Study of sequence stratigraphy of the Early Cretaceous coal measures in Northeastern China

Sequence stratigraphy and coal accumulation of the Early Cretaceous coal measures in the northeastern China have been studied using outcrop and borehole data in this paper. Based on the regional unconformity surface, the erosional base of incise valley fill sandstone/conglomerates, the vertical facies reversal surface and paleontological evidence, a total of six sequence boundaries have been identified, which subdivide the Early Creataceous coal measures into five third-order sequences. SequenceI was developed at the initial subsiding stage. SequenceII and Sequence III were developed during the further subsiding stage. While Sequence IV and SequenceV were developed during the basin Shrinkage Stage. Sequence II represented the early period of the basin subsiding stage and Sequence IV represented the beginning period of the basin shrinkage stage. Strength of coal accumulation tendency from SequenceIto Sequence V was: weak, strong, weak, strong and weak. During these periods the relative balance between the increase rate of accommodation space and the peat accumulating rate favored the accumulation of the regional thick coal seams. These two sequences correspond to the lower coal seams and the upper coal seams.