Investigations of the Walvis Ridge and environs

Abstract

Abstract taken from Dissertation Abstracts International? year? page 275-B:

No sills deeper than about 1950 fm are known on the Walvis Ridge east of 4°W. The cold, nepheloid Antarctic Bottom Water (AABW) that has recently been discovered north of the Walvis Ridge is entering the southwestern Angola Basin from the Cape Basin through the Walvis Passage near 36°S, 7°W. The AABW in the southern Angola Basin is not detected by its temperature or light scattering north of 30*S

A large number of guyots recently discovered in the region 30° to 43°S, 12° to 4°E, southwest of the main Walvis Ridge, rose to the sea surface in the Eocene. The summits of the guyots lie at depths of 600 to 800 fm, about the same depth as the shallower parts of the main Walvis Ridge. Shallow-water fossils from two guyots 600 fm (1100 m) deep suggest that the volcanic activity on them ceased in Eocene time, when their distances from the axis of the Mid-Atlantic Ridge were about 100 and 700 km respectively, and that the morphologic expression of the Mid-Atlantic Ridge was slight at that time. Seismic and piston-coring evidence from sediments in the Cape Basin can be interpreted to suggest that the relief between the basin floor and the crest of the Mid-Atlantic Ridge was low during the Cretaceous and Early Tertiary

Several small abyssal plains were formed at the base of the Walvis Ridge as a consequence of its uplift. The calcareous turbidites flooring one of the plains, the Walvis Abyssal Plain (2830 fm, 5170 m, uncorrected) near 25*S, l°E, were most likely deposited by turbidity flows commencing on the broad, gently westward dipping slope of the adjacent, asymmetric Walvis Ridge. An abyssal plain in the Cape Basin at the north- eastern base of the Walvis Ridge has probably received only a minor amount of calcareous sediment from the narrow, steep eastern flank of the Walvis Ridge