--> Abstract: Citronelle Formation, Northeast Gulf Coastal Plain - Stratigraphic and Age Issues, by E. G. Otvos; #90932 (1998).

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Abstract: Citronelle Formation, Northeast Gulf Coastal Plain - Stratigraphic and Age Issues

OTVOS
ERVIN G., Gulf Coast Research Laboratory, USM Institute of Marine Sciences, Ocean Springs, MS 39566-7000

The Citronelle, the most extensive northeast Gulf coastal plain formation between the Mississippi and east Florida, rarely more than 20-30 m thick, includes dominantly or in part coarse- and fine gravelly sands deposited in major and minor stream channels, substantial fine-grained floodplain and channel-fill lithosomes and widespread, locally predominant finegrained, rarely organic-rich floodplain units. Cyclic interlayering of fine and coarse-grained beds and indications of channel bank erosion (minuscule-to-sizable clay/mud clasts) and reworking are very common and stream meander-indicative lateral accretion beds absent. Burrowed-bioturbated inshore and nearshore, gravelly-sandy-muddy, and muddy-sandy lithologies, recognized in a semicontinuous band at several isolated sites between south Georgia and Mobile Bay, AL, include ghost shrimp (Ophiomorpha) and polychaete (annelid) worm tubes, internal molds of veneride and other shallow marine bivalves. These 0.5 to 7 m thick intervals, although otherwise indistinguishable from common muddy-sandy, gravelly-sandy alluvial Citronelle lithofacies types, reflect fluctuating Late Pliocene shoreline positions.

Contrary to earlier Upper Miocene and Pliocene-Pleistocene age assignments based on inadequate vertebrate and plant data, the underlying dated Pliocene units (e.g., Jackson Bluff Fm.) and few enclosed Japanese umbrella pine pollen specimens now provide a firm Upper Pliocene date. Very intensive and prevalent postdepositional changes include local development of iron oxide and/or silica-cemented sandstone ledges and occasional beta lamination in sands, of hematitic grain-coating, pervasive color banding, thick oxi-paleosol development with rhyzomorph root filling/ occasional tree trunk replacement by leached silty sand (hardpanrimmed "cylinders") and silica replacement in petrified tree trunks. Deflated- and karst-associated, enclosed circularelliptical depressions dot Citronelle upland surfaces in the SE Louisiana - western Florida Panhandle, central and eastern Panhandle areas.

AAPG Search and Discovery Article #90932©1998 GCAGS/GCS-SEPM Meeting, Corpus Christi, Texas