鄂尔多斯盆地白垩系粘土矿物的分布特征及其沉积-成岩环境意义

Distribution of the Cretaceous clay minerals in Ordos basin,China and its implication to sedimentary and diagenetic environment

系统地分析了鄂尔多斯盆地白垩系粘土矿物的特征及其沉积、成岩环境意义。研究结果表明:白垩系砂岩、泥质岩的粘土矿物组合以I+C+I/S型、I+C型为主,具有高伊利石含量,较高绿泥石、伊/蒙混层矿物含量的粘土矿物组成特点;其中泥质岩粘土矿物主要为陆源碎屑成因,次为沉积成岩过程中形成的自生粘土矿物,而砂岩粘土矿物兼有陆源碎屑成因和沉积成岩过程自生成因的特征;白垩系沉积时气候总体特征为干旱—半干旱,但局部时段发生干—湿气候波动而处于短暂的湿热气候环境;白垩系沉积物源富含长石等硅酸盐矿物,沉积物质主要自北、南、西向盆地内部搬运沉积;白垩系沉积和埋藏成岩过程中水介质整体上具有盐度较高,偏碱性,富K+、Fe2+、Mg2+的特点,且总体上盆地南部水介质中的这些指标都高于北部。

The paper analyses distribution of Cretaceous clay mineral and its sedimentary and diagenetic significance in Ordos basin. The clay mineral components of the Cretaceous sandstone and mudstone samples are dominated by illite,chlorite and illite/smectite mixed layers in Ordos basin. The clay minerals of mudstones are mainly from siliciclastic deposits,and a small amount is authigenic mineral assemblage formed during depositon and diagenesis,however the clay minerals of sandstones are both from siliciclastic deposits and authigenic mineral assemblage in diagenesis. The clay components and distribution of the sandstones and mudstones show that Ordos basin has totally experienced arid-semiarid climate during the Cretaceous but occasionally humid climate,and the Cretaceous deposits have rich silicate minerals such as feldspar,and the sediments are sourced mainly from the northern,southern and western margins of the Ordos basin. The salinity of sedimentary and diagenetic water bodies both are high,and are rich in K＋、Fe2＋、Mg2＋. It generally shows that the salinity is higher in the south than in the north and the K＋、Fe2＋、Mg2＋ contents are richer in the south than in the north.