EARLY PLEISTOCENE PLUVIAL LAKE ENVIRONMENTS OF THE TECOPA BASIN, SOUTHEASTERN CALIFORNIA, USA

Paleo-Lake Tecopa was one of many pluvial lakes that once existed in the southern Great Basin in response to climatic oscillations but is unique in that it exhibits some of the oldest lake phases in the region. Most well-studied paleolake deposits in the southern Great Basin are of late Pleistocene-Holocene age, but few have continuous records extending to the early Pleistocene, as exhibited by the Lake Tecopa beds. The oldest deposits contain the 2.1 Ma Huckleberry Ridge (HR) ash bed, which previous studies indicate to be enclosed in shallow-lake deposits within an interval of mostly playa deposits. During 2020 and 2021, ~80 total meters of early Pleistocene stratigraphic sections were measured in the southeastern part of the Lake Tecopa basin, and detailed geologic mapping was completed. Field observations reveal as much as 11 meters of open-water lacustrine mudstone below the HR ash bed, north of the area where shallow lacustrine facies were previously described. Calculated sedimentation rates (0.032 to 0.024 m/ky) are used estimate the oldest exposed deposits to be ~2.4 to 2.6 Ma, with continuous lacustrine expression until at least 2.0 Ma. Open-water lacustrine facies during the early Pleistocene were likely concentrated in the north-central part of the basin. Evidence of syndepositional faulting and soft-sedimentary deformation shows potential for changed accommodation and basin geometry during the early Pleistocene. A long-lived lake during the early Pleistocene within the Death Valley region is anomalous and challenges existing models of regional paleoclimate. Analysis of volcanic glass chemistry for additional age control is underway, and X-ray diffraction analysis of authigenic minerals and zeolites within the mudstones and ash beds will help refine lake longevity and geochemical conditions.