深水环境层序边界及体系域的划分——以银根盆地查干凹陷下白垩统为例

Division of the sequence boundaries and system tracts in deep-water environment-A case study on the Lower Cretaceous in Chagan Sag, Yin'gen Basin

孢粉种属突变以及还原硫含量变化对水体深度比较敏感,是划分深水环境层序边界以及体系域的良好指标。银根盆地查干凹陷下白垩统为深水湖相沉积,利用查参1井地球化学、古生物资料,将其下白垩统划分为3个层序,分别与下白垩统巴音戈壁组下、中、上段相对应,并划分了3个层序的体系域。总体而言,从低位体系域、湖侵体系域、高位体系域到湖退体系域,还原硫从低值、高值到低值呈规律性变化,在密集段达到最高值;孢粉种属数量在湖侵体系域急速减少,在湖退体系域呈升高趋势。

The abrupt changes in spore-pollen species and in the content of reduction sulfur are sensitive to water depth, and can be used as indicators for sequence boundaries and system tracts. The Lower Cretaceous strata in Chagan Sag were deposited in a deep-water lacustrine environment. Based on geochemical and paleontological data, the Lower Cretaceous is divided into three sequences, which correspond to the Upper, Middle and Lower members of the Lower Bayingebi Formation. The system tracts of each sequence are also identified. From the lacustrine lowstand system tracts, lacustrine transgression system tracts to lacustrine contraction system tracts, the content of reduction sulfur changed from low, high, to low, and reached a peak in the condensed section; and the number of spore species decreased rapidly in lacustrine extension system tracts and showed an increasing trend in contraction system tracts.