Lacustrine Shale Deposition and Variable Tectonic Accommodation in the Rift Basins of the Bohai Bay Basin in Eastern China
- Received Date: 2015-10-16
- Accepted Date: 2015-10-16
- Available Online: 2015-10-16
Abstract: Organic-rich lacustrine shales are widely distributed in China and have significant potential for unconventional shale gas and oil production although the primary factors controlling the deposition of lacustrine shale are disputed. This work clarifies the different characteristics of tectonic evolution and shale among sub-basins in the Bohai Bay Basin in eastern China as a case study by stud- ying basal subsidence, tectonic subsidence rate, basin extensional proportions and shale chemical cha- racteristics. The paper summarizes the correlation between structure and shale deposition, and con- cludes that tectonic activity is the primary controlling factor for shale development. Episodic tectonic activity controls not only the timing of shale deposition (with the greatest shale deposition occurring primarily during the peak period of basin tectonic activity) but also the spatial distribution of shale (located mainly in areas of maximum subsidence), the migration pattern of shale (conforming to that of the basin subsidence center), and shale strata thickness. Tectonic activity also affects the total organic carbon content and organic matter type in shale. When the tectonic activity was the most active and basal subsidence was the maximum, the total organic carbon content of the shale reached its highest value with organic matter type mainly Type I. As tectonic activity weakened, the total organic carbon content decreased, and the organic matter type changed from Type I to Type I-III.