鄂尔多斯盆地三叠系延长组层序地层格架与沉积相构成

运用高分辨率层序地层学的原理和方法,综合鄂尔多斯盆地野外地质露头、岩心、测井及地震资料,确定了层序界面的识别标志,在上三叠统延长组识别出不整合面和沉积作用转换面两种类型的层序界面。延长组发育7个具有等时意义的层序界面,将其划分为6个长期基准面旋回。根据短—中期基准面旋回的叠加样式,SQ1层序至SQ3层序基准面上升旋回地层样式总体上以长期基准面上升半旋回为主,构成"上升不对称"型旋回结构;SQ3层序基准面下降旋回至SQ6层序地层样式则以长期基准面下降半旋回为主,构成"下降不对称"型旋回结构。沉积相类型及其展布受基准面升降变化控制明显,沉积微相类型以(辫状)河流—(辫状河)三角洲前缘水下分支河道为主。有利储层发育于长期基准面旋回上升半旋回的早中期以及下降半旋回的中晚期。

Sequence Stratigraphic Framework and Sedimentary Facies of Yanchang Formation, Triassic System in Ordos Basin

In terms of the principle of high resolution sequence stratigraphy, sequence boundary marks are determined and two kinds of sequence boundaries of unconformity and shift surface of deposition are identified according to outcrop, core, logging and seismic data in Yanchang Formation, Upper Triassic System in Ordos Basin. There are seven sequence boundaries which classify six long-term base level cycles further in the basin. Based on stacking modes of short-term to medium-term base-level cycles, stratum mode of sequence SQ1 to the rising stage of sequence SQ3 is mainly composed of rising stage of long-term base level cycles which composed rising asymmetry cycle configuration. Stratum mode of the falling stage of sequence SQ3 to sequence SQ6 is mainly composed of falling stage of long-term base level cycles which composed falling asymmetry cycle configuration. Sedimentary facies and its distribution are mainly controlled by the change of base level. Sedimentary micro-facies are mainly composed of braided river and distributary channel of delta front. Favorable sandbo- dies are mainly distributed in the lower to middle stage of long-term base level rising cycles and the middle to upper stage of long-term base level falling cycles.