Geological Society of America

9 Coastal and Shelf Sediment Transport Processes and Products of the Northern Gulf of Mexico

Monday, 21 March 2016
1:30 PM - 5:30 PM
Governor Room

INFLUENCES OF HURRICANES, FLOODS, AND ORGANIC PRODUCTION ON RIVER DELTA EVOLUTION

Paper number: 9-10
Program: Theme Sessions
Time: 4:25 PM – 4:45 PM

Authors

Crawford White Presenting Author
Louisiana State University, Baton Rouge, LA
Samuel J. Bentley
Louisiana State University, Baton Rouge, LA
Kehui Xu
Louisiana State University, BATON ROUGE, LA
Kehui Xu
Louisiana State University, Baton Rouge, LA

Abstract

The modern Mississippi River Delta plain has been largely disconnected from the main distributary by a highly engineered system of levees and floodways. This vast and fragile landscape is experiencing land-loss and is increasingly susceptible to inundation. Intense debate exists in the scientific community as to whether direct fluvial or hurricane-driven re-suspension and sedimentation are the present dominant sources of mineral sediment to the wetland surfaces of the modern delta complex. The relative importance of these sources remains a matter of public discussion and scientific debate, and this lack of clarity strongly influences development of tools, strategies, and policies to conserve coastal Mississippi River Delta lands.

Research fueling this debate has been restricted both spatially and temporally thus far. Furthermore, the contribution of organic production is unknown at these scales. A comprehensive study of the Lafourche and Plaquemine-Balize Mississippi River Delta complexes at a temporal scale similar to that of natural deltaic cycles (10² - 10³ years) is being completed to address the deficiencies in our current understanding. A suite of 38 5m vibracores and 33 co-located 1m piston cores are being analyzed at moderate- to high- resolution for bulk density, grain-size, organic matter, magnetic susceptibility, and X-ray fluorescence to create the recognition criteria necessary to distinguish sedimentary sources for this time period.

For distal subaerial Lafourche cores, shorter timescale ²¹⁰Pb and ¹³⁷Cs (<10² years) data show that despite rapid subsidence and sea-level rise, many studied wetlands are still able to maintain their elevations. Sedimentary accumulation rates in the subaerial components of the Lafourche complex would seem to indicate that following distributary abandonment/cutoff and the elimination of pre-levee and overbank flooding and crevasse sediments, resuspension by cold fronts and hurricanes has become the primary mineral sediment source for affected wetlands. Longer timescale AMS ¹⁴C (>10² years) data is being used to determine the temporal extent of these trends, and to examine the critical time period following Lafourche lobe abandonment circa 600 YBP.

Geological Society of America Abstracts with Programs. Vol. 48, No. 1

doi: 10.1130/abs/2016SC-273622

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