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62-481: The name of the biozone refers to Tropidostoma microtrema , a herbivorous dicynodont therapsid . This biozone is characterized by the presence of this species in association with another dicynodont species, Endothiodon uniseries . 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

124-748: A cephalopod and some echinoids are also found in the north. During the Ecca period the Falklands Plateau collided and then fused with Southern Africa, forming a vast range of mountains to the south of the Cape Fold Belt. This new mountain range was comparable in size to the Himalayas . The northern slopes of these mountains generally dipped steeply into the Karoo Sea which was at its deepest at this point. The earthquakes that accompanied

186-409: A monotonous sequence of shales and mudstones , with some interbedded lenticular sandstones . The Beaufort Group is rich in reptilian, and to a lesser extent, amphibian remains. There is a plethora of both herbivorous and carnivorous reptile fossils. The Beaufort rocks are internationally famous for its rich record of therapsid synapsids (mammal-like reptiles), which mark an intermediary stage in

248-761: A phase of massive erosion, removing a layer several kilometers thick from the African Surface . Nearly all of the Drakensberg lavas were eroded away, leaving a remnant in Lesotho, several small patches on the Springbok Flats in the north of the country, and in the Lebombo mountains along the Mozambique border. Once the layer of hard lava was eroded away, the softer Karoo sediments over the rest of

310-466: A second episode of basalt eruption occurred along the border with Mozambique to form the Lebombo Mountains . A layer of lava more than 4800 m thick was violently extruded at this time. While the Drakensberg lavas form nearly horizontal layers, the Lebombo lavas dip to the east, so it is difficult to gauge how far the lava spread laterally. The uplifting of Southern Africa heralded

372-472: A single continuous 1 to 1.6 km thick lava layer. However, not all of the magma reached the surface, but extruded under high pressure between the horizontal strata of the Ecca and Beaufort rocks. When this magma solidified it formed multiple dolerite sills at various depths throughout the southern and south-western Karoo sediments. These sills vary in thickness from a few centimeters to hundreds of meters. This outpouring of lava coincided with uplifting of

434-590: A small portion of fossils are preserved, a biozone does not represent the true range of that species in time. Moreover, ranges can be influenced by the Signor-Lipps effect , meaning that the last "disappearance" of a species tends to be observed further back in time than was actually the case. Karoo Basin The Karoo Supergroup is the most widespread stratigraphic unit in Africa south of

496-409: Is a biozone that is defined by the range in which the abundance of a particular taxon is highest. Because an abundance zone requires a statistically high proportion of a particular taxon, the only way to define them is to trace the abundance of the taxon through time. As local environmental factors influence abundance, this can be an unreliable way of defining a biozone. Abundance zones are named after

558-433: Is a biozone with the upper boundary being the appearance of one taxon, and the lower boundary the appearance of another taxon. A lineage zone, also called a consecutive range zone , are biozones which are defined by being a specific segment of an evolutionary lineage. For example, a zone can be bounded by the highest occurrence of the ancestor of a particular of a taxon and the lowest occurrence of its descendant, or between

620-401: Is called a biohorizon . Biozones can be further subdivided into subbiozones , and multiple biozones can be grouped together in a superbiozone in which the grouped biozones usually have a related characteristic. A succession of biozones is called biozonation . The length of time represented by a biostratigraphic zone is called a biochron . The concept of a biozone was first established by

682-406: Is conducive for preferential deposition of finer sediment types which formed the mudstone and siltstone deposits. However, the climate was seasonally dry due to the presence of calcium carbonate precipitation in the sandstones . Coarser clastic material was only deposited during seasonal floods. The meandering rivers flowed from a foreland basin that was being formed from the rising of

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744-560: The Diictodon pairs inside alive. This provides an explanation for the near perfect preservation of the Diictodon pairs found in the burrow casts. Other notable fossil material from the Tropidostoma Assemblage Zone includes the first appearance of larger gorgonopsid species such as Lycaenops ornatus , Cyonosaurus longiceps , and Gorgonops torvus . It is noted that gorgonopsians take over from

806-590: The Drakensberg (although technically the "Drakensberg" refers to the entire 1000 km long eastern portion of the Great Escarpment, only about a third of which is capped by the Drakensberg lavas). The magma welled up through long crack-like fissures, with occasional spatter cones, but typical volcanoes were rare. Each surface lava flow was between 10 and 20 meters thick. These flows piled up in rapid succession over 2 million years, to form

868-418: The Tropidostoma Assemblage Zone are predominantly found in the thick mudstone and siltstone sequences . Fossils are often encrusted within the calcareous or micritic nodules. The biozone is characterized by the presence of Tropidostoma in association with Endothiodon . However, the occurrence of these taxa are fairly rare in this biozone and their presence is characterized together with

930-598: The Cape Supergroup , accumulated on the floor of this rift valley. Closure of the rift valley, starting 330 million years ago, resulted from the development of a subduction zone along the southern margin of Gondwana, and the consequent drift of the Falkland Plateau back towards Africa, during the Carboniferous and Early Permian periods. After closure of the rift valley, and compression of

992-635: The Gondwanide mountains in the south. The Gondwanides were the result of crustal uplift that had previously begun to take course due to tectonic activity. The pressure of the growing Gondwanides mountain chain caused the formation of the Karoo Basin where the deposits of the Tropidostoma Assemblage zone, and all other succeeding assemblage zone deposits , were deposited over tens of millions of years. Vertebrate fossils of

1054-618: The Kalahari Desert . The supergroup consists of a sequence of units, mostly of nonmarine origin, deposited between the Late Carboniferous and Early Jurassic , a period of about 120 million years. In southern Africa, rocks of the Karoo Supergroup cover almost two thirds of the present land surface, making part of the 75% of sediments or sedimentary rocks covering the earth including all of Lesotho , almost

1116-504: The Karoo inland sea , into which icebergs which had calved off the glaciers and ice sheet to the north deposited vast quantities of mud and rocks of various sizes and origins. Such deposits are known as tillite . Further north, the ice sheet was grounded also leaving diamictite deposits whenever it partially melted, but, in addition, it scoured the bedrock, leaving behind striations (scratch marks) which can be seen near Barkly West in

1178-675: The South Pole , with the result that an ice sheet several kilometers thick covered much of Africa, and other parts of Gondwana. The glacial deposits from this ice sheet were the first of the sediments to be deposited to the north of the Cape Fold Mountains (and partially over these incipient mountains). The basin into which these sediments settled was deepest immediately north of the Cape Fold Mountain ranges. The ice sheet therefore floated on an inland lake, termed

1240-650: The Triassic Period (220 to 195 million years ago) and had fossilised foetal skeletons of Massospondylus , a prosauropod dinosaur. More examples of these eggs have since been found in the Golden Gate Highlands National Park , situated on the Clarens Formation rocks. Other fossils found in the park include those of advanced cynodontia (canine toothed animals), small thecodontia (animals with teeth set firmly in

1302-497: The basal therocephalians as the top predators from this biozone through to the end of the Permian period. However, smaller therocephalian species such as Ictidosuchoides longiceps remained present. The cynodont species Procynosuchus delaharpeae has been recovered from the upper sections of this biozone. Dicynodont species diversified greatly in this biozone , a speciation trend that continued with this group until

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1364-759: The biozone was renamed the Tropidostoma Assemblage Zone due to the discovery that Tropidostoma fossils were only found within the confines of a certain area. The Tropidostoma Assemblage Zone correlates with the lower Teekloof Formation, Adelaide Subgroup of the Beaufort Group . This biozone is considered to be early Late Permian in age. The rock composition of this biozone is dominated by mudstones and siltstones , ranging from greenish-grey, grey, and dark reddish brown in colour. The mudstones and siltstones , measuring approximately 3 m thick in most outcrops and exposures, frequently contain calcareous or micritic nodule horizons and rhizocretions . Sheet-type single-storied channel sandstones are also found,

1426-573: The 19th century paleontologist Albert Oppel , who characterized rock strata by the species of the fossilized animals found in them, which he called zone fossils. Oppel's biozonation was mainly based on Jurassic ammonites he found throughout Europe, which he used to classify the period into 33 zones (now 60). Alcide d'Orbigny would further reinforce the concept in his Prodrome de Paléontologie Stratigraphique , in which he established comparisons between geological stages and their biostratigraphy. The International Commission on Stratigraphy defines

1488-472: The Cape Supergroup into a series of parallel folds, running mainly east–west, the continued subduction of the paleo-Pacific Plate beneath the Falkland Plateau and the resulting collision of the latter with Southern Africa, raised a mountain range of immense proportions to the south of the former rift valley. The folded Cape Supergroup formed the northern foothills of this mountain range. The weight of

1550-620: The Falkland-Cape Supergroup mountains caused the continental crust of Southern Africa to sag, forming a retroarc foreland system, which became flooded to form the Karoo Sea. Sedimentation, beginning with glacial deposits from the north, but later from the Falkland Mountains to the south, into this depression formed the Karoo Supergroup . About 330 million years ago Gondwana had drifted over

1612-606: The Karoo Supergroup is the Great Karoo in South Africa , where the most extensive outcrops of the sequence are exposed. Its strata, which consist mostly of shales and sandstones , record an almost continuous sequence of marine glacial to terrestrial deposition from the Late Carboniferous to the Early Jurassic . These accumulated in a retroarc foreland basin called the "main Karoo " Basin. This basin

1674-487: The Karoo, and with it the appearance of a wide range of new species, including the dinosaurs , and true mammals during the late Triassic – early Jurassic. As Gondwana drifted north, conditions in the portion that was to become Southern Africa became increasingly hot and arid. Sandstones were the predominant rocks that formed. However, in some areas there was sufficient water to form swamps with consequent coal formation, but

1736-680: The Northern Cape, and in the grounds of the University of KwaZulu-Natal . This layer of tillite, traces of which can be found over a wide area of Southern Africa, India , and South America provided crucial early evidence in support of the Theory of Continental Drift . In South Africa the layer is known as the Dwyka Group . It is the earliest and lowermost of the Karoo Supergroup of sedimentary deposits. As Gondwana drifted away from

1798-673: The South Pole, the glaciers melted, leaving a vast inland sea, extending across South Africa, and neighboring regions of Gondwana. It might have had an opening to the ocean (similar to the Black Sea ) but tidal effects were small. Rivers draining mountains to the north of the Karoo Sea formed large swampy deltas in which plants belonging to the Glossopteris flora flourished. This dense vegetation accumulated as peat, which eventually turned into coal. The coal deposits are confined to

1860-507: The Southern African portion of Gondwana, and the formation of rift valleys along what were to become the sea borders of the subcontinent. As these rift valleys widened they became flooded to form the proto-Indian and Southern Atlantic Oceans, as Gondwana fragmented into today's separate continents of South America , Africa , Antarctica , Australia , India , Madagascar and Arabia . In close association with this rifting,

1922-521: The basin eroded even faster. However, the dolerite sills resisted erosion, protecting the softer Beaufort and Ecca shales beneath them. This created numerous and widespread flat topped hills, known as Karoo Koppies ("koppie" being the Afrikaans term for hill), which are iconic of the Karoo, and, by extension, the South African landscape. The dykes , or vertical fissures which brought the lava to

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1984-448: The basis of their characteristic fossil taxa , as opposed to a lithostratigraphic unit which is defined by the lithological properties of the surrounding rock. A biostratigraphic unit is defined by the zone fossils it contains. These may be a single taxon or combinations of taxa if the taxa are relatively abundant, or variations in features related to the distribution of fossils. The same strata may be zoned differently depending on

2046-441: The bottom of helical burrow casts, which have been attributed to Diictodon . The helical burrows - a generally accepted feature of the Tropidostoma Assemblage Zone - are vertical , spiralling tubes measuring just under 1 m in length. The burrows are found infilled with either fine sandstone or siltstone with calcareous concretions. The burrows were likely infilled during single flood events, suddenly trapping and burying

2108-475: The course of several eruptions was more than 1600 m thick, especially in the east (in present-day Lesotho). This massive lava outpouring brought the Karoo sedimentation to an abrupt end. The name Drakensberg Group is derived from the fact that this layer forms the uppermost 1400 m of the Great Escarpment on the international border between Lesotho and KwaZulu-Natal, often referred to as

2170-504: The course of the laying down of the 6 km thick Beaufort deposits, the massive end-Permian mass extinction , 251 million years ago, extinguished about 96% of all species alive at that time. The global event can clearly be seen in the Beaufort rocks. A few members of the genus Lystrosaurus were the only mammal-like reptiles that survived this event. The Beaufort sediments that were laid down after this event tend to be coarser than

2232-404: The diagnostic criteria or fossil group chosen, so there may be several, sometimes overlapping, biostratigraphic units in the same interval. Like lithostratigraphic units, biozones must have a type section designated as a stratotype . These stratotypes are named according to the typical taxon (or taxa) that are found in that particular biozone. The boundary of two distinct biostratigraphic units

2294-598: The end of the Permian period. A pareiasaur species, Pareiasaurus serridens , various subspecies of the temnospondyl amphibian Rhinesuchus , the fishes Namaichthys and Atherstonia , and fossil plant material of Glossopteris and Dadoxylon have been found. Finally, vertebrate burrows left by Diictodon as previously discussed, vertebrate trackways left by various therapsid species , and coprolites have been recovered. Biozone In biostratigraphy , biostratigraphic units or biozones are intervals of geological strata that are defined on

2356-427: The evolution of the mammals from reptiles. The most abundant herbivores were the anomodonts , whose most primitive forms are also known from the Beaufort rocks. The dinocephalians (terrible head) are so named because of their extraordinary thick boned skulls, which were probably used for head butting during territorial fights. With their 3-meter body length, they were the first large animals to live on land. During

2418-504: The following biozones (from oldest to youngest): The current stratigraphic range of the Tropidostoma Assemblage Zone was previously included within the Endothiodon beds ascribed by Broom . Decades later between the 1970s and early 1990s, Keyser and Smith collaborated on several field trips into known outcrop areas in order to re-evaluate the fossil biostratigraphy . After relevant fossil taxa data had been collected,

2480-496: The following types of biozones: Range zones are biozones defined by the geographic and stratigraphic range of occurrence of a taxon (or taxa). There are two types of range zones: A taxon-range zone is simply the biozone defined by the first ( first appearance datum or FAD ) and last ( last appearance datum or LAD ) occurrence of a single taxon. The boundaries are defined by the lowest and highest stratigraphic occurrence of that particular taxon. Taxon-range zones are named after

2542-508: The formation of the Cape Mountains therefore initiated frequent underwater mud- and rock-slides, forming fan-shaped accumulations of turbidites , which can be seen in the south west corner of the Karoo today (see photograph lower down on the right) the Ecca group also has its members that are named based on the lithologies of the locality they are in . Turbidites have for some time been recognized as petroleum producing rocks, because

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2604-506: The jaw), bird-like and crocodile-like dinosaurs. About 182 million years ago the southern African portion of Gondwana passed over the Bouvet hotspot causing the crust under the Karoo Supergroup to rupture, releasing huge volumes of basaltic lava over the Clarens desert, covering nearly the whole of Southern Africa and other portions of Gondwana.The pile of lava that accumulated over

2666-416: The lower portion of the biozone often containing fining upward sequences. Calcium carbonate precipitation crusts and gypsum “ desert rose ” crystals have been uncovered in the sandstone layers. The preserved rocks show that the depositional environment of this biozone was formed in a lacustrine and overbank environment, which flowed northwards in long, meandering rivers . This low energy environment

2728-418: The lowest occurrence of a taxon and the lowest occurrence of its descendant. Lineage zones are different from most other biozones because they need that the segments its bounded by are successive segments of an evolutionary lineage. This makes them similar to chronostratigraphical units - however, lineage zones, being a biozone, are restricted by the actual spatial range of fossils. Lineage zones are named for

2790-445: The more numerous fossils of the dicynodont species Pristerodon and Diictodon . Diictodon fossils are particularly ubiquitous in this biozone with isolated skull and post-cranial material being most commonly found. In the lower deposits, complete fossil skeletons of Diictodon are more commonly found, often in pairs and curled up together. These intriguing paired Diictodon fossils are invariably recovered from

2852-400: The north of the Karoo Sea had, by this time, been leveled by erosion and begun to be buried under newer sediments.) Several Mississippi-like rivers flowed over the silted up Karoo Basin from the south, creating rich new habitats for a variety of flora and fauna. The terrestrial (as opposed to lacunar or marine) deposits created by these rivers gave rise to the Beaufort Group . It is composed of

2914-530: The northern shores of the early Permian Karoo Sea, and is mined today in the Highveld and KwaZulu-Natal. These sedimentary deposits are termed the Ecca Group of the Karoo Supergroup. They consist largely of shales and sandstones , and extend over the entire former Karoo Sea, but the southerly deposits do not contain coal, even though rivers from the Cape Fold Mountains formed small deltas. Although

2976-529: The ones that preceded them, probably because of a massive die-off of vegetation, which had protected the surface against erosion. These early Triassic sandstone-dominated strata are known as the Katberg formation (within the Beaufort Group), which accumulated to a thickness of 1 km. With time the Beaufort deposits became more fine-grained once again, probably indicating a recovery of the vegetation in

3038-440: The petroleum industry and geologists, who have found them to have rich and readily accessible deposits of oil and gas. Thus the north-eastern Ecca basin is rich in coal, while its south-western corner is becoming renowned for its oils reserves. With the formation of the Falkland Plateau and Cape Fold Mountain ranges, rivers from the south began to dominate the sedimentation in the Karoo Sea, which began to silt up. (The highlands to

3100-625: The quality is poor. The landscape probably resembled the Kalahari desert of today, with rivers like the present-day Orange River or the Nile running through it, sustaining localized areas of Triassic flora and fauna. The Stormberg Group contains South Africa's earliest dinosaur fossils. It also contains the fossil remains of the shrew-sized Megazostrodon , the oldest mammal in Africa. A remarkable array of insect and plant fossils are found in some of

3162-460: The specific taxon they represent. An assemblage zone is a biozone defined by three or more different taxa, which may or may not be related. The boundaries of an assemblage zone are defined by the typical, specified fossil assemblage's occurrence: this can include the appearance, but also the disappearance of certain taxa. Assemblage zones are named for the most characteristic or diagnostic fossils in its assemblage. An abundance zone, or acme zone ,

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3224-665: The strata. The uppermost strata of the Stormberg group were probably laid down under true sand desert conditions, similar to the Namib Desert in Namibia. It was probably as large as the Sahara Desert today, extending from the Cape Fold Mountains many thousands of kilometers northwards over large parts of Gondwana. Only a small remnant of this massive formation can be found in and around Lesotho today. This formation

3286-487: The surface stand out today as linear ridges extending across large stretches of the Karoo. The continued erosion of Southern Africa over the past 180 million years has meant that rocks younger than The Drakensberg Group are almost non-existent over most of the interior. Some of the eroded material from the interior was trapped between the Cape Fold Mountains to the south during the Cretaceous Period to form

3348-417: The taxon in it. A concurrent-range zone uses the overlapping range of two taxa, with low boundary defined by the appearance of one taxon and high boundary defined by the disappearance of the other taxon. Concurrent-range zones are named after both of the taxa in it. An interval zone is defined as the body of strata between two bio-horizons, which are arbitrarily chosen. For example, a highest-occurrence zone

3410-586: The taxon that is the most abundant within its range. A great variety of species can be used in establishing biozonation. Graptolites and ammonites are some of the most useful as zone fossils, as they preserve well and often have relatively short biozones. Microfossils , such as dinoflagellates , foraminiferans , or plant pollen are also good candidates because they tend to be present even in very small samples and evolve relatively rapidly. Fossils of pigs and cannabis can be used for biozonation of Quaternary rocks as they were used by hominids . As only

3472-476: The underwater avalanches that cause these deposits often carry organic matter from close to the coastline, especially near river estuaries and deltas, into the anoxic depths of adjoining troughs. Here it is buried in the turbidite and turns into hydrocarbons , particularly petroleum and gas. The turbidites in the Ecca formation of the Tanqua and Laingsburg Karoo regions have thus, recently, come under scrutiny by

3534-477: The upper strata dinosaurs ), and ichnofossils . Their biostratigraphy has been used as the international standard for global correlation of Permian to Jurassic nonmarine strata. About 510 million years ago a rift valley developed across Southern Gondwana just south of Southern Africa, but extending westward into South America , and eastward into Eastern Antarctica and possibly even into Australia . An 8 km thick layer of sediment, known as

3596-537: The vegetation in the south was not as dense as on the northern shores of the inland sea, several early reptiles such as Mesosaurus are found in these Ecca deposits. This is a fossil reptile found only in Southern Africa and Brazil providing important paleontological evidence of the existence of the Gondwana supercontinent. The northern shores contain mainly fossil plants, pollens and spores. Fossils of

3658-534: The whole of Free State , and large parts of the Eastern Cape , Northern Cape , Mpumalanga and KwaZulu-Natal Provinces of South Africa . Karoo supergroup outcrops are also found in Namibia , Eswatini , Zambia , Zimbabwe and Malawi , as well as on other continents that were part of Gondwana . The basins in which it was deposited formed during the formation and breakup of Pangea . The type area of

3720-546: Was formed by the subduction and orogenesis along the southern border of what eventually became Southern Africa, in southern Gondwana. Its sediments attain a maximum cumulative thickness of 12 km, with the overlying basaltic lavas (the Drakensberg Group) at least 1.4 km thick. Fossils include plants (both macro-fossils and pollen ), rare insects and fish , common and diverse tetrapods (mostly therapsid reptiles, temnospondyl amphibians, and in

3782-580: Was formerly known as “Cave Sandstone” as wind-eroded shallow caves often developed in cliffs made up of these rocks. These caves were later used by the San people who frequently decorated the walls with their paintings . Today the Cave Sandstones are called the Clarens Formation . The oldest dinosaur embryos ever discovered were found in the Clarens Formation in 1978. The eggs were from

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3844-428: 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

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