Geology of the Ciolli Quarry, Tygerberg Hills by EM Langenhoven

The geology of the Ciolli Quarry falls in the NAMIBIAN ERATHEM and encompasses a time span of about 610 Ma and includes highly metamorphosed rocks of the Gariep Province which is limited to the Coastal Belt of the Republic.

Malmesbury Group.
This group and its correlations farther to the east, is limited to the south-western and southern parts of the Western, Southern and Eastern parts of South Africa. It consists mainly of sedimentary rocks which were deposited in a geosyncline, which is deeply folded along axes striking north-west, and underwent faulting and shearing in the same direction during the Pan-African or Saldanha orogeny. The Malmesbury Group is divided by two faults, known as the Franschhoek-Saldanha and Wellington-Piketberg faults.

Tygerberg Formation.
This formation is found in the south-western domain, south-west of the Saldanha-Franschhoek fault. Granites of the Cape Granite Suite are intrusive into it and the Peninsula Formation of the Table Mountain Group rests on it unconformably. It is composed mainly of shale and arenaceous shale, with intercalations of thickly bedded, fine-grained greywache and quartzite. Sedimentary structures, like graded bedding, load casts, collapse structures and cross-bedding may be present in the graywache. The rocks are tightly folded along axes striking north-west and the thickness of the formation can therefore not be determined. The metamorphosed rocks of the Tygerberg group of quarries are locally known as Malmesbury hornfels.