The stratigraphy, sedimentology and structure of the Cango group north of Oudtshoorn, C.P.
Date
1977-12
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
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.
Description
Thesis (MSc.)--Stellenbosch University, 1977.
Spine title: Geology of the Cango Group.
3 Maps in 19 parts from page 194 to page 211.
Spine title: Geology of the Cango Group.
3 Maps in 19 parts from page 194 to page 211.
Keywords
Sediments (Geology) -- South Africa -- Oudtshoorn, Geology, Stratigraphic -- Precambrian, Paleogeography, Geology, Structural