LATE PERMIAN PALEOENVIRONMENTAL CHANGES IN THE XINGCHENG AREA, LIAONING PROVINCE, CHINA: SEDIMENTARY SUCCESSION AND ROOT SYSTEMS

During the late Permian, an alluvial environment prevailed along the northern margin of the North China Plate in the Xingcheng area, Liaoning Province, China. In this region, the middle-late Permian Shihhotse Formation and the late Permian Hamashan Formation record this transition from previous swamp-dominated settings. The two formations are mainly coarse-grained deposits and can be correlated with the Pingdingshan Sandstone, which developed as widespread alluvial facies in the central and southern parts of the North China Plate. Tectonic uplift around the plate due to Variscan orogenic activities probably contributed to the onset of alluvial prevalence, but the sedimentary characteristics in the Xingcheng area indicate that aridification was also an important driver. This is supported by the presence of root systems composed of rhizoliths in the Shihhotse Formation and Stigmaria fossils at the top of the alluvial conglomerate of the Hamashan Formation. Viewed at a larger scale, this basin-wide alluvial episode on the North China Plate was contemporaneous with the Wuchiapingian extreme aridity and followed a short humid interval. The overlying Changhsingian-Induan redbeds mark a paleoclimatic change to semiarid and arid again. The paleoenvironmental changes recorded in the upper Permian and Lower Triassic strata of the North China Plate, therefore, provide essential information for the understanding of late Paleozoic terrestrial evolution.