Pacific Section AAPG, SPE and SEPM Joint Technical Conference

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An Initial Comparison Of The Youngest Paleolake History Of Tulare Lake, CA Between Eastside And Westside Localities

Abstract

Tulare Lake, located in the central San Joaquin Valley in California, was the largest fresh water lake west of the Great Lakes prior to stream diversion in the late 19th century (Preston, 1981). The lake basin is fed by four main rivers: Kern, Tule, Kaweah, and Kings. Lake level prior to irrigation diversion was found to be related to water discharge from those rivers based on hydrologic water balance models (Atwater et al., 1986). Because of this relationship, it is possible to reconstruct the output of those rivers by studying the sediments deposited by Tulare Lake. Subsequent comparisons of Sierran discharge to sea surface temperature records from the eastern Pacific can then potentially aid in forecasting Sierran stream discharge for the next several decades. The original study by Negrini et al., (2006) analyzed Tulare Lake sediments taken from trenches along the west side of the basin back to a date of approximately 12,000 cal yr BP. The latest study by Blunt (2013), based on core was a higher resolution record from the same area and extended the timeframe back to ∼20,000 cal yr BP. This study analyses the top ∼2 m of sediments from trench TL12-01B on the Pixley National Wildlife Refuge on the southeastern side of the Tulare Lake basin. The primary methods repeat that of Blunt (2013) which includes the measurement of carbon:nitrogen ratios and total inorganic carbon (TIC) levels in the sediments. These data were used to test the findings of each study for the other side of the basin. The C:N ratio results from the eastern basin locality show relatively stable levels usually below 10, which are typical of lacustrine-sourced organic matter. The exception is a drastic increase centered at 0.1 meters to values well over 100 that are associated with the input of terrestrial organic matter often accompanying large discharge events. TIC levels vary more systematically exhibiting a gradual increasing trend from negligible values to ∼1.5% toward the present suggesting a gradual shallowing of the lake in the top meter or two of sediments, much like that observed in the sediments from the western localities. Radiocarbon dating of an articulated Anodonta shell found at 0.2 meters from the top of the trench yielded an age of 275±30 14C years B.P. The associated calibrated age places the deposition of the sediments containing the shell between ∼1670 and 1520 A.D.. Thus the age of the Sierran discharge event inferred from the C:N spike in the eastside Tulare Lake sediments immediately overlying the Anodonta shell is consistent with the decade-long megaflood of 1605 A.D. detected in the sediments of the Santa Barbara Basin by Schimmelman et al. (2003).