The stratigraphy, sedimentology and structure of the Cango group north of Oudtshoorn, C.P.

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Stellenbosch : Stellenbosch University
ENGLISH ABSTRACT: This investigation aims at determining the paleogeographic and tectonic setting of a Precambrian suite of low grade metamorphic rocks north of Oudtshoorn, Cape Province, by means of a stratigraphical, sedimentological and structural analysis. The Cango Formation is raised to Group status, while formal names are introduced in a new, more detailed stratigraphic subdivision. The lowest unit, the Matjies River Formation, was deposited in an environment varying from that of an unstable shelf (Nooitgedagt Member) to an isolated platform (Cave Member). The main source area lay to the west. After submergence the turbidites of the Groenefontein Formation were deposited in deeper water. Transport was in a westerly direction along the trough axis, with the main supply from the flanks to the north and south. During subsequent uplift the basin was locally eroded and the Vaartwell conglomerates (partly cannibalized from the Groenefontein Upper Member) were deposited in alluvial fans(polymictic member) and on beaches (monomictic member). Transport was roughly in an easterly direction. Westward transgression of the sea resulted in upward grading of the Vaartwell to infralittoral (Uitvlugt Formation) and circalittoral (Gezwinds Kraal Formation) deposits. The later grade laterally into the fluvio-deltaic sediments of the Schoongezigt Formation, derived from the east. An overall flysch- molasse - flysch cyclicity is in evidence. The regional setting is visualized as an embayment situated at the southern edge of a continent and connected in the southeast to the open sea. The source areas were probably of a non-volcanic nature. The Cango rocks were subsequently deformed by horizontal, northward-directed compression as shown by the style of folding and thrust faulting. The regional strike is arcuate, convex to the north and conforms to the outcrop pattern of the overlying Cape Fold Belt in this area. This is either a post-Cape phenomenon affecting both the Cango and Table Mountain Group, or it indicates that the pre-Cape tread controlled the deformation of the latter. Metamorphism of the Cango rocks did not exceed the lower greenschists facies. The Schoemans Poort Formation was deposited unconformably in isolated depressions (mainly as fluvial sediments) along the margin of elevated highlands after uplift and erosion of the Cango Group. It represents a molasse deposit. A suite of basic rocks subsequently intruded both the Cango Group and Schoemans Poort Formation. The distinctive paleogeography of the Cange Group and the Schoemans Poort Formation precludes any correlation with the possibly time-equivalent Malmesbury Group or Klipheuwel Formations respectively. Seen in perspective the depositional and deformational history of the Cango sediments in all important aspects resembles the marginal basin association of the miogeosynclinal zone. As such they may contribute to a better understanding of the fundamental processes responsible for diastrophic cycles.
Thesis (MSc.)--Stellenbosch University, 1977.
Spine title: Geology of the Cango Group.
3 Maps in 19 parts from page 194 to page 211.
Sediments (Geology) -- South Africa -- Oudtshoorn, Geology, Stratigraphic -- Precambrian, Paleogeography, Geology, Structural