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.

High-resolution environmental magnetic study of a Holocene sedimentary record from Zaca Lake, California

“…Early paleomagnetic studies of these rocks in Southern California (Hornafius, 1984(Hornafius, , 1994 identified magnetite as the primary detrital magnetic phase. Our rock magnetic experiments (Lund and Platzman, 2016) both confirmed the presence of magnetite and identified a remanence carrying iron sulfide phase, presumably greigite (Fe 1-X S) in varying proportions, throughout the sediment column. Temperature dependence of low field susceptibility (Lund and Platzman, 2016) and thermal demagnetization of threecomponent composite IRM (Figure 3a-e) show evidence for the presence of these two magnetic phases in most samples.…”

“…Our rock magnetic experiments (Lund and Platzman, 2016) both confirmed the presence of magnetite and identified a remanence carrying iron sulfide phase, presumably greigite (Fe 1-X S) in varying proportions, throughout the sediment column. Temperature dependence of low field susceptibility (Lund and Platzman, 2016) and thermal demagnetization of threecomponent composite IRM (Figure 3a-e) show evidence for the presence of these two magnetic phases in most samples. In the IRM experiments, the remanent magnetization was found to reside predominantly in the low and medium coercivity fractions, which have similar unblocking characteristics.…”

“…Several radiocarbon dates from this interval were discounted in the earlier studies as being anomalously young and the possibility of instantaneous deposition was discussed (Dingemans et al, 2014). Correlatable PSV data obtained from this interval (Lund and Platzman, 2016), however, corroborate the inference that it accumulated over a period of time and likely reflects a change in local hydrologic conditions. Our magnetic chronology suggests that sedimentation rates were measurably slower during this interval than subsequent time intervals decreasing from an average of 0.3 cm/yr to 0.2 cm/yr corroborating the suggestion of a regime shift at this time (Kirby et al, 2014).…”

“…The age model for core Z-1 C (Figure 2) used in this study is based on a high-resolution paleomagnetic secular variation (PSV) record (Lund and Platzman, 2016). This record has strong serial correlation and a pattern of variability that matches 15 other published PSV records from western North America with radiocarbon dated features.…”

High‐resolution chronology of sediment below CCD based on Holocene paleomagnetic secular variations in the Tohoku‐oki earthquake rupture zone

“…Moreover, such efforts have been summarized as PSV reference curves [ Snowball et al ., ; St‐Onge et al ., ; Turner and Thompson , ]. Because their continuous records are believed to be robust regionally, they have been applied to constrain the age model of sediments, and to correlate site data in lake and marine environments [ Henkel et al ., ; Lund and Platzman , ; Ólafsdóttir et al ., ; Sagnotti et al ., ; Stoner et al ., ; Yang et al ., ; Usapkar et al ., ]. This record is unique for stratigraphic correlations and for use as a dating tool to synchronize the local environments simultaneously to a detailed scale.…”