四川盆地东部寒武系龙王庙组地球化学特征及其古环境意义

在野外露头和镜下薄片研究的基础上，对四川盆地东部龙王庙组碳酸盐岩样品的主、微量元素和碳、氧同位素的组分含量、比值特征等地球化学指标进行系统分析，结果表明：龙王庙组19个碳酸盐岩样品的CaO含量高，集中在47.6%~68.3%之间，平均为59.09%；MgO含量变化大，分布在0.65%~12.8%之间，平均为6.17%；Na₂O 含量高，集中在0.89%~3.14%之间，平均为1.15%；K₂O含量较高，分布在0.03%~2.06%之间，平均为0.43%；相较于同期海水，δ¹³C值明显偏正，分布在-1.533‰~0.908‰之间，δ¹⁸O值明显偏负，分布在-4.957‰~-9.916‰之间，且两者不具相关性。进一步分析MgO/CaO、Sr/Ba、1 000×(Sr/Ca)、V/(V+Ni)等特征元素的比值及古盐度“Z”值、古温度“t”，发现龙王庙组为干热气候、贫氧_缺氧环境下形成的亚热带陆棚（离岸一定距离）沉积；沉积过程中，古气候、古水深、古盐度等表征参数均呈多段式变化，沉积晚期大气淡水作用显著，中期气候最为干热、水深最低、盐度最高，是四川盆地东部白云岩油气储集层最有利的发育时期。

Geochemical characteristic and its paleoenvironmental implication of Cambrian Longwangmiao Formaiton in eastern Sichuan Basin,China

In order to reveal the paleoenvironment of Early Cambrian in eastern Sichuan Basin,we conducted the analyses on petrography,major elements and trace elements,carbon and oxygen isotope composition in carbonate rock samples from four outcrops of Lower Cambrian Longwangmiao Formation.Our data show high CaO concentrations,great variation in MgO concentrations,low rations of MgO/CaO,high Na and K concentrations,low ratios of Sr/Ba and V/(V+Ni),high ratios of 1 000×(Sr/Ca),high δ¹³C values,low δ¹⁸O values and the absence of correlation between δ¹³C and δ¹⁸O values in Longwangmiao Formation.From the bottom to the top of Longwangmiao Formation,1 000×(Sr/Ca) and V/(V+Ni) values decrease on the whole,while rations of MgO/CaO increase systematically and rations of Sr/Ba have lower values in the middle.These evidences indicte a xerothermic continental shelf (offshore) environment under dysaerobic -anaerobic condition in the subtropical zone,with an influx of meteoric fresh water at the later period of Longwangmiao Formation.Therefore,we surmised that the middle sedimentation stage of Longwangmiao Formation has the most xerothermic climate,highest salinity water and most shallow water,which is most favorable for the development of dolomite.