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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 69 (1985)

Issue: 7. (July)

First Page: 1133

Last Page: 1144

Title: Shallow Structure, Stratigraphy, and Carbonate Sedimentary Processes of West Florida Upper Continental Slope

Author(s): Larry J. Doyle (2), Charles W. Holmes (3)


An extensive minisparker, 3.5-kHz, piston-coring survey of the continental slope above the West Florida Escarpment has revealed a Pleistocene sequence of up to 160-msec two-way traveltime, overlying a second, probably Miocene, strong reflector. South of 27°20^primeN the contact between the two is clearly an erosional unconformity and includes a band of karstlike features. The Pleistocene drape thins to a minimum, locally even exposing the second layer, at about 500 m (1,650 ft) water depth and thickens dramatically downslope. We attribute this thinning to the north-south flowing Loop current blocking deposition and scouring the bottom. The ancestral Loop may have been responsible for the erosional unconformity, or it could have been due to subaerial erosion. If the l tter is the case, present depth of the erosional surface suggests as much as 400 m (1,320 ft) of subsidence after its formation.

From its southern limit to 26°40^primeN, two parallel reefs mark the upper slope. Sediments on the upper slope are a foraminifera-coccolith ooze, the compositional equivalent of a chalk deposit. Radiocarbon dating shows ooze below the erosional minimum accumulating at over 30 cm/1,000 years (11.8 in./1,000 years) for at least 25,000 years--a surprisingly high rate--over an order of magnitude greater than that for a compositionally equivalent deep-sea ooze. High sedimentation rates are also reflected in a variety of mass wasting features from creep to massive slides to gravity-induced folds tens of kilometers long. The upper west Florida slope, therefore, is only a temporary resting place for sediments that are moved downslope by mass wasting processes to the West Florida Escarpme t.

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