CLUMPED ISOTOPE PALEOTHERMOMETRY AND PALEOHYDROLOGIC ESTIMATES FOR THE HOLOCENE FROM MULTIPLE LACUSTRINE CARBONATE SOURCES IN THE PAHRANAGAT VALLEY, NEVADA

Recent work has shown that clumped isotopes in lacustrine microbialites, gastropods, and micrites can be used to constrain seasonal temperatures, and through the use of transfer functions, calculate mean annual air temperatures. Within a hydrologic modeling framework, these data can be used to reconstruct past evaporation and precipitation rates (Santi et al., 2020). Therefore, in order to better constrain the climatic history of the southern Great Basin, we applied clumped isotope paleothermometry (denoted as Δ₄₇) to carbonate samples spanning over 13,000 years from the Lower Pahranagat Lake, a shallow, highly alkaline lake in southern Nevada.

Carbonate samples used in this study include micrite and gastropod shells from Theissen et al. (2019), as well as microbialite samples collected from the eastern margin of the lake. Radiocarbon dating indicates the lake core carbonates used in this study span ~6,000 years. Estimates of lake water temperature for the micrite samples range from 0.4–23.3^oC (±3.50^oC). During the middle Holocene (~6,000-4,000 cal yr BP), micrite data show that temperatures were warmer, consistent with previous findings across the Great Basin during this interval. These data show that during the late Holocene (~4,000-1,000 cal yr BP), cooler conditions followed, returning to warmer conditions ~600 cal yr BP.

Radiocarbon dating of microbialite samples extend the temperature record for the Lower Pahranagat Lake back >13,000 years, with Δ₄₇ -derived estimates ranging between 15.6-20.6^oC (± 4.05^oC). The microbialite data show consistently warm temperatures throughout the record, with the warmest conditions occurring around ~13,000 cal yr BP. The warmer temperatures reflected in microbialite samples have two possible interpretations. If the microbialite was formed in shallow lake waters along a paleoshoreline, the results represent lake water temperatures (as with the lake core carbonates). Alternatively, if it was formed at the site of an ancient spring discharge along the lake margin, the results represent varying spring water temperatures. This presentation will discuss results in more detail, and also present additional calculations of climatic and hydrologic parameters.