鄂尔多斯盆地西南缘寒武系辛集组碳酸盐岩地球化学特征及古环境重建

Geochemistry Characteristics of Carbonate and Paleoenvironment Reconstruction of Cambrian Xinji Formation,Southwest Ordos Basin

利用全岩X衍射、主量元素、微量元素和稀土元素分析测试,研究鄂尔多斯盆地西南缘辛集组碳酸盐岩的地球化学特征,恢复其沉积时的古环境。研究结果表明碳酸盐岩矿物含量以方解石为主(63.7%~69.2%,平均为66.45%),其次为石英(20.9%~22.3%,平均为21.6%)、伊利石(3.8%~15.4%,平均9.6%)。主量元素CaO含量最高(30.59%~41.50%,平均为36.87%),其次为SiO2(3.94%~28.30%,平均为14.40%)和Al2O3(1.10%~3.35%,平均为2.08%)。微量元素Cu、Y较富集,Zr、Rb和Sr亏损程度较大,其余元素轻微亏损。稀土元素具有轻稀土富集、重稀土平坦的特征。地球化学特征显示,碳酸盐岩物源具有混合物源的特征,主要为长英质、基性岩混合物,源岩类型为大陆拉斑玄武岩。沉积期古气候为干燥炎热的海相沉积,氧化还原条件以氧化为主。

The X-diffraction,principal elements,trace elements and rare earth elements of the carbonate rocks of Xinji formation in the southwest margin of Ordos Basin were analyzed in this paper.The results show that the carbonate minerals are mainly calcite(63.7%~69.2%,66.45%on average)with quartz(20.9%~22.3%,21.6%on average)and illite(3.8%~15.4%,9.6%on average).The content of main element CaO was the highest(30.59%~41.50%,36.87%on average),followed by SiO2(3.94%~28.30%,14.40%on average)and Al2O3(1.10%~3.35%,2.08%on average).Except Cu and Y,most trace elements have different degrees of deficit,such as Zr,Rb,and Sr.Rare-earth elements are characterized by light rare-earth enrichment and heavy rare-earth flatness.Geochemical characteristics show that the carbonate source is terrigenous clastic material,which the source is mainly feldspathic and basic rock mixture,and the source rock is continental tholeiite basalt.The paleoclimate of depositional period was dry and hot,Marine deposition,and redox conditions was oxidation environment.