The Late Permian/Early Triassic magnetic polarity time scale and plate motions of south China

Abstract

Fossiliferous stratigraphic sections spanning the Permian‐Triassic boundary in south China have yielded a well‐defined magnetic polarity sequence for the Lower Triassic and a more poorly defined sequence in the Upper Permian. Four sections comprising more than 1100 continuous meters of stratigraphic section display a sequence of 11 major reversals of polarity within the Early Triassic (Griesbachian to Spathian stages) and a minimum of two periods of normal polarity in the Late Permian (Changsing and Wujiaping stages). Synthesis of all Permo‐Triassic studies indicates that the lengthy late Paleozoic interval of reversed polarity ended after about two thirds of Permian time had passed. The record of frequent changes of polarity of the geomagnetic field during the Early Triassic is the same record that has been derived from many terrestrial redbed sequences. There is notable agreement in polarity pattern between the magnetostratigraphic‐biostratigraphic record of this study in marine rocks and those of the redbed sequences, indicating that some redbeds may record geomagnetic field history with great accuracy. The similarity of the records implies that a true record of geomagnetic polarity has been obtained for the Early Triassic. The reversal frequency during the Early Triassic was one to three reversals per million years, depending on the actual duration of this time period. Three latest Permian‐Early Triassic paleopoles were derived from this study, which in combination with those of earlier studies indicate that late Paleozoic to present apparent polar wander for the South China Block involved a relatively simple northward motion and that no movement of the South China Block occurred throughout the Triassic. A combined paleopole for the latest Permian‐Triassic of south China is 223.6°E, 46.1°N (N = 4, k = 1161.2, α95 = 2.7).