Master of Science (MS)
Geology and Geophysics
During the last glacial period, river systems responded to the lowering of sea level by incising valleys, extending across the continental shelf, and depositing deltas on the shelf margin and upper slope of surrounding basins. These deltas represent important repositories for sediment delivered to the coastal ocean and provide partial records of sediment discharged from continental landmasses. Over relatively short time scales, like that of the last glacial-interglacial cycle, hinterland drainage areas, relief and lithology can be considered constants while the primary variable of significance is climate change (Syvitski and Milliman, 2007). It is reasonable to assume, therefore, that supply rates would have been different during the last glacial period, relative to the modern interglacial. For the northern Gulf of Mexico (GOM), a recently summarized body of data documents volumes of sediment sequestered in a variety of shelf and shelf-margin deltas (Anderson and Fillon, 2004): from this database, individual workers have suggested the sediment discharge of large rivers was significantly greater during the last glacial period than the present. This thesis tests the plausibility and necessity of these previous interpretations and attempts to move towards a first-generation sediment budget that contrasts interglacial versus glacial periods for river systems that discharge to the northern GOM. Recently developed empirical models of sediment supply (Syvitski et al., 2003; Syvitski and Milliman, 2007) are used to estimate supply rates for modern river systems and the role of glacial-period boundary conditions on supply rates. The spectrum of possible sediment fluxes derived is then used to ascertain changes in sediment supply necessary to account for the observed sediment mass in shelf-margin deltas. This thesis has found that for the last glacial period: (a) model estimates for sediment yield are lower than present values due to temperature depressions; (b) model estimates for sediment discharge are lower, except for the Mobile and Brazos Rivers due to their increase in drainage area; and (c) in all but one case, observed sediment volumes are significantly less than model estimates of sediment discharge over the inferred time periods of deposition.
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Womack, Jill Hattier, "Empirical modeling of late quaternary sediment supply to the Gulf of Mexico shelf margin in a cool lowstand world" (2007). LSU Master's Theses. 2979.
Michael D. Blum