Seismic Stratigraphy of the Western Florida Carbonate Platform and History of Eocene Strata

Abstract:

The stratigraphy of the western Florida Carbonate Platform above the mid-Cretaceous Sequence Boundary (MCSB) is defined using 9,600 km of multifold reflection seismic data tied to 29 wells. Concordant reflections at the MCSB deny subaerial exposure of the platform. A drowning unconformity related to an oceanic anoxic event is a more likely cause of the MCSB. Preexistent structures influenced the MCSB surface which in turn affected subsequent deposition.

Biostratigraphic data tied to magnetobiochronostratigraphic interpretations provide a time-stratigraphic framework of four main units: Upper Cretaceous, Paleocene-Eocene, Oligocene-lower Middle Miocene, and upper Middle Miocene-Holocene. The Upper Cretaceous has two subunits KU1 (Cenomanian-Santonian) and KU2 (Campanian-Maastrichtian). KU1 has continuous, parallel reflections and thickens in lows on the MCSB. In the Apalachicola Basin, KU2 has uniform thickness, discontinuous, subparallel, even-to-wavy reflections, and is intensely faulted. Sonic velocity of KU2 shows a southeastward change from siliciclastics to more carbonate rock. Hummocky-to-contorted seismic facies and thickening of KU2 on an MCSB high suggest a deep-water carbonate buildup.

The Paleocene is thin and Danian strata absent from the Destin Dome to Apalachee Bay. The Eocene margin marked by a north-south belt of west-prograding clinoforms at 85oW developed from a homoclinal ramp to a flat-topped shelf. Landward this margin, a seismic "marbled zone" suggests dolomitic facies. In the Apalachicola Basin, Ypresian-Lutetian (?) sequences form a wedge that thickens to the west. Basinward of the margin Lutetian-Priabonian sequences with lenticular shape and wavy, subparallel to hummocky seismic facies are stacked to form broad, en echelon mounds. Near the Florida Escarpment, and Eocene, elongate mound with disrupted seismic facies restricted progradation of post-Eocene clinoforms.

Post-Eocene strata are of continuous, parallel seismic facies and drape the Eocene surface, thickening in lows. In the Tampa Embayment, Oligocene-Lower Middle Miocene strata form sets of progradational clinoforms that steepen to the southwest as they impinge upon the Escarpment. Truncation of clinoforms has been reported beneath a mid-Miocene unconformity, but apparent truncation of clinoforms can also be observed at the tops of other, older sequences.


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