A late Cenozoic mixed carbonate/siliciclastic system, south Florida: Lithostratigraphy, chronostratigraphy, and sea-level record

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Marine Geology and Geophysics

First Committee Member

Donald F. McNeill - Committee Chair


A new chronostratigraphy is presented from south Florida core borings for early Oligocene-to-Pleistocene mixed carbonate/siliciclastic sediments. Integration of lithostratigraphy, biostratigraphy, magnetostratigraphy, and strontium-isotope stratigraphy shows that mixed sediment distribution and deposition was controlled by a combination of sediment supply, eustasy, and variations in current intensity. Interaction of these variables contributed to the complex lateral and vertical heterogeneity. The new age model provides the basis for the regional stratigraphic history and comparison to mixed sediments from southwest Florida and pure carbonate sediments on Great Bahama Bank.The chronostratigraphy for the South Florida Drilling Project defines periods of sediment deposition and hiatal disconformity during the last 31 m.y. The skeletal limestones of the lowermost unit (Suwannee Limestone) were deposited in the latest early Oligocene (31 to ${\sim}29.4$ Ma), with cessation controlled by mid-Oligocene eustatic lowering. Following an ${\sim}8.1$ m.y. hiatus, deposition of interbedded wackestones to grainstones (Arcadia Formation) initiated in early Miocene $({\sim}21.3$ Ma middle Florida Keys, ${\sim}23.8$ Ma lower Keys). Arcadia Formation deposition continued until earliest middle Miocene $({\sim}15.0$ Ma middle Keys, ${\sim}16.0$ Ma lower Keys), when the Loop Current strengthened in the Gulf of Mexico. Siliciclastic sediments (Long Key Formation), separated from the Arcadia Formation by an ${\sim}8.8$ m.y. hiatus, were deposited during three latest Miocene to latest Pliocene intervals in the middle and upper Keys. The laterally-equivalent fine-grained skeletal carbonates of the lower Keys (Stock Island Formation) coincide with the younger two siliciclastic intervals. The contact with the overlying, latest Pliocene molluscan-rich Fort Thompson-Caloosahatchee equivalent appears transitional. The Key Largo Limestone includes two or three coralline units separated by subaerial-exposure horizons.Application of sequence stratigraphy to this mixed system is complicated by local effects, such as sediment supply and strong currents, beyond a sea-level driven system. Data show that siliciclastics were not responsible for termination of carbonate deposition, as they were emplaced significantly later. Carbonate deposition was not re-established in portions of the mixed system during sea-level highstands in the late Miocene and Pliocene. The establishment of a refined chronostratigraphy and timing of regional events was essential for interpreting the depositional history of south Florida.



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