海侵作用影响下的高分辨煤相序列及其古泥炭沼泽发育模式——以山西北部安太堡上石炭统太原组11号煤层为例

High-Resolution Coal Facies Sequence and Peat Paleo-Bog Pattern during the Transgression

古泥炭沼泽是煤聚集的主要场所,也是含煤地层沉积过程的重要环节。煤相及相关地球化学特征,是指示古泥炭沼泽条件的重要标志。为此,本文以山西北部安太堡上石炭统太原组11号煤层为例,在煤相研究的基础上,结合地球化学研究,从沼泽水体动力条件、盐度和氧化还原性三方面,对煤相及其古泥炭沼泽的发育过程进行了精细研究。结果显示,其演化具有4个特点。第一,煤相包括5种类型,即障壁岛-泻湖低位沼泽相(A)、下三角洲平原低位沼泽相(B)、上三角洲平原低位沼泽相(C)、上三角洲平原潮湿森林沼泽相(D)和山前冲积平原干燥森林沼泽相(E)。第二,煤相发育过程经历了7个演化阶段,每一阶段均为半旋回,旋回内部的演化具有跳跃性,揭示泥炭沼泽水面可能发生过脉动式上升。第三,古泥炭沼泽起始于海进作用,发展于缓慢海退的沉积背景,结束于快速海进事件,整个地质过程明显受到海水入侵的影响,其间沼泽水体的盐度和还原程度呈逐渐降低的趋势,水动力趋于增强,沼泽类型从以A相和B相为主演化为以D相和E相为主。第四,古泥炭沼泽发育期间的海退过程由一系列次级快速海进或海退事件构成,呈现出波动式海退的特征,导致泥炭沼泽类型呈跳跃式演化。最后,该期间最大一次快速海进事件的到来(第Ⅶ阶段),结束了古泥炭沼泽整个发育历史。

Coal accumulation occurs mainly in peat paleo-bog and is also a key link during the sedimentation of coal-bearing strata. Coal facies and related geochemical parameters are important indicators for the paleobog conditions. Thus, based on the coal facies investigation, the authors in this paper, taking the No. 11 coal seam of the Upper Carboniferous Taiyuan Formation as a case, made a high-resolution research of the peat paleo-bog evolvement and its pattern in the sight of the dynamic condition, salinity and redox of the bog water. The results showed the four characteristics of the bog evolvement. Firstly, the coal facies existed in five types, i.e. , the low moors under the barrier-lagoon （facies A）, lower delta plain （facies B） and upper delta plain （facies C）, the wet forest swamp under the upper delta plain （facies D） and the dry forest swamp under the piedmont alluvial, plain （facies E）. Secondly, the coal facies developed in seven evolving stages, each of which occurred in semi-cycle and the facies sequence within each cycle evolved in jump, which indicated a pulsant ascendance of the bog water surface. Thirdly, the peat bog was formed due to a transgression, developed under the setting of the slow regression, and ended at a fast transgression. The whole geologic process was evidently effected by the seawater infall, during which the salinity and reduction potential of the bog water tended to reduce, the dynamic condition tended to increase, and the facies evolved from main A ＆ B to main D ＆ E. Fourthly, the transgression process during the paleo-bog development was made of a series of secondary fast transgression and regression events, and was characterized by the undulation, which Finally, the paleo-bog ended due to the advent of development. resulted in the jumpy exchange of the bog types. the greatest fast-transgression during the bog