Geomorphic History, Geologic Framework, and Hard Mineral Resources of the Petit Bois Pass Area, Mississippi-Alabama

Abstract

ABSTRACT Approximately 200 line-km of high-resolution seismic reflection data, 24 vibracores, historical maps, and aerial photography were used to delineate the geomorphic history, geologic framework, and potential hard mineral resources of the Petit Bois Pass area. Petit Bois Pass is a natural tidal inlet system located between Petit Bois and Dauphin islands at the Mississippi-Alabama state line. Since its opening, the inlet has migrated to the west at rates exceeding 50 m/yr. However, the main channel of Petit Bois Pass has remained relatively stable since 1917, occupying an antecedent topographic depression cut into underlying pre-Holocene deposits. Pre-Holocene deposits form the eastern core of Dauphin Island, where they are subaerially exposed. The pre-Holocene surface dips to the west, providing a platform for the narrow, elongated Holocene spit of Dauphin Island. The pre-Holocene surface crops out on the shoreface at the western end of Dauphin Island 8 to 9 m below mean low water (MLW). Farther to the west, vibracores from the main inlet channel of eastern Petit Bois Pass contain only Holocene sediment, suggesting that the pre-Holocene surface is >11 m below MLW. West of the main tidal channel, the undulating pre-Holocene surface shallows in the central portion of the pass before dipping down to >11 m under Petit Bois Island. It appears that tidal channels associated with Petit Bois Pass occupy pre-Holocene fluvial channels cut by either the Pascagoula, Escatawpa, or Fowl rivers during lower sea level. In the study area, the primary hard mineral resource targets include Holocene tidal inlet channels, ebbtidal deltas, and shoreface sand ridges, while abandoned pre-Holocene fluvial channels are considered secondary.