Greene, Larry¹, Antonio Rodriguez¹
(1) University of Alabama, Tuscaloosa, AL

ABSTRACT: High-Resolution Seismic Stratigraphy of Mississippi Sound, Alabama: Multiple Stages of Incision, Channel Fill and Avulsion

Eastern Mississippi Sound is a 375 km² shallow lagoon extending from behind Dauphin Island from Pass aux Herons in the east to Petit Bois Pass in the west. The Pascagoula/Escatawpa fluvial-deltaic system, a main source of freshwater for Mississippi Sound, flows into the lagoon from the north about 17 km west of Grand Bay. To examine the Late Quaternary evolution of the lagoon and Pascagoula/Escatawpa fluvial-deltaic system, approximately 160 kilometers of high-resolution seismic data (2-15 kHz, 20 ms pulse) were collected from Eastern Mississippi Sound.
These data show at least four unconformity-bound seismic units. The unconformities are irregular surfaces characterized by up to 25 m of relief and are interpreted to have formed during episodes of Pascagoula/Escatawpa fluvial incision. The channels show evidence of reoccupation through multiple stages of incision. The uppermost seismic unit and unconformity was sampled by vibracores collected by the Alabama Geological Survey in 1995, indicating that the youngest unconformity formed during the last lowstand in sea level. Channel fill seismic facies are composed of laminated to acoustically transparent facies interpreted as estuarine and a chaotic to lateral accreting facies interpreted as fluvial. Either fluvial or estuarine units fill some of the channels while others are filled with fluvial at the base and estuarine at the top indicating that channel avulsion was an important process during transgression. This is an ongoing project and future work will focus on developing of a robust chronostratigraphic framework for the field area.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.