Sedimentary Environment of LowerMiddle OrdovicianYingshan Formation in MidWestern Tarim Basin

Key words: 
• Tarim Basin

Abstract: The time equivalent Yingshan Formation in Tarim Basin has been discussed. Based on this, the sedimentary environment of Yingshan Formation was reconstructed, with the aid of outcrops, seismic facies, strata contour map and core analysis, and draw three conclusions as follows: ①The distribution characteristic of platform edge at Daobaowanian Stage and Dawanian Stage and the type of platform were definite. Besides, the viewpoint that the discontinuity of reef and beach along the platform edge was put forward. ②Carbonate sands are wild range and the shape is multifarious. Generally, they are elongate or elliptical and strike of sands is parallel to the platform edge. ③The existence of intrashelf basin was proved. Along the edge of intrashelf basin there are carbonate sands and bioherm, generally sands on windward side and bioherm on lee side. In intrashelf basin sediments predominatly consist of pelagic carbonates, which are commonly rich in organic content.