低位体系域成煤环境与聚煤特征

低位体系域煤层在层序划分中越来越重要,其成煤模式也成为研究的重点问题。本文总结了低位体系域成煤沉积环境,分析了海相和陆相断陷盆地低位体系域煤层的形成环境及其岩性空间变化特征,指出无论是滨海环境还是陆相环境,其成煤环境一般是位于河流下切谷旁边的浅水洼地或者河流阶地。其中,滨海地区低位体系域成煤一般较少,主要发生在晚古生代,煤层顶板为海相沉积(灰岩或泥岩等);陆相环境低位体系域成煤一般在中新生代,常见于辫状河、冲积扇或扇三角洲等,煤层顶底板沉积物颗粒较粗。低位体系域煤层煤质较差,煤层结构复杂,厚度差别较大。滨海地区,煤层硫分较高,灰分较大;而陆相断陷盆地,煤层灰分较高,河流分叉较多,这与湖盆水体动荡性及构造变化有关。

Coal-forming Environment and Coal Accumulation Characteristics of Low Stand System Tract

The coal seam in low stand system tracts becomes more and more important in sequence division and its coal-forming pattern has also become the key problem under study.This paper summarized the coal-forming depositional environment in low stand system tract,analyzed the coal-forming environment of low stand system tract in taphrogenic basin with marine facies and continental facies and its variant spatial characteristics of lithology,and pointed out that no matter what is the littoral or continental environment,the coal-forming environment is generally the area of shoaly depression located at the side of the down-cutting valley or terrace area of rivers.The coal seam of low stand system tract formed in littoral area is lesser,which mainly formed in Neopaleozoic Era and the coal roof is marine facies sedimentation(limestone or clay-stone).The coal-forming of low stand system tract with continental facies is mainly found in Mesozoic-Cenozoic Era,commonly found in the areas of braided stream,alluvial fan and fan delta,etc.,in which the sizes of sediments in roof and floor are coarser.The coal in low stand system tract is of poorer quality,complex structure,enormous difference in thickness,high sulfur & ash content in littoral area,and high ash & more branches in taphrogenic basin with continental facis,which is related to the swing of water body in limnetic basin and tectonic change.