鄂尔多斯盆地西南部延长组高分辨率层序地层划分

本文基于高分辨率层序地层学及沉积学的相关理论,以汭水河剖面、42口井的岩心资料以及97口井的测井资料为依据,对鄂尔多斯盆地西南部延长组进行了层序地层划分。结果显示,研究区内的延长组可划分为4个长期旋回,11个中期旋回。四次长期旋回的最大湖泛面位置分别对应于长9、长7、长4+5及长1油层组。研究发现盆地西南部地区延长组主要的旋回结构样式包括A/S小于1时,以上升半旋回为主的非对称结构;A/S接近1时,上升和下降旋回均保存完整的对称型结构及A/S大于1时,以下降半旋回为主的非对称结构。从南北向和东西向层序地层年代格架剖面分析可以发现,研究区内延长组内部不存在大型的或者区域性的沉积间断和不整合面,研究区延长组上部由于后期的构造抬升作用而被剥蚀,与上覆侏罗系呈假整合接触。

High-Resolution Sequence Stratigraphy Division of Yanchang Formation in Southwestern Ordos Basin

Based on the high‐resolution sequence stratigraphy and sedimentology theory ,in combination with the data of Ruishuihe outcrop profile ,42 drilling cores ,and hundreds of well logging , the authors studied the high‐resolution sequence stratigraphy of Yanchang Formation in the southwestern Ordos basin .The results show that Yanchang Formation can be divided into 4 large‐scale cycles ,and 11 intermediate‐scale cycles .T he highest base level of the four large‐scale cycles are basically corresponded to Chang 9 ,Chang 7 ,Chang 4+ 5 ,and Chang 1 respectively .According to the study , three kinds of main cyclical structures of Yanchang Formation in the southwestern Ordos basin are proposed ,include asymmetry form deepening upwards when A/S<1 symmetric form when A/S≈1 ,and asymmetry form of descending half cycle when A/S>1 .With the analysis of the NS and EW framework of high‐resolution sequence chronostratigraphy ,there is no sedimentary discontinuity and unconformity within Yanchang Formation ,however the top strata of Yanchang Formation were denuded to different extent ,among which the southwest part was denuded seriously ,and the middle and northwest strata were preserved well ,and both of them contacted with the overlying Jurassic strata unconformably .