MAGNETOSTRATIGRAPHY OF THE CONTINENTAL REFERENCE SECTION FOR LATEST PERMIAN THROUGH EARLY TRIASSIC OF NORTH CHINA AT DAYULIN (HENAN PROVINCE)

The Dayulin section in Henan Province contains the thickest well-studied continental-facies succession of uppermost Permian and lower Triassic on the North China Block. This interval is dominated by an influx of fluvial clastics into a marginal-lacustrine setting. We obtained the magnetic polarity zonation for 280 meters that correlates to the majority of the Changhsingian (uppermost stage of Permian) through the middle Smithian (lower substage of the Olenekian Stage). The mean direction, uncorrected for potential sediment inclination shallowing, of 331° declination and 36° inclination (a₉₅ = 6°) is consistent to previous poles from same time period of North China. Applying an inclination correction to the apparent 19°N paleolatitude yields an adjusted value of 30°N. The magnetostratigraphy was correlated to the polarity pattern of the main South China marine reference sections at Meishan (GSSPs of Changhsingian Stage and of the Induan Stage) and at Chaohu (proposed GSSP for the Olenekian Stage). Those astronomical-tuned South China sections enable the projection of standard geologic substages, major excursions in temperature and documented in those South China marine deposits to the succession of fluvial and lacustrine facies at the Dayulin section. The middle through late Changhsingian is a floodplain setting with channelized sands. The end-Permian mass extinction and elevated temperatures of earliest Triassic projects to into a non-fossiliferous clay-and silt-rich interval with lacustrine carbonate horizons that may indicate a local high stand of the regional lacustrine facies. Cross-bedded sandstones interbedded with siltstones of the late Griesbachian through early Dienerian “warm interval” contain microbially induced sedimentary structures(MISS). The projected cooler interval of the latest Dienerian through earliest Smithian is marked by a high accumulation rate of thick cross-bedded sandstones without significant finer-grained interbeds. The warmer middle Smithian is a return to a floodplain setting. This local pattern of more clay-rich sediments during warm climates and increased influx of coarse clastics during cooler climates suggests an alternation between dominances of chemical weathering and of physical weathering, and the greatest sediment influxes occur during the cooler climates.