A >200 ka U-Th Based Chronology From Lacustrine Evaporites, Searles Lake, CA

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 similar to 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 dD values in the core and a nearby speleothem delta O-18 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 similar to 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. Plain Language Summary Searles Lake, California, is currently a dry saltpan; however, in the past, it was a large and deep lake (>200 m). Lake levels have varied with changes in climate. These changes influenced the sediments deposited. Thus, changes in the lake sediments can be applied to understand the past environments of the region. Here, we developed a chronology for a 76-m-long sediment core using isotopic dating methods. The lake sediments contain many different minerals which can be dated. However, some of these minerals formed after the lake sediments were deposited and others have been chemically altered in the time since their formation. We developed criteria for the selection of samples that are the most likely to reflect the age of sediment deposition. We used the selected ages along with statistical modeling to determine the ages of the sediments with depth. We find that the core contains a record that spans over 200,000 years, including the last two glacial cycles. The age model presented here lays the foundation for the exploration of how past climate changes impacted water availability and vegetation in southeastern California.