T98 Long Records of Paleoclimate in the Southern Deserts of North America

Monday, 29 October 2007
1:30 PM - 5:30 PM

LATE QUATERNARY PALEOCLIMATE HISTORY BASED ON TWO LAKE CORES FROM THE TULARE LAKE BASIN, KINGS COUNTY, CA: PRELIMINARY RESULTS

Paper number: T98-16
Program: Technical Sessions
Time: 5:15 PM – 5:30 PM

Authors

Abstract

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.