The Fate of the Mississippi River Sediment Amidst the Waning Phase of the Last Glacio-eustatic Cycle: A Volumetric Quantification and Modelling of Late Quaternary Deposition Coeval with the Cessation of the Late Wisconsin Glacial Stage
Abstract
Attaining a better understanding of paralic sedimentary deposits is of high importance because they provide a key link to understanding sediment fate in a source-to-sink perspective. In order to achieve a greater understanding of sediment dispersal during transgression and regression associated with river deltas, the last such cycle of the Mississippi River delta is studied herein. Previously published maps and borehole data of the Mississippi valley, delta, and shelf deposits have been compiled to discern how the Mississippi locus of deposition fluctuated since the Last Glacial Maximum (LGM). This investigation also estimated river derived sediment volumes during the last 20ka to deduce the volume and rate of sediment that bypassed the shelf onto the slope.
At the LGM (19ka) when the sea level was 120 metres below present, the Mississippi River lay entrenched into the shelf and it built its deltas on the shelf margin. As the base level rose rapidly subsequent to the LGM, the river filled its valleys with sediment in the ensuing retrogradation and formed depocentres in front of and basinward of the valley. As the sea levelled, the river's deltas prograded from the mouth of the valley outside of its valley onto the open shelf. Employing previously published data showed that shelf depocentres migrated widely from the outer to the inner shelf following sea level rise. Published values for the Mississippi River water discharge since the LGM, estimated to have fluctuated to as much as eight times (160,000 m3s-1) that of the present, allowed for the estimation of the sediment discharge for the past 20ka. Using the rate of sea level rise to plot the location of the shoreline with the inferred past river mouth and the delta through time, the rate of volumetric change of the mapped on-shelf deposits was calculated with respect to time. By deducting this rate of volumetric change of mapped on-shelf deposits from the computed river sediment discharge through time, the rate and volume of possible off-shelf deposition since the Last Glacial Maximum was quantified, displaying a higher rate of deposition before the retreat of the shelf margin deltas.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMEP32A..07H
- Keywords:
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- 0442 Estuarine and nearshore processes;
- BIOGEOSCIENCES;
- 1825 Geomorphology: fluvial;
- HYDROLOGY;
- 3020 Littoral processes;
- MARINE GEOLOGY AND GEOPHYSICS;
- 4560 Surface waves and tides;
- OCEANOGRAPHY: PHYSICAL