鄂尔多斯盆地南部三叠系延长组沟谷体系构造成因

Tectonic genesis of Triassic Yanchang Formation valley systems,southern Ordos Basin

鄂尔多斯盆地南部镇泾地区延长组顶部广泛发育沟谷体系,前人多认为是风化剥蚀和河流侵蚀所致。为了进一步厘清沟谷体系的发育特征、分布规律及其与区域构造的联系,基于三维地震资料对断裂的解释和前侏罗纪古地貌的恢复,刻画了延长组沟谷体系,探讨了其构造成因。结论显示,在延长组沉积晚期,受SW向区域构造挤压作用,玉都断裂发生左旋走滑,使延长组未成岩地层发生塑性变形,形成了一系列NW-SE向展布的挤压隆起与谷地;同时NW-SE向的拉张作用形成了NE-SW向的伸展谷地,最终形成了延长组晚期广泛分布的沟谷体系格局。该认识对于鄂尔多斯盆地南部延长组及其上覆的延安组的油气勘探都具有一定的指导意义。

The valley systems widely developed at the top of Yanchang Formation in the Zhenjing area,southern Ordos Basin,is previously considered to be a product of long denudation and river erosion.However,deeper investigation indicates otherwise.In order to gain clearer insights into the connection between the development characteristics and occurrence of the systems with regional tectonics,this study characterizes the systems and discusses their tectonic genesis through analyses of fault interpretation and pre-Jurassic paleogeomorphy restoration based on 3D seismic data.It shows that the main fault(Yudu)experiences a sinistral strike-slip due to a NE-SW oblique compression during the late deposition stage of the Yanchang Formation,causing some layers of the formation that are still in the process of diagnesis to be plastically deformed to form a series of NW-SW trending compressional uplifts and valleys.An almost synchronously occurring NW-SE extension eventually results in the formation of this broadly distributed valley systems.The understanding can be used to guide the exploration of reservoirs in both the Yanchang Formation and overlying Yan’an Formation in the area.