Sedimentary characteristics of clay deposits associated with coal beds and their geological implications for the Eastern Yanzhou Coalfield, North China

摘要

Coal geology, sedimentology, sequence stratigraphy, and geochemistry were used to study the depositional environment, formative mechanisms, and clay layers' distribution of the Eastern Yanzhou Coalfield. The 3rd coal bed and its floor (roof) clay layer were formed in the inter- distributary settings of a river-dominated shallow-water delta system. Clay deposits under 16-1st and 16-2nd coal beds were formed during the transgressive process, whereas clay deposit under the 17th coal bed was formed in event transgression.Through chemical analysis, the clay stone under the 3rd coal bed was demonstrated to be influenced by the brackish water, differently, the clay stones under the 16-1st, 16-2nd, and 17th coal beds were influenced by sea water. The clay stone under the 3rd coal bed was affected by sea water longer than the clay stones of the 16-1st, 16-2nd or 17th coal beds. Also, the exposure time before the peat swamp of the 17th coal bed was longer than that under the 16-1st and 16-2nd coal beds. 3rd coal bed and clay layer were found to have the same distribution rule. Thicker beds were distributed in the south. In the north, the beds getting thinner indicated that the clay stone was formed in active depositional systems. 16-1st coal bed and its floor clay layer distribution reflected that transgression happened from south to north. The 16-2nd coal bed and its floor clay layer distribution indicated that transgression happened from the northwest to southeast, and the 17th coal bed and its clay floor layer distributions demonstrated that the transgression happened in the event transgression.