Stratigraphy and Sedimentary Petrology of Jurassic and Pre

Home , Exeter Sandstone, Interbedding, Petrology, Purgatoire Formation, Stratigraphy, Trujillo Formation

X4 Bareau of Mines and :dinera1Resources Open File Xeport 49 STRATIGRAPHY AND SEDIMENTARY PETROLOGY OF JURASS.IC AND

PRE-GRANEROS CRETACEOUS ROCKS, NORTHEASTERN

NEW MEXICO

APPROVED:

APPROVED: Dean of the Graduate School STRATIGRAPHY AND SEDINIENTARY PETROLOGY OF JURASSIC AND

PRE-GRANEROS.CRETACEOUSROCKS,NORTHEASTERN

NEW MEXICO

Charles John -in, B.S., M.A.

DISSERTATION

Presented to the Faculty of the Graduate School of

The University of Texas in Par.tial Fulfillment

of the Requirements

For the Degree of

DOCTOR OF PHILOSOPHY

THE UNIVERSITY OF TEXAS June 1958 STRATIGRAPHY AND SEDIMENTARY PETROLOGY OF JURASSIC AND

PRE-GRANEROS CRETACEOUS ROCKS, NORTHEASTERN

NEW MEXICO

Charles J. Mankin

ABSTRACT

A field and petrologic study of the continental Exeter, Todilto and

Morrison (Jurassic) formationsin northeastern New Mexico,. has revealed their source area, environment of deposition and paleoclimate. . The-Exeter sandstone, an interior arid-region dune sand, was derived .from a northwestern granitic, metamorphic and older sedimentary source. The Todilto limestone, exposed only in the southwestern part of the area, was deposited as a nonmarine, algal limestone. The Morrison formation contains sediments of alluvial flat, fluvial, lacustrine and aeolian environments. The principal source area of the Morrison was from the northwest and similar to that of the Exeter sandstone, a,lthough the southern margin of the basin had local contributions. Volcanic ash, bentonite beds, plagioclase laths, quartz phenocrysts, apatite, euhedral zircon, and.glass shards indicate volcanic activity in the source area. The upward increase of vacuolieed feldspar, ka,olinite, fluvial sandstones, petrified wood and absence of unstable heavy minerals shows that the paleoclimate changed from arid to humid during Morrison deposition.

.An Early Cretaceous transgression from east to west is represented by the Purgatoire formation. The presence of euhedral (volcanic) zircon

iii inboth the upper Morrison formation and the Purgatoire formation suggests the possibility of depositionat contemporaneity during this transgression.

A second marine transgression, from east to west, is represented by the Dakota formation (Late .Cretaceous). Although the source area for the Dakota was the same as for all of the preceding units, the grain size is co;trser and zircon.is only a minor constituent. The coarser grain size is attributed to a change innrelative amountsof contribution.from igneous, metamorphic and sedimentary rocks. The coarser mode is attributed to a sedimentary source. The decrease in zircon is a result of cess+tion.of volcanic activity.

, Theabsence of unstableminerals, abundant silica-cementationand vacuolization of the feldspar indicates a humid paJeoclimate for both.the

Purgatoire and.Dakota formations.

iV V

CONTENTS

TEXT Page

Introduction ...... 1 Location ...... 1 Physicalgeography ...... 3 Scope of problem ...... 8 Thin-section.analysis ...... 10 X-raydiffraction analysis ...... 11 Grain-sizeanalysis ...... 12 .Heavy mineralanalysis ...... 12 Previouswork ...... 13 Early geologic explorationof northeastern Nes Mexico ...... 13 Recentinvestigations ...... 17 Acknowledgments ...... 19 Stratigraphyand sedimentary petrology ...... 22 Triassicsystem ...... 22 Dockum group ...... 22 .Nomenclature...... 22 Lithostratigraphy ...... 24 Jurassicsystem ...... 27 . Exetersandstone ...... 27 Nomenclature ...... 27 Lithostraitgraphy ...... 30 Grain-sieeanalysis ...... 34 Mineralcomposition ...... 41 Heavyminerals ...... 46 Cementation ...... 49 Paleoctimate ...... 52. Todiltoformation ...... 53 Nomenciature ...... 53 Lithostratigraphy ...... 55 Sedimentarypetrology ...... 55 Morrisonformation ...... 56 Nomenclature ...... 56 Lithostratigraphy ...... 63 Grain-size analysis ...... 67 Mineralcomposition ...... 71 .Claymineralogy ...... 77 Heavyminerals ...... 84 Cementation...... 92 Paleoclimate ...... 94 vi

Page

: 8. : ...... 95 1, +t cretaceous': '.; system 'e; yw7,-@urgatoire formation ...... 95 '9 * i ,; , :& e,' __ ' Nomenclature ...... 95 .. ',.-, : ?,' ? ? d.i Lithostratigraphy ...... 99 1 !i ?, Grain-size analysis...... 102 5 ij' ,;:, '! "" +, Mineral composition ...... 105 ? ': 'J ..~~,,i Cementation, ...... 107 ,~ ,.;i' ;' .. Clay mineralogy...... 108 .. ,, ..... Heavy minerals ...... 108 .. , Paleoclimate ...... 113 i ... ;:> . r2Dakota formation...... I14 ., 'i ".%...< .... ~ ..; ", Nomenclature...... 114 i .., '..I..... *! ...... 1, .. .. Lithostratigraphy ...... 115 ~ ...... '7 ...... 118 ', , .. Grain-sizeanalysis. . '6 .:; Mineralcomposition ...... 121 >. % ....,. '4 ,::;. Heavyminerals ...... 123 \,, ..~...... ,y,% .{ .Cementation...... 126 :\ :\ '' Geologic history...... 130 Triassic period ...... 130 Deposition of Dockum group...... 130 Jurassic period...... 13 1 Depositioaof Exeter sandstone ...... 131 Deposition of Toditto limestone ...... I34 .Deposition of Morrison formation...... 134 .Cretaceousperiod ...... 137 Deposition of Purgatoire formation ...... 137 Deposition of Dakota formation ...... 138 Conclusions...... 139 References...... 141 Appendix...... 148 Measured sections ...... 149 Mitchell Ranch section...... 150 Romeroville Gap section...... 154 San Agustin section ...... 158 Trujillo Hill section ...... I62 Sabinoso.Canyon .section...... 165 Canadian River section ...... 168 Otd Mills .section...... 171 Burro Canyon section ...... 175 Gallegos Ranch section ...... 178 San Jon section...... 182 Pa.ge

Thin.section descriptions ...... 185 Vita ...... 233

ILLUSTRATIONS

Figures Page 1. Prominentphysiographic features of northeastern New Mexico ...... 2

2. Location of map area, measuredsections and subsurfacecontrol points ...... 9 3. Geologicalexploration .of thesouthern high plains. .. 14

4. Locationmap of geologicinvestigations since 1945, northeastern.New Mexico...... 18

5. Geologicmap of Bueyerosarea, Harding'County, New Mexico ...... 21

6. Paneldiagram of Exeter,Todilto, Morrison, Purga- toire and Dakota formations, northeastern New Mexico...... 31

7. Thickness of theExeter sandstone, northeastern New Mexico...... 33

8. Mean grain size in phi units of the upper part of the Exetersandstone, northeastern NewMexico ..... 36

9. Percentage of feldspar in the.Exetersandstone, northeastern New Mexico ...... 43

10. Arealdistribution of percentage of compositeand stretched composite type quartz in the Exeter sandstone,northeastern NewMexico ...... 45

11. Cementtypes of theupper part of theEketer sandstone,northeastern NewMexico ...... 51

12. Thickness of theMorrison formation, northeastern .New Mexico...... 66 viii

Page

13. , Comparison of sorting values vs. mean .size for the Exeter, Morrison, Purgatoire and Dakota formations...... * ...... , . . . . , * . . 70

14.Panel diagram showing clay mineral zonation.of the Morrison formation, northeastern New Mexico , . . 83

15. Percentage of apatitein the non-opaque heavy mineral suite from the Morrison formation, northeastern New Mexico e . , ...... 91 16. Ratio of euhedrat to anhedralzircons.in the Purga-- toire formation, northeastern New Mexico, . . . . , 111

17. Zirconpercentage vs. meangrain size of samples from the Purgatoire and Dakota formations, northeastern NewMexico...... , , . . . , . . . , 127

Tables

1. Evolution of nomenclature of theDockum group. . . 25

2. Grainsize data from the Exeterformation . , . . , 35

3. Roundnessdata from the Exetersandstone . . . , . 40 4. .Heavymherat data from theExeter sandstone . , . 47 5.Grain .size data from the Morrisonformation . . . . 68 6. Percentage of feldsparvs. location .and stratigraphic position in theMorrison formation. . , ...... 73 7. Heavymineral data from the Morrison formation. . 85 8. Grainsize from the Purgatoire formation...... 103

9. Heavy mineraldata from the Purgatoire formation .. 109

10. Grain sizedata from the Dakotaformation . . . . . 119 11. Heavymineral data from the Dakota formation . . . 124 Plates

Page

1 . Photographs of Exeter sandstone ...... 209 2 . Photographs.of Exeter sands.tone ...... 210

3 . Photographs of . Exeter sandstone ...... 211 4. Photomicrographs.of Exeter sandstone ...... 212 5 . Photomicrographs of Exeter sandstone ...... 213 6 . Photomicrographs of Exeter sandstone ...... 2 14 7 . Photomicrographs of heavy minerals from Exeter sandstone ...... 215

8 . Photomicrographs of heavy minerals from Exeter sandstone ...... 216 9 . Photomicrographs of Todilto limestone...... 217

10. Photographs of Morrison formation...... 218 11 . Photographs of Morrison formation...... 219

12 . Photographs of Morrison formation...... 220 13 . Photomicrographs of Morrison formation ...... 221 14 . Photomicrographs .of Morrison formation ...... 222 15. Photomicrographs sf Morrison formation ...... 223 16 . Photomicrographs of Morrison formation ...... 224 17 . Photomicrographs of heavy minerals from Morri- sun formation ...... 225

18 . Photographs of Purgatoire and . Dakota formations . . 22 6 19 . Photomicrographs of Furgatoire formation...... 227 20 . Photomicrographs of heavy minerals from Purga- .toire formation ...... 22 8 Page

21. Photomicrographs of Dakota formation ...... 229 22 . Photomicrographs of Dakotaformation...... 230 23 . Photomicrographs of heavyminerals from Dakota formation ...... 231 INTRODUCTION

The geologic investigation of northeastern New Mexico, has experi- enced a period of neglect. This is partly the result of economic pressures, causing this area to be passed over in favor of the more lucrative oil and mineral-producing districts. Except in recent years, no active geologic investigations have been carried out in this part of the state since the compilation .of the state geologic map by Darton in 1928.

Perhaps, because of the difficulty of field exploration, many workers have been content to Rroduce geologic description and analysis without first studying the rocks in detail. . In the Lightof the present investigation it may be said that this general acceptance of previous data without re- gard to their accuracy has resulted in much confusion and conflict of opinion.

In addition, the lack of detailed studies of mineralogic and grain size distribution has prevented the establishment of source, environment of deposition, paleoclimate and many other factors of these sedimentary strata. Consequently, the paleogeography of the intervals during which these rocks were deposited has been badly misconstrued.

LOCATION

Northeastern New Mexico is part of the southwestern portion of the

Great Plains province, which extends eastward from the front of the

Rocky Mountains as a gently eastward-sloping, relatively flat alluvial plain. In contrast to th.e extensively disturbed mountain chain to the west,

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the Great Plains have undergone little structural deformation. Minor normal faulting, with local graben development, and an occasional gentle fold constitute the visible structure.

In northeastern New Mexico, the province is bounded on the west by the Sangre de Cristo Mountains, on the southwest by the Pecos River

Valley and on the south by the Llano Estacado (fig 1). The latter is an isolated extension of the Great.Plains province, the result of dissection by the -Canadian River. There is no distinctive physiographic boundary to coincide with either the eastern or the northern political boundary of

New Mexico. This region slopes eastward at a .rate of a few feet per mile, interrupted here and there by an erosional escarpment. The Las

Vegas Plateau occupies the central and west-central parts; the Ocate'

Plateau and the Parks Plateau are minor subprovinces situated in the western and northwestern parts. The Clayton Upland.o.ccupies the northeastern part. The Canadian Escarpment, the southeast-facing

"breaks" (a local term for a dissected escarpment) of the Las Vegas

Plateau and Clayton Upland, separates the higher plateau country from the Pecos and Canadian.River Valleys.

PHYSICAL GEOGRAPHY

The importance of stratigraphic control on the geomorphic development of this area cannot be overemphasized. The uplands are flat and relatively featureless and the boundaries are marked by sharp topographic breaks, The rims of mesas are held up by essentially horizontal resistant caprock of either basalt or sandstone, underlain by non-resistant

shale and mudstone. Because of this, toreva.-block slides are common

along the Canadian ,Escarpment. .Parallel slope retreat, suggested to be

an important process of denudation in arid regions (Thornbury, 1954; Penck,

1953; L. King, 1953), is demonstrated along the escarpment.

.Streams drain, with one exception, to the east (fig 1). The Dry

Cimarron heads east of Raton and drains eastward.eventualty entering the

Arkansas River in northeastern 0klah.oma. , The .Canadian River drainage

heads near Raton and flows south and sautheast to Tucumcari. At Tu-

cumcarf, the river course turns east joining the Arkansas River in

eastern Oklahoma. The one exception is th.e Pecos River dralnage that

rises in the southern.Sangre de Cristo Mountains at the southwestern edge

of the Las Vegas Plateau and flows south entering the Rio Grande in west

Texas. Thus it has been described as a headward-growing stream that has captured the watershed of the streams draining inan eastward direc-

tion (Plummer, 1933, p 771).

The major drainage channels are confined to interplateau valleys, which commonly develop narrow steep-walled canyons in their upper

reaches. The dendritic pattern.of the tributary drainage is well-integrated with the major channels. But, because the. tributar.ied are ephemeral, they do not fit the concept of the graded stream.- The major channels, which have a more or less continuous discharge, especially in the down-

stream reaches, do exhibit a profile of equilibrium. Preliminary obser-

vations indicate that the characteristic channel cross-section has a width to depth ratio on the order of 20-30/1. In the upper reaches this factor

decreases to 10-20/1. The effect is a broad, shallow stream channel that

is very sensitive to variations in discharge and sediment.load.

Although detailed topographic maps are not available for most of

northeastern New Mexico, a general picture of the altitude and relief

may be obtained by examination of the state topographic map and supple-

mentary elevation determinations. The country rises from about 4,000

feet'in the Canadian River Valley near Tucumcari to above 8,000 feet

west of Raton along the front of the Sangre de Grist0 Mountains. The

average elevation of the Las Vegas Plateau is over 6,000 feet, whereas

the Clayton .Upland averages slightly over 5,500 feet. The greatest

mesa to valley retief is found along the Canadian Escarpment where the

relative relief between mesas and valleys varies from less than 100 feet

to more than .I, 000 feet, the average being about 600 feet.

Because of the comparatively high elevation the summer tempera-

tures are relatively mild. The daily average summer temperature is

65'-70°F; the daily range is between 55O and 85OF (Visher, 1954, p 24).

Likewise, because of the eievation and geographic position on the southern

edge of the Great Plains, the winter temperatures are quitecold .-. com-.- .

,? pared with the latitude. The daily average winter temperature is 25O- 1 .- . .~~~ ~..~~. ~

35OF; the daily range is between 20° and 60°F. A temperature differ-

ence of ZOOF between the higher northwestern sector and the lower south-

eastern sector is not uncommon.

The average annual rainfa,ll is between 10-20 inches. Most of the rain occurs in July in the form of daily thunderstorms which are very

common on the Great Plains. . These thunderstorms are local in extent,

often covering.only a few square miles. .They commonly discharge less

than an inch of rain but measurements of as much as 4 inches have been

recorded. Although winter rainfall averages only 1 inch, snow, some-

times as much as 3 feet, greatly improves the ground moisture.

Because of the low humidity and scanty rainfall, this area is in-

cluded within the semi-arid regions, where evaporation slightly exceeds

precipitation (Visher, 1954). As is .common in semi-arid regions, there

is a large year to year fluctuation in total precipitation.

Pedocal soils are the most common type although large areas of

pedalfer soils are present. Here, as in .other regions of moderate to

slight rainfall and temperate climatic conditions, the bedrock appears,to

control the soil type formed. But, because of the semi-arid nature of

the region, most of the soils are immature to submature (i.e. no well-

developed soil profile).

Most of the mesas and plateaus develop a pedocal soil profile. A

casual inspection .of the sandstone-capped areas would appear to contra- dict the statement that the bedrock is the controlling factor in the soil formation. But closer inspection will disclose a caliche cap that clearly is not related to the present soil profile. Therefore, the pedocal soil is actually developing on the caliche and not the sandstone. The soil found in the valleys is mostly transported, but some immature profiles are forming at present. Here; .as elsewhere in the region, the underlying material dictates the soil type that is forming. Thus, in areas of Morri-

son formation exposures or residue resulting from erosion of shale,

pedoca! soits are developing. In contrast, similar areas of. Dockum out-

crop aredeveloping pedalfer soils.

The vegetation of the area is typical of prairies with grasses domi-

nant over brush and trees. Isolated stands of pifion pine, spruce and fir,

especially in the higher elevations, give possible evidence for a cooler

and moister climate in the recent past. The other timber includes mes-

quite, juniper and a few cottonwood and salt cedar along the ravines.

Numerous varieties of ca,ctus abound; among these prickly pear and

cholla are the most common. Gramma grasses are the most abundant

vegetation .of the open plateaus. Of these, black gsamma. is by far'.'the

most common. In September when the gramma."heads", the pastures

are virtually black with this variety of grass. Side-oat gramma and pf.5

''c buffalo arealso present andlocally abundant. A. Some control of vegetation by bedrock and soil can be demonstrated,

The juniper and most of the pine, spruce and fir are present only in areas

of pedalfer soil formation. The gramma grasses are not restricted to

pedoca) soils but are much moreabundant on this soil type.

The principle occupation of this region is ranching. The open prairie

country and relatively mild summers make this area a major cattle-

producing region. A minor amount of farming is attempted, but, because

of the yearly fluctuation in rainfall, dryland farming is risky. At the

present time, some irrigation is being attempted. 8

The remoteness of the region, lack of good transportation facilities Jes*e”5 and absence of a nearby market defea,ts the possibility of industrial expan- sion. One uncomman industry is the production of dry ice from the

Bueyeros carbon dioxide fields. . During 1957, three dry ice plants were in operation. The total production for all three plants is about 150 tons per day, The.largest plant is located at the railroad siding of Solano.

Its production is about 100 tons per day. The other two plants are located near Bueyeros (fig 1). The production from these.two plants, which rarely exceeds 50 tons per day, is shipped by truck. Owing to increasing w, 7 operational costs and compe.tition from the beer industry ( y product of t- -,c.., .‘.I ..

SCOPE OF PROBLEM

New Mexico Bureau of Mines and Mineral Resources initiated and sponsored project 77. The project included mapping an area in northeastern Harding County and a detailed study of measured sections in and around this area (fig 2). The purpose of this study was.to obtain a better understanding of the stratigraphy and geologic history of the exposed rock units. For practical reasons the study was limited to the Jurassic and

Cretaceous rocks older than the Graneros shale.

Parts of the summers of 1955, 1956 and 1957 were spent mapping and measuring sections, The map area is bounded on the north and east by the Harding-Union.Gounty line, on the south by 36ON latitude and.on the west by Ute Creek. . The area included within these limits .is 144 .DRY CIMARRON ORATON

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LOCATION OF MAPAREA,

MEASUREDSECTIONS AND SUBSURFACECONTROL POINTS

CHARLES J. MANKIN 1958 02468 h " MILES square miles. . The major feature of the map area is a south-facing escarpment that has numerous re-entrants. Physiographically this area is a transition ,from the Dakota-capped mesas.of the Clayton Upland to the valley floors of Ute and Tramperos Creeks. The difference in elevation between mesa .and valley diminishes from more than 500 feet along .Ute

Creek on the west edge to less than 100 feet on the east edge.

. Two distinct drainage basins are developed in the map area.. Ute

Creek and its tributaries drain the west and .south-central parts; Tram- peros Creek and its tributaries drain the north-central and east parts.

These two drainages are separated by a low drainage divide in the central part of the area. Spring-fed Ute -Creek flows perennially but its tributaries are ephemeral, with the exception of Alamocita Creek which is sprhg fed. Tramperos.Creek and its tributaries are ephemeral.

Sections were measured along the Canadian Escarpment, in the

Canadian River Canyon and along the north-facing escarpment of the

Llano Estacado (fig 2). In addition several sections from other sources were used.

Laboratory procedures involved studies of thin sections, x-ray diffraction patterns, grain-si~eand heavy minerals.

Thin-section Analysis

Thin sections of about 180 samples were analyzed under the petrographic microscope. Mineral composition and texture were analyzed in order to determine, if possible, the source, environment of deposition 11

,~r' and paleoclimatic factors. Some of the more important factors considered

were grain morphology (size and shape of the grains), feldspar content and

condition (fresh or weathered), quartz types (based upon extinction pro-

perties), cementing material and miscellaneous transported constituents,

Intraformational as well as interformational variations of composition and

grain morphology were analyzed and are herein described.under each

rock unit.

X-ray Diffraction Analysis

X-ray diffraction was employed in the identificationaf the clay

minerals. The differentiation of the .clay-mineral species was accom-

plished by the following standard technique:

1). The shale sample was dispersed in distilled water v7 \ 2). The dispersedsample was then.sedimented 0n.a glassslide 1\ii *3). The X-ray pattern was obtained from a Brown Recorder

?;i'J $1 operated in connection with a Norelco X-Ray Diffraction unit 3q '" In order to differentiate montmorillonite-illite mixed-layer structures

from pure montmorillonite and mechanical mixtures of montmorillonite

and illite, solvation in diethylene-glycol was utilized by th,e following

standard technique:

1). The sedimented sample was placed in a dessicator over the

diethylene-glycol

2). The desiccator was placed in an .oven at 75OC for 3 hours

3). The diffraction pattern was obtained by the previous method

~ ~~ No attempt was made to compute relative percentages of clay types in each

sample because of the unreliability of the method (E. J. Weiss; personal

communication, 1957). A generalized clay-mineral zonation of the Morri-

son formation in this region was established as a result of this study.

Grain-size Analysis

-Grain-size studies were employed as a supplementary tool to deter-

mine modes of transportation and environments of deposition. . Sandstone

samples were sieved, and,cumulative curves were ,plotted and statisti-

cally analyzed. The mudstone and shale samples were analyzed by a

.combination of sieve and pipette analysis, and cumulative curves were

also plotted and statistically anatyeed. In addition to studies of mode of

transportation and depositional environment, compa.rison.of various

statistical parameters is useful in differentiating rock units. Compari-

sons of mean size, standard deviation, skewness and kurtosis were

particularly useful in differentiating the Purgatoire sandstone from the

Dakota sandstone in those areas where the upper skLe unit of the Pur-

gatoire is missing.

Heavy Mineral Analysis

Heavy mineral studies were emptoyed as a supplementary tool for

the determination of source and, to some extent, paleoclimatic factors.

The heavy mineral fraction from each sample was removed by the bro-

moform method and the resulting separate was mounted on a glass slide in.Canada Balsam. One hundred grains from each slide were identified

and the results recorded, In particular, composition (identity of the

mineral), morphotogy (size and shape) and condition (weathering or over-

growth formation) were determined for each of the one hundred heavy

minerals counted in each slide.

Additional information on standard analytical techniques of sedi- id mentary analysis may be obtained from references on the subject (Folk, !I 1957; Krumbein .and Pettijohn, 1938; Pettijohn, 1949; Milner, 1952; etc.). -. r PREVIOUS WORK

Early Geologic Exploration of Northeastern New Mexico

Among the many expeditions to cross northeastern .New Mexico in the

exploration of the western arid regions, seven surveys stand out as ex-

ceptional.

The first of these was led by Major-StgphenH. Long in the years

1819-20 (Merrilt, 1924, p 69-70). The expedition was under the direc-

tion of John C. Calhoun, Secretary of War, Because its purpose was I i both military and scientific, Thomas. Say, paleontologist, and Edwin

James, botanist and geologist, were included. The group split into two

parties on the return journey; the southern party cut diagonally across

northeastern New Mexico (fig 3). Although written accounts of this ex-

pedition are sketchy, it is reported that Thomas Say was a member of

the southern party. The result of this expedition was a description of

the geography and physiography of this region. It was responsible prima- D

0 n n < n -

I z t" i

i;i-! I

rily for creating interest inthe further exploration and exploitationof the

West.

The second important expedition was made by Captain R. B. Marcy

and G. G.. Shumard in 1849. .The route, which began .at Fort-Smith,

Arkansas, lay up the Arkansas River to the junction with the Canadian

.River, then up the 'Canadian River to the present site of Tucumcari,. New

Mexico, from there across to the Pecos .River .and up this drainage to

Santa..Fe, New Mexico. From Santa .Fe the route lay south to El Paso,

Texas, and then eastward (fig 33 back to ForkSmith (U..So, 31st Cong.,

1850). The purpose of this expedition was the exploration of the Red

Siver and its tributaries, But, perhaps because of the adventurous nature of these two men, the expedition covered a considerably larger area than originally intended. Their report is primarily an account of the physiography and culture .of this region, although some general observations of the geology are also included.

The third survey was conducted by Lieutenant A.. W. Whipple and

Jules Marcou in 1853, as one .of the five Pacific Railroad Surveys that were established during that year, These surveys were organized to find a practical and economical route for a transcontinental railroad. The route followed by Whipple and Ma.rcou lay along the 35th parallel (fig3).

Because of a misunderstanding between Jefferson Davis, then Secretary .. of War, and Jules Marcou concerning the writing of the report,' the offi- cial report was written by W. P. Blake, using notes and collections made by Marcou (U. S., 33rd Cong., 1854). In addition, Jules Marcou wrote 16

a book entitled Geology of North America (1858), in which he gave a de- " scription of the geology a.long the route of this survey. Although he erred iP/ a age analysis of some of the rocks, his astute observation and careful description resulted in a most remarkable compilation of geologic know- ledge.

Professor-J. S. Newberry in the years 1857-58 accompanied Lieu- tenant J. C. Ives .of the.Corps of Topographical Engineers on an expedition up the Colorado River from its mouth northeastwardto the 36th parallel (Merrill, 1924, p 360-365). From here, he journeyed eastward to Santa Fe and. then, following the route of Whipple and Marcou, eastward to Tucumcari. . At this point his route turned northeastward eventu- ally ending at Leavenworth, Kansas (U. S., 36th.Cong. , 1860).

In 1869, F. V. Hayden conducted an exploration of the southern

Rocky Mountains that began at Cheyenne, Wyoming Territories, on June

29, and followed a route along the east side of the mountain range. The route extended into northeastern New Mexico along the eastern side of the Sangre de Cristo Mountains and the return route lay on the western side of these mountains. Although the exploration was rapid and the amount of country covered enormous, the descriptions of the geology and physiography are surpassed only by the .earlier work of Marcou (1853).

- ~~~ In 1889 the Geological Survey of Texas was organized. The first task of this survey was a regional reconnaissance of the geology and physiography of the state, In 1891 W. F. Cummins conducted an investigation of the Llano Estacado and the country immediately to the west {fig 3). One of the important results of this expedition was Cummins' clarification and re-assignment of the Tucumcari beds- to the Cretaceous. These units, previously described by Marcou (1858) and later Hill in

1888 and 1891, had been assigned to the Jurassic.

N, H. 'Darton, in 1914, conducted an investigation of the Santa .Fe route for the U. S. Geological Survey. The purpose was to describe the physiography and geology along the Atchison,. Topeka .and Santa Fe Rail- road from Kansas.City, Kansas, to Los Angeles, California in.a guidebook (1915). Three other guidebooks were published, one on each .of the major western railroads. The reports were written for the average traveler and therefore contain a better discussion of the physiography and culture of the region than.of the geology.

Recent Investigations

Investigations of northeastern New Mexico by the U. S. Geological

Survey have been published as a series.of Oil and Gas Maps (fig 4). These are areal investigations witha brief description of the outcropping strata and pertinent subsurface information.

The New Mexico Bureau-of Mines and Mineral Resources has published two reports on the geology and ground-water of particular areas.

Currently, Brewster Baldwin, F., X. Bushman and'W. R. Muehlberger are preparinga report on the geology and ground-water resources of

Union County for the Bureau (fig4).

Several Master's theses from Texas Technological College have been 104- 103. """"WC' .. . , 4-37= ..;1

i u . ,.N , . . . ,; : 0. .~ N

I ...... EXPLANATION ......

Dobrovolny,Emssl. Summerson, C.H. and Boles. R.L.(1946)

Grlgps. R. L. md Hsndrlckson. ORA G.E. (1951)

Bochman, G.O. (1953)

Wood,Jr.. G.H., Northrop, S. A. and Grlggs. R. L. (19531

Cooley. Beaumont (19551

LOCATION MAP OF GEOLOGIC INVESTIGATIONS SINCE 1945, NORTHEASTERN NEW MEXICO

BY CHARLES J. MANKIN

NEW MEXICO 1958

048 32 MILES 19

completed on the geology of parts of this region,

Beaumont Cooley, in 1955, completed a Master's thesis at The

University of Texas ,on the geology of an area located inthe Dry Cimarron

.Canyon in northern Union County (fig 4).

.Several other investigations have beenand are currentlybeing carried out in this region. This new impetus for geologic investigation results partly from current uranium explorations and partly because of future oil possibilities.

ACKNOWLEDGMENTS

Dr. Wm. R. Muehberger suggested the problem and with Dr. R. L.

Folk supervised the subsequent research.. Frofess.or R. K. DeFord,

Dr. Keith Young and Dr. E. J. .Weiss served as members of the super- visory committee.

Financial assistance was derived from the New Mexico Bureaw of

Mines and .Mineral Resources, Socorro, New Mexico; the Standard Oil

Company of Texas Fellowship ingeology; the Shell Oil Company Fellow- ship in geology and an instructorship in the department.

Dr. Brewster'Baldwin, of the New Mexico Bureau of Mines and

Mineral Resources, offered many helpful suggestions both during the field work and on the compilation of this report.

Wm. M.. Johnson assistedin the fieid work during the summer of

1956 and Hugh H. Doney assisted in measuring sections during the summer of 1957. To the above mentioned, and the many other friends and associates who assisted me in countless ways, I would like to express my sincere gratitude.

To my wife, Mitdred, who assisted in the field, in the preparation of this manuscript and in other ways too numerous to mention, this thesis is dedicated. R30E R31 E UNION COUNTY R32E 3% E

GEOLOGIC MAPPING: SUMMER. 1955 C. J. MANKiiZ GEOLOGIC BY LES J. MANKIN -130 1958 NEW MEXICO HARDING CO. L 0 I 2 3 4 MILES

~ DEPARTMEHT OF GEOLOGY \

THE UHlVERSlTY OF TEXAS STRATIGRAPHYAND

S'EDIMENTA,RYPETROLOGY

TUSSXC. SYSTEM.

Dockum Group . .. Nomenclature. -- The term Dockum beds was used by, Cummins ,... i I- .

(1890, p 189) for conglomeratic sandstone and.. red shale cropping out in the vicinity of. Dockum, Dickens .County, Texas, but no definite type locality was specified.

Drake (1892, p 231-233) demonstrated that the Dockum beds could be roughly subdivided into three lithologic units: a Lower shale unit; a middle sandstone and conglomerate unit; and an .upper sandstone and. shale unit. He traced these units by means of. measured sections from the .type area in.Dickens,County, Texas, to the Canadian River Valley in the vicinity of Tucumcari, New Mexico,

Gould (1906, p 23) used the term Dockum'formation.. in describing the outcrop in Palo Duro .Canyon. In .a later report Gould (1907, p 23-26) differentiated Drake's .lower andmiddle unitsin Oldham and Potter

Counties, Texas. The upper sandstone and shale unit is missing in these counties. There Gould used the term Dockum group and applied the names

Tecovas formation and Trujillo formation to Drake's lower and middle i units respectively. The Tec0va.s formation was defined for exposures along Tecovas Creek in western P,otter County (Gould, 1907, p 23) and the Trujillo formation from exposures along Trujillo Creekin Oldham County (Gould, 1907, p 26).

Darton (1921) divided the Dockum group, in northeastern New Mexico, into three units. These units, although lithologically similar to the subdivisions by'Drake, may or may not be laterally continuous with them. To the middle unit Darton (1921, p 183) applied the name Santa Rosa sandstone for exposures in .the vicinity of Santa Rosa, Guadalupe County, New,

Mexico. . Although the term Santa Rosa is preoccupied by Dollfuss and

Montserrat inNicaragua .(1868), it seems advisable to retain the na,me.

A separate name is needed for this area because of the questionable correlation with the subdivisions.of Drake and Gould on the Texas High

Plains.

In 1928 Darton (p 32) tentatively correlated the Chinle formation of

Arizona (Gregory, 1917, p 42) with parts of the Dockum group, but did not restrict the Chinle to the upper unit as diagrammed by.Adkins (1933, p

2431, Instead, Darton stated (1928, p 32):

Farther east it /the.Ghhle formation/ is represented in the Dockum group, but the limits of its representatives.in that group have not been .ascertained. Adams (1929, p 1046) introduced the term Dockum -series for all strata of Triassic age present in the Per'mian.Bash. He divided these strata into two formations and following Darton used the term Santa Rosa for the lower unit. For the upper unit, he used the term Chinle shale.

Because continuity of the Ghinle shale can be established fromits type

area into easternNew Mexico (R. K. ~ DeFord; pers.onal communication,

February, 1958), the use of this term is acceptable. It should be re- 24

marked that Dockum series is no longer used as a time-stratigraphic term. _c

Miller (1955, p 39) briefly summarized.the lithostratigraphy of the

Santa,Rosa sandstone in the Delaware Basin,. At the localities described by Miller the Santa Rosa disconformably overlies the Pierce.Canyon formation probably of Permian age,

As detailed geologic mapping of th.e Dockum group is pursued, more local subdivisions may become possible. Parker (1933, p 41) differentiated two such local units in the Dry. Cimarron Valley, Union County, New

Mexico; a lower shale and sandstone named the Sloan.Canyon formation and an upper thin- to massive-bedded sandstone named the Sheep Pen sandstone. In the original description .Parker placed these units above the Dockum group but later work by Stovalland Savage (J939) indicates that these units should be included within the uppermost part of the

Do ckum e

Baldwin, et al. (1958, in preparation) have differentiated two other " local units in the Dry Cimarron Valleyof Union County; a Jower purple- mottled mudstone named the Baldy Hill formation and an overlying red- bed unit named the Travesser formation. . These formations underlie the

Sloan Canyon and Sheep Pen units of Parker.

Because of the lack of detailed mapping of the Dockum group in northeastern New Mexico and because of the very nature of the strata, the correlation of the above-mentioned local units, and many such additional units not herein described, has not been attempted.

Lithostratigraphy. -- Innortheastern New Mexico the Dockum group Cummins,, 1890 T Drake, 1892 1907Gould, .. Darton, 1928 High Plains, Texas lains.,Texas NE NewMexico I Unnamed Trujillo sandstone shale Sandstone I Dockum P shale I beds M Unnamed Tecovas shale shale

Adams, 1929 Parker, 1933 Baldwinal., et 1958 " P.ermianBasin Union Co, , Ne.w Mex, .Union Co., New Mex. I Sheep Pen Sheep. Pen: a 3 Chinle. o ' SloanCanyon k Sloan.Canyon M E Travesser Do'ckum group 4 BaldyHill S anta Rosa Santa 6 Unnamed -

Table 1.. Evolution of.Nomenclature of the Do.ckum Group. -o This. chart repre- .s.eents. the. .evolution..of..namenclature..~zance~ning~e..Darkum.~~up.The terminology refers to different parts of the section in separate localities and does not imply lateral equivalence from one areato another.

N 'p ln i is exposed in the Dry Cimarron Valley, Canadian River Canyon, Canadian

River Valley, Ute Creek Valley, Pec.os River.Vatley, and along the foothills of the Sangre de Cristo Mountains. Low, badland topography is common where the strata form extensive exposures. The lower contact of the Dockum is not exposed in this area, but subsurface information indicates that the contact is unconformable. The upper contact with the overlying Jurassic strata is a regional disconformity with local angular discordance. This angular discordance is easily seen in the Dry Cimar- ron Valley of northeastern Union County. There the strata of the Dockum group are gently folded into a series of anticlines and synclines. Post-

Dockum erosion truncated these structural features and developed local discordance with the Jurassic strata.

The rock types exposed in the map area (fig 5) are pale red purple

(5 RP 7/2), light brown (5 YR 6/4) and moderate reddish brown.(IO R

5/6) siltstone, mudstone and shate with several discontinuous pale red purple (5 RP 7/2), 1-2 ft limestone beds (probably lacustrine), which lens out in a short distance along the outcrop and thereforecannot be used as stratigraphic horieon markers except locally.

At Gallegos (fig 2) a thick sequence of fine-grained sandstone, exposed at the top of the Dockum strata, may be correlative with either the

Santa Rosa sandstone or the Trujillo formation, or may be merely local sandstone strata in the upper part of the Dockum group.

Owing to the lack of stratigraphic control and poor exposures in the map area, a detailed sedimentary analysis of the Dockum group was not attempted. One important mineralogic aspect concerning the Dockum group should be stated. All the terrigenous sedimentary rocks examined contain

2-4% mica and 5-15% fe1dspa.r (both fresh and weathered). Muscovite is not present in the Exeter, Morrison, Purgatoire .or-Dakota formations.

The common cementing materia! of the .terrigenous rocks is calcite; both. siderite and dolomite occur in minor amounts.

The Lacustrine limestone is composed of very fine-grained (3-51.'), anhedral calcite. Ostracods are common in most samples and are abundant in a few. ,

A few fine-grained pebble conglomerates composed of reworked limestone and.siLtstone pebbles are present inthe southwestern part of the map area. These are very Limited in areal extent; some attain a.mwi- mum outcrop length .of 100 yards.

This brief description is included here because these .beds are everywhere present under the Jurassic strata in northeastern New

Mexico.

JURASSIC SYSTEM

Exeter Sandstone

Nomenclature. -- Lee named the Exeter sandstone in describing a 1 persistent sandstone that crops out in the Dry;Cimarron.Valley. Lee stated (1902, p 45):

Near-Exeter post-office a sandstone formation appears between the Red'Beds and the shales CMorrison]. It.lies unconformably upon khe Red Beds.. .. . Lee erred in the spelling of Exter. Gtanton (1905) and.Later ReFord (1927) attempted to rectify this error by using the original spelling. But, because of widespread usage of Exeter for this formation and the fact that the Exter Post Office is no longer in existence, Lee's spelling has been

.accepted.

Sanders (1934) considered the Exeter to he a sandstone tentil within the Morrison formation, but DeFord (1927) and Parker (1934) pointed out that the variegated shale, in .Cimarron .County, Oklahoma, is a part of the underlying .Triassic strataand not a part of the Morrison.

Heaton (1939) correlated the Exeter sandstone with the.Entrada formation of the Four-Corners &.rea .(GilLuly and Reeside, 1927, p 76) and replaced the Exeter with the .latter name.

Dobrovolny and .Summerson (1946) in des.cribing the surface geology and Mesozoic stratigraphy of a part of northwestern Quay. County, New

Mexico, used the term "Wingate (9)sandstone" in referring to the massive- to cross-bedded, medium- to fine-grained unit cropping out unconformably above the Triassic age strata of the Dockum group. The

"Wingate (?..)'I is overlah'with seeming conformity by the Morrison shale in this area.

Bachman (1953) described a sequence of interbedded brownish-red sandstone., siltstone and shale overlying the upper part of the Dock& group in northwestern Mora County. To this unit is given the name

Naranjo formation for exposures near the Village of Naranjo, Mora

County, 'New Mexico. The upper and lower contacts are described as conformable, but loc'ally, the overlying unit is said to contain reworked

fragments.

In the same report Bachman (1953) described a mass.ive, cross-

laminated sandstone to which he gave .the name Qcate .for exposures on

Ocate Greek about a mile and a half east of Ocate, New Mexico. This

unit he tentatively correlated with the Entra.da. Bachman also concluded

that the sandstone .cropping out at Old Mills in the .Canadian River Canyon

is the Ocate of this 1ocaJity. ksupport of this conclusion, he affirmed

that (1953, sheet 2)~:

At Old Mills, east of the mapped area .in Harding County, the ,Ocate ' ' sandstone rests disconformably on strata tentatively assigned to the Naranjo formation,. . .

Wood, Northrop and Griggs (1953) described the relationship of the

Naranjo formation at Old Mills:

They [Naranjo formati04 consist of more than 60 feet of interbedded brown-red sandstone, siltstone, shale, and limestone conglomerate. . The sandstone is fine-grained and the beds range from 1 to 10 feet in thickness. Cross-lamination is common. The base of the Naranjo is not exposed and the formation is .overlain unconformably by the Qcate sandstone.

The writer was unable to verify these relationships at the section .exposed.immediately east of the Old Mills ranch headquarters (now abandoned) located in the .Canadian .River .Canyon. It is possible that the. section described above is not at the same locality as,that measured by the writer.

Measured.Section 57-7, the Old Mills Section, contains the upper beds of the Dockum group, exposed in the canyon floor,.overlain by a thick .outcrop of Exeter sandstone, The term -.Exeter sandstone is accepted herein in place of Entrada, Wingate and Ocate. Although the Entrada and.Exeter may once ha,ve been laterally continuous with each.other, this conclusion should be accepted only after careful study of the intervening area. A similar remark applies to the correlation with the Wingate.

Baker,.Dane .and Reeside (1947) in a re-analysis .of the Jurassic age strata ,of the Colorado Plateau conclude that the Entrada .and Wingate (as defined by. Dutton) were once laterally continuous. They propose to use

Entrada formation in place of Wingate, even though the term Wingate formation has priority, It should be emphasiz.ed here that the correlation of

Entrada into northeasternNew Mexico is based upon a few widely-spaced measured sections: the interpretation of the section and resulting.correla-

tions are questionable.

The originat definition.of the Ocate sandstone had considerable merit.

To propose local names for mapping isolated areas prior to correlation with adja.cent regions is entirely acceptable. .Because the Ocate has been correlated with strata previously assignedto the Exeter sandstone .the local name can be abandoned in favor.of the priority of the latter.

Lithostratigraphy. -- The.Exeter sandstone crops out in a narrow band in the Dry Cimarron .Valley, Canadian River Canyon, along the

Canadian Escarpment, along the north edge of the Llano Estacado, along the front of the Sangre de.Cristo Mountains (except where covered by basalt flows and other Quaternary deposits).. and in many isolated,loCali- ties in th.e northeastern part of the state. 'p' T

PANEL DIAGRAM OF EXETER,TODILTO. MORRISON, PURGATOIRE AND DAKOTAFORMATIONS, NORTHEASTERN NEWMEXICO The lower contact of the Exeter sandstone with the strata of the

Dockum group is a regional disconformity with local angular discordance,

In the area southof Tucumcari, local accumulations of chert-pebble conglomerate are common at the base of the Exeter. One such bed of conglomerate (about 6 inches .thick) occurs at the base of the sandstone on

Pyramid Mountain (fig 2). . The area of the conglomerate is small; it appears to be confined to the margin of deposition of the sandstone body.

Dobrovolny and.Summerson (1946) reported a thin-bedded, gray, fetid limestone within the Exeter on the northwest corner of the Llano

Estacado. This limestone lenses out rapidly to the east.

The upper contact with the overlying Morrison formationis conformable and there is evidence for intertonguing at several locaLities.

In the Dry, Cimarron.Valley,. Cooley(1955) described an intertonguing

,af the Exeter and Wanakah.fbasaL Morrison) formations. Intertonguing was also observed in the map area, and in the sections measured atOld

Mills, Sabinoso Gap, Galtegos Ranch, San.Jon and Pyramid.Mountain.

The main rock type is a massive to randomly cross-bedded, friable, poorly to moderately well-cemented, fine-grained, well-sorted sandstone. The colors range from wKlte (N 9) through.shades of grayish, orange (10 YR 7/4) to pale reddish brown (10 R 5/4). Fresh exposures are commonly white (N 9) rarely yellowish gray (5 Y 8/11.

The cross-bedding in any one outcrop is random with no obvious preferred orientation. The amplitude of the cross-bedding is commonly in excess .of four feet. The bedding planes are smooth and sharp and have a 33

DLA.9 V

i"" i

25 50 miles t CONTOURO- INTERVAL 25 FEET Figure 7. Thickness of the Exeter Sandstone, Northeastern New Mexico. concave form. . Each cross-bed set has a shape that is intermediate be-

tween the true lenticular and the wedge-shaped forms described by Shrock

(1948, fig 208).

Outcrops form steep or slightly rounded bluffs witha chara.cteristic

pitted or honey-comb texture to the surface. The pits range from a few inches to several fee.t in .diameter. Their distribution commonly follows

the cross-bedding.

The ,thickness.of the Exeter formation displays considerable varia-

tion. The isopachous map of the unit defines a broad northeashtrending

positive area .(fig 7). This feature was present during the deposition be-

cause the sandstone thins over the structure. At this contact the Exeter is transitional with the overlying Morrison formation. The sandstone

thickens both east and west from this positive feature to as much as 130 feet.

The northeast trend of this broad archis paraltel to the Sierra Grande

(cretaceous) arch. ”.Grain size analysis. -- In .search .of information concerning the nature of ancient landlocked aeolian deposits,,’ eighteen samples from the report area were sieved, plotted and statistically analyzed. They were

selected to include both areal and vertical variations.

Although the mean size l(Mz) of the sieved samples ranged from 2.034 to 4.226, fine sand to coarse silt, all but two are classified as fine sand.

By plotting the mean size vs. location of sample on a map of north-

eastern New Mexico, a consistent decrease in grain siqe from northwest 57-2-1

San Jon 4.22 0. 23 0.20 1. 03 ""

Pyramid Mtn. 1.23 3. 050.42 0.55

Table 2. Grain Size Data from the Exeter Formation 36

"""""""" 51' 2.0

UNI0.N

_" i

31 i

! ye* RDING I !

I QUAY4.2 I I

I I. I Id. A I 0 25 50 miles Figure 8. Mean Grain Size in Phi Units of the Upper Part of the Exeter Sandstone, Northeastern New Mexico, to southeast is.evident (fig 8). All the samples selected for this plot are

from the upper part of tke Exeter sandstone. The Exeter is composed of

a .single rock type; from top to bottom there is no significant difference

in the grain size or other megascopic properties of the hand specimens.

Therefore, the samples used in establishing this mear,size variation are

considered to represent all the upper partof the unit and not thin, indi-

vidual beds within the unit. . The avera.ge decrease in meansizeis 1.04

per 100 miles. Comparison of this map with the isopachous map of the

Exeter faits to show any significant correlation between mean size and

.thickness.of the formation. ThWfailure would appear to confirm the idea

that the mean size declines in the direction of transportation, and is in-

dependent of the thickness of the unit.

At, the 6ld Mills sec.tion a sample .of the lower:Exeter has a mean

size of 2,93$. .The formation there attainsa thickness of 130 feet and

is separated into.two massive sandstone units by 5 feet of silty shale.

This s+le is lithologically similar to the sbJe that interfingers with the

upper part of the .Exeter. . The lower sandstone may represent an earlier

aeolian dune migration.

The sorting .or inclusive standard deviation(VI; Folk and Ward,

1957) ranges from extremes of 0.23 to 0.65, very well-sorted to

moderately-s.orted. Most of the samples had sorting,coefficients of

0.35-0. 50 or ,within the well-sorted class, typical of recent beaches

and dunes (Folk; personal communication, March, 1958). A plot of the

sorting vs. location of sa.mple. does not reveal a significant trend. In 38

addition, plots of sorting vs. either mean size or thickness of the Exeter

revealed no significanttrend. .

The skewness (SkI; Folk and.Wasd, 1957) or asymmetry of the frequen-

cy curve values range from extremes of -0.20 to J0.42, coarse-skewed

to strongly fine-skewed. Most of the .va.lues fall in .the CO. 30 to io. 10

class or fine-skewed; these values are typicalof dune sands on the Texas

coast (Mason and.Folk, 1958), and helpp'confirm a dune sand.origin for the Exeter. . Three analyses fell in the 40, X0 to -0.10 or near-symmetrical class. A plot of the skewness values vs. location .of the upper Exeter samples ,fails to reveal a significant pattern. Also its correlation with

.other statistical parameters does not reveal important trends.

The strongly fine-skewed curves (0.42) can be explained by the mix- ing of two sedimentary fractions. This sample, from the Pyramid.Moun- tain locality, contains a coarse sand composed of chert particles and a very fine sand derived from the Eketer lithotope. As this locality is near the southern limit of deposition of the Exeter:tithosome it could record a minor admixture of sediment derived from the south (i. e. the coarse chert sand),

The kurtosis (KG)values .of the Exeter samples (Folk and.Ward,

1957), or ratio of sorting between the body of the .curve and the tails, range from extremes of 1.03 to 1. 93, mesokurtic .to leptokurtic. Most of the curves fall within the .leptokurtic range. Three possible explana-

.tions can be presented for this deviation from normal curve for the samples. First, the sediment could have a dual source, that is, the bulk of the material may have been derived fromone area with a minor admix-

ture from anather area. .But, because .the plot of kurtosis vs. location of

sample demonstrated no indication for dual sources, and because of the

absence of mineralogic evidence .of a dual sourcel this possibility has

been discarded.

A second possibility exists: perhaps the transporting and deposi-

tional medium lacked the ability to develop a uniformly-s.orted sediment.

.An ..environment in which large fluctuationsin transporting.energy were

common could develop a. sediment in which the tails had poorer sorting

than the modal fraction.

The .third possibility is one of sampling,technique. In an aeoiian en-,

vironment, in which energy (i. e. wind velocity) fluctuations are common,

a layering of coarse and fine material readily occurs. ,Each individual

Layer may be well-sorted within its size range. If two such layers are

mixed togekher in sampling, the result will be a bimodal sample. Thin-

> '".!. ! section analysis.of these samples indicate small micro-1enses.of finer

material included with the coarser material. These micro-lenses, only

'a few mm long, are distinguishable, without difficulty, only in thin sec-

tion. . Thus perhaps the poorly sorted tails of the curves, particularly the finer tail, is the result of sampling technique in which the entire rock is analyzed including these minor micro-lenses.

Thin sections also show evidence for a minor coarser mode, much

smaller.in percentage than the finer mode, that may be the result of in-

complete sorting. This coarser mode may be explained by a different Angular-Subangular Subrounded Rounded Well-rounded

Sample 57-7-2 .-.Old Mills Section

Angular-Subangular .'Subrounded Rounded Well-rounded

Sample 55-3-1 - Map Area

Table 3. Roundness.Data from the Exeter Sandstone. -- Visual roundness of 100 grains from each sample of Exeter Sandstone (After ,Powers, 1955). .,.. ...c 41

method of transportation. Bagnold (1954) in his study of the Libyan Desert found that the sand-size material was transported by saltation and traction, mostly by saltation. The coarser mode could be the result of transportation entirely by traction.

Compa,rison of the interrelationof mean size, standard deviation, skewness and kurtosis does .not exhibit the heLical trend .thought by some workers to be common to many terrigenous rocks (Folk and:Ward, 1957).

The size range .of tbe samples studied may not be great enough to develop this trend. Additional sampling may indicate such a trend or require some alternative explanation.

Mineral Composition. -- Because the Exe.ter sandstone is well- ."&i.& 3, yo tY sorted and has rounded to well-rounded grains it is classified as a ma- I(' ture to supermature subarkose (i..e. more than 5% and less than 25% feldspar, Folk, 1957). Although a few samples fall into the orthoquartzite class (less than 5% feldsparl, most of the samples conta,in 5-9%. feldspar, orthoclase, microcline and plagioclase occurring in subequal amounts,

Both fresh and badly vacuolized feldspar grains'are present inthe rock. The alteration is a post-depositional phenomenon, however, and is not.the result of ctimatic effects in the source area. .Those samples that are well-cemented with either catcite or kaolinite have fresh feldspar grains, whereas the poorly-cemented and uncemented samples contain vacuolized feldspar. One additional bit of evidence is the occurrence of authigenic feldspar overgrowths. These overgrowths, that are clearly 42

post-depositional, are vacuolized in the poorly-cemented samples, indicat-

ing that their alteration .occurred after their formation.

AIL the feldspar grains are very well-rounded indicating rather se-

vere abrasion.

By plotting the total percentage of feldspar vs. location of sample

for the upper part of the Exeter, a trend of increasing feldspar percent-

age to the south is established (fig 9). Two possible explanations exist . for this phenomenon. .First, the source of the material coutd have been

from the south and abrasion could reduce the.feldspar percentage.. But,

because of the previously-described trend of decreasing mean sizeof

the Exeter from north to south and because a qua,litative examination of

the minerals in the thin section show an increase in roundness from north - to south, this first possibility is ruled out. A second possible explana-

tion for this trend is that the feldspar grains, although probably initially

larger in the source area, because of lesser stability to abrasion owing

to cleavage and hardness (6.0-6.5 for feldspar; 7.0 for quartz),were

abraded faster and thus bypassed the larger quartz in transport and were

deposited in areasof finer mean size. ,Careful examination of the plot

of percentage of feldspar vs. location will reveal that this increase is

not uniform and is, in fact, reversed in places. These inconsistencies

are attributedto a normal mineralogic fluctuation of relative percentages,

where any one sample may be an.extreme for the particular mineral

suite.

Owing to the small percentage .of feldspar in each sample, no quanti- 43

10.4.

DRATON

:OLFAX UNION

CLAZTON

'7 7""""z

M ORA. I RDING ! !

OLAS V, IS 00 0' SA J MIGUEL

QUAY IADALUPE 9

25 50 miles t. O- 8 - Upper ExeterSamples (8) - Lower Exeter Samples

Figure 9. Percentage of Feldspar in the Exeter Sandstone,. Northeastern New Mexico. tative estimate of the ratio of the three types from north to south has been attempted.Qualitative examination, however, suggests that the plagioclase to total feldspar ratio decreases from north to south.

Examin+tion.of the vertical variation of feldspar percentage shows that the total amount decreases upward in most of the measured sections.

Qccasional reversal of this trend is again explained by chance variation.

Quartz sand comprises the bulk of the rock. A subdivision of the quartz into six types and four varieties.of each type was accomplished by point-counting 100 mineral grains %n .each slide'(Folk, 1957).

Analysis of the quartz-type data indicates at least two source-rock types; quartz .with straight to slightly undulose extinction from a plutonic igneous source and a ,subordinate amount of composite and stretchedcomposite quartz indicating a metamorphic source rock. The metamorphic-type quartz is less than 20% and averages only about 10% of the total terrigenous material. . A plot of the composite and.stretchedcomposite quartz types vs. location indicates that possibly most of the metamorphic-type quartz came from the northwest and a northern source was contributing mostly plutonic quartz with only a minor amount of metamorphic quartz.(fig.lO). A comparison of the plots of mean size vs. 1odation.and percentage of metamorphic.quartz types vs. location shows further evidence for two separate source areas,

~ ~, Accessory minerals include about 2% metamorphic rock fragments, - .~~. about. 1%very fine-grained (about3-5r) detrital dolomite/~and about 14% chert. The grain size ,of these accessory minerals is the same as the 45

.RATON

2OLFAX UNION

CL AZTON

M ORA r

"Y..

nLAS V IS 16 16 15s A MIGUEL

I ,,A"" I--"--- 0 TUCUMCARI

QUAY IADALUPE I-

25 50 miles t-6 - UpperExeter Samples (6) - Lower Exeter Samples

Figure 10. Areal Distribution of Percentage of Composite and Stretched Composite Type Quartz in the Exeter Sandstone, Northeastern New Mexico. 46

average grain size of the entire sample. No quantitative estimate .of the percentage of reworked sedimentary material can be made, owing to the severe abrasion that occurred during the transportation and deposition of the Exeter sediment. The result is that all the grains are rounded to very well-rounded and no distinction can be drawn between.quartz derived from a primary source area and that which has been reworked.

In spite of this severe abrasion, no crescentic chatter-marks were observed.on.the grain surfaces. Although some grains appeared to be

,"frosted", this .feature, when .examined under high magnification using water immersion technique, was seen .to be due to incipient quartz overgrowth development, . Thus the .original surface features have been.obscured.

The individual grains in many samples have a thin ciay coating. The orientation of the clay flakes is parallel to the grain surface, but the coating does not completely enclose the individual grains indicating that it is a post-depositiona.1 occurrence. .Although the amount is much too small for x-ray identification, in thin sectionthe clay is birefringent and resembles montmorillonite.

A qualitative study of the dolomite and chert fragments indicates that they are more abundant in the eastern part of the area. This indicates that a sedimentary source was also contributing material to the

.eastern part of the area.

-.Heavy .Minerals. -- A minor percentage .of heavy minerals is contained in the Exeter; it.consists of several color varieties of tourmaline, (I) a, a, a, c

Mitchell Ranch tr

18 1

9.tr tr

30 48

Table 4. Heavy Minerat Data from the Exeter Sandstone 48

pa,le pink and clear garnet, pale yellow staurolite, foxy red (a.dark red) and yellow rutile, zircon, ilmenite and leucoxene. In.addition, a trace of green hornblende was recovered from the Mitchell Ranch section. There is an extreme variability in percentageof mineral species from one locality to another. Tourmaline and garnet constitute the bulk of the non- opaques. Rutile and z,ircon occur only inthe.finer-g,rained samples and a .qualitative examination indicates they are more abundant in the .eastern part of the area. Because of th,e lack of a consistent trend in percentage

.of the different mineral species, no demonstration of two source areas is feasible; perhaps the seeming increasein zircon and rutile in .connection with the decrease in metamorphic-type quartz in some of the eastern samples suggests an igneous source for this part of the Exeter.

ALL the tourmaline grains are well-rounded to very welt-rounded.

Shades of red brown, otive drab, blue, yellow green, yellow brown, gray and black are present. No areaL distribution is evident for these color varieties.

Only the pale pink and.colorless varieties of garnet are present in the heavy mineral suite. The pale pink variety is slightly more abundant than the colorless but neither are restricted to any one area or any part of the section. . All the grains of garnet were originally well-rounded to very well-rounded but secondary solution has resulted in the formation of deeply etched to skeletal crystals. The fluctuation in percentage of garnet from one .locality to another may be partly due to solution. That the solution is post-depositional is indicated by the heavy mineral fraction from completely-cemented samples. Both calcite- and c.elestite-cemented samples contain very well-rounded but unetched garnet, whereas the poorly-cemented to non-cemented samples contain garnet that is strongly etched.

The pale yellow staurolite is deeply etched so that only skeletal crystals remain. It makes up only a trace of the heavy mineral suite and does not occur in most samples.

Both anhedral and euhedral rutile grains are present. The foxy red variety is the most common but some yellow rutile occurs. This forms a very small percentage of the heavy mineral suite and is restricted to the finer grain sizes.

Zircon..occurs both as euhedral crystals and as anhedral grains, which are not abundant and are restrictedto the finer grain sizes.

The opaque minerals that form a large percentage .of the heavy mineral suite are black tourmaline, ilmenite and .leucoxene. NO mag-

netite was found in any of the samples, , AIL the heavy mineral grains are rounded to very well-rounded. Relative amounts of leucoxene, black

b tourmaline and ilmenite have not been computed.

Cementation. -- Two aspects of cementation of the Exeter sandstone

are herein considered: the distribution of the dominant cement type and

the par"'genesis,of multiple-cementation. The distribution .of cement

types for the upper. Exeter (fig 11) appears to show a southeast-trending

strip of calcite cementation. Paralleling this strip are areas of kaolin

cementation andareas of no cementation. One area, in the vicinity of Las Vegas, New Mexico, is cemented with silica in the form of quartz overgrowths. The resulting distribution shows no relation to either thickness of the lithosome, grain size, present structural alignments, or mineral composition.

Five different cement types are recognized in the Exeter sandstone: quartz.overgrowths, limonite, calcite, kaolinite and celestite. Para- genetic interpretation of th.ese cements is difficult particularly when only two or at most three kinds of cement are found in any one sample. There- fore several samples must be used to determine the order of cementation.

In .order for this to have validity for all five cement types, the assump- tion must be made that the sequence is everywhere the same, The examination shows that the silica cement in the form of quartz .overgrowths is clearly the earliest. Next limonite coating over the quartz .overgrowths is shown in several slides.

Because calcite is included within the kaolin .cement in one part and kaolin included within the calcite cement in other parts of the same slide, these two cement types are thought to be contemporaneous. In the well-cemented samples the calcite commonly shows a poikilitic texture (i. e. the calcite is in optical continuity over several mm and contains many sand grains within the single crystal), In other slides the calcite occurs as a rather fine-grained cement; the grain size is finer than the average grain size of the terrigenous material. In some samples, especially where cementation is complete, calcite has replaced the feldspar grains. This replacement is common in plagioclase 51

COLFAX UNION

CL ArTON

-7 L 4

. OLAS VI

I """

IADALUPE i- ad*. 2 5 50 25 miles

.Figure 11. Cement Types of the Upper Part of the Exeter Sandstone, .Northeastern New Mexico. grains, in which it occurs along the albite twin planes.

The kaolin occurs as clear, well-crystallized stacks .of flakes that fill the pore spaces. With the exception of calcite, it contains no visible impurities. The kaolin appears to be a primary cement and not the result of recrystallieation from some other material. No evidence in the form of stages of alteration ,or impurities within the kaolin can be found to support a hypothesis of origin by recrystallization. Also no 1oca.liza- tion of the kaolin in patches can be demonstrated,

The celestite cement, found in only two localities (map area and

Gallegos Ranch section), is probably early, although no direct evidence of its age was found. It may be the result .of small playa ,lakes in which celestite was precipitated as a .result of evaporation.

In addition to the above-mentioned cements, feldspar overgrowths were found on a few grains. These probably antedate the limonite coating and are possibly contemporaneous with the silica cementation, but no conclusive evidence has been found.

The time of cementation is difficult to ascertain accurately, but must have been comparatively soon after deposition. The grains of feldspar and heavy minerals (particularly garnet and staurolite) in those

samples containing.no cement are badly altered and corroded. , To the contrary, the heavily-cemented rock contains fresh grains of feldspar and garnet that show no etching.

Paleoclimate. -- The source and environment of deposition of the

PiLC, . I,. /$i P. ' ?.I, *) :.1 ,r,' 4, c, '. Exeter sandstone,was and. The presence of fresh, .well-rounded feldspar 53

grains, well-rounded dolomite grains and well-rounded chert grains con-

qi.; <>;.i,:$+" .&si..? taining unaltered dolomite crystals ibevidence-of-&e aridity-of-the climate0

Todilto Formation

Nomenclature. -- Gregory (1917) defined the Todilto formation for exposures at Todilto Park, McKinley, County, New Mexico, stating (p. 55) that it there:

. . . , ...... caps an eastward sloping mesa of Wingate sandstone, and consists of 10 feet of resistant compact blue-gray limestone separated into two parts by a few inches of red sandy lumpy shale containing flattened calcareous mud pebbles. Near the top are well- worn fragments of black, white, and gray quartz and chert in quantities sufficient to form irregular bands embedded in the lime- s tone,

Darton (1928), who traced the Todilto into northeastern New Mexico, to the vicinity of Las Vegas as well as along the Canadian.Escarpment, stated (p 34) that:

. , . .it extends along the southern front of the Canadian Escarpment eastward nearly to longitude 104O,. , . .

The writer found strata resembling the Todilto only in the Romero- ville Gap, Section; none were found either in the San Agustin or the

Trujillo Hill Sections (fig 2). These observations agree withHeaton's

(1939) correlation of the Todilto formation into northeastern New Mexico, which shows that the Todilto does not extend east of Las Vegas.

Keyes (1936, p 75) in discussing the Todilto formation of north- 54

western New Mexico concluded that it was a soil regolith or caliche zone.

On the contrary, fish remains reported from these strata (Baker, Dane and Reeside, 1947) indicate that the unit is of either marine or-lacustrine origin.In addition, D. L.Kessler (Koerner, 1930, p 463)collected seventy-five specimens of fossil ganoids (fish), species Pholidophorus. americanus Eastman, from a gray shale exposed on the northwest edge of the Llano Estacado. . The locality is thirty miles east of Santa .Rosa,

New Mexico, The gray shale is above the Dockum group and below the

Exeter sandstone. .Similar fossil fish have been found inthetjundance formation by. Darton in 1899.

Baker, Dane and Reeside (1947), in a re-evaluation .of the correla- tions of Jurassic strata in northwestern New Mexico, placed the Todilto as a member of the Wanakah formation defined by Burbank, 1930. . The term Todilto formationis used herein because .the boundariesof the

Wanakah formation cannot be defined in northeastern New Mexico.

In an ,evaluation.of the nomenclature applied to the Todilto, one big problem must be faced. Is the unit that is exposed at Las Vegas in reality a valid lithic correlative of the type Todilto? The correlation was established by Darton (1928) and later corroborated by Heaton (1939). It is

r f J? 1~1&- 7 notwithin the scope of thisproblem to questionthis correlation, but it , is necessary to point out the possibility of an error. If the limestone cropping out in the vicinity of Las Vegas is not at the same stratigraphic horizon as the Todilto limestone, then the paleogeography for this area

may be in error. , The limestone near Las Vegas may represent only a

&-. 55

local lacustrine environment and not a part of the Todilto lithosome of the

Colorado Plateau.

Lithostratigraphy. -- .The Todilto outcrops in northeastern New Mexico are few; the formation is exposed only in the vicinity of Las .Yegas. It conformably overlies the Exeter, and it, in turn, is overlain conformably by the Morrison formation in,the .one outcrop examined at.RomeroviLle

Gap. Both contacts are sharp and show no evidence of reworking.

The rock is a dark gray (N 3) to black (N I), irregularly bedded, fetid, shaly Limestone. The outcrop thickness at Romerovitle Gap is

16 feet.

Sedimentary petrology. -- Because the Todilto was found in only one measured section (Romerovitle Gap), only one sample was taken.

Megascopically the rock type is crinkly-bedded, fetid, very.fine- grained Limestone. The laminae range in thickness from 0.15 mm to

0.75 mm, the average being about 30 mm. ,The length .of the laminae ranges from 0.50 mm to 10 mm. Most of the laminae have a convex upward form in cross section. When seen as a whole they resemble stacks of overturned saucers.

The laminae are composed of very fine-grained ca,lcite (2-4h or micrite (Folk, 1957). They show an inverse graded-bedding effect with coarser micrite at the top of each lamina. Relatively few impurities are contained within the layers; a few 0.02-0.06 mm quartz or feldspar grains may be included within an individual lamina. .A clay-organic complex occurs between eachlayer with occasional grainsof quartz and

I;’ 56

feldspar.

The rock is strongly fractured and each fracture is filled with medium- to fine-grained sparry calcite (up to 0.40 mm). The fracturing must have taken place before the material was completely consolidated, because one layer may be fracturedand offset without affecting either the layer above or below. Yet, the laminae were consolidated enough to become fractured. That consolidation can take place very early, even prior to buriat is evidenced by some Bahama carbonate samples (R. L.

Folk;personal communication, March, 1958).

The rock bears a strong resemblance to an algal limestone that was disturbed by wave action prior to complete consolidation.

An appreciable amount of heavy hydrocarbons is contained within the rock. Upon etching a sample in dilute hydrochloric acid for 15 seconds, a thick oil film is liberated. This hydrocarbon content may corroborate the other evidence of algal origin.

Morrison .Formation

Nomenclature. -- . Eldridge (1894, p 6) in describing the geology of the Crested Butte Quadrangle, Gunnison .County, Colorado, named the

Gunnison formation for the county. No type .locality was given, but the description stated the formation overlay (presumably disconformably) b maroon conglomerate of Carboniferous .age. Disconforma&y overlying the Gunnison is the conglomeratic, massive sandstone assigned to the

Cretaceous.Dakota formation. The section is composed of a basal, massive, white, quartz sandstone, 50-100 feet thick, Overlying this is a

sequence of drab, green, yellow and pink shale, sandstone and thin lime-

stone beds.

In 1896, Etdridge, in describing the stratigraphy of the Denver Basin,

defined the Morrisonformation for typical exposures near the town of

Morrison,, Colorado. The boundaries are defined (1896, p 60):

Its upper.limit is.sharplydefined by the Dakota sandstone, while the brown and pink sandstone closing the Trias as clearly marks its lower its Limit. H$;a$ sic ,7

The Morrison formation in the type area was divided into three members; a basal sandstone and shale member with numerous thin-bedded

Limestones called the "Atlantosaurus clays" (Marsh, 1877); a middle

massive-bedded quartz sandstone called the "Saurian sandstone"; and

an upper unnamed sandstone and shale member with some .Limestone beds.

These names were derived from the dinosaur faunasfound in each member.

Jenney (1898, p 593), describing the stratigraphy of the Cretaceous

of the BlackHills, defined the nonmarine Jurassic strata as the Beulah

clay, with type locality at Beulah, northeastern .Wyoming.

In San MigueL County, Colorado,, Cross (1899) subdivided the

Gunnison into two formations. The basal sandstone, composed of two

sandstone units separated by a thin, dark gray limestone in the Telluride

Quadrangle, was named the La Plata formation from the type locality of

the La Plata .Mountains. The upper sandstone, shale and limestone

strata was named the McElmo formation for exposures along McElmo Creek in the Telluride Quadrangle.

Knight (1900) in describing the Jurassic strata .of southeastern Wyoming appliedthe .term Shirley - to themarine Jurassic strata. The type locality is.the Shir.Ley Mountains,, Wyoming. For the overlying non-marine strata, he used the name -Como Stage (defined by Scott, 1897, p 477). In 1936 Baker, Dane and Reeside (p 9) revised the nomenclature of

th.e Morrison formation in .the San Juan basin. In this revision, the

Toditto limestone is included as the basal member of the Morrison.

Overlying this is the6alt Wash member (defined by Lupton, 1914, Grand

County, Utah). The upper and,iower boundaries of the Morrison formation in the San Juan basin are disconformable.

Gregory (1938), in describing the geology of the San Juan River country, subdivided the Morrison formation into four members. To the basal, white to brown-stained, cross-bedded sandstone was given the name

Bluff sandstone for exposures at the town.of Bluff, eastern Utah. .The unit is 2.00-350 feet thick in this region, Overlying the Bluff sandstone is a sequence of shale with a minor amount of sandstone. The name Re- capture shale was applied to this unit for exposures aiong Recapture

.Creek, a tributary to the San Juan River. The unit is 100-300 f.eet thick.

A coarse-grained, conglomeratic sandstone, 222-295 fee.t thick overlies the Recapture shale member. . The name.Westwater Canyon sandstone was given to this unit for exposures along West Water Canyon, a,tributary to the San Juan River. The uppermost unit was named the Brushy

Basin shale for exposures .of variegated white, gray, green, purple and red sandstone and shale. At the type locality, in Brushy BasinGreek, the unit has a thickness of 450 feet; elsewhere the thickness varies from

350-470 feet.

Goldman and Spencer (19411, in southwestern.Golorado, demonstrated CIE ,:. the that. theLa .Plata sandstone was,partlylaterally., i/ continuous with En- trada formation and pa.rtly with that of the Morrison. (The name.Gunni-- -son was .repta.cedby Morrison. 1, The lower sandstone of the La.Plata was demons,trated to be the Entrada, whereas the limestone and upper sandstone was equivalent to basal Morrison. The name Pony Express limestone was applied to the basal limestone (middle unit of the La

Plataj of the Morrison formation. The name was first used by Irving

(1905, p 56). The .overlying sandstone unit was named the Bilk Creek sandstone from BiWCreek, a tributary of the San .Miguel River (Goldman , and.Spencer, 1941, p 1750). The term Wanakah (first defined by Burbank,

1930, p 175) was restricted to the shale and marl strata overlying the

Bilk Greek and underlying the next massive sandstone. The massive, cross-bedded sandstone overlying the Wanakah marl was named the

Junction Creek sandstone for exposures along Junction Greek. The upper part of the Morrison formation was not subdivided.

Stokes (1944), in des,cribing the Morrison formationof the .Colorado

Plateau, subdivided it into four members. To the lower sandstone strata

Stokes (p 962) applied the name Salt Wash member (originally defined by

Lupton,1914, p 124). The overlying shale was'named the Recapture

Greek member, This name was derived from Gregory (1938, p 59). . The massive sandstone strata overlying the Recapture Creek was defined as

the Westwater Canyon (originally defined by Gregory, 1938, p 59). .The

upper variegated shale unit was named the Brushy Basin (originally de-

fined by Gregory, 1938, p 59).

In 1944, Waldschmidt and LeRoy redefined the type locality of the

Morrison formation. The new locality was placed (p 1100]: , . . .along the north side of the West Alameda Parkway road cut, SE 114 Sec. 23,. T4S., R70W., Morrison quadrangle, 7-1/2 minute series, Jefferson .County;CoIorado, 2 miles north.of the town of Morrison. It is 277 feet thick at this locality.

The newly designated type locality is divisible into slx lithologic units

(p 1100-1101), from top to bottom b these are: Sandstone and Shaleunit - 76 ft. 6 in. of variegated sandy shales, 15 ft. sandstone at the base

Red Shale Unit - 36 ft. 9 in. of red to maroon sandy shales, several 1 ft. thick calcareous sandstones

Gray Shale and-Sandstone Unit -. 51 ft. 6 in. of gray clays and several 1 ft. beds.of gray calcareous sandstone, basal 8 ft. conglomeratic sandstone contains .some dinosaur remains

Gray Clay and ,Limestone Unit - 49 ft. 9 in. of'interbedded gray clays and non-marine, fine-grained limestone

Gray and Red Shale Unit - 55 ft. of gray and red silty shales Basal Sandstone Unit - 7 ft. of massive to cross-bedded, coarse- to medium-grained,calcareous sandstone

At the type section the basal sandstone of the Dakota formation dis-

conformably overlies the ,Morrison, but the lower contact is not visible.

In the Dry Cimarron, Baldwin et aJ (in preparation) have designated

the basal sandstone and shale, that were previously assigned to the - Gunnison, Colo.

McElmo fm.

Gunnison fm.

Bake.r, Dane,Reeside Gregqry Goldman & Spencer Stokes Waldschmidt (1936) (1938) (1941). (1944) and Leroy (1944) San Juan Basin 1 San JuanCountry I SDuthwestern ..Colo. 1. ColoradoPlateau ,(Tv~e ,I Localitv I 1 Unnamed IBrushyBasin I I Unnamed B rush..Bas.in I I Sandstone .& shale members member I ~ 1 shale I E' members Westwater .Junction Westw.ater Red shale *- wE' E' wE' Canyon mem- Creek ss. Canyon mem- Gray shale d Salt Wash E d FI 0 ber 0 Wanakah 0 ber sandstonel .TIrn member .2 .r(In .*rn 1 I& ';1 Recapture marl &I Recapture .* Grayclay & k Todilto k k k shale k Bilk k Creek. I I limestone I 1ime.stone 2 3 -3 Bluff ss. s Creek ss. s Pony Salt .Wash Express 1s. member

Table 5. This. chart represents the .evolution of nomenclature concerning. the Morrison formation. . The terminalogy refers to different parts of the section in separate localities and does not imply. lateral equivalentsfrnme-area to another, 62

Wanakah formation,(Cooley, 1955, p. 161, as the brown silt member of the

Morrison formation. The "agate bed" is used as a key marker bed in~the

lower part. of the formation (Baldwin et al, in preparationj. ",

In the present paper, the Morris,on is treated as a formation with no

formal subdivisions for northeastern New Mexico. .Gross lithologic

variations may be demonstrated, but these vary laterally as well as verti-

cally. The only persistent unit occurring over most of northeastern.New

Mexico is the ."agate bed". It was not located in a few sections, because

it is either absent or covered,

Lithostratigraphy. -- Lee, in 1902, traced the Morrison formation into northeastern .New Mexico and reported the occurrence of the !!agate

bed" in exposures along the Dry:Cimarron (p 44).

Stanton (1905) discussed the Morrison formation.of northeastern

.New Mexico and southern .Colorado, but concerned himself primarily

with the age and correlation of these strata.

In 1925, Rothrock, in a description of the geology of Cimarron

County, Oklahoma, stated that the Morrison thins and disappears in

the western part of that county (p 32). This presumably would be the

southeastern margin of the strata.

DeFord (1927) pointed out the misinterpretation of the geology by

Rothrock and demonstrated that the formation extended much fartherto

the east. I In northeastern New Mexico the Morrison formation conformably

overlies and in part interfingers.with the underlying Eketer sandstone. The only exception to this is in the Romeroville Gap sectfon where the

Morrison overlies the Todilto formation. The contact is conformable in this .one locality that was examined. Neef (19501, in a sedimentary study of the Todilto, concluded that the Todilto is gradational with.the Morrison formation. The upper contact of the Morrison is a regionat disconformity and,is .overlain by the Purgatoire formationin the eastern part of the area and by theDakota formation in the western part.

The Morrison formation is a polylithologic unit. The highly complex sequence is composed.of terrestrial channel sandstone, shale, mudstone, siltstone, pebble conglomerate, non-marine .limestone and few bentonite and volcanic ash beds. Few, If any, individual beds can be traced for any great distiznce with the exception, perhaps, of the ."agate bed". Even it can.be shown to be composed of not a single bed, but two--sometimes three--separate layers and may therefore be a complex of silica-nodule layers .occupying slightty different stratigraphic positions in different parts~ofOhe &=ea. Odgen (1954, p 914) considers the "agate bed" to be a time-horiqon, probably resulting from alteration of volcanic ash.

The color of these silica-nodule beds is either red brown or gray,

Usually, in a.section where two or more layers .of the "agate bed" are present, the lower one is red brown and the upper one fs gray. These beds are actually sets of disconnected nodules that range in .size from a few inches to a foot or more in diameter. In a few localities continuous layers a few inches thick .can be traced for several tens ,of feet. Only rarely absent, the ."agate bed" occurs in the basal part of the formation, a few feet to a few tens .of feet above the Exeter sandstone. .Where two or more layers occur, they are rarely separatedby more than2.0 feet of section.

The ash beds are more abundant in the west-central part of the region, and are found in.the upper half of the formation. Their thickness ranges from 2 or 3 inches to almost a foot,. The nearly pure ash is soft, powdery, white (N 9j weathering to light gray (N 71. It has an irregular or nodular upper surface and contains little or no foreign material indicating that it has been deposited in situ and hasnot been .reworked. "

Along the Dry Cimarron andin th.e Bueyeros area a few bentonite beds are present in the lower part of the ,formation, whereas throughout the area they occur in the middle and upper parts .of the unit. They are particularly abundant in exposures along,the Dry Cimarron (Cooley,

1955,). These beds range from a few inches to a foot in thickness and are composed of waxy clay containing altered shards that is typical of ? I J7 bentonites.

' A wide variety of colors can befound in these strata. Shades of gray, green, brown and red are prevalent. Variegation is widespread and locally spectacular.

In the map area petrifiedwood and dinosaur bones are present in the upper one-half of the formation and are locally very abundant. The dinosaur bones and most of the petrified wood in the western part of the map area,contain.a small amount of secondary uranium (probably carnotite).

In northeasternNew Mexico the Morrison formation .can be generally separated into three members; a Lower shale, a middle sandstone and an upper shale, This three-fold division is not everywhere applicable. .At many localities the entire section may be dominated by either sandstone or shale or .contain subequaL portions of each rock type. For this reason formal subdivisions of the Morrison formation arenot proposed for northeastern .New Mexico.

The lower shale, which contains the "agate bed", is dominantly a red brown silty shalewith minor green streaking and blotching. Channel sandstone is .present in.severat of the measured sections, notably

Trujillo Hill, .Old Mills and Romeroville Gap. In the Bueyeros area two to four persistent very fine-grained sandstone layers are interbedded with red brown silty shale at the baseof the shale ung. At one locality on Ute Greek in the map area, there are oscillation ripple marks 1 two inches long with a one-half inch amplitude {probably lacustrine) that trend N45OE and occupy the upper surface of the uppermost persistent sandstone layer. .Along the Dry Cimarron and at the Gallegos Ranch section beds of gypsum 1-3 fee.t thick are present at the base of the unit.

The middle sandstone is composed of variable amounts of variegated red brown and pale green sandstone and silty shale. Small lenses of chert- and clay-pebble .conglomerate occur here and there; loca,Lly the conglomerate is abundant. .This unit is best seen in exposures along the walls of the-CanadianRiver Canyon. At several places in the western 66

.""_ """_""" ""-.

ORATON

C 0 L'F A X I UNION ! 1 i!

N M I\G U .E L

/* .4 i -i G JADALUPE I

50 miles t- 25 I CONTOUR INTERVAL 100 FEET

Figure 12. Thickness of the Morrison Formation, Northeastern New Mexico. part of the map area the basal part of this sandstone contains agatized dino-

saur bones.

The color of the upper shale is dominantly pale green although in part

variegated red brown. Channel sandstone and chert and clay pebble con-

glomerate are locally abundant. Volcanic ash beds .are more common

within this .unit, particularly in the Trujillo Hill and Canadian River sec-

tions.

The thickness of the Morrison formation in northeastern New Mexico

ranges from zero to somewhat more than500 feet. .The ,thickest part

of the section~.occursin three areas; Romeroville Gap,. Canadian-River

and Gallegos Ranch (fig 12). The .contours on,the isopachous map.are

generalized and should be assumed to indicate only regional trends.

Local, minor variations are obscured by th.e contour .interval, but a

closer interval is not justified by the available data.

Grain size analysis. -- Nineteen .samples of the Morrison forma- " tion were analyzed by standard grain size techniques. The samples in-

.clude seventeen sandstones and two sandy mudstones.

The mean size of the nineteen samples ranges from 2.236 to 6.676 .

or fine sand to medium silt. The average mean size is about 3.25-3.506

or very fine sand. Six samples have mean size vatues which place them

in the fine sand class. Eleven samples .fall in the very fine sand class.

Only two samptes fall in the silt class, one coarse and.one medium sized.

Of the samples analyzed, the very fine sand is the most abundant, but

volumetrically the mudstone is by far the most abundant kind of rock of Gallegos Ranch 57-10-3 San Jon 4.25 0.25 0. 03. 0.99 South .of Caves Map Area 2. 87 1. 31 0.65 4.64 - .Upper Sample Mtn. 3. 15 Pyramid 0.53 0. 56 1.20

Table 5. Grain Size Data from the Morrison Formation the Morrison formationin northeastern New Mexico.

Although most of the samples analyzed for grain siee are in the very fine sand class, an examination of all the sandstone samples collected indicates ,that the abundanceof very fine sand is probably abnormal. The most common sandstone size is probably in th,e fine sand class.

No areal varidtion in grain sizeis obvious, but there is .a tendency for the sandstone .to become finer to.the east. There is also a tendency in most sections for the sandstone to decrease in size upward with the exception.of the uppermost samples where a minor coarse mode is added.

Thi~minor .coarse mode whichhas better rounding is probably the contribution.of a new source area~.ornew source type.

The sorting or standard deviation values range from 0.25 to 2.63

,or very well-sorted.to very poorly-sorted. The average sorting value is about 0. 70-0. 80 or moderately-sorted. Only one sample has a sorting value that places it in the very well-sorted class. Three samples fall in the well-sorted class, eleven samples fall in the moderately- sorted class apd three samples fall in the poorly-sorted class. OnLy one sample falls in the very poorly-sorted cLass. The nineteen samples of the Morrison formation demonstrate that the Morris,on sedimentwas not as well sorted as the Exeter, Purgatoire or Dakota sediments.

Skewness values of the analyzed samples range from -0.07 to {O. 65 or near-symmetrical to strongly fine-skewed. Three samples have skewness values that place them in the near-symmetrical class. Three samples fall in.the fine-skewed class and thirteen samplesfall in the -. rf rf 0 Standard Deviation strongly fine-skewed class. It is apparent from the skewness values that the depositional environments of the Morrison formation.didnot possess enough kinetic energy to winnow the finer material completely. It is possible .that strongly fine-skewed values, particularly from sediments in the sand-silt range, may be an indication of continental deposits.

Kurtosis values of the Morrison samples range from 0.60 to 4.64

.or very platykurtic to.very leptokurtic. The average kurtosis value is about 1.304,40 or.leptokurtic. Two samples fall in the .very platykurtic class, 4 samples in the platykurtic class, 4 samples .in the mesokurtic class, 6 samples in the leptokurtic cia.ss md 3 samples in.the very leptokurtic class. The samples .show a uniform spread of kurtosis

values through the complete range of classes, , This indicates a high degree of variability inthe .energy of the environment of deposition.

Owing to the extreme complexity of lithologic types in the Morrison formation, no statistical analysis of the. grain size distribution has been attempted. -Mineral composition. -- Thin .sections of 42 samples were studied for mineral composition, texture and cementation. Owing to the lithologic complexity and great variability within.the formation this study represents only a reconnaissance survey of the mineral content, but enough data .are available.to es,tablish certain tentative conclusions concerning b0th.th.e vertical and lateral mineral and textural variations.

The Morrison formationin northeastern New Mexico ranges in com- positipn from subarkose to arkose. It is the most richly feldspathic of 72

all the formations studied, , The amount ranges from about 10% to 40%,% with.orthoclase, plagioclase and microcline present in all of the samples.

In most of the samples, orthoclase and microcline are subequal in amount but the content of plagio.clase is variable. feldspar is present only in small amounts at the base of the unit, but shows a.Iarge rate of increase in quantity in the first hundred feet and small rate of decrease higher in the section. For example, in the Romeroville Gap section the basal sandstone within the .Morrison formation contains 29% feldspar, orthoclase and microcline each comprising 11% and plagioclase 7%. . A hundred feet higher in the section the amount is 38%. The large increment is mostty a .result of an increase in plagioclase. From this maximum of 38% there is a decline to 20% feldspar near the top of the section, The same trend is repeated in each section but the percentage differences become more subtle. In the easternmost sections, a variation of only 5-6% is evident and the total feldspar percentage is less than twenty for a .maximum. Therefore the amount of feldspar not only diminishes upward but also eastward. .The largest decrement is shown by orthoclase and microcline not only verticalIy but laterally as well. The amount of plagioclase diminishes but its decrease'is much less obvious than the decrease of the other two feldspar types. The composition of the plagioclase is in the albite-oligoclase range. No vertical or areal variation in plagioclase composition was noted.

Both fresh and weathered feldspar grains were found in all the samples. In many of the samples, the fresh vs. weathered feldspar ratio %- 3

F! 0 h d rd V $$ % 33 N

s3 E 3 N

s z %-m %rn W 0

%-3 E s?g N mN 74

is approximately unity for orthoclase and microcline, but most of the plagioclase is fresh. This probably indicates a dual source of feldspar.

Most of the feldspar grains are subround .to round; no obvious difference is discernible on the rounding of the feldspar grains except that the plagioclase grains appear.less well-rounded. The rounding increa,ses upward in the section and the feldspar grains of the upper sand appear to have better rounding in the easternmost sections. This decrease of feldspar percentage away from the probable direction of source of the Morrison sediment is reversed in the Exeter sandstone in which the feldspar percentage increases away from the source. The discrepancy is the result of a climatic difference. The arid climate of the.&eter source and deposition did not result in the .ch.emical decomposition of feldspar whereas during .Morrison deposition the warm, humid climatewa.8 in part responsible for feldspar destruction. The weathered grains of feldspar are vacuoliaed; only a few show some sericitization.

The quartz grains were subdivided into classes as previously described. . Common quartz (straight to slightly undulose extinction) is the most abundant type in all of the samples, ranging from about 50% to 70%.

The easternmost samples have the highest percentages of common quartz, but no definite trend has been established. The percentage of strongly undulQse quartz,.aaries from about 5 to 10. . Semi-composite quartz makes up only about 1-37ain any of the samples. Composite and stretchedcomposite quartz types are subequat in amounts and comprise about 3-676 of the total sample. In most of the sections, there appears to be an increase in composite and stretched-composite quartz percentage upward, but the difference is so slight (1-370)that such a trend is not obvious. No geographic variation for these quartz types is discernible. Most of the quartz grains are free from any inclusions. Only about 1-5% of the grains contain either microlites or rutile needles. A few grains contain bubble inclusions. The quartz .grains appear to show an increase in rounding upward in the section, also an increase from west to east, but the change is very slight, because as a whole the quartz .grains throughout the formation are subround to round. A few of the uppermost samples contain well-rounded and subangular quartz grains together indicating that most of the high roundness was inherited from older sedimentary rocks .

Chert is present in all the samples; the amount ranges from a trace to as much as 5%,. Most of the .chert contains inclusions of organic structures including a bryoqoan and some unidentified rods (spicules?).

The percentage of chert increases upward in the section and appears to increase to the east. The vertical increment is 2-5% in most sections, but the increment to the east is only about 1-3%. The grain size of the chert compares with the average grain size for the entire sample, ex- cepting some of the uppermost samples in which the chert grains are sligktly coarser. In one sample of a coarse sandstone the chert made up 20% and its grain size was much larger than the average,

A small percentage (0.5-2) of volcanic-rock fragments and a very few low-rank metamorphic-rock fragments (phyllite) occur in.some of the slides. The volcanic-rock fragments are weathered.making their identification much more difficult. The metamorphic fragments appear to be composed of either phyllite or.low-rank schist. They show considerable deformation resulting from compaction and grain penetration.

Thin (0.5-2 ft. ) discontinuous limestone and dolomite beds are present in the central and eastern parts of the area. They appear to be more common in the eastern part, particularly in areas of maximum deposition. The limestone is composed of very fine-grained (0.005-0.01 mm) anhedral calcite. SDme beds have terrigenous inclusions of sand- size material. One sample of limestone contains triaxial glass shards and euhedral quartz .phenocrysts indicating a .volcanic ash fall. Fractur- ing and healing of the fractures with spa.rry calcite is common. One sample shows two stages of fracture-healing separated by a thin layer of limonite.

The dolomite is composed of fine grained (0. 01-0. 02 mm), anhedral grains. The uniform grain size, lack of crystal development and absence of replacement structure indicate that the dolomite is probably primary. No sedimentary structures such as bedding, cross-bedding, slumping or ripple-marks are visible.

Many of the sandstone samples contain small amounts of clay (usually. less than 5%j buta few sandstone samples contain appreciable quantities (20-30%). No thin sections of pure clay from the Morrison formation were obtained. The clay in most of the samples is green, highly birefringent and index below balsam (montmorillonite or mixed- 77

layer clay). In a few samples the clay is red brown from later iron stain.

This clay probably has the same composition as the clay of the shale sections adjacent to the sandstone and was introduced either during deposition or by later infittration. The clay in thin section shows no dominant orientation. Injsome slides the clay particles are wrapped around the grains and in other samples bear no relation to the grain boundaries. The mudstone samples contain intimate mixtures of silt and clay. The .clay shows no visible bedding. This may indicate continental type of deposition.

X-ray diffraction indicates that the clay of the adjacent shale beds is either a mixture of degraded-itlite and montmorillonite or a mixed-layer montmorillonite-illite depending on the position in the section and its areal Location.

Clay mineralogy. Two aspects of the clay mineralogy of the -- .. Morrison formation are herein described. .First is described a detailed study of four sections to determine the vertical variation .of the clay mineralogy of the formation at these Localities; then several samples from each measured section are analyzed to detect the gross areal clay mineral variations. The detailed study of the vertical clay mineral variation was accomplished by x-ray diffraction of samples collected from two localities within the map area.(fig 5), section 57-6 (Canadian

River) and the Dry Cimarron section measured by Cooley (1955, Pipe- line Canyon section). The Canadian River and the Dry Cimarron sections were selected because they have the best exposures and in addition these sections give good vertical control in two widely-separated areas. Two 78

localities .were selected inth.e map area in orderto determfne areal varia-

tions that occur in small tracts. It was considered that a comparison of

,.., areal variations between the two localities within the map area with the ,, &, areal variations between.two distant tocatities might poirrt out some .j q!.': aspects of the clay mineralogy that would be useful on a regional scale.

~ ,! ,,. .. : 1 .: ; \i A total of fifty-nine powder diffraction patterns were obtained from 8 il I v\c j . z ! twenty-nine samples from the Dry Cimarron section. The basal part of I y :: : 4', the Morrison formation, described by. Cooley (1955) as the Wanakah for- 1, 1, y;, . i %. , ! .>I mation, contains a 10, 5-10. 8A clay. . The diffraction peak shows a , I\.. I <. ! li > , *_' .. .: ! .;. : ,$?.> gradualbuikl-up and a .sharpdecline. Glycolation .separates it into a ',L ;/

.~,- ~ ~ ~ . .. , ~ .~.I : : ., i 10. OA peak and a(15.5A peak with.a corresponding decrease in intensity2/, i, '.. ~.~. *_" ,"-.- ~ . ~ ~... ~.~~. .~ ~.. - ~ .. ' . i ! The 10.OA peak is not characteristic of a pure illite in.that it has an :,_ ,.. , ,'. I /" j. ':, asymmetrical shape. These data indicate tbt there is a mixture .of .. . .',. -. .~.. "~ ~ . . .~ . ~ ., ~~ .. ..- " i weathered or,degraded-illite and a .montmorillonite that will not com- ~ ~.. .- 1.; j \, . . _.. .~. ~. . ~ .~ i" pletely expand to tiiZ?Fa?& 17A ww- .I. Other i mineralsidentified from the diffraction pattern include a poorly-

crystallized kaolinite (ragged 7.2A peak), minor amounts.of calcite

(3.05A peak) and quartz (4.27A and 3.35A peaks).

The pattern of the second sample shows a .14.5A peak and a 10. OA

peak. The 10. OA peak has the same characteristics as,the 10.5-10. SA

peak of the preceding samples. GIycola.tion failed to shift the 14. 5A peak,

Therefore, in addition to the degraded-iltite, the sample contains axon-

expandible clay mineral, probably chlorite or vermiculite. Kaolinite,

calcite .and quartz are also presentin the sample. The third sample is a 15. 1A montmorillonite that readily expands to

17A upon glycolation. When soaked in concentrated KC1 for 2 hours, the

d-spacing decreases to 11.9A and expands readily to 17A after glycolation.

When soaked in concentrated KiC03 for 2 hours, the d-spacing decreases

to 11.7A with a minor potassium-fixation at 10. OA. . Again solvation by

diethylene-glycol expands the structure to 17A. . Soaking.samples in con-

centrated KC1 and concentrated KiC03 for 60 days did not further de-

crease the d-spa.cings and the samples stitl were completely expandable.

The montmorillonite was treated with 0. 01N solution of sodium hexa-

metaphosphate (calgon) for a period of fifteen minutes making it a mono-

ionic Na-montmorillonite. The d-spacing shifted from 15.1A to 13. OA.

This sample a.lso readily expanded to the two layer diethylene-glycol

configuration, This sample was obtained from a 0.5 foot bentonite bed.

This is the earliest record along the .Dry.Cimarron.of appreciable vol-

canic activity.

Above this bentonite bed th.e clay mineralogy is similar to the inter-

val below it. The main clay type is a degraded-illite with varying amounts

of montmorillonite. Except for minor changes in relative amounts, no

major changes are recorded for the next75 feet.

At 125 feet above the base of the formation, the firs.t definite occur- / .rente of a.mixed-layerday is recorded. The x-ray diffraction pattern

shows an intense maximum at 13. OA which separates to a lesser intense

10. OA and a Large 17A maxima when glyco.lated.

Above 125 feet the relative amount of montmorillonite increa.ses until 80

no illite peak occurs on the diffraction pattern. This is between 175 and

200 feet above the base of the formation.

' At 200 feet the first of a persistent occurrence of kaolinite is recorded.

From there .to the top of the formation the clay minerals are montmorillo-

nite and kaolinite in varying proportions. The kaolinite is well-crystallized

,giving diffraction peaks.of 7.22A, 3.56Aand 2.38A in order of decreasing

intensity.

A total of twenty X-ray diffraction patterns were obtained from ten

samples from the Canadian River section of the Morrison formation.

X-ray diffraction patterns of samples from the basal part of the Morrison

formation at this section show a 10..2A diffraction peak. The peak .is

similar to the asymmetricat diffraction peaks from the basal Morrison

samples from the Dry. Cimarron section. Glycolation did resolve a 15. OA

peak that was not apparent prior to glycolation. This degraded-illite

with varying.amounts.of an incompletely expandable clay mineral (chlorite

or vermiculite ?) is present through the lower 200 feet of the formation.

This is identical with the clay mineralogy of the Dry Cimarron section

with,the exception of the thin bentonite beds. These bentonite beds are

not present in the Canadian River section.

From 200 feet to the top of the section the diffraction patterns show i I a maximum between 11. OA and 13.04.. Glycol treatment separates .this

'into 10. OA and 17. OA peaks. This interval is then characterized by a I. mixed-layer clay. The .mixed-layer clay corresponds to the first occur-

~ rence of volcanic ash beds in the.Ganadian.River section. The mixed- '\>I i: layer clay tends to increase in montmorillonite content upward in the sec- ' oca\ ? [L- I tion. This is indicated by an increase in the d-spacing of the unglycolated .. " _.r...?l-.-_ L.. _"- -.." __ ... .~.. - . .~.. . , '. sampleand a correspondingdecrease in intensity of the 10. OA spacing of ' the glycolated sample. No appreciable amount of kaolinite was recorded in any of the samples from the Canadian River section.

In all, twelve X-ray diffraction patterns were obtained from six samples from the locality on the eas.t sideof Green Valley in the map area .(fig 5). Only ZOO feet of the Morrison formation is exposed; the upper 100 feet are covered by landslide debris,

The clay mineralogy of the lower 90 feet of the Morrison formation

C-H consists ofWe mixture of 14A to 15A montmorillonite a.nd degraded- illite. In .addition, a minor amount of kaolinite, calcite and quartz .are present in the samples.

The first occurrence of a true mixed-Layer clay is a hundred feet above the base of the formation. The 12.5A diffraction peak recorded from this clay was separated into distinct 10. OA and a .17A maxima. This /i montmorillonite-illite mixed-layer structure persists to the top of the sampleinterval. The only variation in clay mineralogy within this inter- I

Val is the ratio of montmorillonite to ilkite in the mixed-layer structure.

There appears to be an increasein montmorillonite.

Sixteen patterns were run on eight samplesof the formation from the locality on the west side of Green Valley (fig 5). No difference was recorded between this and the locality on the east side of Green.VaLley. . At this locality the upper hundred feet of the Morrison is not exposed because 82

of landslide debris.

At.:Romeroville Gap the clay mineralogy of the Morrison formation consists of a .mixture of montmorillonite and a degraded-illite. The amounts of the two clay types vary but the variation is not consistent in either direction. The diffraction pattern is almost identical with the montmorillonite and degraded-illite patterns at other localities. At. the very top of the section below the Dako.ta there is an abundance of kaolinite. (L. At SanAgustin thechange from +-tie mixture of degraded-illite and .., montmorillonite .to a,mixed-layer montmorillonite-illite occurs 175 feet 1 above the base of the formation.

' At Trujillo Hill the change takes place between the 100 and the 150-

foot level. Some kaoliniteSome level. foot present,is also I i; At the San.Jon section the ctay mineralogy is all a mixture .of ::2:.. g degraded-illiteand 14. 0-15, OA montmorillonite. .In addition,kaolinite , ...... ~~ . . __ . 9 is a common constituent in all the samples.

The clay mineral samples from Sabinoso.Canyon, Burro Canyon,

Old Mills and Gallegos Ranch were scanned in order to determine the

boundaries of thedifferent clay mineral zones. This zonation is an ~~ attempt to demonstrate the areal distribution of the different clay mineral types. It should be emphasized that these boundaries a.re gradational.

No sharp change in clay mineralogy was Dbserved. It should also be emphasized that the eonation is generalized and should not be empirically applied to any local area within northeasternNew Mexico. I I. ~ """"""""""""_7/ I,.

LAS LEGAS

PANEL DIAGRAM SHOWING CLAY MINERAL ZONATION This clay mineral study indicates that the Morrison formation can be zoned into two clay units; (1) a mixture of degraded-illite and montmorillonite, and (2) a mixed-layer montmorillonite-illite. In addition to these clay mineral types, kaolinite occurs in certain horizons in many areas. ),q:...&: n,7 The lower zone contains degraded-illite and montmorillonite. The mont-1 morillonite in this zone may be in par.t a product of the weathering of chlorite because some patterns show a 14.6A d-spacing that is characteristic of chlorite. This peak will not expand by glycolation which is further evidence that the structure may be held by the brucite layer. In- completely weathered chlorite may account for the minor occurrence of non-expandable 14.6-15A peaks in the lower zone.

The upper zone contains a mixed-Layer montmorillonite-illite with minor amounts of kaolinite. The ratio of montmorillonite to illite increases upward and along the Dry Cimarron clay mineralsin the upper part of the Morrison are composed entirely of montmorillonite and kaolinite. .

-.minerals. -- Seventeen heavy mineral separations and mounts were made by the standard heavy mineral technique.

Ten non-opaque and at least seven.opaque heavy minerals were identified from the Morrison heavy mineral suite. TourmaLine, zircon, garnet,apatite, staurolite, rutile, epidote, kyanite, sphene and chlorite constitute the non-opaque fraction. Ilmenite,, leucoxene, biotite, black . tourmaline, limonite, and possibly some magnetite make up the opaque heavy mineral suite. In addition, three of the slides contain one or two Table 7. Heavy Mineral Data from the Morrison Formation flakes of gold.

Opaque heavy minerats are present in all seventeen slides in amounts

ra.nging from 24% to almost 100%. Leucoxene is by far the most abundant

opaque heavy mineral. Most of the leucoxene shows appreciable rounding;

only a small percentage of the grains are angular to sub-angular. Ilmenite

is the second most abundant opaque heavy mineral. The grain size is

small and uniform. The grains are only slightly larger than the average

zircon grain. . A small amount.of what is herein described as ilmenite is

probably magnetite, but owing to their physical similarities, no distinc-

tion has been attempted. Black tourmaline occurs in a minor amount but

is present in practically all the samples from the Morrison formation.

All the black tourmaline grains are well-rounded. Limonite, possibly

altering from biotite, occurs in a smalt percentage in most of the slides.

It is particula.rly angular and contains inclusions of quartz .ando,ther

foreign debris. The 'grains appear to be composed -of fragmented, platy

incrustations. Hexagonal flakes .of biotite are present in several of the

slides, particularly in samples fromthe upper part of the formation.

One or two flakes of placer gold are present in three slides; 57-9-2,

Gallegos Ranch section, 57-6-5, Canadian.River section, south of caves,

map area.

Tourmaline is present in all the mounts from a trace to as much as

73% of the non-opaque fraction. Most of the slides contain jess than 3070

tourmaline. Almost all the tourmaline grains are-well-rounded; only a

!,8-,)0 #$,,l/.!*'c. few ehhea-rxl grains are present and these are restrictedto the finer grain 87

sizes. The tourmaline group was subdivided.into five varieties based.upon

.color: red brown, olive drab, green, pinkand blue. The red brown and olive drab varieties are the most abundant and are present in all slides..

Although these two varieties .are subequal in amountsin most of the samples, the olive drab variety is slightly more abundant in some of the slides. The green tourmaline variety is third in abundance and subequal to the red brown and olive drab varieties in a few of the samples, The pink and blue tourmalines occur in only minor percentages and are present as traces in many of the slides. Pink and blue tourmalise were absent in some of the samples.

Zircon is present in all the slides from a trace to as much as 74%, but most.of the samples contain Jess than 30% zircon in the non-opaque frac.tion.. The zircon has been divided into four varieties, two based upon form and two upon color. There is a sharp separation between the euhedral-colorless and pink varieties and the anhedral (including rounded) -colorless and pink types. The fact that no zircon was found that would \ 'h II, occupy a position between these euhedra! and anhedral types suggests a .~ k""~' ~. .~ dual source with the euhedral grains the result of(\volcanic activity "...~~...I_. most abundant variety, the anhedral-colorless type, occurs in all the slides, and inseveral samples constitutes practically the entire Eircon percentage. . The second most abundant, the euhedral-colorless variety, is less than 40% of the total zircon. Both the anhedral- and euhedral- pink color varieties are subequal in percentage and are present in only a few samples. These pink variej es commonly constitute a trace to 5-6%

. .. 88

of the non-opaque fraction. .Although both color varieties of euhedral

Eircon are sporadic in their occurrence, they show an overall increase

in percentage upward in the section, but no regional trend.

Garnet is present in thirteen of the heavy mineral samples in amounts I

ranging from 3% to as much as 54%. All but two of the samples contain

less than 25% garnet and seven.contain less than 10%. .The garnet was

separated into two calor varieties, colorless and pink. The colorless

variety is by far the more abunda.nt; the pink variety occurs in only four

samples and has a maximum proportion of one-third of the'tota.1 garnet

percentage in sample 57-9-2 (Gattegos.Ranch section). The garnet grains

present in a few samples. Those samples that show extreme etching of

the garnet contain no pink types, perhaps because the pink garnet has

a greater tendency to decompose chemically. A major part of the etch-

ing is post-depositiona1. One sample contains well-rounded garnet grains

that show only minor pitting whereas the poorly cemented samples an-

.tain only skeletal crystals. . This also indicates that the grains were

rounded before the etching.

Nine samples contain apakite ranging from 5% to as much as 59%.

Five of the samptes .contain more than 40%. The apatite was divided into

two varieties; the euhedral which shows relatively good crystal outline

and the anhedral which either has no crystal form or are rounded. The

anhedral variety is the most abundant constituting the entire percentage

of apatite in a few samples. Appreciable amounts of euhedral apatite .. 89

are present in sample 57-3-10 and 57-3-13 (San Agustin), 57-5-6 (Sabinoso

Canyon) and 57-8-6 (Burro~Canyon). The occurrence of apatite is sporadic but there is a general increase in percentage upward in.the section and a concentration in the central and western parts of northeastern New

Mexico,

Staurolite is present in eleden of the heavy mineral samples in

.amounts ranging from 1%to 27%. . Seven samples contain less than 10%.

Most of the staurolite is .strongly etched and only skeletal crystals are present in .many slides. The sporadic occurrence in variable percentage and the extreme etching,of the grains suggests that at least part of the etching is a result of post-depositional solution.

Rutile is present in only nine samples. No sample contains more than 7%and most of the samples have .only 2% or 33'0, . All the rutile is well-rounded and.of a uniform grain size. The average grain size of the rutile is about the same as the average grain size of the zircon. Two " c'Dlor va.rieties are present in subequal proportions and an occasional .. cloudy variety is present. Owing to the small percentage present in the slides, the absence of rutile is not considered to be significant but merely omission by chance.

Epidote is present in .only one slide (57-2-9, Romer.ovi1le Gap) and constitutes only 2% of the non-opaque fraction. The grains are smaller than the zircon grains, well-rounded and yellow green in color. The occurrence in only the westernmost section is probably a .result of its chemical instability. Kyanite occurs in.sample 57-5-11 (Sabinoso Canyon), bdt makes.up

only 2%of the non-0paqu.e fraction in that sample. The grains are color-

less, subround and have.basal parting. The siz.e of the particles is be-

tween .the average for tourmaline and,the average for zircon. Because

of its small percentage, omission by chanceis probably the reason for

the absence .of kyanite in the other sections, particularly those to the west.

Sphene occurs in two localities in the lower part of the formation.

Sample 57-2-9 (Romeroville Gap) contains 7% and sample 57-9-2 .(Gallegos

Ranch) contains 2% sphene. , The mineral was identified by its high relief,

honey brown color, wedge-shaped crystals and hairline fractures across

crysta!. faces. The indication from the s.canty data suggests that sphene

is restricted to the lower part of the formation.

. Sample 57-2-9 (Romeroville Gap), contains 2%chLorite. The mineral

is identified by the anomalous blue birefringence and micaceous form.

The absence of chlorite in.sections farther eastis .undoubtedly a result of

the mechanical instability of the mineral.

A plot of distribution and relative stratigraphic positionof apatite

suggests an increase in percentage upward in the section and a decrease

in percentage to the southeast. (Swing to the mineral's sporadic occur- 7 1y.+s.. ',.% rence and relative abundance .over large areas, a source I1 b*ic&j?I?c 1 to the northwest is postulated. Also because of increase in apatite per- I I centage upward in the section, an increase in volcanic activity is con- i sidered. . Corresponding to an increase in the apatite percentage is an 1, increase in euhedral zircons. But the earliest euhedraL zircon is slightly IO,*' ," ,"

oRATON

? 0 L F.A X

UNION

CLATTON

'7""". 1"""" "_ i

M ORA I RDING j

3 MIGUEL \ 1 ! ,,A"" r---- 0 TUCUMCARI i Q U A Yo ADALUPE I 0

I 5 - Upper MorrisonSamples (5) - Lower Morrison Samples

Figure 15. Percentage of Apatite in the Non-opaqueHeavy Mineral Suite from the Morrison Formation, Northeastern New Mexico. / canic eruptions were more basic and therefore contained Less zircon, ! 1 i The appearance of hexagonal biotite in association with the apatite and 1 1 euhedral zircon is additional evidence for the postulation of a volcanic ! ' source.

cementation. -- Three cementing agents are common in the Morri-

son formation: silica in the form of quartz overgrowths, calcite and

kaolinite. In addition, minor cementing materials include authigenic

feldspar, opal, chalcedony, celestite and hematite, . All the samples are

cemented to some degree and commonly two or more .cements are pre-

sent in a.slide. Quartz-overgrowth cement is common in the formation

in northeastern.New Mexico. Practically all the atides show some quartz

overgrowth. These overgrowths contain few or no inclusions, and where

well dev.eloped they form interlocking mosaics.

Calcite is the second most abundant cementing material. Two kinds

of calcite are present, microcrystalline and megacrystalline varieties.

The microcrystalline variety commonly develops anhedral crystals that

are less than.O. 1 mm in diameter. . This variety was.found in a few

samples. . The megacrystalline variety is much more abundant. It com-

monly forms large areas in optical continuity; in one slide the calcite

cement is in uniform crystallographic orientation over th.e .entire slide.

In other slides, crystals 1-5 mm in diameter are not uncommon. The

megacrystalline variety has a poikilitic texture in that these large

crystals are filled with sand inclusions. In many of the samples containing megacrystalline calcite, the sand grains are not in contact but appear to

be floating in the catcite, In every slide examined that contains quartz

.overgrowths and calcite as the cementing agents, the calcite is later than

the overgrowth formation. There is no evidence that quartz has replaced

calcite, because no calcite is found between,the nucleus and the over-

growth-and the calcite is not pushed aside by the quartz. . In addition, the

cakite is contemporaneous with the kaolinite becausein some areas the

calcite occurs between the detrital grains and the ka,olinfte and in other

areas calcite veinlets cut through the kaolinite.

Kaolinite is the third most abundant cementing or bonding agent. It

occurs exclusively in patches that rarely eyceed 1 mm in diameter. The

kaolinite is clear, well-crystallized and contains no foreign material, It

is after the quartz.overgrowth formation and prior to the calcite cementa-

.tion. This s.trongly suggests that it is not related to the outcrop weather-

ing.

. Authigenic feldspar is present in several slides. It forms over-

growths Over the detrital nucleus in optical continuity. The twin .la-

mellae are also faithfully reproduced. The overgrowths are fresh but a

few grains show some minor vacuolation. The authigenic feldspar is

found only in those samples that contain a large percentage of detrital feldspar. Overgrowths .occur in equal abundance on .all three feldspar

types.

Celestite .occurs in samples from the Gallegos Ranch section and in ". ". samples collected from Pyramid Mountain. The samples containing 94

celestite were not thin sectioned and therefore its relationship was not de-

termined. It appears to be restricted to the lower part of the formation,

A single Locality in the eastern part of the map area contains a ,carbo-

nate rock that has been completely replaced by chalcedony. This- rock

obviously had an intraclastic texture because pebble-shaped areas,now

replaced by chalcedony, are contained in a matrix of opal cement, .The

rock is thought to have originally been a carbonate because relict struc-

tures .of oolitewand rhombs are present in the so-catted intraclasts. The

minor amounts of terrigenous material, such its quartz and microcline, are unaltered.

Hematite and limonite occur in patches throughout the unit and have no manifest relation to composition, location, texture of the rock or geo- L~7 togic structure.

\ -; PaIeoclimate. -- The Morrison formation in northeastern New ! J

Mexicoexperienced a climatechange during its deposition. Heavy mineral ', \. J

studies, feldspar condition, and the presence of celestite in isolated " . '' . ~~ t. \- .. patchesindicate that the.Lower part of the Morrison was .depositedin-a , ~~

1. relativelydry environment similar tothe environment prevalent during : '. $' ; ". /.. ', the deposition of the Exeter sandstone. The climate became more humid ;, .. ' !; .. ,' during deposition of the upper Morrison. This is indicated by the increas- '.: L( ., ,t ':., .., ~ ingly weathered condition of much of the feldspar and an increase in the qz amount of kaolinite. CRETACEOUS. SYSTEM

Purgatoire Formation

Nomenclature. -- . Early workers along the Front.Range.of the Rocky

Mountains in southern .Color.ado and northern New Mexico mapped the

sandstone and shale units above the typical Morrison strata as the Dakota

formation. In southern .Colorado, the .Rakota was divided into a ,lower

sandstone, a middle shale and an upper sandstone that contained scattered

shale Lenses .

In 1852, Jules Marcou described the strata cropping out in the

Canadian River Yalley at Tucumcari, New Mexicos and classified the strata

cropping out on Pyramid Mountain into Triassic and Jurassic units (fig 2).

Hill's re-examination in 1888 and 1891 of the Tucumc.ari region dis-

closed that at least part of the uppermost strata.on Tucumcari Mountain

should be correlated with the. "Trinity sands" (Cretaceousof Central

Texas).

Cummins (1891) re-evalwted the work of Marcou and Hill andcon-

cluded that the substantial sequence of fossiliferous strata cropping out in the.Canadian River Valley at Tucumcari should be placedin the Cretace- ous. For these strata, exposed on .such outliers as Tucumcari Mountain,

Pyramid Mountain, Mesa Rica , and along the northern escarpment of the

Llano Estacado, he proposed the name Tucumcari beds. The probable type locality'is Tucumcari Mountain (1891, p ZOl), located immediately

southeast of.Tucumcari, Quay. County, New Mexico.

Lee (1901) found some Early Cretaceous marine fossils along the Purgatoire River that he concluded came from the Morrison formation.

Stanton (1905) in a re-examination of these localities demonstrated

that they were actually contained withinfhe shale unit of the Dakota forma-

tion. He concluded therefore that these strata .(the shale and,lower sand-

stone) should be separated from the.Dakota formation, and suggested a

correlation of this lower shale with the Kiowa shale of Kansas.

. Stose (1912) formally proposed 'Purgatoire formation' for the sand-

stone and shaie cropping out in southeastern.Go.lorado above the Morrison

and below the Dakota formations. .He designated the Purgatoi.re River

Canyon in the Mesa de Maya quadrangle as the type ,area.but no exact

type Locality was specified.

Rothrock (1925) extended the Purgatoire formation into northeastern

New Mexico and the Oklahoma P.anhandle. His description showed that

the formation could be divided.into a lower sandstone unit and an upper

shale with interbedded sandstone lentils. .Although he did not formally adopt names for this region, he pointed out that the sandstone unit in

southern Golorado was called the Lytte sandstone member and the upper

shale the Glencairn .shale member of the Purgatoire formation,

DeFord (1927) pointed out that Rothrock, although correct in extend- ing the Purgatoire formation into this region, erred in establishing the lower contact with the Morrison formation thereby including a large part of the latter in the Purgatoire. He stated (p 754):

The true Purgatoire formation consists of just two members: a dark fossiliferous shale about 20 feet thick resting on 15-50 feet of white sandstone. The dark shale corresponds to the Kiowa shale of Kansas, and the white sandstone' to the Cheyenne sandstone of Kansas.

Bullard (1928), in his discussion of the Lower-Cretaceous of western

Oklahoma, further substantiated the correlation of the Kiowa shale and

Cheyenne sandstone as the upper and Lower members respectively of the

Purgatoire formation, In addition, he gave an accurate and.thorough

account of the age of these strata in theOklahoma and.Texas Panhandles.

A correlation of these strata is projected into the Tucumcari region.

Stovall (1943) formally applied the terms Kiowa shale member and

.Cheyenne sandstone member to the Purgatoire formation of the Oklahoma

Panhandle. The U..S. Geological Survey Committee on Geologic Names

accepted this proposal with the following restrictions (Stovall, 1943, p 74):

The .Committee pofnted out that 'Purgatoire' has been recognized as a formation for Colorado and .CimarronCounty, Oklahoma, and perhaps some other places, but has not been extended to Kansas; and that the Kiowa and..Cheyenne a,re formation names in Kansas, and have not been extended to Cimarron County, Oklahoma. ,In view of the forthcoming.Cimarron County report (the present publication), the Committee agreed to extend the Kiowa and Cheyenne into Cimarron County, Oklahoma, as members of the Purgatoireformation - butnot into.Colorado on- into 1" New Mexico. . . .

Dobrovohy and.Summerson (1946) subdivided the Purgatoire forma-

tion in Quay County, New Mexico, into three members: the lower,

Tucumcari shale member; the middle, Mesa Rica sandstone member; and

the upper, Pajarito shale member.

Cooley (1955) in.describing the strata cropping out in-a portion of the

Dry Cimarron Canyon, applied the terms'Kiowa shale and Cheyenne sand-

stone members to the Purgatoire formation. Baldwin "et al. (in preparation) in the forthcoming reporton the geology

of Union..County will remark that:

It is a temptation to state^ that throughout Union County the Pur-

gatoire consistsof an upper mudstone and a lower sandstone, , ..~ , %. . equivalent to the Kiowa shale and.Cheyenne sandstone members in >- . ' adjacent areas of Colorado and Oklahoma.

But owing to some uncertainties concerning the Morrison-Purgatoire

contact, he will probably decide not to attempt the subdivision.

An important aspect of this problem is the relationship of the.Chey- enne and Kiowa members in the Dry Cimarron .Canyon and the Tucumcari,

Mesa Rica and Pajarito members in the Tucumcari area. .The units appear to be welt-definedin both areas and within each area thereappears to be

Little doubt concerning their validity.

Field relationships indicate the probability that ihe Mes.a Rica is correlative with the Cheyenne, and the Pajarito with the Xiowa. An in- tensive investigation of this interval by closely spaced measured sections from Tucumcari to the Dry Cimarron mayshow that the Mesa Rica and

Cheyenne are parts ,of a continuous sandstone lithosome. The Pajarito andKiowa sha,,es probably thin and, to some extent, grade into the lower i

~ sandstone lithosome. . A direct connection between the Pajarito and Kiowa , ...P '\ may rrat. be'-possibleI to demonstrate. Shoutd such a correlation be established, a nomenclatorial problem arises. Which terms or set of terms should be abandoned? First, because .of usage a set of terms should be adopted (for example, Pajarito and Mesa Rica instead of Pajarito and

Cheyenne). Although the terms Kiowa and Cheyenne have precedence, 99

the Tucumcari, Mesa Rica, and Pajarito form a lithogenetic sequence in

their type area. At the present time, it appears advisabkto retain each

set of terms for its respective area,

Lithostratigraphy, -- The Purgatoire formation of northeastern New

Mexico is a terrigenous unit composed largely of sandstone. Shale is

present in variable proportions; it is particularly abundant (nearly 50700)

in the northernand s,outhern parts of the area.

The Morrison-Purgatoire contact is difficult and in places impossible

to locate, particularly where the upper part of the Morrison is composed

of sandstone. An arbitrary field boundary Is based upon the uppermost

occurrence of bedded green or red brown shale. This is used where no

other criterion exists for the establishment of such a boundary, especially

in ,poorly exposed areas. Baldwin et al, (in preparation) wil1,point out ”

this difficulty.

Where the upper shale member of the Purgatoire is present, the

Purgatoire-Dakota contact is readily discernible. This contact is diffi-

cult to establish in localities where the shaleis missing and Dakota sarid-

stone rests upon Purgatoire sandstone. In these areas a subtle color

difference is useful in differentiating the two formations, the Dakota

generally having a yetlowish orange shade. Particularly complex areas are those composedof Morrison sandstone overlain by Purgatoire sand-

stone which is in turn overlainby Dakota sandstone,

The Purgatoire formation is confined mainly to the eastern half of northeastern .New Mexico. North of the map area the Purgatoire is composed of a lower sandstone and an upper shale unit. The contact between these units is conformable and can in places be demonstrated to be gradational. In the map area the upper shale is missing, either by erosion, or non-deposition or by changing facies. h the map area.and along the

Canadian River good evidence is present to demonstrate .erosion. Dakota channels have been cut down into the Purgatoire and perhaps even into the Morrison in certain.localities. Some evidence is present for grada- tion into sandstone .owing to the somewhat greater thickness of the sandstone in the map area and along partof theGanadian River.Canyon and the presence of shale in these areas.

In the southern part of the area the Purgatoire is divisible into a lower shale member, a middle sandstone member and an upper shale

member, containing minor amounts.of sandstone. , The lower shale, which .lies disconformably on the Morrison formation, can be traced from the Texas.High Plains along the Canadian River.Valley to at least as far west as .Mesa.Rica (fig 1). South from the Canadian.River Valley the shale cannot be traced ,owing to lack of exposures. The Lower shale is not recognizable northwar& it probably grades laterally into sandstone.

The middle sandstone, that becomes the lower unit northward, is probably the lithologic correlative of the lower sandstone in the northern part of the area. The .contact with theunderlying shale is gradational.

The .upper shale in the southern part of the area is gradational with the middle sandstone; it is disconformably overlain by the sandstone of the Dakota formation. There, as in the northern part of the area, the 101

upper shale shows evidence of both facies variation into sandstone and pre-

Dakota erosion.

The two main rock types are sandstone and shale. The sands.tone is white (N 9) to very pale yellowish orange (10 YR 9/6) and weathers to pale grayish orange (IO YR 8/41. The shale %.olive gray (5 Y 4/11 to medium gray (N 5) and weathers from medium light gray (N 6) to light gray (N 7).

The .lower shale contains a concentration .of Gryphaea Fiilatata var. tucumcarii near its base, This species .occurs in profusion in all the areas examined in the .Canadian River Valley in the vicinityof Tucumcari.

Locally, thin (1-6 inches thick) lenses of limonite-stained, angular, 1-20 mm cher.t-pebble conglomerate occurs within this tower shale unit. This conglomerate, although.abundaat, cannot be traced more than a few feet.

The sandstone is composed of medium- to fine-grained, well-sorted, relatively well-rounded, quartz grains. Locally, and particularly nea.r the base of the unit, well-rounded, 1-40 mm, chert-pebble conglomerate occurs in thin (0.2-1.0 ft.j, discontinuous lenses. A few clay pebbles are included within the conglomerate particularly nea.r the baseof the unit. An opinion of numerous workers in northeastern New Mexico is that the conglomerate marks the base of the Purgatoire transgression; unfortunately similar conglomerate occurs within both the Morrison and J .Dakota formations.

The upper shale contains numerous sandstone lenses and in places sandstone ,is dominant. Along the Dry. Clmarron the upper shale contains a Gryphaea bed, which, as it is traced westward onto the Sterra Grande I

arch, descends in the unit to become the uppermost sand bed of the under-

lying lower sandstone unit (W. R. Muehlberger; personal communcation,

March 1958).

The thickness.of the Purgatoire formation ranges from zero at the

western limit of deposition to slightly more than 100 feet a.long the eastern

edge of the state. The average thickness in the eastern half of north-

eastern.New Mexico is about 50 feet. .There is consid.erable variation

from place to place, ranging from 30 to.lOO feet in less than one mile.

This is caused by the Purgatoire t~gxq@on~overan uneven surface,

and by the Dakota transgression over the Purgatoire formation, during -~~”” which the upper pa.rt of th.e Purgatoire was eroded and reworkedin numer-

.ous areas. The erosion can be demonstrated by the channels cut into and

in places probably through the Purgatoire formation,

.Grain .sizeanalysis. Thirteen samples, including twelve of sand- ” -- stone and one of sandy mudstone, were analyzed by standa.rd grain size

! analyticaltechniques.

The inclusive mean size values of the samples range from 1.926 to

6.206 or medium sand to medium silt. Most: of the samples have mean

size values of 26-36 or fine sand.

The sorting or inclusive standard deviation values range froma mini-

mum of 0.28 to 3.25 or very well-sorted to very poorly-sorted. Most

of the samples have sorting values of 0.40-0.60 or between the well-

sorted and moderately-sorted classes. With the exception of the sandy

mudstone, no sample has a sorting va.lue in excess of 0,66 or muderately- Standard Sample No. Mean Size .d . Deviation Skewness Kurtosis

Kp-Carbonaceous ss. 1.92 0. 66 0.27 1.31 Map Area 55-8-1 Map Area 0.42 1.93 0. 15 1.23 57-9-17 I I I Gallegos Ranch 2.281.27 -0.21j 0,46 56-3-2 I Canadian .River 0.57 2.30 1.40 0. 24 57-7-16 Old Mills 2.33, 1::: -0.01 1.37 57-8-11 1 1 1 1 2.35 -0.03 1.58 Burro-0.03 Canyon 2.35 55-9-4 Map. Area 0.28 2.40 -0.03 1.06 57-10-9 San Jon 0.41 2.48 0. 06 1.32 57-9-15 Gallegos Ranch 2.73 I 0.430. 52 I 2.00 57-7-13 I Old Mills 2. 82 0. 54 0. 61 2.15 57-10-11 2.95 0.48 0.33San Jon 0.48 2.95 1.13 57-10-13.. San Jon -0. 0.5407 3.77 1.05

~ 56-1-5 San Jon 3.256. 20 0. 71 0.57

Table 8. Grain Size from the Purgatoire Formation sorted.

Inclusive graphic skewness values range from -0.21 to LO, 71 or

coarse-skewed to strongly fine-skewed. Most of the values fall in the

-0.10 to kO.10 or near-symmetrical class. .Only one sa.mple has a value

that places it in th.e coarse-skewed c.lass and only four samples fall in the

strongly fine-skewed c;lass.

The graphic kurtosis values range from a minimum of 0, 57. to 2.15

or very platykurtic to very leptokurtic. Only the sandy muds.tone sample has a value which places it in the very platykurtic class. . Two samples fall in the mesokurtic class; one sample falls in the very leptokurtic class; the remainder of the samples have values which place them in the leptokurtic class. Six of the thirteen samples have kurtosis values that place

them in the middle (1.20-1.40) of the leptokurtic class.

By plotting the four above-mentioned statistical parameters against

each other (i.e. meansize vs. standard deviation, etc. 1, a possible trend

is established. Owing to the lack of sprea,d in mean size for the Purga-

toire samples, most of the points fall into a small cluster and no continu-

ous trend is defined. baddition, several samples are cemented with silica in .the form of quartz overgrowths further increasing the difficulty in obtaining representative grain size results. In spite of these difficulties, a curve can be visualized that may beara relation to the helical trend established by Folk and Ward (1957). The axis of this suggested helical

trend is in,clined about 30° to the mean size axis. .A similar helical trend with an inclined axis was reported by Harris(1957). I05

The development of a helical trend depends upon two major factors, source and environment of deposition. The source must have exerted an important influence on this particular trend because the samples were collected from widely separated localities over much of northeastern.New

Mexico. in order for such a trend to be established from such widely spaced samples, the environment of deposition, which no doubt varied slightly from place to place, must have had only a minor effect. . Deposi- tional fluctuations are probably responsible, however, for causing a scattering^ of the points thus producing a Jess pronounced helical trend. - It must be emphasized that additional data are necessary before this trend , r;r, can be accepted.

Mineral composition. -- Ten thin sections of samples.from the Pur- gatoire formation were studied for mineral composition, texture and cementation. All the samples are from the sandstone parts of the Pur- gatoire, The mineral composition was determined by point counts of

100 grains in each slide. I 3 : .. Allthe samples examined are fine-grained,moderately well-sorted 3, towell-sorted. The grains are rounded to well-rounded,which together I

,> ,'& v. withthe sorting values place all the samples in the mature to supermature ~; .. 1, .. -I class (Folk, 1957). The maturity of the samples ranges from the upper i

I <-' part of the mature class to the lower part of the supermature class. Be- cause all the grains are rounded to well-rounded, including the chert, .. 5 "'. "'. the rounding must have occurred during depositionof the Purgatoire and ; (' was not inherited from older sedimentary rocks. i

, e- . : '.

,- 106

All the samples were classified as orthoquartzite (i. e. less than 5%

feldspar or metamorphic rock fragments). All the samples contain 1%to

4% chert, and most of the samples contain a very small percentage (about

0. 5-1%) of feldspar.

The quartz grains were divided in the same manner as in the preced-

ing analyses of the Exeter sandstone and Morrison formation. Common

quartz (straight and slightly undulose extinction) types range from 67% to

86%. Most of the samples contain between 75% and 80% common quartz.

Undutose-type quartz ranges from 4% to 8%, semicomposite quartz from

1%to 57'0, composite quartz from 37'~ to 11%and stretched composite quartz from 1%to 4%. M0s.t of the quarta grains are free from inclusions.

Microlite imAugi.o-ns. in quartzgrains rarely exceed 5%. Only two samples ~ . - .... .~ ~. .~ .Y contain as much as 6% rutile needle inclusions. In only one sample, 10% .. of the quartz grains observed contain vacuoles.

Arealdistribution plots of sever31parameters, such as different ., ,.: . \! .. quartztypes, inclusion types, feldspar percentage and chertpercentage, , -,

..I.:. do not reveal any significant trends.

Although no source direction has been established by areal distribution studies, several factors can be determined about the source area. d: <,, The presence of chert indicates reworking of older sedimentary material. __

The oc.currence of fe1dspa.r indicates a primary plutonic- source area. A,~.S" - -."" ~ ". .-.". ~' ' 3 minor amount of metamorphic materiaj was contributed as evidenced by " the metamorphic quartz types. Because the sand grains are well-rounded,

-7:. no separation of relative amounts of contribution by each source type is feasible. Additional sampling may Teveal significant trends that are not

evident because .of inadequate data,

Cementation. -- Silica cement in the form of quartz overgrowths is present in every slide of the Purgatoire formation. Pt'forms the principle

cementing agent for the rock although often only incipiently developed.

Secondary clay material is present in most of the slides. Kaolinite is the dominant clay mineral, although an.olive green highly birefringent clay with index above balsam (probably timonite-stained montmorillonite or a mixed-layer structure) occurs in a few of the slides. Both types of

-? clay material were introduced after quartz overgrowth formation because _L

vergrowths. The kaolbite invaria.bty occurs as patchy pore fillings and is composed of well-developed crystals but not in the form of worms. The olive green clay occurs as thin coatings over the quartz overgrowths and oriented parallel to the sand grain surfaces.

The clay probably formed by physical infiltration from the overlying shale. The kaolinite appears to have developed at about the same time as the olive green clay was .introduced. One slide contains a post- kaolinite, limonite stain, probably the result of outcrop weathering.

No good evidence is available to determine the time of quartz cementation, except that it was probably subsequent to deposition and prior to outcrop weathering. The .evidence for formation of the cement after deposition is that the quartz overgrowths interlock and give no indication of having been moved after their formation. . That the cement antedates the outcrop weathering is shown by the lack of correlation of 108

freshness of outcrops and cementation of the samples. For example, the

sandstone in a new road-cut at the San Jon section is well-cemented with

silica in the form of quartz overgrowths. __~i -Clay mineralogy.-- Three shale samplesof the Purgatoire formation were selected for clay mineral analysis by x-ray diffraction. Two of these -3 samples are from the Tucumcari shale member, one from the.San Jon ..x - x- p.. 2 section and one from Pyramid Mountain. One sample was taken from the

sha le in the map area. map theKiowa in (?) shale :- y,! ..i J .. .. ~ i' The x-ray diffraction patterns of the Tucumcari shale member con- u; '. I. c tain maxima at 12A and 7.2ZA indicating the presence of a montmorillonite-.I,' I; illite mixed-Layer clay and a kaolinite clay. Treatment with diethylene- i glycol separated the mixed-layer structure into a 176 and 10A spacing for the interlayers of montmorilloniteand illite respectively. 1 The kaolinite gave sharp diffraction maxima at 7.22A and 3.56A indicating that it is well crystalline.

The Kiowa (1)shale from the map area also contains a mixed-layer

structure and kaolinite. The mixed-layer structure gave an asymmetri- ca) diffraction peak, that is, a gradual, ragged build-up and then a sharp decline following a 10.3-10. 8A peak. Solvation by diethylene-glycol gave a sharp 10. OA illite peak and a ragged peak at 17A. . Although this structure is predominantly micaceous, it should not be confused with a ."degraded illite" because there is a sharp separation between the 10A and

17A peaks.

-Heavy minerals. -D Thirteen samples of the Purgatoire formation in Map.1.92 Area 28

Table 9. .Heavy Mineral Data from ,the Purgatoire Formation 110

northeastern New Mexico and two samples from the lower.Dakota group at

Morrison,, Colorado, were disaggregated. They were washed to remove

the clay fraction. The heavy minerals were separaked by bromoform,

mounted tn.Canada,balsam and 100 grains counted in ea.ch slide. The re-

sults are tabulated in percentage of opaques and the non-opaques were re-

computed .onthe Basis of 100%.

. Zircon, tourmaline and rutile are presen.t in ~11fifteen samples;

staurolite occurs inn four samples; hornblende and garnet oceur in owe

sample each. The opaque heavy minerals inctude ilmenite, leucoxene, black tourmaline [schortite) and miaxor amounts of magnetite and limonite.

'Z~irmnis the predominant heavy mineralof the Purga.toire formation averaging about 70%. Itn.an1y one,sa&le the zircon percentage wa5 less

&ham50 of the non-opaques (47% im sample 57-10-13, San.Jon section).

The zircon was subdivided into four categories: euhedral (1) colorless and (2) pink; anhedral (including rounded) (3) colorless and (4) pink. The anhedral-colorless class contains the highest percentage of zipcon. The

euhedral-colorless class is the second most abundant. .The pink zircon was subequal in proportions of euhedral and anhedral types but it makes up only a minor percentage of the total z,ircon assemblage. There is a

sharp separation between the euhedral and the anhedral types of zircon indicating separate sources. .By plotking the ratio of euhedral to anhedral zircon on a bas.e map of northeastern New Mexico, a southeasterly decrease of euhedral types is demonstrated. Two possible explanat$ons.can be pre-

sented: (1) the decrease could be a resutt of distance from a presumed 111 /.

ORATON

COLFAX UNION

CL ArTON

"I""": -T"----- "_

M ORA 16' k8

RDING

ELAS VE 4s

'S A N MIGUEL

A"" ""-" / I I TUCUMCARI

Q U AY(I IADALUPE 1 I A 0 25 50 miles

T. '- .Figure 16. Ratio of Euhedral to Anhedral Zircon in the Purgatoire Formation, Northeastern New Mexico. B 12

'\ 7 westerly volcaxxic source, or (2.1 it could be a result of an increase in vot-,: 1

~~~ -.~. ". .- ~ani~activity during the transgression. ~BQ~enough data are avai.labb at " the preseai time to exclude either possibility, but a number of closely-

.spaced, sampled Sections along the Dry Cimarron in t$e direction .of the

Purgatoire transgression would probably demonstrate the correct answer.

TourmaIime composes the second most abundzmk non-opaqae heavy mineral group with four exceptions. .Sample 55-8-1 (map area.) amd two samples from the ,lower Dakota group at tke type locality of the MOIT~SQXX,

Morrison, 6calorad0, contain a larger percentage of rutile than of tourmaline. Sample 57-10-13 (San Jon section) contains equal percentages of tourmaline and rutile. No sample contains more than 37% and most of the samples contzin less than 30% tourmaline in the non-opaque fraction.

All the tourmatine grains are rounded to well-round and no eulnedrzl grains were found, although some were fo:rmcd by the rounding of originalty small prisms. The absence of euhedral tourmaline associated witla the euiiredra.1 aircon indicates separate sources for each. The -Tucumcari shale member contains a few small grains of tourmaltne tfmt have colored eahedral ovesgrowths, w%hichappear to be slightly abraded suggesting that they were formed in the source area. Because colored overgrowths are common in low-rank metasedimentary rocks, a metamorphic source is suggested. The tourmaline group was divided into five classes based upon color; pink, red brown, olive drab, dark green and blue. With few exceptions, red brown and olive drab are the most CQmmOPP varieties.

These two varieties occur in subequal proportions, the olive drab being slightly more abundant. The dark green variety is next in abundance and is the most abundant in two samples. The pink and blue classes are present in small amounts, in several samples comprising less than 1%of the tourmaline group and completely absent in a few samples. No consistent trend of percenta,ge or ratio between varieties was established for the tourmaline group.

Rutile, although present in all the samples, commonly makes up less than 10% of the non-opaque heavy mineral suite. Sample 55-8-1 (map area), 57-10-13 (San Jon section) and the upper sample from the lower

Dakota group, Morrison,. Colorado, contain 23%, 22% and 14% respectively.

Most of the rutile grains are well-rounded; few grains show any of the original euhedral form. The yellow and foxy red color varieties are present in subequal amounts and in a few samples, a cloudy gray variety is present.

Staurolite was found in only four samples; 57-8-11 (Burro Canyon section), 57-9-15 (Galiegos Ranch section), 57-10-9 and 57-10-13 (San

Jonsection). No samplecontains more than 8%. Thestaurolite is pleochroic from colorless to straw-yellow and is .strongly etched. Many of the grains are only skeletal crystals.

Miscellaneous heavy minerals include dark green, pleochroic hornblende (3%) that was found in the lower samples of the lower Dakota group at Morrison, Colorado, .and a trace of strongly-etched, colorless garnet was found in 57-9-15 (Gallegos Ranch section).

Paleoclimate. -- A warm, humid climate is postulated for the source 1,s1f .o\ - area during the deposition of the Purgatoire formation in northeasternNew iJ. '''';'.. Mexico,The absence of garnet and apatitefrom the heavy ,/ ~ ..~.~. -...... , ~. .~.. ~ .. ..,. mineral suite of the Purgatoire formation suggests removal by chemical

decomposition. These minerals, which are present in the underlying

Morrison formation, are readily susceptible to chemical weathering,

but at.least garnet and staurolite are resistant to mechanical processes.

Therefore, even if much of the material was derived from reworked

Morrison, chemical weathering would be necessary to remove such

minerals as garnet and staurolite. In addition, the vacuolized feldspar

grains and the small amount of feldspar present in the rock give further

evidence for a warm, humid climate.

The presence of kaolinite in the shale member of the Purgatoire,

although not conclusive 'evidence in itself, could indicate severe weather-

ing in a warm, humid source area. No source area significance can be

attached to mixed-layer clays at this time.

Dakota .Formation

Nomenclature. -- Meek andNayden (1862, p 419-20) defined the

Dakota group with,the spe.cified type locality at, Dakota,. Dakota.County,

Nebraska. .Few exposures of the Dakota are present between the type

locality and the~Front.Rangeof the Rocky Mountains, but because .of

similarity of lithology and stratigraphic position early workers in this

region assigned the basal sandstone and shale units of the Cretaceous to

theDakota group (Hague, 1877; King, 1878; Powell, 1882; etc.).Prior I15

to Powell in 1882 the terms Dakota..Cretaceous, Dakota formation;Dakota

sandstone and Dakota group were used interchangeably (Waage', 1955, p

16). Powell adopted the formation as the basic mapping unit and the term group was abandoned until Walcott (1903, p 21-27) proposed its use as a collection of formations.

An excellent account of the evolution .of nomenclature for the-Dakota formation is contained in a.paper by 'Waage' (1955). In this paper Waage' demonstrates the usefulness.of the Dakota as a group term for the northern Front Range of the Rocky Mountains (Dakota group, in its present connotation, was first proposed by Lee, 1923). . Waage' points out the usefulness of a group term because of the difficulty in discerning formation boundaries in many areas, and because these sandstoneand shale units form a useful lithogenetic sequence. This tithogenetic .sequence can be and is subdivided in many areas, but these subdivisions are not everywhere applicable.

The usefulness of.Dakota group has not been evaluated for the southern

Front Range. Future work may extend the Dakota ,group into northeastern

New Mexico, where, if established, will be useful for a division of pre-

Graneros rock units.

In this paper the term Dakota is used as a formation and applies to the sandstone and shale disconformably overlying the Purgatoire where the Purgatoire is present; elsewhere it disconformably overlies the

Morrison formation. It is .overlain conformab.ly by the Graneros formation.

Lithostratigraphy. -- The Dakota formation is represented across much of northeastern New Mexico by a threefold division; a lower sand-

stone, a middle sandstone-siltstone-shale complex; and an upper sandstone.

Locally, either by facies change or non-deposition, the middle unit may become thin and, in places, disappear. In other areas, the upper unit is thin and locally absent. A few outcrops show a third stratigraphic sequence in which sandstone and shale are present in subequal amounts throughout the section.

The lower sandstone forms a conspicuous cliff along the mesa and upland edges; over much of northeastern New Mexico this sandstone forms the caprock of the uplands. The base of the sandstone is a.regional disconformity represented by channels which cut intoand in places through the Purga.toire formation. A characteristic feature of this unit is tor- rential crass-bedding of 0.5-1.0 ft. amplitude. This cross-bedding is conspicuous in most outcrops and is considered by some workers to be a characteristic peculiar to the Dakota formation in this region. Un- fortunately, such.cross-bedding also occurs in the Purgatoire. The tor- rential cross-bedding in this lower sandstone has both north and south dip directions; one bed of torrentia! cross-bedding may dip south and the overlying bed may contain northward dipping cross-beds. The average dip of the cross-beds is about 25O.

Chert-pebble conglomerate lenses are common to this lower sand- stoneunit. Red, black, tan, gray and white, very well-rounded, 2-40 mm chert pebbles occur in small 1-3 ft. ,lenses, particularly in the lower part of the unit. 117

The main rock type of this lower sandstone is a pale grayish orange

(10 YR 8/5) to pate yellowish brown (10 YR 5/3) weathering grayish ,orange

(10 YR 7/5) to yellowish brown (10 YR 6/5), medium- to.fine-grained,

moderately well-sorted to well-sorted, silica-cemented, quart= .sand-

stone. Limonite cement is present and.locally abundant; it occurs along

bedding planes and joints. In a few places borings a.re present, particu-

larly on the upper surfac.es.of these limonite-cemented bedding planes.

The middle .unit, where present, forms a poorly exposed slope that

is composed of a myriad of small (1-10 ft. 1 sandstone, siltstone and

I shale lenses. In several localities, notably Gonzales Hill (just beyond the southwest corner of the map area), the entire middle unit is composed

of silt-filled borings. In spite of all the evidence for animal activity,

with the exception .of some plant impressions, no fossils were .found in

any of the three units .of the Dakota formation,

The main ro.ck types of the middle unit are pale yellowishbrown

(10 YR 6/Z)to moderate yellowish orange (10 YR 5/6)weathering moder-

ate yellowish brown.(lO YR 5/4) to dark yellowish orange (10 YR 5/5),

slightly friable to hard, fine-grained sandstone to coarse-grained silt-

stone and medium (N 5) to dark gray (N 3), laminated silty shale.

The upper sandstone unit, where present, forms a Jess prominent

cliff than the lower unit, It is largely a thin- to medium-bedded, fine-

grained sandstone with a minor amount of interbedded silty shale. , Plant-

fragment impressions are commonon many of the bedding surfaces and

silica-cementation is pronounced, particularly in the upper part of this

*. >< unit. The contact with the overlying Graneros formation is conformable and probably gradational.

Over much of northeastern .New Mexico, the middle and upper units are missing, having been removed by erosion. ,Where present the contacts between these three units are conformable and in most areas gradational.

The total thicknessof the Dakota formation is unknown for most of

Both pre- and post-Ogallala (late Tertiary)

upper, middle and most of the lower units over

area. In the northeast corner of the state, the Dakota is

Y.4t thick; in the map area, about 160 feet thick: and at Romero- "4 feet thick.

Grain size analysis. -- Eighteen sa.mples of the sandstone parts of " the Dakota formation were ana,lyzed by standard grain size techniques,

The inclusive mean size values for the eighteen samples .range from

1.2ab to 3. S5d or medium sand to very fine sand. Five samples have values which place them in the medium sand class, ten samples fall in the fine sand class and three samples fall in the very fine sand class. Compari- son of the mean size values of the Purgatoire and Dakota samples show that the average Dakota sample is about 0.5b coarser than the avera,ge

Purgatoire sample. With the exception of the sandy mudstone sample from the Purgatoire formation, the Dakota samples have a wider range of mean size values.

The standard deviation values range from 0.21 to 1.48 or very well- sorted to poorly-sorted. Five samples have sorting values .of less than

~~ Table 10. Grain Size Data from the Dakota Formation 120

0. 35 or very well-sorted. Six samples fall in the welt-sorted class (0.35-

0.50) and six samples in the moderately-sorted class (0.50-1.00). Only

one sample (a silty very fine sand) has a sorting value in excess of 1. 00

(1.48) which places it in the poorly-sorted class. The Dakota.sampIes

show a wider range of sorting values than the Purgatoire samples with

the exception of the sandy mudstone (Fx 3.25). The Dakota samples are

subequally divided into very well-sorted, welt-sorted and moderately-

sorted classes, whereas .most of the Purgatoire samples are clustered between well-sorted and moderately-sorted,

Skewness values of th,e Dakota samples range from 0.04 to 0. 89 or near-symmetrical to strongly fine-skewed and all of the samples have positive values. Only one sample has a value that places it in the near-

symmetrical clam. Ten samples fall in the fine-skewed class and the remaining seven samples fall in the strongly fine-skewed class. One noticeable difference between the skewness values of the Dakota samples and those of the Purgatoire is the.la,ck of negative skewness values for the

Dakota. ,In addition, ten of the.Dakota samples are fine-skewed whereas only three of the Purgatoire samples have fine-skewness values.

Kurtosis values for the Dakota formation range from 0.73 to 9.01 or platykurtic to very leptokurtic. Onlyone sample has a value which ~,. places it in the platykurtic class. Five samples have values which place ,~__.. them in the mesokurtic class, eight samples fall in the leptokurtic class and the remaining four samples fall in,the very leptokurtic class. The kurtosis values for both the.Dakota and Purgatoire formations are similar ...... 121

in that both have a predominance of the leptokurtic class.

By plotting the four above-mentioned statistical parameters against

each other, a helical trend may be established which is similar to the suggested helical trend for the Purgatoire samples. But, on the basis .of present data, no definite trend can be resolved.

~ In spite of the lack of a definite helical trend, the plot of mean size vs, standard deviation is particularly useful in that it demomtrates a curve in which the best sorting values.of the Dakota samples have a mean size about 0. 54 coarser than the similar.best sorting values for the P.urgatoire samples. This reflects the difference in the size of the most prominent modes contributed by the source area. The mode of the source material for the Rakota is coarser by 0.54 than the mode of the Purgatoire source material.

Mineral composition. -- Seventeen thin sections from the Dakota formation were studied for mineral composition, texture and cementation.

Point.counts were made on 100 grains in each slide to determine mineral composition.

All the samples can be classified as medium- to fine-grained sandstone. The grains are very well-rounded; no angular grains were found in any of the slides. The roundness and sorting of the grains places'the:. samples in the supermature class (Folk, 1957).

Mineralogically, the samples are composed of quartz, a small percentage of chert and a few grains of heavy minerals. Thus they are extreme examples of the orthoquartzite class. The quartz was divided into

)-<.~, ,::r 122

five classes ba.sed upon extinction properties. These class,es were divided

into four additional categories based upon the presence and kind of inclu-

sions (Folk, 1957).

The comm,on or plutonic-type quartz ranges from 67% to 90%. Most --- ..-.--- of the samples have between 75% and 85% common quartz. The undulose- / ,'type qua.rtz ranges from 1% to 9%. Most of the samples have between 3%

and 7%undulose quartz. . Semi-composite quartz ranges from 1%to 10%

but most samples contain only about 3%.or 470, . Composite quartz varies

from 1%to 13%but again most samples contain oniy about 4%. . Stretched 1 ' composite-type quartz is .only present in about two-thirds of the samples ..~ and in minor.amounts (1-3%) in these samples. * Most of .the quartz .grains haveno inclusions but a .small percentage Y. ~ 1 b of grains containing rutile needles .is present in every slide. This per- i ti , ., . '. u 7 3' 3' h centage ranges from one .or two to as much as .ten. -A small percentage of /T'" (','

microlite inclusions is also present in every slide. . These inclusions

average about 5-10%. . With.few exceptions, less ,than 10% of the grains

in a slide will contain an abundanceof vacuoles. .Notrend for the quartz

types can be established based upon the present data. i ,^

All the slides c0ntain.a small amount af chert, ranging from a trace ' -' .. to as .much.as 7%. Mostslides contain 2% or 3%. .All the chert grains ....

are well-roundedand appear to have a tendency to be. slightlycoarser .. ,.

.-_ thanthe mean size of thesample. Practically all thechert contains ..-..L 1 - ,,: -. ;-

bubble inclusions. .The well-rounded,chert grains together with the corn- .' , .. . ~. ~ .~ -. 7 i'":.i\,v, !'L'. .~ \3, plete absenc.e of angular grainstsuggest that rounding occurred during the t' deposition of the Dakota formation.

Nqt on grain of feldspar was found in any of the 17 slides examined. &I* $cr2y&fiJ A raqe heavy mineral grain is present in the thin section, Tourmaline, . ._" _""" zircon and possibly hornblende have been identified from several of the

slide 8,

-Heavy minerals. -- Seventeen samples of the-Dakota formation were separated by the standard heavy mineral separation technique and tabu-

lated as previously described.

Both fourmaJine and z,ircon.are present in all the slides, Rutile is

present in most of the slides. Staurolite occurs in three -slides and horn-

blende .occurs in only two slides. . The opaque minerals include ilmenite,

leucoxene, hematite and.timonite nodules, black tourmaline and possibly

a minor amount of magentite. Opaque minerals are present in every slide

of the Dakota. . The percentage of opaque minerals varies from 29 to 100;

most samples contain.about 50%. No attempt was .made to subdivide the

.opaque minerals into species.

Tourmaline is the most abundant non-opaque heavy mineral. It occurs

in all slides from as little as 51% to 100%. Most of the samples .contain

about 70-75Va tourmaline. All the tourmaline grains are well-rounded

and most grains are subspherical. Five subdivisions of the tourmaline

were set up based upon color. With few exceptions the red brown and

olive drab varieties are the most abundant. These two varieites are sub-

.equal in percentage, The third most abundant type is the dark green: in

a few slides the dark green is the most abundant. Bright blue and pink tr

30 3'

Burro Canyon

" Gallegos Ranch 45 53 57-9-20 Gallegos Ranch 57 72 Will Harlan Ranch Map. Area 54 72 South of Caves Map Area96 56 Old Hill Road Maa Area 55 55

Table 11. Heavy Mineral Data from the Dakota Formation 125

varieties occur in several of the slides but in minor amounts never ex-

ceeding 5% of the non-opaque minerals. A plot of the areal distribution of

the samples reveals 'no trend as to the percentage or relative amounts of

each color type,

Zircon, which is the second most abundant non-opaque heavy mineral,

occurs inall of the slides in amounts from a trace to as much .as 39%.

Most of the samples contain about 25% zircon. There are four types of

zircon grains: euhedral (I) colorless and (2)pink; anhedrat (including

rounded) (3) colorless and.(4) pink. The anhedral-colorless variety is the

moat abundant. In some samples it.comprises prac.ticaJly the total zircon

percentage. . The second most abundant type is ,the euhedral-colorless

variety with a few exceptions. The anhedrill-pink is third in abundance and in a few slides is more abundant than the euhedral-colorless variety.

The euhedral-pink variety occurs in.only a few samples .and in a minor amount in these samples. In a few samples the anhedrat and euhedral varieties zre subequal in amount, but in most of the s,lides the .euhedral varieties make up less than 1/3 of the total zircon percentage. No trends could be es.tablished from a study of the areal dktribution of the zircon types.

Rutile occurs in eleven of the samples from a trace to as much as

18%. Most of thesamples contain . Allthe grains are well-rounded.

No grains show any origin@ crystal form. The foxy red and yellow varieties are present in subequal proportions, and in one or two slides a cloudy gray variety was found. 126

Staurolite was found in only three samples and in minor amounts (1%

in two samples and 5% in one sample). The staurolite is pleochroic pale

yellow to colorless and so strongly etched that with few exceptions onJy

skeletal crystals remain.

A slightly pleochroic green mineral with the optical properties of

hornblende was found in two samples. The grains are rounded but not so

well as the .tourmaline. In addition, the ends .of the grains are ragged re-

sembling typical grains of detrital hornblende.

A comparison of the heavy minerals of the Purgatoire and the Dakota

formations shows a reversat in the dominant mineral type, The Purgatoire

contains an abundance of zircon whereas in the Dako,ta, tourmaline is the

most common heavy mineral. .A plot of the mean size -of the grains vs, I:, I' dominant heavy mineral type fails to show hydraulic control for this're- Lh@ 7 versa

Dakota formation is probably significant. The euhedral zircon, which is

also present in.the Morrison .associated with an abundance.of apatite and

near-hexagonal biotite, is probably the result of volcanic ac.tion (Catlender ~ <' i ,I :', andFolk, 1958). Theabsence of volcanicactivity during deposition of ..-' ". "' "-- the Dakota formation innortheasternNew Mexico would account for the

decrease in zircon percentqge.

Cementation. -- All the slides are thoroughly silica-cemented in the

form of quartz overgrowths. The silica cement constitutes the principle

bonding material. The cement is clear and shows several growth stages. I The boundary between the detrital grain and the cement is difficult to see a 0

Ii ao 0 a a

a 0 a a' 0 0 0

0 a

(

Percentage owing to the lack of impurities along the contact. Several of the slides

contain in addition to the quartz overgrowths, a Later generation of micro-

crystalline quartz .(chert) cement. These slides show a reversal of the usual order of silica cementation in that the quartz .overgrowthsare first, firjrous silica .second and microcrystalline silica ,last.

Kaolinite is present in most of the slides as a patchy pore filling.

It is clearly after the quartz overgrowth formation. The kaolinite is composed of well-developed crystals and contains no visible impurities.

The crystals are randomly oriented within the pore spaces.

Two of the slides contain tiny (2.-51*)crystals of a yellow highly birefringent and very high relief mineral in the silica .cement. The mineral, which is too small for optical properties to be determined, is probably tetragonal or monoclinic, It may possibly be a uranium or titanium mineral but no conclusive evidence is available. Lts.formation is contemporaneous with the silicification.

Ironsxide occurs as a later stain in the rock and it is probably a result of outcrop weathering.

Owing to the lack of indicator minerals, no positive climatic interpretation can be advanced for the source area during the depositionof the

Dakota formation in northeastern .New Mexico. It is quite probable that a warm, humid climate was responsible for completely removing the feldspar and the climate-sensitive'heavy minerals. In addition, intense weathering of a source area.woutd provide a lot of soluble silica which might cause the extensive 'sitica-cementation. Neverthe.less this .kind of 129

evidence is not conclusive in itself and should be considered 86 more of a suggestion than a fact. GEOLOGICHI.STORY

T~SSICPERIOD , .. . Deposition .of.Dockum Group

The time of deposition of the Dockum group in northeasternNew

Mexico has been dated by. Stovall (1939).and others as Late Triassic. The

dating is based upon vertebrate fossils and ,confirmed by non-marine

mollusca. . The geologic: time interval for deposition of. this group has not

been .ascertained.

The presence of channel sandstone, mudstone with no obvious bed-

ding, lenticular accumulations of non-marine limestone and local, massive

.cross-bedded sandstone suggest a low, floodplain environment. This

floodplain was crossed by numerous stream-channels, dotted with lakes

and accumulations .of dune sand. The abundance of plant fragments and

petrified wood indicates extensive vegetation. The preservation of this

vegetation indicates an extensive reducing environment (an environment

in which the reduction products are preserved). This is substantiated by the occurrence of siderite nodules in many of the samples, iron .carbonate being suggestive of a .reducing environment,

The presence.of orthoclase, microcline and some plagioclase in addition. to muscovite and common.(plutonic) quaktz indicatesan igneous

source, probably a granitic source. A small percentage .of composite and stretched-composite quart= suggests, in addition, some metamorphic contributions, probably schist. Owing to the lack .of detailed study of the Dockum group, a source direction cannot be determined but possibly the material came from thensxposed mountain ranges to the northeast and east. The Quachita Mountains and possibly the Llano Uplift could have

furnished sediments for the Dockum group in this region. '

The oc.currence of both fresh and weathered feldsparand the extensive vegetation and siderite nodules indicate that the environment of the source area, as weIL as the environment of deposition, was warm and humid.

A general epirogenic movement with local folding occurred after deposition of the Dockum group and prior to deposition of the Exeter sandstone. Along the Dry Cimarron the Dockum group is gentty folded. The

Exeter sandstone truncates these folds and is undisturbed except by later gentle warping.

JURASSIC PERIOD

Deposition of Exeter Sandstone

The Exeter sandstone which disconformably overlies the Dockum group was probably depos.ited during the Late Jurassic epoch. . With the exception of a collection of fossil fish (Koerner, 1930, p 463) presumably from beneath the Exeter, no pateontologic data is available with which the Exeter can be dated directly, but its relation with the overlying.Morrison formation can establish an .approximate age. The age of at least part of the Morrison formation in northeasternNew Mexico is established by its Late Jurassic charophyta. Because the Exeter sandstone 132

is conformable and intertongues with the Morrison, a Late Jurassic age

is approximately correct. In.addition, the fossil fish correlate with a

part of the Sundance formation (Juras.sic). But, because of the urrcer-

tainty in the age assignments, no precise time vatue can be assigned to

the hiatus between the Exeter sandstone and the Dockum group. .This

hiatus could well represent a part of the Late .Triassic epoch and much

or most of the.Jurassic period.

The massive, generally southward-dipping crossbeds .of the.Exeter

and the absence .of any nearby associated marine deposits suggests that

t:he formation was laid do‘wn in an interior basin. as dune sand. The pre- \.: ,,“~ ;;tL& \ sence of celestite in jenticular deposits as a cementing agent sugges.ts \ “-2- locat playa lakes,

The eastern boundary of the basin .of deposition roughly coincid.es

with the Texas-New Mexico state.line. Sautheast of Tucumcari.the limit

of the basin trends southwest. .The southern.limit was not determined be-

cause of cover by High Plains gravel.

The surface upon which the Exeter was deposited.has an excess of

100 feet of relief. . This.relief is developed by two long, na.rrow depressions

separated by a platform. . The s.tructura1 features trend.slightly east of

north. The platform has the same trend as the Sierra Grande arch of

Cretaceous age. It is probable that most of the relief was developed

prior to deposition of the Exeter but some relief could have formed dur-

ing the deposition.

Decrease in mean grain siqe of the sand to the south and increase in 133

feldspar percentage to the south for the upper part of the Exeter, in.addi-

tion to the southward-dipping crossbeds, indicates a .northern and north-

western s.ource area. The mineralogy of the Exeter sandstone indicates

that the source area.was composed of igneous, metamorphic and sedi-

mentary rocks. The occurrence of plutonic quartz, abundance of feld-

spar, and heavy minerals such as tourmaline, rutile and zircon suggests a dominant plutonic source. The occurrence of metamorphic-type quartz, garnet and staurolite in addition to tourmaline and zircon indi-

dates some metamorphic rock inthe source area. . Chert and dolomite fragments of sand size indicates a sedimentary source, The source area may then be deacribed as havinga plutonic igneous core with a surrounding metamorphic .belt and overlain by sedimentary strata. The increase in metamorphic type quartz upward in the section and a larger percentage in westernmost samples suggests that the metamorphic contributions were derived.in part from the northwest. .The increase in amount indicates an increase in contribution of metamorphic material.

The aeolian-type crossbedding, occurrence of abundant, fresh, rounded feldspar,. rounded dolomite grains and chert with undissolved dolomite inclusions as well as the presence of lenses of celestite cement indicates that the paleoclimate of both the source area and environment of deposition was arid. The prevailing paleowind direction was to the south to southeast.

The cementation of the-Exeter sansstone took place after deposition and before .outcrop weathering. No definite time can be established with 134

the present data. The quartz overgrowths, calcite and kaolinite are pene-

contemporaneous in their formation.

. Deposition of Todilto Limestone

The Todilto limestone-.conformably overlies the Exet:er sandstone and

is overlain conformably by the Morriaon formationin the one outcrop

studied. Because of this limited study little of the depositional history of

this unit can be determined. The rock is probably an algal limestone that

represents a .somewhat more extensive lacustrine environment than the

playa lakes common.to the Exeter. From this alone is a possible indica-

tion of a .decrease in aridity of the region. , Additional evidence on this paleoclimate is available from the lower pa.rt of the Morriaoqthe deposition of which was probably contemporaneous with the deposition of

the Todilto limestone in~the Romeroville area.

Deposition of Morrison ,Formation

The Morrison formation conformably overliesand intertongues with

the Exe.ter sandstone. Its present southeastern extent is about the same as .for the-Exeter. .Within northeastern New Mexico, the maximum thickness is in excess .of 500 feet. The area of maximum accumulation is almost perpendicular to the platform present during deposition of the

Exeter sandstone. A positive area trending slightly west of north separates the Romeroville basin from the .Canadian River basinof accumulation: The remainder of the area received about 300 feet of sediment. The Morrison formation is similar in depositional history to the

Dockum group. Channel sandstone, mudstone and lacustrine limestone form the basic sedimentary features of this unit. The mineralogy of the

Morrison also resembles that of the Dockum group with one important addition. A flood of volcanic material is recorded in the Morrison formation.

The source of the Morrison sediment including the volcanics was to the west and northwest. The grain size increases in that direction and some of the minerals such as apatite also show a similar increase. The mineralogy of th.e Morrison is similar to the Exeter mineralogy except with a decrease in metamorphic type quartz and an increase in plagioclase feldspar. The source direction is the same as the Exeter and because no interruption in sedimentation can be demonstrated itis probable that the source is common to b.oth units, i. e. plutonic igneous with a large sedimentary cover, The increase in feldspar is a result of volcanic activity and also probably due to increase in relief and more rapid erosion. A study of feldspar, chert grains and the clay minerals indicates that the paleoclimate became more humid throughout deposition of the

Morrison formation. The feldspar grains are more vacuolized higher in the section; the chert grains do not contain carbonate inclusions such as those in the chert from the Exeter, yet both probably were derived from the same, source; the occurrence of kaolinite is increasingly more abundant higher in the section; no reworked carbonate sand occurs in the samples; lacustrine limestone is more abundant: fluvial sandstone is 136

increasingly more abundant; andplant fragments, petrified wood and dino-

saur bones are common in the Morris.on formatiori. The sum total of the

abovementioned facts is substantia.1 evidence that the paleoclimate during

deposition of the Morrison changed gradually from aridto humid,

The depositional environment of the Morrison formation in north-

eastern .New Mexico could be described as a Large, low floodplain with

numerous streams, abundant vegetation and dotted with.lakes. The lakes

were more abundant in the eastern part of the area. Occasional falls of

volcanic ash occurred. These became more numerous during deposition

of the upper part of the Morrison formation.

The first record of volcanic ac,tivity is contained in the nodular red

silica of the "agate bed". .This .bed occurs actuallyas several discon-

nected layers occupying nearly the same stratigraphic position over most

of the southern Rocky.Mountains. They are described by Ogden (1954)

as probably the atteration of a volcanic ash. Thin.section studies of

samples .of the ."agate bed" f om localities in northeastern New Mexico ./:i.4. ,x: ., *.. .*a & ' .#L:.&. q p :&f& 5:&+;,.&,& $. "-J.5'"..('/~.!"! 4 &..--%+e .:<*,.::. .:.i A$..?.?..?. ;-. c - ".

Jindi.de. that this is probably correct. In addition, a low negative index,

low birefringent, probably tetragonal mineral was found in one thin sec-

tion from the "agate bed", probabty a zeolite. Volcanic activity is recorded higher in the section by glass shards, quartz phenocrysts, volcanic-ash beds, apatite, euhedral zircon, plagioclase laths, volcanicrock fragments and bentonite layers. The occurrence of apatite suggests a more basic composition for the volcanic material than rhyolite(R. L.

.Folk; personal communication, Aprit, 1958).

$? In the uppermost samples of the Morrison formation a sand with a

coarser mode was contributed by the source area. The sand gr,ains are

much better rounded indicating an inherited roundness, probably from an

older sedimentary source. The occurrence .of chert related in grain size

to this mode further substantiates the idea .of an older sedimentary source.

CRETACEOUS PERIOD

Deposition of Purgatoire Formation

The Purgatoire formation,represents a marine transgression into

northeastern New Mexico from eas.t to west, . The age .of this unit on the

Texas High .Plains and the Oklahoma .Panhandle is Early Cretaceous, . The

contact with the underlying Morrison formation is a disconformity, The

length of time represented by the hiatus is .not known but some speculation

indicates that the geologic time interval may be rather short. It may well

be that a .part of the Morrison formation was actually deposited .during the

Early Cretaceous epoch andis contemporaneous with some of the Purga-

toire formation. Because of the lack of reliable paleontologic evidence,

the Morrison cannot be definitely assigned this .Cretaceous age. The

main reason for such.a speculation is .the occurrence of a ,large percent-

’ a e of euhedralzircon in the heavymineral suite. This zircon, from all <,;a.., .-, 1% 3 ?., indicationsjcame from,a volcanic source, Because .the upper Morrison ’ )/ \. 4 _I also contains an abundance of euhedral zircon from a volcanic source and

the source area for both units is the same, the idea of near contempo-

raneity is advanced. 138

The paleoclimate of the Purgatoire formation was probably humid. A minor percentage of feldspar is contained in the unit, and the grains are strongly vacuolized. Only the most stable heavy minerals such as tourmaline and zircon are present in the heavy mineral fraction. The chert grains contain no carbonate inclusions. These facts, although not conclusive evidence for the paleoclimate, suggest a humid climate as probable.

The environment of deposition was mainly beach deposits with some deltaic environments suggested by both field and laboratory studies.

These environments received their sediment from a ,northwestern source, probably the same source as for the pre.ceding units.

.Deposition of Dakota Formation

The Dakota formation represents a marine transgression into northeastern New Mexico from east to west, The Late .Cretaceous age of the transgression in this region is based upon a literature survey of papers concerning the Dakota formation in nearby area@.

A disconformity is developed between the Purgatoire and the Dakota formations. The .length of geologic time represented by this hiatus is a small part of both Early and possibly Late Cretaceous epochs. Perhaps the region was uplifted following the Purgatoire transgression and an erosion surface was developed. Then the Dakota formation transgressed over the erosion surface across northeastern New Mexico.

The source area.was probably the same for the Dakota, with the exception of the absence of volcanic material. The mineralogy, excluding P39

volcanic contributions, is the same for both units. The basic difference is the Dakota sediment had a coarser mode than the Purgatoire sediment.

The Dakota transgression can be traced as far west as Arizona where the

Dakota and Mesaverde sandstones are in contact.

The environment of deposition was similar to the deposition of the

Purgatoire. The main environment was a beach with minor lagoon and deltaic areas. The presence of ta,goonat deposits suggests a slower transgression than that represented by the Purgatoire formation.

The paleoclimate was probably humid because of the absence of feldspar and the abundance of silica-cementation.,

The post-Dakota geologic history is not included in this thesis.

CONCLUSIONS

Disconformably overlying the Dockum group in northeastern New

Mexico, is a continental lithogenetic sequence composed of the Exeter sandstone, Todilto limestone and Morrison formation. This sequence was deposited during an interval of geologic time in which the palm- climate changed from arid to humid. The association of volcanic material in the Morrison formation and the Early Cretaceous marine transgression represented by the Purgatoire formation suggestsan Early

Cretaceous age for a part of the Morrison. A probable Late Cretaceous marine transgression represented by the Dakota formation is the last t'~?cr.~'- marine inundation .of northeastern New Mexico. These units had a similar northwestern source which consisted of plutonic igneous, minor meta-

,"> I p$ morphic and substantial amounts.of older sedimentary rocks. REFERE&CES Adams, J. E. (1929).Triassic"- of West.Texas: Am.Assoc. Petroleum Geologists Bull., v 13, p 1045-1055.

Adkins, W. S. (1933) The geology of Texas - Mesozoic Systems, in - " - Sellards, E. H. et al., Thegeology of Texas, v 1: Univ. of TexasBull. 3232, 1007 p.

Bachman, G. 0. (1953) Geology of a portion of northwestern Mora County, " - -New Mexico: U. S.. Geol. Survey Orand Gas Inv., OM 137, 2 sheets.

Bagnold, R. A. (1954) The physics of blown sand and desert dunes: I " Methuen and-Co. Ltd., Lo$odon,5 p.

Baker, A.A. ,.Dane,. C. H. andReeside, J. B., Jr. (1936) Correlation of Juras'sic formations of parts of Utah; Arizona, New Mexico - "" - -andColorado: U..S. Geol. Survey Prof. Paper 183, 66 p. (1947) Revised correlation of Jurassic formations "-of parts of -Utah, Arizona, -New Mexicoand.Colorado:- Am. Assoc. Petroleum Geologists Bull., v 31, p 1664-1668.

Baldwin,Brewster, Bushman, F.-X. andMuehlberger, W. R. (1958)3 Geology and groundwater resources of Union County, New Mexico: " - New Mexico Bur. Mines and Miner. Res., in preparation. Bullard, F. M. (1928)Lower Cretaceous -of western Oklahoma:Okla. Geol.Survey Bull. 47, 116 p. Burbank, W. S. (1930) Revision of geologic structure and- stratigraphy in- the Ouray district of Cozrado, . . . : Proc. Colorado Sci. Soc., " - v 12.

Cooley, B. E. (1955) Areal geology of Dry Cimarron Canyon, Union - " County, -New Mexico: Univ. Texasunpublished M.A. thesis, 93 p. Cross, Whitman (1899) Description of Telluride quadrangle, Colorado: U. S. Geol.Survey Geol. ztas, folio57.

Cummins, W. F. (1890) Permian of Texas and its overlying beds: Tex. "" - Geol.Survey Ann. Rept. 1, p 185-197. 142

Dar.ton, N. H. (1915) Extension of Morrison formation into New Mexico " (abstract):Geol..Soc. &erica.Bull. , v 26, p 113.

(1915) Guidebook of the western United States, Part C. The Santa " .-" " Fe Route: S. Geol.Survey Bull. 613c. "U.

(1921) Geologic structure of parts of New Mexico: U. S. Geol. . "" Survey Bull. 726, p 173-275.

(1928) "Red beds" and associated formation in New Mexico: U.. S. "3 " Geol.Survey Bull. 794, 356 p.'

DeFord, R. K. (1927) Areal geology of Cimarron County, Oklahoma: Am. Assoc. Petroleum- GeologistsBull., v 11, p 753-755.

Dobrovolny, Ernest and Summerson, C. H. (1946) .Geology of northwestern -Quay:County, -New Mexico: U. S. Geol. Survey OiTand Gas Inv. , Prel. Map 62.

Drake, N. F. (1892). Stratigraphy of the Triassic formation of Northwest - .- -Texas:Tex. Geol. Survey Ann.. Rept. i, p 227-24r Eldridge, G. H. (1894) Description -of sedimentary formations - Anthracite Crested Butte quadrangles,. Colorado: U. S. Geol.Survey Geol. Atlas, folio- 9.

(1896) Mesozoic geology, in Emmons, S. F., et al., Geology of theDenver basin.in Colorydo: U. S. Geol.Survey Mon. 27, " -p 51-'150.

Folk,.R. L. (19571 Petrology of sedimentary rocks: Austin, Hemphill's ., . - - Book Company.

' and Ward, 'W.. 6,(1957) Brazos River bar: a study in the Tignifi- " " cance of grain size parameters: Jour. Sed. Petrology,- v 27, " p 3-26. - Gilluly, James and Reeside, J. B. , Jr. (1927). Sedimentary"- rocks of the San Rafael Siwell and some adjacent areas in eastern Utah: U. S. - "- " - Geol. Survey Prof. Paper 150-D.

Goldman, M. I. and Spencer, A. C. (1941) Correlation of Cross' La Plata " s.andstone,southwestern.Colorado: Am. Assoc, Pxleum Geologists Bull., v 25, p 1745-1767. 143

Gould, C. N. (1906) The geology and water resources of the eastern portion - " - -. of the Panhandle of Texas: U. S. Geol.Survey Water-Supply " " Paper 154.

(1907) The geology and groundwater resourcesof the eastern por- - ~ " - tion of the Panhandle of Texas: U.. S. Geol.. Survey Water-Supply -"Paper 191.

Gregory, H. (1917) Geology of the Navajo country - a reconnaissance E. " of parts Arizona, New Mexico and Utah: U."S. Geol. Survey "of "" Prof. Paper- 93. (1938) "-The San Juan country, a geographic - andgeologic reconnaissance of southeastern Utah: c. S. Geol. 'Survey Prof. Paper 188. " _c

Hague, Arnold (1877) Colorado Range, in-, Arnold, Emmons, S..F. 3- Descriptive geology, U. S. gexogical exIjloration of'the .fortieth " " parallel (King): Prof.Papers Eng'. Dept. U. S. Army, no.18, v 2, p 39-41.

Harris, J.. R. (1957) Origin and petrology of the Sabinetown Formation, " " WilcoxGroup,Bastrop County, Texas: Univ. of TexasMaster's

~ Thesis.

Hayden, F. V. (1869) Preliminary Field Report of the United-States Geo- - " " logical Survey of Colorado and.New". Mexico: U. .S. Geological Survey oforadoand New Mexico, Washington, Government Printing Office.

Heaton, R. L. (1939) Contribution to Jurassic stratigraphy of Rocky Mountainregion: Am. Aszc.Petroleum Geologists v 23, p 1153-1177. Irving, J. D. (1905) -Oredeposits of theOuray district, Colorado: U. S. Geol. SurveyBull. 260. "-

Jenney, W. P. (1898) Field observations in the Hay Creek coal field, in 7 """- Ward, L. F. et al. , The Cretaceous formation of the Black Hills - "" as indicated by the fossil plants: U.. S. Geol.. Survey Ann, I Rept. - "" 19,pt. 2, p 521-946.

Keyes, C.. R. (1936) Stratigraphical geotogy - Todilto.limestone -in unique pose: Pan-American Geoiogist v 66, p 74-77. _c

S. King, Clarence (1878) Systematic geology, "U. geological exploration of the fortieth parallel: Prof. Papers Eng. Dept. U. S. .Army, no. -18, v 1, p 278'-305. King, L. C, (1953) Canons of landscapeevolution: Geol. Soc.America " Bull., v 64, p 721-752.

Knight, (1900) Jurassic rocks southeastern Wyoming:Geol. SOC. W. C. "of America.Bull., v 11, p 377-388.

Koerner, H. (1930) Jurassic fishes from NewMexico: Amer. Jour. of E. ." Science, 5th.series, v 19.

Krumbein, W. C. (1934) Size .frequency distribution of sediments: ' Jour. ,- - Sed. Petrology, v 4, p 65-77.

and Pettijohn, F. J. .(1938) Manual of sedimentary petrography: New York, Appleton-Century-Crbftz hc., 549 P.

Lee,. W. T. (1901) The Morrison formation .of southeastern.Colorado: - -, Jour. Geol. Bull., V 9, p 343-352.

(1902) The "orrison shales of southern Colorado and northern - -, -New Mexico:. Jour. Geol. Bull, ,' V 10,p 36-58. (1923) Continuity"-of some oil-bearing sands of.Coloradoand " - Wyoming: U. S. Geol.Survey Bull. 751-A, pr

Lupton, C. T. (1914) Oil and E near Green River;Grand County, Utah: " "- - U. S. Geol. Survey Bull. 541.

Marcou, Jules (1858) Geology of NorthAmerica: Ztircher and Furrer., " Zurich, 144 p.

Marsh,. 0. C. (1871) Notice of new dinosaurian reptiles" from the Jurassic formation:Amer.. "- Jour. Sci. 3rd series, v 14, p 514-5f6.

Mason, C. C. andFolk, L. (1958). Differentiation of beach,dune, and , R. - " aeolian flat environments by size analysis, MusqIsland, Texas: " " Jour. Sed.- Petrotogy, in press. Meek, F. B. and Hayden, F. V. (1862). Descriptions "-of new Lower;Silurian, (Primordial), 'Jurassic, Cretaceous, and- Tkrtiary fossils, . . . . : Acad. Nat. Sci. .Phila. , Proc., v 13, p 419-420. -

Merrill, G. P. (1924) The first one hundred years of American geology: 7" " New Haven, Yale Univ. Press, 773 p.

Miller, D. N., Jr. (1955) Petrology of Pierce Canyon redbeds, Delaware Basin Texas and New MexiS-d: Univ. Texas .unpublished Ph. """- D. thesis. Milner, H. B. (1952) Sedimentary pktrography: London Thomas Murphy and Go., 666 p,'

Neef, G. H. (1950) Sedimentation of the Todilto Limestone in San Miguei " " Count NewMexico: Texas Te.ch.unpublished M. S. thesis. dt" Ogden, Lawrence (1954) Rocky Mountain Jurassic time surface: Am. Assoc. Petroleum Geologists Bull., v 38,- p 914-916,

Parker, B. H. (1933) Clasticplugs ""and dikesof the Cimarron Valley area of Union.Countyi -NewMexico: ~ Jour. Geol. Bull. v 41, "-p 38-51. (1934) Eighth annual field- conference: Kansas Geol. .Sot. Guide- book,

Penck, Walther (1953) Morphological analysis land forms; a contri- "7"of bution to physical geology;: London Macmiltan and Company. " Pettijohn, F..J. (1949) Sedimentary rocks:- New York, Harper and Brothers, 526 p. Plummer, F. B. (1933) -The geology of Texas - Cenozoic Systems, in Sellards, E. H. et al. The- geology "' of Texas v 1: Univ. 07 Texas Bull. 3232., 1007 p.

Powell, J. W. (1882) "Plan of publication: U. S. Geol. Survey 2dAnn. Rept., p XL-XLVII.

Powers, M. C. (1953) A new roundness+" scale for sedimentary particles: Jour. Sed. Petrology, v 23, p 117-119.

Rothrock, E. P. (1925)Geology of Cimarron.County, Oklahoma:Okla. Geot. Survey Bull. 24, TO7 p. Sanders, C. W. (1934) Geology ""-of Two Buttes dome in southeastern Colorado: Am. Assoc. PetroleumGeologists Bull., v 18, P 860-870.

Scott, W. B. (1897) An introduction -to geology: New York, The Mac- millan .comsny.

Shrock, R. R. (1948):Sequen.ce in layered rocks: New York, McGraw- Hill Book Company, In;, 507 p. Stokes, L. (1944) Morrison formationand related deposits in and W. - " adjacent to the Colorado Plateau: Geol. . Soc. America Bull. " v 55, p 951-992.

Stose, G. W. (1912)Descriptfon.of" the Apishapa quadranple,. Colorado:

U. S. .Geoi. ~ SurveyGeol.. Atlas, folio ,186.

Stovall, J. (1943) Stratigraphy of the.Cimarron Valley (Mesozoic W. " Rocks), in.Schoff, S,'L. .Gyologx and gr'ound water resources " - 7 of Gimarron County, Oklahoma: Okla. Geol. .Survey Bull., 64, - 7 317 p. and Savage, D. E. (1939). A Phytosaur in.Union.County, New " I_ Mexico, with notes .on thecstratigraphy: Jour. Geol.. .Bull. V ."" ."" , 47, p 759-766.

Thornbury, W. D..(1954) Principles of $eomorphology: New York .John Wiley and.Sons, Inc., 618 pr

U.. S. 31st Congress (1850) Report of Captain R. B. Marcy: in Senate Executive Documents 64, vY4, p 169-227: - ,-

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Waldschmidt,. W. A. arrd LeRoy, L. W. (1944).Reconsideration "of the Morrison formation in the type area Jefferson.County, Colorado: ""V ""V Geol. SOC. America.Bult.v 55, p 1097-ili4. Wood, G. H., Jr., Northrop, S. A. andGriggs, R. L, (1953) Geology and strat

Introduction

Except for the Mitchell Ranch .Section measured in.August 1956, the following sections were measured during September 1957. Thick- nesses were measured with a Jacob Staff and 6-foot steel tape. The

Mitchell Ranch Section, however, was measured with an alidade and stadia rod and 6-foot steel tape.

The following set of thickness values were employed:

Laminated ...... Less than 1 in. Platy-bedded...... 1-3 in. Thin-bedded ...... 4 in. - 1 ft. Medium-bedded ...... 1-2 ft. Massive ...... More than 2.ft.

Colors of samples were taken from the Rock-Color Chart (Goddard, et al., 1951). Both fresh and weathered colors are described. " The grain-size is expressed in 6 (phi) units (Krumbein, 1934, p.

65-77), except for the pebble siqes of the conglomerates which are given in millimeters. MITCHELL RANCH SECTION

FEET 650- -

250-

600- -

- 200-

550- -

150- -

100-

50- -

0- 150

MEASURED SECTION 56-2

.Mitchell Ranch Section

Location. -- North.fork of Tequesquite-Creek, 2.4 miles north of

Albert, Harding County, 'New Mexico, on.the Mitchell Ranch. . The

traverse begins at the creek and runs northwest up the hill. The

mea.sured section begins at the baseof the.Exeter in the creek and ex-

tends northwest to the hillcrest where it ends in the upper part of the

Dakota formation. The section was measured by:Wm. .M. Johnson and

.C.. J. Mankin (August 1956).

Unit No. .Description Thickness " in.feet " Top of Hill

Dakota ,Formation

16. Sandstone and shale; platy- (1-2,in. ) to thin-bedded (up to 10 in. ), mottled pale red (5 R 612) and gra,y- ish.orange (IO YR 7/4) weathering to light grayish orange (10 YR 8/4), hard, silica-cemented, very. fine-grained (3.86), moderately-sorted, quartz sandstone interbedded with laminated, yellowish gray (5 Y 7/21 weathering to yellowish gray (5 Y 8/1), crumbly,slightly silty shale. The shale is present only along bedding planes in the lower 213 of theunit ...... 63

15. Poorly exposed silty shale; laminated (? )9 yellowish gray...... 26

14. Quartz sandstone; torrentially cross-bedded (4-8 in. beds dipping southeast) grading upward .to massive (2-4 ft.), yellowish gray (5 Y 7/2) spotted with moderate red (5 R 5/4) weathering to medium yellowish brown (10 YR 5/2), hard, silica-cemented, fine-grained (2.4-2.86) (coarser material near base of unit),moderately well-sorted ...... -87 Tot+J.Dakota.Formation. ... 176 I5 I

Unit No. , Description Thickness " -_in.feet Purgatoire Formation

13. Covered, in part, slightly silty shale; laminated to nodular-bedded, gray to pale gray ...... 37

12. Quartz sandstone; randomly cross-bedded a& base grading upward.to massive-bedded (2-3 ft.), pale yellowish orange (10 YR 8/6) weathering to pale yellowish brown (10 YR 6/2), very slightly friable, silica-cemented, graded-bedding in upper part, medium- to fine-grained (1.2-2.4d), well-sorted: contains 2-20 mm light colored,chert pebbles in the basal part of the unit ...... -57 Total Purgatoire Formation, . 94

Morrison.Formation

11. Covered, pale green .silty shale and mudstone , 31

10. Quartz sandstone; platy- (1-2 in.) to thin-bedded (up to 1 ft..), very light gray (N 8) speckled with moderate yellowish brown (10 YR 5/4) weathering to pale yellowish,brown (10 YR 6/2), slightly friable, silica-cemented, fine-graine'd (2.36), poorly-sorted; contains several laminated, p?le yellowish green (10 GY 7/2) weathering to grayish yellow green (5 GY 7/21, tough, silty shale and mudstone beds ......

9. Very silty shale and mudstone; laminated to nodular -bedded, dark grayish yellow green (5 GY 6/2) weathering to medium greenish gray (5 GY 7/1), conchoidally-fracturing;contains several 6-10 inch, similarly colored, silica-cemented siltstone beds ......

8. Quartz sandstone; platy- (1-3 in.) to thin-bedded (up to 8 in. 1, grayish green (10 CY 5/21 weathering to medium grayish yellow green (5 CY 6/2), very hard, silica-cemented, very fine-grained (3.68), moderately-sorted; contains several pale green, silty shale layers ...... I52

Unit No..Thickness Description " in feet " 7. Very.. poorly exposed, very silty shale and mudstone; laminated to nodular-bedded, pale green, conchoidally-fracturing ...... 60

6. Quartz sandstone; thin-bedded (up to 1 ft.),. light greenish gray (5 CY 8/1) weathering to very light yellowish gray (5 Y 9/1)% hard, silica-cemented, very fine-grained (3. Sb), moderately-sorted .... 6

5. Mudstone;covered, laminated, variegated pale green and pale brown, conchoidally-fracturing silty shales and a few thin-bedded (up to 1 ft. ), hard...... 52

4. Quartz sandstone; thin- (up to 1 ft.) to medium- bedded (1-2 ft.), very light gray (N 8) speckled with moderate yellowish brown (10 YR 5/4) weathering to medium yellowish brown (10 YR 5/2), hard, silica-cemented, medium-grained (1.44), poorly-sorted ...... 7

3. Covered, silty shale and mudstone; nodular-bedded, pale brown, conchoidally-fracturing ...... 48

2. Quartz sandstone; medium- (1-2 ft.) to mass.ive- bedded (2-4 ft.), very pale orange (10 YR 8/2) weathering to very pale yellowish brown (10 YR 6/2), very slightly friable, silica-cemented, fine- grained (2.6Q), moderately well-sorted; interbedded with laminated, grayish orange pink (5 YR 7/2) weathering to very light brown (5 YR 7/4), tough, very silty shale ...... -47 Total Morrison Formation ... -3.32- 35 ,Exeter-Sandstone 4

1. Quartz sandstone; massive, randomly cross- bedded, yellowish gray (5 Y S/l) weathering to yellowish gray (5 Y 7/2), friable, slightly, silica- cemented, fine-grained (2.39), well-sorted .... 16 153

Unit No. Description Thickness " in feet " Dockum Group- Unit not measured. Top exposed in creek.

Totalsection...... bq v ROMEROVILLE GAP SECTION

FEET

-?I -

!O - 300- 9 -DAKOTA FM. - 8 - 250- 7 - - 550- 6 -

500- -

450-

400- -

350- LS. ss. MEASURED SECTION 57-2

Romeroville Gap, Section

Location. -- In Romeroville, 5 miles south of La.s Vegas, New

Mexico, the section begins within the Exeter sandstone on the east bank

.of a gully on the north side of U. S. 84, then extends eastward through

the highway gap where it ends in the Upper Dakota sandstone. "The beds dip eastward at angles ranging from 30' at the base to 23' at the top.

The section was measured by H. H.. Doney and C. J. Mankin (Sep- tember 1957).

U nit No. Unit Description Thickness " in feet "

Top of Cuesta

Dakota .Formation

21. Quartzsandstone; medium-bedded (1-2 ft.) grading upward into thin-bedded (1-2 in.), very pale orange (10 YR 8/2) weathering to moderate yellowish brown (10 YR 5/4), very slightly friable, silica- cemented, alternating layers of medium-grained (1.9$), moderately well-sorted and fine-grained (2. 8d), well-sorted; contains borings and symmetrical ripple marks in upper layers. . Ripple marks strike N20°W...... , . . , ...... , 18

20. Quartzsandstone; lenticular (0. 5-2 ft.),pale red (10 R 6/2) weathering to pale grayish yellow (5 Y 8/3), hard, silica-cemented, veiy fine-grained (3. sa), moderately-sorted; contains black, carbonaceous wood fragments. The channel sands are contained in a fissile, medium gray (N 5) weathering to light gray (N 71, tough, conchoidally- fracturing,slightly silty shale , ...... 29 Unit No. Description Thickness " in feet "

19. Quartz sandstone; medium-bedded (1-2 ft. 1, channelled, yellowish .gray (5Y 7 /Z) weathering to grayish orange (10 YR 7/41, hard, silica- cemented,medium-grained (1.46), moderately- sorted; contains gray, tan and white, sub-rounded to well-rounded, 2-10 mm., chert pebbles ...... 10

18. Sandstone and mudstone; platy-bedded (1 -2 in. 1, light yellowish gray (5 Y 9/11 weathering to yellowish orange (10 YR 7/6), hard, silica-cemented, very fine-grained (3. 86), we.11-sorted, quartz sandstone interbedded with laminated, very light gray (N 8) weathering to light greenish gray (5 G 8/1)9 tough,conchoidally-fracturing mudstone ... 24

17. Quartz sandstone; medium-bedded (1-2 ft. } to slightly cross-bedded (4-6 in. }, pale yellowish orange (10 YR 8/6) weathering to pale grayish orange (10 YR 7/3), slightly-friable, silica- cemented, fine-grained (2.26), well-sorted ..... 33 7 Total Dakota Formation. ... 114

Morrison .Formation

16. Silty shale; rudely-bedded to laminated, yellowish olive gray (5 Y 612) weathering to yellowish gray (5 Y 7/2)~, indurated to friable; contahs small (0.5-1 ft. ), lenticular mudstone ...... 18

15. Conglomeratic quarts sandstone: massive (2-3 ft.), dusky yellow (5 Y 6/4) Weathering to yellowish olive gray (5 Y 6/2), slightly friable, silica-cemented, medium-grained(1.26), poorly-sorted, contains clay and chert pebbles ...... 11

14. Mudstone and shale; platy-bedded (1-3 in. ) to laminated, irregular-bedded, dusky olive.brown (5 Y 5/41, weathering to moderate brown (5 'YR4/41, very hard to tough, silica- and carbonate-cemented, interbedded ...... 36

13. Mostly covered silty shale and mudstone; reddish brown and pale green...... 243 Unit No. Description 'hickness " in feet "

2. Quartz sandstone; thin-bedded (0.5-1 ft. ), very pale orange (IO YR 8/21 weathering to light grayish brown (5 YR 6/3), very hard, silica-cemented, fine-grained.(Z. 7d), well-sorted ...... 14

1. Very poorly exposed silty shale and mudstone; pale green...... 26

10. Quartz sandstone; platy-bedded (0.5-2 in. ) becom- ing thin-bedded toward top (0.5-1 ft.), pinkish gray (5 YR 8/l) weathering to grayish .orange pink (5 YR 7/2), very hard, silica-cemented,fine-grained (2. 5d), well-sorted ...... 48

9. Partly covered silty shale and mudstone; reddish brown, ...... 15

8. Quartz sandstone; platy-bedded (1-3 in. 1, irregular- bedded, pale yellowish brown (10 YR 612) weathering to pale grayish brown (5 YR 4/2), slightly friable, silica-cemented, very fine-grained (3.2$), moderately well-sorted, interbedded with similarly colored silty shale and mudstone ...... 24

7. Poorly exposed, mudstone and fine-grained sandstone; reddish brown and pale green...... 25

6. Quartz, sandstone: platy-bedded (1-3 in. ), randomly cross-bedded (up to 6 in. ), grayish orange pink (5 YR 7/2) weathering to brownish gray (5 YR 4/1), hard, silica-cemented, very fine-grained (3.8d), moderately-sorted ...... 26 5. Poorlyexposed, silty shale; reddish brown, . , . . 29

4. "Agate bedtt - Small (up to 1 in. ) nodules of moderate red (5 R 5/4) silica in a matrix of greenish gray silty shale ...... I

3. Shale and mudstone; irregular, fissile, greenish gray (5 CY 6/1) weathering to yellowish gray (5 Y 7/21, tough, slightly calcareious, silty shale grading upward into a hackly-fracturing, pale brown (5 YR 5/2) weathering to a grayish orange pink (5 YR 7/2), hard,silica-cemented mudstone . . , . . -20 Unit No.Thickness Description " in feet " TotalMorrison.Formation . . . 535

Todilto limestone

2. Slightlyshaly limestone; irregular, discontinuous- bedded, crinkly, fetid, dark gray (N 3) weathering to pale yellowish brown (10 YR 6/21, hard, aphanitic...... , ...... , . . , . , . . . 16 -Exeter sandstone 1. Quartzsandstone; massive (3-5 ft. ), yellowish gray (5 Y 711) weathering to pale orange brown (5 YR 6/2), friable, slightly silica-cemented, fine-grained (2.641, well-sorted , . . . . . (exp.osed) 5

Baseexposed ofnot unit in gully. -

Totalsection...... , 670 SAN AGUSTIN SECTION

FEET - 300-

650- -

250-

600- -

200-

550- -

150-

500-

100-

450- ". 50-

400-

0- OOCKUM OR.

350- MEASURED SECTION 57-3

San Agustfn Section

Location. -- Travel 8 miles east from Las Vegas, New Mexico, on

State Highway 65 to State Highway 104, then south 8 miles to the Canadian

Escarpment. The traverse extends from the base of the Exeter sandstone northward along the highway into the upper Dakota sandstone. The beds dlp northward at 2O. The section was measured by K. H. Doney and C.

J. Mankin (September 1957).

Unit No. Description Thickness " in feet " Top of escarpment -Dakota Tormation 19. Sandstoneand silty shale; medium-bedded (1-2 ft.) grading upward to platy-bedded (1-3 in. ), very light yellowish gray (5 Y 911) weathering to yellowish gray (5 Y 7/3), very hard, silica- cemented, fine-grained (2.64), very well-sorted, quartz sandstone interbedded with thin (1 -4 in. ), irregular, brownish gray (5 YR 4/1) weathering to light brown (5 YR 6/51, fissile, slightly carbonaceous,silty shale ...... 43

18. Quartzsandstone; massive (2-3 ft. channelled, very tight gray (N 8) weathering to dark yellowish orange (10 YR 6/61, very hard, silica-cemented, medium- .to coarse-grained (1. Ob), poorly-sorted, conglomeratic; contains white, gray, tan and black,2-16 mm, well-rounded, chert pebbles ... 25

17. Quartzsandstone; massive (2-4 ft. ), white (N 9) weathering to dark grayish orange (10 YR 6/41> hard, silica-cemented, fine-grained (2. 8$5]>very well-sorted; contains a few conglomerate lenses near the upper part of the unit ...... 26 7 Total Dakota Formation. .. 94 159

Unit No. Description " Thickness in feet Morrison Formation "

16. Siltyshale; poorly exposed, laminated to nodular- bedded, dusky olive brown (5 Y 6/6) weathering to moderate olive gray (5 Y 4/21, tough; contains a few conglomeratelenses ...... 47

15.Silty shale; laminated at base gradingupward to nodular-bedded, grayish yellow green.(5 GY 8/1), tough; contains thin (0.2-1 ft. ), mottled, light brownish gray (5 YR 6/1) and light olive gray (5 Y 6/1) Weathering to brownish gray (5 YR 5/1), hard, aphanitic limestone beds at the base of the unit. The upper part of the unit contains massive (1-3 ft. ), yellowish gray (5 Y 8/ 1) weathering to dusky yellow (5'Y 6/4), hard, silica-cemented, fine- grained (2.8#), moderately-sorted, quartz sandstone beds and lenses. One white (N 9) weathering tolight gray (N 7), soft,powdery, volcanic ash bed &4 occurs in upper part of unit ...... d49 14. Quartzsandstone; massive (2-4 ft. ), randomlycross- bedded, moderate grayish yellow (5 Y 7/5)weathering to dusky yellowishgray (5 Y 7/3), hard, silica- cemented, coarse- to very coarse-grained (O#), poorly-sorted,contains chert and clay pebble .... 17

13.Silty shale andmudstone; platy-bedded (1-2 in. ) to laminated, mottted greenish gray (5 GY 6/11 and light brownish gray (5 YR 6/1) weathering to moderate brown (5 YR 4/4), grading upward to greenish gray (5 G 7/1) weathering to light greenish gray (5 G 8/1), hard, silica-cemented, interbedded; contains a white (N 9) weathering to light gray (N 7), soft, volcanic ash bed and several mottled light brownish gray (5 YR 6/1) and greenish gray (5 GY 6/1) weathering to light olive gray (5 Y 6/1), aphanitic limestone lenses in the middle of the unit...... 81

12.Quartz sandstone; massive (2-4 ft. 1, brownishgray (5 YR 6/11 weathering to yellowish gray (5 Y 7/1), hard, silica-.cemented, fine-grained (2. 781, moderatelywell-sorted ...... 8 Unit No. Description Thickness " in feet "

11. Silty shale; laminated to nodular-bedded, mottled dull grayish red purple (5 RP 4/2) and greenish gray (5 GY 6/11 weathering to light brownish gray (5 YR 6/1), tough,conchoidally-fracturing; contains several similarly colored mudstone beds and lenses ...... 17

10. Quartz sandstone; medium-bedded (1-2 ft. 1, mottled light brownish gray (5 YR 6/1) and pinkish gray (5 YR 8/1) weathering to light brownish gray (5 YR 7/1), hard, silica-cemented, in.terbedded layers of fine-grained (2.26) and very fine-grained (3,56), moderately well-sorted; contains some silty shale lenses (up to 6 in. long) and a discontinuous boring surface ...... 45

9. Slightly silty shale; laminated to nodular-bedded, grayish red purple (5 RP 5/2) weathering to light brownish gray (5 YR 6/1j, tough, conchoidally- fracturing ...... 2

8. Quartz sandstone; massive (2-4 ft. ), mottled greenish gray (5 GY 6/1) and light brownish gray (5 YR 6/1) weathering to pale brown (5 YR 6/2), hard, silica-cemented,fine-grained (2.64, poorly- sorted...... 31

7. Mudstone; partly covered, platy-bedded (1-2 in. ), light brownish gray (5 YR 6/1) weathering to very light brownish gray (5 YR 7/1)# tough, conchoidally- fracturing ...... 13

6. Quartz sandstone: medium-bedded to massive (1-3.. ft. )> light brownish gray (5 YR 6/1) weathering.to very .light brownish gray (5 YR 7/1)2 very hard, sitica- cemented, very fine-grained (3.2$), moderately well-sorted ...... 14

5. Mudstone and sily shale; laminated.to platy-bedded (1 -2 in. 1, brownish gray (5 YR 5/1) weathering to very light brownish gray (5 YR 7/1}$ hard, silica- cemented, irregularly-fractures ...... 2 161

Unit No. . Description Thickness " in feet "

4. Quartzsandstone; medium-bedded (1-2 ft.), in places randomly cross-bedded, light brownish gray (5 YR 6/1) weathering to pale orange brown (5 YR 6/21, very slightly friable, silica-cemented, very fine-grained (3.141, moderately-sorted .... 20

3. Mudstoneand silty shale; poorly exposed, medium- bedded (1-2 ft. ), brownish gray (5 YR 5/1) weathering to light brownish gray (5 YR 6/1), hard, silica-cemented ...... 42

2. Mudstoneand silty shale; poorly exposed, laminated to thin-bedded, brownish gray (5 YR 5/1) weathering to pale brown (5 YR 5/21, hard, silica- cement; contains several light olive gray (5 Y 5/2) weatherhg to yellowish gray (5 Y 7/2), hard, silica-cemented, very fine-grained (3.6d), poorly- sorted, quartz sandstone beds ......

Total Morrison Formation, .

Exeter sandstone

1. Quartzsandstone; massive (4-8 ft.),randomly cross-bedded, Light gray (N 7) weathering to yellowish gray (5 Y 7/1), hard, silica.-cemented, fine-grained (2.8d1, well-sorted ......

Dockum group

Unit not measured. Red beds exposed near base of slope.

Total section ......

r ._ TRUJILLO HILL SECTION

400- -

350- DOCKUM OR. -

300-

- FM , 250- -

200-

150- 162

MEASURED SECTION 57-4

Trujillo Hill Section

Location. -- New Mexico State Highway 65, 112 mile south .of Trujillo,

New Mexico. The traverse extends along the highway in a northwest direction from the base of the Eketer sandstone and ends near the.tpp of the

Morrison. The upper Morrison contact with the Dakota has been eroded back and is not exposed along the traverse. The beds dip northward at angles of less than lo. The section was measured by H. H, Doney and

C. J. Mankin(September 1957).

Unit Description Thickness ”No. in feet ”

Top of slope (in uppermost Morrison Formation)

Morrison Formation

8. Poorlyexposed, silty shale andmudstone, pale green...... 15

7. Quartzsandstone; massive (4-6 ft. 1, cross-bedded at base, white (N 9) weathering to grayish orange (10 YR 7/4), hard, silica-cemented, medium- grained (1.98), grading upward to fine-grained (2.5d), well-sorted ...... 49

6. Siltyshale; laminated to nodular-bedded,variegated pale grayish brown (5 YR 4/2) and pale greenish gray (5 G 612) weathering to pale brown (5 YR 512) and very pale green (5 G 7/21, tough,. fractures conchoidallyl contains numerous thin- bedded (0.5-1 ft. ) to massive (2-4 ft. j, very pale orange (10 YR 8/2) weathering to grayish orange (10 YR 7/4) and mottled very pale orange (10 YR 8/2) with moderate yellowish brown (10 YR 5/2) weathering to grayish orange (10 YR 7/41, hard, silica-cemented, mostly fine-grained (2.36), moderately-sorted, quartz sandstone channel deposits. The Lower part of the unit contains a 163

.Unit No. Description Thickness “ in feet ”

white (N 9) weathering to light gray (N 71, soft, powdery, volcanic ash bed ...... 153

5. Quartzsandstone interbedded with siltyshale; medium-bedded (1-2 ft.), pale yellowish green (10 GY 7/2) weathering to light olive brown (5 ‘Y 5/4), very hard, silica-cemented, fine-grained (2.761, poorly-sorted, with clay and chert pebbles; laminated, pale green (5 G 7/2) weathering to very pale green (5 G 8/21, tough ...... 5

4. Mudstoneand silty shale; laminated to nodular, variegated .grayish red purple(5 RP 3/2) and very light olive gray (5 Y 6/21 weathering to brownish gray (5 YR 4/1) and light yellowish gray (5 Y 9/1), tough, conchoidally-fracturing; some thin (0.5-1 ft. ), similarly colored, aphanitic, sility limestone beds and a few similarly colored, silica.-cemented siltstonebeds ...... 94

3” Quartzsandstone; platy-bedded (1-4 in. ), randomly cross-bedded, highly lenticular, light gray (N 7) weathering to very light brownish gray (5 YR 7/11, hard, silica-cemented, very fine-grained (3.441, moderately-sorted ...... 23

2. Siltyshale; laminated, variegated pale grayish brown (5 YR 4/2), very dusky red purple (5 RP 212) and light brown (5 YR 6/41 weathering to grayish orange pink (5 YB 7/21, pale red purple (5 RP 5/21 and grayish orange (10 YR 7/41, tough, conchoidally- fracturing, containing a few thin (0. 5-1 ft. ]* similarly colored, aphanitic limestone and mudstone beds. 47 ...... TotalMorrison.Formation. .. 386

Exeter sandstone

1. Quartzsandstone: massive (4-6 ft.), mottledvery pale orange (IO YR 8/2) and white (N 9) weathering to pale grayish brown (5 YR 6/2), slightly friable, silica-cemented, medium-grained (1.84)* very well-sorted ...... 39 164

Unit No. Description Thickness " in feet " Dockum group

Unit not measured. .Red beds exposed near base of slope. - Totalsection. . . . , . . , 425 SABINOSOCANYON SECTION

450-

400- -

350- -

300- 165

MEASURED SECTION 57-5

Sabinoso Canyon.Section

Location. -- Travel 29 miles west-southwest of Mosquero, New

Mexico, on State Highway 65. Turn right (northwest) on branch road to

Sabinoso and travel 3 miles. The section is located about 300 yards east of the road. The traverse begins within the -Exeter sandstone and extends eastward up the scarp along.an old abandoned road. The top of the section is in the Lower'Dakota formation. The section was measured by

H. ?A. Doney and.G. J. Mankin (September 1957).

Unit Thickness Description "No. in feet " Top of scarp -Dakota Formation 12. Quartz sandstone; vaguely cross-bedded grading upward to platy-bedded (1-3 in.), grayish orange (10 YR 7/41 grading upward to yellowish orange (10 YR 7/6) weathering to a moderate yellowish brown (10 YR 5/4), slightly friable to hard, silica-cemented, fine-grained (2.0-2.64), moderatetywell-sorted ...... 59

Morrison Formation

11. Silty shale .md mudstone; laminated to nodular- bedded, pale grayish yellow green (5 GY 8/2) weathering to very pale grayish yellow green (5 GY 9/21,tough, conchoidally-fracturing ..... 47

10. Quartz sandstone; medium-bedded (1-2 ft. 1 to slightly cross-bedded, very light gray (N 8) speckled with dark yellowish. orange(IO YR 6/6) weathering to very pale orange (10 YR 8/21, hard, silica-cemented, medium-grained (1. ld], poorly- sorted,chert pebble, conglomerate. The .chert pebbles are well-rounded, light colored, 24mm pebbles...... 11 Unit No. Description Thickness " in feet " 9. Mudstone and interbedded silty shale; partty covered, laminated (up to 1 in. ), pale brown (5 YR 5/2:} weathering to grayish orange pink (5 YR 7/21, tough to hard, partially silica-cemented, conchoidally-fracturing. A thin (6 in. ), white (N 9j weathering to light gray (N 71, soft, powdery, volcanic ash bed is present in the middle of the unit ...... 81

8. Quartz sandstone; medium-bedded (1-2 ft. 1, light gray (N 7) speckled with moderate yellowish brown (10 YR 5/4) weathering to pale orange brown (10 YR 7/2), very slightly friable, silica-cemented, medium-grained (1.9$), moderate.ly well-sorted . . 25

7. Poorly exposed, silty shale and interbedded mudstone; Laminated to nodular-bedded, pale yellowish green (10 GY 712) weathering to very pale yellowish green (10 GY 9/2), tough, conchoidally- fracturing ...... 14

6. Quartz sandstone; medium-bedded to massive (1-3 ft. 1, pale orange (10 YR 7/.2) to iery pale orange (10 YR 8/2) weathering to duller shales of similar colors, extremely hard, silica-cemented, fine- grained(2.0-2.4$), moderately well-sorted . . , . 24

5. Slightly silty shale; partly covered at top, laminated to nodular-bedded, variegated pale green (io G 6/2) and grayish red purple (5 RP 3/2) weathering to lighter and duller shales of the same colors, tough, conchoidally-fracturing,containing two, white (N 9) weathering to light gray (N 71, soft, powdery, 3 -4 inch volcanic ash beds in the upper l/3 of theunit ...... 60

4. Quartz .sandstone; medium-bedded (1-2 ft. 1 to randomly cross-bedded, yellowish gray-(5 Y 8/11 speckled with grayish orange (10 YR 1/43 weathering to moderate yellowish brown (10 YR 6/41, slightly friabte, silica-cemented, fine-grained (2,8$), moderately well-sorted; contains small, discontinuous,pale green, silty shale stringers. . 32 Unit No. .Description Thickness " t in feet "

3. Siltyshale; very poorly exposed, laminated to nodular-bedded, very pale brown (5 YR 612) grading upward to grayish brown.(5YR 5/219 crumbly to tough, irregular-fracturing; contains several platy-bedded (1-3 in. ), pale yellowish brown (10 YR 612) weathering to pale brownish orange (IO YR 7/3), hard,silica-cemented, fine-grained siltstone beds...... 101

2. Quartzsandstone; thin-bedded (up to 1 ft.) to massive (2-3 ft. )$ light brown (5 YR 6/4) speckled with moderate yellowish brown (10 YR 5/41 weathering to dark yellowish brown (10 YR 4/31, friable, slightly silica-cemented, fine-grained (2. 2dI2 very well- sorted; interbedded with laminated, very pale brown (5 'YR 612) weathering to grayish orange pink (5 YR 7/2), tough, slightlysilty shale ...... -39 Total MorrisonEormation ... 434

Eketer sandstone

1. Quartzsandstone; massive (2-4 ft. )9 lightbrown (5 YR 6/41 speckled with grayish.orange pink (5 YR 7/21 weathering to grayish orange brown (5 YR 6/3), friable,slightly silica-cemented, fine- grained (2.7b), welt-sorted ...... (exposed) 35

Base of unit not exposed at base of abandoned road grade. - Total section ...... 528 CANADIAN RIVER SECTION

FEET

12 PURGATOIRE FM. 250-

200-

150-

100-

50-

MORRISON FM. ss. 0- MEASURED SECTION 57-6

Canadian River Section

Location. -- New Mexico State Highway 120 at the.Canadian River

Crossing, 11.4 miles west of Roy, Karding County, New Mexico. The

section extends up the west side of th.e canyon along the highway where it begins in the upper part of the Exeter and ends in the lower Purgatoire formation. The section was measured by H. H. Doney and.C. J. .Mankin

(September 1957).

Unit No. Thickness Description ” in feet ” Top of bluff

Purgatoire Formation

12. Quartz sandstone; massive (2-3 ft. 1, grayish yellow (5 Y 8/4) weathering to dark grayish orange (10 YR 7/61, friable,slightly silica-cemented, medium- grained (1.94), moderately welt-sorted; contains some well-rounded to sub-rounded, white, tan., redand black, 2-16 mm, chert pebbles ...... ,

Morrison.Formation

11. Slightly silty shale and mudstone; laminated to nodular-bedded, variegated pale grayish purple (5 P 5/2) and grayish yellow green (5 GY 7/2) weathering to pale red purple (5 RP 6/2) and ligh&,greenish gray (5 G 8/11 (green shades are more abhndant), tough; contains numerous 3-10 inch thick, white (N 9) weathering to light gray (N 7j0 soft, powdery, volcanic ash beds throughout the section and several thin-bedded (up to 1 ft. ), colored similarly to the shale beds, hard, silica-cemented siltstone and aphaniticlimestone beds . . . . . i ......

10. Quartz sandstone; medium-bedded (1-2 ft. ), very light greenish gray (5 G 9/11 weathering to moderate grayish yellow green (5 GY 7/31, very slightly friable, silica.-cemented, fine-grained (2.28) moderately-sorted,clay fragm.ent bearing . . . , . Unit No. Description Thickness " in feet "

9. Very slightly silty shale; laminated, variegated browntsh gray (5 YR 4/11 and moderate greenish gray (5 G 7/1)weathering to light brownish gray t5YR 6/1) and light greenish gray (5 G 8/11, soft; contains numerous 1-10 inch thick, white (N 9) weathering to light gray (N 71, soft, powdery, volcanic ash beds and severat platy- to medium- bedded (0. 5-2 ft.), pale green .(5 G 7/2) weathering to grayish green (10 GY 5/2}, hard, silica- cementedsiltstone beds . , , , ...... 151

8. Quartz sandstone; platy-bedded (1-3 in.) to massive (2-3ft. light greenish gray (5 GY 8/1) weathering to moderate yellowish gray (5 Y 7/1j, hard, silica-cemented, very fine-grained (3.38), moderately well-sorted: contains discontinuous, laminated, grayish yellow green-(5 GY 7/2)weathering to moderate greenish gray (5 G 7/1), tough, slightlysilty shale layers . . . , . . . , . . . . . 51

7. Very poorly exposed silty shale and mudstone; variegated,light brown and green. . . . , . . . . . 24

6. Quartz sandstone; platy-bedded (1-3 in.) to massive (2-3 ft.), moderate brownish gray (5 YR 5/11 weathering to very.light brownish gray,(5YR 7/1), slightly friable, silica-cemented, fine- to very fine-grained (2.5-3. 2dj9 moderately sorted; contains discontinuous, laminated, similarly cotored, siltyshale layers ...... 33

5. Partly covered, silty shale and mudstone; laminated to nodular-bedded, variegated grayish.red (IO R 4/21 and moderate red purple (5 RP 5/21 weathering to moderate brownish gray (5YR 5/1) and pale red purple (5 RP 6/21? crumbly to tough; contains

several platy- to thin-bedded (1-6 in. )$ similarIy colored,hard, silica-cemented, siltstone beds . , . 98

4. "Agate bedsc'l two, thin (1-6 in. )2 nodular, pale pinkish gray (5 YR 9/1j9 silica beds in a matrix of redbrown silty shale , ...... , e . . e . . 1 Unit No. Description Thickness " in feet "

3. Quartz sandstone; medium-bedded (1-2 ft. 1, grayish orange pink (5 YR 7/21 weathering to moderate yellowish brown (10 YR 5/2), hard, calcite- and silica-cemented, fine-grained (2.Sd)$ moderately well-sorted; contains spheroidal (0.5-1 ft.) nodules of calcite ...... e ......

2. Silty shale; laminated to nodular-bedded, pale brown (5 YR 5/21 weathering to moderate brown (5 YR 6/3), tough. , .. . . . , . . e . e ...... Total Morrison Formation . . .

Exeter sandstone

1. Quartz sandstone; massive (3-4 ft-), grayish orange pink (5 YR 712) weathering to pale yellowish brown (10 YR 6/2), very friable, very slightly silica- cemented, fine-grained (2.761, well-sorted;contains thin (1-6 in.), taminated, pale brown (5 YR 512) weathering to very pale brown (5 YR 6/2), soft,silty shale layers , e . . , , . . . . (exposed) 32

.Base of unit not exposed in canyon bottom

Totalsection . . , ...... OLD MILLS SECTION

FEET

550- DOCKUM OR. -

500- -

550-

500- -

450-. -

400- MEASURED SECTION 57-7

Old Mills Section

Location. -- The Old Mills ranch headquarters (now abandoned) in

the Canadian River Canyon due west of Mills, Harding County, New

Mexico. The traverse extends from the canyon floor up the east wall of the canyon. The section begins at the base of the Exeter and ends in the Dakota formation. The section was measured by H. H. Doney and C. J. Mankin(September 1957).

Unit No, Description Thickness " in feet " Top of canyon wall

Dakota .Formation

20. Quartzsandstone; thin- (0.5-1 ft. 1 to medium- bedded (1-2 ft. )8 very light gray (N 8) weathering to yellowish gray (5 Y 8/11, hard, silica-cemented, fine-grained (2. fib), well-sorted ...... 15

Purgatoire Formation

19.Poorly exposed, silty shale andsiltstone; laminated, medium dark gray (N 4) weathering to medium light gray (N 6),tough...... 65

18.Quartz sandstone; medium- (1-2 ft. 1 to massive- bedded (2-3 ft. ]# very light gray (N 8) weathering to very pale brown (5 YR 6/Z), friable, slightly silica-cemented, fine-grained (2.2b), well-sorted; contains a few well-rounded, gray, tan and black, 2-16 mm,chert pebbles ...... -40 Total PurgatoireFormation . . 105

Morrison Formation

17.Quartz sandstone; massive (3-4 ft.light gray (N 7) to very pale orange (10 YR 8/21 weathering to very pale yellowish brown (1.0 YR 7/21, slightly Unit No.Thickness Description " in feet "

friable, silica-cemented, fine-grained (2.741, moderately-sorted; grades upward to a medium- grained (1. Zd), poorly-sorted, chert and clay pebble conglomeratic, quartz sandstone ...... 42

16. Poorly exposed, silty sha,le and mudstone; pale olive (10 Y 6/2) weathering to grayish yellow green (5 GY 7/2); contains two, 3-6 inch thick, white (N 91 weathering to light gray (N 7), soft, powdery, volcanic ash beds in the lower 1/3 of the unit . . , . 107

15. Quartz sandstone; medium-bedded (1-2 ft. 1, white (N 9) spotted with pale orange brown (10 YR 7/3) weathering to pale yellowish brown (10 YR 6/21, slightly friable, silica-cemented, medium-grained (1. 84), moderately-sorted ...... 9

14. Exposed only at base, silty shale and mudstone; pale green...... 27

13. Quartz sandstone; medium-bedded (1-2 ft. mottled very light gray (N 8) and pale yellowish brown (IO YR 612) weathering to light yellowish brown (10 YR 7/21, slightly friable, silica- and limonite-cemented, medium-grained (1. 581, moderately-sorted ...... I ...... 5

12. Partly covered, silty shale; variegated pale green and pale brown...... 36

11. Quartzsandstone; medium-bedded (2 ft.greenish gray (5 GY 6/1) weathering to moderate brown (5 YR 4/41, extremely hard, silica-cemented, fine- grained (2. 4d13 moderately well-sorted ...... 4

10. Mostly covered, silty shale and mudstone; pate green...... 24

9. Quartz sandstone; thin-bedded (up to 1 ft. 1, pale grayish orange pink (5 YR 8/21 weathering to very pale yellowish brown (10 YR 7/2), friable, slightly silica-cemented, very fine-grained (3.04)$ well- ink $" sorted...... 32 I 173

Unit No. Description Thickness " in feet "

8. Silty shale and siltstone; variegated pale brown and pale green......

7. Quartz sandstone; massive (3-5 ft. ), grayish orange pink (10.R8/2) weathering to yellowish gray (5 Y 7/2), friable, very slightly silica-cemented, very fine-grained (3.28), moderatelywe,ll-aorted. Color becomes darker brown toward base and cementation much more complete ......

6. Slightly silty shale and silica-cemented mudstone; laminated to platy-bedded (1-2 in. 1, variegated pale brown (5 'YR 5/2) and pale green (IO G 7/2) weathering to very pale brown (5 YR 6/2) and very pale yellowish green (10 GY 8/2), tough. . , 5. Silty shale; traces of red brown nodules (1 -3 in. ) of silica '("Agate bed"? ) in a matrix of pale brown ...... 1

4. Silty shale and siltstone; platy-bedded (1 -2 in. ), light pale brown (5 YR 5/3) weathering to very pale brown (5 YR 6/2), hard ...... Total Morrison Formation . .

Exeter sandstone

3. Quartz sandstone; massive (3-5 ft.), grayish orange pink (5 YR 7/2) weathering to very pale yellowish brown (10 YR 7/21, friable, slightly silica-cemented, fine-grained (2.3B1, well- sorted......

2. Slightly silty shale; laminated, pale brown (5 YR 5/2)......

1. Quartz sandstone; massive (3-5 ft. ),. light brown (5 YR 6/41 weathering to very pale brown (5 YR 6/2), friable, silica-cemented, fine-grained (2. 78), well-sorted ...... -59 Total Exeter Sandstone ... 135 174

Unit No. Description Thickness " in feet "

Dockum Group 7

Unit not measured. Forms floor of valley. c

section , , , ,W ---, Total ...... <0- BURRO CANYON SECTION

FEET 500-

""" """

400- """ """-""_ "_"

350- ss.

MORRISON FM.

250-

200- MEASURED SECTION 57-8

Burro Canyon Section

Location. -- State Highway 65, 10.9 miles west of Mosquero, Harding

County, New Mexico. The traverse begins at the culvert in the bottom of the canyon.and extends eastward up the ravine to the top of the hill.

The section begins in the upper.Exeter and ends in the tower Dakota formation. The section was measured by H. H. Doney and C.. J. Mankin

(September 1957).

Unit No.Thickness Description " in feet " Top of hilt

Dakota Formation

14. Quartz sandstone: medium-bedded (1-2 ft. ) to massive (2-3 ft. ), pate grayish orange pink (5 YR 8/2) weathering to very pale yellowish brown (10 YR 7/21, slightly friable, silica-cemented, medium-grained (1.24), moderatelywell-sorted . . 17

Purgatoire Formation

13. Quartz sandstone; covered at top, cross-bedded at base (6-8 in. amplitude) grading upward to massive (2-4 ft. ), pale grayish orange (10 YR 8/4) weathering to pale yellowish brown (10 YR 5/3), hard, silica-cemented,fine-grained'(2.44), well-sorted; contains clay pebbles at the base of the unit . . . , 69

Morrison Formation

12. Silty shale and mudstone; poorly exposed, laminated to'nodutar-bedded, very pale olive (10 Y 7/.2) weathering to grayish yellow green (5 GY 7/21, crumbly to tough,conchoidally-fracturing. . 95

11. Quartz sandstone; thin-bedded (up to 1 ft,) to massive (3-5 ft. ), yeltowish gray (5 Y 8/1) 176

Unit No.Thickness Description " in feet "

weathering to pale grayish orange (10 YR 7/4), very slightly friable, silica-cemented, fine- grained (2.54). moderately-sorted ...... 34

10. Mostly covered, silty shale and mudstone; laminated to nodular-bedded, variegated moderate greenish gray (5 GY 7/1) and grayish red purple (5 RP 4/2) weathering to light greenish gray (5 GY 8/11 and moderate grayish red (5 R 5/2), tough, conchoidally-fracturing ...... 90

9. Quartz sandstone; medium- (1-2 ft.) grading upward to thin-bedded (up to 1 ft. ], pale grayish orange (10 YR 8/4) spotted with moderate yellowish brown (10 YR 5/4) weathering to dusky yellowish brown .(lo YR 2/2), friable, silica- cemented,fine-grained (2.6$), poorly-sorted; contains thin (up to 1 ft. thick), pale brown silty shale lentils ...... 26

8. Poorly exposed, silty shale; laminated, pale green...... 6

7. Quartz sandstone; medium-bedded (1-2 ft. ), cross- bedded, pale grayish.orange (10 YR 8/3) weathering to very pate yellowish brown (IO YR 7/21, slightly friable, silica-cemented, fine-grained (2. 0-2.4$), moderately-sorted ...... 8

6. Mostly covered, silty shale; laminated, variegated pale green and pale brown ...... 17

5. Quartz sandstone; medium- (1-2 ft.) to massive- bedded (2-4 ft. ), cross-bedded, pale yellowish gray (5 Y 8/2) weathering to very pate yellowish brown (10 YR 7/2), slightly friable, silica-cemented, very fine-grained (3. 3$)$ moderately well-sorted . . , . 20

' 4. Silty shale and mudstone; laminated- to nodular- bedded, variegated moderate brown (5 YR 4/21 and moderate yellowish green (IO CY 6/2)weathering to pale brown (5 YR 5/2) and pale grayish yellow green (5 GY 8/2), tough, conchoidally-fracturing . . 74 Unit No. Description Thickness " in feet

3. "Agatebed"; verydiscontinuous beds of 3-6 inch thick, red brown and gray, silica nodules in a matrix of brown silty shale ...... 1

2. Mudstone; irregularly-bedded to laminated,light brown (5 YR 6/41 weathering to grayish orange brown (5 YR 7/3), crumbly, soft ...... -31 Total Morrison Formation.. . 401 -Exeter Formation 1. Quartzsandstone; massive (2.-4 ft. ), mottledgray- ish orange pink (5 YR 712) and moderate brown (5 YR 415) weathering to light pale brown (5 YR 5/3), very slightly friable, calcite- and silica- .cemented, fine-grained (2.9#), well-sorted; contains calcite nodules ...... (exp.osed) 4 Base of unit not exposed in canyon bottom - Total section ...... 49 1 GALLEGOS RANCHSECTION

FEET- -

750- 400- - -

700- 360-

- DOCKUM - OR. 650- 300- - -

600- 250- -

550- 200- -

500- -

450- .

MEASURED SECTION 57-9

Gallegos Ranch Section

Location. -- 2. 8 miles north of Gallegos Ranch headquarters on State

Highway 39, 24.8 miles southeast of Mosquero, Harding :County, New

Mexico. The section extends from the base of the escarpment at the base of the Exeter, west to the top of the plateau where it ends in the lower

Dakota formation. The section was measured by H..H. .Doney and C. J.

Mankin (September 1957).

Unit No. .Description Thickness " in feet " Top of escarpment

Dakota .Formation

21. Quartz sandstone; platy- (1-3 in.) to thin-bedded (up to 1 ft. 1, very pale orange (10 YR 8/2) weathering to pale yellowish gray (5 Y 8/21, friable, silica-cemented, fine-grained (2.841,well- sorted ...... 41

20. Slightly silty shale; laminated to nodular-bedded, very pale brown. (5 'YR 6/2) weathering to very light brownishgray (5 YR 7/11? crumbly,soft ...... 4

19. Quartzsandstone: thin-bedded (up to 1 ft.cross- bedded (6-8 in. dipping southeast), pate grayish orange (10 YR 8/5) weathering to grayish orange (10 YR 7/41, hard, silica-cemented, fine-grained (2.84), wetl-sorted ...... 41

18. Quartzsandstone: massive (2-3 ft. white (N 9) weathering to very pale orange (10 YR 8/2), friable, slightly silica-cemented, fine-grained (2.1$)$ moderately-sorted; contains numerous 1-3 inch limonite-cemented nodules and 1-6 inch Long borings on the upper surface of the unit ...... -39 TotalDako,ta,Formation .... 125 Unit No. Description Thickness " .. in feet " Purgatoire Formation

17. Poorly exposed, silty shale; laminated, pale brown., *' + ...... 9 16. Quartz sandstone; medium- (1-2 ft.) to massive- bedded (2-4 ft.), cross-bedded in a few places, very pale orange (10 YR 8/2) weathering to dark grayish orange (10 YR 6/4), hard, silica-cemented, fine-grained (2.54), moderately-sorted; contains numerous 4-20 mm, pale green, flattened, clay pebbles in the base of the unit ...... -39

Total Purgatoire Formation. , 48

Morrison.Formation

15. Mostly covered, silty shale; la,minated, variegated medium brown (5 YR 4/2) and pale grayish green (10 GY 6/2) weathering to very pale brown (5 YR 6/2) and grayish yellow green (5 GY 7/2), crumbly to tough; contains thin (3-6 in, ) mudstone ...... 149

14. Quartz .sandstone$ medium-bedded (1-2 ft.), pale olive (10 Y 6/2) weathering to pale yellowish brown (10 YR 6/2), slightly friable, silica-cemented, fine- grained (2. 74)? moderately-sorted ...... 5

13. Mostly covered, silty shale and mudstone; laminated, pale green...... 26

12. Quartz sandstone; thin-bedded (up to 1 ft.), cross- bedded (dipping east), yellowish gray (5 Y 8/1) weathering to moderate grayish orange (10 YR 6/4), slightly friable, silica-cemented, fine-grained (2.24), moderately-sorted ...... 16

11. Mostly covered, silty shale and mudstone; laminated to platy-bedded (up to 1 in. ), pate green,...... 41

10. Quartz sandstone; medium-bedded (1-2 ft.), very pale orange (10 YR 8/2) weathering to pale yellowish brown (10 YR 6/2), locally pale reddish brown (LO R 5/41 weaihering to moderate reddish brown (10 R 4/4), hard to very hard, silica-cemented, medium- grained (1. 24), poorly-sorted ...... 9 Unit No. Rescription Thickness " in feet " 9. Silty shale and mudstone; laminated to nodular- bedded, pale olive (10 Y 6/21 weathering to grayish yellow green (5 GY 7/21, crumbly to conchoidally-fracturing ...... 47

8. Quartz sandstone; thin-bedded (up to 8 in.), yellowish gray (5 Y 8/1) weathering to moderate yellowish brown (10 YR 5/2), hard, silica-cemented, very fine-grained (3.241, poorly-sorted; contains some sand-sized clay particles ...... 9

7. Mudstone; platy- (1-3 in.) to thin-bedded (up to 9 in. ), grayish yellow green (5 GY 7/2) weathering to pale grayish yellow green (5 CY 8/2), friable, poorly consolidated ......

6. Mudstone; platy- (1-2 in. 1 to thin-bedded (up to 8 in. ), light olive gray (5 Y 6/1) to Light brownish gray (5 YR 6/11 weathering to very pale yellowish brown (10 YR 7/2), very friable, silica-cemented: contains a .2 foot poorly-sorted, very fine-grained (3.441, quartz sandstone at the base of the unit .... 12

5. Very slightly silty shale; laminated to nodutar- bedded, moderate brown (5 YR 412) weathering to very pale brown (5 YR 6/2), tough, conchoidally- fracturlng ...... 95

4. "Agate beds."; two discontinuous layers of 1-6 hch thick, red brown, silica nodules in a .matrix of brown silty shale ...... 1

3. Quartz sandstone; thin-bedded (up to 1 ft.), very pale orange (10 YR 9/2) weathering to very pale .. yellowish brown (10 YR 7/21, friable, slightly silica-cemented,fine-grained (2.44), moderately- sorted; interbedded with laminated light brown (5 YR 6/4) weathering to pale brown~(5UR 5/21, soft, silty shale ...... 25

2. Silty shale; laminated to thin-bedded (up to 10 in.)$ Light brown (5 YR 5/6.) weathering to brown (5 YR 5/4); interbedded with friable, slightly limonite- 18 1

Unit No.Thfckness Description " in feet "

cemented, fine-grained (2.4$)$ very poorly- sorted,quartz sandstone , . . . , . . . . , , , . . -54 TotalMorrison.Formation . . 516

Exeter Sandstone v 1. Quartz sandstone; massive (3-5 ft. ), cross-bedded, brown (5 YR 5/4) weathering to moderate brown (5 YR 4/2), friable, fine-grained (2. 8d), moderately well-sorted ...... , . . . . . 68 Dockum -Group Unit not measured, forms base of escarpment, -

Totalsection. , . . . . . I . 757 SAN JON SECTION

250-

200-

150-

100-

50- MEA.SURED SECTION 57-10

San Jon .Section

Location. -- State Highway 39, 8.6 mites due south of San.Jon, Quay

County, New Mexico. The traverse extends from the roadbed to the southwest up the escarpment. The section begins within the upper Exeter sandstone and ends at the caliche caprock above the lower Dakota formation, The section was measured by,H. H. Doney and~G.J. Nankin

(September 1957).

Unit No. .Description Thickness " in feet " Caliche, forms caprock

15. Caliche; nodular-bedded, light to dark gray, soft to hard, aphanitic ...... 22

.Dakota Formation I

14. Mostly covered, silty shale and mudstone; laminated to platy-bedded (1-3 in. ), dark gray to black, slightlycarbonaceous ...... 21

13. Quartz sandstone; thin- (0.5-1 ft. ) to medium- bedded (1-2 ft. ], mottled very light gray (N.8) and moderate yellowish orange (IO YR 7/61 weathering to pale yellowish brown (10 YR 6/21, friable, slightly silica-.cemented, very fine-grained (3. 84), moderately well-sorted; contains numerous 1-2 inch, thin, rodlike impressions ...... -17 TotalDakota.Formation ... 38

Purgatoire Formation

12. Slightly silty shale; laminated to nodular-bedded, moderate greenish gray (5 GY 7/11 weathering to light gray (N 7), crumbly to tough ...... 36

11. Quartz sandstone; medium-bedded (1-2 ft. ), yeLlow- ish gray (5 Y 8/1) weathering to very pale yellowish 183

Unit No.Thickness Description " in feet "

brown (10 YR 7/2j, friabte, slightly silica- cemented, very fine-grained (3.34), moderately well-sorted ...... 7

10. Verysilty shale; platy-bedded (0.5-2 in. ), very pale yetlowish green (10 Y 9/2), weathering.to pale yellowish gray (5 Y 8/2), friable, slightly silica- cemented...... 4

9. Quartzsandstone; medium-bedded (1-2 ft. ), mottled pale yeltowish.gray (5 Y 8/11 and grayish yellow (5 Y 8/41 weathering to moderate yellowish gray (5 Y 6/Z), friable, slightly silica-cemented, fine-grained (2. Id), well-sorted ...... 24

8. Quartzsandstone; laminated, irregularly-bedded, mottled grayish yellow (5 Y 8/4) and gra,yish yellow green (5 GY 7/21 weathering to very pale orange brown (10 YR 7/3), friable, clay- and silica- cemented, fine-grained (2.441, very poorly- sorted; contains silty shale micro-lenses (less than 1 inch .long) ...... 11

7. Veryslightly silty shale; laminated, light olive gray (5 Y 5/2) weathering to moderate yellowish orange (10 YR 7/6), tough, plastic; contains some carbonate- cemented mudstone lenses (up to 3 in. thick) and marinefossils...... 43 c TotalPurgatoire Formation. . 125

Morrison Formation

6. Veryslightty silty shale; laminated, va.riegated pale brown.(5 'Y 5/2) and pale green (5 G 7/2) weathering to very pale brown(5 YR 612) a& grayish yellow green (5 GY 7/2), tough, conchoidally-fracturing ...... 15

5. Quartzsandstone; thin-bedded (up to 0. 5 ft. ), gray- ishorange, fine-grained ...... 2

4. Silty shale andmudstone; laminated to nodular- bedded, moderate brown (5 YR 4/41 weathering 184

Unit No, .Description Thickness " in feet " to pale brown (5 YR 5/2), tough, hackly- fracturing ...... 24

3. Quartzsandstone; thin-bedded (up to 10 in. ), moderate grayish yellow (5 Y 7/41 weathering to pale brown (5 YR 5/2), friable, clay- and silica- cemented, very fine-grained (3.94), poorly- sorted, ...... 5

2. Poorlyexposed, mudstone and.silty shale; nodular- bedded, grayish yellow green (5 GY 7/2), weathering to light greenish gray.(5 GY 8/11, tough, conchoidally-fracturing ...... -18 Total Morrison.Formation ... 64

Exeter Sandstone

1. Quartzsandstone; medium-bedded (1-2 ft. ), pale yellowish orange (10 YR. 8/61 weathering to pale yellowish brown (10 YR biz:), friable, clay- and silica-cemented, very fine-grained (3.9$), poorly- sorted...... (exposed) 28

Base of unit not exposed at roadbed. L Total section ...... 277 Thin-section Descriptions

I. SAMPLE NUMBER AND LOCATIQN: 'Section from which the sample was taken and the location within that section.

11. NAME OF ROCKGrain size: prominent orthochemical cements, textural maturity, notable or unusual transported constituents, main rock name.

III. MEGASGOPIC DESCRIPTION: Sedimentarystructures, color, hardness, rock type.

IV. MICROSCOPIC DESCRIPTION:

A. Texture, -- Grain size (extreme, 16-84%, median),grain shape, textural maturity.

B. Authigeniccements. -- Kind,percentage, relative distribution, paragenetic relations.

C.Mineral composition. --

I. Quartz - type,percentage, properties

2. Feldspar - type,percentage, properties

3. Chert - type,percentage, properties 4. Miscellaneousterrigenous material -.type, percentage, properties

D. Remarks. --

.(After.Folk, 1957) 186

I. Exetersandstone: 56-2-12 - MitchellRanch.Section, middle of upper 1/3 of unit.

11. Fine-grainedsandstone: kaolin and calcite cemented, mature, chert- bearing subarkose.

III. Massive-bedded, very pale orange (10 YR 8/2), speckled with 2-4 mm,white (N 9) nodules,slightly friable, sandstone (fresh sample).

IV. A. Grainsize: extreme, 1.3-3. 86; 16-84.%, 1.8-2.66;mean, 2, 3d. Bimodal with minor coarse mode, Grains are sub-rounded to well-rounded; the larger grains are well-rounded. Mature to supermature terrigenous rock.

B. 1. Quartz.overgrowths are first stage in cementation, occur on most grains but comprise a ,small percentage of totaL cement. Transparent and well-developed but no interlocking between grains,

2. Kaolinite is developed in patches of more than 1 mm. in diameter; probably contemporaneous with calcite cementation. Individual kaolin flakes are well-developed and clear.

3. Calcite occurs in small patches with a distribution about 1/3 as much as kaolinite; developed as patches of small anhedral crystals.

c. 1. Quartz:common, 65%; undulose, 9%; semi-composite, 4% composite 5%~stretched composite 5%; total 88%. Micro- lites and vacuoles occur in kess than.l/3 of the grains.

2. Fe1dspa.r: orthoctase, 3%plagiocla.se, 1%; microc.line, 3%; total 7%. Most of the feldspar is vacuolieed and all of the feldspar is well-rounded.

3. Chert:contains inclusions and bubbles, total, 3%. Rounded to well-rounded.

4. Metamorphic rock fragments, probably schist, 2%,rounded. Dolomite, I%, composed of 3r anhedral grains. I. Exetersandstone: 56-4-11 - GaltegosRanch.Section, middle of lower 113 of unit,

II. .Fine-grainedsandstone: celestite cemented, supermature, chert- bearing subarkose.

II&Massive, obscurely-bedded, pale pinkish gray (5 YR 9/11, friable, sandstone (fresh sample),

IV. A. Grainsize: extreme, 1.0-3.54; 16-84%, 1.7-2.54;mean,2.04. Grains are rounded to very well-rounded; a few well-rounded but broken grains. Supermature terrigenous rock.

B. 1. Quartz overgrowths. - occur on a very few grains and only partially developed on most of these.

2. Calcite cement. - isalated, scattered patches of anhedra) and euhedral cement; occurs on top of quartz overgrowths and underneath celestite.

3. Celestite cement. - .entire slide cemented with areas 2 mm and more across =.single crystals, Commonly occurs in tabular to rod-shaped crystals.

c. 1. Quartz:common, 73%; undulose, 8%; semi-composite, 2%; composite, 2%; stretched composite, trace; total, 8570. Microlites, rutile needles and vacuoles occur in less than 115 of the grains.

2. Feldspar:orthoclase, 4%; plagioclase, 2% microcline, 5% total, 11%. Grains are fresh, only a fewvacuolized. All grains are very well-rounde-d.

3. Chert: contains inclusions (dolomite rhombs) and bubbles, total, 2%. Verywell-rounded.

4. Reworked dolomite grains, total, 1%;very well-rounded. 188

I. ,>&et,, sandstone: 57-2-1 - RomerovilleGap.Section, sample was taken from top of unit, about 2 feet below contact with Todilto lime- s.tone. Beds dip 25' to the northeast.

11. Fine-grainedsandstone: quartz overgrowth cemented, mature, chert-bearing,subarkose.

III. Massive, moderate dusky yellowish gray (5 Y 7/3), very hard, sandstone (fresh sample).

IV. A. Grain size:extreme, 1.5-4.28; 16-84%, 2,.2-.3.08; mean, Z. 64; unimodal distribution. Grains are sub-rounded to rounded with only a few well-rounded grains. Mature terrigenous rock.

B. 1. Quartz.overgrowths. - commonand well-developed on most grains. Many areas show interlocking of grains as a result of overgrowth development.

2. Kaolin cement. - a few, small, scattered patches; occurs .on top of quartz overgrowths.

C. 1. Quartz:common, 52%; undulose, 19%; semi-composite, 2%; composite, 9%; stretchedcomposite, 6%; total, 88%. Less than 1/4 .of th.e grains have vacuoles, rutile needles or microlites. .Overgrowths are present on almost all grain types.

2. Feldspar:orthoclase, 4%microcline, 2%; plagioclase, 2% total 8%. .All the grains are vacuolized and a few grains are sericitized.

3. . Chert: well-rounded grains containing bubbles and 3p dolomiterhombs, total, 2%.

4.Metamorphic rock fragments: rounded schist fragments, total, 2%. 189

I. Eketersandstone: 57-5-3 - Sabinoso.Canyon Section, sample taken from top of unit, About 3 feet below contact with Morrison.

11. Fine-grained sandstone: quartz overgrowth and kaolin cemented, supermature orthoquartzite.

III. Thin-bedded, dark orange pink (5 YR 7/4) spotted with pale brown (5 YR 5/2), slightly friable, sandstone (slightly weathered sample).

IV. A. Grain size:extreme, 1.0-4.54; 16-84%, 1.7-2.54; mean, 2.14. Bimodat, with a very mfnor coarse mode. Grains are rounded to well-rounded. A few broken grains, but these are also well- rounded.Supermature terrigenous rock.

E. 1. Quartz overgrowths. - common .on almost all grains, well- developed interlocking with adjacent grains.

2. Kaolin cement. - occurs in patches, but is .abundant in the rock. ,It is probably'pre-limonite stain but no conclusive evidence is present.

3. Limonite stain. - occurs throughout the sample and is clearly post-quarte overgrowths.

C. 1. Quarte:common, 62%; undulose, 17%: semi-composite, 3% composite, 10%; stretchedcomposite, 3%; total, 95%. Less than 1/10 of the grains contain vacuoles, rutile needles or microlites.

2. Feldspar:none.

3. Chert:trace, inclusions and bubbles. I 4,Metamorphic rock fragments: rounded schist fragments, 2%. I. . Exe.ter sandstone: 57-7-2 - Old Mills.Section, sample was taken from the top of the unit.

11. Fine-grainedsandstone: calcite and kaolin cemented, supermature, chert-bearing, feldspathic orthoquartzite.

111. Massive, grayish orange pink (10 R 8/21, s.Lightly friable, sandstone (fresh sample).

IV. A. Grainsi5e: extreme, 1.0-4..04;16-84%, 1.6-.2.4$; mean, 2. ld; slightly bimodal with minor coarse mode. Grains are rounded to very Well-rounded. A few broken, but well-rounded grains, Supermature terrigenous rock.

B. 1. Quartz .overgrowths. - present on only a few scattered grains, clear with vague nucleus boundaries.

2. Kaolin cement, - a few scattered patches, but very minor.

3. Calcite cement. - widely distributed throughout the entire sample, single crystals ,of greater than 2 mm. in diameter.

C. 1. Quartz:common, 76%; undutose, 7%; semi-composite, 5%, composite, 3%; stretchedcomposite, 3%: total, 94%. Microlites, rutile and vacuoles occur in less than 1/5 of the grains.

2. Feldspar:orthoclase, 1%;microcline, 2%; plagioclase, trace; total, 3%. .All of the feldspar is fresh and well- rounded.

3. .Chert: relatively clear with only bubbles and a few dolomite rhombs as inclusions,total, 2%. Rounded to well- rounded.

4. Metamorphicrock fragments- s,chist fragments, 170, I, Morrison formation: 57-2-12 .- Bomeroville Gap, 220 feet above the base of the formation.

LT. Fine-grainedsandstone: quartz-overgrowth and feldspar- overgrowth cemented, mature, chert-bearing, volcanic arkose.

III. Platy- to thin-bedded, very light gray (N 8) speckled with moderate yellowish brown (10 YR 5/4)., slightly friabie sandstone (fresh sample).

IV. A. Grainsize: extreme, 1.4-4..54;16-84%, 2.2-3.04; mean, 2.64.WeLl-sorted, unimodal, near-symmetrical distribution, The grains are rounded. .A few broken grains. Mature terrigenous rock.

B. 1. Quartzovergrowths. - well-developedthroughout entire slide. Clear and show no growth stages. Form inter- .locking mosaic.

Z. .Feldspar overgrowths. - many feldspar grains have overgrowths. M0s.t of the overgrowths are unaltered but a few are slightly vacuolized.

C. 1. Quartz:common, 44%; undulose, 8%; semi-composite, 3%composite, 2%; stretched composite, 3%;total, 60%. Practically all of the grains are free from any inclusions. A few rutile needle inclusions.

2. Feldspar:orthoclase, 13%; plagioclase, 13%; microcline, 12%; total, 38%. All of the feldspars are vacuolized, some strongly vacuolized.

3. Chert:contains a few inclusions,total,2%.

4. Volcanic rock fragments: weathered, black groundmass with phenocrysts (quartz and feldspar ?), total, trace.

D. Presence of authigenic feldspar in continental deposits. 1.92.

I. Morrison.formation: 57-3-5 --SanAgustin.Section, 100 feetabove

base of unit, 3 foot sandstone bed. ~

II. Veryfine-grained sandstone: slightly calcite cemented, submature, volcanic arkose.

III. Medium-bedded, light brownish gray (5 YR 6/1), very slightly friable sandstone (fresh sample).

IV. A. Grainske: extreme, 2.4-8.04; 16-84%, 3.0-4.'56; mean, 3..6$. Poorly-sorted,unimodal, strongly fine-skewed distribution.The grains are sub-angutar to sub-round. A few roundedgrains. Less than 5% clay. Submature terrigenous rock,

B. 1. Calcite. - occurs in small patches over clay coated grains. Small crys.tal size, poorly cemented.

C. 1, Quartz:common, 51%;.undulose, 5%; semi-composite, 1%; composite, 2% stretchedcomposite, 2%total, 61%. Less than.l/lO of the grains have inclusions, commonly microlites.

2. . Feldspar:orthoclase, 8%; plagioclase, 19%; microcline, 11%;total, 38%. The orthoclase and microcline,are subequally fresh and vacuolized. Most of the plagioclase is fresh. The orthoclase and microcline show better rounding than the plagioclase.

3. Chert:contains inclusions, total, trace. .Well-rounded.

4. Volcanicrock fragment: strongly weathered, dark groundmass containing plagioclase microlites. 193

I. Morrisonformation: 57-3-20 - SanAgustin.Section, 190 feet from top of formation.

II. Veryfine-grained, muddy sandstone: calcite cemented, immature, chert-bearing, volcanic arkose.

III. Medium-bedded, mottled tight brownish gray (5 YR 6/11 and pinkish gray (5 YR 8/1,),hard sandstone (fresh sample).

We A. Grainsize: extreme, 1.8-84; 16-84%, 2.4-5d; mean, 3. 56. Poorly-sorted, unimodal, strongly fine-skewed distribution. The grains are sub-round. Some angular and some well- roundedgrains are present. 10% clay.Immature terrigenous rock.

B. 1, Calcite. - occurs in .scattered patches but in.optical continuity over each patch. Poikilitic texture to the cement.

C. 1. Quartz:common, 54% undulose, 5%; semi-composite, 2.% composite, 1%;stretched composite, 1%; total, 63%. Only 4% of the grains have microlite inclusions.

2. Fetdspar:orthoclase, 10%; plagioclase, 12%; microcline, 12%; totat, 34%. The orthoclase and micrbcline are subequally fresh and vacuolieed. Most of the plagioclase' is. fresh.

3. . Chert: contains bubbles and a few inclusidns, total, 2%. The grains are rounded.

4. Volcanicrock fragments: strongly weathered, dark gr.ound- mass,total, 1%.

D. Clay material is olive green montmorillonite and possibly some illite.

r" j. .: ,,,A) .I_ I. Morrisonformation: 57-4-14 - TrujilloHill Section, 240 feet above base of formation, 2 foot sandstone lentil.

11. Fine-grainedsandstone: slightly quartz-overgrowth cemented, submature,chert-bearing, volcanic subarkose.

III. Medium-bedded, slightly cross-bedded, very light gray (N 8) speckled with dark yellowish orange (10 YR 6/6), hard sandstone (weathered .sampLe).

IV. . A. Grain size: extreme, 1.6-84;16-84%, 2.3-3. 2b; mean, 2. 7d. Well-sorted,unimodal, fine-skewed distribution. Grains are round. A few angular and a few well-rounded grains. Less than 5% clay. . Submature terrigenous rock.

B. 1. Quartz .overgrowths.- present on only a few grains and incompletely developed.on these grains.

2. Limonite. - occurs as streaks and patches as a weathering product.

.c. 1. Quartz:common, 64%; undulose, 7%; semi_composite, 1% composite, 4%~stretched composite, 3%total, 79%. Only 1/10 of the grains contain inclusions, commonly microlites.

2. Feldspar:orthclase, 5%; plagioclase, 4% microcline, 5%; total, 14%* The orthoclase and microctine are mostly vacuolized but all of the plagioclase is fresh.

3. Chert: contains only a few bubbles and minor inclusions, total, 5%

4. Volcanic rock fragments; strongly weathered, dark groundmass, quartz and glass shards, total, Z,%. I. Morrisonformation: 57-5-6 -.Sabinos0Canyon.Section, 140 feet above base of unit.

11, Veryfine-grained sandstone: catcite cemented, mature, chert- bearing, volcanic arkose.

III. Medium-bedded, randomly cross-bedded, yellowish gray (5 Y 8/1), ,very slightly friable sandstone (fresh.sample)..

IV, A. Grainsize: extreme, 2.2-4.56; 16-84%, 2.9-3.56;mean, 3. 24. Well-sorted, unimodal, slightly fine-skewed distribution.The grains are round. S.ome angularfeldspar laths. Mature terrigenous rock.

B, 1. Calcite, - presentthroughout entire rock. Few grains in contact.Optical continuity over large area. Poikilitic texture.

C. 1. Quartz,: common, 57% undulose, 5%: semi-composite, 2%; composite, 2%; stretched composite, 3%total, 69%. A very few grains contain inclusions, mainly microtites.

2. .Feldspar:orthoclase, 11%; plagioclase, 7%microcline, 10%; total, 2.8%. Most of the orthoclase and microc'line' is strongly vacuolized but most of the plagioclase is fresh. The plagioclase is more angular.

3. Chert:contains only a.few bubbles,total, 2%. Thegrains are rounded,

4. Volcanicrock fragments: weathered, dark groundmass with feldspar microlites, total, 1%. I. Morrisonformation: 57-5-13 - SabinosoCanyon-.Section, 130 feet from top of unit.

II. Fine-grained sandstone: quartz ,overgrowth and calcite cemented, mature, chert-bearing subarkose.

Kt. Thin-bedded, light gray (N 7) speckled with .moderate yellowish brown .(lo YR 5/4), slightly friable sandstone (weathered sample).

IV. A. Grain size: extreme,1.1-4.54; 16-84%, 1.6-2.56; mean, 2.18, Welt-sorted,unimodat, near-symmetrical distribution. Grains are sub-angu1a.r to round. Most of the grains are subround.Mature terrigenous rock.

B. 1. Quartz overgrowths. - occur on many grains butnever completely enclosing the detrital grain.

2. Kaolinite. - occurs in patches as a well-crystallized, clear, pore-filling clay.

3. .Calcite. - occurs in patches as a.fine-grained cement. Contemporaneous with the kaolinite.

4. Limonite. - occurs in streaks and patches as a weathering phenomenon.

C. 1, Quartz:common, 69%; undutose, 3%; semi-composite, 4%composite, 4%; stretched composite, 3%total, 83%. Very few grains .contain inclusions, either microlites or rutile needtes.

2. Feldspar:orthoclase, 4%; plagioclase, 4%; microcline, 5%; total, 13%. All of the feldspar is strongly va.cuo- lized.

3. Chert:contains bubbles and inclusions, total 4% All grains are rounded. I. Morrisonformation: 57-7-9 - OldMills.Section, 210 feetabove base of unit.

11. Fine-grainedsandstone: calcite and kaolinite cemented, mature, chert-bearing subarkose,

III, Medium-bedded, greenish gray (5 GY 6/11, very slightly friable sandstone (fresh sample).

IV. A. Grainsize: extreme, li3-8$; 16-84%,1.7-2.6Q; mean, 2. Z$. Well-sorted, unimodal, slightly fine-skewed distribution. The grains are rounded with the exception of some silt-sized quartz grains. Less than 3% clay.Mature terrigenous rock,

B. 1. Quartz .overgrowths. - occur on only a few grains but occur throughout the slide. Never . completely developed on -any grain,

2. Kaolinite. - occurs in small (less than 5 mm) patches but is extensively developed in the rock as a clear, well- crystallized, pore-filling clay with no preferred orientation to the crystals.

3. Calcite. - occurs in patches (5 mm and over) and is in .optical continuity throughout the entire rock. Poikilitic texture.

C. 1. Quartz:common, 66%; undulose, 6%; semi-composite, 2%: composite, 3%: stretchedcomposite, 4%; total, 81%. About 1/10 of the grains contain inclusions, mainly microlites.

2. Feldspar:orthoclase, 5% plagioclase, 6%; microctine, 6%; total, 17%. Most of the orthoclase and microcline is vacuotiaed but only about half of the plagioclase is vacuolieed.

3. Chert:contains inclusions and some bubbles, total, 2%. I. Dakota formation: Kd-S I Map Area, top of unit on west side of Padillo Gap at top of hill below thin caliche cap.

11, Fine-grainedsandstone: microcrystalline (chert) silica cemented, supermature, chert-bearing orthoquartzite.

Ur. Medium-bedded, light gray (N 7), extremely hard sandstone (fresh sample).

IV. A. .'Grain size:extreme, 1.2-3.5$; 16-84%, 1.8.-2.56;mean, 2.24. Well-sorted,unimodal, near-symmetrical distribu- .tion. All grains are well-rounded. . Supermature terrigenous rock.

B. 1. Quartz.overgrowths. - occur:.throughout slide. Clear and show several growth.stages.

2. Fibrous silica (chalcedony). - developed over the qugrtz overgrowths -and is uniformly distributed throughout slide.

3. Microcrystalline silica (chert). - well-developed throughout slide, fills.alt pore spaces, grades from fibrous silica.

G. 1. Quartz:common, 83%; undulose, 5%; semi-composite, 2,%; composite, 6%; stretched composite, 3%; total, 99%. About 1/3 of the grains have inclusions, commonly vacuoles.

2. Chert:contains bubbles and inclusions, total, 1%.. All grains are well-rounded,

D. Reverse of usual order of silica cementation. I. Purgatoire formation: 55-8-1 - Map Area, east side of Harlan Valley at base of sandstone unit.

11. Medium-grainedsandstone: quartz-overgrowth cemented, supermature, chert-bearing, feldspathic .orthoquartzite,

Lzr. Massive, very pale yellowish orange (10 YR 9/6), slightly friable sandstone (weathered sample).

IV. A. Grain size:extreme, 0.5-3.5d; 16-84%,1.4-2.2d; mean,. 1.94. Well-sorted,unimodal, coarse-skewed distribution. The grains are well-rounded. . Supermature terrigenous rock.

B. 1. Quartzovergrowths. - incompletelydeveloped, but occur on mo6.t grains. Clear, thin Layer,no inclusions.

2. Kaolinite. - clear, well-crystallized, pore-filling clay. Occurs in isolated patches and everywhere is found over the quartz-overgrowths.

3, Limonite. - occurs in streaks and patches, probably a weathering phenomenon.

C. 1. Quartz:common, 75%; undulose, 7% semi-composite, 5% composite, 6%: stretched composite, 3%; total, 96%. Microlites, vacuoles and rutile needles .occur in .slightly more than 1/10 of the grains. Rutile needles are the most common.

2. Feldspar:orthoclase, 1%;plagioclase, --.I microcline, l%&total. 2%. . The grains are well-rounded and strongly vacuolized.

3. , Chert:contains bubbles and in.clusions, total, 2%. The grains are Well-rounded. I. Morrison formation: 56-4-5 - Map, Area, north.of Harlan Ranch on west side of HarlanValley. ., Sandstone ledge just above "agate bed".

11. Fine-grained sandstone:. c&Lcite cemented,mature, chert- bearing subarkose. m. Thin-bedded, pale yellowish gray (5 k 8/3), hard sandstone (fresh sample).

IV. A. Grainsize: extreme, 1.3-4.56; 16-84%, 2.2-2.96; mean, 2. 56. . Well-sorted, unimodal, symmetrical distribution. The grains are rounded witha few well-rounded grains, particularly in the coa.rser sizes. Mature terrigenous rock.

B. I.. Calcite. -.the entire slide is.one crystal of calcite. The terrigenous grains are not in contact, Poikilitic texture.

C. 1. Quartz:common, 66%; unduiose, 6%; semi-composite, 3%; composite, 4%; stretched composite, .I% total, 80%. Less than 1/10 of the grains have inclusions.

2. .Feldspar:orthoclase, 3%; plagioclase, 6%; microcline, 4%total, 13% The plagioclase is fresh.and orthoclase and microcline is vacuolized.

3. Chert:contains some inclusions, total, 5%. The grains are well-rounded.

4. .Biotite:near-hexagonal flakes, total, 2%. 201

I. Purgatoireformation: 57-6-7 - CanadianRiver-Section, 1 ft. above base of unit,

11. Fine-grainedsandstone: quartz-overgrowth cemented, supermature, chert-bearing, feldspathic .orthoquartzite,

II1. Massive, grayish yellow (5 Y 8/4), friable sandstone (fresh sa.mple).

IV. A. Grainsize: extreme, 1.2-3.46; 16-84%, 2,0-2.86; mean, 2.36. Well-sorted, unimodal distribution. Grains are rounded to well- rounded, a few very well-rounded grains. Supermature terrigenous rock.

B. I, Quartz.overgrowths. I the first stage in cementation, o.ccur onalmost all grains, Thickness 0.01-0.1 mm.Clear, shows no growth stages. 2. Montmorillonite. - olive green, birefringent coating over quartz .overgrowths-. Infiltration from overlying shale.

3. Kaolinite. - clear, well-crystallized clay, occurs as pore- fillings. Probably after montmorillonite infiltration.

C. 1. Quartz:common, 67%; undulose, 8%; semi-composite, 4%; composite, 11%; stretched composite, 4%total, 94%. Microlites, vacuoles and rutile needles occur in about 115 of the grains;

2. Feldspar:orthoclase, 1% plagioclase, 1%; microcline, 2%; total, 4$ ALL of the feldspar is well-rounded and strongly vacuolized.

3. Chert:contains inclusions and bubbles, total, 2%. Well- rounded.

,. ., ; .._. ' '.. . .*.. 202

I. Purgatoireformation: 57-10-11 -.Sari Jon.Section,sandstone lentil within the lower ,Pajarit0 shale member.

JL Fine-grainedsandstone: poorly quartz-overgrowth cemented, mature, chert-bearing, feldspathic orthoquartzite.

UI. Medium-bedded, yellowish gray (5 Y 8/11, friable sandstone (weathered sample).

IV. A. Grain size:extreme,. 1.4-4.4d; 16-84%, 2.2-3. ld; mean, 2. 68. Well-sorted, unimodal distribution, slightly fine-skewed. Grains are sub-rounded to rounded, a few grains are well- rounded.Mature terrigenous rock.

B. 1. .Quartz .overgrowths. -.incompletely developed,. but present on most grains. Most development is incipient.

2. Limonite. - minor amount of iron stain, probably outcrop weathering.

C. 1. Quartz:common, 83%; undulose, 4%; semi-composite, 1%; composite, 3%; stretchedcomposite, 1%; total, 920~. Only 1/8 of the grains contain vacuoles, rutile needles or microlites,

2. Feldspar:orthoclase, 1%; plagioclase,trace; microcline, 1%; total 2%. . All of the feldspar is rounded and vacuolized,

3. Chert:contains bubbles and inclusions, total, 4%. All of the chert is rounded. 203

I. Purgatoire formation: 57-7-16 - Old MillsSection, top of sandstone unit (Cheyenne ?).

II. Fine-grainedsandstone: quartz-overgrowth cemented, supermature, chert-bearing, feldspathic orthoquartzite.

III. Medium- to massive-bedded, very light gray (N 8), friable sandstone (fresh sample).

IV. A. Grain size:extreme, 1.3-4.OB;16-84%# 1.7-2.64; mean, 2.2Q. Well-sorted,unimodal, near-symmetrical distribution. Grains are roundld to well-rounded; most of the grains are well- rounded, . Supermature terrigenous rock.

B. 1. . Quartz.overgrowths, - well-developed on all grains, clear and show no growth stages. .Form. ,an interlocking mosaic with straight contacts between adjacent overgrowths.

2. .Kaolinite. - well-crystallized,clear clay. Occurs as pore- fillings and is probably later than quartz overgrowths.

C. 1. Quartz:common, 76% undulose, 8%; semi-composite,. 3%, composite, 4% stretchedcomposite, 3%~total, 94%. About 1 /5 of the grains contain vacuoles, rutile needles or microlites. Vacuoles are ,the most abundant.

2. .Feldspar:orthoclase, 1%;plagioclase, --;microcline, 170; total, 2%. . AI1of the feldspar is strongly vacuolized. The grains are well-rounded.

3. Chert:contains bubbles and inclusions, total, 4%. . The grains are well-rounded.

4. Igneous rockfragments: quartz.and vacuolized.orthoclase ! compositegrain, total, trace. X. Purgatoireformation: 57-8-11 - Burro Canyon.Section,base of sandstone unit.

II. Fine-grainedsandstone: quartz-overgrowth cemented, supermature, chert-bearing, feldspa.thic orthoquartzite. i III. . Gross-bedded, pale grayish orange (10 YR 8/4), hard conglomeratic sandstone (fresh .sample).

IV. A. Grainsize: extreme, 1.2-4.04; 16-84%,, 2.1-3. 06; mean, 2.76. Well-sorted,unimodal, near-symmetrical distribution. Grains are rounded to wetI-rounded. The larger grains are well- rounded to very well-rounded. . Supermature terrigenous rock,

33, 1. Quartz..overgrowths. - well-developed on all grains. Clear and show no growth stages. Form interlocking mosaic.

2. Kaolinte. - clear, welt-crystallized, pore-filling clay. Occurs after the quartz.overgrowths and only in isolated patches.

c. 1. Quartz:common, 80% undulose, 5% semi-composite, 3%; composite, 4% stretched composite, 4%; total, 96%. About 1/6 of the grains contain vacuoles, rutile needles or microlites. Vacuoles are the most abundant.

2. Feldspar:orthoclase, 1%; plagioclase,trace; microcline, 2%; total, 3%. The grains are strongly vacuolized and well-rounded.

3. Cher't:contains bubbles and inclusions, total, 1%. The grains are well-rounded. 205

1. . Dakota formation: 57-5-19 - Sabinoso.Canyon Section, base of lower sandstone unit.

II. Fine-grained sandstone: quartz-overgrowth and kaolin cemented, supermature,chert-bearing, orthoquartzite.

ID. Platy-bedded, grayish orange (10 YR 7/4), slightly friable sandstone (weathered sample),

IV. A. Grainsize: extreme, 0.7-3.54; 16-84%, 1.7-2.54; mean, 2. 04. . Well-sorted, unimodal, near-symmetrical distribution. Grains are well-rounded, a few broken, but rounded, .Super- mature terrigenous rock.

B. 1. Quartzovergrowths. - well-developed,clear and show some growth stages. In some places grades into fibrous silica (chalcedony). Overgrowths form an interlocking mosaic throughout most of the slide.

2. Kaolinite. - occurs as a well-crystallized, clear, pore- filling clay. No preferred orientation.of crystals. . Dis- tribution is in isolated patches.

3. Limonite. - occurs in streaks and patches as an iron stain probably related to weathering.

C. 1. Quartz:common, 82%; undulose, 3%; semi-composite, 2%; composite, 12%; stretched composite, 1%; total 100%. About 1/10 of the grains contain inclusions, usually microlites.

2. Chert: , containsbubbles and inclusions,total, trace. Grains are well-rounded and smaller than average grain size of rock.

D. Unusually high percentage of composite qua,rtz. 206

I. Dakotaformation: 57-2-28 - Romeroyille Gap Section, top of upper sandstone unit, beds dip 25O NE. II. Medium-grainedsandstone: quartz-overgrowth and kaolinite cemented, supermature, chert-bearing orthoquartzite.

III. Platy- to thin-bedded, mottled pale red (5 R 6/2) and grayish orange (IO YR 7/4), hard sandstone (fresh sample).

IV. .A. Grain size:extreme, 0.4-2.86; 16-84%, 0.9-1.6.b: mean, 1.14. Verywelt-sorted, unimodal, slightly coarse-skewed distribution. All grains are well-rounded, not one angular grain is present in the slide. Supermature terrigenous rock.

E. I. Quartz.overgrowths. - well-developedthroughout slide. Show some growth stages, contain no inclusions. In places grades into fibrous silica (chalcedony) and then into microcrystalline silica (chert),

2. Kaolinite. - occurs as well-crystaJlized,clear, pore- fillingclay, No orientation.ofcrystals. Small (1-5 mm) patches throughout rock.

C. 1. Quartz:common, 67%; undulose,4%; semi-composite, 10%; composite,13%; stretched composite, 2%: total 96%. About 1/5 of the grains have inclusions, usually rutile needles.

2. . Chert:contains bubbles and in.clusions, total, 4%. Grains are well-rounded.

D. High percentage of composite quartz and rutile needle inclusions. I. Dakotaformation: 57-8-L3 - Burro Canyon section, base of lower sandstone unit.

a. Fine-grainedsandstone: quartz-overgrowths cemented, supermature, chert-bearing orthoquartaite.

ILT. Medium-bedded to massive, pale grayish orange pink (5 YR 8/2), sLightty friable sandstone (fresh sample).

IV. A. Grainsize: extreme, 0.7-3.54;16-84%, 2.0-2.76; mean, 2.44. Well-sorted, unimoda.1, near-symmetricaldistributlon. .All grains are well-rowded. A few broken grains. Super- mature terrigenous rock.

B. 1. Quartzovergrowths, - occur'throughout slide as a thin Layer on all grains (0.01-0.05 mm). Clear and show no growth stages. 2. Kaolnite. - a few patches of clear, well-crystallized, pore- filling clay (1-5 mm).

C. 1. Quartz:common, 71%; undutose, 7%; semi-composite, 6%; composite, 7%; stretchedcomposite, 7% total, 98%. About 1/5 of the grains have inclusions, commonly microlites.

2. . Chert:contains bubbles and inclusions, 2%. All grains are well-rounded. 208

I. Dakotaformation: 57-3-32 - SanAgustin Section, top of uppersand- stone unit.

11. Fine-grainedsandstone: quartz-overgrowth cemented, supermature orthoquartzite.

111. Medium- to platy-bedded, very light yellowish gray (5 Y 9/1), very hard sandstone (fresh sample).

IV. A. Grainsize: extreme, 1,5-4.OB; 16-84%, 2.2-2.94; mean, 2.64. Well-sorted,unimodal, near-symmetrical distribution. All grains are well-rounded. . Supermature terrigenous rock.

B. 1. Quartzovergrowths. - well-developedthroughout slide. The overgrowths are thin (up to 0.02 mm), clear but some inclusions occur along boundary with detrital grain.

I. 2. Kaolinite. - a few small (less than 5 mm) patches of clear, well-crystallized, pore-filling clay.

C. 1. Quartz:common, 83%; undulose, 5%; semi-composite, 2%; composite, 8%; stretchedcomposite, 1%; total, 100%. About 1/6 of the grains contain.inclusions, commonly microlites. Plate 1. Photographs of Exeter Sandstane " -,.

a. Outcrops of Exeter sandstone along creek, looking west across Ute Creek in the northwestern part of the map area. The sandstone is 60 feet thickalong the creek, . The mesa is capped by Quaternary basalt. .Bench below cap is held up by Dakota sandstone.

b. Outcrop of Exeter sandstone, looking southwest on the east side of Ute.Creek, western part of the map area. Honeycomb-weathering is aligned along crossbeds. The shale cropping,out beneath the massive sandstone is a part of the Dockum group. The Exeter-Morrison conta.ct is placed at the top of the.massive sandstone. ..

Plate 2. Photographs of Exeter Sandstone " ". a. Contact of the Dockum group with the overlying white Exeter sandstone. View south on the east side of Ute Creek, southwestern part of the map area, Uaidentifi- able bone fragments were collected from the Dockum group at this lacality.

b. . Close-up view of contact of the Dockum group with the Exeter sandstone. Same Locality as a.- ... Plate 2. Plate 3. Photographs .of Exeter Sandstone " - a. Contact of the Exeter sandstone with the Morrison formation, looking west at Galtegos Ranchsection. The contact is ptaced .at the top of the massive sandstone. The lower part of the Morrison formation contains sandstone beds similar to the underlying Exeter sandstone.

b. Contact of the Exeter sandstone with the Morrison formation, looking east on the east side of Tequesquite Creek at the Mitchell Ranch.section, The contact is placed at the top of the massive cliff-forming sandstone. Note the interbedding.of Exeter and .Morrison rock types. a. Plate Photomicrographs1 .- of. Exeter Sandstone "4. a. Microcline grain showing grid-twinning surrounded by quartz .grains. The microcline is better rounded than most of the quartz and shows no alteration. The rock is cemeqted with kaolinite and calcite, Gallegos Ranch section.Nicols crossed.Xl50.

b. Plagioclase grain showing albite-twinning.surroundedby quartz grains. The plagioclase is better rounded than most of the quartz grains and shows no alteration. Some of the quartz grains show undutose extinction. Note the small patches of calcite cement surrounding the plagioclase grain and elsewhere in the slide. Southwestern part of map area. Nicolscrossed.Xl25. ,.

Plate -5. ..Pho.tomicrographs of Exeter.Sandstone " a. Detrital dolomite grains with micro-sparry overgrowth fringe. The matrix .surrounding the grains is mostly kaolinite with a small amount of calcite. Mitchell Ranch sectian.Nicols crossed X140.

b. Representative view of Exeter sandstone mineralogy. Quartz and microcline comprise all of visib.le grains. Note the' feldspar is well-rounded and fresh.. A small amount of quartz overgrowth cement ia present in the ' slide.Canadian River section. .Nic.oLs crossed XIOO. .. a.

" Ptate 6. Photomicrographs of. Exeter Sandstone " -

a. ~ Celestite occurring as a cement. The acicular structure of the celestite is present throughout the slide. The growth of the cement has pushed the grains apart leaving many .grains .!'.floating". Upper sample from Gallegos Ranch section, Plane polarized Light.X100.

b. . Quartz .grains showing calcite veins cutting patches .of kaotinite cement. hother areas in.the same slide kaolinite is present on top of calcite. . Southwestern part of the maparea. Nicols crossed. X13.0. Plate 6. Plate 7. Photomicrographs of Heavy Minerals from Exeter ” - .- .- .- Sandstone

.a. Strongly etched staurolite showing development of crystal faces by. solution. Sample of uncemented Exeter sandstone. Central part of map area,. Plane polarized light X240.

b. Str.ongly etched garnet showing crystal face development. , Sa.mple of uncemented Exeter sandstone. .Southwestern part of map area. Ptane polarized light X175.

c. . Well-rounded and unetched garnet from calcite cemented sample from the Exeter sandstone. Gatlegos section. Ptane polarized light X160.

d. Well-rounded and unetched garnet from celestite .cemented sample from the .Exeter sandstone. Gallegos Ranch. Plane polarizedlight.XI50.

e. Well-.rounded tourmaline gr.ain from same sample as b. .Note the absence of etching to form crystal faces, PI%e polarized light X175.

"Plate 8. Photomicrographs '-3 ,of Heavy Minerals .from Exeter &ndstone "-

a. Photograph of strongly etched garnets and one well- rounded but broken, dark tourmaline grain. Southw'estern map area. PLane polarized light X95.

b. . Strongly etched staurolite in center with.a,Less strongly etched garnet (left-center) and well-rounded, dark tourmaline grains. Grains from a .slightly calcite- cementedsample. Canadian River section. Plane pqLa.- rized Light X.L20.

"Plate 9. .Photomicrograph.of Todilto Limestone ,, . c Micrite Laminae separated by sparry calcite. A few quartz grains are present between the two laminae at the top of the photograph. The dark areas area result of hydrocarbon .content, . Romeroville Gap section, Plane :. :. potarieed light X60. c Plate Photographs of Morrison Formation "IO,. " , a. View looking west on .the eas.t side of Ute. Creek in the northwestern part of the map area, south.,of road on Gallagher Ranch. Upper part of the Morrison formation.

b. View looking west at the Gallegos .Ranch section. Lower part of the Morrison formation showing .Exeter- type sandstone interbedded with typica.1 Morrison shale. Bluffs in background are composed of Morrison sitt- stone and shale. b.

'late 10. Plate 11, Photagraphs of Morrison.Formation ” ,- a. Looking northeast at Trujillo WLL section.Middle part of Morrison formation; siltstone, mudstone and shale capped by a 2.5 foot white sandstone. . Exposure is about 20 feet high.

b. View looking north at Trujilto Hill section .of a channel sandstone in the lower part of the Morrison formation. The channel sandstone is about 12 feet wide and about 2 feet thick.

Ptate Photographs of Morrison.J?ormation ”1Z. 3 a. Looking northwest at the,Canadian River section. Rockhammer is resting on-a 4-inch volcanic ash bed, The -ash has been indurated by minor post-depositional alteration.

b. Looking northeast at the Canadian .River section. Rockhammer is resting on a 6-inch ,limestone bed.in the upper part of the Morrison formation. The next resistant overtying bed is a silica-cemented mud- s tone. . .. .

Plate 13. Photomicrographs of Morrison Formation ” a,. Calcite cemented quartz sandstone. . Sampte from the upper part of the Morrison formation. Most of the grains show .appreciable .rounding. U.pper Morrison, central part of map area. Plane polarized.tight X90.

b.Mudstone. Sample from the upper part of the Morrison formation,. Canadian River section, Note lack of bedding in the clay and’lack of orientation of the quartz sitt particles. Plane polarized light X80.

Plate 14. Photomicrographs of Morris,on Formation ” -

a. Plagioclasegrain showing a’lbite-twinning surrounded ’ by quartz grains. . The plagioclase is more angular than most of the quartz grains and shows no alter.ation, Pro- bably.from a v.olcanic source. The .rock is cemented with quartz overgrowths and .a minor amount of kaolinite. UpperMorrison, Old Mills section. Nicols crossed.XS0.

b. Igneous rock.fragment in center view. Microcline fe,ld- spar grain with four quartz grains. The fra,gment is well-. rounded. . The microcline is partly vacuolized. The rock is cemented with sparry calcite and some kaolinitein patches, Upper Morrison from Mitchell Ranch .section. Nicols crossed X75.

Plate 15. Photomicrographs .of Morrison..Formation "

a. .Chert grainin center view showing relict structure.of a replaced bryozoan. . Sa.mple frnm a coarse saridstone in the upper part of the Morrison, Romeroville Gap section., Plane polarized light X40.

b. Plagioclase feldspar grains (right-center and upper- right) showing vacuolization. The grains are well-rounded. Compare with .Ptate 14a. Middle Morrison, west-central part of map area,, NicoIs crossed X85,

Plate 16, Photomicrographs of Morrison Formation " - a. Quartz phenocryst in a limestone containing terrigenous material. The shape and association with.other material suggest a volcanic origin, Upper Morrison from Trujillo Hill section. Plane polarized light X175.

b.Same sample as a. Triaxial glass shard present in center view, Thz shard has been aLtered.to chalcedony. Plane potarized light X175.

Plate 17. Photomicrographs .of Heavy Minerals from Morrison " " Formation -

a. . Euhedral, zone zircon from upper Morrison, Old Mitts section,Probably volcanic origin. Plane polarized Light x110.

b. Euhedral, acicular zircon from upper Morrison,: Sabinoso Canyon section. Characteristic shape of volcanic zircon. Plane polarized light X130.

c. . View showing two distinct zircon types; euhedral and anhedral. The sharp differentiation suggests a dual source. Upper part of Morrison, Burro Canyon. Plane 'po.larized light X95.

.d, Apatite grains, upper 'part of Morrison, Burro .Canyon, one euhedral and one r.ounded. Sample from upper Morrison, Canadian.River section. PLane polarized Light X110.

e. . Euhedral zircon containing microlite.and .negative crystals. Sample from middle Morrison, Old .&LIS section. Plane polarized light X130. I. f. Hexagonal biotite flake from an upper Morrison sample, Canadian .River section. Plane polarized light X90. a. b.

C. Plate 18. Photographs of Purgatoire and Dakota Formations " - " a. View looking northwest in map area on the west side of Ptidilta Gap. Shows disconformable contact of the overlying .Dakota formation with the Purgatoire (inkline)..

b. View looking west across the .Canadian River north of the measured section. Contact of the darker, overlying ,Dakota with the white Purgatoire (ink ,line). Morri- son formation under covered slope, Exeter sandstone expased in creek bottom.

Plate 19. Photomicrographs of Purgatoire Formation " - a. Quartz-oyergrowth-cemented sandstone.The overgrowths are clear, contain no inclusions, join adjacent grains often with no visible break. Canadian River section.Nicolg crossed..XlZ5.

b. Plagioclase feldspar grainin center view showing .strong vacuolization.Remainder of slide is quartz. The rock is weIl-cemented by quartz.overgrowths.. Gallegos Ranch section.Nicols cr0sse.d X105. 'I

Plate 19. Plate 20. Photomicrographs .of Heavy Minerals from Purgatoire " " -. Formation

a. Euhedral and anhedral zircon grains fr.om the Purgatofre formation.at the .Canadian.River section. Plane polarized light X210.

b. . Euhedrat and anhedral zircon with some well-rounded tour.maline grains. The zircon is much.more abundant

than tourmaline. . Central map, area.~ Plane polarized light XZ10. ...

Plate 21. Photomicrographs of Dakota Formation " , -.- a, Quartz-overgrowth-cementedorthoquartaite. The overgrowths .are clear and welt-developed. Pra.ctically the entire rock is cemented by silica. Central map area. Nicols crossed X65.

b. Fibrous silica (chalc.edony) cemented ,orthoquartzite, The fibrous silica formsan interlocking mosaic :of cement between detrital grains. .Note the rounding and severalquartz types. San Agustin section. Nicols crossed X50, c ..

PLate ZZ. Photomicrographs of Dakota Formation " - a. Stretched composite quartz grain showing the perfect rounding achieved by some of the Dakota material. The .cement around the grain is kaolinite. Central map.area. Nicols crossed X125.

b. Quartz-overgrowth-cementedorthoquartzite. The rock is composed of nothing but detrital quartz, chert and a few heavy minerals cemented with qua.rtz overgrowths. Romeroville Gap section. Nicots crossed X85. a.

1 .. .

Plate 23, Photomicrographs .of Heavy Minerals frsm Dakota " " .__ Formation

a. Well-rounded tourmaline grains with two well-rounded zircon grains. Tourmaline is by far more abundant thanthe zircon. Western map area. Plane polarized light X175.

b. Welt-rounded tourmaline with five rounded zircon grains. Not .one Dakota sample .contained more zircon than tourmaIine in the heavy mineral suite. San Agustin eec- tion. Plane polarized Light X175.

VITA

Charles John~Mankin, son of Mr. and Mrs. Green Mankin, was born on January 15,1932, in Dallas, Texas. He graduated from 0zona.High

.School in 1949 and went to the University of New Mexico for one year wherehe studied.ChemicaA Engineering. 1n.September of 1950,he enrolled in The University of Texas where he later received his B. s. degree in geology in August of 1954. InSeptember of the same year, he enrolled in ,graduate school atThe University of Texas where he ,received his M. A. degree in geology in.August of 1955, and later his Ph. D; degree in geology in June of 1958.

On September 6, 1953, he was married to Mildred .H. Hahn daughter of Mr.and Mrs. Amzy A. Hahn of Burnet,Texas. He has onechild, . a daughter, btirn November 12, 1957.

Permanent address: Box 806

Goldthwaite,Texas

This dissertation was typed by Dorothy Jean Rieger. May 24. 1974

Dr.Charles J. Mankin, Director Oklahoma Geological Survey The University of Oklahoma Normac. OK 73069

Dear Dr. Mankin:

Yesterday Dr. Richard Jahns was going through' some material of Max V

Sincerely,

(Mrs. ) Jo Drake Administrative Assistant and Secretary n ScnooLo~GEOLOGY

THEUNIVERSITY OF OKLAHOMA

NORMAN * OKLAHOMA

July 18, 1960

Dr. Max Willard New Mexico Bureau of Mines Socorro, New Mexico

Dear Max;

Received your letter upon returning fromthe field. We have been currently investigating the presence ofsome borate minerals in some of the gypsum beds in western Oklahoma.Looks like we will be able to get a rather complete story on the origin of the borates in an evaporite sequence. In the course of this investigation we have also found a new clay mineral and a new sulfate apatite mineral. I agreewith your comments concerning my thesis. I should havedone the montmorillonite-illite ratio when 19sdoing this work. Unfortunately, it was oneof the things that I did not know about until much later. I am afraid that I have learned more about clay mineralogy since completing my thesis than I ever did during the course of the study. All of the data was placed on file at the University of Texas when I left. I have found that apparently in moving the CedcEngineering department into a new building the patterns and sampleswere lost. I think that it would be almost useless to try to locate this material. There is one thing that couldbe done. I could resample the Morrison section at one or twoof my localities and redo the x-ray workon that part of the section. However, because I am currently very busy with several projects for the Oklahoma Geological Survey on clay mineralogy as well as the above mentioned projects, I doubt that I will be able to.get to it until late this fall. If you feel that it shouldbe included, I will make plans to do it as soon as possible. 1 am wondering if a separate publication on the clay mineralogy would not be advisable. A study of the clays and a particular investigation of the bentonite beds with emphasisupon possible zeolites would be very fruitful. One of my future projects for the Oklahoma G3ological Survey will be the clay mineral investigation of the Morrison formation in the Oklahoma panhandle.

Let meknow your feelings upon the clay idea. If you think that it should be in this paper, I will try to make plans to resample the necessary material sooh. If you think that a separate study should be made, perhaps we could work out something Wgme (1) I could do it, (2) participate with you on the study, (3) youdo it, We'have excellent facilities here for clay work. We have an emissionspec., electron mic., spectrophotometer, infra-red, andx-ray fluoresence as well as a good wet analysis lab. Perhaps a joint study between the OGS and the Bureau couldbe worked out. I don't know what problems there would be with this. SCHOOLOFGEOLOGY

THE UNIVERSITY OF OKLAHOMA NORMANOKLAHOMA

In any event I am open to suggestion about this. Themain problem that I have is that I don't want to become involved in something that wouldn't lead to a SenWcontinuing study. I find that isolated studies of mahy things while interesting aren't very productiveover the long had.. Alss, I can ill-afford to pass up OGS support for very long financially. I will appreciate hearing fuom you concerning what should bedone.

My regards to everyone out there.

Sincerely youps, I

Charles J. Mankin Dear Charlie:

It ia unfortunate that the charts and samples yere lost.

I disCu6sed with the Director of.the Bureau 'the possibilttlee of a separate study of the days and it appears that Ve are not in a position to start any new projects at present. mnce, SltxIOugh I am personally interested in a study of the type you suggested and 8m flattered by your of'fer, I 8m afraid there is no chance at least for the present. kzasmuch aa I feel that the clay study is a most sigaiflcant part of pur thesis I vould cwtalnly agree with your spggwstion to resample and restudy the Monlson section. Any delay in publication, I am certain, is justified and uil.3. not .cause ths Bureau auy inconvenience.

mat rem, THEUNIVERSITY OF OKLAHOMA NORMAN . OKLAHOMA

June 17, 1960

Dr. Max Willard New Mexico Bureau of Mines and Mineral Res. Socorro, New blexico

Dear Max;

I am returning the negatives for the pictures that I think should be included in my tome. I have selectedonly twelve. I hope that the negatives will be satisfactory because in all of our moving around the original plates have been misplaced and I have been unable to find them. If the negatives are not satisfactory let meknow and I will have new plates made. I hope that my delay in hturning these negatives has not hampered the preparation of the manuscript. It seems that all that I havebeen able to get accomplished this Spring is to teach a few classes and get a few graduatestudents through the mill. I guess this Oklahoma climate was too much for me as I havebeen sort of out of action for the past month and am just now getting back into th@ swingof things. I am still moving at a saails pace but it is much faster than I was able to goa couple ofweeks ago.

Because I have been so tardy in beturning material I hardly have the right to ask but is it possible to determine about when the tome will be coming out? The photographs that I think should be included are; Plate 1 - fig. a and b- Plate 2 - fig. Plate 3 - fig. x Plate 10 - gig. a andb Plate 11 - fig. 2 and 9 Plate 12 - fig. 21.and b- Plate 18 - fig. 2 and b- Thanks for being so patient with me. Let me know if the photos are unsatisfactory. Sincerely yours,

Charles J. Mankin Ass It. Prof. Geology

I have listed cormnents below concerning the editorial comments that have been made on my tome. I am going to send these back with the thesis and will send copies of the photos that I think need to be included at a slightly later date. I am going to havenew negatives made for these photosbecause the copies in my thesis are particularly bad. I am sure that this can be impmoved.

Page vi - Sorry but I can't seem to make out what is meantby this coment. Page 5 - ... winter temperatures are colddr than would be expected when compared with the latitude . . . Page @ - . . . buffalo grass are also present . . . Page 8 - . . . nearby market lessens the . . . SomeC02 has been produced by the brewing process but I suppose that it is now surplanted by moremodern methods. I can find noup to date information on this subject. The statement doesnot add to the subject and I think it can be removed without any trouble. Page 12 - The heavy mineral fraction from each sample (ungraded) was removed . . . Here I am stating that the total heap mineral fraction was removed and analyzed. Page 14 - . . . by the earlier workof Marcou in 1853. Marcouts book was published in 1858 but his work was done in 1853 and a report was Published in 1854. Page 18 - That is correct that the Wood et a1 map went to the state line. I was attempting to show here that both Wood et a1 and Griggs covered the same area. Page 36 - Note that this map refers only to the upper Exeter samples. On the previous page (35) there are two samples from the Exeter at Old Mills, 57-7-1 and 57-7-2.The latter sample is fromthe upper Exeter. The l&&%ample is from the lower. Page40 - I'm not sure that this diagram has any significance. It is based upon far too few observations, but Folk thought it should be included in the tome since I did someof this work. If you think that it shouldbe inclu-ded the followim is the correct data on it. Page2.

Page 41 - The reference to the table should gowhere you have inserted it if this table is to bk .included in the text. Page 42 - I think that south or at best southeast would be indicated direction on basis of diagram of mean size. Petrographic trend of mineralogy indicates same general conclusion.

Page 44 - Metamorphic-type quartz is most common in western part of map. Straightextinction to slightly unddlose quartz in the eastern part. Perhaps metamorphic rock fragments should not be classed as assessory minerals but certainly dolomite is a mineral. The rockfragments act as &8 indiuidual grains in a terrigenous section. Page52-53 - I have noqualms about indicating that the climate of the Fxeter was arid. However, if you feel that this point should behedged it is OK by me. Page 57 - this is a quoteand as such cannot be altered. However, it couldbe stated .. .. . closingthe Trias firiassicJ as clearly . . . . i, n. Page 61 Table 5. This table omitted in the contents and Bable 5 ui - was d appears as grain size of Morrison p. 68. -.k 9 Page 78. The 15.58 peak is probably a vermiculite but the sample contains so much other material that a careful study of this mterial was virtually A,< impossible. The sentenceshould probably read; These data indicate that there is a mixture of illite and %?Et&& (or possibly chmiirite). The assymmetry of the illite peak may indicate a partial removalof K ions from the inter-layer position. Page 79 - After re-evaluating what youhave said about this problem, I think, I realizethe point that youhave been t-g to make. It take a while for E

DlckRoland all thought that it was a regular interstratification. I 't know how strongly they would feel about this point though. Page 80 - Thesame conunent applies as that on page 79. .

/9 by X-Ray diffraction; Jour. Sed. Pet., v. 29, p. 77-86. Page 3.

Page 82 - Not expanded; if solvated with ethylene glycol, it would be 17A. Page 84 - I agree that the montmorillonite could by altered volcanic ash instead of chlorite alteration. Page 85 - Heavy Mineral Chart. % total heavy minerals are nt ,t recorded as I don't feel that this has much significance. % total hc Savies is a very local variation, as for examplea heavy mineral pmacer. The graph therefore reads;

Thenon-opaques have been recompdl Thenumber in doubt is not 57-10-13 but 57-1Q-5. San Jon Section. This unfortunately occurred when the field sheets were transferred into final data. The original San Jon section which I measured includes much of the Eockumwhich I excluded from Eonsideration in the thesis. I $bought I had double checked all ofthem but I slipped upon this one. Page 86 - perhaps should read as follows; . . . well-rounded; only a few euhedral-prismatic grainsare present. . . Page 87 -Work by Folk and previous work by Poldervaart indicates that euhedral-accicularzircon grains indicate volcanic activity. The association of these zircon grains with the remaining evidence of volcanic activity supports this hypothesis. Page 89 - Two color varieties, yellow and red, are present in subequal . . . . Page 90 - Abundant floods of any heavy mineral such as apatite that occurs more or less randomly in a stratigraphic section cannot come from the normal exposure of some source.Apatite, particularly in euhedral form could well be derived from a volcanic source. Apatite is very common in volcanic sections. I doubt though that I can support a basicvolcanic source In fact I think that an andesitic or perhaps even a rhyolitic source is muchmore feasible from a study of the plagioclase. There is no question ofa volcanic source from the other evidence of bentonites, volcanic rock fragments, altered glass shards and plagioclase feldspar abundance, as well as altered ash beds. The question then resolves to a source for the zircon and apatite. The volcanicsource is the most logigal. Perhaps onemeans of solving a part of this problem is an age dating of a selected group of the zircons. I hope that this can bedone within the next year. Dr. Lhon Silver from Caltech and I plan to do something on this in the future. Page 4.

Page 93 - Yex, the kaolinite is authigenic. Also, the celestite I am suce is authigenic. Page 94 - Garnet, staurolite,apatite, epidote, etc. are not chemically stable. The absence of th&onstituents, at least their decrease, with no accompanyingchange in the stable minerals suggests achange in the chemical environment, not a change.in source lithol$&. A change in source lithology would be reflected in total mineralogy. Climatic changes would be rdflected only in those minerals that are susceptable to weathering. Page 98 - this quote wiZ1 have to bechanged or omitted. Page lo5 - Chert rarely undergoes more than one cycle of erosion, especially in thefine- ained material. However, this statement does not indicatethat chert cad)68 ossibl reworked. Page 106 - Quartz containing micmite inclusions rarely exceeds 5%. R&-@ the occurrence of filldspar indicates a plutonic or granite-gneiss source area. Page 107 - This sentencecould bereworded. Themeaning here is that the clay material is present only on top of the overgrovrths. Page 108 - These spacings indicate an interstratification, not a mechanical mixture.

Page 109 - Correct heading was omitted. Should be as youhave indicated Pgge 120 - The terms platykurtic, mesokurtic, etc. are used to describe kurtosisvalues. Folk (1957) Petrology of Sedimentary Rocks. Page 126 - Add to references ; Callender, Dean L. and Robert L. Folk (1958) IdiomorpMc zircon, key to volcanism in the lower Tertiary sands of Central Texas; Amer. Jour. Sci. v. 256,p. 257-269.