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Abstract

Presently, the continental margin of the southeastern United States (Fig. 1) forms a zone of transition between the actively building, steep-fronted carbonate platform of the Bahamas and the typical eastern North American terrigenous clastic-dominated, drowned, shelf-slope-rise configuration. This region of the continental margin is underlain by two major sedimentary basins—the Blake Plateau Basin and the Carolina Trough (Fig. 2)—which are different in shape, basement structure, and history. Indeed, the two southern basins show some of the greatest contrasts of any basins of eastern North America, especially in their early response to rifting and in the change from rifting to drifting. The region has experienced abrupt major changes in geological conditions, most notably the onset of Gulf Stream flow in the early Tertiary.

Morphologically, the area is dominated by the broad, flat Blake Plateau at about 800-1,000 m water depth (Fig. 1). The plateau is bounded to the east by the extremely steep Blake Escarpment, descending to 5,000 m water depths. To the west, a short continental slope rises to a continental shelf. This Blake Plateau morphology characterizes the margin east of Florida and north of the Bahamas. North of Florida the margin merges into the typical shelf-slope-rise morphology. Just north of the Blake Escarpment and its northern projection, the Blake Spur, the Blake Ridge extends away from the continental slope at water depths exceeding 2,000 m (Fig. 1). This broad ridge is a Cenozoic, sedimentary drift deposit controlled by bottom currents. (For the reader who is beginning to wonder why half of the features of this region seem to be named "Blake", the Blake was a Coast Survey steamer from which investigations off the southeastern U.S. were carried out in 1877 to 1880. Ferromanganese nodules were discovered on the Blake Plateau at that time [Murray, 1885].)

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