Discussion on the Origin of the Sinian Tempestites in the Nwrthwestern Margin of Tarim Basin

Sinian tempestites is proved for the first time in the northwestern margin of the Tarim Platform, which occur in the upper sub-formation of the Sugiterblack Formation of Upper Sinian System (simply called "upper sub-formation" land can be divided into two types: l.Calcarenaceous tempestites which lie in the nearshore-deposited clastic rocks in the middle and lower parts of the upper sub-formation. 2.Sandy tempestites lie in the shallow-shelf-deposited carbonate at the top of the upper sub-formation. The calcarenaceous tempestites consist of calcirudites. calcisiltites. calcarenites. oolitic limestones and residual oolitic limestones, calcarenaceous sandstones, calcilutites and mudstones. The calcirutes are abundant with sharp eroded boundarys at the bottom and many multi-orientation marks. Scour and fill structures, graded beds and a variety of hummocky cross-stratifications are usually found in the typical tempestites. The synthetic idealized tempestite sequence is composed of seven divisions above the erosional base. They are coarse-grained calcirudite division A (winnowed lag), graded division A. massive dividion B. hummocky cross-stratification division C. planar parallel lamination division D. ripple cross-lamination division E and pelitic division F from the bottom to the top. In comparison with the synthetic idealized tempestite sequence, the sectional structures may be divded into 12 types of quasi-complete, incomplete and complex sections and 9 of which occur in the calcarenaceous tempestites. They represent different stages of storm development controlled by storm intensity, the way of storm moving and current effect, duration of storm and depth of sea water.