豫东地区石炭—二叠纪含煤岩系层序—古地理与聚煤规律OA

The eastern Henan Province is located at the southern edge of the North China Basin and is currently one of the main areas for coalbed methane exploration in China.The Permo-Carboniferous is the main coal-forming period in this area,and the coal measures were deposited in the marine-terrestrial transitional environments,being characterized by a wide and stable distribution.On the basis of drilling date,outcrop sections and geophysical logging date,the sequence stratigraphic framework was established for the Permo-Carboniferous coal measures in this area.Based on the regional unconformity surface,the coal-bearing series in the study area are subdivided into three third-order sequences.Combined with formation,percentages of limestones,mudstone thickness,sandstone to mudstone thickness ratios,coal thickness contour map,restore the sequence of the palaeogeographical maps,the main palaeogeographical unit with delta plain,barrier island,tidal-lagoon,and carbonate shelf.The coals in sequence Ⅰ and sequence Ⅱ were mainly formed in the tidal-lagoon environment,while the coals in sequence Ⅲ were formed in the delta plain and tidal environment.Among them,the major coal seam(A-0,A-5)in sequence Ⅰ and the major coal seam(B-1)in sequence Ⅲ are well developed.The A-0 and A-5 coal seam were formed in a peat swamp developed from the offshore shelf settings,located near the initial flooding surface and the end of the HST in sequence Ⅰ where the slow rate of sea level rise and thus the slow rate of accommodation space growth was balancing with the slow rate of peat accumulation,A-0 coal seam developed well in Zhecheng area and A-5 coal seam developed well in Huaiyang area.The B-1 coal seam was formed in the peat swamp environment developed from of the fluvial-dominated shallow water delta plain,near the maximum flooding surface of sequence Ⅲ where the fast sea level rise and thus the fast growth rate of the accommodation growth was well matching the high rate of peat accumulation.The balance between the rates in peat accumulation and the rates in accommodation space creation is a key condition for coal accumulation in the sequence stratigraphic framework.The B-1 coal seam developed well in Zhecheng,Huaiyang and Taikang areas.