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Areal and Lateral Changes in a Major Trailing Margin Turbidite--"Black Shell" Turbidite

C. M. Prince, R. D. Elmore, R. Ehrlich, O. H. Pilkey

The Black Shell turbidite on the Hatteras Abyssal Plain, the largest turbidite mapped, covers at least 44,000 km2, with a volume > 100 km3. Between 100 and 140 km in width and up to 400 cm thick, it extends at least 500 km from the mouth of Hatteras Canyon. It has been correlated with 35 piston cores using grain size, mineralogy, and quartz sand or silt morphology. The fine-grained top of the turbidite can be recognized from quartz silt morphology. Derived from a failure on the upper continental slope, the turbidity current was channeled to the southeast through Hatteras Canyon to the Hatteras Abyssal Plain. Shapes of quartz silt and sand indicate that the slope failure involved an initial flow composed of sediment from an unlithified sand-rich dr pe (now found in the lower parts of the turbidite) followed by mobilization of a partially lithified clay-rich substrate. Once on the plain, the current separated into a sandy phase, flowing south in the central section of the plain controlled by topography, and a lutitic phase which traveled southeastward for several tens of kilometers before veering to the south in the eastern section of the plain. As the sandy phase reached the Blake Outer Ridge, it was deflected to the southeast, overriding the lutitic phase on the eastern margin of the plain. There was also an interfingering of the phases due to lateral spread. The pattern of sedimentation of the trailing margin Black Shell turbidite is markedly different from that observed in leading continental margins. It has also provided a datu for lithostratigraphic studies on the Hatteras Abyssal Plain.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.