伊舒地堑构造演化的沉积充填响应

伊舒地堑是一典型的转换伸展型盆地,它以构造上和沉积上的不对称结构,沉降中心的明显迁移和快速沉降充填为主要特征。本文应用盆地充填记录、盆地构造格架和盆地沉降史分析论证了伊舒地堑构造演化过程中不同级别的幕式裂陷作用,确定了幕式裂陷作用的沉积响应。此外,文章还总结了3种类型的沉积体系域构成样式和沉积特征。

THE TECTONIC EVOLUTION OF YISHU GRABEN AND ITS DEPOSITIONAL FILLING RESPONSE

Yishu graben is a typical transform-extensional basin. This graben is bounded by a steep dipping transform fault on the northwestern side and subparal lel normal faults on the southeastern side, with very thick marginal fan complex es indicating contemporaneous sedimentation along the faults. It is infilled wit h Tertiary sediments of up to 6000m thick, in which a series of different scaled hiatuses and tectonic inversion events have been discerned during hydrocarbon e xploration in the basin. According to regional and local unconformity and corres ponding conformities, the basin infilling of the graben may be subdivided into t hree tectonic sequences, among which the major infilling sequence TS2 may be fur ther subdivided into three sequences sets and fourteen sequences. Based on the s equence stratigraphic framework, depositional system tracts that are characteriz ed by marginal fan complexes on both sides of basin and deep or shallow lacustri ne deposits in the central part are reconstructed. The subsidence curves show th at the graben had undergone several rapid subsidence episodes, which have been i nterpreted as result of a multiple stretching of the lithosphere. Integrative an alysis of the depositonal structural features shows that regional tectonic stres s system experienced a transformation from dextral tenso-shear, through thermal subsidence to sinistral compresso-shear under a general extensional background. The composite mechanism of extension and transform dominated the graben evolutio n and affected to depositional infilling style in different evolutionary stages, the spatial configuration of depositional system and its relationship with unco nformities. The conclusions have been applied with some success to prospection o f reservoir and hydrocarbon source-rock distribution and lithologic-stratigrap hic traps in this basin.