| Katberg Formation | |
|---|---|
| Stratigraphic range:Early Triassic Induan-Olenekian ~252–247 Ma | |
 Hillside overlooking Gariep Dam where Katberg Formation rocks are known | |
| Type | Geological formation |
| Unit of | Beaufort Group |
| Underlies | Burgersdorp Formation |
| Overlies | Balfour Formation |
| Thickness | up to 1,000 m (3,300 ft) |
| Lithology | |
| Primary | Sandstone |
| Other | Mudstone,calcareous concretions |
| Location | |
| Coordinates | 30°30′S26°00′E / 30.5°S 26.0°E /-30.5; 26.0 |
| Approximate paleocoordinates | 65°00′S23°36′W / 65.0°S 23.6°W /-65.0; -23.6 |
| Region | Eastern Cape &Free State |
| Country | South Africa |
 | |
TheKatberg Formation is ageological formation that is found in theBeaufort Group, a major geological group that forms part of the greaterKaroo Supergroup in South Africa. The Katberg Formation is the lowermost geological formation of the Tarkastad Subgroup which contains the Lower to MiddleTriassic-aged rocks of theBeaufort Group.Outcrops and exposures of the Katberg Formation are found east of 24 degrees onwards and north ofGraaff-Reniet,Nieu Bethesda,Cradock,Fort Beaufort,Queensdown, andEast London in the south, and ranges as far north asHarrismith in deposits that form a ring around theDrakensberg mountain ranges.[1][2][3][4][5]
The Katberg Formation overlies theBalfour Formation of the Adelaide Subgroup and theBurgersdorp Formation of the upper Tarkastad Subgroup, all pertaining to the greaterBeaufort Group. The appearance of the Katberg Formation rocks starkly differs from the underlying Balfour Formation due to its highsandstone content and reddish coloredmudstones.[6] The high sandstone content of the Katberg Formation, which range from light olive grey, greenish grey, or light brownish grey in color, is a key characteristic of this formation. However, the rocks of the Katberg Formation are differentiated into southern and northernsedimentaryfacies which grade laterally into one another from the south upwards. The southern and northern Katberg Formation deposits also vary drastically in thickness.[7][8][9]
The southern Katberg Formation deposits are the most sandstone-rich, comprising approximately 90 percent sandstone and are fine to medium-grained. Along thecoastoutcrops and exposures, especially close toEast London, the Katberg sandstones are coarse-grained and containpebbles up to 15 centimetres (5.9 in) in diameter. In the north the sandstones remain consistently fine-grained and exhibit fining upward cycles. The ratio between the sandstones and mudstones grows more equal in the northern deposits, making differentiation between the northern Katberg and Burgersdorp Formations tricky in areas. The Katberg Formation reaches its maximum thickness near East London at 1238 m, thinning out gradually northwards. The sandstones are predominantly tabular although exhibit some planar and trough cross-bedding along with horizontal laminations and ripple cross-laminations. The sandstones contain much thinner beds of brownish-redshale and reddish to purple and some minor greenish mudstones, which are frequently structureless or horizontally laminated. Mudstones become redder in colour in the upper Katberg deposits as it grades laterally into the Burgersdorp Formation. Intraformational mudclasts,pedogenic andcalcareousnodules are found commonly throughout.[10][11][12]
The appearance and proliferation of the sandstone deposits, especially in the southern and lower Katberg Formation, marks the change to analluvial fan andbraided river environment in the EarlyTriassic due to the presence of coarser-grained sandstones that lack fining upward sequences. Due to the ongoing biotic crises in the aftermath of the Permo-Triassic extinction event, rampant erosion took place as there was a stark drop in plant and animalspecies diversity. This resulted in unstableecological niches. The environment at this time was alsoarid and hot where the rivers seasonally ran dry. When the rainy season arrived,flash floods took place. In the northern Katberg, a drop in the level of preserved sandstones reveals that by the beginning of the MiddleTriassic ecosystems were beginning to stabilize after thePermo-Triassic extinction event. The presence of fine-grained sandstones and more plentiful mudstones show that there was a decrease in energy levels in the depositional environment, meaning that the fast flowing braided rivers were steadily replaced by slower flowing,meandering river channels. The environment was stillsemi-arid, however, due to the presence of the redder mudstones.[13]
The Katberg Formation documents the marked drop inspecies abundance due tobiotic crises that followed thePermo-Triassic extinction event. The most ubiquitousfossils found are different species ofLystrosaurus as the Katberg Formation contains the rocks of theLystrosaurus Assemblage Zone. The most common fossils found are those ofLystrosaurus murrayi andLystrosaurus declivis. In the lower Katberg Formation, complete and sometimesmummified articulated skeletons ofL. murrayi andL. declivus are found inbone beds containing several individuals. The bone beds are almost always overlain bymudstone infilled withsandstone and capped by other coarse-grained sediments. This provides substantial geological andtaphonomical evidence that theseLystrosaurus died near to dried upriver channels and weremummified in thearid climate before their remains were buried byflash floods.[14][15]
ThePermo-Triassic extinction event caused the extinction of allgorgonopsians and almost alldicynodont species except forLystrosaurus and a select few other species such asMyosaurus gracilis.Therocephalianspecies experience aLilliput effect where only smallerspecies survived and thrived after theextinction event. By the upper sections of thebiozone,ecological niches began to recover as evidenced by the appearance of newspecies.Cynodonts experienced the greatest diversification withspecies such asThrinaxodon liorhinus andGalesaurus planiceps being found.[16] Smallprocolonphonidparareptiles such asOwenetta kitchingorum andProcolophon trigoniceps are also found in the Katberg Formation. In addition, the earliest ancestors ofArchosauria appear in the lower Katberg Formation.These species are known asarchosauromorphs andarchosauriformes. Examples of these areProlacerta broomi andProterosuchus fergusi respectively.[17][18] Notably, the Katberg Formation frequently yields burrow casts left byLystrosaurus.[19]
The lower Katberg Formation is known to correspond in age with theSanta Maria Formation of the upperParaná Basin in southernBrazil.[20]
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