Paleomagnetic Secular Variation and Environmental Magnetism of Holocene-aged Sediments from Tulare Lake, CA

Abstract:

The lake-level record from Tulare Lake, CA has been shown to provide valuable constraints on late Pleistocene and Holocene channelized runoff from the Sierra Nevada mountain range into the San Joaquin Valley of California, one of the world’s most prolific agricultural centers. This project focuses on the use of magnetic properties of the Tulare Lake sediments in order to test previous results by dating the sediments and determining the relative lake level at the time of deposition. Shallowing lake conditions were identified leading up to a prominent unconformity from magnetic mineralogy and grain size indicators, primarily decreasing ARM/IRM and S-Ratio values suggesting coarser grain sizes and more oxidizing conditions. Approximately half of the samples possessed well-behaved paleomagnetic directions suitable for paleomagnetic secular variation dating. The results indicate that the sediments below the unconformity were deposited approximately 7600-6700 ¹⁴C years ago (~7600 to 8500 cal yr B.P.), and the sediments above the unconformity were deposited approximately 2200-500 ¹⁴C years ago. The ages of the corresponding sediments are consistent with the time intervals during which lake level was predicted to be above the elevation of the Poso Canal site before and after a mid-Holocene regression.