基于沉积微相的野外露头剖面准层序分析——以鄂尔多斯盆地奥陶系临汾晋王坟剖面马家沟组为例

鄂尔多斯盆地奥陶系为广泛的陆表海碳酸盐岩沉积,其东部马家沟组岩相特征、岩石组合类型和旋回性丰富多样。通过对本区临汾晋王坟剖面的奥陶系马家沟组地层进行精细测量,笔者从剖面的沉积特征入手,进行沉积环境和沉积微相的分析,并以沉积微相的纵向演变规律为基础,结合准层序向上变浅的本质特征,识别划分野外露头剖面的准层序。研究区马家沟组共识别出32个准层序,可分为两种类型:准层序类型Ⅰ跨越若干微环境,相变向上为浅;准层序类型Ⅱ沉积于同一个微环境,向上有层厚的渐变趋势。两种类型准层序的形成取决于沉积物供给、短周期海平面升降和地层沉降三者之间的关系和相互作用。研究区内的准层序类型Ⅰ发育广泛,较为常见,类型Ⅱ则发育较少。

Parasequence analysis of the field outcrop sections based on the sedimentary microfacies analysis: An example from the Ordovician Majiagou Formation in Linfen, eastern Ordos Basin

On the basis of the precise measurement of the Ordovician Majiagou Formation strata and sedimentary microfacies analysis of the Jinwangfen section in Linfen,eastern Ordos Basin,32 parasequences have been discriminated for the Majiagou Formation,and may be classified into the following two categories.The parasequence I spanning a number of micro-environments displays the shallowing-upward facies transition whereas the parasequence II deposited in a single micro-environment displays a thickening-upward trend of the sequences.The former is wide-spread while the latter is seldom in the study area.The formation of the above-mentioned types of parasequences tends to depend on the relationship and interaction of sediment supply,short-term sea-level fluctuations and stratigraphic subsidence.