柴达木盆地北缘马北地区碳酸盐胶结物特征及意义

综合运用岩石学、矿物学和地球化学等方法,对柴达木盆地北缘西段马海凸起北部下干柴沟组下段砂岩储层中碳酸盐胶结物的形成环境和物质来源进行了系统研究.结果表明,该区下干柴沟组下段砂岩储层中存在2种方解石胶结物类型,即它形泥晶方解石胶结物和半自形微晶方解石胶结物;其碳同位素值分布范围在-7.1‰～-3.3‰,平均为-4.9‰;氧同位素值分布范围在-11.3‰～-9.6‰,平均为-10.3‰;古盐度Z值分布范围为107.0～115.6,平均为112.1.说明研究区储层砂岩中方解石胶结物的形成与早成岩阶段的有机质脱羧基作用有关,有少量有机碳的加入,成岩流体主要是来自碎屑和大气中的淋滤淡水. 

Characteristics and significances of carbonate cements in northern Mahai region, northern margin of Qaidam Basin

Based on lithology,mineralogy and geochemistry,the generation environment and source for carbonate cements in sandstone reservoirs in the lower position of the Paleogene Lower Ganchaigou Formation in the north of the Mahai Uplift which located in the northern margin of the Qaidam Basin were studied systematically.Two types of calcite cements were found,including xenomorphic micrite and hypidiotopic microcrystalline.Their carbon isotope values(δ13C) ranged from-7.1‰ to-3.3‰ with the average of-4.9‰,and the oxygen isotope values(δ18O) ranged from-11.3‰ to-9.6‰ with the average of-10.3‰.The Z-values of paleosalinity ranged from 107.0 to 115.6 and the average value was 112.1.The generation of carbonate cements in sandstone reservoirs in the study area might be related to the decarboxylation of organic matters during the early diagenetic stage.A little organic carbon also participated in the reaction.Diagenetic fluids mainly came from clast and atmospheric freshwater.