Publication Date

2013-12-18

Availability

Open access

Embargo Period

2013-12-18

Degree Name

Master of Science (MS)

Department

Marine Geology and Geophysics (Marine)

Date of Defense

2013-11-25

First Committee Member

Gregor P. Eberli

Second Committee Member

Donald F. McNeill

Third Committee Member

Mark Grasmueck

Abstract

High-resolution multibeam bathymetry and sub-bottom profile data from offshore Great Bahama Bank, covering an area of 6,500 km2, allow an assessment of the evolution of the slope and basin environment. The data reveal a substantial variability in the slope morphology. Three different sedimentary processes (downslope mass gravity flows, margin collapse, and contour currents) control this variability in slope morphology. The deposits that result from these processes produce a consistent facies distribution along the slope, consisting of four morphofacies: 1) a steep upper slope with an onlapping sediment wedge, 2) a toe-of-slope with redeposited carbonates, 3) a basin floor covered with pelagic sediments, and 4) an elevated seafloor with pockmarks. The margin and uppermost slope is steep and cemented, with declivities ranging from 20° to 70°. The steep slope is onlapped by a sediment wedge that reaches a thickness of 100 m and extends >5 km basinward. The lower slope and toe-of-slope is dominated by coarse-grained sediments and debris from mass-gravity flows. Most of the coarse-grained sediment is funneled through closely spaced gullies on the middle slope and deposited as turbidite beds at the toe-of-slope. These turbidite deposits are arranged in lobes and apron system. In this area fine-grained sediment is largely winnowed away by ocean currents. Margin and slope instability add to the strike variability. Four segments of the platform margin collapse have been identified. Margin collapse features are characterized by crooked and convex bankward morphology. The smallest collapse margin scar is 3 km long and the largest scar is more than 20 km long. The 20 km long scar eroded bankward more than 350 m and produced an extensive megabreccia on the adjacent slope and basin floor that extends tens of kilometers from the margin. Contour currents that flow in the Old Bahama Channel transport drift sediment to the basinal are of this study where they interfinger with bank-derived the toe-of-slope deposits. The surface of the drift deposit is littered by thirty pockmarks generated by water and gas escape. The close proximity of these pockmarks to the Cuban fold and thrust belt indicates that the degassing is related to overpressure from by tectonic activity.

Keywords

multibeam bathymetry, carbonate slope, variability, density current, contour current, margin collapse, deep-water.

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