Sea Level and Geostrophic Current Control on Carbonate Shelf-Slope Depositional Sequences and Erosional Patterns, South Florida Platform Margin

Abstract

High-resolution seismic reflection profiles across the shelf-slope margin between the Dry Tortugas and Key West, Florida, indicate that sea-level fluctuations and the eastward flowing Florida Current are major controls on late Quaternary sequence stratigraphy. The study area, a transition zone between the open south Florida shelf and the lower Florida Keys island/reef system, is typified by a shallow shelf with reef margin adjacent to a deeper lower-shelf/slope. The lower-shelf/slope is composed of stacked or prograding sequences that downlap and pinchout on the Pourtales Terrace. Strike oriented stratigraphic sections exhibit many sea-level controlled features such as lowstand erosion, transgressive unconformities, and highstand system tracts. Lowstand reefs, notches, or barriers are observed as deep as 150 m below present sea level. Depositional styles change along-slope from west to east. The western portion of the study area is characterized by thick, low-amplitude, prograding sequences related to abundant supply of sediment through off-shelf transport during high sea-levels as well as along-slope reworking by Florida current. Part of this section has been severely eroded by along-slope currents producing localized cut-and-fill structures and widespread erosional unconformities. To the east, a thinner section of high-amplitude reflections is common seaward of the lower Florida Keys reef tract system.more » This study provides a new evidence of how strong geostrophic boundary currents along with fluctuating sea levels have interacted to control depositional sequences on a carbonate slope in the Florida/Bahamas platform complex.« less