Late Quaternary palaeoceanographic record in giant piston cores off South Africa, possibly including evidence of neotectonism

Abstract

Three giant piston cores were recovered in 1996 from the slope and rise off South Africa by the MARION DUFRESNE. The cores are MD962084, NW of Cape Town, MD962080, SSW of Cape Town and MD962077 off East London in the Natal Valley. MD962084 (35.28 m) contains a detailed record of the Quaternary variability of the Southern Benguela, whereas MD962080 (22.23 m) records latitudinal variations in the position of the Subtropical Convergence. Sediments of hypothermal periods are dominated by Neogloboquadrina pachyderma (right-coiling) and, in MD962080, higher proportions of very fine quartz sand, washed off the continental shelf during lowstands. In contrast, sediments of hyperthermal periods are dominated by Globorotalia inflata and increased amounts of the tropical Globorotalia menardii, which is also found in trace amounts in the hypothermal periods. This shows that Agulhas water transfer never completely ceased, even during equatorward excursions of the Subtropical Convergence during hypothermals. Three major turbidites of quartz sand characterise the Natal Valley core, MD962077 (35.54 m) and they have ages of 510, 340 and 250 ka. If they were triggered by major earthquakes, it is argued that an even bigger earthquake is overdue, 250 ka after the last one.