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.