鄂尔多斯盆地延长组长10_1期沉积特征

Sedimentary characteristics of sandstone in Chang 10_1 stage of Yanchang Formation in Ordos Basin

鄂尔多斯盆地三叠统延长组长101期发育河流—三角洲—湖泊沉积体系,河流相中辫状河道和曲流河道,三角洲相中辫状水下分流河道、陆上分流河道、水下分流河道和河口坝等沉积均发育砂岩。在沉积相研究的基础上,分别对各沉积微相砂岩的沉积特征进行了深入研究。鄂尔多斯盆地西部的辫状河道、辫状分流河道及辫状水下分流河道砂岩主要发育有冲刷面、槽状交错层理、板状交错层理和平行层理等,以向上变细的正粒序为主,砂岩粒度概率曲线主要为两段式或三段式;盆地东部的曲流河道、陆上分流河道、水下分流河道和河口坝砂岩主要发育有冲刷面、槽状交错层理、板状交错层理、平行层理和砂纹层理等,以向上变细的正粒序为主,见向上变粗的逆粒序,砂岩粒度概率曲线主要为两段式或三段式,可见四段式。通过进一步的对比分析,认为盆地内长101期辫状河道、辫状分流河道、曲流河道和陆上分流河道中砂体较发育,辫状水下分流河道、水下分流河道和河口坝砂体次之。

The fluvial-delta-lacustrine depositional system develops for long in Chang lOt stage of Triassic Yanchang Formation in Ordos Basin. The sedimentary microfacies as braided channel and meandering channel of fluvial facies, braided subaqueous distributary channel, land distribntary channel, subaqueous distribntary channel and mouth bar of delta facies all develop sandstones. Based on the sedimentary facies study, the sedimentary characteristics of each sedimentary microfacies sandstone are deeply studied. The result shows that scour surface, trough cross-bedding, tabular cross-bedding and parallel bedding mainly developed in sandstone of braided channel, braided distributary channel and braided subaqueous distributary channel distributed in the west of the basin with fining-upwards normal cycle as the dominate feature. The grain-size probability curve of sandstone mostly has two steps or three steps. In the east of the basin, scour surface, trough cross-bedding, tabular cross-bedding, parallel bedding and sand bedding mainly developed in sandstone of meander channel, land distributary channel, subaqueous distributary channel and mouth bar with fining- upwards normal cycle as the dominate feature while coarsening-upward inverse cycles can be recognized as well. The grain-size probability curve of sandstone mostly has two steps or three steps, moreover, four steps. Further comparative analysis indicates that sand bodies are mostly developed in braided channel, braided distributary channel, meandering channel and land distributary channel, followed by braided subaqueous distributary channel, subaqueous distributary channel and mouth bar in Chang 101 stage.