The structure of the Eastern Walvis Ridge and the adjacent continental margin

Abstract

Abstract provided by author:

A compilation of all the available bathymetric, magnetic and seismic reflection data over the eastern Walvis Ridge and adjacent continental margin, including the drawing of contour charts, has enabled the structure of both these features to be discussed in some detail. From this discussion, tentative conclusions can be drawn as to the nature and origin of the eastern Walvis Ridge and of the continental margin between 17 and 28°S

East of 4 degrees E the Walvis Ridge consists of two mutually perpendicular sections - the Frio Ridge and Valdivia Bank - which trend approximately east-west and north-south, respectively. The Frio Ridge consists of two, parallel, steep-sided basement ridges which are associated with oceanic fracture zones, as are sections of northern and southern Valdivia Bank, from where the fractures can be traced across the Cape Basin

Both sections of the Ridge have been uplifted in the past, with accompanying volcanism apparently more common in the vicinity of fracture zones, and vertical faulting predominating on central Valdivia Bank, which is probably an uplifted block of oceanic crust. This uplift may have occurred about 80 m. y. ago, when a change in the direction of sea-floor could have resulted in the build up of stresses within a zone of rapid change in spreading rate postulated in the vicinity of the Walvis Ridge

A difference in spreading rate north and south of the Walvis abutment could also be responsible for the marked change in margin morphology present at the abutment, with different basement structures underlying the margin in the north and the south. Initial rifting of the South Atlantic is thought to have occurred between 127 and 130 m. y. ago. Several prominent sediment reflectors are identifiable on the rand in the adjacent Cape and Angola Basins, including one which tentatively correlated with horizon A