PRELIMINARY STRATIGRAPHY AND 14C CHRONOLOGY AT CONVICT LAKE (EASTERN SIERRA NEVADA)

The Sierra Nevada Range serves as California’s headwaters, supplying drinking water to >23 million people, as well as ~75% of the freshwater used for agriculture and hydropower in the Sacramento-San Joaquin delta. Climate change threatens to alter the hydrology of the Sierra Nevada Range in complex ways that are not fully understood. Long, well-dated lake sediment records from the eastern Sierra Nevada region may prove valuable for learning more about how mountain hydroclimate and ecology have changed in the late Quaternary, but many of these lakes are understudied from a paleolimnological perspective. Convict Lake, for example, is situated behind an exceptionally well-preserved chronosequence of Pleistocene-aged terminal moraines, yet little is known about the environmental history of the Convict Creek valley or the surrounding Sherwin Range since the last deglaciation. We conducted a stratigraphic analysis of Convict Lake (Mono County, CA) using CHIRP seismic reflection and a radiocarbon-dated sediment core to address this knowledge gap. Preliminary analysis of seismic profiles reveals three units within the basin fill that are separated by chronostratigraphically significant surfaces defined by reflection truncations (below) and onlap (above). These data suggest that lake level changes help to shape the stratigraphy of the basin. A relatively long (~9.5 m) percussion piston core was retrieved through conformable strata in Convict Lake’s deepwater depocenter. Numerous plant macrofossils were present in the strata, and 14 horizons were radiocarbon dated using these materials. The core is characterized by variability in facies (lacustrine silts, tephras, gravity flow deposits, glacial outwash, and till), as well physical properties, geochemistry, and pollen assemblages. Preliminary results indicate important stratal transitions in the late Pleistocene, as well as in the late Holocene, driven by environmental changes.