Abstract:

The Cambrian and Ordovician dolomites are important reservoir rocks of Lower Paleozoic carbonate in Tarim Basin，which can be divided into five genesis types according to various characteristics such as cores，microscopic features，textural components and macro-geology. In this paper，the micro textures of TypeⅡfine crystalline dolomite and TypeⅢmedium-coarse crystalline dolomite are described in detail，with the fine crystalline dolomite characterized by three attitudes and two textures. The TypeⅢdolomite can occur in bigger caves and fractures as a fill，which has a mosaic texture and may contain both TypeⅠand TypeⅡdolomites. The sedimentary combination and distribution pattern of the dolomites are discussed，and the favorable development zones of various types of dolomite，such as evaporatedˉseawater type，mixedˉwater type，karstification type，burial type，deep-dissolution type and syngenetic rudaceous type，are pointed out.

Key words: genesis type, distribution, dolomite, Tazhong area, Tarim Basin