塔北地区西部上寒武统硅质沉积成因研究OA

The origin of siliceous material in dolostones of the Upper Cambrian Lower Qiulitage Formation in the western margin of Northern Tarim Basin was investigated using germanium/silicon(Ge/Si)ratios together with major-and trace-element geochemistry.The dolostones contain 65.40%-99.49%SiO2(mean value>90%)and yield Ge/Si ratios of 0.12-2.74 μmol/mol(mean value=0.54 μmol/mol),far below typical hydrothermal end-member values of 4-25 μmol/mol;samples close to the Mana igneous body show elevated ratios.Ge/Si correlates positively with Fe2O3 but shows no relationship with Al2O3.Taken together,the low Ge/Si ratios and low Al2O3 contents indicate that the silica precipitates mainly from residual seawater and is subsequently overprinted,to a limited extent,by hydrothermal fluids that produced vein-hosted aggregates.Al2O3 contents increase systematically from east to west across the study area,pointing to a westward decrease in hydrodynamic energy that favours the accumulation of fine-grained terrigenous detritus on the restricted platform.These findings place important geochemical constraints on the silica provenance and diagenetic history of the Lower Qiulitage dolostone reservoirs and have implications for deep hydrocarbon exploration.