Title page for ETD etd-04072005-210612

Type of Document Master's Thesis
Author Velardo, Brian
URN etd-04072005-210612
Title Detailed Geochronology of the Mississippi Sound during the Late Holocene
Degree Master of Science (M.S.)
Department Oceanography & Coastal Sciences
Advisory Committee
Advisor Name Title
Samuel J Bentley Sr Committee Chair
Gregory Stone Committee Member
Harry H Roberts Committee Member
Jaye Ellen Cable Committee Member
Yoko Furukawa Committee Member
  • hurricane Lili
  • tropical storm Isidore
  • radiochemistry
Date of Defense 2005-02-18
Availability unrestricted
The Mississippi Sound is a bar-built estuary that parallels the Mississippi Coast. It is bounded on the west by the St. Bernard lobe of the Mississippi River delta, Mobile Bay to the east, and the Gulf Coast barrier islands to the south. Few studies have investigated the late Holocene history of Mississippi Sound. In the present study, historical deposition in the Sound has been investigated using core data collected throughout the western, central, and eastern Mississippi Sound.

The sediments within Mississippi Sound compose a complex depositional system that have responded to changes in sea level and hydrodynamics. Two factors that influence the wave dynamics within Mississippi Sound are changes in water depth and exposure to the open Gulf of Mexico. Decreases in water depths have an inverse relationship to the shear velocity produced by waves. Thus, by decreasing water depth from 3 m to 2.5 m, the shear velocity (U*), produced from a wave with H = 0.9 m and T = 4 s, would increase from ~0.006 m/s to 0.008 m/s. These changes may be recorded in the sedimentary fabric as changes in the sedimentary facies from a low-energy muddy facies to a higher-energy sandy facies. However, increased exposure to the open Gulf of Mexico allows for larger deep-water waves to impact the Sound. Therefore, by exposing Mississippi Sound to increased wave energy from the Gulf of Mexico, conditions become favorable for the deposition of the higher-energy sandy facies in the deeper water of Mississippi Sound. The sedimentary fabric and geochronology data of recent deposition suggest that physical processes actively rework the sediment in the top 5 cm of the sea-bed; however, biological processes continuously rework the sediment to a depth of 10-12 cm resulting in the destruction of most of the physical stratification. Tropical cyclones impact the sedimentary fabric such that they are recorded as sandy event beds within a muddy matrix. Approximately 8-26% of the sediment column was deposited by recordable storm events in the Western Mississippi Sound, whereas smaller storm events and typical estuarine processes deposited the other 74 92% of the sediment column.

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