Soils of arid regions

Abstract

Steep convex-bankward embayments into carbonate platform margins, often called “scalloped margins”, have been observed in ancient examples and along modern platform of the Gulf of Mexico and the Caribbean region and are interpreted as erosional features produced by large-scale margin failures. Multibeam bathymetry data from the southwestern corner of Great Bahama Bank (GBB) image four margin failures and their associated erosional products. The bankward-convex embayments range in diameter from 3 to 23 km. The largest and southernmost collapse produces a scalloped margin while the other three are not changing the generally linear platform margin. The typical slope angle of the upper slope in this portion of GBB ranges from 20 to 40° with the margin break at ~ 60 to 65 m water depth. But in the four areas of platform margin collapse the slope angle increases and the margin break is shallower. The largest collapse eroded more than 350 m of the bank margin with an estimated ~ 15 km3 of platform margin materials shed onto the adjacent slope. These margin collapses shed large debris blocks to the toe-of-slope and basin floor some tens of kilometers from the platform margin. In the southernmost segment margin collapse is followed by slope failures that produce mass transport complexes (MTC) that litter the lower slope and basin floor. The largest block in one MTC is 2000 × 800 m in dimension and is displaced by 1.2 km.The margin collapses are more common along the southwestern GBB than the northern portions of GBB where large-scale slope failures are more common. This lateral distribution is attributed to the tectonic activity in the vicinity of the Cuban fold and thrust belt. Faults breaking the modern seafloor and Holocene growth strata on the Santaren Anticline document neo-tectonic activity within the belt. Thus, tectonic activity and associated seismic shock might be the primary trigger for the margin collapse and occurrence of the scalloped margin along the Old Bahama Channel.