Origin of dolomite of the lower Cambrian Longwangmiao Formation, eastern Sichuan Basin, China

Combined elemental and isotopic geochemistry of dolomites in the lower Cambrian Longwangmiao Formation, eastern Sichuan Basin with petrographic observations has been investigated to determine the origin of these dolomites. Our data show that these dolomites are mostly located in the middle and upper parts of the Longwangmiao Formation, and most of them commonly occur as crystalline dolostones, whereas they less commonly occur as a dolograinstone. The dolomite contents of the dolostones range from 64 to 97%. The Mg/Ca ratios of these dolomites vary from 0.6 to 1.2, with an average of 0.8. These criteria divide the Longwangmiao dolomites into two types, according to either a positive correlation (type-A) or negative correlation (type-B), which exist between the MgO and CaO contents. Type-A dolomite consists of micritic-to-fine crystals (