Degree

Doctor of Philosophy (PhD)

Department

Geology and Geophysics

Document Type

Dissertation

Abstract

The lower plain of the Mississippi River Delta contains approximately five coastal sedimentary basins that are topographically defined, and one shelf-crossing depocenter (the Birds Foot Delta). These depositional systems receive varying quantities of sediment from fluvial and marine sources and have rates of coastal land loss that are roughly inversely proportional to fluvial sediment supply. To combat land loss along these regions, Louisiana has launched a historic campaign to sustain and regrow coastal lands using, in part, river sediment diversions. Fine sediments constitute the majority of sediment load in the Mississippi River, but are under-studied with respect to dispersal processes, particularly in terms of sediment supply to distal deltaic bays and wetlands. To expand the knowledge of fine sediment dynamics along distal coastal marshes, two distinct, contrasting field areas along southeastern Louisiana are studied. The first, Fourleague Bay, is actively nourished by fresh sediment from the Atchafalaya River. The second, Terrebonne Bay, has not had an active fluvial connection in over a century. Using push cores, vibracores, carbon dating, grain size analysis, loss-on-ignition testing, bulk density, seismic CHIRP data, and natural and anthropogenic radioisotopes 7-beryllium, 210-lead, and 137-cesium, rates and patterns of sediment accumulation on both the shallow bay bottom and marsh platforms are calculated from seasonal to centennial timescales. Results indicate 1) riverine sphere of influence for nourishing mineral sediments is at least 25 km from the river mouth; 2) there exists a synergistic relationship between mineral sediment input and organic sediment production; 3) paleochannels may provide resiliency for marsh platforms established above them; 4) environmental processes control the physical properties of sediment.

Committee Chair

Bentley, Samuel

Available for download on Friday, March 11, 2022

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