The geology of the Western Cape testifies to the former existence of a late Precambrian supercontinent, its fragmentation, the closure of an ocean between the South African and South American continental precursors (Kalahari and Rio de la Plata cratons), the accumulation of marine sediments and limestones, and their compression during a collision between these cratons. This event took place during assembly of the southern supercontinent of Gondwana, over 500 million years ago. During the Cambrian the landscape of the western and southern parts of the Cape was eroded to form an alluvial plain with granite hills. From the Ordovician to the Carboniferous this plain intermittently subsided. The resultant Agulhas Sea, which at times extended from Vanrhynsdorp in the north to beyond Port Elizabeth in the east, and which was bordered by mountains to the west and north, received considerable volumes of sediment. These sediments were lifted and folded during the Permo-Triassic Cape Orogeny to form the mountains of the Cape Fold Belt, which are capped with erosion-resistant sandstones, whilst softer shales are locally preserved in downfolds.
After Gondwana rifted, a remnant of the Rio de la Plata craton remained attached to South Africa where it underlies the vineyards of the Coastal Region. Erosion was rapid under the warm, wet conditions which prevailed through much of the Cretaceous. By the end of the Cretaceous the main topographic features of the Coastal Region had already been roughed-out. Sculpting of the landscape into its modern form took place during the Tertiary and Quaternary, a time of sub-aerial erosion, pronounced changes in sea level and climatic variation, tending toward increasing aridity. The form of the modern landscape reflects the abilities of the rock structures and materials to resist protracted weathering and erosion.
Author: J. Wooldridge
ARC Infruitec-Nietvoorbij, Private Bag X5026, 7599 Stellenbosch, South Africa
Email: wooldridgej@arc.agric.za
Keywords: geology, landscape, South Africa, terroir, vineyard, Western Cape, wine