Mississippi-Alabama outer continental shelf topographic features formed during the Late Pleistocene-Holocene transgression

A geophysical survey of the outer Mississippi-Alabama continental shelf revealed 3 types of topographic features: reef-like mounds (RLM), isobath-parallel ridges, and shallow depressions. RLM appear to be bioherms. Their bases cluster in two isobath bands, 105 to 120 m and 74 to 82 m, implying the late Pleistocene-Holocene transgression was non-uniform. The deeper RLM probably formed during a slow sea level rise at the beginning of the deglaciation. An 11 ka BP C super(14) age was obtained from the summit of one, at a depth of 90 m. Depth relationships suggest the shallower RLM and most ridges formed about the time of the mid-deglacial Younger Dryas cooling episode.