2007 GSA Denver Annual Meeting (28–31 October 2007)

Paper No. 14
Presentation Time: 5:15 PM


PALACIOS-FEST, Manuel R.1, NEGRINI, Robert M.2, BARON, Dirk2 and SCHNEIDER, Christine L.3, (1)Terra Nostra Earth Sciences Research, LLC, P.O. Box 37195, Tucson, AZ 85740-7195, (2)Department of Physics and Geology, California State University, Bakersfield, 62 SCI, 9001 Stockdale Highway, Bakersfield, CA 93311, (3)Department of Geology, University of California, Davis, One Shields Avenue, Davis, CA 95616, mrpalacios@tnesr.com

During the summer of 2005, two 15 m cores were collected from the west side of the Tulare Lake basin near Kettleman City, CA. One core was taken adjacent to a 2.5 m deep trench excavated into the stratigraphy lakeward of a prominent highstand shoreline informally named the Rambla shoreline. The upper part of this core replicated the stratigraphy from this trench including several lacustrine units indicative of lake-level variations during the Holocene. The stratigraphy of the lower part of the core consists of red bed alluvial fan sediments including a coarse-grained layer containing redeposited Tertiary marine fossils (e.g., echinoderms and molluscs) from the Kettleman Hills.

The second core was taken from a site transitional between the highstand shoreline and depocenter. Radiocarbon dates on bulk sediments containing micron-scale charcoal fragments suggest a sedimentation rate such that 60,000 years may be represented by the 15 m deep core. Ostracodes were scarce in the lake plain core, but four different species were found (Cyprinotus glaucus, Limnocythere paraornata, Cyprideis beaconensis, Candona patzcuaro). The presence of L. paraornata at a core depth of 6.5 m indicates that Tulare Lake water was dilute (<800 ppm TDS) sometime prior to 20,000 yr B.P. Magnetic susceptibility from the base upward to a depth of ~4.5 m in the lake-plain core varied with a peak-to-peak amplitude of 100x10-6 cgs units around a mean value of 150x10-6 cgs units. Between 4.5 m and 1 m depth susceptibility was extremely low, increasing in the uppermost meter to 50-75x10-6 cgs units. L. paraornata was found in sediments with a mean susceptibility of 150x10-6 cgs units suggesting that fresh water environments were consistent with higher values of susceptibility. If this hypothesis is correct, then a susceptibility high between 5 and 6 m may be a signature of a deep lake during the most recent glacial maximum.