area. The terraces studied are fill terraces (Fig. 3), and are not likely to be of tectonic origin. Although longitudinal'profiles of the terraces diverge downstream (Fig. 4), tectonics are not required to explain this relationship. Climatic change may account for the formation of the terraces.

! llm 86 Soils that formed in alluvium and eolian fines of Holocene to early Pleistocene or latest Pliocene (?) age near Yucca Mountain are characterized by distinctive trends in the accumulation of secondary clay, CaCO , and 3 opaline SiO2 that correspond with the

ages of the surficial deposits. Both CaCO 3 and opaline SiO2 appear initially as coatings on the underside of clasts and over time form cemented and indurated horizons (Table 3). There is no macro- or micromorphological evidence that suggests that the silica cementation occurred under climatic conditions cooler and (or) wetter than those of the present climate. Vesicular A (Av) horizons have not formed on the coarse, gravelly Holocene deposits in the Yucca Mountain area. On the older deposits where Av horizons have formed, there is no relationship between the thickness of the Av horizon and age of the underlying deposit. The Av horizons are

consistently between 5 and 10 cm thick. Quantified field properties, by the Harden method, vs log age of the deposit are are all significant at the 5% level except melanization and color paling (Fig;. 5). The profile indices also clearly slow a relationship with log age of the deposit (Fig. 6). When the four properties with the highest r2 values vs log age are combined and compared to the same field properties on similar-aged deposits from the Las Cruces, New Mexico area, the index values are very similar in the two areas on similar aged deposits. This suggests that compared to an area with independently-dated deposits the age estimates for the deposits in the Yucca Mountain area, based on field properties, are not unreasonable (Table 4). 87

The accumulation of secondary CaCO3 , clay, silt, and opaline

5102 is determined on a horizon basis by deducing the initial amount

assumed to have been in the soil parent material from that In the

present soil horizon. Profile sums of horizon weights of these

components suggest that CaCO 3 , clay, silt, and opaline SiO2

accumulate at a logarithmic rate (Table 5). However, these rates

may be primarily a function of the erosion and of secondary material

loss from the older soils, and the voiames determined for these

constituents may only be minimum values. The long term rates for

properties dependent primarily on eolian additions is probably

better expressed by linear rate.

Holocene aged soils (Qic) have accumulated CaCO3 , clay,

silt, and opaline SiO2 at a higher average rate than the older soils

(Fig. 9). Accumulation rates are dependent upon the availability of

eolian material on the soil surface and sufficient precipitation to

move the material into the soil. Increased rates of accumulation of

CaCO], clay, silt, and opaline SiO2 during the Holocene can be

attributed to several possible climatic scenarios associated with

the Holocene-Pleistocene climate change. The accumulation rates

suggest that precipitation since the stabilization of Qic has not

been a limiting factor, and that climatic change was not sufficient

to significantly decrease rates of accumulation. This suggests that

the climatic change was the result of decreases in temperature

.rather than precipitation.

No one long term rate of accumulation approximates the

actual profile sum for CaC03. clay, silt, or opaline S1O2 for a

given aged deposit. The predicted profile sums using rates from 88 deposits that are known to have experienced at least one cycle of

climatic change tend to underestimate the actual profile sums.

These discrepancies in estimating the actual age are either (1) age errors on the deposits, (2) long term accumulation rates are off for

that age range, this may be accounted for by erosion on the denosits

that the long term rates are calculated from, or (3) represent much

greater additions or CaC0 3 , clay, silt, or opaline SiO2 than the

potential rates of accumulation predicts.

Soil properties that commonly exhibit changes with time and (or) climate include clay, CaCO 3 , and opaline Sio 2 . Host of these

properties are strongly influenced by vertical position in the soil profile. With the exception of soils formed on deposits of Q2c age, clay, CaC03, and opaline SiO 2 maximums occur in the same horizon.

On Q2c deposits the maximum amount of pedogenic clay Is in a zone

immediately above the zone with the maximum amount of pedogenic CaCO 3 and opaline SiO2 . In nearly all of the soils in this study, the maximum amounts of CaCO 3 and opaline SiO 2 occur in the same horizon, and in these horizons opaline SiO 2 is more abundant than

CaCO 3 •

The mineralogy and relative abundance of soil-clay minerals are strongly related to the climate, but they also changes with the

time and with depth in the profile. The pedogenic clays in the

Yucca Mountain soils have developed in very low-clay parent

materials. There has been little change In the soil-clay mineralogy over time, in spite of climatic changes that have occurred since the

stabilization of these deposits and Initiation of soil development (Fig. 16). 89 The relationship between soils and climate can be approximated by evaluating soil water balance and leaching indices. Two climatic models of the glacial climate, one based on packrat midden evidence and a second on pluvial lake chronologies, were used along with modern climate data from Beatty, Nevada to calculate the soil water balance (Figs. 17-19). The Papadakis method of calculating potential evapotranspiration was used in this study (Table 9). The Holocene soil water balance calculations suggest that no soil water will percolate to depths using climatic data on a mean monthly basis. Translocation of dissolved and solid material within the soil can be attributed to periodic high precipitation storm events. Both models of the glacial-maximum climate predict that at the high end of the elevation transect soil water percolation will occur during the cooler winter months, as well as during high-precipitation storm events. When moisture is available for translocation, soluble salts and CaCO move downward 3 in solution and precipitate at depths approximated by the estimated depth of the wetting front. Depth plots of percent CaCO for 3 soils formed in Qlc-aged deposits suggest that near the upper end of the transect the modern-climatic soil moisture conditions are sufficient to translocate the available CaCO3 (Fig. 20). Carbonate accumulates near the surface on the Qic aged deposits at the low end of the elevation transect, but appears to be translocated to greater depths, below the-base of the soil, at higher elevations where precipitation is greater. With increasing elevation, soils on the Q2b deposits that have experienced at least one climatic change have different CaCO3 90 depth plots than the Qlc deposits (Fig. 20). Generally with

increasing elevation and precipitation in the Q2b soils, CaCO3

increases rather than decreases in amount, and increases in amount to the depth of maximum CaCO 3 accumulation with increasing elevation

and precipitation (Fig. 20). The older soils tend to reflect the

effects of leaching during occasional wetter years much more than do

the younger soils. As a result, the older soils do not show trends

in the accumulation of CaCO3 with elevation (Fig. 21).

The different trends in accumulation in CaCO3 on the Qlc and

Q2b soils could be due primarily to two climatic influences: (1)

additional moisture during a glacial maximum as determined from the

water balance calculations, and (2) the likely changes in the

effective precipitation during a glacial maximum. With only modest

increases in the precipitation, the depth to which CaCO3 would be

translocated and deposited in a soil would be greatly increased. Without change in precipitation, CaCO3 can be translocated deeper by merely decreasing the temperature of the soil water and thus increasing the solubility of CaCO3 . This temperature increase of available moisture may represent increased precipitation during the warmer su-er months during a glacial maximum.

A computer model was used to generate an approximate vertical CaCO3 distribution in the soils in the Yucca Mountain area. Parameters used to generate the model describe the physical characteristics of the deposit, CaCO3 influx rates, and climate.

The model was run using the Spaulding (1985) glacial-maximum climate model for 30,000 yrs followed by 10,000 yrs of the modern climate

(Fig. 22). This climatic change was generated both abruptly and IIII

91 gradually. By comparing the computer-generated model to field data for the depths and distributions of CaC0 3 , the model-generated data

suggest that the climatic change at the Holocene-Pleistocene

boundary was gradual.

Several future studies of the soils in the Yucca Mountain

area have been planned in order to expand and clarify the findings

of this study. They include the following: (1) soil thin-section

analyses and total chemistry in order to help determine the genesis of the silica-cemented horizons; (2) a relative dating study of the

degree of preservation of bar-and-swale topography, degree of

rounding and size of surface boulders, and degree or sorting and

packing of desert pavements; (3) evapotranspiration measurements

with weighing lysimeters and evaporative pans with the Water

Resources Division of the U.S. Geological Survey; (4) stable oxygen and carbon isotopes in the pedogenic silica and opal phytoliths for

paleoclimatic indicators; (5) the relative abundance and distribution of tobermorite (?) and its relationship to mixed layer

clays, palygorskite and sepiolite; (6) a more refined and complete

stratigraphy for the surficial deposits in the NTS area. IFI]I

92

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APPENDICES Appendix A. Soil field descriptions for the Yucca Wash and Fortymile Wash area, Nevada Test Site. r

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a mae a m a -m amuma a m me a m wain a a cue * B mace. a a S .3 * a Na * . . 4 4 . .. I. U 4 444 4 'a., 4 A * Cm. * By 4 .3 C a Cm 3 4 em a a - -mm - m a -- ge C S -m - a * 41 CC 0 -4 a-B 3. Ca * 4. a 0 - ma m a - 4 A *A Ama a -m a- ma LA 0 a 4 as mu

o - - - a * am me 00 a SID** a, Va., 4'4 Na a .4 a a

aUd 3.4 33 - m - C U -g 'a.O -3 a m a V 0 - .4 0 a 4 -. 4 a B 24 44 .4 4 a*a4 Am 3 pm a m ma ma a. C A BA 4 4 4 a. a. a. mm -- m a a a Am mama a a U U ma ma Ba 4d 4 4 so 5 a sB a a S am a a U S a a. ma ma A A A 0 -q AA a m a a am am 'a A A A a Br B am A. A' A a C B S. Ba B Cm am as' -- A. 0 a a a a a m a N N

901 6 4 6 4 6 4 36 40 33 -- 4 * 3 40 34 3 * 4 3 3 U 3 U. 46 33 440 3.3 - U3 *4 33 V. - 4 * 0gS :2 3 4 6 -4 0 3 4 - 33. 43 4 S 40 4 3 3 I U 3 I I! 'i lb- II 33 6 433 63 3 3333 33 3 U 5 *60 * 33 333 3 3 V 0 6660 44 36 630 4 44 43 a * 00# 3. 3 3 U 63 3 0 flU 3 6 3. 04 3- ag' 0 3 U 0 U U U 4, U U ue1 U 6 3 3 S 4-4 33 3 - - - U 4 4a. -b -- 46 a. a *36b 6 * a. 4 - 03 0 * a. 34 534 3 - 4 4 6 a. a a 4 06 4 3 - 4 4 4 66 * 6 4 4. AS. 6 &9 3.3. 4 3 I 0 3 *o am -b S a 2: * U U - 43 g 43. a : : * * & Us. 3 U us U 3 - - 3m a a o 0 uSa. 4 4 so us aesoese a I.' 4 ,440 44 3. 0 0 33 U U * a 4 4 4444* 44 4444444 4 0 OS U 4. 4. W-0 *34 4 4 4 44 3.4 4 * 3 * u S ,: -% ft S S : z : to4 64 a. 44 3 6434 44 43634b4 4 -3 * .3 . . .3.3 3 - S - a. 4 4 44 4 a. * .3.3 4 4 4 3 a a uae 3; 3 3 0 4 4 444 44 4 4 44443;;;------ 4 3 3 333 33 ou 0 6. 0 0 0 00 3 3 3 3333 4444444 3 * 4 *6. 69 3 6 3666 b4 .34 4 4 4 44 - .3 -. S a.: - 4 444 44 4 6 3. 6444 44 3666664 4 * .3 . .3 .3.3 3 44 .3 '3 - 3 4 4 44 4 4 6 * 0 .3 4 3 .3 4 4 a IA * U 443 33 p p 3 p 33 43 93333 .3 a I I- I* I-pp Pp u e * P I pp pp 3Pp ppp 3 3 p 3 3 I 8 3 34 I 8 3 p p p pp £ '4 4 a * 4 64 34 0 6* a - 0 434 : - :: 34P C a 33 643 a. 3 9 4 4 * - 3 I- 44 343 5 4 0 4 * - 4 4 * 343 333 -3 3 * 3 4 4 * 3343w.. ma s a 3 3 3 3* 3 3 3U04 OIg I3 6 3 3 3 .334 3 a 036 U 3 33 33 3 3. 4. 3883 * -33 8 * S S 3 U 04 4 O U 4.3 44 04 333 3 - 3 U. U 0 U U 6300 £ p .3 4 3 3 V 338 646 U 333 -- p U U 4 U o 0. 63 V U 3 U 0' 3 3 3 0' 333 -3 - . 3 5 33 33 93 33 - 3 3 a 0 003 - * - 3 3 3 33 § 0 0 440 44 4 0 34 63 4 4 0 03 @9 6-4 433 3 4 4 - 4 6 40 - 4 3 3-3 33 04 @43 a * 4 0 0 4 06 * U V 3.30 3 3 3 33 33 3* 34 03.3 3 U U * Va. 33 * 3 5 3 33 3. 3*3 3. 6 S N V 1 6 3.0 U o I 3 3 * V * 3 3 333 33 * a * *S..3u* 3 3 3 5 33 33 03 333 'I' * 3 S U 6. 3 * .*8* 33 S. * 33 6 S 3 3 33 - .3 *U .3.3.3 4.3 5 . * 0.33 3 0 33 * 3 0 .3 .3 .3 .3 .33 .3. 333 aS 3 33.3.3 .3.3 334 .3 * S 0 0 3* .3 .3 .3 .3 .3 3.3 I . 3s 3 a S 6 3 3 3 - 3 0333 OS *.3 .4. 34.. 4 -4.-* @3 -- 3-ar 5 & 3 - 4. * --- - a *0 66.. * 34 443* 0. -30.a.. 44 - - 3.3 -4 - a. * 4 - & 43 3-3 33 * * 3 3-3 6 .33 43.3 3.3 *33 34- - 3 - 3 3 & U 433 em .3 4 3. * 3 03 3 It - - 3 0 uS 33 3 0 33 * 0 3 3 36 so 4 3 9 @ 30 0 * a a 3 3. * 40 43 4m 3 3 3 3 - 6 43 .3 4 3 U U * 33 3 333 3 6 4.34.34.3 .3 U -3 -3 0 Us Urn 33 4 44 3.3343 .3 3 444 4 U3 - - - 0-0 3 - 0 - - @0 4 @9 a- -Se s 4 4 - - -0- - u -3- - @0 3 -3 a

43 4 -. 3 I 3 4 * - 4 4 4 4 3.3 - lo w 4 a 6 6l03 0 0 3 U 6 -'3 .3 3 3 3 4. .44 3 * i3 W0 V U 3. 0 3. I V I - U V U V 43 0 0 1 3 3 3 w0 0 333 3 3 3 3 3 4 4 3 0 4 3

901 107

3 a a U am a £ a * a S * 3 a a-o Ac a a. S a 3 a a. S a - a 3 a * 0 4 4. a 3 * a * a a a m a a £ a * 3 a 3 a as a-a U a * mm * 6 a a -a-m La a a U a. U aa * U a S S. 4 4 U U ma S 93 a a U * U Iam a S am * * a U I a a ft as a S 'a a S a La 3 a 3 3 33 a ma * 0 * U a 9 * S 0 - a 4 a -a. I a -.- a.. a 0 .0 S - mma a.. a So s-I a ma mmmd a a * - ft a... a.** *.a 'lb a a. a. a o a a a a '.3U au 4 ft 0 4 I ft Oft ft ft a ft 3 ft a 4 a.dft 5 5 0 mm aft U a a U ftgmm a. S so .me g a -a S U * a.a a a - ma I U 43 a ft - ft. - - a. a U U a * 5ft* 00- S *. 46 - a a a. -a * -a .9 * 0 5 ma as a * Sal - ft- 3 a. a.a.a U S. :. zi :. S S.. * a a S a a a -a a. .a. a. a. a. . * * *@i a.-. a. a. a. a. a ama a am Ua *afta * a a a Ua a a. U a U * S a a * 'a a mm. 'mm mm a a *a 5 aaa a meL a.. a a a £ aa * a U a a a a ft Sftft S. S U a * a h ft ft4ft ft.a ft a * U 0 ft 6 * ft ft ftftft * . . ft ft . SSft ft fta ft O U *mmft ft a ft 4 *u. we a aa.. ft ft a a. ft5 ft a a a a. 1. U a a 9 U .mm a a am a a a -a a a * - ft a mma ft am a.. mm a a a mm a.. a-a aa -. a a. a U -a a mm efta. a a- a mm -. S ma. a mm ft S mm-a * -s a mu.e * gfta a- ** a. mm a am a mm I mma a ft ftft3ft * U ama a mm a 9mm. - S a. a ftaftftft - mm3 S a U ft fta ft ft"-a U ft mm ft ft ES 0 ft ft 40 -l m 5- ft ft 4 p p ft 4ft ft a ft 4 * a - ftp ft ft ft - - ft - mm m-a Z Z U ama.l.m S a .8 U .8.8 .8 U a. am .8 mm ft a.8 S *11a : 1 *, U ft .8 U .8 .8U ft U * a ft 4 .4. ft ft a ffftf~mtf ft ft ft ft *s ft ft ft ft ft 4 4 4 ft ftE ft a a ft ft ft ft ft. ft 4 ft 4 4 ft ft. a * - a. . *ft . ft ft a ft am ft ft * 4. a * ft 4 mm as &94as ft ft ft* a ma ft a 4 - ft a ft ft ft ft ft ft . a a OS * * .0 ft ftft ft ft 4 ft ft ft 0 00 * S ftft ft a ft * a ft a a ft ft C ft ft -- a a ft ft U ft ft a * S ft. ft ft ft 0 0 em aft ft ft ft ft ... 4 ftft. - ft ft s-mm ft ft ft a mm' ft ft a * 4 ft ft ft ft. ft .01 ft 4 4 .m ama. ft ft ft ft ft a ft aft ft ft maft 5 ft ft ft ft mft ftftma. a ft. ft ft ft ft * a a a * Uft mmi SO ft ftft ft ft ft ft ft ft ft ft-.. fto. ft * 55 * S a S ft ft a am ft a ft ft ft ftUft ii am ftftfta-a ft Ofte U SI, 3. * mm 3 5 , -a a .9. a mmmm. mm a m mm* mm3 mm9 aa mm a mm mm. a a.. aamm 4 as Sft4 4 4E ft 00 ! ft 4 ft4 a ft ft. 0 - - - 9 - ft a a a ft ft.!.. - ft mm at ft ft a a ma a .3 a a ftmmin *ft ft a a a ft a a a am U 4S 40.3mm mm - a ft a a 4 maft ftft ft a a ft - ft a..ft a Ua 3mm * ..a ft.ft 4 a a asii a a. ft I ml * a DI * a a. - *mm a- a a mm * a a mm - ft * w * a a a.a * aS *r; a. ft a ft ftft ft ft S. 0 0' - aft Ofta ft a. ft -ft aft ft. ft ft ft

wmmmmý 108

gem go.bbs b.c a £ mu. a a a a a a 0 U C S 0 'C, egg a - p p S S c *gu soft S C S C 6 C a 'Sb bb lb C Ia U e.g. C ft U U ft a - UU ft * ba * U 4 a 4.4 mm. ft U age C 0 a U g a gag CC -- ca Lb go. ammo. CO a U 3 3 BSU 3. a - a a. C C U C 553,3 a S S a La gag * b*b ego a B * C. CC * gaaa age. C 0Og S 6 aafta ace cc "ft-ft ft. -

a.g0 S C a . - a a a ft aft ft a - a

S 4t. a.: ft a Ca a U 0 a. Uft ft *0 0 65 Se 50 a. ftft S U ft a ft 0 4-.6 ft U &m -e S S I.e. gt C U * - SUe ft- eaa SO aaqft - a a A a 1 a. * S cm ft ft 06 a c a ft. gg ftg. ft ft S. * C -C S a .g a. Os cc e c * ft C ftc cc G,eft C. U S

U S 55 ft S ft ft - a Cc a a as aa go a * U sea *b

ft 6 550 SO ftOUee ft ft ft4ft 4a 4a44 2. . ft ft ft ft ft ftU Urnese soft fft ft ft a I a a 0 S S a A a ft a a S ggcg a lag . oft A,z U SSCC ftft bUSz!f ft aft 3 U ft o * ftOO a' S U U b C cc I I ccc Sm ftp. C U aftag C 0 lug aft a ft a ft ft ft a - a ft ft ... mumg C b cA A.. .8 A b U * ft 0 - ft ft ft*4 0 5a45ft * ft ft ft ft a a' ft ftft ft44ft4 U U .8 C S .8 U .8 U U .1 .8.8 4 C U.8 U .8.86 - * I UtJJ.au 4 g UU ft@UEd U C 4 a ft ft B 4 ft 4 .5 .4 4. ft. ft S S -. ft ft ft 4. .5 .4 ft S S S S ft * ft S S a ft ft ft . .5 5.* ft ft. ftft ft * ft 5 ft ft 4 4-U B. -u * S ft4 Bus ft ftaft ma * ft * ftft ft a B U ft ftft ft ftft U ft EBftft U ft ft ftft ft ft ftft ft ft ft ft ft ft ftft ftft S. * .5 * 55 5 S S.. ft ft p.8.85 aUJ a S CS * . - - ft a ft ft ft ft ft ft S 4 C 4 8.8 S - ft ft * ft 4 ft 4 Iu. S U ftft ftft ft B S .5 .4. 4. ft ftftft S %a ft adj ft ft aft ft ft: fti ft S S S .5% ft -S 4 .5 *6 ft S *% S *ft masst ftc ft ft ft Ba- .a . ft -S ftft * B 8 mu f to A5 A ft Oft ft ftal 5. B U ftftft ftft C ft ftft ft ftft fta ft ft ft ft ft 2 . Oz Z 0 * U ft ft U SB. S ft ft ft ft ft ft ft - - ft .. .:. CS * S ft ft ft ft ft - - ft ft ii 3 dd C., a C 3 I a e 083 aCe S U U I c acc : ::44: :68:: :: IV, aS U 1. C S ftC ft40 a - ft* * ft afte SO. S-4C"ft S - ft ft ft A a. a - ft ft ftfft a. ft A *fa ft fft S Wa" - a a" S a * caL U: IIa U. 3 a 0CM Mu. U CS a a ftftft *ftft ft4es aC'a.

Ca -ii a a , , , * C ftI a C I 2'U ag S ft 6 C * ftc Cc a * a a B C ft CA aft cc . ft S * ft* ft a ft. ft ftc U ft U. S ft - W fta ft -ft a" - - - r

109

6S 6 44 * a 66 aaa a * 66 U a 64 466 * . 3) U * 06 33, a 3 aa 606 6 6 0 0066 - .. a 0.6 0 * 6 6 60 gag * CA. 4 e.g. a 06 466 606 0 U 4 aaa U 0 a. * so. a 660 0 0 0 6640 6-4 £ 066 6 00 * S U U S U U U - * .. 44 444 U a a a a 6 - - - 4 6 * 44 664 6 6 U 60 6664 4 64 604 - - 0664 *06 * 6mg U 4* P 0 3 4 - a * 664 60 - - - S 0 40 * S. -6 U 6 6 --- 3 0 - -- 0 6 * C - - - a. OOga -a a 6 - 6 U oem - - * 0@ 0 * 064 Oa - a 0 sea

6 * - - a * U B.- - - *0S- a a * S 0.6. 6 4 6 & 0 0 6 66 a. a a. * 0 4 a a a & a 6 6.6 * 6 a ml sag * .66 * a 6600 .S a -a 4 0 S - a.. 0 a 6 - 6. ma 6. a 60 0-0 6. ma .2 0 60 6-6 6.6.6. a. 0 * U -- earn mom - *6. 60 a 4 u -. 0 am em -. .6 U 0 * 0 * *gge 6 66 - -- * 6.-0 a OSSa--a 0-6 - -a 0 * 6- 60 V S ma ZIIII 6.6. 6. S. S 6 .1.. "6. 6.6. Li * 6.6. 6. 0 * *6 0 6 0 .0 60. 06 60 & 6... 666 6 6 6 666 66. 6 6 * .60 6 * 60 * 6 660 6

4 00 a OS. a U Urn a 6 6 £654 a Ca 0 B 6 6 6660 S 60 0 * *aa a U * e.g a aamo 0 0645 0 0 00 .0 a a.45 0 4 4a *eaa a am 0 a * *64 a a 0 a a Sea 4 a a a a a a a a - a a U * *aa

U U6 a 6.6 S a 0I a a a a a 0*4 a a ,* U 6 a a a 6. a oa 6. m* 66. 6.6 6. a U 060 0 S * & a 6 0 V * Vs 0 * 0 a. ma IV V 6 6 66. oSam U 0 S 6 U U 65 6 * *6 I U ama g * * a - a a 0a a U a a a I a a a a U 6 S 6 44 a a a- a 4 -I U 4. a wa w a. S U 6 .851 U .5-ames U 04 U w Ma-a a 0 U 6 a * *** 4 a 6 -a. a 'a 45606 4 4 a a a - a am U a a a - a aa a ,55.. .5 US 0 0 * a *ee S 0 - a a U a U 0 aZZ2 U ee s. go 4 I a *4 0% 4 a a 4 a a a a aaaU a a a a a a a 01 * * *aO a a a a - .aaI: 60: . L 1 63 0664 -a 64 06.6 * em 6 6 ; 0 0. x! co: 0

C 000 ow aws S U a U 451 00 I I 4 040 a

a1 % ii*6 S * 6 V as 460 6 -. a £ a a a 'A 0* S. 6.6 0 6* * S. a - a -aa 6 0 * 6' -- -- a -a a a 0* S. -- S. -- 110

Key to Appendix A *

Horizon Boundary Topography Distinctness smooth 5 va very abrupt w wavy a abrupt i irregular c clear b broken g gradual d diffuse

Soil Texture S sand SCL sandy loamclay loam co coarse LS loamy sand CL clay f fine loam 5l sandy loam SiCL silty clay vf very fine sandy ciay L loam Sc SiL silt loam C clay clay Si silt Sic silty

Soil Structure Grade Size Type granular m massive vf very fine (v thin) gr platey sg single grained f fine (thin) pl I weak m medium pr prismatic columnar 2 moderate co coarse (thick) cpr angular blocky 3 strong vco very coarse abk (v thick) sbk subangular blocky (20) If two structures - listed as primary and secondary

Soil Consistence Dry Hoist wet so,po non-sticky or plastic lo loose lo loose or plastic very friable ss,ps slightly sticky so soft vfr sp sticky or plastic hard fr friable sh slightly vs,vp very sticky or plastic h hard fi firm vfi very firm vh very hard firm eh ex hard efi extremely

Clay Films Horphology Frequency Thickness ped face coating vf very few n thin pf thick br bridging grains few Mk moderately 1 thick pore linings 2 common k po gr gravel coats 3 many

CaCO EfPervescence on matrix 0 - none in matrix. diss - disseminated; discontinuous. e - slightly, bubbles are readily observed. es - strongly, bubbles form a low foam. ev - violently, thick foam "Jumps" up. III

Key to Appendix A (continued)

* For more information, see Soil Survey Staff 1951 and 1975 I/ Texture is based on lab analyses 2/ Sampled for phytolith and pollen analyses 7/ Sampled for U-trend dating Wa/ Soil ped thin section 4-b/ Rock thin seq;ion 57 Sampled for 1OCl analyses T/ White carbonate is whiter than 10YRS/0 Appendix B. Soil Profile Index Values F-. 113

zal.':- VA.-.-E

RUEIFICATION tiio~ug:19ci ------, Sispit 'to'z:on Depth Color Color Norsilized I Prohile Weightto (cem 11 12 property thickness property stan

C~ 0.~00 .(PCu 0.00Q

Fm.4OAo 0.1)( 0.(,(, 0.0

I (.00 mm..- * L. 0.v0. Off 1.5 0. C..C.c* c. 0.05 03,9 7.0:7 !ý:z 00 C..CIN v

4.C' A. Ill t'' 0.0) 0, ('.11 O 15.471 .1 5.'.0 o.o: v.13 0.75 4.4: Uin *d*i* '.'!. 0.00 0.1. e.cs 3',*(t(. A.2~ U* 0. le e.

.6 '. S.';. e 2('.0) V. ("* ('.11 10.11" 24 4.N 2Ck .3,' 0.C".'

0.o0:* r. 4- 0. U.!, 73 0.oo1 5.47 (I. (to 0.00 0.1 159.01 a 0 1e 0.00 0.00 15.;`2 EN 18 46 20.00 0.0O1 0.30 0. 00 2.955 C14.0.q 46 170 ~0.0 39.16 0.ON0 0.00 15.05 2CvIA 170 220 bo.00 15.79 0.00r 0.071 3.01 4. 0 5 0. 0 0.3:1 0.W' 34.45 0.1It 5 12 0. V.O 0.16 0.(ii) 10. 41 5v.(10' 0.03 107 15. ('0 107 0.00 6.64 21.02 am 0.00 2Wv 0.00 0.00 0.00O 23.04 .8.tjqtm1 21.05 21tiqske2 0 4 0.00 v.0. 32.11 0.14 4 15 0.oil 0.0Oh 0.00 0.00 21.06 Hpl b 0.00* 0. isO 0.0011 V. ~ 20.00 0.0"( 0.11 2.32 55 144 0.00o 0.21 1B. 74 144 196 Wv. 00 0.0'.' 0.It 11.*05 21.07 Xtqn 18a 231 0.0(. 0.0C. 0.01) - I

114

S".L% F:LE INEEX VAL'ES RUBIFICATIOk iaixisu@219Y -...... ) Saa;le Hor::o" Depth Color Color Worsaai:aO X Profile Neightea Ica! ii #2 property thickness property mein

11.01 -v 0 4 0.(' C.00 0.0. 29.59 0.P70 A 4 15 0.00 0.0c 0.00 0.C"

11.04 21tBOi 41 9% 40.0. 20.0v 0.16 7.58 !1.OG 32qm 1,50 4.00.00 5.00 0.21 12:

0 4 0.'., 14 0.1CI, 0.00 4 0.0'. 14 47 0. C' Et 0. 0;, 4.56 12.04 29•1 47 C.OE 10..00 W:" 0.21 531 0.1'. 12.05 415k: 1'5 0. I-(, 0.19 4.42 I '.k.- 2t*41y' 144 60.00 0.01 0. 00 12.07 Bq~t 144 C.0.00 0 0.00 0.00 0.00 14.01 A 90.00 2E 0.00 0.00 14.01A 0. O" 28 54 Cs.0,. 0. 11 2.14 20.00 0.11 5.56 14.04 2E%, 54 I(, 5v.00 1 .,? 121 25. 0 •0. o:) C.131 1.64 14.05 '31:t ('.0'0 0.11 14.06 5q14ivlb 15. 20.00 3.20 0.11 14.07 4;0,•': 15' 60.•0 0.00 IC.OE AEP3 221 .E4 0.1,: 20.00 0.00 0.05 0.': 56.09 0.:7 20.:-1 A; 0 I0.0050.00 20.0: Av2 0.00 0.03 0.2N 6 64 35.00 20. 01 A 19 0. O, 0. I1 3.63 6.95 42 2i-.60.0000 0.32 20.05 21tjqk25t~q' 3.75 64 76 60.00 0.00 0.32 114 60.00 70 0.000.W~: 0.32 12.0. 20.07 2bt'qk2-2 60.vO 114 152 0.00 0.32 12.00 20.06 21tjq#2-1 190 60.00 0.00 152 0. 32 12.00 20.00 o.Wo 5.0 H' 0.11 0.5L 44.0: 0.1' 0 5 0.00 5 2 0.Ov' 0.(10' 0.0'v 5.6 5B, 20 45 5.1: 0.07 0.66 60.00 0.3t 3.47 5:04 22tb 45 56 0.00 0.42 21.05 5.05 21tq'. saoI"~ 40.•00 19.32 5.0O 2vtqt 106 164 SO.O 0.32 0.0') 0.00 0.00 5.07 2Cqn 164 263 K

115

SOL: PFY[LE INHEI VALUES RUBIFICATIOk iaixaue.l1QO ------Saiale Hoil.on Depth Color Color Noruali:ed I Profile weighted (c1 41 iC property thickness property span

11.01 Av 0 11 0.0,0.00 6.00 0.005 18.21 0.11 18.02 A 11 3: 0.00 o.Mo- 0.00 0.' 18.0C it 3 40 20..05, 0.0, 0.11 0.74 11.k,4 2bt3$j 4(, 66 M5.00 0.00 0.29 7.911, 18.0! B•tqi 66 12A 40.,40 30.0, 0.18 M.5 l8.Cot .: 12i. lot) 9;•0.•, 0.01,0 0.00 , 0.0O

9 0. (,10 0.00 0.0C .. 4N 9 21 8.02 Fti 70.0', 0.!3 4.4: 0.00 7. i7 6.v 2.1t 21 35 II0(.00 68 (.0.C. 0.55 eE 6.vL5 2f 20.00 0.20 E.4: 8.05 2Xk C.1 21h 0.00 1.01 0.00 70.00 S.F3 AY 1; 20.00(, 0.1b 1.79 4: 0.0(5 16.0• Et 0.47 2.05 4; 58 7.11 2 bq 30. (0t 0.,00 0. 17 16.05 15.47 t.nci100'; 0(,.(0' 0.477 Zqu. 150 4.,.',', 0. 15.79 2; q3J 100 0,.00 15.7. 207 0.00 215 cr 15M V. Yi 12.00 o(.00 0.3,2 A 0 10 0.0C 0.00 40.2E 0.17 1.02 Ot 10 2.5 0.00 0.21 0.00 2itqol 25 4: 40.O0 0. •., 3.58 1.04 26tqt'.6 C..00 1.10 42 So 60.00 0.00 4.42 1.08 3Uqebl 5o 70 50.00 0. W' 0.0( 4O q."2 0.00 1.109 70 115 60.00 0.00 0.21 0.0 115 167 0.0%V 0.32 13e. 1.11 5Cn•) 167 19 0.00 8.84 5rt. 66.00 0.20 1.12 195 A19;:* 0S.M0 18.75 0.00 19.01 AvI 0 4 0.00 000(,, 0.00 43.•37 0.0o Av2 C..0( 0.00 4 0.00 0.21 0.0,. 19.0: sk 9 13 40.06( 0.V.. 4.21 0.84 10.04 IN 17 0'.O., 0.84 17 0.37 19.05 Btqp 29 0.00 80.00' 0.26 4. 4 4. 29 0. 3 4.74 19.07 2• qf. 47 72 6(!.0(, 0.0, 7.69 19.01E &"Pq&2 72 ISO' 60. 0C 0. 0V 0.32 24.63 116

L "-:,.E '-.. EIh VALUES 9 RUHHElATIOtd (m.jutz~Iu~ ,J* --.------Sisple mcri :ot Depth Color Color Norsalinea X PrOile weightta (cat 11 I property thiCkness property smtar

6.01 AV 0 bi ý.': 0.0(1 0.Oc 0.oN 53.42 C0.01 6.02 Pt 6 1ý'. 80.00 0.00 0.4 Z 1.6e 100. 1:Co.. (o1(1 0.29 12.lO 6.04h. 52 101 POO0 0A.0 0.42 2V'.6 b.05 I~i! is: W~. -', oýoo00 d A24.5 0.06 3c~k 1:? 2'.i 0C. 00 0.0 0.21 1b.21 6.07 :41 "(0 'd-5 99i. 6. 0'.O O.'0 Of.0

2.01 Av 0 3 0.00 0.00* 0.00 0.00 41.e7 0.21 2.2 310 10~0 0.0' 0,,.05 0.37 2.0o: by 10 19 10. 0. 0.00 0.05 0.4" 0.425qm'ý 19 '3 4 30.0(K 90. N. 0.29 4.34 2.05 21tqtiv 34 R,) 90'.1)0 0.00v 0.4? 15.1t 2.07 i~tqs 19- 52 100.0Oc 0.00 (s.42 131.89 2LOS &*q 5:6114 10M00 0-6 0.05 3.26 2.09 2., 114 M9 1i.0' 0.00M (-.05 4.37

221.01 Av 0 1C. 0.00v 0.001c 0.00 0.00. 60.42 0.3: 22L.0'E N. 4101 96.5. 0*.00. 0.42 4.63 2.3 21 62 F0.00 .00 0.42 17.2a &M.-4 1.& 62 92 0V. 0.00c 0.32 1.47 02.05hop. 92 14 K0.OC 0.0 0.:1. 25.05 117

SOIL PROFILE INDEX VALUES KELANIZATION (u6xatut1S5) Siaple Horizon Depth Color Color Normalized I Frofiile Uighted (Ic) I1 12 property thickness property man ------0.00 0.00 0.00 0.00 FMA-2 0.00 0.00 0.00 0.00 FhA-3 0.00 0.00 0.00 0.00 FWA-4 0.00 0.00 0.00 0.00

YKA-I 0.0( 0.00 0.00 0.00 Y04-2 0.00 0.00 0.00 0.00

7.01 A 0 1.5 0.00 0.00 0.00 0.00 1.94 0.02 7.02 Cox 2 19 10.00 0.00 0.12 1.94 7.03 2CkoM 16 100 0.00 0.00 0.00 0.00

4.01 A 0 3 0.00 0.00 0.00 0.00 0.00 0.00 4.02 Ski 3 9 0.00 0.00 0.00 0.00 4.03 26k2 9 60 0.00 0.00 0.00 0.00 4.04 2Ckn 60 100 0.00 0.00 0.00 0.00

17.01 A 0 6 0.00 0.00 0.00 0.00 0.00 0.00 17.02 ly 6 24 0.00 0.00 0.00 0.00 17.03 2Ckn 24 120 0.00 0.00 0.00 0.00

13.01 A 0 9 20 .00 0.00 0.24 2.12 2.12 0.02 13.02 IN 9 21 0.00 0.00 0.00 0.00 13.03 2Bq! 21 73 0.00 0.00 0.00 0.00 13.04 2Ckqn 73 136 0.00 0.00 0.00 0.00

15.01 A 0 1i 10.00 0.00 0.12 2.12 3.76 0.02 15.02 IN IE 4U 5.00 0.00 0.06 1.65 15.03 26qk 46 lIN 0.00 0.00 0.00 0.00 15.05 2Ckn 170 220 0.00 0.00 0.00 0.00

3.01 Av 0 5 0.OC 0.00 0.00 0.00 0.00 0.00 3.02 Avklj 5 12 0.00 0.00 0.00 0.00 3.03 2tJ 12 45 0.00 0.00 0.00 0.0 3.04 2ttjqskl 45 63 0.00 -10.00 0.00 0.00 3.05 2Btqak2 V3 107 0.00 0.00 0.00 0.00 3.06 2Ckqn 107 210 0.00 0.00 0.00 0.00

21.01 Av 0 4 0.00 0.00 0.00 0.00 2.59 0.01 21.02 IN 4 15 0.00 0.00 0.00 0.00 21.03 ik 15 33 0.00 0.00 0.00 0.00 21.04 21tjqkjbl 3 55 10.00 0.00 0.12 2.59 21.05 21tjqakbl 55 144 0.00 0.00 0.00 0.00 21.06 3sqakb2 144 lob 0.00 0.00 0.00 0.00 21.07 3Ckqn 166 2303 0.00 0.00 0.00 0.00 - E

118

RE L A N IZ AT ION (sa xi u vB • j ------

Sam;le Horizon Dec.• Color Color Normallzed A Profile oueghted s; 61 I; property thickness property ear

11.01 A 0 4 0.GO 0.00 0.0" v.oO 0.v 0.o'0 :.:A 4 15 0.oC100 0.00 uv 11.0. 2Rtj 15 42 0.00 0.(M0 0.oi 0.00 11.04 2&tqgk. 4: 90 ( ,w.0 0.00 0.00

11.06 3qs,X.00 15. i70 0.00 0.00 0.Ou

0 4 0."0 0.Oc 0.04 0.24 (..'' 12.o12 Av: 4 14 0.00 0.00 12.0: Et 14 47 0. UX, 0.0o. 47 1M5 0.00 0.00.00V (1.00 12.04 2W4 0.00 105 UOA 0.00 0.0('0 12.05 29*2 0.,00 12: 144 0.00 0.00 O. '0 0.00 12.07 Sq~b 144 200 0.00 0.0v 0.H0. 0.00 0.00 0. 0A 0. 1,0 14.01 A 0 B 0.00 28 0.00 0.00 0.00. 14.04 iv 6 0.00 54 0.00X 0.00 14.i0P 1 26 0.00 0.00 54 0.00 0.E. 14.04 29Btbkq 107 0.00 0.0': 0.00 0.00 14.05 Uk;b 1011 121 0.0o 121 0.00 0.00; 0.00 14.0. 3qs•1o 152 0..1 15; 221 0.00 0.00 0.00 14.0' 4EqNk2: 0.00 I1.09 4Pv:b 6q..' 230 0.00 0.00 161 0. N. 0.12 0.94 4.04 0.03 20.01 A,1 0 0.00 0.10 0.00 2C.0202 A* B 0.00 0.00 0.00 0.00 20.0Crw 19 42 0.00 0.02 0.00 2.5i 20.04 iMtjq 42 64 10.00 0.00 0.00 1.41 2(1.05 2Btjq0 1 64 76 0.00 0.00 0.00 26.06 2Stjqk2-1 76 114 0.00 0.00 0.00 0.00 20.07 2tjqk2-2 114 152 0.00 0.00 152 190 0.00 0.00 20.0i 21tjqk-.3 0.00 10.00 0.00 0.00 2.41 0.01 0 0.00 0.12 S.0.1 ON 0.00 0.00 1.7. 5 20 0.0( 20 45 50.00 0.00 0.00 0.00 0.4e 45 56 0.00. 5.04 2ktb 0.00 0.00 0.00 5.05 2Btqskb 56 106 0.00 0.00 0. 00 5.06 2ftqb 10l 164 0.00 0.00 0.00 0.00 5.07 2Cqn 164 263 119

SOIL PROFILE INDEX VALUES KELANIZATION (aaxeuu:85I ------I Sam;v!e Hora.on Depth Color Color Norailized X Profile keighted Ica) 11 #2 property thickness property seav ------o------o------eo-- ~ • -- •*- •- 19.01 Av 0 0.0i 0.00 0.00 0.Of, 01.o:0 . 18.02 A 11 3 0.00 0.00 0.00 0.6c 18.03 It 33 40 0.00( .00 0.00 0.0c 19.04 2t0tqj 4. 66 0.00 0.0(( 0.00 0.01) 1.05 2ttqo 6 1aM 0.01 0.00 u.i,.O.v 18.06 3Ko 12;? 16ck 0.00 0.00 0.00 0.00

e.01 Av 0 9 0.00 0.00 0.00 2.92 0.01 0o.(1 6.0,2 st 9 21 0.00 0.00 0.24 2.92 0•.00C'.00 I.03 21tz 21 35 0.00 0.00 0.00 0.00 6.04 2kqm 35 68 0.00 0.00 0.00 0.00 8.05 2t b6 100 0.00 0.00 0.00 0.00 6.05 2Ck 10(, 210 0.00 0.09 0.00

13 0.00 0.24 3.06 5.54 0.47 16.01 Av 0 20.000.00I 16.02 sw 13 30 5.00 0.00 0.0O 1.00 1c.03 It 3, 4. 0O.0. 0.00 0.12 1.53 59 16.i4 20tW 43 0.00 0. 00. 0.00 0.00 Ht.05 2iq 56 100 0.00 0.00 0.00 0.00 It.06 21qa indc10,, 150 (.01) 0.00 0.00 0.00 16.07 20qt 10( 150 0.00 0.00 0.00 0.00 16.06 2Cvqn 15M 207 0.00 0.00 0.00 0.00 1.01A 0 10 0.00 0.0W 0.00 4.53 0.02 0.00 0.68 1.02 It 10 25 10.00 0.00 0.06 1.03 21tqM1 25 42 10.00 0.00 0.12 2.00 1.0421tW2 42 56 0.00 0.00 0.12 1.65 1.08 3•qstl 5o 70 0.00 0.00 0.00 '.00 1.09 4Kq.b2 70 115 0.00 0.00 0.00 0.vO 1.10 50k 115 167 0.00 0.00 0.00 0.00 1.11 5Cnk 167 195 0.00 0.00 0.00 0.00 1.12 5Cn 195 290 0.00 0.00 0.00

19.01 A,! 0 4 0.00 0.06 0.24 0.24 0.0- 0.'0 0.0, Av2 4 9 0.00 0.00 0.00 19.07 sk 9 13 0.00 0.00 19.44 6v 13 17 0.00 0.0( 0.0i 0.00 1q.05 Itqm 17 29 0.00 0.00 0.00 0.00 19.0t 2ktqs 29 47 0.00 0.00 0.00, 0.00 19.07 2kqzl 47 72 0.00 0.00 0.00 19.08 2kq&2 72 15') 0.00 0.00 0.0(1 120

"R.,. ';,:FIEINDEX VALUES flEL~hI!A•TION tsa..:muas9•, ...... , Sa:le moriZon Depth Color Color Norealized I Proiile keightec II I propertv thickness property sear

6.01 Av 0 l..OC 0.cuc, 0.12 u.71 0.71 0.;. 6.02 it 6 1(5 0.0W 0.(I 0.0'1 0. ,c, 6. 04 2.qA I e -& 0.u0 -4C.(,,0 0.0v 0 .I".* 6.04 •eq 52 101 0.0( 0.00A 0.0J 0.0, 6.05 3 lot.I0S: 0.0. 0.(1;.C, ..

2.01 A 0 3 0.0K 0.00 0.(, 0.0." 5.89 0.( 2.02 A 3 10 5.00 0.00 0.0C-2 0.41 2.0: Bv 10 19 15.00 0.0M 0.18 1.5i 2.04 2Uqa 11 34 I0.;10 0. (,, 0.12 1.76 2.05 2Bt;v N4 70 5.0( 0.(.0 0.0. 2.12 2.07 ftq% 1. 5 Q. ý1 0.000. 0.0 0.0c. *.0.0 q 52 114 0.00 0(. 00 0.00 0.0, :.0; 11 114 107 0. O, 0.vuC 0.CI 0.00

2&.(,I AY 0 10 0.0'. 0 .04 0.00 0.00 0.bA 0.R0 2:'. 8. 10)41 5.OC O.0 0.06 0.65 2.2 . 21 ;2 0.R00 0.00 0.00 0.00 2..04 Pm b 9. 0,e. 0.00 0.0, 0.00 2V.05 Dh 9 1R4 M.10 0.00 0.00 0.,, 121

vAI:.1. COLOA-FALINS isix'umab.), ------* Color Color Noruailzed I Profile keiqptea Ice i# 1: property t•tcineis proverty meHI

Fm--: . 0.000 0.01

(I.it 0. '0h 0.0w 0.0'X

7.¢2 ;, 0 1.5 u.00 R.)0 o.'o o.oo 2 1i o.00o .O 0.00 .: o .oo 7. 0 2CPo 0.00 0.00 4. 15. 0.00 0.00 0.A' 0.0('. 9 0 ('.00 0. N, 4.C.: iii 0.i") Q 0.00 V.vO 0. ('.00 0. Of 4.04 2kn 6(' 100

17.0. A 0 t 0.y:' 0.00 "6.00 0.00 0. N0 0. V, 6 0.00 0.00 17.;: ew 24 0.00 0.0') 1". k: 1~.C

0 C.(- " 0.00 0.0,01 1v.93 v.09 13.0! A 0.00 O.N.0.00 9 21 0.00 0.00 0.00 21 73 V.O 0.00 139 0.17 10.93 U.04 2C•qn 73 0.00 0.00 0.00 0.00 O.O0 0.00 15.01 A 0 19 0.00 Is 46 0.00 (1.000.00 0.00 0.00 0.00 0.0t. 0.00 41 170 0.00'0.00 0.00 0.00 15.05 2Ckn 170 220 0.00 0.42 0.42 0.06 3.,.1 •. 0 5 5.600 5 12 0.0•) 0.00 0.00 0.00 0.00 0.00 3.(3 21tkj 12 45 0.OC., 0.00 0.00 0.00 3.04 29tjqeil 45 93 0.0 0.0. 0.00 3.05 2ftjqtF 83 1(.7 0.00 0.CO 0.00 :.06 2tkqn 10 210 0.00 0.00 0.00 0.00 0.00 21.01 Av 0 4 0.00 0.0K 0.00 0.00 21.02 1. 4 15 0.00 0.00 0.00 21.03 Ik 15 33 0.00 0.00( 0.00 0.00 21.04 21tjqijbl 33 55 0.00 0.00 0.00 0.00 0.00 21.05 2Btjqmkbl 55 144 0.00 0.00 0.00 21.06 3Hqit.2 144 186 0.00 0.00 99Q .00 0.00 21.07 3Ctqn 166 233 122

SEL FFO:,i.E INDEA 'JAL'E"' COLOR-PKLINE ------...... --- Sm,:ie t'or-:Wr. Depth Color Color t:rslll-:@ I Prohie eIlghted (W !1 1'.:pro;erty thIcIness property meLn 0.,C o.o': 11.0!i. 0 4 0.00 O.v 0.V. .Ov 11.0.CA 4 15 0.00 0.0, 0.00 0. 1.&: it: 15 4. ,.oo o.oo u.o' o.oc" 11M. :i•,q 42 90150 0.0. 0.,,• u.0 o.':'

11.06 340.qb 1•( 170 0. .00.,O O. 0.N 0.0 16.01 Adi 0 4 0.00 ('.- ' 00 .0, . O. 0.00 12.c2 Avb 4 14 0.')( c.Oo 0.oil 0.00 (I.: Et 14 4. o. v'.' 0.00 0.0" 0.00 12.04 2Ri1 47 105 0.ut- o. C,.' 0.,00 12.05 21k2: 12" 0.00 0).00 0.00 0.0" 12.c 23tqrni 12: 144 0.,0 0. 0.00 0.00 12.,7 5q0b 144 2 909..0 0.00 0.00 0. .•: 0.0N. 0.00 14.0! A , 9 0,00 O.O, 0.06 0.00 14.02E w e 2, 0.0,0 0.(c,0 (,..0 0.oil 0.00( 14. -0j! 29 5. 0.0(, .u.('. 0.0c, 14.04 2ktji. 54 IF7 0.In. 0.O0 0.0(' 0.0', 14.05 U3 t 107 121 ,.0. 0.00 0.0o, 0.0N. 14.06 •SIrlb 121 15 0.21( 0 0.0c 0.00 0.00 14.07 4?9;P: 15t 221 0.0c 0.,00 0.00 0.00 14.01 403D 221 210 0.0(, 0.00 0.00 (.00 0.00 . 20.0 Avl 0 6 0.00 0.00 0.00 0.00 20.02 Av2 6 19 0.00 0.00 0.00 0.00 20.'03 I3 1' 42 0.0cc 0.00 0.00 0.00 0.00 20.04 2btjq 42, 4 0.00 0.00 0.00 20.05 2Bt.q'l 6, 76 0.00 0.(, 0.00 0.00 20.06 2Ut:#q2-1 7b 114 0.00 0.00 0.00 0.00 2,.7 25tjq0I2-2 114 152 0.00 0.00 0.00 0.00 20.0E 2Etjqk".-! 152 1•0 0.00. 0.0i 0.00 0.00 0.08 5.01 A 0 5 0.00 0.00 0.00 0.0(, 20.67 S.0 it 5 20 0.0 O.0 0.010 0.00 5.0,: f 20 45 10.00 0.0. 0.17 4.17 .O. 5.04 2?tt 45 56 0.00 0.0O 0.0 C 5.05 2Btq§Vb 56 106 0.00 0.00 0.00 0.00 5.06 2t.qo 1oe 164 0.00 0.0( 0.00 0.00 5.07 2Cqn 164 26 10.00 0.00 0.17 16.50 -I

123

E3%* PCR1LE INOE' YALUE5 COLOR-FALING (maxiAuU'60 ------. Nelghted Ccior Color Norialized X Profile actr l! 1 property tN.ciness property mcan

0.00 0.0(' !e.oi •A 0 11 0.(I 0.00 0.00 0.0'1 16.02 A 11 3• •0. 0.00 0.O0 O.0(1 0.00 0.• 18.0i t 31 40 0.00 M10 0.00 0.0N 6.O" 26te2 4" 66 0.00 0 -1;. 0.0c o.v,. 16. •5 4?qk ba 1N 0.0. 0.•0 0,I0 0 It.Ob 1PL 120. O1 999.00 0.00

8.0! A, 0 q 0.00 O.U0 0.00 0.0C 0.00 0.00 21 O.C.0 0.00 8.02 6t1 9 0.00 0.00 35 0.00 0.00 0.:; 2it: 21 0.00 0.00 6b 0.0(, 0.00 9.04 2bqt 35 0.00 0.00 6E too 0.00 6.05 20 10 0.00 0.00 0.00 9.05 2Ck 10N 0.00 0.00 0.00 16.01 Av 0 0.00 0.00 30 0.00 16.02 IN 1w 0.00 0.O0 0.00 42 16.0: it 10 0.0( 0.00 0.17 0.00 43 59 0.00 0.00 16.04 26;1 '07 0.0(0.00 0.000.0". lb.05 DI 5E 0.00 0.00 0.00 10.06 28qt 'nc! 1L"0150 0.00 0.00 ib.07 21q1 100 0.O0o0.00 0.00 150 0.0c 0.00 1o.O8 2Cfrq t150 207 0.(10 0.00 0.00 1.C? 10700 10.0('0 0 0.00 0.07 0.00 3a.3 L0.13 1.01 A 10 25 0.00 1.02 it 0.00 0.00 0.0 42 0.00 1.03 28tq0l 25 0.00 0.00 0.0K 42 56 0.00 1.04 20tqb2 0.00 0.00 0. 00 70 0.00 1.06 3vqebl 56 0.00 70 115 999.00 0.00 1.09 4Kqab• 40.00 34.07 115 S107 0.00 1.10 58k 0.00 0.00 0.00 1.11 5Unk 167 0.00 0.170.00 0.00 290 0.00 1.12 5en 195 0.00 0.17 0.07 1.50 0.00 4 10.00 19.01 Art 0 0.00 0.00 0.67 1~4 9 10.00 kv2 0.00 0.00 9 13 19.0~ 11 0.00 (0.00 0.00 0.00 0.00 0.00 0.00 19.c~i IN 1:' 29 0:00 0.00 19.05 Itqq 0.00 0.00 0.00 29 47 0.00 10.06 2t.tqm 0.00 0.0v 0.00 72 0.00 19.07 2kq1m 47 0.0( 0.00 7 150 0.00 0.00 19.06 24q12 2 124

COLOR-PALIN6 (11xisl.:b(I------I Profile me~g!ted sam:1! Hor1:Of UFO Colr Color moraaliz@i "in its' 116 propertv thi~kness propertfy

. C'.Q C". ;1 21 105, 0. 01* 0.OC 125

Ei"' RUILE !NOEJ VLUES COLOF-L06HTENINE Imiximum,:9------...... -- Siamle Hor::on Depth Cclor Color worfalaued A Profile weigbttd (eli |1 Ci property thickness propert mean p; Fu---l------0.------0---0 ------0. 0' 0.0" 0.0l, 0.00 FkA-2 0.k0(, 0. 0 0.00: 0.00 0. 0.1: 0.00' FWA-4 0.0C' 0. 00 yk;-% .CO'. C..0'.O.Oil O.o. (1.LO 0.c: 0.0 0.0.0(

7.01 A 0 1.5 C.tiu 0.13 0.19 1.2"1. 0.-1 0. 01) 0. -o© 1.0i, 7.02 Cox 2 I01e 7.03 2Ci, 18 0.0 C.'.0O Of. 0.00

4.01 A 15. Oi 0.0( 0.00 0.00 21.75 0.2: 4.002 Bkl 0.00 0.25 1.50 4. 0* 25B. 9 60 0.00 0.CO 0.25 12.75 4. 4 2Ckn 60 10', 0. (u 0.19 7.50

17.01 A 0 6 0.O0 0.0'. 0.00 27.13 0.0E 17.0" Em 624 .0" 0.19 3.3. 2Ckn 0.00 0.25 24.00 17..,03 24 120 0v.00, 0 a 0.00 O.00 0.00 11.36 v.OE 13.01 A .5.W 0.00 1.02 ti 9 21 0.00 0.0( 0.00 ,:.251 11.0'. 2Fqj 21 73 20.W50.0)(5.00: 0.00 01.06 B.l Z0xq. 13 0.00 13.04 73 100.00 .00 0.1 ' 15.01 A 0 I1 10.00 0.00 0.00 0.00 17.13 0.02 15.02 Ow 15 46 20.0.00 00 0.00 0.00 0.00 15.0: 26qk 46 170 5.00 0.00 0.06 7.75 15.05 2CKn 170 220 15.00 0.00 0.19 9.35

..01 Av 0 5 0.0(1 0.13 0.63 17.8 M.id 3.02 Rvkj 5 12 10.00 0.00, 0.1" 0.ea 30: Mkit 12 45 0.0(, 0.00 0.00 3.04 2Btjqt'l 45 83 20.0' 0.25 9. 5u 3.05 28t1 a 83 10, 20.00 0.W 0.25 6.00 S:06 2Ckqn W(7 210 0.00 0.00 0.00 0.00 10.00 0.00 6.98 0.0: 21.01 Av 0 4 0.Ov 0.13 0.50 21.02 IN 4 15 0.00 0.00 0.00 0.00 21.03 Sk 15 33 5.00 0.00 0.06 1.13 0.00 0.00 0.00 21.04 2$tjqkjbl 330"55 0.00 144 0.*00 0.00 0.00 21.05 2Btjqmktb 55 0.00 0.13 5.25 21.06 3qsqkb2 144 186 lO9.Oo 0.001 21.07 3Ckqn 186 23 0.0(0 0.00 r 126

:.ý-*0F.1iE IN.Ni VALUJES

COLOP-LAIH6N!INE (BarLIusz(il ------5ainle Huna~n Depth Color Color mo'malized I Pa~m~~~ Ice; Ii 6 property thickness property Ninn g:

U. C- A. 0 4 (14~ 0.cl0 0.0(, 0.00 3c.0 C.. 41 C1.0(1c 0.C. 0.00 0..0( 11.04 8~ 1!42 9( 0 .0 0.0Oi 0.29 IT.got'

11 .06 3P qri ISO 71704,.1% 00 O; 7.r:

0 4 0.0(t C..(lei U:e~ A.! O.N 0.0." N.44 o~ 4 14 0.0(0 0.00 0.00 14 47 0.CIO 0.06 12.0! 1h..1 47 !05 0.19 10.08 1.0i 2i8qm: 105 120 50. V. 12(! 144 0.00 0.05( 1:.,(7 iq 144 2C " 0.00 14.0! A 0.00 0.31 0 a 10.94 00 8 14.0: Big 0.00 0.00 2E 54 0.00 0.13 0.00 0.0c 14.0-A t ii 0.(0. 9.94 121 0.00 0.0 0.0DO 0.01) 14.Ot TOE-qailc is: 0.19" 0.0.* 14.07 4Ev;'in 1521 2T'.. 0.0-, 0.oo 14.06 41kjc 230 0.ov 0.00 0,.00 05.00 0.0, A.0.01 AvI 086 0.00 0.00 10. Ai A.2 0.Oki 0.0R. 0.0Ok 20.014 in 19 42 0.00 0.00 0.00. 20'.04 28±j,, 42 64 0.00 0.00 0.00. 0.00 0A0 64 76 0.00 0.00 0.00 20.07 21tjqt2 76 114 0.00 33.18 0.0'1: 10. 00 0.oil 0.00 114 1S2' 0.01, 0.00 20.00. 2tjqQ-T 10.00 0.(00 0.00 0.00 0.00 5.01 A 0.0(. 0.00 0.00" 0.63 5 20 0.0'.P 0.00 10.00 0.0NO 0.44 5.04 Not 45 Ue 0.00 0.13- 5.05 21tqoo 56 00. 0.01) 6.25 .Ot 2ttqb 106 104 50.00 25.3e 5.07 2Cqn 164 263 0.N. 0.00c - U

41

127

rr'FO..E INN,~ VA-uES COLOR-LI6STEN!N6 Iaxisue i-; ------.----- SuDl.e t$ori:on Depth Color Coior Norea!ized X Prof:i! ILeght.e ics' I' I: property thicness pro;,ert 1 iair, PP ------o ------oo ------o ------o oo------ee eoe o-eo .1.• 0 11 15.0. 0.0V 0.19 2.ue 19.4. c1. I•'" St 3• 4u C'.•(' C,.0,(: 0.)' (.00 1•.(4J ;t':l,4') 6 0(.? 0.0(1 0.Ou ¢., 16..5O IV, 12. 99. 0. ON. 0 06 1.,.5:. IE.O, •,r 120 Io0 999.,0'0 ¢,.0.',0 0.0) 0.00,

0.00 1.0? 5tI 9 .00 21 0.00 0.00 C. a.o; .st: 21 ;5 0.O 0.25 12. '.3a 8.,04 2•q 12.382.'.05.( e. 05 2. 35 68 0,00 0.36 0.69 8.;5 2C, 0.0•' 0.13 13.75 16.01 bt 55','?0.0.t 0. Oi"l 20.'1*0 0.00 0.ON Im.('2 Sw 0.00 0.01.1 0.00 0.00 it.0: it .I5 43) 10. oc. 0.00; 0.00 0.0,0 4 1e.; 2Btqý 4U 59 0. 00( 0.000.C0 0.25 3.75 U)"56 Is(, 1T 0.00 0.00 0.63 1o.06 2kq* rc)100• 15C, 0.00 1o0Q15') 9q9.00 0.,00 0.02 16. 07 25qe 0.000.00' 0.00 0.00 0.00 l6.0i ?,Crqn 150 207 0.00 0 1,H 0.00 0.00 0.00 1.01 A 0.00 0.0 0.00 4.006 0.00 1.0' it 10 25 0.00 1.03• ?Etbl 0.00 0.00 0.00 25 4 0.00 0.00 0.00 0.00 1.04 2btqb2 42 56 20.50.0000 0.00 1.0 '05 415l1 5 70 0.63 6.75 05.00 0.00 1.09 4Uqm: 70 115 50.00 0.00 0.00 1.10 511 115 167 0.00 0.13 6.50 1.11 5CKr 16' 195 20.00 0.00 0.25 7.00 1.12 5E. 195 290 20.00 0.00 0.25 23.75 47.63 0.O0 19.01 Ad 0 4 10.00 0.13 0.50 AV." 4 q 0.00 0.I1 0.630 20.00 9 13 0.00 0.25 1.00 5.00 1.04 I. 13 17 0.00 0.06 0.25 15.00 19.05 itq# 17 29 20.00 0.19 2.25 50.00 19.06 2btqe 29 47 20.00 0.44 7.88 50.00 1.07 2bqel 47 72 0.00 0.61 15.63 19.09 2kqa2 72 15s( 20.00 0.25 19.50 128

S'i:PAOFILE INDEX VALUES COLOR-L]SHTENINS (eazxteu=01 -...... Sample Horizon Depth Color Color Noralizzed I Profile veighted (Co! II 12 property thickness property near pp

------6.01 AV 0 6 0.00 0.0c. 0.00, 0.00 81.50 0.Ov 6.02 St 6 10 10.00 0.00 0.13 0.50 6.0: 20q1 10 52 30.00 20.00 0.31 13.13 b.O04 ýG 52 101 20.00 0.25 12.25 101 1i!3 40.00 0.C.6 0.50 2t.00 6.06 JCkq 15 230 10.00 0. 0 6.07 XCIq, 230 30v 999.0' 0.00 0.00

2.01 At 0 :3 10. N 0.01 0.13 0.31B 96.25 0.4P 2.02 A 3 10.0 0 0.0. 0.1: 0.69 2., By 10 0.00 0.00 0.0) 2.04 2SqeNv 19 34 0.00 0.1! BS 10.00 1. 2.05 2htazy 34 7(, 0.00 0.00 50.00C 0.01. 2.07 Ktq* 19 0.60.00 0.63 20.63 2.09 •q 50.00 52 114 0.5, 31.0( 2.09 2ý 114 1•7 0Q.00 0.50 41.50 10 40.00 22.01 Av 0 0.25 2.50 6e.O0 0.37 22.0: 5. 10 21 0. 0'. 0. 10 0.00 22.0: K 21 62 50.00 0.000.06 0.6e3 25.63 2Z.04 KP 62 194 45.00 0.00 0.5e 16.9E 2.05 bkqe 92 20. (C. 0.25 23.00 - UF

129

Total texture (eaxisue:90: ------> Sisple horn:on Depth Normalized I Proftle beighted (ca) property thickness propertv Bear pp

------o------i------o------o-- o------FN!4-1 0. 0 0.11 0.0(1 F.- 0. ,(, FmsA-4 0.00 0.(.0 0. R,) vsA-I 0.06 YN•-2 0.00 7.01 A (P 0.00 0.00 0.'40 2 18 0.00 7.02 Co) 0.01 0.00 7.03 2kox 12 0. OC. 0. % 0.50• 4.It A 0 0. P• 28.94 0.29 9 4.0(! Hl 0.22 1.*33 4.,03 23'2 9 60 0.44 22.67 100 4.04 2CKn 60 0.11 4.44

17.01 A 0 6 0.20 1.33 ,3.1.3 0. 0., 17.0: ON 6 124 0.11 2. W 17.03 CP. 24 0.00 0.00 1.O0 2. o 1.01 A 0 9 0.11 1.02 I. 9 21 1. 3 33.03 29qj 21 73 0.00 0.00 13.04 2C qn 73 138 0.00 0.000

15.01 A 0 1E 0.22 4.00 44.89 0.20 15.02 IN 1 4& 0.26 7.76 15.03 2BQk 46 170 0.22 27.56 15.05 2Ckm 170 220 0.11 5.56

3.01 Aw 0 5 0.56 2.79 34.44 0.16 3.02 Av~j 5 12 0.76 5.44 3.03 20tkJ 12 45 0.67 22.00 3.04 23ajqsk! 45 23 0.11 4.22 0.00 3.05 '3tjqak2 0.00 3.06 2Ckqn 107 210 0.0(,

21.01 Av 0 4 0.56 2.22 52.29 0.22 21.02-1. 4 15 0.44 4.96 21.0" fk 15 33 0.33 6.00 21.04 29tjqvjbl 31 55 0.44 9.79 21.05 26tjqskbl 5.5 144 0.28 24.72 21.06 3Bqskb2 144 186 0.11 4.67 21.07 3CMqv 196 23: 0.00 0.00 130

Total terturin 1s&?imug:Qw ------Sn,;1e horimo Depth~ NC'rma'.1ze I Profile Ne-;'nted (cs) ;'oper'.y th,-krness propert, *uan ;;

11. N AV 0 4 M:~ 1.I: 4.8; (1.3 E 110. 4 15 C1.44 4.6; II.P: 26tl 15 421 0.44 2 11.04 ?6;t;mi 421q( 0.'., 2b~J

12. 01 A.-I 4 I.3 1. 7 56.67 O.! AU4 14 1:.;.Ba 14 47 (-.56 t I . C-4 291 4? 105 (..&4 M5.-'e 12.05 ;by.' 1N! 12(- .11 1.6*7 12 .6F, ' 120,144 0.11 .0

14.0! A 0 B .: 2.67 BE.;.. 14.0 is P 2S, (0.T 7.71 14.0: e' 26 54 (.44 1.5 14.C,4 2fti~q 54 10 (-.44 2: .!*

14.06 3Eqmmtlb 121 1Z (1.22, 6s 14.07 4q-iqsb 152 1 0.44 1'* 1L.CE ff6j 221 2'0N 0.22 2.A",

20.1 v10 011 CAS~ 51.69 0.'47 2M1.0 AV,. a 19 0.22 2.44 2. m19 42 0.3' 7.67 20. '.4 Ztjq- 42 64 0.31" 7.T33 20.C1 29tjqt.1 64 h~ 0.33J 4.00 20.06 2tq -1 76 114 0.22 e.44 2C,.07 2100'21-2 114 152 0.1): 12.67 20.05 ?6tjqk2-19 152 194 0.22 e.44

9.01 4 0 5 -0'.22 -1.11 10.3 0.04 5.0? ek. 5 2-- -0.21 -. 2.*0,545 0.00 (1.Oil 5.04 26?tb 45 56 0.?? 1.6 7 5.05 2Ftqmib 56 1-6 (-.22 11.11 5.06 2ttqb 160 i64 ('.00 0.09' 5.07 2Cqn 1W 2t: 0.00 0MM, - m -'01F 131

Total teoture (axifulU9O -...... oam:le ýori:on Depth NWrmail:ed I Proiile ke:q9ted Ira" prope-ty Uticknuss property mean pp ------0.33 3.67 is..21 0).11 18.(,1 AV II 1.22 1M. C A 4,0 0.22 1.56 V., 0.22 5.-6 12'3 C,..!I 6.0', 1e. •.152E :i 12{0 I ') 0,00 0.0'.( Is.' :,t

9.01A v 0 9 0.44 4.00 (. I: stl 9 21 1.00 6.C'2 3.11 6.03 2fi2 21 35 0.22 35 cE 0.11 •.7 .042I qs 3.56 0. 11 10012• 8.05 2.1 0.00 74.99 6.24 1•.01 Av 0 13 0.:3 4. 3 5.b7 16.0,2 Sw C.3 4.3 16.03 Pt 30 4. 0.01 4•58 16. 0.42ltqF 0.44 16.05 2V 59 01) 0.22 1U.06 2tqa Inc) H-(, 15.: "II P•0",F;lP 0.22 15'?20• 0.11 1.0' 21•C 95.11 0.33 0 10 0.22 2.22 1.01 A 0.22 L.33 1.02 i t 25 42 17.00 1.04 21tq 1.00 14.00 1.04 2Itqt 2 42 56 50 70 0.33 4.67 15.00 : 70 115 0.22 115 167 11.56 1.10 5h~ 0.22 '.22 16' 0~5 1.161 5Cr:, 0.22 21.11 I.1.2 5n 195 290 1.33 0 4 0.22 61.69 19.CI9.OE I AV2t, 1 qh 2.22 49 0.4 AV2 1.3 9 1: 0.3! 13 17 1.33 19.04 9. 0.3U 17 P9 6.6" 19.0OF btqs 0.:1 6.00 2M.tq 9 29 47 19. Ot 0.33 10.07 ! 47 72 20.qv 0.44 34.07 19.0OE 2ý.qa2 72 150 El

132

Total tu~ture Ismuaxxu90 ------Sar,!e Hapinor Depth Norealiled I Profile Veiq~ted ice) property thickness property sea' ;c ------NiA . 2.00 1".5c C..A b~:Bt 6t 0.5t 2.22

R.03kQ4 .92 !1C, 0.00 A.0,

b.07 "A 23'IC. 1:~ 0.00y

2.0: A, 0 0.44 1.313 79.8! (,.41 2.2 310 0.44 3.11 2.C4:6 101C. 0.56 5.00c 2.04 N9avv 195 . .67 2.10852etqe 34 70 O.J. 14.00 2.07')Itqa 19 52 0.5t 19.3 2.08 Kq N2114 0.411 13.78 2.09 2r. 114 157 0.2!: 19.44

22.01 A4 0 10 0.50 5.5~ 6 .1 03 2:. E"9 10 'il 0.89 9.E 2..:121. 62 .0.3 1W. 67 220a 62 92 C.2. b.6. 122.5D 92114 o..2. 20.44 133

STRu7TURE ii~lu=:, .dIape Mlori=-r. Depth Nortalized i Profile hu1gete. fca* propert-f thickness property mea

Fm-A, 0.0,) F6o- 4 O ,, O yoW ;' 0. .m, 0. (i. YRA-: C'.I

7.0! A '01.5 0.2.5 0.E 0." E 0.0:0 7.02 CoC 2 16 0.Q0. 0.00 7.0: 2CDOI 0. 01, €0.C.', 0' A.)I A 0.50, 1.50 39.50 0.34 3.0W 4.02 OkI 39 0.50 4.Q 2•F2 9 6(' 0.67 34.00 4.04 26C, 6') 1IvO 0..00

0 6 17.0, A 0.42 2.5':' 5.50 0.05 17.. B-ZD 6 24 0.17 0.004. Ov' 24 12C 0.0V 0.00 ITO.C.I A 13.0;! A 09 10.00 0.07 13.02 Bi i 21 0. 3, 1IT0 :5q, 21 7 0.SO 13.04 2ckqr 0.0S 0.00 15.01 A 0 1I 0.50 9.003.33 23.00 0.10 15.02 IN 18. 46 0.50 14.005.50 15.0: 2Bqk 46 17(, 0.00 0.00 15.05 2rfrn 0.00 170 220 0.000. O0

3.01 Av 05 0.67 12.33 0.06 3.02 Avkj 5 12 3.03 26trj 12 45 0.17 5.50 3.04 21tjamkl 45 83 0.00 0. (,v 3.05 2btjqak2 63 107 0.0• 3.06 2Ckqn 107 210 0.00 0.00

21.01 Av 0 4 0.67 2. s7 20.08 0.09 21.02 IN 4 15 6.5H 6.420.00 21.03 Sk 15 33 0.00 0.00 21.04 29tjqkibl 3: 55 0.50 11.00 21.05 2Btjqtkbl 55 144 0.00 0.00 21.06 31qakb2 144 186 0.00 0.00 21.07 3Ckqn 186 233 0.00 0.0(0 toNI

134

STPUTUFE (8axlmuu:60o Sample Ncri:om Depth horalih:ed I Profile keipted !cm! property thickness property lean

------N------11.01 A, 0 4 0.83 32.50 0.19 4 15 11.04 2Et:s 15 42 0.50 13. 50 0.25 12.0,'. 49(0 I%I2U17V 1I(. 0.00 0.001 (,.,i,$. 0.0 0 4 "1. ee.67 0.44 4 14 0.5E 12.0: at 14 47 0.67 22.0. 12.04 2pl1 47 IC'5 120 43.50 12.06 28tqx'2 105 0.00 0.0j 120 144 0.47 16.00 12.07 1q0b 144 208: 0.00 0.00o

14.01 A 0.4 40.33 0.18 14.02 2. 8 28 2.67 14. 03' 29k Ua 54 0.5c. 14.04 Zt~kq 54 10I 0.00 0. •5 0.5," 14.05 *bj0 107 121 0.33 14.Ot 31qsklb 121 152 14.07 42qs 2t 1s: •: 0.0•, 0.00 14.08 4*ijo 221 2310 0.00 0.00 4.00 20.01 AvI (.8 0.07 2.67 32.93 0.17 20.0?2Av2 * 19 20.03 O. 7.17 19 42 0.50 11.50 20.04 2tjq 42 64 0.V3 7.33 20.05 26tjqrl 64 76 0. 4:3 4.00, 20.06 2ttjqk2-I 76 114 0.00 0.00 20.07 25tjqk2-2 114 152 0.00 20.08 29tjqk2-3 152 1I0 0.00 0.00

5.01 A 0 5 0.42 2.09 33.09 0.13 5.02 O. 5 20 0.37 5.00 5.07 at 20 45 0.17 4.17 5.04 29th 45 5S 0.67 7.33 5.05 2f1tqk•b 56 10• 0.00 0.00 5.06 2Ktqb 106 164 0.25 14.50 5.07 2Cqn 164 263 0.,00 0.Ot, K I 135

I STRUCTURE (SaxieusP60) Saa;!e HA'ron Depth Koraill:ed 1 Prof:il belghted (COl property thickness property lein ------18.01 A 0 1I 9.71 34.46 0.22 j 0.00 0.0'. II 18.0• Bt 40 0.5e 4.09 I 40 21.6? 60 0.67 IN• 0. (0 0.0) I 12' 0. 711 0.C-0' 9.01 A• 09 0.67 6.00 93.25 0.4('. 9.0: 8tl 9 21 11.00 8.04 2Mt2 21 35 9.33 6.04 2Kqm 35 bi N0.25 (.9: 6.05 2r 26.67 0.00 8.05 2Ck 100 21 0.75 0.000.25 4.33 43.50 3.63_ 16.01 4v 0 13 0.0C. 16.0: 1. 13 30 ('.33 5.67 lo.0• 8t 30 43 0.75 9.75 lo.04 26tqv 43 5e 0.'5 11.25 10') 0.00 0.00 1o.05 2Fq 59 0.00 t5u v.25 16.0. 21qs 1nci 10K 12.50 0.00 i 16.07 2iqm 100 150 O.0C' 0.0v i 16.O9 2Ck're 150 0.00 10 3.33 3o.92 0.13 1.CH A 10 f 1.02 It 25 0.50 8.75 0.50 1.03 2Btqbl 25 42 8.5C 42 56 0.50 7.00 1.04 22tqt2 0.(,( 1.08 3Kqabl 56 70 0.67 9.33 115 0.00 1.09 4kqen2 70 0.00 0.00 1.10 5Wk 115 167 0.00 1.11 5Cnt 167 15 0.25, 1.12 Con 195 290 0.00 0.00 0.67 0 4 2.67 46.92 0.0Q 4 9 0.b7 3.33 lq.C119.C.3 A.1All 1.3 9 13 0.•3 0.59 1q. 04 IN 13 17 2.33 0.93 19.05 BtqG 17 29 1.17 19.06 2KtqS 29 47 21.00 47 72 0.25 6.25 19.0e 2Kql. 7"215') 0.00 0.00 136

STRUCTUPE (agj*j:2usi= Saispie Sor::cs Depth Noreisaeo I Prof:le Meighted lcel property thickness property ieip

6.01 Av 0 6 0.67 4.00 41.00 0.00 6.0'& Bt 6 10 0.5c 2.L b.03 2qrt 1W 52 (1.83 3,1.00 6.04 `0,g; 52 1(1 0.00 0.04 6.05 7*q 10! 153 0.00 0.0'. 6.0 CZq 153 2:0 0.00 0.00, 6. ?73c..+ 23v.';., o. .. ,

2.01 Av 0 3 0.67 2.00 1230.17 0.63 2.02 A 3 10 0.33 2.33 2.03 by 10 19 0.5; 4.56 2.04 2Sqavy H 34 0.8. 1-..5 2.05 2Stqmy 34 70 0.92 3!.0 2.07 t.tqs 19 52 0.83 27.5(! M2.E 552 114 0.67 41.330 2.05 2K 114 1;7 0.0c C.00

22.01 Av 0 10 0.75 7.50 71.00 0.3. 20'.02 10 21 0.50 5.50 22.,03 I, 21 62 0.67 27.: 22.04 Ka 62 92 0.00 0.00 22. 05 lrqm 92 184 0.33 30.67 137

DRV CONSISTENCE (aaxzmus-:I0) ------Sample Horizon Depth Normalined X Proille weighted ([cm property thickness property sean pp

Fw•-1 0.00 0.00 0.(10 0.00 Fký-3 0.00 0.0oil FA-4 0. 0(; 0.00

0.('0 C.00 v.00 0. 0ý

7.01 A 01.5 0.10 0.15 0.15 0.00 7.02 Cox 2 18 0.00 0.0. 7.03 2Ckox 0.00 0.Ok

4.01 A 0 3 0.10 0.30 11.70 0.12 4.0' Bkl 3 9 0.20 1.20 4.0 2b.2 9 60 0.20 4.04 2Ckn 60 I0V 0. V. 0.00

17.01 A 0 6 0.10 0.60 2.40 0.02 17.02 IN 6 24 0.10 1.8V, 17.03 2Ck. 24 120 0.00 0.00 0 9 13.01 A 0.10 0.90 ).30 0.05 13.C2 iN 9 21 0.10 1.20 13.03 2kqn 21 73 0.10 5.20 13.04 ?Ckqn 73 138 0.00 0.00

15.01 A 0 le .0.10 5.80 35.80 0.16 15.02 ew 18 46 0.15 4.20 15.03 23qk 46 170 0.20 24.K. 15.05 2CXn 170 220 0.10 5.00

3.01 Av 0 5 0.15 0.75 27.35 0.1I 3.02 Avkj 5 12 0.20 1.40 3.0. 28t" j 12 45 0.20 6.60 3.04 21tjqmal 45 83 0.30 11.0 3.05 21tjqmi2 83 107 0.30 7.20 3.06 2Ckqn 107 210 0.00 0.00 0 21.01 Av 4 0.15 0.60 83.75 0.36 21.02 Iw 4 15 0.20 2.20 21.03 3k 15 33 0.10 1.80 21.04 2Btjqkjbl 33 55 0.30 6.60 21.05 28tjqskbl 55 144 0.50 44.50 21.06 3RqMkb2 144 186 0.50 21.00 21.07 3Ckqni 166 233 0.15 7. 5 138

Dfi CONSISTENCE (saxieualo1) ------Sasple HMcm:or Depth Norailized I Profile Weighted (cs) property th:ckness property mean pp ------11.01 4A 0 4 0.10 0.40 37.60 0.22 11.0: A 4 15 0.10 1.10 11.03 2?tj 15 42 0.30 9.10 11.04 2Btamk 42 90 0.50 24.00 11.05 2E; 90 15 0.00 0.0( 11.06 3Kqmgb W5.170 0.20 4.00

12.01 Avl 0 4 0.10 0.40 36.00 0.19 12.02 Av2 4 14 0.10 1.00 12.03 It 14 47 0.20 6.60 12.04 2Bkl 47 105 0.25 14. 5 12.05 29Y: 105 120 0.I0 1.50 12.06 26tqgtb 12N 144 0.50 12.00 12.07 Bqkb 144 2'00 0.00 0.00

14.01 A C!8 0.10 0.80 512.00 0.2. 14.02 li e 2E 0.10 2.00 14.02 2Bk 2a 54 0.10 2.6K 14.04 22,tkq 54 107 (,. ,.J 0.00 14.05 "Optj 107 121 0.2,15 14.-A 3fqailb 121 152 0.50 15.5'" 14.07 4*qm2b 152 221 0.40 27.60 14.0H 4hjb .221 21( 0.00 0.0(1 20.01 Al 0 19e 0.10 22.4c 0.12 20.02 Av2 6 0.10 1.10 20.01 BD 19 42 0.10 2.30 20.04 2Btjq 42 64 0.20 4.40 20.05 2BtJqkl 64 76 0.20 2.46 20.06 2Btjqt2-1 76 114 0.10 3.80 21.07 26tjqk2-2 114 152 0.10 3.60 20.09 2ktjqk2-3 ISN 190 0.10

5.01 A 0 5 0.00 0.0(i 3. .15I 0.15 !.02 60 5 26 0.05 0.75 5.03 Sk 21 45 0.1,. 2.50 5.04 2Mtb 45 56 0.30 3.30 5.05 2atqaob 56 U15 0.40 20.00 5.06 21tqb 106 184 0.20 11.60 5.07 2Cqn 164 203 0.0c. 0.00

i 139

DRf CONSISTENCE (oaxisuatlOOi ------Saiple Horn:on Depth NoWaIized I Profile Neighted icmO property thickness property mean pp -e-----l----t------e-----lt--i------18.0k A1 0 11 0.10 1.10 45.90 0.29 16.0iA 34 0.00 0.00 18.0" et T" 40 0.10 0.70 18.04 2ftqI• 4C 66 0.30 7.8i .05 2Etc 66 121 0.:0 16.20 1 5.06n 120 Iv', 0.50 20.60

8.01 Av 0 9 0.10 0. 90 0.14 8.02 0t1 9 2! 0.00 8.07 2?t: 21 35 0.40 8.04 2bq& 0.40 66 8.05 2F 21(, 0.10 9.60 60A5 2M 10(, 0.00 0.00

1c.0l Av 0 0.00 0.00 62.2i 5.18 lb.02 0: 1' 30 A.00 0.00 43 43 0.01) 0.00 Ib.04 :EtI 5; (4.0 21.00 16.05 :ýq 5.50 1.,07 26g Inc) 10O 150 0. 5 17.50 100 150 (I.UP 15.00 207 0.10 5.70

1.01, A 0 10 0.00 0.00 31.20 0.11 1.02 Pt 10 25 0.00 0.00 1.0 2etqbl 25 42 0.20 42 2.60 1.04 28tqo' 56 0.20 7.00 1.09 4kqml2 56 70 0.50 7.00 70 115 0.40 0.00 5b 1.10 115 167 0.00 0.00 1.11 5Cnm 167 195 0.0c• 0.00 1.12 5cq 195 290 0.00 0.00 19.01 Avi 0 4 0.00 57.20 0.00 Av2 4 9 0.20 1.00 9 13 0.0c. 0. 0 19.04 O. 13 17 0.00 0.00 19.05 *tqt 17 29 0.50 6.00 19.06 2ktqe 29 47 0.50 5.00 19.07 2pqtl 47 72 0.40 10.00 19.0i 2kqU2 72 156 0.40 31.20 140

DRV CONSISTENCE (sixisurna10Ci ---- am~ie Horizon Depth Korulhned I Profile weigIh.ea (Cal property th,.,.Vnss property mean p; ------a.01 AV 0 6 99.00 0.00 2.0 00 b.02 a91 6 10 999.00 .V 6.0! A2~ 10 5A 5iz. 0'. 0.01 0.ý4 3ým4 5: 101 0.5c. 24.5:; b.05 itq 10 1 M5 0.10 e..ý 6.0o6 1 5i4s 2301 0.00 0.00 6.07 3CK;4 2030. 0.:: 0.oil

2.01 Aw 0 0~01.110 70.30 0.7c, 2.:~3 10 0. (0v 0.c0 2. o1 19 0.0v 0.0k0 2.04 9,qewv 1; 34 A.4* 6.00 A.05 26tqsy 34 h~ 0.40 14.40 2.07 ktqui !q 52 0.50 16i.5O 2.05 Vq 52 114 0.40 614.6", 2.0; B~. 114 0j7 0. V. 9.31%

22L.01 Av 0 H, 0.5 (5.50 64M7 0. ''5 r'.2 S 10 21 0. 1i 22.0(," 21 62 0. 5% 20.50j 22.04 t'.m b; 92 0.50 I5.0 2205 0kq2 9194M 0. ý0 27.o( 141

AO!ST CONSISTENCE (Laxisual1OO! -----) £ar;le Hori:on Depth Normali:ed A Profle keighted ice! I property thi:kness propertY HAP P;

99i. CIO 0. Vo 9?5.00 0.00 0.00 FIA-4 99;. 00 0.00 .co

o.0. 0.ot:* 7.01 A 0 1.5 0.00 19 7.02 Cox 2 0.0 7.0: '4kC 18 100

0 T 0.00 0.00 0.00 4.01 A SO0 0.00 4.02 Eui 0.00 999.00 0.00 4.0 2U2 999.00 0.00 4.04 21Cn bO 100

17.01 A 0 6 0.00 O.R. 0.09 6 24 999.00 0.C0( 0.00 17.• 2t 24 1N 999.00 6.00 0. 00 13.01 A 0 9 999.00 0.00 0.0W 17..C.2 1% 9 21 99.00 :1 73 999.00 0.00 999.00 0.00 13M.4 2ckqn 73 139 9100 0.00 0.00 0.00 15.01 A 0 1e 59i.00 0.00 15.02 5. 19 4a 999.00 0.00 15.03 28qk 4t 170 999.00 0.00 15.05 2C~n 170 220 999.00 0.00 0.00 0.00 3.01 Av 0 5 999.00 0.00 3.02 Avtj 5 12 45 999.00 0.00 0.00 3.04 29t~qmkl 45 9. 999.00 3.05 2EtJqaI2 83 107 99q.O0 0.0's 101 0.00 Z.06 2Ckqn 210 37 999.00 0.00 0.00 0.00 21.01 Av 0 4 4 999.00 0.00 21.02 I. 15 15 0.00 21.0: 9k W9.00 99,.00 0.00 21.04 2ttjqkjbl 2,'. 55 0.00 21.05 25tlqeh11 144 144 999.00 0.00 21.06 31qtkb2 166 999.00 0.00 21.07 3Ciqi 2M

I A 142

HOIST CONSISTENCE tialyikul-W)ý - --- wotnralitd I Fro4ill Wauqhted Slaapl Woinnf Depth P; !cgm. property thickness ProPertY 11an 0.00 0.00 110 ~ 0 4 999.0c. 0.00 110A415 995.0c, 0.01) Ntl 15 42 99.0 0.06 11.07 0. 11.04 2Stqk 42 911 .0(

0.(,( 0.00 0.0 12.01 Av1 4 i9990. q . " Ii:.C2 ;42 4 14 1,.;.S 14 47 9.9.; 251.1 47 105 99.0 0.00 12.04 0.011 12.05 " t2 105 120 959.011 2tmb 10144 .0. 0. 11.06 0.00i. 12.07 6q. b 144 200 9iU 00 (a.CI O.0 A 0 6(8 0. 14.01 0.5.0A 14.02, iv 9 29 0.015 2P ~ 3 54 a99;.v 14.0 .11 14.M Bl'.1q 54 107 9 00 70lit 107 1.21 99i.00 14.05 0.00 14.06 jEqav,1t 12,1152 9i.0) 0.0%, 4bqg-'D M.: ::i-1 i 14.0-7 0.00 !4.06 ARAj 26212Z ~0 0.00c 0.1A0 W9.V. 0.00 0.00 20.0 1 iq 9 999. 0-*.00 20.04 Sw 19 42 995.Q0 0.00 0.00 21tiq 42 64 999.00 20.04 0.00 28001k 64 76 995.00 20.05 0.00 2St~qk2-1 76 114 M9.00 20.06 0.0 2S-tjqk2-2 114 15: 95.0 20.07 0.(00 20.4 .St IQk2-`0 152 190 95.0 0.00 0 5 9W.00 0.v0 0.0c, 5.01 A C.0o. IN 5 20 915 -.k)( 5.02 0.K" 5.0* sL 20 45 99q.(10 2Btb 45 56 9"9.01) 0.00 5.04 0.0oi 5.0cis tqttb 56 lot, 959.00 0.00 5.06 2Ktq0 ~ 10i16 999A0 0.W 5.07 2Cqn 164 2t? 99.X. 143

mr,!ST CONSISTENCE (AMaxU6216', --- Samnie Horizon Depth horgaliled x Proi11t helghtec (Cal property thicknesS property meel.P;

0 11 994.00 0.0( 0.0oc . U.

I1E.~e. &33 6 IN 99.;Q6, 0.0'.

1.c:b 120 10 59.Mo 0.00

At 0 9 0.0( 6.01 99ý. 0C( 0.00 8.02 EtI 9 21 99q.0.C 21 305 0.0 E.04 2.qB ?3566 0.1) 0.00 8.05 16V 6a 100 0.0(. 8.05 2U~ 0.0(1 W,.0 16.01 AV 0 13li 0.00 0.00 995.(00 16.0 bt. 0.00, 4 90;.C00 It.0 2itq' 56 100 99.0c, 0.00 (I.00 qa flu Loo) 150 it. OVA2 0.00 100 ISO 9q5. 00 16.0 2Iq1 150 207 0.LK 999.00, 0 10 0.00 11. 9v 0.04 I1.01 A 999 .00 i0.W 1.024 it 10 25 25 42 995.00 0.00 1.0 ýf26ltqq1 0.00 2ftp:2 42 56 999.*00 1.04 GO' U40m1 56 70 0.20 2. 1.0i 9.0N 40qtb 70 115 0.2", 1.09 0.00 1.lH, R 115 167 0.00 167 195 0.0c. 0.00 1.11 5Cnk 0.00 1.12 ,,Cn 195 290 0.00 0.00 0.00 0.0(. 10.01 Aivi 0 4 99i.00 4 q 959. COO 0.00 ..Av2 0.00 19.0:4 sk 9 13 991.O0 0.oil 19.0 so 13 17 999.*00 17 29 99.0c 0.00 19.059 Itqa 0.00 19.06 21l.tqu 29 47 W9.00 999.00 0.0') 19.07 2Kqsl 47 72 999.00 0.00 19.06 2Lqa2 72 150 4 144 I

RO1ST CONSISTENCE (laaziaw10ID ..... Sa fiilr,:or Dmpth Normal::ud I Profile Wuighted (cu property thickness property lean P;

.1v0 6 0.20 1. 2% 2.0 0.100 it 6 10 0.20 - 0.9') b.32KQA 10 ; 94;.6C. M..0) 6.C4 "JkI.; 52 10 999. 00 0.vO 6.05 1 9i9t.~V0 0.00 6.(.zC; 5 23') i9~.00 0.00 6.0? 2 Wq 999.00v.CQ

21v0 z 99M.0 0.00 0.0i, 0.00 2.?~10 993.0c. 0.00 2.OT By 10 19 995c.0 0.00 2..42qa~ 15 34 95.O0 0.00 2.M. 21tzey 34 70 W9.00. 0.0( :.07 Ktqm 19 5d' q99.00 0.00 Me0 k.; 52 114 991.0i, 0.00 2.;b114 037 W9.00 0.0(1

2'.01 AV 0 10 99-1.CO (.000.00 0.00 0O C-E 10 21 95.0 0.A00 21 62 999. (1 0.00 2:ý.C4 ka 0.'Ks~~ 2:.05 Bkql 51 184 ii.N 0.0; I 145

I PH (&a;:zmutm'.S) ------Depth Norsainze x Profile Ueighted SjAp.e iZori:n Bean Ica) property thjckness property ------0...--- .. ------0.04 00 F -: 0.('5 G.O0 0.21 0.N o.Q10 0.19

5.:0 C.-M 7.01 A 0 1.5 o.(,5 C'..•:. 2 18 0.05 0.75 7.02 Cox 4.45 5 10' 0.oS 7. 2U.o 9.69 0.09 0.19 0.17 5.25 4.0: BkI 1.05 4.0' 28-:1 0 9 0.,:)5 4.04 2Cin 9 60 4.g3 0.04 v.13 0.79(.:' 17.01 A 6 24 0..! 24 120 17.,• 2Cvn 20.94 0.15 09 0. i3 2.95 9 21 13.02 1w 21 73 13.0C 24qj 0.10 6.e 13.04 2Cqn 7: 17FE 0.11 0 1I 0.22 23.96 15.0'1 A 5.29 46 0.19 15.02 ON i1 14.53 4U 170 0.12 15.0: 21q3 0.09 0.14 15.05 2Cirn 710 220 0.30 11.9 0.06 3.01 •v C'.do 0 125 0.09 I & 5 3.02 Avk': 12 45 0,109 3.91 V.O: :"kj 45 0.10 3."A 28:jqm14 .3107 4.47 3.05 2Stjqei2 1.77 107 210 0.02 30.06 2Ckq1% 0.05 0.01 26.75 0.11 21.01 Av 0 4 0.13 1.45 8h 4 15 21.02 15" 3 0.15 2.62 21.0T Bk 3: 55 0.13 2.89 21.04 2BtjqAjb1 55 144 3.5c, 21.05 2Stjq%'bl 0. (A 7.32 144 196 0.17 21.06 3•qikb2 0.19 B.Ba 21.07 3Ckqn 166 233 146

I

PH (11-imlU12.51 ------S11;S! Hcri: Deptft Norea11zed x Pr~iile Neighttd 'ct. property thickness property Rein~

11.733 0.;.! I 11.01 A-1 0 4 O0.27 1.10 4 Is 0.22 11.0', ?10 15 42 4? 9v 0.17 0.22 0.:, 11.0-. 73IQIa 170 0.05 12.0,. Avl 0 4 0.87 10. *11 0.05 4 14 0.223 4.3.4 14 4', 0.01 12.04 2is 1 47,105 0.17 12. ý5 28k: 105 M2 0.01 120 144 0.07 112.06'UtBq 144 2W0 0.03 1.76

14. C-1A 1.*85 11.92 0.05 14.029wI 0.23 4.6 14.03 '6.k 54 0.(5C 54107 0.0Z 1.36 14.04 B2 107 01.ý1 14.0! 148ilz~ 121 0.01 15?i 0.0 0.7z 14.08 Ovk:e 221 0.15 1.3ý

0.3 2. 42 09.6 0.10 20.01 Awl 0 19 z 20.024 Av2 0.30 3.33 0.l5 7.95 20.1 19 20.04;~ 42 0.19 4.15 20.05 2itjqkl 64 0.05 0.55 20.06 2Btjqk1-1 7o114 0.00 0.11 20.07 2Dtjqk2-2 114 152 0.01 0.43 20.0E 21tjqk2-3 152 190 0.01 0.43 0.13 5..01 A 0 5 0.12 0.59 33.07 5 20 0.19q 2.83 20 45 0.15 5.04 2ttb 41 56 0.1? 1.29 56106 0.13 6.57 5.06 2ktqb 10t W6 0.09 5.14 5.07 21.qn 164 0.13 13.01 147

Sig;lt mo,::an Depth NouiZ: A Profile Neighteo "Ca property thicvnUss property selat

16.0: AV 0 11 6.(,4 0.44 19.20 0.12 IE. 04 A It 18.o0'! itT40v 0o 0.Z

0~ 1.4* !4.69. 0.(17

0.5 5.01 A: IV 0.57. 1.74

504 14.81 1.213 25tqm 0 Nq. 30 86.06 30 1.34 1.11 4: 0.7?2& 0.15 i:i100 4.4C 10': 0.04' 150 27 0.t 34.69i 0.12 o 1 2.01 1.0! A ý v. 14 3.2el 1o 25 0.14 25 42 3.21 42 56 2.'4 1.C.4M2tq2 0.5 0.76 1.05 3kqmbl1 56 70 70 115 1.09 U.qi 2 0~. Q2 115 167 1.10 WF 0.0 3.52 1.11 5Cly 167 145 115 2W0 0.20t II, 9 0.10 0.5i 1-1.57 0..00 0 4 4 q 0.70 13 0. *2 0.18 19.C-4 Ew 17 OASG 1q.05 btqf 21 2P 47 3.3 4.('. 19.07 2Kqtl 47 72 LO: 19.08 ~q2KQ IV) 148

PH4(la:::mGus:7 )------4 aEIPII Hc:o Depth Noralin:ed k rO1le hu~ghtlc (:6. p',opurt tbclfless proptrtv stir

6.01 AV 0 6 6J, .49 24.0 . 6.02 it 0.v.10 &41

t.o" 2 ;I 0.0o.i

6.114'A0

AV .1 o.1.5 :: .

2. 2

26201t21 62 000.'

2 .5 9 ~~92 1EI 6..15 A1419

br, bridge; po~poreg, pf~pea 41ce-, clriaut CLAi FILM INDEA ------sa~ppl Horizon L.ptDEO r pa pi ci NoruFI I 1 profhig Wto ICA.,11 12 1 C'i616U 1! 2 pro thl~ck prop &*p

0 0 0 0 F-2 0 0 C, 0 0 0 C.A 0 0 0 0 0. 0(l e.': I., 0 0.0' V. C0 0 0 0 C. 0.0" 0.0.* C,0 0 0 0~

0 1.5 0 V 0 0 0 0 0.00 C'.. 2 1s 0 0 0 0.00 0.* 7.0'2~ 1e INu 0 I) 0 0 -0 4.0! A 0 0 0 C. C' 0 0.C-V w.d 70 0 0.54 0 0 0 Ii 0 0.00 60 0, *0 0 0.0c. .0e 0, 0~* 24 C,.06 0.0 14.04 270.q 7?1210 0.01. 0.clV 0 0 0 0 0 9 0 0.Wv 15.01 A 0 0 0 0 21 0 0. (,'C 7:'4 0.v.6 0 0.0c0 13.02 IN 0 C00 0 6.0c0 18 0.0 0 0 0 0.00 0 0 0.00 1S.0 "1Aqw 1e 46 0.00 4U170 0.00 0 0.06 IS.05 2-6'.n M7 0.00 (1 0 0.00 Id.01 Av 0 5 0 0 0 0 0.00 0 P0.54 0.2' 5 12 C. 0, 0 0 0.46 :.23 3.02 2691 12 45 0 70 60 0 0.69 22.8a 3.04 2itjqmk 45 0' 0 0 45 0 0 0 0 0.4a 17.54 C: 107 0 50 0 0 0 0 0 0.29 3.06 2Ck~qv'107 210 0 0 0 0 0.00, C, 0 0 0. 0 0 0 138 21 .01 Av 0 4 0 0 50 0.35 20.00 0 0 00 21.02 lot 4 15Sc. 0 0 0 0 0.K a.77 21. 09p lk 15 0 0 0 0.00 0 0 0 0.00 21.04 2ibtzqkjb1 70 0, 0.54 55 0 0 0 0 11. 21.05 21tj qitfb 1 55 144 0 0 0.00 0 0 0.00 21.06 31qmvb2 144 0 0 0.00 0 0.00 2,'.0? 3C1.qr. 196 2:31 0 0.00 -w

150

br. bridge; po,porg; pi,ped face; -I'clast CL.AY FILM I NDE------aS'ri e 4c1 ni: Dept br PC Pf cl No'aal x r~of-Im 1,i,, f(g'. 1::C 16 1#26162 16 prop ttick prop sell

1)I~94 000 0 0 0 0 0.C00 0.00 44.31 0. 2t 4 1SC 00 Q0 0 0 0O.cO*n 11.0~26t 15 4210 0 C 00 0Ov 00 1:.4It'~ 42 9( v*00)0 0.54 25.;; 11.5~ 0~ sc 0 ~0 0 0 00 0 0.31 16'4'c ~~~~ Y*17(-i~ o0 0 0 0 oo .c

0201v040 00 0 000 c'0 c'!. .) A~.: 4 14 C00 C0(- 0 C 0 C. 0.0% .0 12.0: it 14 47 0 0 0 0 (-0 0 0 0.0;) .0 12.0A B~pi 47 1f 1 0 .05'0 C. 0 0 0. 0.54 1. 12.05 2E.Z 10! 110 P 53C 0 0 0 0 0 0.54 6.(,E U.00 'Ptq b 12N 144 C C00 60 0 05-) 0.54 1-.c2 07;pt 144 :.-0C, 0 0 0 0 0 0 0.00 O.00 14.01DA 0 6 0 0 C C- 0 4 0 0 0 0.0-0 0.00 45.42 .20 1.0: iw 2,E0 c. 0000 Ow . c 1.:2kk 16 !4 f, 00 C 0 0 0.00 0.0C0E 14042tjq 54 10 C, 0 4 0.00 0.0O l 3j t 10Ir--" 0 0 C 0 5(- 0 0.!5 4.E! 14.0t 34t 1,1t- 121 152, 0 0 0 0 0 0 0 0.'1 9.54 14.0 5"6~ &` 1 C0 0 0 5')0 040 O..ei 2a.54 14.Oi 46W~o 221 2h 0 0 0 0 70 0 0 0 0.50 4.5N

I00AV! 0 0 0 0 0 0 0 0.00.;- 31.31 (.16 200i5 19 0 0 70 0 9 0 0 0 0.54 5.12 2(j.03 Ev 19 42 0 0 0 0 0 oo0 0.0,1 0.00 20.04 Nt:;q 42 64 60 0 C 0 0 0 0 0 0.42 9.31 20.05 2ttjqkU 64 7. 0 0.0 0 (.0 0 0 0.00 0.00 20.06 26tjO~-l 76 114 60 0 0 0 0 0 0 0 0.4? 16.08 N--07 FEtjqk.2-2 114 152 0 0 0 0 0 0 C, 0 ('.00 0.00 2;'.H 2Etjqr2-3 15? 191) 0 0 0 0 0 00 0 .oý! 0.00

5.1A 0 5 0 (' 0 0 0 0 0 0 0.00 0.Oi 63.42 0.24 5 24 0- -o o o to 0.0 0 S.:i. 20 45 C 0 0 0 0 0 (, 0 O.Oi 0.00 5.04 NOt 45 50 0 00 6575 0 00 0.65 7.19 5.05 21tqtka 56 106 70 0 0 0 0 0 0 0 0.50 25.00 5.06 2I~tqb 10. 164 70 0 0 0 0 0 0 0 0.54 31.23 5.07 2Cqp 164 2630 0 00 000o0 0.00 0.00 a.."WAA flo

151

up~. bridge'. pojoorl; pf.Ped fact; C1,9lI~t CLAY FILM INDEX ------Neigh po pi cl tKo!II1 I Pta'illi 5a HiNr1:on Deptth br prop span ~ I,~ii12ii: i. r; t~ic'

0.00 .' ~5L ~ Av 1100 0 0 0 0 2.o 4f. 0 0 at i fj 0.4: LEOu:Et 0 0 0.77 20. 0 1 B, 4f b6 0 o 7%. t12(0 0 L(05. 0 0 (,.%It~: 0 0.0 U.0c, -'zv 12' It'00 ~0 0 0

91 I) (I 0.?7 0 100 21 0 0 0 V U U QP (I U 2.. 21 0 0.R! 35 00 0 0 0 be 0 0 0 0 0 0.0.) DBt 0 ;~U4H2 ; 10 0.0) 0 0 0 0 0 0 0 (I 0 oI.0 C *1'I 0 0 (I 4; 0 er 0.062) 0 It 0 0 V 0.00 4 59 0 0 00 U V (9 0 C' .10 15') 0 0.00 0.00 mtIN 0 0 0 0 0.g 15': 0 0 0 V 0.00 6.0i1 0.23i 0.00 10.5E~ VA.(I I.. 0.00 0 K c V 0 0 0 0 0.00c 25 0 0 0 0.5 10 I, 0 0 0.00 t.5 0 70 0 o.5f. 1.o0: ?itqt 1 42 0 0 0 0 0 42 56 0 Pi 1.04 '4it qt2 0 0 56 70 0 0.0~ 00C 0 0 00 70 115 0 0 0 0 0 0.0' 107 0 0 0.00 0.00 !15 00C0 iC 00 167 M~ 0 (J 0.0 0 (I 095 290 0 :~0.0v 0.0 oi.00 0'I 0 0 19.0'. Av I 4 ý0 0 0 0 0.2 1 0 0 40 0 0 0 0 0 0 13 0 0 0 0.0~ 0 0 0 0 17 0 0 0 0 0 47 0 0 0 0 0 0.i 29 -to 85 0 0.167 12.1 DUtqv 47 0 0 0 ISM0 0 0 0.00 0.0 7 0 0 0 0 il 0 00 M.~ 09.0E 21.4 K 72150 0 0 00 0 0 I 152 br. bridge! PCOOMrw P4,pta face: cl,clastt CL41 FILM INE! ------x Profile Weiý Sapeol::r DeWt br pa, pf ciIs c'aal (cri 61 12 111: 11 1!it 1: pre; t.:tk VrD; &Wa ------0---- I---0------'/ 0 0 0 o 0 C 0 0.C.' 0.U 0 0 0 0. 0 5: 0 0 0 0 0 0 0.0') 1 0 0 1(1 I 0 0 I: 0 (I 0 0.0(1 is: 0 0 0 0 0 I) U C.C 0.01~) 4 2!P 2.0 0 (00 65.4 0.:7. 0 0 0.00 2.T 32rqkt 0 0 10 34 0 C. 0.4V2 0 0 00 (I 0 0.00 1110 50 0 2.02 .1-a 0 0 -0.42 e'70 19 197 0.01 0.C, 0 0.35 0 0 '0 0.1.-" 52 0 0 0.31 V 0 0 0.00 :14 0 0v'El 0.2c I.. 7.61 ¶1.04 0 I(, 0 0 40 0 0 0 0 0 0 lv 217 0.0 21 C.0 C' 2.-. 0 1 0 0 0 0 0 0 0 62 92 0.W,' 2:.04 t & I) V 0 Z-60!tv;t 9: 184 153

INDEI VALUE - RUBIFICATION I RELANIZATION --- ' morizofl 1r-dex PrO42ie Weighted Si;e Di:~£epto.ASus neraa1h:2 horl:on (Cal prop'# propml thickness Inge: mail -- -0.0------0.---- 4------.-- I.* 2. I cuI,..1. 0.17 0.01 0.00 0.*05 I). (.3 0.216

v.19o.::.c 0.01(i.o3

0.41 O.Ot- 0.0~ 1.2 11 0.0 1 7.0! ; 0 1.5 7.0: Cov d! 18 M.11 .0 7.0: MCIo Is10.1 0i.05 15.2:. 0.15 7 0.15 0.45 1.'7 0.25 1.51 4.O1 o. 60 1.5 0.1422 11.45 100 0.51 0.04 4.04 2E~r 0.e4 4.11 0.03 0 6 0.E.14 6 (.49 0~.0Y I. 1-7 (!.1I51'. C. 17.K?2~r :4 2 1.Bc b.H 0.05 21 1.44 (1.21 I 0.14 6.11 1.35 21 0.37 0.05 2.71 0.10 0.01 0.96 1.04 2C~qa' 73 0.17 2.98 27.03 0.12 0 19 1.16 15.01 A 0.15 5.12. 15.0 1S 46 1.28 Oi B 0.12 15.15 15.01F 2Wq 4. 170 0. (6 3.78 15.05 2ci n 170 220 0.5.1

0.20 I..C2 24.44 0.1' 3.01 Av 5 12 2.fil 2.05 10.04 ;.0,; 2591j 45 45 2.10 O.3o 8l 1.*37 7.44 0.15, 3.b3 d26tne".2 83107 3.05 0.00 0.25 I.f.Ot20~qn 107 210 0.25 0.99 34.85 0.15 21.01 Av 0 4 0.26 3.10 21.02 Sw 4 15 0.5e 0.08 1.49 21.03 Ik 2.1t4 6.72 21.04 2Btjqtihl 13.07 55 144 1.0.3 0.15 21.05 26tiqalbt 6.19 21.0tc 38qsW 144 lft 1.05 0.34 3.18 21.07 Z3Ciqn 186 253- -- 6.Vj -44"46ý -

I

154

INDEX VALUE - RUSIFiCATION & MELACIZATAION --- , Horizon Index Sis,,!e hor::On Depth 'Sum norsalized Ihorizon Proi:le keigtitec ics; prop.4 pro;? thickness Inde"2 mean

11.01l Av 1) 4 1.54 0.22 11.0.2 A 4 is 1.M I.i.It II . 3 2EtJ 15 42 1.71 0.24 42 90 15. 0.5v5 Is,, 1.7 6.4o 0 4 12.012 AV ,6 12.O4 4 14 1.35 31.5 0.16 12.0: Av 0.14 6.37 14 47, 47 1CA 105 12ý 1.06~ 0.(11 122.0c Htqer 1.24 1.6 144 0.2 10 144 2(K 1.155 12.11 0.15 4.44 1.45 14. 01ýAi 0.15 14.0: "ilb 25B54 0.14 0.21 54 1 0.21 1.6; 14.04 a25JqaY.1b 107 1.2,1 121 152, 14074qm 2b 2.012 14.(,E 4?v;t 0.19 4.42 1.44 0.15 Av I 0.11 20.01 086 4.13e 30.53 0.16 AV' 1.91 0.08 20.02 8 P~ Tv.V? fin 19 20. 04 42 2Btjq 42 64 0.21 0. 5! 20. 0521tjqtl 64 78 1.35 1.11% 20.06 2btjqk2-1 76 114 1.*06 20.07 2Btiqk2-2 114 152 0.76 1.57 20'.0Ci21tj qk2-` 152 194 0.65 0.24 21.92a 0.21 5.01 A 0 5 0.412 32. C" 0. 112 5.02 bm 5 20 0.4? 5.03 Bi. 20 45 0.44 0.09 4.ft 5.04 21tt, 45 56 2.45 5.05 MIqiOD 56 lte 1.67 5.06 b~tqb 10i 164 1.*31 5.071 2Cq!- 164 263 '.131 w-.

155

I INDEi VALUE - RdiIFIATION & RELANIT:~ION I 94ort~or 1de .eOamcr1:::. Depth Isum noralsin:e I horiM., Profile klip-ted I Ic~'! prop'S prop) th-c~imst nce; Kea-;

t* 11I 1.:7 (.1.1 1.'i 26..5 .1

-1 !;: 0.07 0.01 I

E. it4; 0v 6 2.62 9.' s.-

S.0! A. 5 2.14 0.:i 2.75 0.1? 6.:K iu 79 5d e.04 4ý 2. L.44 E.5 7.14 2.V.' 4v. 4c '47 13 1.4t 0.14 2.30 3': 4; -. 71 4; 56 a. C, 0."1 59 7.~ 1.02) et ':' I&' 0.75 lv': 1Sf, 1. Oe 1..04 M2E:2 1.75t 1.00: 38.9i7 0.1-0 C' 1(, 0.53 1. bi :Cvq~t 10 25 2.3 21542 0.6b 6..: 1.0 4402 0.11 5.74 4256 0.55 0.05 1.02 R 56 70 3.07 0.308 7.94 70 115 I. IN, 0.41) 115 167 3.41 IMo: 28tq 16? 195 0.19 195 6.4Q 19.04 2Btq 24( 2.97 0.074 0.09 1.05 stqe~ 0 4 0.69 35. 33 0.00 1.20 4 9 0.17 9 13 0.5? 0.67 19.01 AvIm 13 17 1.26 17 24 0.41 4.92 29 47 0.45 8.04 47 72 0.21 5.21 19.08 2KQ02 72 150 0.16 14.07 .. h.. *. -ujý- - I giefifillamigh,11110M

156

INDEX VALUE -RU6IFICATUNO I flEANIZATION -.

Sat;'e hori:or' Depth ISum norta~iized I barizor Froalui Nuighted (ell proput prop~ thickness Inde-,.-Near,

&.01 '0 139L 0.21C 1.1; 25.44 C..~ 6.41 Ft 6 1i 2.20 0.31 1.6 6.0 V~q 10 51i 1.41 0.2.!d .64 6.04 35. 521 101 0.9' 0.14 6.77 t*.05. '1q 5 .~2o .4 19 6.0o rwq 1!3 ."N 0.3. 0.04 3.45 6.07 3C; 2".1 300 0.07, 0.0: 1.(;4

2.01 Av 0 11 1.21 0.17" 0.52. 5E.!,. 0. TpK' 2.C.2 A 3 V, 0.89 0.13 O.B; 2.0", By IQ'19 1.149 0.20 1.78

;.04 2j;0 1q 3.t4 2.56 0.37 5.54 2.05 26tqmý 34 7(, 2.97 0.42 15.2e 2.07, p sq1.2 2.6e 0.4) 13.57 2.09 eq 52,114 1.66 0.24 14.71 2.04 26r. 114 1S7 M.4 0.0", 5.63

22.014 A-. 110 1."& 0.45 2.49 3P.12 0.21 22.0: 4 ~ 10 21 2.4i 0.! 3.5I &..0:". 21 62 1.it 0.2e 11.3! ~.0~s8292 I.1 0.16 4.6; 2..05 iKqt 9218I4 1.216 0.1a 18.56 157

WkDEI VALUE - COLOP PALING & COLOP L16STENINS Horizon [ndev Saapie Hor,:or. Depth (Sue no, zjlzed i norizon Preiie ilWeunted ldexn RIeaf kcm, prop!' prop' tocknisI

• 0.04 o."l 0.0(11 FmA-2 0.17 .0 0.0V 0.05 0.01 0.00 0-021 vJP 0.0-011

00. CIA-' ,.t1 0.C0(

0.11 1.01 O.O1 7.01 A 0 1.5 0.54 0.06 0.26 7.0: CoQ' : Is 0.11 0.64 7.01 2CkoD 1 10) 0.05 0.0, 0.€1 1e.12 0.16 4.01 A 0 w 0.4c 0.14 1.02 4.0: sfi : 9 IME 0.7: 12.12 4.0 :Ek2 9 ,) 1.st O.4 1.97 4.04 2..*n 6. 10t 0.-3 0.05 ,.75M.1 6.21 0.05 17.01 A 0 t (..7 O.OB 1.45 17.0: is 6 24 0.5E M4 3.5i 17.0- 2C.n 24 120 6.4 1.55 e.97 0.06 13•01 A (1 9 1.21 0.17 1.305 in 5 21 0.71 0.11 13.0:. 2.40 04.,0*i~l• 21 7. 0.02 0.05 3.0t 13.04 2CXqn 73 I3 0.39 0.6• 0.16 2.67 20.67 0.09 15.01 A 0 1H 1.04 0.16 4.47 15.02 Da 16 46 1.12 46 170 0.60 0.09 10.66 115.0: 2,"'t 2.87 15.05 2CDn 170 220 0.4' v.M6 1.17 22.01 0.10 3.01 AV 0 5 1.64 0. 2 2.15 3.021 Ad 5 12 2.15 0.31 6.55 3.03 25tkj 12 45 1.21 0.26 6.65 3•.04 25•qel 45 83 1.23 0.16 3.2: 3.05 28tjqag2 83 107 0.94 0.1. 0.25 3.06 2Ckqn 107 210 0.02 0.00 0.26 1.06 30.97 0.13 21.01 Av 0 4 1.65 3.10 21.02 iw 4 15 1.97 0.28 0.09 1.05 21.03 Bk 15 33 0.64 0.27 21.04 2Btjqkjbl 33 55 1.91 0.12 10.40 21.05 25tjqmkbl 55 144 0.92 0.13 5.46 21.06 Sqamkb2 144 186 "0.91 0.07 3.16 21.07 ICkqn 196 23 0.3)4 158

INDEL VALUE - COLOF PALING I COLOF LI6HTESNNS Hor':on Inde'" Sis;le Horm::n Depth (Sue norsal:ved I horizon Prcf:!9 Weighted Icts propil prop; thicrelss 1noey mea"

I.6: 0 4 1.5' 0.22 0.86 "02.4 0.19 A 4 15 1.72 1i.C-4 0.16 15 42 5.8(1 11.04 0.01 14.,-q II.0i 2itq.I 42 90 2.14 0.19 28k c 90 15!" 0.78 6.71 ll.Oc Z 156 171) 0.92

0.1' ('.5: N:oAV 0 4 N~. 2?. 0.iq 4 Is 0.15 1.52 14 47 7. 6 12.04 28': 0.21 18.!. 1.6! 12.05 2tqb 12(1 0.76 0.11 12f. 144 2.02 0.20 1144 20(, 0.11 12.0o SqOf 0.05,0. I.Z 1.60

14.01 A o e 1.21 0.17 LI* 35.55 0.15 14.0: 8w 9 26 1. 05 6.0: 2e 54 1. ,9 0.15 4.05 I! 14.04 54 107 0,. E., 0. 10 4.98 14.0! 107 121 1.34 0.19 2.41 I. ;34 14.06 121 152 0.20 15 2!12 1.24 0.18 12.23 14.06 221 230 O.Me 0. 1Z 3.50

20.01 08 0.85 0.12 0.97 22.54 0.12 20.02 AV2 B 19 0.22 I.O02.88 20.02 Av 2 19 42 1.26 0.18 4.20 20.04 42 64 1.*48 0.21 4.65 1.:13 20.05 20t 1qk I 64 76 0.91 (0.1" 20.06 21tjqk2-1 76 114 0075 0.11 4.06 8. 20. 07 21tj qk2-2 114 152 0.44 0.06 2.41 20.OE 2Btjqk&2-3 152 1%v 0.03 0.05 1.81

5.01 A 0 5 0.44 O.Oe 12.550.! 1 33.44 0.13 5. v2 5 20 0.35 0.05 0.75 0.10 2.51 5.0,. 20 45 0.7.,) 0.30 2&Btb 45 56 2.07 3.25 0.20, 5.05 2Btqr.vb 56 106 1.36 9.65 5.06 2Ktqb 106 164 1.51 0.22 12.55 5.07 2Cqn M14263 0.30 0.04 4.•2 159

INDEx VALUE - COLOR FAL4T6 i COLO; L1U"!ENIN

Sauw Hoi:o' Depth (Sus norail::ud I horizop Profile kelghtgc (WI prop!; prop! tnmhesm mnde; R~eif

0 it 1.45 0.2.1 E.~ 2c4i O.!

1. a' '3 4.', 1.45 0.21 1.45 N8028t~k C,' ot 2.:3 0." 8.65

(1 9 .14 :'-1 S 0.1?7 9 21 2.01 0.42 4.44 v.4 4.7'5 2.44 11.48 0. 0! 019* 56.02 itt

0 13 0.17 So 0.7E 85.07 2f 4: 1.15' .*05. 0.1 1.5i 2.90 15: 0.;! "0.13 it 150: C,. -'5 0.4:5 2.15 2~0itq'l 'U, ('.2 7.40 1~.04 2Btq. 4:. '.4 14.1 lo25 3.85 25 42 2.39 0.130 1.0;1 4 . 42 56 2.44 0.15 56 70 2. 8N 1.12 5t 2.19 7v 115 1.(.* 0.05 115 16" 1.*05 167 195 0'.60 0.20 1M &M, 0.6( 9.o Ziýtqfi 0.18 4.61 0.15 1.0' Ztqt., 0' 1.43 36.12 0.W, 6.85 4 1.i7 0.47 9 (,.g. 17.10 17 1.62 0.25 17 2.615 29 47 3.?0i 0.15 47 722 1.*77 72 1.2N. - - - -

I9

160

1rTENING INDE'. VALUE - aOUAi~ ~C

o~~~Pci eg~ $,o~mi Dtpth (SUzrnouaI:ed Hcri::ri el ;co' propel prop. t~i:.fliIs Inde.

* I'I

:f~ A: El 10 1.1A.0

* 2~~.0: by o~ oi

2.05 12~upt ~ i. .* 2 ~2.07 ýtq? ~ 5 3~05 14.5 * 1. ve 'q 5 114 Lit1 0. "o .Q 1:4 0r0..4 V.1: 11.14 0 C'1. M.'s 2.64 40.11 0.:

:.:r21 e: 2.14 0.'f1 112.55 2-4 ,.r 6: K2 1.37 .0 5E 92184I .a 0117 5. size distribution C. Laboratory Methods--particle Appeldif gypsum and soluble salts, density, percent carbonate, (PSD) bulk- and on ignition (Lt), PH, silica, percent organic carbon and loss clay mineralogY.

(PSD) ptle Size Distribution a weight basis by mm) was measured on Percent gravel (>2 Measurements were sample in the laboratory. sieving the bulk in bouldery sure that gravel estimates to make checked with field was thought to If percent gravel underestimated. deposits was not with field the value was corrected have been underestimated,

observations. were removed matter and then silica Carbonate, organic was removed 1965). Carbonate size analyses (Day, before particle either dilute H2 0 2 and organic matter with with IN NaOAc or 10 EHC, just in a water bath to Samples were heated or 'Clorox" bleach. complete and subsequently the reaction was below boiling until was removed Pedogenic silica next pretreatment. rinsed before the to just below in a 5% Na2 CO3 solution by heating the sample gm used for each 25 ml of solution was boiling. One hundred rinsed. about one hour, then was treated for sample. Each sample samples from horizons three times. However, Treatment was repeated 12 hours before being were treated up to were well-cemented that will be in phi units, but fractions were measured rinsed. PSD size silt, and clay (Table 1). Sand, in USDA size classes reported is in the major discrepancy in both methods; boundaries are equal

the silt size fraction. 162

Table 1: Particle Sizes in Phi units and USDA Size Classes

Measured Reported US Std sieve Phi Classes an mesh ntmber unit USDA Size 2.0 sand (2.0-1.0 mm) 1.0 18 0 very coarse sand (1.0-0.5 mm) 0.5 35i coarse sand (0.5-0.25 mm) 0.25 60 2 medium (0.25-0.10 mm) 0.125 120 3 fine sand sand (0.10-0.05 mm) 0.053 270 4.25 very fine + silt (0.05-0.02 mm) <0.031 pipet 5 co med fi + vfi silt (0.02-0.002 mm) <0.0156 "6 9 co + med clay (0.002-0.9'005 mm) <0.00195" fine clay (<0.0005 mm) <0.00049 "11

total sand (2.0-0.5 mm) 2.0-0.053 0-4.25 5-6 total silt (0.05-0.002 mm) 0.053-0.0019ý5 (<0.002 mm) <0.00195 9-11 total clay

Bulk Density, were made on Three to eight bulk density (BD) measurements (Chleborad and others, paraffin-coated ped samples from each horizon ped was opened to 1975). After the density was measured, each where large assure that gravel was not present. In horizons ped samples, measured percentages of gravel were unavoidable in the bulk density of the bulk density was adjusted to account for the ped samples to gravel. Equation (1.1) was used for gravelly The assumption is estimate the bulk density of the <2 =m fraction. from the bulk sample, made that the known percent gravel measured gm/cm3 not the ped sample, has a bulk density of 2.6 Equation (1.1) BD2m (gmn (2mm) 6 3 <2mm (cm3 totalr volume)-((-gU >2 am)I(2. gm/cm )) -a. - - -.

163

The excavation method and Equation (1.1) were used to samples for determine the bulk density of the fresh alluvium hole in the Fortymile Wash and Yucca Wash alluvium. A shallow bag, then surface of the fresh alluvium was lined with a plastic the > and filled with water to determine the volume. The weight of density means (2 mm fractions were measured in the laboratory. Bulk When the and standard deviations were calculated for each horizon. values standard deviation exceeded 0.1 gm/cm3, the outlying density were omitted.

Percent Carbonate, Gypsum and Soluble Salts

Pedogenic carbonate was measured on a Chittick apparatus in (Dreimanis, 1962). Gypsum and soluble salts were measured Geological solution by electro-conductivity (Marith Reheis, U.S.

Survey, written communication, 1984).

Percent Organic Carbon and Loss on Ignition (LOt)

Organic carbon was measured using the Walkley-Black (LOI) was titration procedure (Allison, 1965). Loss on ignition of calculated by the difference in weight loss at heat treatments 0 for 1 hour. 105 0 C for 4 hours (soil moisture factor) and 540 C pH After pH was measured in a ratio of 1:1 soil:water slurry. the electrode, I hour of equilibration, samples were stirred with was read. allowed to stand for I minute, and then the pH 164 Silica

The weight loss after the removal of carbonate, organic

matter and silica cement is used to estimate the percent extractable

pedogenic silica (Appendix C). The known percent of carbonate and

organic matter are used to calculate the weight loss of these materials, and the remaining weight loss assumed to approximate the

percent silica. Although this estimate is referred to as a percentage, it is at best an index or trend that correlates to field

observations In relative amounts of pedogenic silica.

* Clay Mineralogy

X-ray diffraction traces (CuK alpha radiation) were run on

oriented samples of the clay and silt fractions on a "MINIFLEX'

defractometer. Samples were run air-dried, glycolated, and heated

0 0 to 300 C and 500 C each for one hour. Tiles were placed face down

on a glycol-saturated towel, instead of saturating in a desiccator. and the particle size distribution Appendix D. Effects on of opaline silica. after the removal by the clay mineralogy fractions were effected All of the particle size YW-16 was size distribution for removal of silica. Particle 1). The surface silica removal (Table compared before and after to the to early Holocene and due soil at YW-16 is late Pleistocene to treatment than responded very differently lack of silica cement, Percentages of sand mid-Pleistocene soil. did the underlying buried the younger soil, virtually unchanged in and clay increase or are probably due to silt decreases. This is .whereas the percentage of fraction, and aggregates in the silt (1) dissolving silica-cemented in silica. of silt particles high (2) total or partial dissolving the ash and phyto major cause as much of The latter could be the of samples of contrast, the same treatment liths are silt size. In sand fraction and in major losses in the the buried soil results (Table 1, Fig. 1). the clay-size fraction corresponding gains in silica cement. the dissolution of the This seems to be due to that only to the above assumption There are problems related PSD results. X silica influences the the dissolution of pedogenic tobermorite, are that some clays, notably ray diffraction proves not noticeably effect However this alone may destroyed (Fig. 2). is abundant fraction unless the mineral the abundance of clay-size

and is dissolved. in the (syn)) were produced Synthetic Nepheline (Nepheline were dispersed with sodium laboratory after samples hydroxide to remove (or) treated with sodium hexametaphosphate and recognized In any Nepheline has not been pedogenic silica cement. 1977). area (Quinlivan and Byers, of the rocks in the study 166

T3ble 1. Comparison of sand, silt and clay before (j and after (2) silica removal on soil profile YW-16. +-s represent a relative gain in the size fraction after the removal of opaline Si0 2, and -'s a relative loss.

Horizon Z sand Z silt %clay texture Av (1) 59.60 28.90 11.60 SL (2) 68.88 16.39 14.73 SL +9.28 -12.51 +3.13

Btl (1) 48.37 40.30 11.30 L (2) 66.15 16.57 17.28 SL +17.78 -23.73 +5.98

Bt2 (1) 57.00 26.30 16.60 SL+ (2) 62.77 21.73 15.50 SL+ +5.77 -4.57 -1.10

2Btqkb (1) 63.48 32.30 4.08 SL (2) 31.01 21.54 47.45 C -32.47 -10.76 +43.37

2Kqb (1) 80.30 14.50 5.20 LS (2) 42.93 '24.88 32.18 CL -37.37 +10.38 +26.98

2Bqmkb-1 (1) 82.74 16.00 1.10 LS (2) 69.16 14.68 16.17 SL -13.56 -1.32 +15.07

2Bqmkb-2 (1) 74.60 22.90 2.60 LS (2) 56.24 24.11 19.65 SL+ -18.36 +1.21 +17.05

* 2Ckqnb (1) 87.00 11.30 1.51 S (2) 82.16 12.31 5.53 LS -4.84 +1.01 +4.02 4 S-a'q

167 Table I continued.

i v co 8 Z cc a depth. before after Z change before after Z change 13 7.9 3.3 -4.6 6.0 3.8 -2.2 30 3.5 3.0 -0.5 4.3 3.1 -1.2 43 5.2 3.1 -2.1 5.2 3.0 -2.2 58 * 18.9 4.1 14.8 14.8 4.4 -10.4 100 * 24.4 7.1 17.3 18.8 5.2 -13.6 150 (1)* 20.2 9.8 10.4 17.3 10.4 -6.9 150 (2)* 14.6 6.8 -7.8 14.8 5.0 -9.8 207+ * 40.5 18.0 22.5 26.6 20.0 -6.6

Z red a Z fl a depth before after Z change before after Z change 13 6.4 7.4 1.0 37.8 31.0 -6.8 30 4.9 6.8 1.9 35.6 28.8 -6.8 43 6.4 6.2 -0.2 39.3 26.5 -12.8 58 * 10.4 4.3 -6.1 19.3 9.0 -10.3 100 * 13.0 6.0 -7.0 19.7 12.3 -7.4 150 (I)* 13.8 11.8 -2.0 31.4 20.2 -11.2 150 (2)* 13.9 7.9 *6.0 30.I 17.9 -12.2 207+ * 9.0 17.2 8.2 10.4 15.6 5.2

Z v fi a depth before after Z change 13 1.5 23.4 21.9 20 0.1 24.4 ; 4.3 43 0.9 24.0 2?3.1 58 * 0.1 9.1 9.0 100 * 4.4 12.4 8.0 150 (1)* 0.0 17.0 1.7.0 150 (2)* 1.2 18.6 1L7.4 207+ * 0.5 11.3 1L0.8

* Field recognizable silica accumulations 168

Percent Change

-40 -20 0 20 40 !-sand silt-:, clay L 1 r I

• I .

50 ii I~7- I

-I E 100- -i .j

"0)

- sand-! silt ![I-clay 150.

200

classes due to Figure 1. Percent change in particle size profile YW-16. Total % the removal of pedogenic silica cement in depth. sand, Z silt, and 2 clay are plotted vs

I - -.. -.- - --m----'.--. -

169

Tobermorite i t.g* I., I eathered mica IsA*

we - .0 ~

AV 4-13 am ,.SIAI Kaolinite 3.41

!Mixed Layer 4.46A

AFTER V..I

ao i No 1 to 2I 80 311

Nepheline dSA a Nephefine 4 4 tq'•

8-306am NaPheline (Uyn) Nephellne (Wyn) 4.01P

S V '

ao s 6o 2 Itss so as

Quartz

I. PPIagIOCIlas S.t 'S P,.giocs, a.,s .. "

111 80-41 am I

Dolomite

%'., '.ISC. AFTER % 20 a te is to as So ss

A 11 Io 1.o s.0 6.0 4.0 2.55 ge

Figure 2. An example of clay mineralogy alteration owing to the removal of pedogenic silica. Traces are for profile YW-16 before and after the removal of pedogenic silica. The three horizons in a depth sequence all have approximately 15% clay, with a net gain or loss of +5 to -1% after treatment (Table 1). Toberuorite is the only clay mineral destroyed by the treatment. 170

Appendix E. Laboratory procedure for measuring pedogenic opaline silica using a spectrophotometer.

Introduction

There is little agreement on the best method to extract and

measure pedogenic silica (Jackson, 1969; Yuan and Breland, 1969;

Elgawhary and Lindsay, 1972; Torrent and others, 1980; Hallmark and

others, 1982). A siunmary of the literature and subsequent

laboratory tests produced an extraction and colorimetric

determination to most accurately measure pedogenic silica

This procedure is based on the reaction of dissolved silica

and ammonium molybdate in an acid medium (pH 1.0-2.0) to form the

yellow silicomolybdate complex which is subsequently reduced by

sodium sulfite to form blue molybdosilicate (No-blue). Because

phosphate produces a similar molybdate complex that absorbs in the

same wavelength range, oxalic acid Is added to suppress phosphate

interference.

All reactions when possible should be carried out In Ni,

stainless steel, or plastic (polypropylene or nalgene) containers to

avoid Si contamination from glass. Where plastic is specifically

stated, either of the other two container types can be used.

Glassware is used for dilutions, prolonged contact (>2 hours) with

glass Is not recommended.

Summary of Procedure

1) Grind, oven-dry, then weigh 1.0 gm soil sample for Si

extraction.

2) Disperse by sonication

j 171

3) Remove both cementing agents CaCO 3 and iron-oxides, and organic

matter.

4) Mix all the necessary reagents and working standard.

5) Extract soil silica.

6) Pipet working standard and sample aliquots into volumetric

flasks.

7) Add reagents.

8) Run samples on spectrophotometer - consider time to warm up

spectrophotometer if necessary.

Soil Sample Preparation

1) Sieve soil and crush to desired size. The size should vary with

the largest particle size of your sample. A suggested size

would be slightly larger that the dominant size fraction in

fine-grained deposits (e.g., medium sand for a loess parent

material), and ground finer in coarse-grained deposits. Only

1.0 gm of sample is required for the procedure.

2) Oven dry sample for one hour at 105 0 C, then lightly crush in an

agate mortar to break up aggregates.

3) Weigh 1.0 gm of sample.

4) Wash sample with distilled water into a plastic centrifuge tube

or bottle, filling to half the voltume. Disperse by sonication

(Busacca and others, 1984) for 10 minutes. Choose the

sonicator'setting that produces the most cavitation bubbles

within the sample. To find that setting, simulate the

sonication step with water only and same container so you can

see the bubble action. Starting from the zero setting, as you 172

turn the dial, the number of bubbles is the setting to use for

you samples. It is important to stir the sample while it is

being sonicated, otherwise the grains just pack together at the

bottom of the container and do not get the full benefit of the

treatment. Since conventional stirrers do not fit inside the

centrifuge tubes, Sharon Feldman (Dept. of Agronomy and Soils,

Washington State University, Pullman, written communication,

1984) suggests blowing air into the sample. This is simply

done with tygon tubing connected to the lab bench air valve.

Blow in just enough air to keep the soil in suspension. Once

the sonicator is on, it does not take much air to keep the soil

in suspension.

5) Remove carbonate then organic matter with the same procedures

used in grain size analysis, but do not remove the sample from

the plastic tube. It is not necessary to remove organic matter

from soils that contain very little of It (e.g., arid

environment soils with <1% organic matter). If appreciable

amounts of free iron oxides are present, they should also be

removed by the dithionite method (Jackson, 1969).

6) Wash samples with distilled water. Centrifuge for a half an hour

at a setting between 2500 and 3000 rpm, or until the

supernatant is clear. Repeat if necessary. The time may vary

for individual samples. -

173 Reagents 6 N HC1 - Dilute 50 ml concentrated HC1 (37% or 12.1 N) to 100 ml. Ammmonil, molybdate solution - Dissolve 100 gm ammonium paramolybate tetrahydrate (emonlua solybdate) [(NH4 ) 6 Mo7 02 4 .4H 2 0J in 600 ml H2 0, warm and stir to obtain complete dissolution. When cool, transfer to a volumetric flask, adjust pH to 7-8 with concentrated HaOB and dilute to 1.0 liter. 2 ml/sample is used.

Oxalic acid solution - Dissolve 100 gm oxalic acid (C2 H202 .H20) and dilute to 1.0 liter. 2 ml/sample is used. Reducing Agent - Dissolve 0.5 gm l-aztno-2-napthol-4-sulfonlc acid and I gm anhydrous sodium sulfita (Na 2 SO3 ) in 50 ml water. Dissolve 30 gm sodium bisulfite (NaHSO 3 ) in 150 ml water. Mix the two solutions in a plastic bottle and allow the reagent to sit for a few hours in the refrigerator. The supersaturated solution should form a precipitate that must be filtered before use. If the precipitate is not allowed to form before using, it will form a white precipitate in your colored samples. If this happens throw the samples out and start again with a

reducing agent that has formed a precipitate and has been filtered. Refrigerate this reagent when not in use; it is

unstable and should be made fresh every week. Total volume

200 ml. 2 ml/sample is used. 174

Silica Extraction

1) Amorphous soil silica is extracted with 0.5 N [OH or 0.5 N

KaOH. Sharon Feldman (Dept. of Agronomy and Soils, Washington

State University, Pullman, written communication, 1984) prefers

to use KOH because it is less damaging to the silicate clay

minerals. See Jackson (1969, Sec. 11-27) for quantitative

measure of the kaolinite and halloysite peaks following NaOH

extraction of Si. Dissolve 2.3 gm reagent grade KOH pellets,

or 2.0 gm NaOH pellets, in 100 ml of H2 0 ia a plastic

container, or dilute stock KOH or NaOH solutions to 0.5 N.

2) Soil:solution ratio is 1:50 (1 gm/50 ml or 0.5 gm/25 ml).

Perform the entire extraction procedure under a fume-hood.

3) Prepare a boiling water bath. It is important that the

temperature remain stable. Heat the 0.5 N KOH (or NaOH)

solution to 100 0 C.

4) Place the room temperature sample in a plastic container, in the

bath, and add the correct amount of heated 0.5 N KOH (or

NaOH). Allow reaction to continue for exactly 2.5 minutes

(Torrent and others, 1980).

5) Remove from hot bath, and cool rapidly in an ice water bath.

Remove and centrifuge the sample for 10 minutes at 1600 rpm,

then immediately decant the 50 al of supernatant into a 100 ml

volumetric flask.

6) Add 10 ml room temperature 0.25 N KOH (or NaOH) per 1.0 gm sample

to centrifuge tube. Mix well. Centrifuge and decant into the

100 Ml volumetric flask containing the original 50 al of

extract. This completes the removal of amorphous Si. 175

7) Dilute to volume with distilled H20.

Standard Silica Solution

Stock Solution (use I or 2)

1) Clean pure quartz crystal in concentrated HCl for one hour, then

rinse. Grind quartz to pass through a 100 mesh sieve. Heat

quartz to redness in a crucible for a brief period to dry.

Cool and store in an air tight vial. Add 0.1070 gm ground

quartz to a Ni crucible containing 2.0 gm solid NaOE. Cover

crucible and heat to a dull red for at least 10 minutes. After

melt is cooled, dissolve in 50 ml of water and allow to sit

overnight. The next day acidify with 1 N H2 SO4 to a pH of to 1.5. Transfer to a 1.0 liter volumetric flask and dilute

volume. Resulting stock solution is 50 mg Si/1 (ug/ml or

ppm). Store in a plastic bottle. American 2) Use atomic absorption silicon standard available through

Scientific Products (1984-85 Cat # S7385-14, $13.91), 500 ml of

1000 mg Sl/l.

Working Stock 200 ml for a 1) Dilute 20 ml of the 50 mg Si/l standard stock (1) to

final concentration of 5 mg Si/l. to 200 ml. 2) Dilute I ml of the 1000 cg Si/ 1 standard stock (2) Si/l. (1000 ug Si/ml)(l ml/200 ml) -. (5 ug Si/ml) - 5 mg 176

Procedure

to ml volumetric flask and bring 1) Add 1.0 ml 6 N HCi to a 50 H20. volume with distilled

Standard Curve Development the working stock 20, (30, 40, 50) ml of 2) pipette 1, 5, 10, 15, water for your flasks. Use distilled into the 50 ml volumetric are brought to volume (see zero standard. When they 0, 0.1, 0.5, standards will contain instructions below), these 5.0) mg Si/l. Label them. 1.0, 1.5, 2.0, (3.0, 4.0,

Sample Color Development the silica of sample solution, from 3) Add a I ml aliquot flasks. extraction, to the volumetric

Best to all standards and samples. This next section applies is allowed for color the same period of time results are obtained if to label and samples. Be careful development in the standards everything.

to 30 ml. down carefully and dilute 4) Wash sides of flasks molybdate solution 5) Add 2.0 ml ammonium color minutes. Yellowish allow to react for 20 6) Swirl to mix and

develops if Si is present. to and let. stand 10 minutes acid solution. Mix 7) Add 2.0 ml oxalic Do not allow to which may be present. complex any phosphates will be minutes or low Si results stand much more that I0 obtained. 177

8)Add 2.0 ml reducing solution and take to volume with distilled

water.

9) Wait 20 minutes for complete reaction. It will be blue if Si is

present. NOTE: If a sample solution develops to a darker blue

than the highest standard (2.0 or 5.0 mg Si/l), either I) make

a higher standard >2.0 mg Si/l, 2) redo it with a smaller

sample aliquot, or 3) dilute the original (unknown) Si extract

and use a 1.0 ml or larger aliquot.

10) Mix the solutions well. Measure the absorbence with a red

phototube at 625 um. Adjust the sensitivity multiplier to

position 2. The first cruvette should always contain the 0

standard. Measure standards at least three times.

11) If you have to redo any number of samples make up a new set of

standards. They should be stable over the one half to one hour

it take to do the initial reading, but no longer.

Comments

1) Aging of reagents changes the standard curve. Always run

standard solutions with samples as a check.

2) Variation in sample temperature shows little colorimetric 0 0 effect. Permissible range is 18-29 C (65-85 F) 178

Calculations

the Determine the mg of Si in each sample from a regression on absorbences of the standards:

1) Calculate the linear regression for the standards where

x - mg Si/1 of standard

y = absorbence reading

The correlation (r 2 between x and y should approximate 1.0.

2) Take the calculated linear regression and solve for the curve value.

absorbence = b(curve value) + a

curve value = (absorbence - a)/b

3) Use this equation to determine the curve value of the Si in mg

Si/l.

4) fmg Si =Im Mo-blue soln) z Si = ml /• m l sample aliquot) (ml diluted extract) 1000 gm oven-dried soil

(1000 combines conversion of mg .Si to gm Si and conversion to Z)

If you 1) use 50 ml volumetric flasks for Mo-blue solution, 2)

dilute 50 ml Si extract to 100 ml, 3) use a I ml sample aliquot

for Mo blue determination, and 4) use 1.0 gm soil, the

calculation is:

(mg~i\~50 ml Si- g1Si 1.0oml (100 ml) 1000 1.0 gm size, bulk Appendix F. Laboratory Analyses--particle salts, organic carbon, density, carbonate, gypsum, soluble ignition, pH, and silica by oxidizable organic matter, loss on values are estimations. weight. Starred (*) bulk density 180

** -,a rI. .0 in Cq~ ).c, c,. * - I -I ,. I *~~~ 4it Ca.%04., ~ ,

II 6. a' -u a I - a

9a

- I f Ii I -~ ~ - '.a-~ - U. Oi C"= 4 a- a U. - I ?4 N - N 0-*' 2. - 2 - V .04 - a C. a" - V I.. Cd C. - :. .-. q . 4.1 C 2 4 % Cl 2. N 2 h) - a -' N - I' , q 2 ii * t) ,) t C.. C. I14 d LI M~ 'I P1 C, V'...Q C:.:::: 'iN -C. N 2 I 4 -. V :. .. - **. :e - :. C. Cl N - C. V NV 2 'iN :. 2. dj4 S1 Ca V V * - I N V CI N C. ------.Cq - J,.. P1 P1 a 4 C, a. - q a- t. 4 a 4 N O Ii - I'. -. N p., a.N V 2 S @4@. N4A g. N C, 2. N N * .1 2 .1? - V 4 N U2 2 4 q -. 2.12 N N 2 . 1 - a a P.4V C4 "' Cd I. a .4 -C Cd - .5 N t'CI :4 a' N N V ..I 4) a 00* ONa : .6 I. P1 10'-dN I U. 4 N 2. N -. N Cl C. N *I a: N - a C. C2N - a - a (4 .0t N14 I'.P1VC - C. U' V ;. #* V a*. a N .CNNN 42.4 a w1N aNJil w~.2..I a ) '1 Ca N C V.0'~~~~~~~1 V2 (d .U..V* N d) V 4- 4) ~~~Nr4:~~ N .1 VC;4j a; 0: Nd: 5.4' Cl . 2. a. Cl

I P1cg- EaI2NT!,z: t CI~a~i2.N ~ P1 , 0.1C ,,j NN r. 40 el z W. * - I a- 4F. IoN11) 44 I. )$ I

ILL a , z-k . aavz ) ' di I a or U t4 r4N1 I4 Z. o Ca. N - I so C. N

-. 2.... .b a-. "I if... ACl '-I - N I V 0 N XNPriA - P ...... a , t0 Q ------9'. IA P1 P1 N Cl N e. C4 . C.

viU) U V S. ,~q1,*- 3. 6 -a q) S. p., U, Cd p.. S N 9.. I U. I h. 2. t

S U 4 U U U Ca Ca Ca U)

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181

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' aa 192 Appendix G. Representative Dates for the Quaternary deposits, NTS

•Stratigraphic Unit 1 Age Method Location Katerial Dated (ka)

Qlb 140 years channel trenching correlation (Bryan, 1925) Qic Charcoal in 14C 8.3±0.075 Amargosa River, fluvial gravel Beatty NV

Q2a Slopewash 40±10 U-trend Crater Flat Trench 3, NTS Slopewash 41±10 U-trend Yucca Mountain Trench 13, NTS Fluvial gravel 47±10 U-trend Yucca Mountain Trench 2, NTS Q2b Fluvial gravel 145±25 U-trend Yucca Mountain Trench Fluvial gravel 3, NTS 160±18 U-trend Gravel Pit, Shoshone CA Colluvium 160±90 U-trend Yucca Mountain Trench 13, NTS Q2s Fluvial sand 160±90 U-trend Jackass Flat ETS Trench, NTS Q2c Fluvial gravel 270±30 U-trend .Crater Flat Trench 3, (younger) " NTS 270±30 U-trend Jackass Divide Trench, NTS Fluvial gravel 310±30 U-trend Rock Valley Trench 1, NTS Q2c Fluvial gravel 430±40 U-trend Jackass Divide Trench, NTS (older) " 430±60 U-trend Crater Flat S Trench, Beatty Q2e Bishop Ash 738±3 Geochemical Jackass Flat and correlation Amargosa Desert, NV QTa Basalt Ash 1.11±0.3 Geochemical Yucca Mountain Trench 8, (older than) my correlation NTS, and Crater Flat Trench 1, Beatty NV Ash 2.1±0.4 Fission Carson Slough, Amargosa (younger than) my track Desert

1 Analyzed by:

4 1 C: S. W. Robinson, U.S. Geological Survey, Menlo Park, CA. U-trend: J. N. Rosholt, U.S. Geological Survey, Denver, CO. Geochemical correlation on Bishop Ash: G. A. Izett, U.S. Geological Survey, Reston, VA. Geochemical correlation on Basalt Ash: D. Vaniman, Los Alamos National Laboratory, Los Alamos, NM. Fission track on Zircon: C. W. Naeser? U.S. Geological Survey, Menlo Park, CA. S- -a, - -

193

Appendix J. Use of pollen, spores, and opal phytoliths from three different aged deposits as paleoclimatic indicators.

Three soil horizons from different aged deposits (Table 1)

were submitted to the University of Kansas Palynology Laboratory to

evaluate the potential for stratigraphic and paleoenvironmental use

of Quaternary pollen, spores and opal phytoliths. Samples were

selected at depth in an attempt to look at pollen and phytoliths

deposited with the unit and out of the range of modern

infiltration. The analyses were preformed by Glen Fredlund,

Wakefield Dort, Jr., and William C. Johnson, and completed in

January of 1985.

Table 1. Samples analyzed For pollen, spores and opal phytoliths

Sample No. Unit Age Profile No. Horizon depth I Qic 10 ka FW-4 2Btk 9-60 cm 2 Q2a 40 ka YW-1W 2Btqkjlb 25-42 cm 3 Q2b 150 ka FW-3 2Btk 12-45 cm

Pollen

The pollen count in the soil horizons was low compared to

similar aged lake sediments, but not insignificantly so. The major

problems in interpretation are associated with redeposition of older

pollen and post-depositional translocation from the surface. An

additional problem is the predicted slow response of vegetation in arid environments to climatic change (Thompson, 1984). Evidence

from the comparison of packrat midden microfossils and pollen data suggest that pollen is a much more continuous record of vegetation

change, but does not offer the very local taxanomically precise discontinuous records of packrat middens (Thompson, 1984). 194

Taking these limitations of pollen data interpretation into consideration, the three samples do suggest some interesting

preliminary results. Consistently Sample 2 biotically represents a wetter and (or) cooler environment than Samples 1 and 3.

Very little aboreal pollen (AP) including pine (P) which indicates a wetter or cooler climate, were present in the three samples (Fig. 1). The greatest amount is found in Sample 2, and where no other AP is found in Samples 1 and 3, a small amount is present in Sample 2.

Nonaboreal pollen (NAP) taxa dominates the three pollen assemblages (Fig. 1). All of the species identified are currently present in the study area. Therefore at best these data can be used to interpret wetter and (or) cooler climatic conditions, than indicators of aridity. Of major interest, is the fact that in most cases or subdivisions of the NAP, Samples I and 3 are similar and

Sample 2 has more or less than the other like samples.

The final subdivision of pollen is either deteriorated or mechanically damaged. There is significantly a greater amount in

Sample 1 ('10 ka) which could be associated with the increased eolian activity due to decreased vegetative cover associated with the Holocene climate.

In summary, the 40 ka Sample 2 is probably correlative to the onset of cooler and (or) wetter glacial climatic conditions in the NTS area. Samples I and 3 represent warmer and (or) drier interglacials. S-.AM& -. km 3*- -- k S:

195

70

60

40

20

10

0 P AP+ LS Art Art+ CA tph NAP+ irmaped

= 10ka = 40 kaM 150 ka

Figure 1. Relative frequency of pollen in three different aged soil horizons. Sample 1 is 10 ka, Sample 2 is 40 ka and Sample 3 is 150 ka. (P) Pinus sp. or Pine; (AP+) other aboreal pollen primarily Juniperus spa and Quercus sp.; (LS) low opined Asteraceae or ragweed; (Art) Artemisia sp. or sage; (Art+) other Artemisia sp.; (CA) Chenopodiaceae-Amaranthaceae or Cheno-Am primarily Atriplex sp. or saltbush; (Eph) £phedra sp. or Morman tea; (ILHAP) other nonaboreal pollen Including grasses; (danaged) deteriorated, mechanically damaged or indeterminate pollen. ------'-. -. - - *1*- -- ------. -. -

196

Opal phytoliths, aquatic organisms and ash.

Other information on paleoclimate could come from the

examination of opal phytoliths and aquatic organisms in the same

samples used for pollen analyses. Heavy-liquid fractionation

permits recovery of other light silicates along with opal

phytoliths. Opal phytoliths are formed by the precipitation of

silica in and among the living cells of plants. These silicate

bodies maintain their morphological consonance after the death and decay of the plant. A simple morphological classification of these

bodies is the grass family (Poaceae) and non-grass families (Twiss and others, 1969; Twiss, 1983) (Fig. 2). Aquatic organisms recovered include diatoms, sponge spicules and chrysomonad cysts.

Volcanic ash shards were also retrieved.

There is no significant difference in the percent of grass and non-grass phytoliths present with age of the sample (Fig. 2).

The major difference between samples occurs in the aquatic organisms and ash. Aquatic organisms do not necessarily represent a local wet environment because they are easily wind-transported great distances from dry playas. Ash can be derived both from the eolian component and in situ weathering of the parent material. The greater amount of aquatic organisms and ash in Sample 2 could be interpreted as (1) a drier climate increasing the possibility that playa sediments are susceptible to eolian transport, or (2) a wetter, climate capable of translocating aquatic organisms and ash into the soil profile. I favor the latter of the two mechanisms. rr --

197

70

Go

50 I 40

30

20

10

0 Gr-n3 Phytgikhs Other Phlvtcqiths Aqwstk Orgyunsms Asut

lCM10* 40~Im = lSO0 u

Figure 2. Relative frequency of opal phytollths, aquatic organisms and volcanic ash In three different aged soil horizons. Sample I is 10 ka, Sample 2 is 40 ka and Sample 3 Is 150 ka. Crass Phytoliths - total Poaceae family phytoliths; Other Phytoliths Irregular, aberrant and-unique phytoliths; Aquatic Organisms Including diatoms, sponge spicules and chrysomonad cysts; Ash 'light' volcanic glass shards. 198 Grass Phytoliths

In order to look at the paleoclimate in more detail the

grass phytoliths were subdivided to the tribe level (Fig. 3). Each

tribe exhibits a unique adaptive propensity reflecting the regional

climate. Festuceae grasses are associated with cooler sagebrush

steppes like the Snake River Plateau today, Chlorideae are short

grasses and associated with warmer and more arid regions like the

American Southwest today, and Paniceae is associated with the native

tall-grasses of the true prairie vegetation in the Eastern Great

Plains today. Phytoliths in the elongate catagory have no subfamily

Implications and occur in other monocots as well as grasses (Fig. 3).

The data indicate that grass phytoliths from Sample 2 are from a slightly wetter and (or) cooler climate than that of the other two samples. The presence of greater amounts of Festuceae suggests that during the formation of these phytoliths the climate was more temperate, like that In northern Nevada today. Samples 1 and 3 are more alike and indicate drier and (or) warmer conditions than that of during the deposition of Sample 2 (Fig. 3). 199

70

40

40

10

0

7#tuceulg OlorisgeI Panic•gw

= 10 ka M 4-. ka E I10 ko

Figure 3. Relative frequency of grass (Poaceae) phytoliths in three different aged soil horizons. Sample I is 10 ka, Sample 2 is 40 ka and Sample 3 1s 150 ka. -- - 466". -

200 Appendix I: Soil parameters used to model calcic soil "development. Parameters define a fresh alluvial sample with a sand texture and minimum vegetation. The maximum rooting depth is between 40 and 60 cm.

Twenty c~mpa tments each 10 cm thick. Particulate carbonate equals 0.1 gm/cm /105yr. Climatic data are in Table 3.

Compartment Hoisture Content Parent Soil AWC Present Permanent Material Temperature PCO-2 / _./ ET Wilting Point -exp CaCO3 10 OC 1V ex 1 0.049 0.02 0.018 0.27 3.50 16.5 0.25 2 0.049 0.02 0.018 0.27 3.20 17.9 0.20 3 0.049 0.02 0.018 0.27 3.00 18.8 4 0.15 0.049 0.02 0.018 0.27 2.70 19.0 0.10 5 0.049 0.02 0.018 0.27 2.50 19.3 0.10 6 0.049 0.02 0.018 0.27 2.50 19.3 0.10 7 0.049 0.02 0.018 0.27 2.55 19.3 0.05 8 0.049 0.02 0.018 0.27 2.60 19.3 0.05 9 0.049 0.02 0.018 0.27 2.63 19.3 0 10 0.049 0.02 0.018 0.27 2.66 19.3 0 11 0.049 0.02 0.018 0.27 2.68 19.3 0 12 0.049 0.02 0.018 0.27 2.70 19.3 0 13 0.049 0.02 0.018 0.27 2.75 19.3 0 14 0.049 0.02 0.018 0.27 2.80 19.3 0 15 0.049 0.02 0.018 0.27 2.90 19.3 0 16 0.049 0.02 0.018 0.27 3.00 19.3 0 17 0.049 0.02 0.018 0.27 3.10' 19.3 0 18 0.049 0.02 0.018 0.27 3.20 19.3 0 19 0.049 0.02 0.018 0.27 3.30 19.3 0 20 0.049 0.02 0.018 0.27 3.40 19.3 0 1/ Calculated for sand from Salter and Williams (1965). 2/ Atmospheric PCO2 at surface, decreasing until the maximum rooting depth between 40 and 60 cm, and again gradually increasing with depth. 3/ Actual soil temperature values from Rock Valley, NTS, averaged from 3/67 to 12/72 (Romney and others, 1973). 4/ Estimated percent of total evapotranspiration occuring In each compartment. 201

Appendix H. Horizon weights of carbonate, clay, silt, and opaline silica. 202 a U. 0.

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