Diagenetic environments of calcite veins hosted in marine carbonate rocks in middle Yangtze region of South China

Analyses of thin slices,cathodoluminescence and carbon—oxygen isotope of calcite veins hosted in marine carbonate rocks distributed around Jingshan County in the middle Yangtze region of South China indicated that,two crystal forms including radial calcite and isometric texture calcite could be identified in calcite veins in the Triassic and the cathodoluminescence intensity was different.The Permian and Ordovician fractures were mainly filled with isometric texture calcite veins and the cathodoluminescence intensity was similar with that of the surrounding rocks.The δ¹³C_PDB value of calcite veins ranged from -6.76‰ to 4.01‰ and the δ¹⁸O_PDB value ranged from -17.95‰ to -5.67‰,indicating the marine phreatic environment and the mixing phreatic environment for calcite veins deposition.Calcite veins in the Triassic were sedimentary origin,and part of calcite veins in the Permian and the Ordovician suffered latter diagenetic fluid dissolution.Fluid generated from organic-matter maturation effected the formation of calcite veins in the Permian to some degree.