Determination of second-order stratigraphic sequences in continental extensional basins

Based on the boundaries and interior depositional evolutions of second-order sequences in the continental extensional basins and their coupling relations with the tectonic actions and subsidence histories,the Paleogene strata in the Cenozoic basins of the eastern China can be divided into 4 or 5 second-order sequences.The boundaries of those second-order sequences generally belong to the regional angular unconformities.The fossil assemblages and sedimentary characteristics of a single second-order sequence in upper interface are much different from the underlying ones.Some large-scale low-stand fans are usually developed at the bottom of sequence,and a large-scale transgress-regressive succession is presented in the second-order sequences.The second-order sequences are corresponding to the episodic stages of tectonic evolution,and their boundaries are resulted from the tectonic affairs such as reverse of tectonic,tilting and rotating of fault block,intruding of magma,breaking forth of volcanic and change of tectonic stress field.The second-order sequences in the continental extensional basins are controlled by the regional tectonic actions.So,the genetic relationship of sequences with tectonic actions can be used to determine the second-order sequences.