Degree

Doctor of Philosophy (PhD)

Department

Geology & Geophysics

Document Type

Dissertation/Thesis

Abstract

Episodic overbank flooding and sediment resuspension events (such as cold front passages or tropical cyclones) are recognized as important natural components for wetlands maintaining vertical equilibrium with sea-level. However, the relative importance of these components to an anthropogenically unmodified delta complex remains unclear. This study uses sediment cores to describe the relative importance of these vertical accretion components the Lafourche and Balize Deltas of the Mississippi River. Existing wetlands of the abandoned lower Lafourche receive no direct fluvial sediment, but instead are supported by sediment resuspended by tropical cyclones and cold fronts that pass over them. Wetlands of the modern Balize delta are similarly supported, but do still receive about 5% of their annualized mineral sediment from the river directly. Tropical cyclones comprise 27 ± 21% of annualized delivery in the Lafourche, and 14% in the Balize. Both locations receive more than 70% of the mineral sediment from other resuspension events, such as cold fronts. Part of this work relied upon XRF scanning of collected wet sediment cores. Modern XRF core scanners can log > 9 m day-1 at 10 mm x 10 resolution, and create not only elemental profiles but also a way to estimate water content, mineral content, organic matter and total organic carbon. Using a method of tropical cyclone event detection that traditionally relies upon loss on ignition, these XRF-derived estimates are shown to produce approximately the same results as their LOI counterparts, regardless of how well they represent their respective true values of mineral, water, or organic content. Finally, XRF-derived estimates of the ratio of bromine to total organic carbon (Br:TOC) were created and used to differentiate fluvial and tropical cyclonerelates deposits. In the absence of historical records of tropical cyclone activity or river flooding, Br:TOC can effectively parse mineral sediments of these sources apart and potentially supercede more expensive and time-consuming biostratigraphic or chemostratigraphic methods.

Date

8-22-2017

Committee Chair

Bentley, Samuel

Available for download on Tuesday, August 20, 2024

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