鄂尔多斯盆地东北缘延安组划分与对比

内蒙古鄂尔多斯盆地东北缘高头窑地区中侏罗统延安组是一套河流—滨湖相为主的中生代陆相沉积岩系,岩性主要中粒—中细粒长石砂岩、粉砂岩(泥质粉砂岩)、黑色页岩、黏土岩夹煤层,其中产大量的植物化石。根据岩性特征及采集化石的研究结果表明,不存在晚三叠世地层,并缺失下侏罗统,且延安组的时代应为中侏罗世。通过不同地区中侏罗世地层对比,认为盆地中延安组发育极不均衡,中部沉积厚度大,但不成煤;而盆地边缘沉积厚度较薄,且成煤较好,横向上具有明显的差异性。

STRATIGRAPHIC DIVISION AND CORRELATION OF THE YAN'AN FORMATION IN THE NORTHEASTERN MARGIN OF THE ORDOS BASIN, CHINA

The Mid-Jurassic Yan’an Formation outcrops in the Gaotouyao area along the northeastern margin of the Ordos Basin, Inner Mongolia. It is a Mesozoic continental sedimentary succession dominated by fluvial-lacustrine facies consisting of medium to medium-fine grained feldspathic sandstone, siltstone (muddy siltstone), black shale, and clayey rocks intercalated with coal seams and rich in plant fossils. Lithostratigraphic and paleontological research indicates that the previously defined Yanchang Formation does not exist in the research area, strata of Lower Jurassic age are absent in the research area, and the Yan'an Formation should be Middle Jurassic in age. By comparison of the Middle Jurassic strata in different areas, it is recognized that the Yan'an Formation is not uniformly developed across the Ordos Basin. The Yan'an Formation is thick but contains no coal seams in the central Ordos Basin. It is thin but contain coal seams in the marginal Ordos Basin.