Feature and Origin of Dolomite Filling in the Upper Cambrian-Lower Ordovician Dolostone of the Central Uplift,Tarim Basin
ZHANG Jun-tao1 HU Wen-xuan1 QIAN Yi-xiong2 WANG Xiao-lin1ZHU Jing-quan3 ZHANG Hong-an2 SU Juan2 WU Shi-qiang3(1.Department of Earth Science, State Key Laboratory for Mineral Deposits Research, Naning University, Nanjing 210093;2.Northwest E&P Company, SINOPEC, Urumqi 830011;3 China Academy of Sciences, Institute of Geology and Geophysics, Beijing 100029)
Two genetically distinct dolomite fillings are recognized in Lower Paleozoic dolostone in the Upper Cambrian-Lower Ordovician dolostone of the Central uplift, Tarim basin: rhombus and saddle dolomite fillings, which occur in different diagenetic considerations and have different character. The former crystal exhibits homogeneous, the later crystal is composed of three distinct parts that are rim, clitellum and core. Stratigraphic, petrographic and geochemical date suggest, rhombus dolomite filling deposited steadily and source of Mg2+ is from the altered seawater. However, material source of saddle dolomite filling is hydrothermal dissolution of dolomite. The formation of saddle dolomite filling, three parts of which formed in different phase, is associated with faulting. The deposition of dolomite filling is porosity decreasing, but saddle dolomite is a sign of dissolution.