About This Item
Share This Item
Along the deep margins of carbonate platforms, classic submarine fan deposition typically does not occur. Rather, coarse turbidites and debris flows are deposited as a wedge-shaped apron of debris that parallels the adjacent shelf edge. The carbonate slope north of Little Bahama Bank is a good example of a wedge-shaped base-of-slope debris apron. This slope consists of a relatively steep (~4°) upper slope (200 to 900 m, 660 to 3,000 ft) that is heavily dissected by small (50 to 150 m, 160 to 500 ft, in relief) submarine canyons; and a broad, smooth, gentle (1 to 2°) lower slope (900 to 1,300 m, 300 to 4,300 ft), devoid of any well defined canyons or "fan valleys." The upper slope developed during the Tertiary as a prograding slope-front-fill facies of fine-grain d, peri-platform oozes, whereas the lower slope has developed as a chaotic-fill facies of large slide blocks, coarse debris flows, and turbidites. Sediments along the upper slope are derived from both the overlying water column and the adjacent shallow-water banks. Sediments along the lower slope are "internally" derived via submarine cementation and subsequent submarine sliding of upper slope sediments. Debris flows are generated by these submarine slides and evolve from mud to grain-support, and commonly develop turbidity currents along their tops as they travel across the lower slope. As such, this base-of-slope apron can be divided into: (1) a proximal apron facies, characterized by thick (up to 5.5 m, 18 ft) mud-supported debris flow deposits and thick (up to 2.6 m, 8.5 ft), coarse- rained turbidites interbedded with subordinate amounts of peri-platform oozes; and (2) a distal apron facies, consisting of thinner, grain-supported debris flow deposits, and thinner, finer grained turbidites interbedded with subordinate amounts of peri-platform oozes. Seaward of the distal apron facies is a basinal facies of thin (< 20 cm, 8 in.), fine-grained turbidites interbedded with peri-platform oozes that comprise 60+ % of the near surface sediments.
Such a model for base-of-slope, peri-platform carbonate sedimentation offers an alternative to the submarine fan model for those geologists and explorationists working with ancient carbonate mass-flow deposits. A good understanding of modern carbonate slope processes and products should aid in unravelling the complex stratigraphy of ancient carbonate slopes.
End_of_Article - Last_Page 521------------