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19-588: Previously known as the Dicynodon Assemblage Zone, the name of the biozone refers to Daptocephalus , a medium-sized dicynodont therapsid . It is characterized by the presence of this species in co-occurrence with Theriognathus microps , and Dicynodon lacerticeps . The first fossils to be found in the Beaufort Group rocks that encompass the current eight biozones were discovered by Andrew Geddes Bain in 1856. However, it

38-401: A higher propensity for containing a significant clay fraction. Although often mistaken for a shale , siltstone lacks the laminations and fissility along horizontal lines which are typical of shale. Siltstones may contain concretions . Unless the siltstone is fairly shaly, stratification is likely to be obscure and it tends to weather at oblique angles unrelated to bedding. Siltstone

57-413: A second-order subaerial unconformity . These sedimentary rocks comprise greenish-grey mudrock with siltstone lenses in the lower to middle sections of the biozone , which are indicative of a low-energy fluvial environments with meandering rivers. It is in these rocks that fossils are most commonly found. As the biozone reaches its termination, its contact with the overlying Katberg Formation marks

76-456: A sharp change in the lithology. The sedimentary rocks change to being sandstone-rich with these sandstone bodies commonly appearing within outcrops of brownish-red shale and reddish mudstone . The appearance and proliferation of these sandstone deposits marks the change to braided river systems where sands were only deposited with the finer sediments being washed further downstream. Fossil abundance and preservation quality does not change across

95-438: Is a clastic sedimentary rock that is composed mostly of silt . It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility . Although its permeability and porosity is relatively low, siltstone is sometimes a tight gas reservoir rock, an unconventional reservoir for natural gas that requires hydraulic fracturing for economic gas production. Siltstone

114-798: Is an unusual rock, in which most of the silt grains are made of quartz . The origin of quartz silt has been a topic of much research and debate. Some quartz silt likely has its origin in fine-grained foliated metamorphic rock, while much marine silt is likely biogenic, but most quartz sediments come from granitic rocks in which quartz grains are much larger than quartz silt. Highly energetic processes are required to break these grains down to silt size. Among proposed mechanism are glacial grinding; weathering in cold, tectonically active mountain ranges; normal weathering, particularly in tropical regions; and formation in hot desert environments by salt weathering. Siltstones form in relatively quiet depositional environments where fine particles can settle out of

133-487: The Daptocephlaus Assemblage Zone display a great diversity of vertebrate fauna. These include its current type species Daptocephalus and other dicynodonts such as the ubiquitous Diictodon , Dinanomodon , and Pristerodon . Various species of burnetiamorph Biarmosuchians and Rubidgenae Gorgonopsians are also found. Therocephalian species such as Moschorhinus kitchingi and

152-664: The Karoo Basin in South Africa . An additional species, D. huenei , is known from the Usili Formation in Tanzania and was formerly assigned to the genus Dicynodon before a study in 2019 recognised that the type specimen belonged to Daptocephalus . This Anomodont -related article is a stub . You can help Misplaced Pages by expanding it . Siltstone Siltstone , also known as aleurolite ,

171-627: The Karoo Basin , it was found that there has been some taxonomic confusion with Dicynodon fossils. In addition, recent taxonomic studies have shown that Daptocephalus is indeed its own species, and is only found within the confines of the biozone. Subsequently it was renamed the Daptocephalus Assemblage Zone. The Daptocephalus Assemblage Zone is located only in the upper Balfour formation and lower Normandien formation east of 24°E. These formations all fall within

190-660: The Kutuluksaya and Kulchomovskaya Formations of Russia, and with the lower Buena Vista Formation of the Paraná Basin , South America. Daptocephalus Daptocephalus is an extinct genus of dicynodont synapsid , which was found in Late Permian strata, in a biozone known precisely for the presence of fossils of this dicynodont, the Daptocephalus Assemblage Zone , in

209-548: The Adelaide Subgroup of the Beaufort Group , sediments of which were formed in a large retroarc foreland basin in south-western Gondwana . The biozone is subdivided into the lower Daptocephalus - Theriognathus subzone and the upper Lystrosaurus - Moschorhinus subzone. This satisfies the appearance of Lystrosaurus maccaigi below the Lystrosaurus Assemblage Zone boundary, and

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228-578: The boundary, however, species abundance does due to the extinction event, and also the preservational style of the fossils. More isolated skulls are found in the Permian, whereas in the earliest Triassic, curled up complete skeletons are more common as are bonebeds. These lithological and taphonomic changes are used as evidence for the sudden drying of the climate associated with the Permian-Triassic extinction event . The lower to middle zones of

247-557: The clay and silt fraction is composed of silt-sized particles. Silt is defined as grains 2–62  μm in diameter, or 4 to 8 on the Krumbein phi (φ) scale . An alternate definition is that siltstone is any sedimentary rock containing 50% or more of silt-sized particles. Siltstones can be distinguished from claystone in the field by chewing a small sample; claystone feels smooth while siltstone feels gritty. Siltstones differ significantly from sandstones due to their smaller pores and

266-463: The disappearance of the lower subzone taxa Theriognathus , Dicynodon , and Procynosuchus delaharpeae . At the time of sedimentary deposition, the Karoo retroarc foreland system was in an overfilled phase, and purely terrestrial sediments occupied the Karoo Basin at this time. Two fining-upward sequences are observed in the sedimentary stratigraphy of Daptocephalus biozone, bounded by

285-673: The earliest cynodont Charassognathus gracilis also appear. Parareptile species, namely captorhinids , the Younginiforme Youngina , and a variety of temnospondyl amphibians, fishes, and plant fossils such as Glossopteris are likewise found. The upper zones as the Permian-Triassic boundary approaches, there is a marked drop in species diversity as the Permian-Triassic extinction event began to take its course. The Daptocephalus Assemblage Zone dates to approximately 254.5 to 251 Ma, and correlates with

304-404: The following biozones (from oldest to youngest): These biozone divisions were approved by paleontologists of the time and were left largely unchanged for several decades. The Daptocephalus Assemblage Zone was first named after the dicynodont Daptocephlaus leoniceps by James Kitching due to the high prevalence, and localized appearance, of this species. However, the name of the biozone

323-499: Was changed to the Dicynodon Assemblage Zone as it was argued that Daptocephalus was in fact a juvenile of Dicynodon . In addition it was thought that Dicynodon was a more suitable taxon for global biostratigraphic correlation of other Karoo-aged basins, namely to those in Zambia , Tanzania , China , and Russia . In recent years, with new paleontological finds and updated logging of geological formations and biostratigraphy of

342-428: Was not until 1892 that it was observed that the geological strata of the Beaufort Group could be differentiated based on their fossil taxa . The initial undertaking was done by Harry Govier Seeley who subdivided the Beaufort Group into three biozones , which he named (from oldest to youngest): These proposed biozones Seeley named were subdivided further by Robert Broom between 1906 and 1909. Broom proposed

361-419: Was prized in ancient Egypt for manufacturing statuary and cosmetic palettes . The siltstone quarried at Wadi Hammamat was a hard, fine-grained siltstone that resisted flaking and was almost ideal for such uses. There is not complete agreement on the definition of siltstone. One definition is that siltstone is mudrock ( clastic sedimentary rock containing at least 50% clay and silt) in which at least 2/3 of

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