R. M. Mitchum, Jr, 1978. "Seismic Stratigraphic Investigation of West Florida Slope, Gulf of Mexico", Framework, Facies, and Oil-Trapping Characteristics of the Upper Continental Margin, Arnold H. Bouma, George T. Moore, James M. Coleman
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The post-Early Cretaceous geologic development of the West Florida Slope was studied by analysis of 2,500 n.m.(4,630 km)of seismic sparker lines and seven core holes. Slope deposition was not a simple, continuous process, but was interrupted by significant depositional breaks that appear in the faunal record and as reflective events on seismic profiles. Sediments between these breaks are interpreted as genetically related sequences that can be mapped and used to interpret slope stratigraphy.
At the end of the Early Cretaceous the presents lope are a was abroad shallow-water shelf which probably extended westward to the present West Florida Escarpment. This escarpment is interpreted as mostly a constructional shelf margin forming a gulfward extension of the Washita-Fredericks-burg trend of Louisiana and Texas. The role of major faulting as a controlling factor in producing the escarpment was not investigated in this study, although we failed to observe major faults on our sparker data. Late Cretaceous subsidence of the shelf produced a rapid transition from shallow -to deep-water carbonates, with water depths in the order of 3,000 to 6,000 ft(900 to 1,800 m)on the outer slope by the end of the Cretaceous. Deep-water conditions prevailed throughout the Cenozoic as the area gradually filled to its present bathymetric configuration.
Lowermost Tertiary beds along the outer slope commonly are crumpled and distorted. Post-Eocene topographic lows tend to be filled with Oligocene and early Miocene beds.During the middle Miocene large clinoforms of argillaceous carbonate built as progradational features from shallow -water areas on the north. Thinner upper Miocene beds were deposited as lenses on the clinoform slopes. Pliocene and Pleistocene deposition continued this trend to its present configuration. The DeSoto Canyon area has a long Cenozoic history of nondeposition and erosion.
Lithified shallow-water dolomite and limestone are present in Lower Cretaceous and lower most Upper Cretaceous beds. Younger sediments consist mostly of unlithified deep-water carbonates with planktonic foraminifers, coccoliths, and radiolarians associated with varying amounts of terrigenous clay. Mineralogically, the carbonate is mostly low-magnesium calcite, but Pleistocene sediment also contains some high-magnesium calcite and aragonite. The mineral dolomite is present in Pleistocene, Pliocene, and upper most Miocene unconsolidated sediments as well as in Lower Cretaceous lithified beds. Possibly the younger dolomite formed in deep-water unlithified sediments at or near water depths in which they now are.
The most common sedimentary structures are banding and burrowing. The banding consists of alternating light(coarse)and dark(fine)layers of carbonate that form couplets varying in thickness from less than 0.5 in.(13 mm)to more than 6 in.(15 cm). The banding is very regular, and grain size is a function of the relative abundance of foraminifers, coccoliths, and clay matrix. The couplets may be formed by small, frequent density currents, but the mechanism is not understood. Burrow mottling commonly is superimposed upon the banding structures and may destroy them partly or completely. Questionable turbidites, more than 6 ft (180cm) thick, are present in some calcareous clay sequences in the northern part of the slope.
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Framework, Facies, and Oil-Trapping Characteristics of the Upper Continental Margin
The Gulf of Mexico covers an area of more than 1,500,000sq km, has a maximum depth of about 3,700m, and includes many of the geomorphic features of large oceans.The continental shelf, slope, rise, and abyssal plain comprise the major physiographic provinces of the guldf and contain avariety of subprovinces distinguished by topographic character and geomorphic history.
The gulf shelf is a relatively smooth, gently sloping surface marked locally bylow-relief featuresformed by sea-level fluctuation during the Pleistocene, reef growth, near-surface movement of diapiric salt and mud, and faulting. Shelf width varies from about 280km off the Florida and Yucatan Peninsulas to less than 10km at the Mississippi Delta. The continental slope consists of a considerable variety of physiographic subprovinces and individual features that encircle the deep gulf floor.
The distinctive subprovinces of the gulf slope have evolved in response to reef building and constructional sedimentation on the Florida and Yucatan carbonate platforms; erosion, nondeposition, slumping, and fault ing in the Straits of Florida and Yucatan Channel; salt diapirism and differential sedimentation in the region off Texas and Louisiana; the largeaccumulation of mainly Pleistocene sediment on a former continental slope seaward of the Mississippi Delta; tectonic uplift and diapirism in theGolfo de Campeche; and shale mobilization of feastern Mexico. In contrast to the greatly varied, irregular topography of the continental slope,thedeep seafloor of the gulf (composed of continental rise and abyssal plainprovinces) is an almost featureless plain smoothed by turbidite and pelagic sedimentation and marked locally bylow-relief knolls, sedimentary aprons, and small-leveed channels.