LATE QUATERNARY GLACIATION OF THE NORTHERN GREAT BASIN: CHRONOLOGY, CLIMATE, AND KEY QUESTIONS (Invited Presentation)

Evidence of late Quaternary mountain glaciation is widespread across the northern Great Basin of southwestern North America, representing an important record of high amplitude climatic change over orbital to sub-millennial timescales. G. Osborn played an important role in developing the glacial record in this region by documenting the distribution and morphology of glacial features, paving the way for subsequent work on glacial chronology. Here, we report on (1) the cosmogenic chronology of glacial deposits in eight ranges spanning >800 km across the entire northern Great Basin and (2) inferences of Quaternary climate change based on these and other records. Results indicate that the penultimate glaciation is temporally aligned with marine oxygen-isotope stage (MIS) 6 in the Sierra Nevada, Ruby, and Wasatch Ranges, which is consistent with mountain glacial chronologies elsewhere in southwestern North America and suggests that regional glaciation was in step with orbital forcing and global ice volume change. Deposits of the last glaciation (MIS-2) are better preserved than MIS-6 features, and sequences of dated moraines reveal some temporal structure within the overall glaciation. Terminal moraines were last occupied by ice during the latter part of the Last Glacial Maximum (LGM), ca. 22-19 ka. In many valleys, glaciers readvanced to (or persisted at) maximum or near-maximum lengths at 19-16 ka. The earlier LGM advance occurred while most Great Basin pluvial lakes were below their highstand shorelines, suggesting that regional climate was cold but dry, favoring glacier maxima but limiting the expansion of lakes. In contrast, later ice advances overlapped in time with highstands of most pluvial lakes, suggesting a climatic shift to conditions that augmented mass budgets of both glaciers and lakes. Although the chronology of the last glaciation is broadly consistent across the northern Great Basin, the causes and magnitudes of millennial-scale climate variability during the LGM and last glacial-interglacial transition remain unresolved. The glacial record from this region should be further developed to better understand the timing and pace of subsequent ice retreat in order to clarify temperature and precipitation changes during this key time interval.