Submerged shorelines and landscape features offshore of Mossel Bay, South Africa

Abstract

Coastal geomorphic systems have been studied widely to understand the responses of shorelines to fluctuating sea levels. Submerged shorelines, remnant of Pleistocene sea-level lowstands, are well preserved on the South African continental shelf. This paper describes work undertaken to better understand offshore coastal environments now submerged by high sea levels off the South African south coast near Mossel Bay, offshore of the Pinnacle Point archaeological locality. Multibeam bathymetry and side-scan sonar reveal evidence of past sea-level fluctuations and submerged coastal landscape features on the seabed. These results form the basis of an ongoing palaeoenvironmental reconstruction for this part of the shelf. We describe seven significant geomorphic features that show a submerged environment that differs significantly to the immediate adjacent coastal plain. However, these features are comparable to other stretches of the present South African shoreline that serve as modern analogues. We propose that features on the continental shelf primarily reflect geological substrate, gradients and Pleistocene sea-level fluctuations. Early modern humans were likely to have had a different set of resources to use in this Pleistocene landscape compared to those available along the presently exposed coast.

Southern Hemisphere anticyclonic circulation drives oceanic and climatic conditions in late Holocene southernmost Africa

“…The Gouritz River catchment drains almost all sequences of the Cape: the Malmesbury Group and the Cape Granite Suite as the oldest "basement" rocks (Rozendaal et al, 1999;Johnson et al, 2006;Milani and de Wit, 2008); the thick siliciclastic sequence of the Cape Supergroup (Thamm and Johnson, 2006;Newton et al, 2006); and the Karoo Supergroup, which was terminated by the extrusion and intrusion of the extensive Drakensberg basalts and dolerites (Duncan et al, 1997). The southern cape continental shelf and the broad, shallow plain, low-relief coastal plain mantled with Pleistocene/Holocene deposits comprise the submerged and emergent portions of a continuous feature (Cawthra et al, 2015). The south coast is characterized by a series of eastward-opening log-spiral bays that extend for approximately 20-40 km between adjacent west-east-trending rocky headlands.…”

“…During winter, plumes of warm Agulhas Current water have been observed to advect onto the shelf by southwesterly winds (Lutjeharms and van Ballegooyen, 1988). Cawthra et al (2015) describe the morphology of the area as a generally smooth, wide continental shelf of low gradient (see location in Fig. S1 in the Supplement).…”

Palaeoecology of giraffe tracks in Late Pleistocene aeolianites on the Cape south coast

“…2,3 Aeolianites outcrop along much of the Cape south coast. In this area, a broad continental shelf is currently submerged but various authors have postulated the role of this shelf and its link to submerged landscapes [4][5][6] -the opening of a landscape over which mammals could migrate without the impact of the Cape Fold Belt 7 , supporting populations that were hunted by ancient people and carnivores and fossilised in caves and rock shelters 8,9 .…”

Geology and archaeology: submerged landscapes of the continental shelf: an introduction

“…They include technological advances in the reconstruction of deeply submerged palaeolandscapes and assessment of their archaeological potential (Cawthra et al 2015;Foglini et al 2015;Sakellariou & Galanidou 2015), detailed predictive modelling of the environmental and archaeological potential of submerged landscapes (Ward et al 2014), the discovery, interpretation and wider significance of underwater archaeological sites (Abelli et al 2014;Nutley et al 2014), detailed analysis of shoreline changes and their human impact combining geological, palaeoenvironmental and archaeological evidence (Ryabchuk et al 2014;Galili et al 2015;Kulkova et al 2015), and the effect of sea-level changes on patterns of human dispersal in key areas (Antonioli et al 2014;Glørstad 2014;Wurster & Bird 2014). Glørstad (2014) describes the peopling of Norway following the retreat of the Scandinavian ice sheet.…”

“…A different geological environment is investigated by Cawthra et al (2015) on the tectonically stable continental margin of South Africa. This region is of particular importance because caves along the present-day coast have long stratified sequences with some of the earliest evidence for AMH populations and indications of early use of marine resources reaching back as far as 160 kyr ago.…”