Structural Features and Proto-Type Basin Reconstructions of the Bay of Bengal Basin:A Remnant Ocean Basin Model

Remnant ocean basin is a key to understand the plate suturing and subsequent uplift and erosion of orogen. The Bay of Bengal Basin （BOBB） provides a typical example to analyze the remnant ocean basin structures, evolution, and relationships between depositional filling and uplifting of the Himalayan Orogen. Thirty-nine seismic profiles as well as interval velocities of well BODC3 were used to compile isopach maps of the basin. Among the seismic data, 26 seismic profiles were applied to estab- lish 8 cross sections. The cross sections suggest the basin is asymmetric, bounded to the west by the eastern continental margin of India （ECMI） with graben-horst and to the east by the Sunda conver- gence margin dominated by trench-arc system. The BOBB is characterized by a prominent down flex- ure structures caused by huge amount of Bengal fan turbidite sediments accumulation. Our isopach maps and chronology data collected from adjacent regions reveal the initial development and fast southward growth of the Bengal fan were related to the early and major stage uplift and erosion of the Himalayan Orogen, respectively. The BOBB has experienced a critical transition from an ocean basin to a remnant ocean basin at Late Oligocene. Such basin structures and evolution features indicate the BOBB provides whole records of oblique convergence of the India and Asia plates, and the early and major stage evolution of the Himalayan Orogen.

Evolution of Low-Angle Normal Faults in the Enping Sag,the Northern South China Sea: Lateral Growth and Vertical Rotation

Low-angle normal faults(dip<30°,LANFs)are widespread in the northern margin of the South China Sea where the maximum crust thickness is approximately 30.0 km.Based on 3 D seismic survey data and drilling wells in the Enping sag,evidences for LANFs that initially formed at high-angles are discussed.After a detailed investigation of extensional fault system and description of 3 D fault geometry,the initial fault dips under the model of distributed vertical simple shear are also calculated.The results indicate that the present-day dip angles of the LANFs are in the range of 12°to 29°,and the initial fault dip angles are in the range of 39°to 49°.Deep seismic imaging suggests that the upper crust in the footwall block of the LANFs was tilted at an angle of ~14°to 22°due to the isostatic rebound during rifting.Moreover,the temporal and spatial sequences of the lateral growth of the LANFs have been investigated by the seismic interpretation of four isochronous stratigraphic interfaces,which demonstrates that two individual fault segments propagated towards each other and subsequently,were hard-linked during the Early Eocene.

Geochemical Characteristics and Accumulated Process of Heavy Crude Oil of Chunguang Oilfield in Junggar Basin, China

Chunguang oilfield is a new focus of the exploration in Junnggar Basin with the heavy crude oil distributing in Jurassic, Cretaceous and Tertiary strata. Based on the analysis of the geochemistry and fluid inclusion in the reservoirs, the source, accumulated period and process of the heavy crude oil reservoir has been investigated. The results indicate that the heavy crude oil can be divided into three types based on the degradation and sources. The heavy crude oil was mainly derived from the Permian source rocks, and latterly mixed by the heavy crude oil generated by the Jurassic source rocks. The accumulated period of the heavy crude oil has two stages. One was ranged from Cretaceous to Paleogene and the heavy crude oil was sourced from Permian source rocks of the Shawan depression and latterly mixed by the heavy crude oil generated by the Jurassic source rocks. The second period was from Neogene to present and the heavy crude oil was mainly derived from the Jurassic source rocks. Combined with the geological evolution, the heavy crude oil accumulated process has been recovered.