| dc.description.abstract | The present drainage patterns of the Harts and Molopo Rivers have developed
in consequence of crustal movements associated with the initiation of
the Griqualand - Transvaal Axis of uplift towards the end of the Tertiary
Period, The development of this axis along a northeast-southwest Precambrian
lineament, which now forms the divide between the Harts River and the Skoonspruit
drainage and Vaal River, caused disruption of the pale □ - Nossob, the
pale - Dry Harts, and the pale - Harts Rivers. The disruption of these
rivers, which were southward-draining tributaries of the Vaal River during
the Tertiary, culminated in the evolution of the present physiographic features
of the area lying to the north-west of the Vaal River between Klerksdorp and
Barkly West, Tectonic movements also resulted in a significant reduction of
the volume of water draining into the Vaal River from the north, This fact,
coupled with the diastrophic steepening of the slope of the pre-Karroo surface
on which the Vaal River was shifting towards the south-east, contributed
to the formation of the "older" high- level gravel terraces on the right bank
of the Vaal River.
A complementary effect of the south-eastward tilt of the land on the
southern side of the Griqualand - Transvaal Axis was the reduction of the
gradients on the pediplaned surface which lay to the south-east of the Vaal
River. This gave rise to the formation of numerous pans which now constitute
the Pan Veld of the north-western Orange Free State,
A sedimentary petrological investigation of the sandy soil in the catchment
area of the upper Harts River, which is cultivated mainly for the production
of maize in the districts of Lichtenburg and Delareyville, shows that it is
a polygenetic type of soil, Both its grain-size characteristics and heavymineral
composition point to the fact that it is a hybrid soil composed of
different proportions of locally derived pedological material and a component
of aeolian sand with a north-westerly provenance, As the aeolian sand
is completely integrated with saprolite of the Tertiary erosion surface and
predates the disruption of the Pliocene drainage, it is considered to be
possibly middle to late Tertiary in age. | en_US |
