新疆塔中石炭系层序地层学研究——一个克拉通内坳陷盆地的层序地层框架模式

ON THE CARBONIFEROUS SEQUENCE STRATIGRAPHY IN THE TAZHONG AREA,XINGJIANG——A MODEL OF THE SEQUENCE STRATIGRAPHY FRAMEWORK OF INTRACRATONIC DEPRESSIONAL BASINS

塔中地区石炭纪原型沉积盆地属挤压性克拉通内坳陷盆地。在石炭系中可识别出3个Ⅰ型层序界面和3个Ⅱ型层序界面,据此,划分出5个沉积层序。它们具有标准层序所具有的地层特征,相当于三级海平面升降旋回的沉积单元。在区域上或全球范围内这些旋回基本上具可对比性。与被动大陆边缘型盆地相比,其层序地层框架具有明显的差异,主要表现为缺失低水位早、中期的沉积体系,深切河谷不发育,代表最大海泛期的凝缩层不发育;Ⅱ型层序界面较普遍,海岸平原沉积体系发育,在潮湿气候条件下常与陆架型扇三角洲体系共生,组成海陆交互的岩相框架。

The original Carboniferous basin in the Tazhong area is a compressional intracratonic depression. The Carboniferous stratigraphic succession of the basin is rather well developed, only the topmost Maping Formation being absent. Three type I sequence boundaries and three type I sequence boundaries are recognized within it. In accordance with the above six sequence boundaries , the Carboniferous system is divided into five depositional sequences, which have the stratal characteristics of the standard sequence. These depositional sequences can be well correlated laterally in the studied area. The time spans for forming these sequences were different, roughly e-qual to the sedimentary stratal unit of a third-order eustatic cycle, which can be correlated with the rise and fall of regional and/or global sea level. However, the regional tectonic setting and sedimentary environment geoverned the formation and development of the sequences to some degree.The framework of sequence stratigraphy of the intracratonic basin in the studied area differs from that of the passive continental-margin basin in the following aspects: lack of the depositional systems of early-middle lowstand; absence of continental break, poor development of the deeply incised valley and condensed section of the maximum sea-flood, good development of the type I sequence boundaries and coastal plain depositional systems coexisting with the shelf-type fandeltas under the conditions of wet climate, which consequently led to the formation of a lithofacies framework of sea-continent alternation.