page_title: Marine geology of the Cape Peninsula and False Bay
section_title: Malmesbury group deposition
hierarchical_section_title: Marine geology of the Cape Peninsula and False Bay / The geological structure of the region / Malmesbury group deposition
caption_attribution_description: English: Schematic section of possible tectonic setting during deposition of Malmesbury group
context_page_description: The Cape Peninsula is a peninsula that juts out into the Atlantic Ocean at the south-western extremity of the African continent. At its tip is the Cape of Good Hope. The peninsula forms the west side of False Bay. The three main rock formations are the late-Precambrian Malmesbury group, the Peninsula granite, a huge batholith that was intruded into the Malmesbury Group about 630 million years ago, and the Table Mountain group sandstones that were deposited on the eroded surface of granite and Malmesbury series basement about 450 million years ago. The sand, silt and mud deposits were lithified by pressure and then folded during the Cape Orogeny to form the Cape Fold Belt, which extends along the western and southern coasts. The present landscape is due to prolonged erosion having carved out deep valleys, removing parts of the once continuous Table Mountain Group sandstone cover from the Cape Flats and leaving high residual mountain ridges.
  At times the sea covered the Cape Flats and Noordhoek valley and the Cape Peninsula was then a group of islands. During glacial periods the sea level dropped to expose the bottom of False Bay to weathering and erosion.
context_section_description: The late-Precambrian age Malmesbury group is the oldest rock formation in the area, consisting of alternating layers of dark grey fine-grained greywacke, sandstone and slate, seen along the rocky Sea Point and Bloubergstrand shorelines, and from the Strand to Gordon's Bay. These sediments were originally deposited on an ancient continental slope by submarine slumping and turbidity currents. The sequence was subsequently metamorphosed by heat and pressure and folded tightly in a NW direction during the Saldanian orogeny so that the rock layers are now almost vertical. These rocks were, in most places, scoured by wave action during past periods of higher sea level.
caption: Possible tectonic setting during deposition of the Malmesbury group. (after Compton 2004)
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