Dolostone from the South African Continental Slope

Abstract

ABSTRACT Reports of lithified dolostone from deep-water environments are relatively rare. A large quantity of dolostone has recently been recovered from a single station on the South African continental slope at a depth of 790 m. Microspar-sized protodolomite crystals make up about 90% of the rock; other components are mostly silt-sized terrigenous grains and hematite dendrites. The rocks are covered by a brown carbonate fluorapatite-illite-hematite crust and rock surfaces have a distinctive pattern of ridges, grooves, and depressions. The origin of this dolostone facies is uncertain, but is believed to be the product of refluxing brines which originated at shallower levels on the shell Subsurface migration of these hypersaline, Mg-rich brines dolomitized the carbonate sediments through which they passed. The surficial depressions, grooves, and ridges are attributed to submarine solution and the crust to submarine replacement while the semi-lithified rocks were exposed on the sea floor.