PRELIMINARY STRATIGRAPHY AND CHRONOLOGY OF CONVICT LAKE (CA), EASTERN SIERRA NEVADA

Situated in California’s Sherwin Range behind a series of prominent moraines, Convict Lake is among the most visually striking glacial lakes in the eastern Sierra Nevada. The history of Convict Lake is not well known, but its sub-alpine location, open hydrology, and bathymetry hint at a late Quaternary sedimentary record that may be amenable for paleoenvironmental reconstruction. Here, we report initial results from a sediment coring and seismic profiling expedition completed on Convict Lake in 2018. High-resolution CHIRP seismic profiles were used to map the distribution of coarse and fine-grained facies on the lake floor, and identify coring targets with relatively intact stratigraphic sections. A percussion piston corer was used to raise a ~9.5 m long core from the lake, which was analyzed for lithofacies, physical properties, and radiocarbon chronology. The lower portion of the core consists of dense green muddy sands, silts, and diamicton that were likely produced by glacial activity. The upper portion of the core consists of black-dark grey, massive to banded muds with occasional beds of coarse siliciclastic detritus or tephra. These muds likely reflect lacustrine deposition with periodic influences from gravity flows and volcanic eruptions on deepwater sedimentation. Terrestrial plant macrofossils were common in the upper muddy portion of the core, and initial radiocarbon dates suggest that a lake was present in the basin by ~9.5-9.3 cal ka. Density and p-wave velocity measurements provide the opportunity to tie the core to the seismic grid and develop an improved spatial perspective on the basin’s physical stratigraphy.