Stratigraphy, depositional history, and pore network of the Lower Cretaceous Sunniland carbonates in the South Florida basin
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The South Florida Basin of the eastern Gulf of Mexico represents a vast, undisturbed carbonate system that extended from the Florida Keys through the Tampa-Sarasota Arch. In South Florida, extensive subsurface data and analogous modern environments provide an opportunity to unravel the evolution of this system from shoreline to shelf-margin. This study examines the changing facies and the pore network of the Latest Aptian-Early Albian Sunniland interval. Stratigraphic results are closely comparable with contemporary carbonate platform studies in the northern Gulf of Mexico. The Sunniland Formation was deposited during a major transgressive-regressive sequence. The Sunniland interval is divided into five third-fourth order, transgress-regressive depositional cycles (S-1 to S-5) in south Florida using sequence analysis of shelf-interior facies succession. In these sequences, facies proportion, faunal composition, and stratal geometries of the shelf-interior are found to be the result of the changing accommodation trends and ocean chemistry. As in the Comanche Platform in South Texas, the detrimental effects of oceanic anoxic event 1B may fundamentally drive the evolution of platform morphology in the eastern Gulf of Mexico as: • Rimmed shelf (crisis phase: S1) • Distally steepened ramp (anoxic/dysoxic phase: S2, recovery phase: S3, S4) • High-angle rimmed shelf (recovery to equilibrium phase: S5). Within this hydrocarbon-producing trend, the lowered sea level at the end of S4 enhances the reservoir quality in the high-energy settings including back-reef debris aprons, tidal shoal-complex and carbonate beach by dissolution. The tight sabkha-tidal flat facies in S5 forms the reservoir seal, whereas the medium-fine crystalline dolomites in S3 may not adversely affect and likely facilitate the migration of hydrocarbon self-sourced from the high TOC, argillaceous mudstone in S2.