Syndepositional Fault Controlling on Depositional Filling of the Third Member of Shahejie Formation in Beitang Sag

In the continental lake basin whose structures were extraordinarily active, tectonism is an important factor in controlling the sequence and the depositional filling of the basin. This article reports the assemble patterns of syndepositional fault in the third member of Shahejie （沙河街） Formation in Beitang （北塘） sag. The results show that the comb-shape fracture system and the fracture transformation zone were developed in Beitang sag. These assemble patterns obviously controlled the sand-body and spatial distribution of sedimentary system. However, the steep slope belt of fault terrace, the multistage slope belt and the low uplift gentle slope belt controlled the development of sequence styles. Analyses of the spatial-temporal relationship of the assemble pattern of syndepositional faults and the sedimentary system help predict the favorable exploration zone.

The important turning points during evolution of Cenozoic basin offshore the Bohai Sea:Evidence and regional dynamics analysis

The Cenozoic basin offshore the Bohai Sea underwent a multicycle-rifting during its evolutionary process, which resulted in the multiple unconformities in the strata. The tectonic activities shown by these unconformities have different manifestations and influences on the basin evolution. The authors systematically analyze the tectonic evolution characteristics of the sags off-shore the Bohai Sea with a large set of hydrocarbon exploration data. The analysis reveals that two phases of tectonic activities during the late depositional stage of the third member of Shahejie Formation (about 38 Ma) and the late depositional stage of Dongying Formation (about 24 Ma) reflect the significant changes in the basin's features and structural framework before and after these tectonic activities. As a result, the two phases of tectonic activities are recognized as important turning points (i.e., tectonic transitions) of Cenozoic basin evolution. The regional dynamic backgrounds of the two phases of tectonic transitions are also discussed. It is suggested that the early tectonic transition occurred at about 38 Ma under such regional dynamic back- ground that a huge kinematics adjustment happened between Eurasian Plate and its neighboring plates, i.e., Pacific Plate and Indian Plate. Meanwhile, the Tan-Lu Fault's slip reversed from left lateral to right lateral. The late tectonic transition occurred in late Paleogene (about 24 Ma) and reflected the Himalayan orogeny's influence on the Chinese continent and even the Asian continent; at the same time, the stress field produced by the escape tectonics was related to the Himalayan orogeny, superposed on the pre-existing stress field, and then enhanced the right lateral slip activity of the Tan-Lu Fault.