GRAIN SIZE ANALYSIS OF SEDIMENT CORE SAMPLES FROM SEARLES LAKE, CALIFORNIA: STEPS TOWARD INTERPRETING LAKE EXPANSION AND CONTRACTION IN THE DESERT SOUTHWEST

Extreme drought in southern California has the potential to impact ecosystems and millions of people, but the climate mechanisms that control regional water availability are poorly understood. It is important to understand the causes of extreme droughts so they can be better predicted in the future. This is challenging because of complicated physical relationships within the climate system and because of a combination of natural and anthropogenic causes. One way to determine past climate events is through the use of lake sediment cores. The sediment that accumulates in lakes is sensitive to water availability. Grain size analysis can indicate changes in lake levels because clay deposition is often a result of deep water and silts and sands indicate shallower water or dried up lake floor where sediment can be blown across the lake bed or transported by small ephemeral streams. Together, these processes provide a physical link between sediment grain size and past lake water balances. One such lake that contains an amazing history is Searles Lake, located in southern California. The lake sediments contain alternating mud and evaporite layers which correspond to wetter and dryer conditions at Searles Lake over the last ~150,000 years. Today, the lake is mostly evaporated. Here, we examine the grain sizes of samples from mud and evaporite layers from drill cuttings between the interval of 350 feet to 440 feet to examine the correspondence of grain size and physical stratigraphy. Our initial grain size analysis of mostly evaporites, interpreted as dryer climate, show higher percentages of larger grain sizes compared to the mud samples, mostly clays which correspond with deeper lake conditions. The grain size analysis from Searles Lake provides an initial framework for further study of the cycles of drought in the desert southwest.