Bottom Sediments of the Atlantic Shelf and Slope off the Southern United States

Abstract

The submarine geology of the South Atlantic continental shelf and slope of the United States has been described using data from bottom sediment samples collected aboard the Research Vessel T. N. Gill in 1953-54, combined with information from the geologic literature. Patterns of distribution of sediment types and characteristics show several broad trends. Shelf sediments are mixtures of quartz and shell fragments in various proportions with minor amounts of phosphorite (probably collophane) and a local concentration of glauconite. Offshore, the Gulf Stream has produced a pelagic bottom sediment composed of foraminiferal and pteropod tests. Locally coral fragments are common downstream from the Florida Straits and zones of irregular bottom topography in the inner margins of the Blake Plateau indicate probable strong current scour and transport. The contemporary deposition is restricted to the zone of pelagic sediments, a narrow coastal belt bordering the Georgia-South Carolina marsh coast and the nearshore south of Cape Hatteras. Mineralogical studies suggest that two provinces are represented. One of these produces a predominance of epidote in the central shelf; the second is one in which staurolite is characteristic of the southern and northern shelf. Minor element contents of the carbonates reflect the high strontium aragonitic mollusk fragments on the shelf and the low-magnesium, low-strontium contents of the calcitic pelagic foraminifera. Similar sedimentological distributions have been described by Niino and Emery (1961) for the China Sea shelf and slope in the region of the Kuroshio Current.