鄂尔多斯盆地东缘上三叠统延长组砂体结构与层序地层学研究

Stratigraphic architecture and sequence stratigraphy of Upper Triassic Yanchang Formation in the eastern margin of Ordos Basin

运用层序地层学原理,对鄂尔多斯盆地东缘上三叠统延长组长7—长4+5曲流河三角洲露头进行深入的研究,划分出低位体系域、湖侵体系域和高位体系域,其内部砂体骨架是由席状化水下分流河道、曲流型分流河道、辫状型分流河道沉积构成。阐述了鄂尔多斯盆地东缘上三叠统延长组层序格架和砂体结构特征,建立了鄂尔多斯盆地层序地层格架内砂体分布模式,构建了层序地层格架内砂体结构与相对湖平面响应模式图。研究表明随湖平面变化层序格架内砂体结构发生规律性变化,低位体系域早期侵蚀,晚期充填呈复合状砂体;湖侵体系域砂体呈孤立状;高位体系域早期砂体发育不全,晚期呈席状砂体。

According to the theory and approach of the sequence stratigraphy,we have investigated the meandering river delta outcrops of the Upper Triassic Yanchang Formation along the eastern margin of Ordos Basin,and identified LST,TST,and HST. Four types of distributary channel depositional systems,including sheet-like subsurface distributary channel,meandering channel and braided channel,which built delta sand body framework,have been identified from the Chang 7 Member to Chang 4＋5 Member in Yanchang Formation. Sequence stratigraphic framework and sand body architecture have been illustrated; furthermore,stratigraphic architecture and delta sand-body framework model and sandbody framework related to the relative lacustrine level change have been established. The study demonstrated that the sand-body architecture should have evolved regularly in response to relative lacustrine level change in Ordos Basin; the sand body may have eroded in early LST,and amalgamated channel-filled sand-body was expected in late LST; isolated channel-filled sand-body occurred in TST; during early HST sand body was absent,and sheet-like sand body took place during late HST.