THE PRELIMINARY STUDY OF THE CHANGXINGIAN(LATE PERMIAN)ORGANIC REEFS IN THE WUXI DISTRICT,SOUTHERN JIANGSU

Two types of limestones of different shades, locally named the "black and white Changxingian limestones", were developed in southern Jiangsu (including part of northern Zhejiang) during the Changxingian of the Late Permian. The "white Changxingian limestones" are composed dominantly of shallow-water carbonate rocks which are characterized by high carbonate content and comprise bioclastic and intraclastic limestones, whereas the "black Changxingian limestones" consist of deepwater carbonate rocks which are noted for organic matter and comprise micritic limestones interbedded with chert bands. Two facies belts have been distinguished in southern Jiangsu: Changzhou—Suzhou—Huzhou carbonate platform facies and Shazhou—Wuxi—Guangde foreslope facies. The comparison of palaeogeographic settings, reef-building organisms, and stratigraphic sequences in the Gaoshan section, Wuxi with those in the Upper Yangzi area has revealed the development of the periplatform organic reefs at the boundary between deep-and shallow-water carbonate rocks (i. e. the "black and white Changxingian limestones") in southern Jiangsu. Thus this has opened up good prospects for the hidden reef communities in the transitional zone between deep-and shallow-water carbonate rocks along the Middle and Lower Yangzi areas as well as in the southern Yellow Sea. Finally, hydrocarbon potentials of the "black and white Changxingian limestones" are briefly discussed in this paper.