Results of the Paleomagnetic analysis and the dating of the BZK0402 core
Magnetic stratigraphy samples were collected for precise dating at depths within the BZK0402 core (30°59'29''N, 118°46'31''E). Oriented block samples were generally obtained at 0.2 m intervals, although this was dependent on core recovery (overall recovery was 94.7%), resulting in some sampling intervals being as large as 0.4–0.5 m. Samples were taken by pushing a hollow non-magnetic cube directly into halved unconsolidated sediment cores. Semi-consolidated sediments were initially carefully cut using a thin stainless-steel spatula before the plastic sampling cubes were pressed into the halved core. A total of 40 samples for Alternating Field (AF) demagnetization analysis were obtained during this study. Paleomagnetic measurements were performed on a 2G-755R Superconducting Rock Magnetometer in the Paleomagnetic and Rock Magnetism Laboratory of the Institute of Earth Environment, Chinese Academy of Sciences, Xi’an, China. Sample processing and analysis was undertaken in a magnetically shielded environment and alternating demagnetization specimens were directly measured using a 2G-755 Superconducting device. The measurements were performed in 15 steps at 0, 50, 80, 100, 120, 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, and 800 Gauss for systematic demagnetization. Paleomagnetic demagnetization results were evaluated using orthogonal diagrams and principal component directions were computed using a least-squares fitting technique employing at least three successive data points that define a linear trend directed clearly towards the origin of the orthogonal plot. All sample measurements and processing was undertaken using the PaleoMag 3.1 software package. Three samples were obtained from the BZK0402 core. These samples were dated using AMS 14C dating at the Xi'an Accelerator Mass Spectrometry Center, Xi’an, China. The results of the Paleomagnetic analysis and the radiocarbon dating of the BZK0402 core provide evidence of the Gothenburg geomagnetic excursion at depths of 6.5–7.2 m, indicating that this paleo-lake records a high sedimentation rate.