Abstract The northeastern Gulf of Mexico coast retains a relatively undisturbed record of paleoshoreline deposits dating from the late Tertiary to the present. The excellent preservation of these features results from long-term conditions of low to moderate wave action, a wide and low-gradient platform, and tectonic stability. The general lowering of sea level from Pliocene rime to the present is evident in the decrease in elevation of terrace features with age. The episodic sea-level swings of the late Quaternary and Holocene are recorded in both submerged and raised shoreline features preserved in coastal and nearshore areas. Highstand shoreline features are identified on the basis of morphology, elevation, texture and radiometric dates. Lowstand sequences are identified through seismic data, borehole lithology, and nearshore morphology. The modern coastal zone includes an extensive barrier-lagoon system, major shoals and a large lobate delta actively prograding into an estuary. Many of the present coastal features have direct analogs in both the elevated and submerged paleoshoreline deposits.

ABSTRACT The distribution and composition of the coastal and inner-shelf clastic sediments of northwest Florida have been strongly influenced by the activity of the Apalachicola River. The largest river in the northeastern Gulf of Mexico, the Apalachicola has dominated sedimentation in the region since Neogene time. High-resolution shallow seismic investigations of the inner shelf, combined with coastal borehole records, indicate that the bulk of the clastic sediment cover of the coast and inner margin is late Quaternary in age, and probably Sangamonian or younger. Late Quaternary sea level fluctuations have exerted a major influence on the timing and character of sedimentation in the Apalachicola Embayment.