Earth and Planetary Sciences ETDs

Publication Date

5-13-1975

Abstract

The extensive evaporite deposits of the Namib desert occur in an area bounded by the Ugab River on the north and the Kuiseb River on the south. Smaller deposits which are concentrated on the coast occur north and south of these boundaries. The deposits occur as a blanket deposit up to 20 feet (6.1 meters) in thickness and extend inland for a distance of approximately 55 miles (90 km) and extend 110 miles (176 km) between the northern and southern boundaries. The deposits are composed mainly of gypsite, but there are two locations where anhydrite is the predominant form present. These deposits represent deposition of secondary anhydrite under nonmarine conditions. Previous investigations of the deposits ascribed the origins to either marine transgressions or the aerial transport of hydrogen sulfide inland from the coast and its reaction with the surficial calcium carbonate deposits to form gypsite. The use of sulfur isotope determinations and a field study of the distribution and characteristics of the deposit demonstrate that the previous theory of hydrogen sulfide origins (Martin 1963) was unable to explain the depositional system. The sulfur isotope values (+16.3 permil average) were very different than would be expected if the deposits were derived from a sulfur source resulting from the bacterial decomposition of oceanic sulfate. The presence of primary anhydrite in the underlying precambrian schist, the presence of very saline subsurface waters, and the distribution of the deposits indicate that the source for the blanket surficial deposits may be associated with the underlying precambrian schist and the movement of ground waters from the highlands to the coast with an attendant increase in salines from highland to coast.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Douglas Gridley Brookins

Second Committee Member

Gary Perrin Landis

Third Committee Member

Roger Yates Anderson

Language

English

Document Type

Thesis

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