A newly recognized transgressive formation of late Pleistocene (Sangamon) age, along and off the Mississippi-Alabama coast, contains rich foraminifer and molluscan faunas reflecting its dominantly shallow-nearshore and open-marine depositional conditions. In some areas brackish-estuarine-embayment facies prevailed. The formation is overlain by the regressive alluvial-fluvial Prairie and the mainland barrier-beach-dune Gulfport Formations. Correlative units were identified in southeastern and southwestern Louisiana and probably also may be present in appropriate stratigraphic positions along the rest of the north and northwestern Gulf Coast in units the ages of which have not been established with certainty.

Drilling indicated that all pre-Biloxi Pleistocene marine units have been eroded in the Mississippi-Alabama coastal and nearshore zones. Similarly, no pre-Gulfport Pleistocene barrier ridges or other relict shoreline features could be established along the northern-northeastern Gulf Coast. Both facts point to Pleistocene regional uplifts in this coastal area, in sharp contrast to the tectonic style of the adjacent Mississippi River delta region.