Identification and Paleogeographical Implications of Middle Triassic Carbonate Slope in Xiacheng——Shaijingtan Area,West Qinling Mountains

The carbonate platform slope is a slope break zone between the carbonate platform and the deep-sea basin. The deposition and the deformation of sediments are controlled by gravity. Its study has important palaeogeographical implications and economic significance. A great number of carbonate debris flows,syndepositional faults and truncation structures have been found in Middle Triassic in Xiacheng. Also,carbonate debris flows exist in flysches of Middle Triassic Gulangdi Formation in Shaijingtan. In order to reconstruct the paleogeographical environment in this area,the carbonate microfacies are analyzed,with identifications and discussions. The analysis on these sediments and sedimentary structures reveals that a continental slope exists from SEE to NWW along Xiacheng—Shaijingtan in Middle Triassic. They are mostly deep-water carbonate sediments in Xiacheng and terrigenous clast in Shaijingtan. This slope is nearly a carbonate platform in NNE,and has a transition to deep-sea sediments in SW.