Well‐dated lacustrine records are essential to establish the timing and drivers of regional hydroclimate change. Searles Basin, California, records the depositional history of a fluctuating saline‐alkaline lake in the terminal basin of the Owens River system draining the eastern Sierra Nevada. Here, we establish a U‐Th chronology for the ∼76‐m‐long SLAPP‐SLRS17 core collected in 2017 based on dating of evaporite minerals. Ninety‐eight dated samples comprising nine different minerals were evaluated based on stratigraphic, mineralogic, textural, chemical, and reproducibility criteria. After the application of these criteria, a total of 37 dated samples remained as constraints for the age model. A lack of dateable minerals between 145 and 110 ka left the age model unconstrained over the penultimate glacial termination (Termination II). We thus established a tie point between plant wax δD values in the core and a nearby speleothem δ18O record at the beginning of the Last Interglacial. We construct a Bayesian age model allowing stratigraphy to inform sedimentation rate inflections. We find that the >210 ka SLAPP‐SRLS17 record contains five major units that correspond with prior work. The new dating is broadly consistent with previous efforts but provides more precise age estimates and enables a detailed evaluation of evaporite depositional history. We also offer a substantial revision of the age of the Bottom Mud‐Mixed Layer contact, shifting it from ∼130 ka to 178 ± 3 ka. The new U‐Th chronology documents the timing of mud and salt layers and lays the foundation for climate reconstructions.
- NSF-PAR ID:
- 10281284
- Date Published:
- Journal Name:
- GSA Bulletin
- ISSN:
- 0016-7606
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Ancient lake deposits in the Mojave Desert indicate that the water cycle in this currently dry place was radically different under past climates. Here we revisit a 700 m core drilled 55 years ago from Searles Valley, California, that recovered evidence for a lacustrine phase during the late Pliocene. We update the paleomagnetic age model and extract new biomarker evidence for climatic conditions from lacustrine deposits (3.373–2.706 Ma). The MBT′5Metemperature proxy detects present‐day conditions (21 ± 3°C,
n = 2) initially, followed by warmer‐than‐present conditions (25 ± 3°C,n = 17) starting at 3.268 and ending at 2.734 Ma. Bacterial and archeal biomarkers reveal lake salinity increased after 3.268 Ma likely reflecting increased evaporation in response to higher temperatures. The δ13C values of plant waxes (−30.7 ± 1.4‰,n = 28) are consistent with local C3taxa, likely expanded conifer woodlands during the pluvial with less C4than the Pleistocene. δD values (−174 ± 5‰,n = 25) of plant waxes indicate precipitation δD values (−89 ± 5‰,n = 25) in the late Pliocene are within the same range as the late Pleistocene precipitation δD. Microbial biomarkers identify a deep, freshwater lake and a cooling that corresponds to the onset of major Northern Hemisphere glaciation at marine isotope stage marine isotope stages M2 (3.3 Ma). A more saline lake persisted for ∼0.6 Ma across the subsequent warmth of the late Pliocene (3.268–2.734 Ma) before the lake desiccated at the Pleistocene intensification of Northern Hemisphere Glaciation. -
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Abstract. The use of the climatic anomaly known as the “4.2 ka event” as thestratigraphic division between the middle and late Holocene has prompteddebate over its impact, geographic pattern, and significance. The anomalyhas primarily been described as abrupt drying in the Northern Hemisphere atca. 4 ka (ka, thousands of years before present), but evidence of thehydroclimate change is inconsistent among sites both globally and withinNorth America. Climate records from the southern Rocky Mountains demonstratethe challenge with diagnosing the extent and severity of the anomaly.Dune-field chronologies and a pollen record in southeastern Wyoming revealseveral centuries of low moisture at around 4.2 ka, and prominent low standsin lakes in Colorado suggest the drought was unique amid Holocenevariability, but detailed carbonate oxygen isotope (δ18Ocarb) records from Colorado do not record drought at the sametime. We find new evidence from δ18Ocarb in a smallmountain lake in southeastern Wyoming of an abrupt reduction in effectivemoisture or snowpack from approximately 4.2–4 ka, which coincides in timewith the other evidence of regional drying from the southern Rocky Mountainsand the western Great Plains. We find that the δ18Ocarb inour record may reflect cool-season inputs into the lake, which do not appearto track the strong enrichment of heavy oxygen by evaporation during summermonths today. The modern relationship differs from some widely appliedconceptual models of lake–isotope systems and may indicate reduced winterprecipitation rather than enhanced evaporation at ca. 4.2 ka.Inconsistencies among the North American records, particularly in δ18Ocarb trends, thus show that site-specific factors can preventidentification of the patterns of multi-century drought. However, theprominence of the drought at ca. 4 ka among a growing number of sites in theNorth American interior suggests it was a regionally substantial climateevent amid other Holocene variability.more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1130/B35857.1
