Yoredale cycle,including limestone,coal seam and terrigenous clastic rock,is characterized by direct sedimentary contact between coal seam roof and marine limestone.Previous studies have given several completely different causes for this cycle.In order to explore the real formation mechanism of the cycle,the sedimentary characteristics of coal accumulation period in geological history are compared with the sedimentary regularities of modern vegetation, peat—swamp and carbonate rock.The analysis results show that the plants were extremely prosperous in the coal accumulation period of geological history,and dominated the basin evolution stage.Under the confinement of advance vegetation,extremely less terrigenous debris input into the basin,forming a dynamic peat—swamp.After the peat—swamp is covered by water,even shallow water is very clear.The formation of limestone is promoted by the interaction of aquatic organisms with the deposited organic matter,and the subsequent diagenesis cementation.From the top of the coal seam to the bottom of the limestone,it represents the littoral without detrital input, forming a sedimentary sequence with gradually increasing water depth.Limestone and underlying coal seam are continuous deposition.The formation of Yoredale cycle is due to the limitation of terrigenous clastic input by advance vegetation,which leads to clear and normal transgressive and regressive sediments.Although the thickness of limestone and coal seam is not very large,the lateral continuity is good.The coal seam thickens and the limestone thins in the direction of terrigenous source,while the coal seam thins and the limestone thickens in the direction of sea.Thick coal seam can be formed in the continental direction of the Yoredale cycle.The discovery of the truth of Yoredale cycle has laid a solid foundation for the study of sedimentary paleogeography and sequence stratigraphy,as well as accurate regional correlation and exploration of coal accumulation regularity.