ABSTRACT

The most widespread unit on the northeastern Gulf of Mexico coastal plain, the Citronelle Formation consists of almost exclusively unconsolidated siliciclastic deposits. These range from sandy-gravelly to clayey-muddy sediments. Rhythmic intercalations between different lithotypes are common. Fine-grained sediments and coastal deposits are more frequent components in the Formation than previously assumed. Burrowed-bioturbated estuarine- inshore and probably nearshore marine beds of variable thickness occur sporadically in a belt between south Georgia and Mobile Bay, Alabama. As far as southeastern Louisiana, only alluvial facies were recognizable west of the Bay. Callianassid Ophiomorpha burrows, polychaete (annelid) worm tubes, clay-filled polychaete burrow traces and, at one locality, molluscan molds represent shifting coastal lithosomes. Except for occasional plant matter, intensive diagenetic alterations destroyed all body fossils.

The Upper Miocene and Pliocene/Pleistocene age assignments, based on inconclusive vertebrate and plant data, have invited further scrutiny. Underlying and/or laterally correlative foraminifer-dated units, as the Jackson Bluff Fm., and newly uncovered Sciadopytis pine pollen from organic-rich beds provided firm proof for the Late Pliocene age of the Citronelle. Constraints of global climate, sea-level history, and the epeirogenically raised Citronelle upland surface elevations suggest a 3.4-2.7 Ma, possibly even narrower age range. Deposition ceased before the end of the Epoch. Numerous enclosed and oriented depressions of circular-elliptical outline between the central Florida Panhandle and SE Louisiana formed as deflation basins after active Citronelle deposition ceased and prior to the Sangamonian Pleistocene interglacial. The deeper, steeper-walled depressions in the eastern Panhandle are of covered karst origin.