GEOLOGIC CHARACTERIZATION OF THE MIDDLE BARATARIA BAY RECEIVING BASIN: THE INFLUENCE OF STRATIGRAPHY ON SEDIMENT DIVERSION PROJECTS

On the lower Mississippi River Delta, ongoing loss of wetlands due to environmental and anthropogenic activity continues to be a challenge for coastal restoration. Barataria Bay, one of the largest receiving basins for the Mississippi deltaic complex, is a significant example of this crisis. One major mechanism to counteract land loss is the proposed Middle Barataria Bay river-sediment diversion, which would seek to re-direct the Mississippi river’s sediment load back into the marshland, to build new land and sustain existing wetlands.

To better understand the geology and stratigraphy of the receiving basin, twenty-five sediment vibracores were collected from a 115 km² study area, core length ranging from 2.0 to 5.0 meters. Density measurements at 1.0 cm intervals were performed using a GeoTek Multi-Sensor core logger, while grain size and organic content analyses were completed at 25 cm to 50 cm spacings. Combined with radiometric dating for significant peat layers and clay contacts, regional stratigraphy is being tied to geochronology.

A surficial marsh-peat layer is 0.3-1.6 m thick, which suggests a wide range of recent deposition rates possibly guided by topography and local subsidence. The surficial peat layer is extremely organic-rich, with the organics lost on ignition rising as high as 89.1%. Additional peat strata appear at ~2.5 m depth in several cores, documenting earlier sediment-starved wetland development during the prior subdelta cycle, which is generally characterized by upward fining from medium sand to mud, to the modern surficial wetland peat. Ongoing radiocarbon and stratigraphic analysis of cores, including the buried peats, will provide a more detailed understanding of the geologic development of the receiving basin floor.