Sedimentation Dynamics and Stratigraphy of Middle Breton Sound Estuary, Southeast Louisiana: Spatiotemporal Evidence for Subdeltaic Evolution
Master of Science (MS)
Geology and Geophysics
Subsurface core borings have provided a fundamental understanding of stratigraphic architecture and depositional processes in the Mississippi River Delta. Careful observation of lithostratigraphic successions has led to the realization that delta plain construction is marked by a cyclic repetition of depositional events that occur in a consistent temporal manner. Crevasse splay-generated subdeltas are a primary driver of sedimentation in the modern Balize delta, and it is postulated that older lobes operated in a similar fashion. This study aims to determine the depositional processes that govern Middle Breton Sound estuary, an area within the geographic framework of the Plaquemines delta lobe, and to temporally constrain their occurrence through stratigraphic analysis and radiometric dating. Twenty-five vibracores, up to ~5-m long, were collected from the study area and underwent whole-core density, grain size, and loss-on-ignition analyses. To provide age control, ten samples from the cores were chosen for radiocarbon dating. Grain size analyses of 252 downcore samples demonstrated that silt is the dominant grain size, a finding consistent with that of other receiving basins in the area. Loss-on-ignition testing revealed that organic-rich sediments are primarily concentrated in the first meter of the vertical profile with smaller yet appreciable peaks between two and three meters depth. Five lithofacies were identified based on physical properties and correlated to distinct subdeltaic depositional environments. 14C dating of in situ bivalve shells and the base of surficial peat yielded calibrated ages of ~1150 and ~350 calendar years B.P., respectively. The lithofacies assemblages and depositional timeframe of the sediments in Middle Breton Sound are consistent with modern subdelta deposits. It is inferred that crevasse splay deposition in the study area occurred sometime between 1000 and 500 years B.P. and more likely took place in the more recent portion of the timeframe due to the relatively short amount of time (i.e. decades) needed for marsh colonization following the onset of the subdelta cycle. For a more precise depositional chronology, future studies should consider optically stimulated luminescence (OSL) dating of detrital quartz grains found in splay cycles.
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Bomer, Edwin Jefferson, "Sedimentation Dynamics and Stratigraphy of Middle Breton Sound Estuary, Southeast Louisiana: Spatiotemporal Evidence for Subdeltaic Evolution" (2016). LSU Master's Theses. 3707.