ABSTRACT

Twenty-eight piston cores have been investigated in a study designed to compare and contrast the sediments and sedimentary processes in two adjacent but topographically distinct portions of the Carolina continental rise. Cores were collected from both the high relief portion of the continental rise encompassing the Hatteras Canyon-Hatteras Outer Ridge system and the adjacent relatively smooth and uncomplicated portion of the continental rise to the south. Sand grains are found concentrated in distinct sand layers (greater than 1 cm) and laminae (less than 1 cm) in the entire study area, but the characteristics of the sand layers are distinctly different in the two regions.

Sand layers from the Hatteras Outer Ridge-Hatteras Canyon system are abundant, often graded, poorly sorted, and contain shallow water shells and unique occurrences of pyrite cementation. In contrast, the sand layers and laminae from the continental rise adjacent to the ridge-canyon system are less abundant, not graded, better sorted, and finer in grain size than the ridge-canyon sand layers. Light mineral assemblages from both regions indicate a source north of Cape Hatteras.

In addition to grains concentrated in layers and laminae, very fine sand grains are also evenly distributed in minute quantities throughout the sediment column. The relative size, mineralogy, and even dispersion of these grains are constant throughout the study area and display no changes that can be related to local topography, indicating a slow, continuous depositing mechanism.

Analyses of both sand layers and dispersed sands suggest that turbidity current transportation is important only in the canyon vicinity. To the south, lateral flowing bottom currents are responsible for secondary transportation of sediments originally introduced via rapid downslope movement and slow settling. This two-step process of sediment transported by turbidity currents through the Hatteras Canyon System and subsequently redistributed by bottom currents has been a major contributor of material for Quaternary mantling of the continental rise south of Cape Hatteras and probably as well for the Blake-Bahama Outer Ridge.