Date of Award

Winter 12-7-2018

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)

School

Ocean Science and Engineering

Committee Chair

Dr. Davin Wallace

Committee Chair School

Ocean Science and Engineering

Committee Member 2

Dr. Jessica Pilarczyk

Committee Member 2 School

Ocean Science and Engineering

Committee Member 3

Dr. Michael Miner

Abstract

Coastal systems in the Gulf of Mexico are threatened to reduced sediment supply, storm impacts and relative sea level rise (RSLR). The geologic record can provide insights of geomorphic threshold crossings (formation, progradation, transgression, destruction) to these forcing mechanisms to predict future barrier evolution to climate change. The stratigraphic framework and antecedent topography directly influence coastal evolution over geologic timescales. This study synthesizes ~2100km of geophysical data, 700+ sediment cores, and 63 radiocarbon dates to regionally map two sequence boundaries, multiple ravinement surfaces and fourteen depositional facies. One marine isotope stage (MIS) 6 valley’s fill provided up to 300 x106 m3 of sand to modern systems through transgressive ravinement during the Holocene. Repeated storm breaches or tidal inlets correspond to paleotopographic low’s in the MIS 2 surface.

A Holocene geomorphic evolutionary model was created for Petit Bois and Dauphin Island from available data, highlighting RSLR rates and sediment supply. As the MIS 2 surface was flooded, tidal/wave scour supplied sand to migrating marine shoals. These rapidly transgressing shoals converted drowned paleovalleys to estuaries starting about 9ka. Islands formed in their modern positions about 6ka, when sediment supply was high and RSLR rates were 2mm/yr. Between 4ka-1750 CE. Islands prograded due to RSLR rates of 1-0.4mm/yr and sufficient sand supply from alongshore and inner shelf sources. Currently, the islands experience RSLR rates of 3.61 mm/yr and reduced sediment supply resulting in barrier degradation. This study provides geologic evidence of coastal geomorphic thresholds related to RSLR, sediment supply and antecedent topography.

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