鄂尔多斯盆地上三叠统延长组沉积体系特征及演化

Characteristics and evolution of the sedimentary system of Upper Triassic Yanchang Formation in Ordos Basin,China

在野外剖面观察、岩心描述及测井、测试资料分析的基础上,综合前人研究成果,对鄂尔多斯盆地上三叠统延长组沉积体系的类型、特征进行了详细分析,并深入讨论了鄂尔多斯盆地延长组沉积体系垂向上的演化规律。结果表明:鄂尔多斯盆地延长组主要发育冲积扇、扇三角洲、河流、河流三角洲、湖泊和湖泊浊积扇六大类沉积体系。长8期湖盆开始形成,主要发育神木-乌审旗、安塞和正宁-合水等三角洲沉积体系;长7期湖盆进一步扩展,三角洲规模萎缩;长6期湖水大面积退缩,三角洲前缘连片,面积最大,东北三角洲前缘已推进至吴旗-甘泉一线,西南缘推进至华池-庆阳一带;长4+5期以浅湖亚相为主;长3、长2期以三角洲平原沉积为主;长1期湖盆继续萎缩至消亡,局部出现沼泽环境。盆地沉积体系的演化,在纵向上构成了五套储盖组合。

Based on observing outcrops, describing tests, as well as labor measurements, this paper cores and analyzing the data of well logging and analyzes the sedimentary system of the Upper Triassic Yanchang Formation in Basin involving the classification and characteristics of the system, and detailed discusses the rule of vertical evolution of the sedimentary system. The result shows that the depositional system of the Yanchang Formation in Ordos Basin composes of alluvial fans, fluvial deposits, fan deltas, braid deltas, meandering river deltas, and lakes. During No. 8 period of Yanchang Formation, the lake basin formed. In the study area, there developed the Shenmu-Wushenqi delta, Ansai delta and Zhengning-Heshui delta, and so on. In No. 7 period of Yanchang Formation, the lake basin further developed, and the delta began narrowing. The lake water largescale held back in Member 6 of Yanchang Formation. The delta fronts connect each other and possess the largest area. The delta fronts arrive at Wuqi-Ganquan in the northeast and Huachi-Qingyang in the southwest. In No. 4＋5 period of Yanchang Formation, the shallow lake was the main subfacies. During No. 3 and No. 2 periods of Yanchang Formation, the delta plains developed dominantly. In No. 1 period of Yanchang Formation, the lake basin continued shrinking until it died out, and swamp environments appeared partly. The evolution of the basin sedimentary system in the basin has formed five sets of reservoirs and cap rock assemblages.