Sediment Provenance and Paleoenvironmental Change since 25 ka in Western North America: Constrained by the Evolution of Clay Minerals of Tulare Lake, California.

• Main Author: Pyles, Christine G.
• Other Authors: Guo, Junhua, Negrini, Rob
• Format: Master Thesis
• Language: English
• Published: California State University, Bakersfield 2016
• Subjects: Mineralogy; Greenland; Greenland ice cores
• Online Access: https://hdl.handle.net/20.500.12680/4j03d223f

The bulk and clay mineralogy of sediments from Tulare Lake recovered from core TL05-4A were examined to identify sediment sources of the terrigenous lake sediments and to interpret paleoenvironmental change since the most recent glacial maximum (~25 ka) in southern California. Bulk assemblages are composed mainly of composite clay followed by quartz, feldspar/plagioclase, and calcite. Gypsum and bassanite are also identified. The clay mineral fraction consists of smectite, illite, kaolinite, and chlorite. Weathering proxies indicate physical weathering mainly dominated in the source areas since 25 ka. The Late Pleistocene is characterized by the Tioga glaciation and the climate was mainly cool and dry, however five warming events roughly equally spaced between 25 and 21 ka are recognized by smectite/illite ratios. High smectite/illite ratios indicate a limited supply of runoff and low clay with higher quartz and feldspar contents indicate a shallow lake. During the Pleistocene-Holocene transition there is great variability in climate oscillations with the glacial advances of the Tioga 3 and 4 glaciations. This transition may have resulted in the decrease of the smectite/illite ratio perhaps indicating an increased supply of illite-rich sediments from the glaciated high elevations in the Sierra Nevada. During the Holocene, two warm intervals from ~ 10.7 – 9.4 ka and ~ 8.2 – 5.2 ka are suggested from the high sulfate intervals indicating a dry/warm environment. These warm intervals are concurrent with the maximum temperature of the middle Holocene. A noticeable decrease of clay minerals occurred at 8.2 ka which is possibly due to glacial advance associated with the globally recognized 8.2 ka event first identified in climate records from Greenland ice cores. Low smectite/illite ratio indicates increased lake levels following the 8.2 to 5.2 ka warm interval. Due to low resolution sampling slight changes in climate were not detected in the clay mineral record after 5 ka.