四川盆地白垩系粘土矿物特征及古气候探讨

The Cretaceous Clay Minerals and Paleoclimate in Sichuan Basin

四川盆地是中国白垩纪最具代表性的陆相沉积盆地之一,主要发育一套广布的红色碎屑岩沉积,且膏盐、沙漠相沉积发育。本文在前人地层古生物学研究的基础上,借助粘土矿物气候指标、结合沉积物碎屑成分,着重讨论了中侏罗世—古近纪早期四川盆地及周边地区的气候状况及演变过程。碎屑组份统计分析认为盆地北部边缘早白垩世早期构造因子起主导作用,而盆地南部白垩纪气候因子起主导作用,说明构造活动对沉积物影响不大。粘土矿物组份主要以蒙脱石和伊利石为主。多数样品蒙脱石和伊利石同时出现,指示沉积物源区为干冷与暖湿交替的气候环境;局部层段只有伊利石,指示干冷气候。同时,所有样品伊利石化学指数值均大于0.5,说明粘土矿物经历了强烈的化学风化作用,盆地内部为暖湿气候。

The Sichuan Basin is one of the most representative basins in Cretaceous terrestrial basin, in which a suite of red clastic deposition, especially gypsum and desert facies had been widely deposited. Based on previous study, climate marker of clay minerals, composition of the rocks, this study discusses climate and its evolution of the Sichuan Basin and adjacent areas in the Middle Jurassic to the Early Paleogene. Our experimental results suggest that the Early Cretaceous tectonic factors played a dominate role in the northern margin of the Basin, whereas the south was predominated by weather, suggesting that tectonic activity had little effect on sedimentation. The main clay minerals in the redbeds are illite and smectite. Both Illite and smectite are present in most samples, implying that climate of the source area was cool and arid. Illite present locally stands for a cool, dry clmite. Chemical index of the illite samples is higher than 0.5, indicating that clay minerals had undergone strong chemical weathering and interior of the Basin had a relatively warm and wet climate.