e , "1 i ELSEVIER Physics of the Earth and Planetary Interiors 89 (1995) 281-295 PHYSICS OFTHE EARTH ANDPLANETARY INTERIORS Permian-Triassic magnetostratigraphy South China new results from Friedrich Heller a,*, Chen Haihong b, Jon Dobson a, Maja Haag c a Institut fiir Geophysik, ETH-H6nggerberg, CH-8093 Ziirich, Switzerland b Institute of Geology, Chinese Academy of Sciences, P.O. Box 634, Beijing 100029, People's Republic of China e Centre des Faibles Radioacticit~s, Laboratoire mixte CNRS-CEA, Avenue de la Terrasse, F-91198 Gif-sur-Yvette, France Received 26 November 1993;revision accepted 23 August 1994 Abstract 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 magnetiza- tions 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. 1. Introduction One of the most prominent features of the geomagnetic field during the Palaeozoic is the occurrence of the Kiaman polarity superchron (Irving and Parry, 1963; Khramov and Rodionov, 1981). This period of continued reversed polarity was thought to have lasted for about 60 Ma * Corresponding author. between the Upper Carboniferous (Westphalian) and the Upper Permian (Tatarian). More recent studies have put new constraints on the age limits and duration of the Kiaman superchron. Di- Venere and Opdyke (1991) have confirmed that its onset must postdate the Early Westphalian (approximately 310 Ma; time scale of Haq and Van Eysinga (1987)). The younger end of the Kiaman, when the Illawarra mixed polarity zone begins, however, falls nearer the boundary be- tween the Lower and Upper Permian, within the 0031-9201/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0031-9201(94)02993-8