APPLYING URANIUM-SERIES ISOTOPE GEOCHEMISTRY AND GEOCHRONOLOGY TO GREAT BASIN PLEISTOCENE PALEOHYDROLOGY

OSF Preprints
Daniel Enrique Ibarra

Abstract

The widespread lake systems of the Basin and Range during the late Pleistocene indicate substantially greater moisture availability during glacial periods relative to modern. To determine the hydrography of the most recent lake cycle, we dated shoreline tufa deposits from wave-cut lake terraces in Surprise Valley, California. The lake hydrograph is constrained by 230Th-U ages on 22 tufa samples paired with 15 radiocarbon ages. This new lake hydrograph places the highest lake level 176 m above the present- day playa at >15.23 ± 0.36 ka cal BP (14C age). During the Last Glacial Maximum (LGM, ~19 to 26 ka), Lake Surprise stood at moderate levels, 65 to 99 m above modern playa. Temporally, the Lake Surprise highstand slightly postdates the Lake Lahontan highstand and corresponds to several post-LGM highstands and stillstands of smaller lake systems farther east. To further evaluate climatic forcings associated with lake-level changes, we use an oxygen isotope mass balance model combined with an analysis of predictions from the Paleoclimate Model Intercomparison Project 3 (PMIP3) climate model ensemble. Our isotope mass balance model predicts minimal precipitation increases of only 2.5 to 18.2% (average = 9.5%) during the LGM rel...Continue Reading

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