| Popis: |
The Sundarbans is one of the largest coastal wetland sites in the world that covers an area of approximately one million hectares in the delta of the Ganges and Brahmaputra (G-B) rivers located across Bangladesh and India. This thesis sets out to examine sedimentation taking place in the western, 'abandoned' tidal delta over the course of the mid-to-late-Holocene epoch, c. last 4000 cal yr BP. This will focus on investigating the dominant sources and depositional processes through grain-size distributions, mineralogy, and high-resolution core-scan derived geochemistry of sediments for provenance and depositional process indicators. By approximately 5000 cal yr BP, the Ganges River had largely abandoned the western delta complex underlying the present day Indian Sundarbans and migrated eastward towards its present day course. The western extent of the old G-B delta is now considered to be undergoing net erosion, at least since the middle ofthe 19th century. This thesis seeks to test and challenge these assumptions. The results from this thesis suggest that sedimentary provenance is dominated by a mixed Ganges-Brahmaputra source, composed mainly of silicate weathering products, with the possibility of greater Ganges inputs. The depositional environment is characterised by a sedimentary facies record similar to that of a muddy-tidal flat with a dominant fining-up of the grain size distributions, capping what may potential sub-tidal ridges. Radiocarbon results reveal an overarching trend in stratigraphically anachronous dates that are potentially indicative of fluctuating depositional processes present throughout the Sundarbans. Sedimentation processes in the Sundarbans appear to reflect the ebband flood-tidal conditions which may be overprinted by monsoonal variability. A novel development in the methodological approaches pursued in this research has been through the compositional data analysis (CoDa) framework. The Sundarbans may be considered to be a dynamic sedimentary depositional environment that is under constant flux. |
