Magnetostratigraphic Study of Meishan Permian-Triassic Section, Changxing, Zhejiang Province, China

摘要

The authors present new paleomagnetic results obtained at the Meishan Permian-Triassic (P/ T) boundary section, Changxing County, Zhejiang Province. 330 samples in Changxing Group of Permian, 9 samples at P/T boundary, and 25 samples in Qinglong Group of Triassic are studied. Thermal and alternative filed demagnetization isolated a stable magnetization from most samples. This stable magnetization was thought to be acquired at or close to the time of formation of the rocks. The constructed polarity column shows that the bottom of the sampling section is forming a short reversed polarity. Above this short reversed polarity, there is a normal polarity, which lasts about 1.0 Ma. Below this short reversed polarity, are present 6 normal polarities and 7 reversed polarities between the upper Lower Changxing and Upper Changxing Group. Near the P/T boundary, the magnetization polarity transfers from reversal to normal, and the normal polarity may characterize the rest of the section. Susceptibility measurement of 550 samples shows a sharp change at the P/T boundary and a high correspondence with the minor-frequency cycle of sedimentary. The spectrum of susceptibility indicates that there are 4 sedimentary cycles during 252-248 Ma in the section.