PERMIAN-TRIASSIC MAGNETOSTRATIGRAPHY - NEW RESULTS FROM SOUTH CHINA

Continuous marine sediments of Permian to Triassic age are widely distributed over large areas in Southern China. They offer the potential for developing magnetostratigraphic columns to investigate the polarity status of the palaeomagnetic field. Three carbonate sections on the Yangtze platform, which represent mainly the Upper Permian but also parts of the Lower Triassic and possibly parts of the uppermost Lower Permian, contain a long-term main R-N-R-N-R polarity succession throughout the Permian. This signal is hidden under-strong overprint magnetizations of variable origin and can be mostly obtained only from directional trends of the natural remanent magnetization during demagnetization rather than from clear stable end-point directions. The new Chinese polarity sequences are in accord with magnetostratigraphic records from the former USSR and Pakistan. Depending on stratigraphic assignment of the lithological formations studied, either they include the boundary between the Lower and Upper Permian and give evidence that the Kiaman reversed polarity superchron had ended before the Upper Permian, or the formations all belong stratigraphically to the Upper Permian, with the oldest reversed interval to be correlated with the reversed zone in the Midian stage of the palaeontologically well-dated Nammal section in Pakistan. This zone is preceded by at least one normal polarity zone at Nammal so that the end of the Kiaman superchron would not be observed in the new Chinese sections.