近海型含煤岩系沉积学及层序地层学研究进展

Advances in sedimentology and sequence stratigraphy of paralic coal measures

层序地层学是近20年来发展起来的一门新的方法学科,并在聚煤作用分析中得到广泛应用。作者就近海型含煤岩系沉积学研究历史以及煤系层序地层学研究方法及有关问题进行探讨,认为近海环境的聚煤作用实际上是海平面(基准面)上升过程中发生的,同时提出煤层厚度受泥炭堆积速率与可容空间增加速率的控制:靠陆一侧冲积平原和三角洲平原沉积环境中,厚煤层主要出现在最大海泛面位置;而靠海一侧障壁—潟湖或碳酸盐岩台地沉积环境中,厚煤层主要出现在初始海泛面的位置;但就整个三级复合层序来说,层序中厚度最大、分布最广的煤层主要分布于可容空间增加速率最大的最大海泛面附近的位置。对于中国晚古生代近海型煤系中常见的"根土岩—煤—石灰岩"序列,聚煤作用发生于海相石灰岩"滞后时段",即在海侵之后、海相石灰岩层真正沉积下来之前的时段,这一时段可容空间增加速率与泥炭堆积速率平衡,有利于聚煤作用发生。

Sequence stratigraphy is a newly developed methodological subject over last two decades and it has obtained significant application in coal accumulation analysis. This paper discussed the brief history of sedimentologieal research, coal sequence stratigraphy research methods and related aspects of the paralic coal measures. Paralic setting is characterized by the vast fiat topography and the frequent marine transgression, which is favorable for the multi-staged coal accumulations. In this setting, coal accumulation mainly occurs in the process of sea level （base level） rise and the coal seam thickness is controlled by the peat accumulation rate in balance with the rate of accommodation creation. On the landward of the paralic setting which is represented by alluvial plain and delta plain environments, thick seams tend to be formed at late transgressive systems tract or early highstand systems tract around the maximum flooding surface. In contrast, on the seaward of the paralic setting which is represented by the barrier - lagoon or carbonate platform sedimentary environments, the thick seams tend to occur at the early transgressive systems tract around the transgressive surface （initial flooding surface） or the late highstand systems tract. In a third-order composite sequence, the thickest and most widely distributed coal seams are mainly distributed near the maximum flooding surface. It is proposed that the coal in the ＂seat earth-coal-marine limestone＂ successions was formed during the ＂lag time＂ of marine limestone deposits - prior to the real deposition of carbonates after transgression. During this ＂lag time＂, the development of balanced accommodation creation rates and peat accumulation rates might favor the accumulation of thick coals.