SEDIMENTATION DYNAMICS AND STRATIGRAPHY OF BRETON SOUND ESTUARY: IMPLICATIONS FOR THE IMPLEMENTATION OF SEDIMENT DIVERSION STRUCTURES ALONG THE MISSISSIPPI RIVER

Over the past century, the Mississippi River Delta and associated wetlands have been disappearing due to a combination of natural and anthropogenic factors. Located along the east bank of the river, Breton Sound is one of the largest interdistributary basins within the delta and has been subject to rapid wetland degradation. This study aims to constrain the temporal scale of avulsions and splays within the upper reaches of Breton Sound through a combination of stratigraphic analysis and radiometric dating. Understanding the long-term sedimentation dynamics from river to estuary can in turn provide guidance for the implementation of sediment diversions along the main channel of the Mississippi River.

Twenty-five vibracores and piston cores were collected from a ~80 km² region in Breton Sound estuary. Cores were analyzed for bulk density using a Multi-Sensor Core Logger, then split lengthwise, photographed, and described for stratigraphy. Loss-on-ignition and grain size analyses were performed on all cores at 25 - 50 cm sampling intervals. Radiocarbon dates are being obtained for the base of peat and other organic-rich packages observed in the cores.

The stratigraphy of the Middle Breton cores is characterized by four distinct sedimentary facies: marshy peat, prodelta mud, interlobe basin silty sand and mud, and open bay mud. A volume frequency distribution of ~250 down-core samples indicated grain size modes of coarse clay to fine silt (5-10 µm), coarse silt to fine sand (50-100 µm), and medium sand (400-500 µm). Peat isopach maps show a general trend of thickening away from the main channel of the Mississippi River. Base of peat radiocarbon dating will constrain the local time boundary between the end of overbank flooding and the onset of marsh growth. ¹⁴C dates taken from above and below organic-rich layers at depth will clarify whether the section corresponds to in situ marsh from a previous delta lobe or mobilized organic matter from a storm event.