Paleoenvironmental reconstruction of a glacial-age sediment core from Baldwin Lake, Southern California: Is there a climate connection

A sedimentological and high-resolution petrographic analysis was conducted on a glacial-age (20,000-65,000 cal yr BP) sediment core from Baldwin Lake, Southern California. The results of this research represent the most comprehensive, terrestrial climate record from Southern California during the last glacial to date. These results are used to characterize the different sediment types and to investigate the difference in depositional processes and environment between the core's three predominant sediment types: massive, semi-laminated, and laminated sediments. Massive sediments are commonly associated with a blocky texture and/or desiccation cracks, are organic-poor, have high magnetic susceptibility values, and are coarser grained. Thin-sections from massive sediments reveal a homogenous sediment fabric. Sub-centimeter-scale laminated and centimeter-scale semi-laminated sediments are generally organic-rich, have low magnetic susceptibility values, and are finer grained. Thin-sections from laminated and semi-laminated sediments reveal diffuse sub-millimeter- to millimeter-scale laminae. These data are used to define four sediment facies, each related to specific depositional processes and environment: (1) a playa lake; (2) a perennial shallow lake; (3) an intermediate lake with variable lake level; and, (4) a perennial deep lake. Comparison of Baldwin Lake facies to long term winter-summer insolation curves shows evidence for orbital-time scale variability. Winter-summer isolation is linked to changes in winter storm activity and the occasional influence of the North American monsoon. At centennial-to millennial-time scales, Baldwin lake sediment proxies show a notable correspondence to the GISP2 delta18O ice stadial-interstadial record. This multi-proxy study will provide a baseline sedimentological and climatological study for comparison to similar arid environment basins.