Abstract:
The stratigraphy , sedimentology and geochemistry of. the upper Transvaal
Sequence rocks in the northern portion of the Rooiberg Fragment are
researched.
The Leeuwpoort Formation of the Pretoria Group was deposited in a fluvial
palaeoenvironment. The basal arkosites in this unit reflect braided stream
deposition, whereas the overlying shaly arkosi tes represent upward- fining
cycles of point bar sedimentation. The uppermost main Leeuwpoort shale
probably formed in a floodplain palaeoenvironment. The overlying
Smelterskop Formation arenites indicate high energy flood conditions in a
proximal fluvial palaeoenvironment. The extrusion of andesi tic lavas acted
as an agent of change during the deposition of Smelterskop Formation
sedimentary rocks.
The upper and lower contacts of the Smelterskop Formation are disconformable
and conformable, respectively. However, non-deposition of the main shale of
the upper Leeuwpoort Formation and erosion by succeeding Smelterskop
sedimentation in some areas, created local disconformities at the base of
the Smelterskop Formation.
The scattering of Si02 binary plots recorded in the geochemistry of the
Rooiberg Group rhyolites indicates extensive alteration of these rocks.
Petrogenetic conclusions drawn from the geochemistry must therefore be
treated with caution. However, empirical data indicates two lava types,
defined by major and trace element geochemistry and geographical position.
