ABSTRACT

A field of "lower continental rise hills" situated on the seaward flank of the Hatteras Outer Ridge was investigated with a grid of bathymetric profiles, a continuous seismic reflection profile, and short (1.2 m) gravity cores.

Throughout the field investigated the lower continental rise hills are not isolated "hills" but rather are linear waveforms with fairly regular distribution and orientation. The waveform parameters are as follows: trough-to-trough wavelength between 3 and 12 km, trough-to-peak amplitude between 10 and 100 m, crestal lengths of tens of kilometers trending NW-SE, asymmetric with steeper limb facing SW. Core samples recovered from the hills contain lutite and clay. The NW-SE crestal orientation and morphological similarity of these linear lower continental rise hills to megaripples or dunes are evidence that their development is related to deposition controlled by the deep Western Boundary Undercurrent, which flows southwest over the continental rise.

The waveforms may extend down to reflection horizon A (Late Cretaceous-Eocene). The similarity of the waveforms to megaripples that extend continuously from horizon A to the present ocean bottom in the Argentine Basin implies that the North and South Atlantic have been open and intercommunicating at least since the initiation of the waveforms