ORIGIN OF THE BRECCIAS FROM THE UPPER PART OF THE QINGLONG GROUP IN THE LOWER YANGTZE AREA

The breccias from the upper part of the Qinglong Group (East Ma'anshan Formation) in the Lower Yangtze area, which were previously interpreted to be the gypsum-solution products, consist mainly of debris flow breccias, with small amounts of tectonic breccias and gypsum-solution breccias. The gravel fragments from the debris flow breccias are derived from: (1)the tidal flat deposits in the lower member of the East Ma'anshan Formation. This kind of the fragments are composed dominantly by dolostones and mixed dolomitic and calciferous rocks, with small amounts of limestones, and (2)the platforms generated prior to the East Ma'anshanian. This kind of fragments are composed mostly of limestones, with small amounts of siliceous rocks, carbonaceous shales and clastic rocks. The matrix in the breccias consists principally of dolomite, calcite and carbonate rock fragments, including small amounts of siliceous rock fragments and quartz. The breccias are matrix-and grain-supported, and exhibit massive and stratified structures. In general, the debris flow breccias in the study area are confined to the slope zone; tectonic brecciass to the gypsum basin, slope and tidal flats and gypsum-solution breccias to the gypsum basin.