CHARACTERISTICS AND ORIGIN OF DOLOSTONES IN YINGSHAN FORMATION, LOWER AND MIDDLE ORDOVICIAN, NORTH OF CENTRAL TARIM BASIN

There are large amount of dolostone and wide spread dolomization in Yingshan Formation of Lower and Middle Ordovician in North of central Tarim basin,the strata is composed of all kinds of dolostone, limy dolostone, dolomited limestone and limestone which are inter-bedded with different thickness and deposited on carbonate platform. The dolostone includes sparry dolostone, residual-grained dolostone, residual limy dolostone and algae dolostone. By analyzing the attitude, minerlogy and geochemistry of the dolostone, the origin of dolostone is regarded as a kind of replaced one at near-surface in evaporated sea water which can be interpreted in such model as tidal evaporating dolomite-forming and flowing-down dolomite-forming.