Late Quaternary evolution of the northwest Florida coast and margin: Development of a conceptual model for identifying and characterizing shelf sediment deposits

The objective of this investigation was the interpretation of the late Quaternary history of the northwest Florida margin and the development of a conceptual model for understanding the late Quaternary evolution of the regional coast and margin. The study area extends from the coastal Alabama-Florida border eastward to the mouth of the Ochlockonee River. Sea-level history, paleogeographic and coastal evolution data, paleoclimate data, granulometric data, beach profiles, sedimentary transport process data, historic charts and maps, subsurface seismic data, and granulometric data were the primary inputs to the model. Three sites were chosen for further investigation, including seismic data and vibracore acquisition. Nine vibracores were collected. Forty-eight sediment samples from the nine vibracores and analyzed for granulometry. The environments of deposition were interpreted for each site (and vibracore location), based upon the sedimentary structures found in the vibracores and the suite grain size statistics. Grain-size analyses indicate that the samples are of riverine origin, and that the source is likely to the east, probably the Apalachicola River. This supports the idea that the Apalachicola River is the major source of clastic sediment throughout the Quaternary in this region. Using interactive GIS, the new and existing data were utilized in the development of a conceptual model incorporating shelf paleogeography and locations of potential shelf sand bodies. Potential shelf borrow areas were identified based upon their bathymetric expression and/or prediction of paleoshoreline locations based upon sea-level history. As a result of the application of the conceptual model to the northwest Florida shelf, thirteen potential offshore sand features were identified. The characteristics of each sand feature were examined, including granulometry, color, water depth, thickness, areal extent, and total sand volume. The model was developed to facilitate the identification and characterization of shelf sedimentary deposits using the above tools. Many such deposits may be utilized in the future as sources for beach renourishment projects. Users of this model should be able to predict where shelf sand bodies may be located, and should be better able to determine where to focus geophysical and sedimentological field sampling. With the understanding of the buried paleogeography of the shelf and its expression in bathymetry, the conceptual model can aid in interpreting paleogeographic history within an area of interest. Such information can be valuable as a supplement to the sea-level history for the area. Using all of these elements -- a reliable conceptual model, a solid understanding of the paleogeography and sedimentary processes of the area, and a comprehensive GIS database -- researchers will be able to identify and characterize offshore sediment bodies for more intensive study, both for geologic investigations and for coastal renourishment projects.