The Bengal Fan: architecture, morphology and depositional processes at different scales revealed from high-resolution seismic and hydroacoustic data

Abstract

The Bengal Fan has developed as a result of the collision of India with Asia, resulting in the orogeny of the Himalayas. Erosion of the Himalayas since Eocene times had formed the largest submarine fan on Earth today. Accordingly, the Bengal Fan is well suited to study the tectonic and climatic history of the Himalayas, but also to analyze architecture and depositional processes of submarine fans and channel-levee systems in general. In this thesis, the active channel-levee system of the Middle Bengal Fan is described by a combined analysis of Parasound and Hydrosweep data. Morphological parameters of the channel and the structure of the levees are analyzed. The results are used to describe the built-up of the active channel-levee system, which is mainly controlled by frequent avulsions within the system leading to numerous cut-off loops. The development of the system is then discussed and compared with other submarine fans. Furthermore, high-resolution seismic data are used to reveal the structure of the active and buried channel-levee systems on the Middle Bengal Fan. Downfan changes of the individual channel-levee systems are analyzed, and differences between the systems are discussed. Two evolutionary scenarios for the active and one buried system are developed and discussed. Finally, the reservoir potential of channel-levee systems in the study area is described. Additionally, high-resolution seismic data collected on four long east-west profiles located on the Middle and Lower Bengal Fan are analyzed. The architecture of surface and buried channel-levee systems and their downfan variations are revealed and the built-up of distinct channel-levee complexes on the upper Middle Fan is discussed. The seismic stratigraphy of the southern profiles is linked to results of DSDP Site 218 and of the ODP Leg 116 site. The seismic results are discussed with respect to deformation events in the central Indian Ocean and to tectonic and climatic events in the Himalayas.