Abstract
The Citronelle Formation is the most widely occurring, surficial geologic unit along the northeast Gulf of Mexico. It is a siliciclastic unit consisting primarily of sands and gravels with varying amounts of clay and minor amounts of mica and heavy minerals. Historically, the unit has been thought to be a fluvial deposit of Pliocene age. Evidence presented here suggests, at least in part, a marine origin. In some pits and exposures in southern Walton and Okaloosa Counties in western Florida, sediments that are referred to the Citronelle Formation contain well preserved Ophiomorpha, bivalve mollusk casts, shark teeth, terrestrial vertebrate fossils and other trace fossil remains. Various types of bedding, including cross bedding, occur. These apparent nearshore marine depositional facies are the focus of this investigation which will attempt to determine the paleo- environmental depositional regimes, age, and how this facies relates to the Cirtonelle Formation.
Field work was conducted and data were gathered from exposures and outcrops within the study area. Stratigraphic sections were measured and described. Where feasible, sediment samples were collected for sieve analysis. Further sampling of trace fossils (Ophiomorpha) and body fossils was conducted for analysis. Cross-bedding orientation was recorded from one locality to determine predominant paleo-current direction. These data, when combined, support the hypothesis that these sediments that have been mapped as Citronelle Formation represent nearshore, marine facies. However, their placement in the Citronelle Formation still remains questionable due to the lithologic similarity of overlying and underlying units.
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