Palynology and paleoecology of strata associated with the Ohoopee river dune field, Emanuel county, Georgia

Abstract

Fourteen auger holes were drilled through ancient dunes near the Ohoopee River in Emanuel County, Georgia. Driller's logs and sieve analyses show that the wind‐blown sands of the dune field overlie a layer of coarse sand and gravel, which in turn overlies clayey Late Tertiary strata. Clay‐rich sediment recovered from two of the holes contained diatoms, sponge spicules, and other siliceous marine microfossils, while clay analyses from seven other holes revealed the presence of the clay mineral attapulgite (a variety of palygorskite). Twenty‐two sediment samples collected from six of the drill holes contained sufficient organic material to warrant palynological analysis. Eighty‐one taxa of pollen, spores, and algal cysts were used along with the diatoms, clay analyses, and stratigraphy to indicate probable ages and environments of deposition of the sediments. Both the diatoms and the attapulgite indicate marine depositional conditions. Overlying the marine units, but below the eolian sands we found rare occurrences of the extinct or extirpated genera Casuarinidites, Sciadopitys, Pterocarya, and Momipites. We believe these support a Late Tertiary age interpretation for the clayey strata. The presence of taxa such as the Cyrillaceae, Nyssa, Sphagnum, Myriophyllum, and Pseudoschizaea in the uppermost Tertiary units indicates that these sediments accumulated in freshwater wetlands. Our interpretation of the depositional history is that Late Tertiary marine strata accumulated first, probably during the Miocene. As sea level dropped fluvial and paludal conditions led to the accumulation of freshwater swamp/marsh sediments and probable stream sands or gravels later in the Tertiary. Exposure of the Inner Coastal Plain during the Pleistocene resulted in the formation of dunes that migrated over the Tertiary strata at the site of deposition.