滇黔北威信凹陷晚二叠世含煤地层划分与对比研究

Stratigraphic classification and correlation of the Late Permian coal-bearing formation in the Dianqianbei Weixin Depression

长期以来滇黔北威信凹陷晚二叠世含煤地层划分较为混乱,为了有利于该区地质工作的开展及对比研究,作者从岩石地层和层序地层两个方面对晚二叠世含煤地层进行了划分与对比。在筠连-彝良怀来以西地区,整个晚二叠世含煤地层为宣威组陆相地层,在威信-毕节青场一线以东地区,晚二叠世早期为海陆交互相的龙潭组,晚二叠世晚期为浅海相的长兴组。两者之间地区的整个晚二叠世含煤地层为龙潭组,该区域的龙潭组上段与西部的宣威组上段及东部的长兴组可对比,该区域的龙潭组下段与西部的宣威组下段及东部的龙潭组可对比。从层序地层来看,东部的龙潭组与西部C5煤层以下的含煤地层(即龙潭组下段或宣威组下段)相对应,东部的长兴组与西部C5煤层以上的含煤地层(即龙潭组上段或宣威组上段)相对应。研究区的龙潭组具有穿时性,即从晚二叠世早期到晚二叠世晚期,龙潭组从东到西在不断抬升。

For a long time,the late Permian coal-bearing formation in the study area were divided into chaos. In order to make the geological survey and geological exploration work successfully carried out in the future,the authors divided and contrasted the Late Permian coal-bearing formation from two aspects: lithostratigraphy and sequence stratigraphy. The whole Late Permian coal-bearing formation is the Xuanwei formation of continental strata in west area of Junlian-Yiliang Huailai. In the east of the Weixin-Bijie Qingchang,the early Late Permian is the Longtan formation of marine-terrigenous facies,and the late late Permian is the Changxing formation of neritic facies. The whole late Permian coal-bearing formation between the two regions is the Longtan formation. The upper section of the Longtan formation is comparable to the upper section of the Xuanwei formation in the west and the Changxing formation in the east.The lower section of the Longtan formation is comparable to the lower section of the Xuanwei formation in the west and the Longtan formation in the east.From the sequence stratigraphy,the Longtan formation in the east is corresponding to the coal-bearing formation below the C5 coal seam in the west( the lower section of the Longtan formation or the lower section of the Xuanwei formation),the Changxing formation in the east corresponds to the coal-bearing formation above the C5 coal seam in the west( the upper section of the Longtan formation or the upper section of the Xuanwei formation). The Longtan formation in the study area is time-penetrating,that is,from the early late Permian to late Permian,and the Longtan group is rising from east to west. The Longtan formation in the study area has the characteristics of diachronism,that is,from the early late Permian to late Permian,the Longtan formation is rising from east to west.