Abstract
M.Sc. (Geology)
The Mzimvubu River, situated in the Eastern Cape Province of South Africa, drains
essentially strata of the Late Carboniferous to Jurassic Karoo Supergroup with minor
intersection of the underlying Devonian Msikaba Formation near the mouth of the river at
Port St. Johns. Rock- and river sediment samples were collected at specific points from within
the Mzimvubu River drainage basin, based on changes in the geology through which the
rivers flow. Detrital zircon age population data was obtained by LA-ICP-MS for each sample
in order to meet the two-fold objective of the study; firstly to investigate the reliability of
using detrital zircon grains as indicators of sedimentary provenance and secondly to
determine possible source areas for the Karoo strata and underlying Msikaba Formation.
Through the comparison of detrital zircon age population data for the rock units of the Karoo
Supergroup and Msikaba Formation to that of the river sediment, it is concluded that detrital
zircon grains hold value in deciphering the geological history of a sedimentary basin. This
interpretation is based on similar distributions and trends that are present in both the zircon
age populations of the rock- and sediment samples. However, complexities associated with
detrital zircon analysis pertaining to rock type and depositional settings are noted and
therefore certain procedures that can be implemented during field sampling have been
suggested in this study so as to ensure accurate results are obtained. This will further ensure
that reliable interpretations of the geological history of a sedimentary basin are achieved.
Additionally, by utilising the detrital zircon population data obtained in the first part of the
study in conjunction with published scientific data, the provenance of the Karoo Supergroup
in the southeastern part of the Main Karoo Basin has been determined. From this data it was
determined that, especially the upper part of the Karoo Supergroup in the Eastern Cape
Province of South Africa, was deposited much later than previously thought and that many of
the stratigraphic layers in the Karoo Basin were deposited coevally in different parts of the
basin with lithostratigraphic boundaries being time-transgressive. Ultimately the data allowed
for the construction of a tectono-sedimentary model to explain the deposition of the upper
Cape- and Karoo Supergroups that started with the deposition of the Msikaba Formation in a
passive continental margin setting, to deposition of the lower part of the Karoo Supergroup in
an Andean type of foreland basin, with rifting starting during the times of deposition of the
Molteno Formation. The deposition of the Molteno-, Elliot- and Clarens Formations took
place as Gondwanaland was breaking apart coeval with the formation of the Karoo Igneous
Province.