Relative paleointensity of geomagnetic field during the last 9000 years estimated by the pseudo Thellier method from the bottom sediments of Lake Shira, Northern Khakassia

Abstract

The results of rock magnetic studies and determination of relative paleointensity from sediments of Lake Shira, Khakassia, are presented. The NRMcarrier minerals were determined from the hysteresis parameters, thermomagnetic and X-ray diffraction (XRD) analyses. The age of the sediments was determined by radiocarbon dating. According to these measurements, the column spans about 9100 years. The qualitative determinations of relative paleointensity were obtained from linear segments of the pseudo-Arai–Nagata diagrams. The quality of the determinations was evaluated by the following criteria: number of points used to calculate the slope; quality criterion (q), fraction ofNRMdestroyed in the paleointensity determination interval, and relative paleointensity determination error (σ). According to rock magnetic studies and XRD analysis, the magnetization carriers are represented mainly by single-domain and pseudo-single-domain magnetite and hematite. The comparison of the obtained series of relative paleointensity data with both the model paleointensity values calculated for Shira coordinates from various models (CALS10K.1b [Korte et al., 2011], PFM9k.1 [Nilsson et al., 2014], HFM.OL1.AL1, CALS10k.2 ARCH10k.1 [Constable et al., 2016]) and with absolute paleointensity, as well as the aggregate results of the studies on sedimentary and igneous rocks and on archaeomagnetic objects has shown that these data are in good agreement with each other and have common trends. This provides a rationale for using this methodology to determine paleointensity from sediments of modern lakes using the pseudo-Thellier method.