Controls on facies distribution and stratigraphic preservation in the Ganges-Brahmaputra delta sequence

Abundant sediment supply and accommodation space in the Bengal Basin have led to the development of a major Late Quaternary delta sequence. This sequence has formed in a tectonically active setting and represents an important example of a high-energy (marine and fluvial), high-yield continental margin deposit. Recent studies have detailed the delta's stratigraphy and development, noting that tectonics and sediment supply control the Ganges-Brahmaputra more significantly than in many other delta systems. These ideas are developed here through a discussion of the effects that spatial and temporal variations in tectonics and sediment-supply have had on deltaic processes and sequence character. Unique and differing stratigraphies are found within the delta system, such that fine-grained sediment preservation is favored in areas of active tectonic processes such as folding, block faulting, and subsidence. Coarse-grained deposits dominate the stratigraphy under the control of high-energy fluvial processes, and mixed fine-coarse stratigraphies are found in areas dominantly influenced by eustatic sea-level change. Overlaid upon these spatially varying stratigraphic patterns are temporal patterns related to episodic events (e.g., earthquakes and rivers avulsions) and long-term changes in climate and sediment supply. Modeling is also used to investigate the influence of a variable sediment supply on sequence character. Results show that the timing and magnitude of sediment input, relative to sea-level rise, is a significant control on the subaerial extent of the delta and the relative dominance of alluvial and marine facies within the sequence. (C) 2002 Elsevier Science B.V. All rights reserved.