Paleomagnetic chronostratigraphy of late Holocene Zaca Lake, California

Abstract

We have developed a paleomagnetic secular variation (PSV) record from Zaca Lake, California, that spans the last ~3200 years. The record is derived from detailed (2 cm) sampling of core 09-1C, which is 873 cm in length. The paleomagnetic remanence is carried jointly by magnetite and greigite. The greigite appears to form in the anoxic bottom water of the lake and/or at the sediment/water interface. The paleomagnetic remanence has a very simple characteristic remanence, which demagnetizes straight to the origin between ~10 and 80 mT. This remanence has strong serial correlation and a pattern of variability that strongly matches 15 other published PSV records from Western North America. In all, 23 radiocarbon-dated PSV features, which were identified in the core, provide an independent timescale for dating the Zaca Lake core and an independent means of correlating Zaca Lake sediments to other Holocene lakes of the Western United States. We have also compared our paleomagnetic chronology with a previously published radiocarbon-based chronology from Zaca Lake (Feakins et al., 2014; Kirby et al., 2014). Our chronology is not significantly different from the radiocarbon-based chronology for the last 2000 years. However, the radiocarbon dates appear to be anomalously young in the older part of the lake record where correlatable PSV features suggest ages that are ~300–500 years older than the radiocarbon dates. Our analysis suggests that the PSV feature ages are a better estimator of lake sediment age in this interval.