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X-Ray diffraction of lacustrine minerals as an indicator of Late Pleistocene and Holocene Paleoclimate, Tulare Lake, California
Tulare Lake, CA, is the terminus of several major rivers fed by Sierra Nevada stream discharge. Over the last several decades, the study of Tulare Lake sediments has established the climate history for the Pleistocene and Holocene. In this study, Late Pleistocene to Late Holocene sediments were analyzed with an x-ray diffractometer, and bulk and clay mineral variations were investigated. The results showed strong correlations to the previously documented climate records. Larger amounts of Sierran discharge throughout the Late Pleistocene and Holocene is observed by increased weathering of illites and the supply of greater proportions of detrital minerals. During the late Pleistocene Bølling- Allerød interglacial period, glacial melt water transported high amounts of coarse, illite-enriched, weathered granitic sediments to Tulare Lake, which reduced the bulk clay-size fraction and the smectite:illite ratios. Frequent monsoonal storms during the Holocene Thermal Maximum at 8 cal ka BP induced high-stand lake levels and an increase in total clay deposition. The frequency of storms declined during the late Holocene because of decreasing summer and increasing winter insolation. This resulted in low-stand lake levels, slower sedimentation rates, a decrease in smectite:illite ratios, and an increase in calcite precipitation.
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