A 36C1 Chronology of Lacustrine Sedimentation in the Pleistocene Owens River System

A 36C1 chronology of lacustrine sedimentation in the Pleistocene Owens River system

NANCY OLGA JANNIK Department of Geology, Winona State University, Winona, Minnesota 55987 FRED M. PHILLIPS Department of Geoscience, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801 GEORGE I. SMITH Branch of Sedimentary Processes, U.S. Geological Survey, M.S. 902, Menlo Park, California 94025 DAVID ELMORE Department of Physics, Purdue University, West Lafayette, Indiana 47907

ABSTRACT INTRODUCTION sedimentary record of alternating marls and evaporites. Its lake waters deposited evaporites We have used 36CI to date climatically sen- Until now, the most continuous record of during arid periods, and carbonates and clastics sitive saline-lake sediments from hydrologi- Quaternary climatic history has been found in during humid periods. The record left behind is cally closed basins in southeastern California, deep-sea sediment cores, particularly in the lsO thus sensitive to major fluctuations in the water primarily sediments from Searles and Pana- content of foraminiferal tests. Deep-sea sediment balance. Using our 36C1 dating of the sediments, mint basins. During wet periods of the past cores are most informative with regard to cli- together with previous U/Th, and paleo- 2.0 m.y., lakes that formed in the closed ba- matic phenomena that directly affect the ocean magnetic chronologies, we present a climatic sins fluctuated in size in direct response to the (for example, ice volume, isotopic composition and hydrologic history for this part of the balance between runoff and evaporation. We of the ice, water temperature, carbonate content southwestern United States during the entire have compiled a chronology for the KM-3 of ocean water). Ice volume, the above parame- Quaternary Period. core from Searles Lake, based on ages deter- ter most strongly related to events on land, is a mined by ^Cl for the evaporites, together reflection of climatic events predominantly at Owens River System with those determined by 14C and U-Th series high mid-latitudes. The areas of greatest poten- for younger sediments, and by magnetostratig- tial impact of future climatic change due to the The distinctive geomorphic characteristic of raphy for older sediments. This chronology, concentration of human population, however, the Great Basin section of the Basin and Range along with other criteria, such as correlations are mid-latitude continental areas. Deep-sea sed- physiographic province of the western United between Searles and Panamint basins, the iment cores thus provide limited understanding States is the abundance of hydrologically closed chloride budget, and sedimentology, is used of past climatic changes in mid-latitude conti- basins into which surface-waters drain. In east- to reconstruct the history of lake fluctuations nental environments where the information is ern California and western Nevada, playas and in the paleo-Owens River system. We infer most needed. small saline lakes mark the locations of closed that Searles Lake desiccated at most twice One reason for the lack of data in this crucial basins which once received waters from the since 600 ka: during the interval around 290 area is that there are very few accumulations of paleo-Owens, Amargosa, and Mojave Rivers ka, and from 10 ka to the present. The lake continental sediments that are continuous, cli- (Fig. 1). Within each paleo-drainage system, the history curve shows that the Holocene Epoch matically informative, and capable of being nu- closed basins were hydrologically connected is anomalously arid. Major overflows from 1 merically dated. One mid-latitude continental during wet periods of the past 3.0 m.y. due to Searles to Panamint occurred during the in- environment that could potentially provide sed- the interaction between climatic, hydrologic, tervals between 1.3 Ma and 1.0 Ma, 750 ka iment accumulations with these qualities is and geomorphic conditions. Each basin sequen- and 600 ka, 500 ka and 400 ka, and 150 ka closed-basin lakes. Lake levels in closed basins tially served as the terminus of the drainage sys- and 120 ka. fluctuate in response to the balance between tem until it overflowed into the next basin (Gale, Comparing the lake-fluctuation chronology precipitation and évapotranspiration in the wa- 1914). Extent of overflow during each wet pe- to the <5lsO record of marine foraminifera, we tershed (Street-Perrott and Harrison, 1985). riod depended on the volume of runoff and the infer that the strongest similarity is in the pe- Fluctuations in the amount of precipitation are rate of evaporation. During the most extreme riodicities of the cycles-40 to 50 kyr before caused by factors such as climate change and wet periods, the three paleo-drainage systems the Matuyama/Brunhes magnetic reversal tectonism. Comparison of the effects of these coalesced, with Lake Manly in Death Valley (730 ka) and 100 kyr thereafter. We find, factors show that climatic changes produce fluc- serving as the common ultimate sink. however, that at Searles Lake this fluctuation tuating lake levels, whereas tectonism produces The present-day Owens River drains an area in the lake chronology is modulated by long-lasting changes in lake levels (Smith and of about 8,500 km2, yet most of the runoff is longer-term cycles of aridity and humidity. Street-Perrott, 1983). derived from about 16% of the catchment area Thus, although the mid-latitude Quaternary We report here on 36C1 dating of sediment that lies on the eastern slope of the Sierra climate record reflects the mid- to high- cores from Searles and Panamint Lakes in latitude ice-volume fluctuations that dominate southeastern California. The Searles basin con- 1 ls In this paper, we follow the convention of using the the marine O record, it also contains evi- tains a nearly continuous sediment record from "yr" and "m.y." for periods of time, but "a" for dates dence for climatic forcing of a different type. at least late Pliocene time. The core reveals a before present (ka, Ma).

Geological Society of America Bulletin, v. 103, p. 1146-1159, 10 figs., 1 table, September 1991.

1146 119' 118"

119° 118° 117° 116° 115°

Figure 1. Map showing locations and drainage patterns of the paleo-Owens, -Amargosa, and -Mojave River systems. 1148 JANNIK AND OTHERS

Nevada (Lee, 1912, see Fig. 1). The impressive are yellowish gray to olive-green gray in color various basins would permit correlation be- Sierra Nevada massif creates such a strong rain- and contain sparse to abundant diatoms and os- tween them and thus reconstruction of the lacus- shadow effect that even during the most extreme tracodes. Coarser layers of fine- to medium-silty trine history. Previous studies at Searles Lake wet periods of the past, when individual drain- sand are found near the bottom of the core. have reported 14C dates to about 45 ka (Stuiver, age basins coalesced into one system, most of the China Lake was a broad, shallow (less than 1964; Stuiver and Smith, 1979), U/Th dates to runoff probably still originated in a small, high- 12 m), infrequently saline lake during wet peri- 230 ka (Peng and others, 1978; Bischoff and altitude portion of the combined drainage area. ods. Subsurface sediments consist of silt- to others, 1985), and paleomagnetic reversals be- Thus, precipitation that fell directly on the sur- sand-sized clastic sediments with some clay lay- ginning at 730 ka and extending to 3.15 Ma faces of the lakes in the paleo-Owens River ers. Smith and Pratt (1957) noted the presence (Liddicoat and others, 1980). An altered ash at system was a negligible contribution to the lake of diatoms, ostracodes, and mollusks. Authigenic 168.6 m has been tentatively correlated with the water budget. Such lakes are classified as "am- gaylussite (Ca-, Na-carbonate) is found in the Lava Creek B ash (610 ka) (Hay and Guldman, plifier" lakes after Street-Perrott and Harrison upper portion of the core, as is calcite. Both of 1987). The radiometric chronology of most of (1985), for which there exists a simple relation- these are found as crystals or disseminated in the the mid-Pleistocene stratigraphic sequence (be- ship between basin runoff, lake evaporation, and clastic sediments. There are no beds of salines. tween 230 ka and 730 ka), however, has not yet 36 lake area. The third lake in the chain was Searles Lake, been established. In this study, we report C1 The equilibrium surface area of a closed-basin which served most frequently as the terminal dates covering this interval for both Searles and 36 lake under natural conditions is strictly depend- sink of the paleo-Owens River drainage system. Panamint Valleys. The C1 method was pre- ent on the relationship of precipitation and évap- At a lake elevation of 665 m, Searles Lake coa- viously tested on intervals that were independ- otranspiration over its entire watershed (Halley, lesced with China Lake to form one large lake ently dated; the preliminary results were report- 1715). Any changes in this relationship result in (Figs. 1, 2B). One of the most complete records ed by Phillips and others (1983). Evaporite 36 a change in terminal lake depth, which directly of late Cenozoic sedimentation in the western minerals suitable for C1 dating are lacking influences its lake area, and the cumulative lake United States is revealed in a 930-m, surface-to- from the Owens and China basins. area in the drainage basin (Benson and Paillet, bedrock core (KM-3) recovered from Searles 1989). Figure 2A shows, on a cumulative basis, Lake in 1968 (Smith and others, 1983). Shal- CHLORINE-36 DATING the lake surface area as a function of lake depth lower cores have been described in detail by in each basin for the entire paleo-Owens River Gale (1914), Smith and Pratt (1957), Smith and Natural Production system, based on modern topographic data. Fig- Haines (1964), and Smith (1979). The stratig- ure 2B is a diagrammatic cross section of the five raphy as revealed in the cores consists of distinct Chlorine-36 (t^ = 301 kyr) is the only lakes that comprised this system. At maximum beds of soluble evaporites and fine-grained plas- long-lived unstable isotope of chlorine. It occurs pluvial conditions, the total lake surface area of tic "muds." The "muds" are composed of clastic naturally in the atmosphere (meteoric), at or the paleo-Owens River s3'stem was approxi- silts and clays, alkaline earth carbonates (arago- slightly below the Earth's surface (epigene), and mately ten times the historical surface area of nite, calcite, and dolomite, gaylussite, and pirs- in the subsurface (hypogene) (Bentley and oth- Owens Lake. sonite), and in some places disseminated saline ers, 1986). Several reactions are significant in In this study, we reconstruct the lake-level minerals (especially halite). Although this mix- producing 36C1 in these zones: cosmic-ray spalla- history of the paleo-Owens River system. We ture is not "mud" in the usual sense, we retain tion of heavier nuclei, principally 40Ar, potas- have not attempted to include Death Valley in the established terminology (Smith, 1979). sium, and calcium; thermal neutron absorbsion this study because of the sparsity of subsurface The saline layers contain a variety of evapora- by 36Ar, 35C1, and 39K; and muon capture by tive minerals, ranging from thick beds of mas- data and difficulties in quantifying the Mojave "OCa. River and Amargosa River contributions. sive pure halite to thin layers of trona, nahcolite, The cosmic-ray-induced interactions are im- thenardite, hanksite, northupite, burkeite, and portant mainly in the atmosphere, at the Earth's borax. Stratigraphie Record surface, and in the upper 30 m of the lithosphere During wet periods, Searles Lake rose to 695- and hydrosphere (due to cosmic-ray attenuation Subsurface sediments supply evidence that is m elevation and overflowed into Panamint Val- as a function of the cumulative mass along the invaluable in reconstructing the chemical and ley, which contains a small northern basin and a ray path, below the top of the atmosphere). physical history of a lake in a closed basin. What larger southern basin. The overflow filled the Owing to the relative abundances of the differ- follows is a brief description of the general na- southern basin first. When the lake reached an ent target elements in different terrestrial envi- ture of the sediments that underlie the floors of elevation of about 520 m, the northern basin ronments, spallation of '"'Ar is the most each of the successive basins in the paleo- began to receive overflow. The lithologic log important meteoric reaction, and spallation of Owens River system. Figure 2C shows a from a 300-m core recovered from the center of calcium and potassium (in low-chloride rocks) 35 generalized stratigraphie column of the sedi- the southern basin shows a sequence of clastic or neutron activation of C1 (in high-chloride ments underlying each basin. sediments, ranging from clay to silt or sand, with rocks) in near-surface rocks is the most impor- The first sink in the paleo-drainage system two thick interbedded zones of massive pure hal- tant epigene reaction. Neutrons involved in the was Owens Lake, although Mono Lake, north ite (Smith and Pratt, 1957). Minor amounts of hypogene activation reactions are derived from of Owens Valley, upon occasion overflowed to carbonates and gypsum are also present. A few the decay of U- and Th-series elements. The Adobe Lake, which then overflowed into the ostracodes and several horizons rich in forami- reaction involving muon capture by "^Ca is im- Owens River (Fig. 1). A 280-m core from be- nifera were found in this core. Ostracodes and portant only at depth in Ca-rich rocks. For a 36 neath the surface of Owens Lake reveals sedi- diatoms were present in a core from the north- more complete discussion of C1 production, ments that are predominantly massive or lami- ern basin, which contained no halite beds. A see Bentley and others (1986). nated clay with interbedded silts. Evaporites are 300-m core drilled near the center of Death Val- absent, except in the top meter where they are a ley, the ultimate sink of the paleo-Owens River Chlorine-36 in the Hydrologic Cycle result of the 20th Century desiccation that re- system, revealed alternating thin beds of muds sulted from artificial diversion of the Owens and salines (Hunt and Mabey, 1966). Chlorine (including its isotope 36C1) is River (Smith and Pratt, 1957). Most of the clays Independent dating of the sediments in the strongly hydrophilic and travels conservatively Figure 2. A. Plot of lake area Cumulative Lake Depth (m) versus cumulative depth for the 200 300 400 500 600 700 800 paleo-Owens River system. Cumulative depth refers to the depth of runoff that filled each successive basin. Letter "A" correlates to a point upstream from Owens Lake (cumulative lake depth = 0). The other capi- tal letters mark locations of sills which correspond to lake area when overflow to the next basin began. Sill elevations are in parentheses. B. Diagrammatic cross section of the five lakes in the paleo-Owens River system. Let- ters correspond to sills as shown in 2A. C. Generalized cores from each of the closed basins. Unit A+B in the KM-3 core is reconstructed from a nearby core (289M). Units G, F, D+E, C, and A+B refer to the unit names in the Mixed Layer in core KM-3. Abbreviations of units in the KM-3 core: BM, Bottom Mud; LS, Lower Salt; PM, Parting Mud; US, Upper Salt; OM, Overburden Mud. Depth Depth (m) OWD-1 MD-1 KM-3 PAN-3 DV-1 (m) r~ o o-i

— 50 50-

rvsTi S-.S S«.

SjWjigp^ljjS Unit 100 A+B 100-

150 150-

— 200 200-

— 250 250- «« — 300 sand 300-

[~~| evaporites 350 350- HI lacustrine mud

lacustrine/playa — 400 sediments 400- 1150 JANNIK AND OTHERS

through hydrologic systems with minimal chem- studies involving low-level samples, such as con- 36 dM,c i ical interaction. Meteoric C1 is washed or falls tinental salines, have therefore been overcome. icr (3) out of the atmosphere with stable chloride (de- dt 36 rived predominantly from sea spray). Epigene Results and, in the case of constant C1 influx (i36): 36C1, derived from the weathering of rocks, can dM g also move in either surface water or ground The measured ratios and uncorrected 36C1 3 36 136 - ^-36^36 = —7— (4) water, whereas hypogene C1, derived from ages for salines from Searles and Panamint dt subsurface neutron-activation reactions, predom- Lakes are presented in Table 1. These uncor- Rearranging and integrating equation 3 over inantly enters the deep ground-water system. In rected ages (t) were determined by using the time yields the Owens River system, geothermal springs are standard radiometric decay equation a major source of waters with high chloride con- 36 MCi = ¡ci(t0 - td) (5) tent and low C1/C1 ratio. Contributions of dis- (1) charge from these springs along the drainage ^36 V Ri / and doing the same for equation 4 system result in a progressively lower 36C1/C1 where Rm is the measured ratio for the sample, ratio downstream (Jannik, 1989). In the paleo- M = ^(l-e^-g) R| is the initial ratio and X36 is the decay con- 36 (6) Owens closed-basin drainage system, all chlo- stant of 36C1. ride isotopic species were carried to the terminal 36 After C1 is locked into evaporitic chloride with the assumption that Ma and M36 = 0 at t0 sink, where 36C1 was incorporated along with minerals in the terminal sink, the radioactive (t0 = time infilling began), and td = time of halite stable chloride in evaporites. Mass-dependent clock is started. An initial ratio (Rj) of 56 x 10~15 deposition. Substituting 5 and 6 into 2: fractionation of chlorine isotopes during these 36C1/C1 was used for all samples from Searles 36 _ M i (l -e-W'>) processes will negligibly affect the C1/C1 ratio and Panamint basins. This initial value was the 36 36 ^ ~ "77 ^—I —> {') (Kaufman and others, 1984). 36C1/C1 ratio of the Upper Salt (the youngest Mci id^36(to " td) Searles Lake evaporite unit derived from Owens Methodology River runoff) measured by Phillips and others then: 14 (1983) and adjusted for the 10 ka C age of the R. unit. This value reflects mixing of large amounts A At In the Owens River system, salines from Rd-Ri (1 - e~ » ) (8) 36 Searles and Panamint Lakes were sampled from of low C1/C1 hypogene chloride from hot *36(to - td) X36At springs with smaller amounts of high 36C1/C1 cores. Sampling of salines was restricted to pure where At = tQ - td, and R( = M36/MCI at t = t0. chloride from meteoric and epigene sources, as halite crystals where possible. The exterior por- The present ratio (Rp) reflects the ratio at the tion of selected crystals was removed by dissolu- discussed previously. time of deposition (Rd) with subsequent decay tion in deionized water to reduce risks of Most of the samples from Searles Lake were after burial. Therefore: possible contamination. The remaining portion from saline units (with interstitial muds) that A d R, X31,A, X:l< ,d of the crystal was dissolved in deionized water. precipitated slowly, but continuously, allowing Rn = Rde "' (1 - e~ )e~ ' . (9) P AgN03 was then added to precipitate the chlo- equation 1 to be used directly. Six samples from """ X36At ride as AgCl. Purification of the AgCl was nec- Searles Lake (126.5 m, 179.0 m, 190.7 m, 293.0 Rearrangini g and solving for time of deposition essary to remove sulfur, which is an interfering m, 399.3 m, 401.3 m), however, were from sa- (td): isobar during accelerator mass spectrometer line units that were determined to be the result -1 /Rp A36At \ (AMS) analysis. Sulfur was removed by re- of rapid precipitation during episodes of major (10) td = —In peated dissolution in ammonia and then repre- lake regression. Soluble chloride in these sam- a36 \Ri / cipitation by one of two means: (1) the addition ples, therefore, resided in the lake waters for of nitric acid or (2) evaporation by heating long intervals before incorporation into the Equation 10 was used to calculate corrected (Bentley and Davis, 1982; Jannik, 1989). evaporites. To account for 36C1 decay during 36C1 ages for the Searles Lake samples listed 36 The samples were analyzed by AMS at the this residence time, a corrected C1 age must be above (Table 1). The length of residence (At) Nuclear Structure Research Laboratory, Univer- determined. Because we lack independent in- was estimated for each sample based on chloride 36 sity of Rochester, New York, according to tech- formation on the C1 and stable chloride in- budget methods (described below). In general, niques developed by Elmore and others (1979, fluxes, these must be assumed constant in order the magnitude of the residence time corrections 1982). Accelerator mass spectrometry is an ul- to perform the corrections. Although this con- is small. The 36C1 ages for Searles Lake, along trasensitive form of mass spectrometry. The fa- stancy cannot be demonstrated, it appears rea- with ages determined by other methods, are cility at the University of Rochester consists of sonable for fluxes that are integrated over long presented in Figure 3. The chronological uncer- two mass spectrometric analyzers separated by a periods of lake history. tainties in Table 1 and Figure 3 reflect only the 36 nominal 16 MV model MP tandem Van de The ratio at the time of halite deposition (R

TABLE 1. CHLORINE-36 MEASUREMENTS AND AGES FOR CORE SAMPLES and by magnetostratigraphy for those at greater than 300 m were used because those methods Location Sample Depth Unit« ^ci/ci Uncorrected Residence Corrected (m) Searles Lake (* 10"15) 36C1 age time (At) 36C1 age are more precise within the age ranges repre- only (Ma) (Ma) (Ma)t sented at these depths (Fig. 3).

Searles Lake, California SLC-1 3.0 OM 48 ± 10 0.067 ± 0.010 Three samples, collected at 6.4 m, 19.2 m, KM-3 core SLC-4 6.4 US 80 ±6§ and 227.5 m, were observed to have anoma- PRE-1" 14.2 US 55 ± 3 0.010 i 0.022 36 SLC-3 19.2 US 75 ± 15§ lously high C1/C1 ratios. The high value at PRE-2" 32.5 LS 55 ± 3 SLC-11 114.0 ML(C) 29 ±3 0.286 ± 0.047 227.5 m was checked by processing a fresh crys- SLC-5 126.5 ML(C) 24 ± 3 0.368 ± 0.058 0.059 0.339 ± 0.058 tal of halite from the original sample. The sec- SLC-14 140.8 ML(C) 23 ± 2 0.386 ± 0.040 SLC-5.3 153.0 ML(C) 21 ± 3 0.426 ± 0.067 ond measurement was also high. We tentatively SLC-15 161.8 ML(C) 14 ± 5 0.602 ± 0.192 36 SLC-12 179.0 MUD+E) 12 ± 1 0.669 ± 0.038 0.001 0.668 ± 0.038 attribute the high C1/C1 ratios to contamina- SLC-6 187.0 ML(D+E) 14 ± 3 0.602 ± 0.105 tion, and these values are not used in our chro- PRE-3" 190.7 ML(D+E) 8.9 0.799 ± 0.051 0.015 0.792 ± 0.051 36 PRE-4" 206.5 ML(D+E) 7.7 ± 1 0.862 ± 0.060 nology. A high C1/C1 ratio of a sample from SLC-7 227.5 ML(D+E) 130 ± 33§ SLC-8 293.0 ML(G) 3 1.27 ±0.176 0.006 1.27 ±0.176 401.3 m was first reported by Phillips and others PRE-5" 304.3 ML(G) 6.6 ±2 0.929 ± 0.156 (1983). This depth interval was resampled, and SLC-10 399.3 ML(G) 2 ± 1 >1.50 0.003 >1.50 SLC-9 401.3 ML(G) 2 ± 1 >1.50 0.003 >1.50 the remeasured ratio was very low, supporting PRE-6" 401.3 ML(G) 42 ± 8 the suggestion by Phillips and others (1983) that Panamint Valley, California PVC-1 18.2 80 ±3§ the first sample may have been contaminated DH-3 core PVC-5 40.9 33 ± 4 0.230 ± 0.050 0.175 ± 0.075 PVC-10 68.3 33 ± 3 0.230 ± 0.041 0.175 ± 0.075 during laboratory preparation. The correspond- PVC-15 136.0 92 ±7§ ing 36C1 age for the new ratio is consistent with PVC-18 160.5 19 ± 2 0.470 ± 0.043 0.392 ± 0.090 the ages of adjacent samples (Table 1) and is •Units for Searles Lake cores plotted on Figure 2C. used in the chronology presented in Figure 3. ^Adjusted 36CI ages as discussed in text. §36C1/C1 greater than initial ratio (Rj); ages cannot be determined. Ratios measured at 161.8 m and 187.0 m have "PRE samples from Phillips and others (1983). large uncertainties, and the value at 187.0 m represents a reversal. In order to present a final mint units are lower case) and lower-salt layers Discussion of Ages from Searles Lake Cores data set that is internally consistent and as accu- (between 21.3 and 48.5 m, and 129.3 and 161.8 Determined by Chlorine-36 rate as possible, the values for these samples m, respectively). A computer program was writ- were not included in our chronology. Ages de- 36 14 36 ten to implicitly solve for a "corrected" age, td, Ages determined by C1 are concordant with termined by the C, U-Th, C1, and paleo- given the measured Rp, at an estimated t0 in- those determined by other methods for the in- magnetic methods to produce the chronology of ferred from the Searles chronology. The time for tervals where more than one method can be Searles Lake sediment are connected by a line in beginning of infilling (t„) for the upper salt in employed. For interpretations made during this Figure 3. This data set includes the ash layer at Panamint Valley was inferred to be 290 ka, study, however, ages determined by 14C and 168.6 m which is correlated with the (610 ka) and for the lower salt, 550 ka. The corrected U-Th series for samples from less than 100 m Lava Creek B ash (Hay and Guldman, 1987). 36C1 ages for Panamint Lake are presented in Table 1.

Figure 3. Ages determined for sediments from the KM-3 core, Searles Lake. Chlorine-36 dates from this study and Phillips and others (1983); Carbon-14 ages from Smith (1979); U-Th series ages from Bischoff and others (1985); tephra age from Hay and Guldman (1987); paleomagnetic age control as determined by Liddicoat and others (1980). Abbreviation of units described in Figure 2C. Units above the Bottom Mud (BM) are grouped together and denoted by (*).

KEY Ages determined by:

• Chlorine-36 (with error bars)

V Carbon-14

® Ash

o U-series (error bars within symbol)

e Magnetostratigraphy (with error bars)

Age (Ma) 1152 JANNIK AND OTHERS

Prior to using 36C1 as a geochronometer for tive AIR as a function of depth through the for the dated depth intervals was determined. buried continental evaporites, the following entire core (Fig. 4 A) reveals a change in slope at Then, for each AIR value, ages were linearly three conditions must tie fulfilled: (1) the about 400 m, which reflects a change in the interpolated between the dated points. We then 36C1/C1 ratio of the inflow to the terminal sink sedimentation rate. This is due to a change of plotted cumulative AIR as a function of time must be nearly constant, (2) any post-deposi- environment in Searles basin from persistent (Fig. 4B). Although the AIR-accumulation rate tional production of 36C1 must be negligible or perennial or playa lakes to a regime character- does show variations, it is relatively constant for calculable, and (3) the chloride in analyzed ized by perennial lakes that underwent periodic long periods and is more regular than the age samples should have remained immobile within regressions that resulted in rapid precipitation of curve (Fig. 3). Finally, the AIR ages (Fig. 4B) halite crystals since the time of primary evaporites containing little AIR (Smith and oth- were correlated with AIR depth intervals (Fig. deposition. ers, 1983). The acid-soluble components include 4A). The resultant "AIR-interpolation age" ver- Agreement of 36C1 dates; from this study, and Na, Ca, and Mg carbonates, as well as Na, Ca, sus depth is shown in Figure 5, with numerically those presented by Phillips and others (1983), and K sulfates and chlorides. In this study, ac- dated points included. This plot is more realistic with independent dates supports the assump- cumulation curves for AIR, chloride, sodium, than a simple linear depth interpolation, in that tions of a nearly constant 36C1/C1 influx and sulfate, carbonate, and calcium were constructed many evaporitic intervals do show higher sedi- negligible post-depositional 36C1 production by from the above analyses and the depth versus mentation rates. cosmic-ray reactions for Searles Lake. Hypo- age curve in Figure 3. gene production calculated for these sediments Acid-Soluble Components was not significant for samples younger than 1.0 AIR-Interpolated Ages Ma. Subsurface chloride translocation is more With ages interpolated as described above, difficult to determine and quantify; therefore an The slope changes in Figure 3 indicate that the accumulation of chemical species of interest effort was made to sample primary crystals. there were major fluctuations in the deposition can be plotted over time. The accumulation The anomalously high 36C1/CI ratios in Table rate in Searles Lake. At least part of the reason curves for calcium and carbonate are shown in 1 are most probably due to field or laboratory for these fluctuations is clear. Large amounts of Figure 6A, sodium and sulfate in Figure 6B, and contamination. Overall, the data are internally certain solutes (principally sodium, chloride, and chloride in Figure 6C. The curves for sodium, consistent and in good agreement with inde- carbonate) accumulated in the lake waters over sulfate, and chloride are quite different from the pendent dates. long periods of time. Then, when environmental calcium and carbonate curves (Fig. 6A). The change caused a large decrease in lake volume, contrast is due to the solubilities of the elements. SEDIMENTARY CHRONOLOGY OF these solutes precipitated out rapidly as beds of Calcium carbonate minerals are relatively insol- SEARLES LAKE—KM-3 CORE nearly pure evaporite minerals (Stuiver, 1964). uble; thus calcium has a short residence time in Intervals showing clear examples of this phe- the lake waters and a relatively constant rate of Smith and others (1983) reported a strati- nomenon include the Upper Salt and parts of deposition in the sediments. Therefore, the cal- graphic, mineralogical, and geochemical study Unit C. The large fluctuation in deposition rate cium accumulation curve resembles that for of the KM-3 core. The core was divided into caused by this phenomenon makes it difficult to AIR. The similarity between the two tends to 254 intervals based on lithology, and detailed interpolate ages on the basis of depth. support the AIR-interpolation procedure. chemical analyses were performed on each in- Sedimentary components such as AIR that On the other hand, chloride, sodium, sulfate, terval. Each analysis involved determining the have a short residence time in the lake waters and some carbonates form relatively soluble percentages of the acid-insoluble residue fraction should not be subject to this type of fluctuation minerals and thus tend to be stored in the lake and ten elements in the acid-soluble fraction. in deposition rate. In an effort to more accu- waters until they are precipitated during epi- The acid-insoluble residue (AIR) fraction of rately interpolate sediment ages between numer- the sediments includes clastics of fluvial (pre- ically dated points, we developed a method for dominantly from local runoff) and eolian origin, interpolation between radiometric data points and authigenic silicates. Examination of cumula- using the AIR data. First, the cumulative AIR Figure 4. A. Cumulative acid- insoluble residue (AIR) plotted against depth, within interval 700 m to surface, for the KM-3 core, Searles Lake. Letters correspond to the names of units in the Mixed Layer. (*) refers to the Upper Units which overlie the Mixed Layer (from bottom to surface, Bottom Mud, Lower Salt, Parting Mud, Upper Salt, and Overburden Mud). B. Plot showing accumulation of acid-insoluble residue (AIR) for the past 2.0 m.y. in the KM-3 core, Searles Lake. (*) refers to the units that overlie the Mixed —'—r t 1 I 1 I 1 P I 1 ' I 1 I 1 'I—T 700 600 500 400 2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Layer. Abbreviation of units Depth (m) Age (Ma) described in Figure 2C. CHRONOLOGY OF SEDIMENTATION, OWENS RIVER SYSTEM 1153 sodes of low lake level or desiccation. Their ac- 0 cumulation rates, therefore, show a characteristic stair-step pattern (Figs. 6A, 6B, 6C). 40- Chloride is of particular interest because it BM stays in solution until the lake is very close to 80- desiccation, due to its high solubility. If the chlo- A+B ride input rate has remained constant, a mass balance of chloride can yield information on the 120- lake overflow history. Evidence for relative constancy in the input of dissolved solids, especially 160 chloride, can be found in the relative constancy of the calcium, carbonate, and sodium accumu- D+E lations (Figs. 6A, 6B). Further support comes E 200- from examining the rate of chloride accumulation during periods when Searles Lake was ap- CL 240 O) parently the terminus of the river system. For Q example, during the period between 1.7 and 1.55 Ma (Unit G of the Mixed Layer, Fig. 6C), 280 the lake level fluctuated rhythmically about a fairly low baseline, producing a very regular 320 stair-step pattern. Another example is the period between 0.024 Ma and 0.01 Ma (Lower Salt to 360-| Parting Mud), for which independent evidence indicates that Searles Lake was the river terminus, except for relatively brief overflows to Pa- 400 namint Valley (which does not contain halite of these ages). For the first period, the chloride 440 -2 accumulation rate at KM-3 was 0.20 kg m 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -1 2 yr , and for the second, 0.18 kg m yr The Age (Ma) similarity of these rates, separated in time by 1.5 KEY a V / m.y. is further evidence for the relative constancy of the chloride input. We conclude that it Ages determined by: is unlikely that the stair-step-like deposition • Chlorine-36 (with error bars) ffi Ash pattern of sulfate, sodium, and chloride is a re- + AIR interpolation o U-series (error bars within symbol) sult of input variations. Smith (1976) also con- cluded that the chloride load of the Owens V Carbon-14 e Magnetostratigraphy (with error bars) River since 20 ka was approximately constant. The modern CI rate of 5.9 * 106 kg yr1 Figure 5. Chronology for the KM-3 core, Searles Lake, for the past 2.0 m.y. Ages based on (Smith, 1976) can be compared to a recon- radiometric and magnetostratigraphic ages as shown in Figure 3 as modified by acid-insoluble structed rate of input. The reconstructed rate is residue (AIR)-interpolation method. Abbreviation of units described in Figure 2C. Units above calculated based on the chloride accumulation the Bottom Mud (BM) are grouped together and denoted by (*). rate determined above. First, the fraction of the Upper Salt chloride (Clus) contributed in one is 448 x 109 kg (Smith, 1979). Thus, the If Searles Lake had always been the terminus year is calculated as reconstructed annual input (CI yr"')R would of the river system since 2.0 Ma (425-m depth), equal 6.7 x 106 kg yr"1. This value is quite and given an average chloride input of 0.19 kg CL -1 6 1 2 -1 1 Clus yr (11) similar to the historical value (5.9 x 10 kg yr" ) irr yr (at the location of KM-3), the total Clf/unit presented by Smith (1976). The agreement of chloride accumulation should have totaled 3.85 5 2 where Clac is the average chloride accumulation the measured value and the reconstructed value x 10 kg m" . Instead, the total accumulation is rate (as discussed above at KM-3, 0.19 kg m~2 is additional support for our assumption of ap- only 1.63 x 10s kg m"2 (Fig. 6C). The intervals yr"1; Fig. 6C), and Clx/unit is the total chloride proximate constancy of chloride input. of "missing" chloride can be identified by draw- per unit area in the Upper Salt (at KM-3,0.12 x In the analysis below, we explain the large ing lines of constant 0.19 kg m~2 yr-1 input rate 105 kg m"2; Fig. 6C). The fraction of Upper Salt variation in chloride deposition rate based on on the stair-step pattern sections of the accumu- chloride contributed in one year would be equal hydrologically driven changes in basin intercon- lation curve (when Searles Lake was the termi- to 1.5 x io-5 yr"1. This portion of the Upper nection, assuming a constant chloride influx. Al- nus) in Figure 6C. Two of the most significant Salt chloride attributed to one year is then mul- though this assumption is clearly only an episodes of chloride loss, indicated by long, sub- tiplied by the total chloride in the Upper Salt: approximation, it seems more realistic than the horizontal slopes, can be seen in the intervals extreme (and otherwise unexplained) variations between 1.3 and 0.95 Ma and between 0.30 and 1 Clus yr- x (Or) = (CI yr~')R (12) in chloride influx necessary to explain the fluc- 0.03 Ma. The most plausible mechanism of loss tuation in deposition based on changes in chlo- is overflow from Searles Lake into downstream where C1T, the total chloride in the Upper Salt, ride input. basins. The chloride deficit is not attributed to 1154 JANNIK AND OTHERS

either deposition in upstream basins (since cores from those basins reveal no evaporites; Fig. 2C), or to eolian deflation (Jannik, 1989).

Sedimentation Rates

The chronology of the KM-3 core presented in this study (Fig. 5) reflect; the rate of sediment accumulation in Searles Lake. A change in slope is inferred to indicate a change in the nature of sedimentation. The irregular pattern in Units C and G reflects abrupt changes in relatively short time intervals, whereas the more linear patterns of Unit F and the Bottom Mud show a fairly consistent trend for long periods. Apparent rates of deposition were estimated by linear regression. The overall rate for the sediments in KM-3 for the past 2.0 m.y. is 20 cm/1,000 yr. The rates for each unit in the Mixed Layer and for the Bottom Mud are shown in Figure 7. The Lower Salt, Parting Mud, Upper Salt, and Overburden Mud were combined into one section. Unit C is comprised of salines with inter- Age (Ma) bedded mud layers. The apparent rate of deposition is 15 cm/1,000 yr (Fig. 7). The age curve for Unit C, however, has three segments which exhibit a distinct stair-step pattern, similar to that observed in Unit G. The apparent sedimentation rate for two of the segments is 28 cm/1,000 yr (Fig. 7). They are separated by an interval (between 550 and 420 ka) exhibiting a subhorizontal slope with a sedimentation rate of 4 cm/1,000 yr. The anomalously low rate is attributed to unusually persistent low lake levels or, possibly, lack of sufficient absolute age control (Jannik, 1989). The apparent rates of sedimentation for the units overlying Unit C cannot be directly compared to that of units underlying Unit C because the overlying units are less compacted. Similar- ity in the patterns of accumulation, however, are observable (for example, a stair-step pattern). If the less compacted units are considered to be more indicative of modern rates, then the average rate of mud deposition from the base of Unit A+B to the surface is about 34 cm/1,000 yr, and the rate for salines, 4 to 10 times higher.

LAKE-HISTORY RECONSTRUCTION Age (Ma) The KM-3 core recovered from Searles Val- ley is one of the most complete records of Pleis- Figure 6. Plots showing the mass accumulation through time of (A) calcium and carbonate, tocene lacustrine sedimentation in the world. (B) sodium and sulfate, and (C) chloride in the KM-3 core, Searles Lake. Chloride accumula- Our reconstruction of the lake history for the tion curve for the KM-3 core shows intervals in which possible overflow to downstream basins paleo-Owens River system is based primarily occurred (brackets), with subsequent loss of chloride from the accumulation curve (arrows). on the information revealed in the sediments An average accumulation rate of 0.19 kg m~2 yr-1 is inferred. (*) refers to the units that overlie recovered from the KM-3 core and, to a lesser the Mixed Layer. Abbreviation of units described in Figure 2C. CHRONOLOGY OF SEDIMENTATION, OWENS RIVER SYSTEM 1155

extent, the cores from the other basins. Although detailed studies examining other criteria such as shorelines and exposed lacustrine sediments can also serve as a basis for lake history reconstruction, this study concentrates on the record revealed in the subsurface cores. The following is a brief discussion of the criteria used.

Sedimentological Criteria

In Searles Lake, the two dominant types of interbedded sediments—muds and evaporite minerals—are apparent from macroscopic ob- servation of the KM-3 core. Muds deposited during the past 2.0 m.y. represent times of medium to high lake levels, and lithologic and mineralogic variations within the muds signify changes in the chemical nature of the lake waters (Smith, 1979). The mud color itself also suggests lake depths and environments of deposition. For example, black or dark green muds usually are a product of deep, possibly stratified, perennial lakes with a reducing sedimentation environment; more yellowish or orange muds Age (Ma) indicate an oxygenated, and presumably shallow or unstratified, lake environment. The yellowish Figure 6. (Continued). muds may also indicate ash layers (yellow color due to oxidized biotite). Saline layers represent times when the lake was smaller and more concentrated. The mineralogy of the salts depended upon temperature, ion concentration, and the type of solutes avail- 100 cm/100)000 yr j * able. Salt mineralogy is also an indicator of lake salinity at the time of precipitation (Smith, 60- 32 cm/1000 yr f BM 1979). Beds of monomineralic salts are inter-

33 cm/1000 yr preted as products of winter cooling and salini- ties between about 3% and 15%; beds of 120 moderately soluble monomineralic or bimineral- ic salts, that probably crystallized throughout the year, indicate lakes with low to medium salinity E 180 (15%-30% salinity); and beds of multimineralic sz salts of the more soluble species indicate a highly saline lake (greater than 30% salinity). ® 240 Other criteria useful in analyzing lacustrine sediments include structures such as laminations, 300 mineral habits, grain sizes, and abrupt or grada- tional sedimentological boundaries (Smith, 1979). 360 Correlation with Panamint Valley

420-i—1—i—1—i—1—i—1—i—1—i—1—i—1—i—'—i—1—i—1—r Our correlation between the Searles and 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Panamint basins is shown in Figure 8. One of the Age (Ma) assumptions necessary for correlation of Searles Lake overflow events with Panamint Valley Figure 7. Sedimentation rates for the KM-3 core, Searles Lake, grouped into segments with saline deposition is that most of the chloride least-squares trend determined for each segment. Abbreviations of units described in Figure 2C. originated in the paleo-Owens River system and Units above the Bottom Mud (BM) are grouped together and are denoted by (*). not from local sources. There is a strong case for 1156 JANNIK AND OTHERS

AGE (Ma) KM-3 3 AGE (Ma) DEPTH (m) Unit C, Fig. 6C). We propose two overflows 0 • between 450 ka and 350 ka which would have 0.006 ' w 0.010 carried chloride into Panamint Lake. A possible 0.024 overflow from Searles Lake between 24 ka and 0.039 -0.175±0.075 10 ka is also shown in Figure 8. The chloride 50 — that would have been carried into Panamint Lake is in evaporites that are disseminated in the 0.154 0.175±0.075 playa deposits found in the top 25 m of the Panamint core (Smith and Pratt, 1957). The his- 100 — tory of overflows into Panamint Valley can be 0.286 refined by considering the chloride budget in Searles Lake.

150 — Chloride Budget 0.392±0.090 0.584 As noted above, large amounts of chloride are "missing" from Searles Lake compared to the 200 — amount that is expected when we assume an approximately constant influx from the paleo- Owens River. Overflows from Searles Lake may be inferred from the intervals with subhori- 250 — zontal slopes on the plot of chloride accumulation as a function of time (Fig. 6C). Three of the overflows since 1.0 Ma may be inferred to have occurred between 700 ka and 600 ka, 500 ka 300 — and 400 ka, and 150 ka and 120 ka. These last lacustrine/playa sediments two intervals match reasonably well with the • 36C1 dates of 392 ± 90 ka and 175 ± 75 ka (both corrected) for the lower and upper halite inter- sand 350 — IS vals in Panamint Valley, suggesting that these • two desiccations correspond with the termina- evaporites tions of the two overflow events (Fig. 8). The two dates of 175 ± 75 ka at the top and bottom 400 — of the upper halite may indicate rapid deposi- lacustrine mud tion, but the large analytical uncertainties do not permit a firm conclusion. Figure 8. Correlation between Searles and Panamint Valleys. Unit abbreviations for the The inference that the Panamint Valley halite KM-3 core shown in Figure 2C. beds are the result of Searles Lake overflows may be further tested by "adding" the chloride in the Panamint halite into the Searles Lake mass-accumulation plot (Fig. 9). The calculation a paleo-Owens River source. First, local runoff sediments in Panamint that were carried by the of the Panamint chloride mass in Figure 9 takes in the Panamint basin is not of sufficient quan- overflow from Searles Lake. into account the difference in valley geometries tity to sustain a lake of any significant size As noted previously, two subsurface zones by multiplying the Panamint kg m~2 values by (R. Smith, 1976); second, examination of the dominated by halite underlie Panamint Valley. the ratio of the area of the Searles playa to the geology of the Panamint drainage basin does not The chloride in the Panamint Valley upper salt area of the Panamint playa. The combined chlo- reveal any rock units that could supply a suffi- is hypothesized to have begun residence in ride accumulation in the two valleys, 2.2 x 10s cient quantity of chloride. Correlations between Searles Lake at about 290 ka (after deposition of kg/m2, approximates a constant influx of 0.19 an overflow from Searles Lake and the corre- Unit C, Fig. 6C). Figure 6C indicates that just kg m~2 to Searles since 650 ka and accounts for sponding halite in Panamint are based on prior to 290 ka, Searles Lake desiccated and nearly all of the "missing" chloride during this sedimentary chronology, chloride accumulation deposited its entire chloride content, an event period, supporting the overflow hypothesis. 36 in Searles, and C1 ages. Correlation between that was followed by a new cycle of chloride Nevertheless, the chloride missing from the an overflow from Searles Lake and the corre- accumulation. An overflow event at some point period prior to 650 ka is not accounted for. sponding clastic unit in Panamint is more pro- after 290 ka carried chloride into Panamint There are no significant halite beds in Panamint blematic, however. There are no detailed Lake where it stayed in solution until it was Valley between 160.0 m and the bottom of the analyses of the sediments from Panamint Lake; deposited as salt. Similarly, the chloride in the core (303.5 m; extrapolated age: ~1.5 Ma). The therefore it is difficult to distinguish between Panamint Valley lower salt is postulated to have lost chloride may have been transported to lacustrine and playa sediments. At this time, we begun residence in Searles Lake at about 500 ka Death Valley during an overflow of the lake in are not able to determine the amount of clastic (after deposition of the lowermost salt unit in Panamint Valley. CHRONOLOGY OF SEDIMENTATION, OWENS RIVER SYSTEM 1157

Lake History

The reconstructed history of the five lakes in the paleo-Owens River system for the past 2.0 m.y. is presented in Figure 10 along with a marine S18p curve and a generalized stratigraphic column/of the KM-3 core. The S180 chronology is a composite record proposed by Williams and others (1988); heavy values (increase in pos- itive direction) of 5 '«O are indicative of increas- ing global ice volume. The reconstruction of lake history is based primarily on characteristics of sediments in the KM-3 core (Smith, 1979), the reconstructed chloride budget for Searles and Panamint basins, and the new 36C1 ages for salts in Searles and Panamint Valleys. During the interval between about 2.0 Ma and 1.2 Ma (Unit G in KM-3 core), Searles Lake was the usual terminus for the paleo- Owens system. The stratigraphic record is characterized by a cyclic pattern of mostly green muds intercalated with beds of nearly pure halite. Green muds are indicative of a medium to deep perennial lake; the halite beds are indica- Age (Ma) tive of a shallow and highly saline lake. The inference that there was one period of desicca- Figure 9. Chloride mass accumulation for the past 2.0 m.y. for Searles Lake. An estimated tion between about 1.5 Ma and 1.45 Ma, al- mass accumulation of chloride in Panamint Valley is added. An average rate of 0.19 kg m~2 is though interrupted by a brief period of shallow shown as determined in Figure 6C. (*) refers to the units that overlie the Mixed Layer. lake levels (1.46 Ma), is supported by the pres- Abbreviations of units described in Figure 2C. ence of brown mud containing anhydrite, probably indicating that playa conditions prevailed briefly in Searles Lake. The chloride accumula- levels were reduced periodically to depths shal- periods during the deposition of Unit C. Playa tion curve for Unit G (Fig. 6C) shows the typical low enough to deposit evaporites. An overflow sediment (characterized by coarse grain size and stair-step pattern of a soluble solute as discussed event could be inferred for the period between dominance of clastic detritus and halite), at above. The lack of chloride accumulation at 900 and 800 ka, but the lake could have been depths between 122 and 114 m, indicate two KM-3 between 1.5 Ma and 1.45 Ma supports consistently deep with only minor overflow(s). intervals of complete desiccation in Searles basin the proposed period of desiccation, inasmuch as During the interval between 700 ka and 600 ka, during the interval dated to between 330 and the chloride would be in temporary residence in we propose at least two possible overflows of 290 ka (Unit C), although the small thickness of China or Owens Lakes. Our estimated ages (ex- Searles Lake into Panamint Lake. We also pos- playa sediments suggests only brief intervals of trapolated) of the bottoms of cores from Owens tulate overflow from Panamint Lake into Manly subaerial conditions. Between 290 ka and 150 and China Lakes are younger than this age, and Lake in Death Valley during each event because ka (Unit A+B in KM-3 core), the interbedded thus interpretations based on those cores do not there is a lack of salt in Panamint. The chloride muds and salines (stratigraphy from Searles confirm or deny this hypothesis. accumulation curve shows a major loss of chlo- Lake cores other than KM-3; Smith and others, The interval between 1.2 Ma and 1.0 Ma ride during that time (Fig. 6C), and the small 1983) appear to represent deposition in fluctuat- (Unit F in KM-3 core) was apparently a period number of salt beds in core KM-3 indicate that ing shallow lakes. The long subhorizontal slope of major overflow for the entire paleo-Owens Searles Lake was rarely very shallow at that on the chloride accumulation plot (Fig. 6C) for system. All lakes are inferred to have been at time. this interval is partially due to lack of data be- overflow levels (except possibly Lake Manly), For most of the time since 600 ka, Searles cause of KM-3 core loss. The upper salt in and as is apparent from the long subhorizontal Lake was once again the terminal sink. The Panamint Valley (175 ± 75 ka) is correlated slope in the chloride accumulation curve (Fig. abundant and sometimes-thick salt beds demon- with the overflow event starting at about 150 ka 6C), chloride was lost from the Searles waters to strate that the lake in Searles basin was fre- (lower portion of the Bottom Mud), which we downstream lakes. The deep, perennial, over- quently intermediate to small in size. Evidence propose was the last major overflow event from flowing lake in the Searles basin is recorded by from the KM-3 core and from the chloride ac- Searles in the paleo-Owens system. During the massive black and dark-green muds. cumulation curve indicates that probably there interval 100 ka to 24 ka (upper portion of the Searles Lake was again the terminus during were overflow events between 440 ka and 400 Bottom Mud, Lower Salt), the interbedded most of the interval between 1.0 Ma and 0.6 Ma ka, and 380 ka and 350 ka (Unit C in KM-3 muds and salines indicate deposition in fluctuat- (Unit D+E in KM-3 core). The chloride accu- core), and between 150 ka and 120 ka (Bottom ing shallow lakes. Evidence from the KM-3 core mulation curve (Fig. 6C) shows a subdued Mud), but there is no sedimentological evidence and the chloride accumulation curve, along with stair-step pattern, which suggests that high lake that Searles was a deep, perennial lake for long other evidence (R. Smith, 1976; G. I. Smith, 1158 JANNIK AND OTHERS

Age (Ma) that prior to about 700 ka, the period of these 2.0 1.9 1.8 1.7 1-6 1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 lake-level fluctuations was approximately 50 kyr. Subsequent to 700 ka, the major fluctuations show a longer period. The period of the ocean-water 180 fluctuations was about 40 kyr prior to the Matuyama/Brunhes reversal at about 730 ka (Watts and Hayden, 1984), and 100 kyr after it (Hays and others, 1976). These correspond to periodicities of the insolation fluctuations at high latitudes, but the shift from a 40-kyr to a 100-kyr period in the marine record at 700 ka has not been satisfactorily explained (Ruddiman and Wright, 1987). In contrast to the strong correspondence of the two records, there are some marked differences in the amplitude of certain of the fluctuations and in the presence of long-period fluctuations in the Searles record. The marine lsO curve is characterized by an almost monot- —i onous similarity in the amplitude of the individual cycles. The paleo-Owens River system *r lake-level curve, on the other hand, exhibits 3 much greater variability in the cycle amplitude ChlnaLake '77 m m Owens Lake " (Fig. 10). Smith (1984) perceived a 400-kyr period in the major hydrologic regimes indicated B • i « i « i • i » i i i • i i < » i « i ------by the history of Searles Lake, which our results I >, ' I I |I VJ ls 2.0 1.9 1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5,'0.4 0.3 0.2 ^0.1 /0. tend to confirm. The marine <5 O record does / • / // not show such a periodicity. Especially high lake phases occur at about 1.1 Ma, 620 ka, and 150 ka. The intervals separating the maxima also appear to show characteristic differences from each other (for example, the interval prior to 1.2 Ma has generally low lake levels, that between ™ 250 200 150 50 0 C Depth (m) 1.0 Ma and 0.6 Ma high levels). Evidence for a |~1 lacustrine playa/sediments [_J evaporites lacustrine mud similar periodicity at various locations around the globe has been noted by Jensen and others Figure 10. A. Composite oxygen-18 record from Williams and others (1988). B. Recon- (1986). structed lake history for the paleo-Owens River system for the past 2.0 m.y. The gray-shaded Another feature of interest in the paleo- areas in the figure show possible correlations between inferred major overflows from Searles Owens lake-level curve is the anomalous aridity Lake and the marine lsO curve. The dashed lines are drawn to the corresponding unit in the of the Holocene. The mixture of halite and KM-3 core. C. Generalized log of core KM-3, Searles Lake. Abbreviations of units are de- coarse-grained clastic sediments in the Over- scribed in Figure 2C. burden Mud is diagnostic of playa and shallow saline-lake conditions and is very distinctive. It is also virtually unique in the Searles sediment col- 1987; Benson and others, 1990; Dorn and oth- Quaternary from a mid-latitude continental set- umn. The absence of similar sediments during ers, 1990), indicate an overflow event in Searles ting in order to evaluate the correlation between nearly all earlier interpluvial periods may possi- Lake between 24 ka and 10 ka (Parting Mud). climatic changes in this location and the higher- bly result from tectonic as well as climatic fac- During much of the past 10 kyr (Upper Salt latitude ice-volume fluctuations revealed in the tors. The entire lake-level curve for the past 1.2 and Overburden Mud in KM-3 core) in the 618O of marine foraminifera. Previous investiga- m.y. seems to show a gradual trend toward in- Owens River system, there has been only tions have shown that the paleoclimatic history creasing aridity. This is similar to the trend enough runoff from the Sierra Nevada to create from the paleo-Owens River lake system exhib- toward lighter deuterium content of ground wa- a small- to moderate-sized saline lake in the its both marked similarities to, and strong differ- ters (preserved in fluid inclusions) over the past Owens basin, except for one brief Holocene ences from, the marine record (Smith, 1984). 2.0 m.y. in the Death Valley area (Winograd pluvial period. The most striking similarity is in the periodicity and others, 1985). Together with Smith and of fluctuations during some episodes. One epi- others (1983) and Winograd and others (1985), CONCLUSIONS sode (represented by Unit G of KM-3) of the we hypothesize that the trend may be attributed Searles sediments exhibits an obvious regular al- to the gradual uplift of the Sierra Nevada over One of the primary goals of this study was to ternation of evaporites and muds. The chronol- this time. Nevertheless, the marked difference obtain an independent climatic record for the ogy developed in this paper (Fig. 10B) indicates between the penultimate interpluvial period, CHRONOLOGY OF SEDIMENTATION, OWENS RIVER SYSTEM 1159 when Searles Valley contained a sizable lake of ported by National Science Foundation Grant Lee, C. H., 1912, Water resources of a part of Owens Valley, California: U.S. Geological Survey Water-Supply Paper 294, 135 p. moderate salinity, and the present part of the EAR 8313745. Liddicoat, J. C., Opdyke, N. D., and Smith, G. I., 1980, Palaeo-magnetic polarity in a 930-m core from Searles Valley, California: Nature, v. 286, Holocene, in which even the first lake (Owens no. 5768, p. 22-25. Lake) in the chain contains only a small lake, Phillips, F. M., Smith, G. I., Bentley, H. W„ Elmore, D., and Gove, H. E., 1983, dating of saline sediments: Preliminary results from Searles Lake, must be ascribed to climatic rather than tectonic REFERENCES CITED California: Science, v. 222, p. 925-927. Peng, T. H., Goddard, J. G., and Broecker, W. S., 1978, A direct comparison of changes. Clearly, the Holocene is climatically Benson, L. V., and Paillet, F. L., 1989, The use of total lake-surface area as an C-14 and Th-230 ages at Searles Lake, California: Quaternary Re- different than earlier interpluvials, with the pos- indicator of climatic change: Examples from the Lahontan Basin: Qua- search, v. 9, p. 319-329. ternary Research, v. 32, no. 3, p. 262-275. Ruddiman, W. F., and Wright, H. E., Jr., 1987, North America and adjacent sible exception of the interpluvial ending at Benson, L. V„ Currey, D. R., Dorn, R. I., Lajoie, K. R., Oviatt, C. G., Robin- oceans during the last deglaciation, in The geology of North America, son, S. W., Smith, G. 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N., 1982, Application of AMS to hydrology, in quirements by the year 2000: U.S. Geological Survey Professional Kutchera, M., ed., Second Annual Symposium on Accelerator Mass Paper 1005, p. 92-103. the previous interpluvial are supported by other Spectrometry: Argonne, Illinois, Argonne National Laboratory, p. 193. 1979, Subsurface stratigraphy and geochemistry of late Quaternary paleoenvironmental studies at geographically Bentley, H. W., Phillips, F. M., and Davis, S. N., 1986, *C1 in the terrestrial evaporites, Searles Lake, California, with a section on Radiocarbon ages environment, in Fritz, P., and Fontes, J. C., eds., Handbook of en- of stratigraphic units, by M. Stuiver and G. I. Smith: U.S- Geological distant sites (for example, Gascoyne and others, vironmental isotope geochemistry: Amsterdam, the Netherlands, El- Survey Professional Paper 1043,130 p. sevier, Volume 2Br p. 422-475. 1984, Paleohydrologic regimes in the southwestern Great Basin, 0-3.2 1981; King and Saunders, 1986). If this possibil- Btschoff, J. L., Rosenbauer, R. J., and Smith, G. I., 1985, Uranium-series dating my ago, compared with other long records of "global" climates: Qua- ity is borne out by further investigations, it will of sediments from Searles Lake, California: Documentation of dif- ternary Research, v. 22, p. 1-17. ferences between land and sea climate records: Science, v. 227, 1987, Searles Valley, California: Outcrop evidence of a Pleistocene lake imply that the Holocene is not a good model for p. 1222-1224. and its fluctuations, limnology, and climatic significance, in Hill, M. L., Dom, R. I., Jull, A.J.T., Donahue, D. J., Linick, T. W., and Toolin, L. J., 1990, ed., Centennial field guide, volume 1: Geological Society of America, reconstruction of paleoecological patterns dur- Latest Pleistocene lake shorelines and glacial chronology in the western Cordilleran Section, p. 137-142. ing previous interpluvial periods. Such differ- Basin and Range province, U.S.A.: Insights from AMS radiocarbon Smith, G. I., and Haines, D. V., 1964, Character and distribution of nonclastic dating of rock varnish and paleociimatic implications: Palaeogeography, minerals in the Searles Lake evaporite deposit, California: U.S. Geologi- ences in interpluvial climate might possibly be Palaeoclimatology, Palaeoecology, v. 78, p. 315-331. cal Survey Bulletin 118I-P, p. P1-P58. Elmore, D., and Phillips, F. M., 1987, Accelerator mass spectrometry for Smith, G. I., and Pratt, W. P., 1957, Core logs from Owens, China, Searles, and pertinent to the massive megafaunal extinctions long-lived radioisotopes: Science, v. 236, p. 543-550. Panamint Basins, California: U.S. Geological Survey Bulletin 1045-A, at the end of the Pleistocene; the aridity causing Elmore, D., Fultin, B. R., Clover, M. R., Marsden, J. R., Gove, H. E., 62 p. Naylor, H„ Purser, K. H„ Kilius, L. R„ Beukens, R. P., and Litherland, Smith, G. I., and Street-Perrott, F. A., 1983, Pluvial lakes of the western United loss of watering holes, and/or a change in flora. A. E., 1979, Analysis of 36CI in environmental water samples using an States, in Wright, H. E., Jr., gen. ed., and Porter. S. C., ed., Late- electrostatic accelerator Nature, v. 277, p. 22-25. Quatemary environments of the United States: Minneapolis, Minnesota, Haynes (1984) proposes that the aridity caused Elmore, D., Tubbs, L. E., Neuman, X. Z. Ma, Finkel, R., Nishiizumt, K., University of Minnesota Press, Volume I, chap. 10, p. 190-212. competition between already stressed mega- Bear, J., Oeschgan, H., and Andree, M., 1982. ^Cl bomb pulse Smith, G. I., Barczak, V. J., Molton, G. F., and Liddicoat, J. C., 1983, Core measured in a shallow ice core from Dye 3, Greenland: Nature, v. 300, KM-3, a surface-to-bedrock record of late Cenozoic sedimentation in fauna and humans at decreasing numbers of no. 5894, p. 735-737. Searles Valley, California: U.S. Geological Survey Professional Paper Gale, H. S., 1914, Salines in the Owens, Searles, and Panamint Basins, south- 1256,23 p. water sources. eastern California: U.S. Geological Survey Bulletin 580-L, p. 251-323. Smith, R.S.U., 1976, Late Quaternary pluvial and tectonic history of Panamint Gascoyne, M., Currant, A. R., and Lord, T., 1981, Ipswichian fauna of Victoria Valley, Inyo and San Bernardino Counties, California [Ph.D. thesis]: In summary, although comparison of lake Cave and the marine paleociimatic record: Nature, v. 294, p. 652-654. Pasadena, California, California Institute of Technology, 300 p. Halley, E., 1715, On the cause of the saltness of the ocean, and of the several Street-Perrott, F. A., and Harrison, S. P., 1985, Lake levels and climate recon- levels in the Owens River system with the deep- lakes that emit no rivers: Royal Society of London Philosophical Trans- struction, in Hecht, A. D., ed., Paleoclimate analysis and modeling: New sea curve shows some similarities, it also actions, no. 6, p. 169. York, John Wiley, chap. 7, p. 291-340. Hay, R. L„ and Guldman, S. G„ 1987, Diagenetic alteration of silicic ash in Stuiver, M., 1964, Carbon isotopic distribution and correlated chronology of shows strong and systematic differences. We be- Searles Lake, California: Clays and Clay Minerals, v. 35, no. 6, Searles Lake sediments: American Journal of Science, v. 262, no. 3, p. 449-457. p. 377-392. lieve that these differences reflect climatic proc- Haynes, C. V., 1984, Stratigraphy and late Pleistocene extinction in the United Stuiver, M., and Smith, G. I., 1979, Radiocarbon ages of stratigraphic units, in esses important at the mid-latitudes. More States, in Martin, P. S., and Klein, R. G., eds.. Quaternary extinctions: A Smith, G. I., Subsurface stratigraphy and geochemistry of late Quater- prehistoric revolution: Tucson, Arizona, The University of Arizona nary evaporites, Searles Lake, California: U.S. Geological Survey Pro- detailed investigations in the paleo-Owens sys- Press, p. 345-353. fessional Paper 1043, p. 68-73. Hays, J. D., Imbrie, J., and Shackleton, N. J., 1976, Variations in the Earth's Watts, R. G., and Hayden, M. E., 1984, A possible explanation of differences tem, and additional studies in other closed ba- orbit: Pacemaker of the ice ages: Science, v. 194, p. 1121-1132. between pre- and post-Jaramilio ice sheet growth, in Berger, A., sins, have the potential to greatly advance our Hunt, C. B„ and Mabey, D. R„ 1966, Stratigraphy and structure of Death Imbrie, J., Hans, J., Kukla, G., and Saitzmen, B., eds., Milankovitch and Valley, California: U.S. Geological Survey Professional Paper 494-A, climate: Dordrecht, The Netherlands, Reidel, part 2, p. 599-604. understanding of Quaternary climatic change in 162 p. Williams, D. F., Thunell, R. C., Tappa, E., Rio, D., and Raffi, I.. 1988. Jannik, N. O., 1989, Lake history in the paleo-Owens River system, California Chronology of the Pleistocene oxygen isotope record: 0-1.88 m.y. B.P.: the mid-latitudes. for the past 2.0 Myr based on 36CI dating of evaporites from Searles Palaeogeography, Palaeoclimatology, Palaeoecology, v. 64, p. 221-240. Lake [Ph.D. thesis]: Socorro, New Mexico, New Mexico Institute of Winograd, I. J., Szabo, B. J., Coplen, T. B., Riggs, A. C., and Kolesar, P. T„ Mining and Technology, 190 p. 1985, Two-million-year record of deuterium depletion in Great Basin ACKNOWLEDGMENTS Jensen, J.H.F., Kuijpers, A., and Troelstra, S. R., 1986, A mid-Brunhes climatic ground waters: Science, v. 227. p. 519-522. event: Long-term changes in global atmosphere and ocean circulation: Science, v. 232, p. 615-622. We thank Kerr-McGee Corporation, particu- Kaufman, R., Long, A., Bentley, H. W., and Davis, S. N., 1984, Natural chlorine isotope variations: Nature, v. 309, p. 338-340. MANUSCRIPT RECEIVED BY THE SOCIETY JUNE 7,1989 larly Gale Moulton, for access to the KM-3 core King, J. E., and Saunders, J. J., 1986, Geochelone in Illinois, and the Illinoian- REVISED MANUSCRIPT RECEIVED JANUARY 21, 1991 Sangamonian vegetation of the type region: Quaternary Research, v. 25, MANUSCRIPT ACCEPTED JANUARY 23,1991 and other Searles cores. This research was sup- p. 89-99. FINAL ILLUSTRATIONS RECEIVED MAY 17,1991

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