Abstract:

On the basis of the new results of the CCSD (China Cretaceous Continental Scientific Drilling) and the integrated information concerning tectonic basin classification and 3D description of the Songliao Basin (SB), we reevaluate the type, tectonic evolution, and geodynamics of the SB according to systematical analysis of tectonic setting and basin fillings. The SB is on the northeast marginal zone of MongoliaNorth China Plate. It is united with the Siberian Plate by the MongoliaOkhotsk suture belt to the north, and connected with the Pacific Plate by SikhoteAlin accretionary belt to the east. The vertical filling successions of the SB can be subdivided into three tectonostratigraphic units by two regional unconformities which are on the top boundaries of the Yingcheng (K1y) (ca. 110 Ma) and Nenjiang (K2n) (ca. 79.1 Ma) Formations, respectively. The three tectonostratigraphic units are block faulting (Huoshiling to Yingcheng Formations), interior sag (Denglouku to Nenjiang Formations), and structural inversion (Sifangtai to Yian Formations) sequences. The block faulting sequence is a kind of volcanic rift basin, and the latter two all belong to the type of interior sag basin. In the block faulting period (150110 Ma), synrift volcanogenic successions were formed under the impact of regional extension that may be caused by the Plate reorganization from two sides, the northern and eastern active continental margins. The postrift basin fills (11079.1 Ma) may result from the superimposed subsidence of both post volcanic thermal declining and regional strikeslip pullapart effect. Widespread and thick source rocks deposited because of the high rate and undercompensation of sedimentation in this period. In the structural inversion period (79.140 Ma), depocenter of the SB migrated northwestward, and the basin was shrinking to demise. This was a result of the regional compression that should be caused by the Pacific Plate subduction under the eastern margin of the Eurasian Plate in the MidCretaceous to the Middle Eocene.

Key words: Late Mesozoic Songliao Basin, volcanic rift/interior sag basin, North China/Siberian/Pacific Plate, Xilamulun River/SikhoteAlin/MongoliaOkhotsk suture belt