厚煤层成因机制——天文周期控制的多期次泥炭沼泽叠加模式

Genetic mechanism of thick coal seams:astronomical-forcing superimposed multi-staged swamp model

蕴含丰富地质信息的厚煤层是重要的地质碳库及地质信息库,我国是煤炭资源大国,华北、西北、东北、华南等聚煤区都发育有厚煤层。传统煤田地质学认为,厚煤层是泥炭沼泽潜水面上升速度与植物遗体聚集速度长期处于均衡补偿状态下的连续聚集产物。但现今发育的泥炭沼泽单层最大厚度仅为20 m,考虑泥炭到烟煤成煤过程受到高达约6∶1的压实比例,均衡补偿成因解释厚煤层的形成可能存在一定的不合理性。基于煤岩学、层序地层学、旋回地层学的理论和研究方法,对不同盆地厚煤层中反映气候变化的天文周期信息开展研究。结果表明,厚煤层中煤岩显微组分以及灰分在垂向上的周期性变化和沉积间断面的存在,是多期次泥炭沼泽叠加形成厚煤层的重要依据。泥炭沼泽多期次叠加及厚煤层中煤岩显微组分的周期性变化均受当时的气候环境演化影响,而气候环境的演化又受控于天文周期。综合已有的厚煤层成因观点和实例研究,提出受天文周期控制的多期次泥炭沼泽叠加成煤理论和模型,用于解释厚煤层的成因机制。

Thick coal seams contain rich geological information and are important geological carbon pools.China is a country with abundant coal resources,and the thick coals were developed in the northern China,northwestern China,northeastern China,southern China,and other coal accumulation zones.According to the traditional theory of coal geology,thick coal seams are the product of the long-time equilibrium compensation between the rising water table and the accumulation of plant remains in paleo-swamps.Equilibrium compensation is proposed to explain how thick coal seam is formed.However,since the maximum thickness of a single modern peat bed is only 20 m,and from peat to bituminous coal the peat will be subjected to up to 6 times compaction,it is unreasonable to explain the formation of thick coal seam by equilibrium compensation.The vertical and periodical variation of coal macerals and ash yields in thick coal seams and the hiatal surfaces existing within the coal section reflect the multi-staged development of coal-forming swamps.Based on the methodology of coal petrology,sequence stratigraphy and cycle stratigraphy,this study has investigated the astronomical periodic signals preserved in thick coal seams,and has found that the superimposed pattern of peat swamps and the variation of maceral compositions and yields in coal seam are influenced by the paleo-hydrology in paleo-swamp which is closely related to the climatic changes induced by the forcing of astronomical cycle.Considering the existing views and case studies on the genesis of thick coal seams,we put forward a new mechanism for the thick coal accumulation,i.e.,the astronomical-forcing superimposed multi-staged swamp model.