Mississippi Fan, Gulf of Mexico—Physiography, Stratigraphy, and Sedimentational Patterns
Published:January 01, 1978
G. T. Moore, G. W. Starke, L. C. Bonham, H. O. Woodbury, 1978. "Mississippi Fan, Gulf of Mexico—Physiography, Stratigraphy, and Sedimentational Patterns", 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 Mississippi Fan, located in the northeastern part of the Gult of Mexico, is a gentle, arcuate pile of clastic sediments derived primarily from the ancestral Mississippi River drainage basin. The fan is confined by the Florida Escarpment on the east and the Texas-Louisiana-Florida continental slope on the north and west. On the south the fan abuts the Yucatan Escarpment and merges to the southeast with the Florida Plain (3,300 m) and to the west with the Sigsbee Plain (3,500 m). The radius of the fan from its apex (at a water depth of 1,200 m) to the plains is about 350 km. The fan has a surface area of about 170,000 sqkm, slightly smaller than New England.
The upper fan contains a partly leveed channel cut into older fan sediments. The channel is filled with late Pleistocene (Wisconsin) fine clastic sediments. The middle part of the fan, typical of many, is composed of a massive complex of fan channels that has constructed a crown or suprafan upto 500 ma bove the surrounding fan surface. The lower fan is characterized by smooth, gentle slopes that contain depositional distributary channels.
Reflection seismic profiles from the 1969 USNS Kane Gulf survey show sufficient continuity of seismic character to permit subdividing the upper part of the sedimentary section into three seismic stratigraphic units. Unit A, the youngest, consists of aproximal facies of disrupted seismic zones and a distal facies of generally parallel reflections separated by transparent zones. The former is interpreted to be channel, slump, anddebris-flow deposits, and the latter is turbidite flows interbedded with hemipelagic sediments. Unit A is correlated with the Sigsbee (Pleistocene) seismic unit; the fan formed during the time represented by unit A.
Two older intervals were mapped to show the relation present in this region before fan development. Unit B contains three or four bands of generally continuous reflectors that gradually converge down the lower fan and on the plain. These are inferred to be turbidite sequences. Unit C is largely an acoustically transparent layer, indicative of homogeneous hemipelagic sediments.
Computer-generated isopach maps of each unit allow study of the Neogene-Quaternary regional depositional patterns. Sediments comprising unit A exceed 3 km in thickness on the middle fan. Unit B thickens rather uniformly to the north and northwest, which suggests that the source was from that directional so. The oldest section mapped, unit C, is distributed more uniformly over the area.
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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.