On the False Bay side of the Old Lighthouse at Cape Point, the contact between the older, light gray, Cape Granite and the younger, overlying, Table Mountain Group sandstone, is tilted down towards the north to Smitswinkel Bay, where the largest fault in the Cape Peninsula is situated.
As a UCT geologist, I have viewed Smitswinkel Bay many times because the largest fault in the Cape Peninsula is situated there.
The area features the start of a coastal outcrop of orange-brown Table Mountain group sandstone that stretches south to the old lighthouse at Cape Point. The sandstone base then rises a little above sea level as light grey Cape Granite is revealed below the new lighthouse at the very tip of Cape Point.
North of the sandstone outcrop in Smitswinkel Bay is the beach, north of which is a coastal outcrop of granite that continues northwards past Miller’s Point, Froggy Pond and Boulders to Simon’s Town. The base of the sandstone, above Smitswinkel Bay, is just above road level. The base is 100m above sea level, north of the fault, and just below sea level, south of the fault, which runs from southeast to northwest just south of the road from Smitswinkel Bay to the entrance to the Table Mountain National Park’s Cape of Good Hope section. This means that the fault caused a downthrow of 100m to the south of a block from Smitswinkel Bay to Cape Point.
The inhabitants benefit from springs along the line of the fault, which last moved, accompanied by a major earthquake, 130 million years ago in the Early Cretaceous period as the supercontinent Gondwana split up and as the coastline of present-day Uruguay started moving westwards at a velocity of a few centimetres a year, the speed at which one’s fingernails grow.
I have recently worked with a resident of Dresden, Dr Kerstin Drost, who used sand-size zircon crystals to date the time-gap between the lowermost formations of the Table Mountain group, the basal, thin-bedded Graafwater Formation, named after a town northwest of Clanwilliam, and the overlying, younger, thick-bedded cliff-forming, Peninsula Formation, seen best from the cable car. The rocks are around 500 million years old and the time-gap is about 15 million years. Our best outcrop, the one we dated, is at the top of Ou Kaapse Weg. – Weekend Argus
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