Paleoecology of shallow-marine carbonate environments, middle Eocene of Peninsular Florida

Abstract

The middle Eocene Avon Park Formation of west central Florida contains a carbonate sequence that accumulated under supratidal to shallow subtidal conditions. Vertically repetitive sedimentary sequences document transgressive regressive, open marine to shoreline cyclicity. Newly discovered cross-bedding and abundant fossils support these paleoenvironmental interpretations. The rocks are dolomitic and bioclastic packstones and grainstones. Allochems are chiefly benthic foraminifers, bivalves, echinoids, and algae. Planar cross-bedding occurs within megaripple sets. Bed thicknesses, lateral extent of bed types, and paleocurrent directions are nonuniform, indicating migrating or shifting hydrodynamic regimes. Trace fossils, including Ophiomorpha, are well preserved and suggest maximum water depths of three to four meters in a shoreline transition zone. Invertebrate, vertebrate, trace, and plant fossils represent more than 70 species. Abundant irregular echinoids (clypeasteroids, spatangoids, cassiduloids, and a holectypoid) also suggest sandy shoreline conditions. Erosional truncations of burrows indicate periodic storm action along the shoreface. Modern environmental and ecological analogues to this study area include the south Florida shelf and the Bahamian Platform. Mud-free, carbonate sands displaying megarippled cross-beds and extensive burrowing occur adjacent to sea grass beds with finer-grained sediments and greater faunal diversity/density. Shifting conditions often result in redistribution of facies.