Milankovitch cycles recorded by the Late Permian volcanic ash layers in southwestern China

Abstract

The volcanic activity during the Cenozoic is thought to be forced by Earth's orbit, as it exhibits the Milankovitch cycle. However, the pattern of volcanic activity before the Cenozoic is still unclear. In this study, we studied the volcanic ash-bearing layers preserved in Upper Permian in Southwestern China and analyzed the cycle of volcanic activity from Emeishan Large Igneous Province (ELIP) during the waning stage of Emeishan mantle plume activity. Mineralogy, geochemistry, and gamma-ray (GR) data were used for high-resolution identification of volcanic ash-bearing layers. Al2O3/TiO2, aluminum normalized Th and Sn, and positive anomalies GR data can reflect volcanic ash input. The 206Pb/238U weighted age of zircon ranges from 256.00 ± 2.00 Ma to 251.47 ± 1.29 Ma, indicating synsedimentary volcanic ash. We apply cyclostratigraphic analysis to convert data from the depth domain to the time domain, and then utilize the multitaper method to analyze the cycle of volcanic activity of ELIP. Spectral analysis results reveal that the volcanic activity has long eccentricity (405-kyr), obliquity (∼33-kyr), and precession (∼20-kyr) periods. We propose the astronomical orbital forcing in volcanic activity during the Late Permian, and we have discovered volcanic activity cycles on a larger timescale of astronomical orbital periods (405-kyr long eccentricity). Volcanic activity was significantly correlated with sea level and climate change. During periods of low sea levels, the hot climate causes rapid sea level change, leading to rapid changes in crustal stress and strong volcanic activity. The absolute sea level controls volcanic activity, and the high sea levels suppress volcanic activity.