Cenozoic Coal Accumulation Regularity And Controlling Pattern In China Offshore

For a long time,the cognition of coal accumulation regularity in China offshore is very limited,distribution of coal seams,spatiotemporal migration of coal accumulation,major geological factors of coal-controlling pattern and other basic information about coal accumulation are lock of systematic cognition.In this paper,by using coal field geology,tectonic geology,sedimentary geology and paleoclimate analysis,following conclusions have been drawn:The Cenozoic coal-bearing strata of the coal-accumulating basin in the China offshore are mainly developed during the Eocene to the Oligocene.The Coal-bearing strata developed five sedimentary facies types,named river,fan delta,delta,lake and lagoon-tidal flat.They can be divided into 14 sedimentary subfacies and 20 sedimentary microfacies.Based on the results of geophysical logging interpretation of drillings in China Offshore,we found that coal seam in China has the characteristics of thin layer thickness,large number of layers and wide distribution.Based on coal petrology experiments,it is revealed that the coal rank in the South China Sea is steam-fat coal,and the coal rank in the East China Sea and the Bohai Bay basin is lignite-long flame coal,which has the increasing trend from north to south and from east to west.Based on the organic maceral composition,two kinds of coal types are divided,namely concrete marsh and shallow concrete marsh.Combined with trace element test results,we reveal that the frequently fluctuation changes of sedimentary background have profound influence on the development of peat swamp and coal seam.Based on the geological interpretation results of the seismic profile,we found that the development of the coal-bearing strata is obviously controlled by Syndepositional fault,the structure of the " asymmetrical graben" is developed,and the fault angle of the Pearl River Mouth Basin is larger.The activity of the coalbearing basin with the syndepositional faults are gradually weakened from the Eocene ? the Oligocene ? the Miocene.The activity of faults in north,East is stronger than that in south,West,respectively.Based on the characteristics of tectonic,tectonic evolution process of the coal-bearing basin is divided into five stages: the Rift ? stage,Rift ? stage,Rift ? stage,the thermal subsidence stage,and the new structure stage.Coal accumulation is mainly controlled by the three rift period.Based on the above research,the result show that the main coal accumulation period in China Offshore changes newer from north to south,and the main coal-bearing strata is raised from north to south,the coal accumulation scope is gradually expanded from east to west.We also found that the difference of rift-depression transformation time,tectonic stability and depositional environment are the main controlling factors of the characteristics of the Cenozoic coal accumulation.At last,the tectonic-sedimentary coal-controlling pattern of typical basins in China offshore is established.