Paper No. 10-4
Presentation Time: 5:10 PM
QUANTIFYING THE GRAINSIZE OF CLASTICS IN LOWER SALT UNIT FROM SEARLES LAKE, CA: STEPS TOWARDS UNDERSTANDING PALEOCLIMATIC CHANGES
Today, drought conditions are common in the Southwestern United States. However, this has not always been the case. Paleoclimate archives indicate many fluctuations from wet to dry conditions on time scales from centuries to millennia. The causes are well hypothesized, but distinguishing them and characterizing the spatial and temporal patterns of moisture balances in the larger region is best done with a network of continuous and high resolution paleoclimate records. One such location is Searles Lake, CA which is well known for containing a long and near complete record of deposition spanning the last ~3 Ma. In 2017, a new sediment core was collected from the surface of the dry lakebed to a depth of 76 meters. The core contains alternating layers of salt (evaporite minerals) and mud which generally indicate dry and wet conditions over the last ~150 ka. Prior work from Smith et al., 1979 and 2009 established the general stratigraphy of the basin. Here, we present grainsize data from six mud layers contained within the Lower Salt (~25-38 m depth). Samples were pretreated to disaggregate and isolate clastic grains and grain size was measured using a Beckman Coulter LS 13 320 particle size analyzer. Of the more than 100 samples analyzed, the dominant grain sizes range from 0.04 to 200µm. Within this range, we observe several characteristic grain size distributions within the units. From bottom to top the distributions are left skewed become more right skewed and then shift back to a left skew distribution. This implies coarsening and fining patterns. Interpreting these data with other pilot data that suggest finer grain sizes occur during wetter conditions and coarser grainsizes are found during dryer conditions. Our measurements, suggest fluctuations in lake levels occurred within the muds, indicating more variability then just the dominant alternations of salt and mud (dry and wet). Future work will include expansion of the grainsize record to the salt units and deeper in the stratigraphy. These data will be combined with other proxy data to provide a detailed depositional and climate history of the basin.