Seismo-stratigraphic Study of The Northeastern Bengal Fan Deposits off the Rakhine coast Myanmar: Geometry and Characteristics of Deep-water Channels

Abstract

On the basis of a high resolution 3D seismic survey with long record length, which was originally acquired in 2012 for oil and gas exploration in deep water area off the Rahkine coast Myanmar, an integrated 3D seismo-stratigraphic study was carried out in the northeastern part of Bengal Fan, aiming at identification and description of various types of submarine channels in the thick interval from Eocene to Holocene during which the Bengal Fan had been developing, and further at a framework of seismic stratigraphy for the Bengal fan deposits in the study area. It is revealed by seismic interpretation that the total thickness of Bengal Fan deposits in the study area ranges from 6500m to 8000m, which is bounded by seabed on the top whose depth ranges from 1300m to 2100m and the Eocene unconformity at base which is postulated to be the time of first deposition of the fan shortly after the initial India-Asia collision. In addition, seismic interpretation also indicates that the Bengal Fan is thickened to the north and east due to oblique subduction of India plate to Eurasian plate. Various types of submarine channels with varied dimension, such as confined channel complexes, aggradational channel-levee complexes and individual isolated channels could be identified in the thick interval of submarine fan deposits because of their highly erosive features on seismic section and sinuous and/or linear characteristics on stratigraphic slices of seismic attributes. It is observed that most of these channels are NW-SE oriented which may imply that they are mainly derived from north rather than from Indo-Burma Ranges to the east. There are, however rarely, submarine channels that are flow from northeast to southwest in Pleistocene, which may represent minor east provenance of the fan deposits in the study area. The changes regarding to geometry and scale of these submarine channels are visible on seismic sections which are approximately perpendicular to the orientation of the channels. The Tertiary-Quaternary succession has been subdivided to six informal stratigraphic units on the basis of five seismic stratigraphic interfaces which were defined according to the changes of submarine channels. Each interface could be relatively easier to be traced because of better continuity on seismic section than underlain and overlain seismic reflectors, and presumed to be the top of a condense section that represents a sea level high in history. At the bottom of the analyzed succession, Bengal Fan deposits in the study area start with a stratigraphic unit characterized by low amplitude seismic reflectors without channel identified. Above it, there are four stratigraphic units featured by confined channel complexes with various scale and stacking type, which eroded to the older sub-fan surface and is comparable to the middle and lower fan channels on the modern Bengal Fan. The confined channel complexes in the first units are relatively less developed. Then in the second and third units, confined channel complexes are extremely developed with some kind of difference in erosive depth and cross sectional area. In the fourth units of confined channel complexes, the scales of the channels are relatively small and individual channel are more developed. The upper most stratigraphic unit is characterized by large channel-levee complexes with spectacular Gull wing levee, these channels do not cut into older stratum, which are comparable to the upper fan valley on the modern Bengal fan.

AAPG Datapages/Search and Discovery Article #90336 ©2018 AAPG Asia Pacific Region, The 4th AAPG/EAGE/MGS Myanmar Oil and Gas Conference, Myanmar: A Global Oil and Gas Hotspot: Unleashing the Petroleum Systems Potential, Yangon, Myanmar, November 13-15, 2018