查干凹陷白垩系至新生界不整合类型和特征

 查干凹陷经历了极其复杂的构造活动过程,形成多个不整合类型.在系统划分该凹陷白垩系至新生界不同级次层序的基础上,识别了各级层序界面的不整合类型,提出了一种新的不整合类型划分方案.根据不整合面上下地层几何关系、地震反射终止形式和不整合面成因机制(构造和沉积),将查干凹陷不整合划分为2大类：角度不整合、平行或微角度不整合,进一步划分为7种基本类型：褶皱型、断褶型、削蚀型3种构造不整合以及超覆型、退覆型、顶超型、整一型4种沉积不整合.在这7种基本类型的基础上,按照A/B-C·D代码系统划分不整合类型的新方法,将查干凹陷不整合细分为9小类：上超/整一-超覆型、上超/顶超-超覆型、上超/削截-超覆·削蚀型、上超/削截-断褶·退覆型、整一/削截-削蚀型、整一/削截-褶皱型6种角度不整合类型,以及整一/顶超-顶超型、整一/整一-整一α型、整一/整一-整一β型3种平行或微角度不整合类型.各级层序界面不整合类型的基本分布规律是,洼陷中心主要发育平行或微角度不整合类型,向外渐过渡为角度不整合类型,高级次层序单元(如一级层序、构造层序和超层序)界面常发育多种角度不整合类型并作为主体,低级次层序单元(如层序)界面常发育多种平行或微角度不整合类型并作为主体.

The Types and Characteristics of Unconformity Surfaces from Cretaceous Through Cenozoic in Chagan Sag

Chagan Sag has experienced the extremely-complex tectonic activity processes and formed several unconformity types. Based on the systematical subdivision of different-order sequences from Cretaceous through Cenozoic in the Sag, the unconformity types of different-order sequence boundaries are identified, and a new classification scheme for unconformity types is put forward. Mainly according to the geometrical relationship between the two sides of unconformity plane, the seismic reflection termination style, and the unconformity formation mechanism (tectonism and deposition), the unconformities in Chagan Sag are divided into two categories, including angle unconformity and parallel-or-slight-angled unconformity, and further divided into seven basic types, including three kinds of tectonic unconformities, such as fold unconformity, fault-fold unconformity, and truncation unconformity, and four kinds of depositional unconformities, such as overlap unconformity, offlap unconformity, toplap unconformity, and concordance unconformity. Based on the seven basic types of unconformities, and according to the new method that divides unconformity types based on A/B-C·D code system, the unconformities in Chagan Sag are subdivided into nine sub-types, including six angle unconformity types, such as onlap/concordance-overlap type, onlap/toplap-overlap type, onlap/truncation-overlap truncation type, onlap/truncation-fault-fold offlap type, concordance/truncation-truncation type, and concordance/truncation-fold type, and three parallel-or-slight-angled unconformity types, such as concordance/toplap-toplap type, concordance/concordance-concordance α type, and concordance/concordance-concordance β type. The basic distribution law for the unconformity types of different-order sequence boundaries is that parallel-or-slight-angled unconformity types are mainly formed in sub-sag center and angle unconformity types at outskirts, and the boundaries of high-order sequence units, such as first-order sequence, tectonic sequence, and super sequence, usually have a variety of angle unconformity types as their main body, and the boundaries of low-order sequence units, such as third-order sequence, usually have a variety of parallel-or-slight-angled unconformity types as their main body.