NEOGENE TO RECENT STRATIGRAPHY AND DEPOSITIONAL REGIMES OF THE NORTHWEST FLORIDA INNER CONTINENTAL-SHELF

The late Neogene to Recent depositional history of the inner shelf off northwest Florida was investigated using high-resolution seismic reflection data. Two principal sedimentary provinces, the Apalachicola Embayment and the Alabama-Florida Shelf, are distinguished by different structural trends and sequence stratigraphy. A transition from carbonate to terrigenous clastic deposition occurs vertically and laterally from east to west. The dominant controls on deposition have been sea level history and location of fluvial systems advancing southward and infilling the Apalachicola Embayment. In the Apalachicola Embayment. the upward carbonate-to-terrigenous transition correlates with a change from relatively flat lying reflections, to prograding clinoforms, and then chaotic and reflection-free sequences. Carbonate deposition in the middle and late Miocene is inferred to have occurred during highstands of sea level with minor input of terrigenous material. In the late Miocene, a major erosional unconformity and associated river valley entrenchment cut deeply into the flat-lying carbonate section. Subsequent deposition is distinguished by broad prograding clinoforms and an increase in terrigenous material in an open shelf environment. In the late Pliocene, sea-level fluctuations generated a stratigraphic record dominated by offlapping, seaward-thickening sequences. The interaction between sea level and fluvial supply to the shelf became very important as shifting river inputs resulted in locally thick depocenters bounded by erosional unconformities. Four primary areas of fluvial-deltaic input in the Plio-Pleistocene are identified based on the distribution of channels and prograding clinoforms interpreted to be delta front deposition. The present inner shelf is a sediment-starved clastic depositional regime.