歧口凹陷缓坡带层序地层模式

Sequence stratigraphic models on gentle slope of Qikou depression

根据层序地层学原理及构造-沉积关系,对歧口凹陷缓坡带构造样式和层序地层模式进行研究,并分析二者之间的相互关系。依据构造特征将歧口凹陷缓坡带划分为外带、中带、内带3个构造地貌单元,进而将其分为低角度-多断-斜坡型缓坡、低角度-多断-单坡折型缓坡和高角度-多断-多坡折型缓坡3种缓坡构造样式。在歧口凹陷缓坡带沙河街组内部划分6个二级层序和16个三级层序,建立其层序格架,阐明其内部沉积特征。针对3种不同类型的缓坡,分析构造控制下的沉积层序展布特征。结果表明:层序具有不完整性,低位体系域较不发育,湖侵体系域和高位体系域分布广泛;在空间上,由北向南层序的数量减少,厚度减薄,各层序的完整程度也降低;缓坡构造样式控制层序类型和地层结构。

According to the principle of sequence stratigraphy and the relationship between the tectonic structure and deposition,the structure pattern and sequence mode were studied on the area of gentle slope of Qikou depression.And the relationship between tectonic structure and deposition was analyzed.Three types of structure unit were discriminated according to the tectonic characteristics on the area of gentle slope of Qikou depression.They were outside-belt,middle-belt and inside-belt respectively.And then three structure patterns were ascertained,they were low angle-multifaults-ramp slope,low angle-multifaults-simplex break slope and high angle-multifaults-complex break slope.Six second order sequences and sixteen third order sequences were identified,and the sequence frame was built and the deposited characteristics in interior sequence were described in Shahejie formation in the area.The distribution of the sequence controlled by tectonic effect was analyzed in each of structure pattern.The results show that sequences are of incompleteness.Low-order system tract deposited in a few local regions.Lacustrine trans gressive system tract and high-order system tract deposited in all the depression.The number of sequences decreases,the thickness of sequences reduces and the completeness of sequences decreases from the north to south.The type of sequence stratigraphy and formation structure are controlled by the pattern of tectonic structure.