Abstracts Category : Other

Dating Deltas

by Elizabeth L Chamberlain

Deltas are highly complex landscapes characterized by dynamic processes of growth and decline that may be driven by a multitude of factors. A greater level of understanding of deltaic processes is now possible through luminescence dating approaches, which enable the direct dating of clastic deposits. This dissertation applies luminescence dating to identify fundamental mechanisms of delta evolution in a pre-anthropogenic system over centennial to millennial timescales. Topics explored here include the rates and patterns of land-building, and the primary drivers, rates, and spatial variability of subsidence. In addition to applications, this dissertation makes contributions to the science of luminescence dating through the development of new techniques and assessments of luminescence characteristics of sediment in two megadeltas, the Mississippi and Ganges-Brahmaputra-Meghna deltas. The results herein show that river-dominated deltas operating under natural conditions grow in a radial pattern where sediment resources are directed by avulsions that occur over a broad spatial zone extending well landward of the delta, and decline in elevation due largely to compaction induced by sediment loading. Zeroing (or bleaching) of the luminescence clock is tested through a new "Bleaching Index" that compares multiple signals obtained from polymineral sediment, and through measurements of modern analogues. These tests show that quartz silt is likely to be well-bleached in large river-delta systems, a finding which extends the prospects and geographic range of luminescence dating. 1 Elizabeth L. ChamberlainAdvisors/Committee Members: (author), Trnqvist, Torbjrn E. (Thesis advisor), (Thesis advisor), School of Science & Engineering Earth and Environmental Sciences (Degree granting institution).