Abstract:
A palynofacies study of the lower number 4 coal seam in the Highveld coalfield of the Karoo
Basin, South Africa, was conducted to get more insight into the palaeoenvironment. The
lower number 4 coal seam was sampled near Secunda, approximately 200 km south east of
Pretoria.
The Main Karoo Basin is classified as a retro-arc foreland basin, which covers an area of
approximately 700 000 km2 and can reach a maximum thickness of up to 12 km. The
accumulation of coal in the Karoo Basin occurred during the Permian in the Vryheid
Formation of the Ecca Group.
There are two palynofacies assemblages representing different depositional environments.
The first palynofacies assemblage identified in the bottom section of the coal seam is
characterised by the presence of high amounts of spores and equidimensional phytoclasts.
This indicates that it may have formed during wet cooler conditions with less transport.
The second palynofacies assemblage and top section of the coal seam is characterised by
an increase in bisaccate pollen grains and improved sorting of the phytoclasts. This
signature may indicate a higher fluvial influx into the swamp with the higher amount of
taeniate bisaccate pollen grains showing that the palaeoenvironment was warmer during
deposition. The Protohaploxypinus sp. from the glossopterid plant was the dominant flora in
the upland area while the lowland is indicative of fern wetland communities.
The lower number 4 coal seam depositional environment therefore changed from swamp to
increased fluvial input into the swamp.
There are also barren samples that were due to the igneous intrusion in the proximity of the
sampled area. The igneous intrusion formed a devolitalisation zone that reached a thickness
of 17 to 19 m. The increase in temperature adjacent to the dolerite dyke caused the organic
matter surrounding it to mature, which could possibly create gas pockets.
