鄂尔多斯盆地中东部下二叠统山西组二段沉积相

SEDIMENTARY FACIES OF MEMBER 2 OF SHANXI FORMATION OF LOWER PERMIAN IN THE MIDDLE-EASTERN ORDOS BASIN

从露头分析和岩心观察入手,应用现代沉积学原理,对鄂尔多斯盆地东缘山西组二段露头和盆内岩心中的沉积序列及构造特征进行详细描述。山二段砂岩露头及岩心中广泛发育韵律层理、块状层理、侧积交错层理等高流态层理,露头砂体为透镜状,并在一定范围内相互切割、叠置成宽度和厚度巨大的带状砂层,体现了辫状河高流态及辫状河道砂体频繁摆动、迁移的特征。通过岩石沉积相、测井沉积相、砂体厚度、古地形结合古地理背景等多因素综合分析认为,山二段沉积时期研究区发育远源砂质辫状河—"浅水型"三角洲沉积体系,自北向南依次发育冲积平原辫状河、辫状河三角洲平原、辫状河三角洲前缘、前辫状河三角洲或滨海浅湖相,并识别出辫状河主水道、河漫沼泽、三角洲前缘河口坝等多种亚相、微相类型,明确认为辫状河主水道部分形成的宽厚巨大的主砂带是有利勘探相带。

Sedimentary sequence and tectonic features of outcrops and cores in Member 2 of Shanxi Formation in the east edge of Ordos Basin are studied with modern sedimentary mechanisms. Rhythmic stratification, block stratification and lateral accretion cross stratification are widely found in outcrops and cores of Member 2 of Shanxi Formation. Outcrop sands are lenticular, cutting each other and piling to Iarge sand belts, due to frequent migrations of braided-river sands. Based on studies of rock sedimentary facies, well logging sedimentary facies, sandbody thickness, palaeotopography and palaeogeologic background, it is pointed out that, when Member 2 of Shanxi Formation deposits, sandy braided-river and shallow water delta system is formed, which can be divided into alluvial plain braided-river, braidedriver delta plain, braided-river delta front, frontal braided-river delta or seashore shallow lake facies from north to south. Braided-river main channel, alluvial marsh, delta front debouch bar are distinguished. Main sand belt with large width and thickness proportion in main channel of braided-river is favorable for petroleum exploration.