Feature and Origin of Dolomite Filling in the Upper CambrianLower Ordovician Dolostone of the Central Uplift, Tarim Basin

Key words: 
• saddle dolomite /
• rhombus dolomite /
• Upper CambrianLower Ordovician /
• central uplift /
• Tarim Basin

Abstract: 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 Mg2+ 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. 