Understanding Mississippi Delta Subsidence through Stratigraphic and Geotechnical Analysis of a Continuous Holocene Core at a Subsidence Superstation
Abstract
Land-surface subsidence can be a major contributor to the relative sea-level rise that is threatening coastal communities. Loosely constrained subsidence rate estimates across the Mississippi Delta make it difficult to differentiate between subsidence mechanisms and complicate modeling efforts. New data from a nearly 40 m long, 12 cm diameter core taken during the installation of a subsidence monitoring superstation near the Mississippi River, SW of New Orleans, provides insight into the stratigraphic and geotechnical properties of the Holocene succession. Stratigraphically, the core can be grouped into three sections. The top 12 m is dominated by clastic overbank sediment with interspersed organic-rich layers. The middle section, 12-35 m consists predominately of mud, and the bottom section, 35-38.7 m, is marked by a transition into a Holocene-aged basal peat (11,350-11,190 cal BP) which overlies densely packed Pleistocene sediment. Radiocarbon and OSL ages show up to 6 m of vertical displacement since 3,000 cal BP. We infer that most of this was due to compaction of the thick underlying mud package. The top 70 cm of the core is a peat that represents the modern marsh surface and is inducing minimal surface loading. This is consistent with the negligible shallow subsidence rate as seen at a nearby rod-surface elevation table - marker horizon station and the initial strainmeter data. Future compaction scenarios for the superstation can be modeled from the stratigraphic and geotechnical properties of the core, including the loading from the planned Mid-Barataria sediment diversion which is expected to dramatically change the coastal landscape in this region.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFMOS23B1396B
- Keywords:
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- 1222 Ocean monitoring with geodetic techniques;
- GEODESY AND GRAVITY;
- 4315 Monitoring;
- forecasting;
- prediction;
- NATURAL HAZARDS;
- 4215 Climate and interannual variability;
- OCEANOGRAPHY: GENERAL;
- 4556 Sea level: variations and mean;
- OCEANOGRAPHY: PHYSICAL