ABUNDANCE AND DISTRIBUTION OF CARBONATE CONSTITUENTS IN SOME SOUTH AFRICAN COASTAL AND OFFSHORE SEDIMENTS

Summary

The dominant sand-sized carbonate constituents of South African coastal and offshore sediments are molluscs, echinoderms, coralline algae, cirripedes, bryozoans, benthonic foraminifers, planktonic foraminifers, and ostracods. Fragments of these organisms make up more than 98% of the carbonate fraction in the samples studied. Each organism has a distinctive skeletal structure that allows identification in thin section.

The relative abundances of many taxa in sediment show trends with respect to geographic position. Sediment samples close to the present shoreline abound in fragments of shallow-water organisms such as molluscs, cirripedes, and coralline algae, whereas the carbonate fraction on the outer shelf and upper slope is dominated by planktonic foraminifers. Similarly, shelf sediments east of the Agulhas Arch mostly contain fragments of shallow-water organisms whereas sediments to the west contain more planktonic foraminifers.