The stratigraphy and sedimentation of the Bokkeveld group
Date
1972-03
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT:
A detailed stratigraphic investigation of the Bokkeveld
Group along seven regularly spaced profiles, supported by heavy mineral studies, permits definition of the upper boundary of the sequence.
There is a distinctive increase in the brookite percentage from the
base to the top of the Group.
From west to east the sequence displays cyclic deposition which
gradually fades out southwardso Five sheetlike arenitic wedges in
the west intertongue southwards with lutite ; only the lower three can be traced eastwards.
Lithological nomenclature has been introduced. Marked
consistency of the lower units as contrast ed with variability of the
upper sequence forms the basis of major subdivision into a lower
Ceres Subgroup and an upper Traka Subgroup. Each fundament allithological unit (formation) is described in relation to its
outcrop area.
Grain-size distribution, palaeocurrent orientations and other
directional structures have been investigated mainly in the arenaceous
units and analysed by modern computer methods . The coincidence of
palaeo current orientations, isopach patterns and southward diminution
of grain-size , proves that a general southward and westward directed
palaeoslope prevailed during sedimentation. The grain-size distribution suggests shallow marine to beach deposition. The stratigraphi coccurrence, orientation and fossil- and -sediment association support
this conclusion.
In the west the elongate Clanwilliam basin, flanked by
marginal shelves, merged southeastward with an east-west trending 'shelf'
or basin with marked eastward axial pitch ( Agulhas 'basin'). Cratonic
borderlands existed to the north (Bushman Mountain land) and west
(Atlantic Mountainland) of the Clanwilliam basin. Similar borderlands
flanked the Agulhas 'basin' to the north (Nuweveld and Winterberg
Mountainlands) and possibly south (Antarctic Mountainland). Lithofacies and isopach contour patterns are closely related, revealing a direct
relationship between structural grain and sedimentation, a marked
northward increase in sand, as well as an overall predominance of
the finer elastic fraction in the Bokkeveld Group.
The sedimentary history of the sequence deals with a
shoalwater deltaic-marine complex, subjected to marine transgressions
and regressions in a tectonically unstable setting.
The Bokkeveld Group, predominantly a regressive sequence,
forms a separate entity of the Cape Supergroup marked by a lack
of supermature sediment.
The two tectonically dissimilar basins which received the
sediments of the Bokkeveld Group were probably inherited weaknesses
of the continent.
Geen afrikaanse opsomming beskikbaar.
Geen afrikaanse opsomming beskikbaar.
Description
Thesis (D.Sc.)--Stellenbosch University, 1972.
Keywords
Geology, Stratigraphic, Sedimentation and deposition -- South Africa -- Cape of Good Hope, Bokkeveld Mountains (South Africa), Dissertations -- Geology