A sequence stratigraphic analysis and coal accumulation of Late Triassic coal measures in the Baoding Basin

Principles and methods of sequence stratigraphy for drilling cores and well logging have been used to research these coal measures' sequence stratigraphy and coal accumulation.Twelve sequence boundaries were identified,which subdivided the Daqiaodi Formation into 1 second-order sequences,3 third-order sequences,and 11 fourth-order sequences.Vertically,the strength of coal accumulation of the second-order sequence of the Daqiaodi Formation was characterized by increased first and then decreased,with the most favorable time of coal accumulation occurring in the middle highstand system tract(SIII2).In the early of fault basin evolu-tion(SIV1-SIV5),the main coal seams' location close to the lowstand system tract,the early transgressive system tract and the middle-late stage of highstand system tract of the fourth-order sequence.In the middle-late stage of fault basin,with the reduction of the subsidence rate of basin basement and the position of the main coal seams transferred to nearly the maximum flooding surface.