Pleistocene Palaeogeography of the Agulhas Bank

Abstract

Palaeogeographies of the Ajplhas Bank for three low sea-level stages during the Pleistocene are presented (-140 m, -IOO m and -50 m). Although they are specifically considered in relation to the last transgression (Flandrian, post-Weichsel/Wurm), they are applicable to any of the previous glacial periods. In each case, the bedrock geology and expected superficial sediment cover are outlined, and general conclusions as to soil types, terrain, drainage, etc., are presented. The extended courses of local rivers in the Pleistocene are postulated from bathymetric and sedimentological data.

The genetic legacy of lower sea levels: does the confluence of rivers during the last glacial maximum explain the contemporary distribution of a primary freshwater fish (Pseudobarbus burchelli, Cyprinidae) across isolated river systems?

“…1), occurrence of this lineage in the Goukou River system cannot be explained by confluence during lower sea levels. Dingle & Rogers (1972) and Birch (1980) proposed that the Goukou River system had a common confluence with the Gourits River system (Fig. 1).…”

“…1 Map of the Agulhas Bank region of the southern coast of South Africa where P. burchelli samples were collected (Breede lineage = blue circles; Heuningnes lineage = red circle; Tradou lineage = green circles). Currently isolated river systems and possible LGM palaeoriver courses based on the geological literature (solid lines according to Dingle and Rogers (1972)or dashed lines based on the available bathymetry) are also shown. Insert maps show the Tradouw catchment with collection localities and the position of the study area in relation to South Africa and Duiwenhoks river systems would have formed a western palaeoriver system, whereas according to Birch (1980) and Dingle & Rogers (1972), the Goukou River system would have had a common confluence with the Gourits River system to form an eastern palaeoriver system.…”

“…Currently isolated river systems and possible LGM palaeoriver courses based on the geological literature (solid lines according to Dingle and Rogers (1972)or dashed lines based on the available bathymetry) are also shown. Insert maps show the Tradouw catchment with collection localities and the position of the study area in relation to South Africa and Duiwenhoks river systems would have formed a western palaeoriver system, whereas according to Birch (1980) and Dingle & Rogers (1972), the Goukou River system would have had a common confluence with the Gourits River system to form an eastern palaeoriver system. The Heuningnes River system would have had a common confluence with the Breede and Duiwenhoks river systems before reaching the -130 m sea level, unless it flowed in a more westerly direction compared to the direction proposed in Fig.…”

“…1). Based on palaeoriver courses that were reconstructed by Swartz et al (2009), using the bathymetry of South African Navy Charts, seismic profiling of offshore sediments by Birch (1980) and reviews published on offshore stratigraphical, sedimentological and bathymetric studies (Dingle & Rogers, 1972;Dingle et al, 1987), it is proposed that exposure of the Agulhas Bank would have allowed adjacent rivers to coalesce before reaching the -130 m sea level, forming two major historical river systems (Fig. 1).…”

Aeolianite and barrier dune construction spanning the last two glacial?interglacial cycles from the southern Cape coast, South Africa

“…OIS 3 is characterized by rapid fluctuations in climate and ice5volume and five highstands have been identified, centered on 32, 36, 44, 49-52 and 60 ka ago with sea levels between 570 and 540m (Lambeck and Chappell, 2001). OIS 2 includes the LGM followed by a period of rapid ice decay when approximately 50 million km3 of ice melted from the land5based ice sheets, raising global sea level in regions distant from the major glaciation centres, such as South Africa, by about 110-130m (Dingle and Rogers, 1972b;Illenberger, 1996;Barrable et al, 2002;Ramsay and Cooper, 2002). The past 12,000 years define OIS51 or the Holocene, when ice volumes and climate were largely similar to those of today (Lambeck et al 2002). Although hampered by the level of precision associated with the chronology, two observations can be made of the apparent relationship of aeolianite deposition to sea level.…”