辽西八道壕煤盆地层序地层与成煤环境分析

Analysis on the Sequence Stratigraphy and Coal-forming Environment of Badaohao Coal Basin in Western Liaoning Province

辽西黑山—彰武地区分布有一系列早白垩世断陷成因的陆相盆地,其中以八道壕煤盆地含煤性最好。本次工作在八道壕煤矿深部勘探区,采用二维地震、钻探、测井等对八道壕组进行了层序地层和成煤环境分析。八道壕组可分为三个三级层序,下部第1层序(Sq1)为冲积扇注入湖盆形成的水下扇—扇三角洲沉积体系,湖侵域和高位域各含一个煤组,湖侵域退积的水下扇边缘和高位域扇三角洲前缘都有厚煤层发育。早期冲积扇自盆地西南注入湖盆,煤层发育在断陷较深的中北部,自西侧盆缘断裂附近向东超覆。Sq1湖侵域的煤层比高位域的煤层分布面积要大。盆地南部冲积扇主体部位粗碎屑岩增多,上、下煤组的煤层均向南变薄尖灭。由于物源区构造抬升冲积扇向湖盆的进积作用加剧,八道壕组中上部第2、3层序粗碎屑沉积物增多,湖盆水域面积缩小,煤层不再发育。

A series of Early Cretaceous terrestrial faulted coal basins distributed in the Heishan-Zhangwu district, western Liaoning Province, China. The study area Badaohao Basin is the best one with thick coal seams. By use of two-dimensional seismic, drilling and geophysical logging, a study of sequence stratigraphic and coal-forming environment analysis of Badaohao Formation in the exploration deep area of Badaohao Coalmine has completed. Three third order sequences can be divided in the Badaohao Formation. The lower first sequence Sql consists of subaqueous fan-fan deltaic depositional system caused by an alluvial fan intruding into a lacustrine basin. There are two coal seam groups occurred in each of the transgressive system tract and high-stand system tract. In transgressive system tract thick coal seams developed in front of the regressive subaqueous fan whereas in high-stand system tract thick coal seams developed in front of the progressive fan-delta. In early coal forming stage the alluvial fan emptied into the lacustrine basin from the southwest faulted area and thick coal seams developed in the central north deep depression of the basin, overlapping from the west to the east. Coal seams of transgressive system tract developed more extensively than that of high-stand system tract. Both coal seams in transgressive and high-stand system tracts all became thinner and pinch out to the south where the alluvial fan conglomerates increased. Due to uplift of the source area the alluvial fan progradating rapidly in the basin, the second and third sequences of the middle and upper parts of Badaohao Formation contains mainly coarse clastic deposits and the water area of the basin reduced, nearly no coal seams developed any more.