High-Resolution Stratigraphy of a Sandy, Ramp-Type Margin—Apalachicola, Florida, U.S.A.
Heather A. McKeown, Philip J. Bart, John B. Anderson, 2004. "High-Resolution Stratigraphy of a Sandy, Ramp-Type Margin—Apalachicola, Florida, U.S.A.", Late Quaternary Stratigraphic Evolution of the Northern Gulf of Mexico Margin, John B. Anderson, Richard H. Fillon
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High-resolution single-channel seismic data were collected on the middle shelf to upper slope, offshore Apalachicola, Florida, to characterize fluvial–deltaic stratigraphy on a sandy, ramp-type margin. On the west Florida shelf, deltas exhibit wedge-shaped geometries. Clinoform angles are relatively steep (∼ 3°), and bottomset bed development is minimal, suggesting deposition in a relatively high-energy environment.
Chronostratigraphic control for the study area is absent, so ages of deltaic units were inferred from the updip pinch-out elevations, offlap break elevations, and stratigraphic relationships. From the stratal relationships, we infer that at least three glacioeustatic cycles (OIS-9 to OIS-1) were imaged. Five units were identified, with unit 1 being the youngest.
Sediment volume for unit 4 (OIS-7 to OIS-6) was four times greater than unit 2 (OIS-5 to OIS-4). Unit 2 drainage was line-sourced and deposited deltas with a shore-parallel steep seaward margin. In contrast, unit 4 drainage was point-sourced and deposited elongate deltas on the shelf.
Highstands were dominated by deltas deposited on the middle to outer shelf. Subaerial exposure of the inner shelf and the development of an extensive braid plain characterized lowstand deposition. Lowstand incised fluvial valleys, canyons, and deep-water fans are absent. The transgressive systems tract is characterized by valley fill and sand ridges on the inner shelf and backstepped deltas and slope wedges on the middle shelf to upper slope.
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The northern Gulf of Mexico margin encompasses a variety of depositional settings characterized by different drainage basin size, physiography, fluvial morphology, climatic setting, and structural and diapiric activity. This, plus the abundance of long sediment cores and platform borings from oil industry activities, make it an unparalleled natural laboratory for sedimentological and stratigraphic studies and for testing sequence stratigraphic concepts. This volume contains twelve papers describing results from high-resolution stratigraphic studies of late Quaternary strata of the northern Gulf of Mexico, from the mouth of the Apalachicola River to the Rio Grande. These papers focus on fluvial response to climate and base-level change, variations in delta growth and evolution across the shelf, lowstand delta-fan evolution, the evolution of transgressive deposits on the shelf, the preservation of these deposits. The robust chronostratigraphic frameworks developed for the different study areas allows comparison of stratal geometries produced by contemporaneous depositional systems operating under identical eustatic conditions. This volume will appeal to sedimentologists and stratigraphers interested in source to sink issues, such as how various forcing mechanisms influence strata formation on continental margins.