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

Abstract

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.