蒙古国南部–西南部晚二叠世海相含煤盆地发育和煤层赋存规律

Developing of Late Permian Coal-Bearing Marine Basins in South-Southwest Mongolia and Regularities of Coalbed Occurrence

摘要: 蒙古南部及邻区的残留海盆经历了早–中二叠世和晚二叠世两大演化阶段，反映在沉积上是从粗碎屑岩开始向上变细并夹灰岩的两大旋回。晚二叠世南戈壁盆地的塔温陶勒盖组岩性上可分为三段，发育底部、下部、中部、上部和顶部五个煤组。成煤作用的开始有东早西晚之势，含煤海盆的反转则西早东晚。基于主要矿田的含煤地层的发育和分布总结了煤层赋存规律，分析了堆积位置和同生正断层对煤层发育的影响。因碰撞造山带坍塌而发育伸展盆地，兼之东西向断层的伸展和近北东向断层的张扭，使南戈壁盆地晚二叠世保持为一开阔海盆，宽阔的滨海平原上能长期且多次发育泥炭沼泽而成为富煤盆地。因西南蒙古海侵及南戈壁盆地扩大，上部煤组堆积期是成煤作用的全盛期。

Abstract: One of the main features of evolution of the south branch of the Paleo-AsianOceanwas that there developed residual marine basins after disappearance of the oceanic crust. In southMongoliaand its neighboring areas, the residual marine basins experienced two developing stages: Early-Middle Permian and Late Permian. Correspondingly, two main sedimentary cycles could be recognized, and each one was an upward-fining succession composed of the basal conglomerates and upper fine clastic rocks. The Late Permian coal-bearing strata in theSouthGobiBasinis named the Tavan Dolgoi Formation, which can be separated into three members lithologically. Five coal seams occurred during Late Permian, called the basal, the lower, the middle, the upper and the top seams respectively, which showed a tendency that the coal-forming process might be earlier in the east and reversal of the marine basins earlier in the west. Based on analyses of the stratigraphic columns and distribution of coal-bearing strata in the main orefields, the regularities of coalbed occurrence were summarized, which pointed out the roles of depositing locations and contemporaneous normal faults in the coal-forming process. To be an extensional basin related to collapse of the collisional orogenic belt, superimposed the rifting of the latitudinal faults and the transtension of NE-striking faults, resulted in the South Gobi region to keep on a wide marine basin during Late Permian, and the peat marsh developed repeatedly in the open littoral plain for a long time, which made it become a coal-rich basin. The transgression occurred in SW Mongolia and theSouthGobiBasinexpanded during deposition phase of the middle coal seam, so that the deposition phase of the upper coal seam was a flourished time for coal-forming process.