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

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 seamLMare 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.