Soom Shale | |
---|---|
Stratigraphic range: Hirnantian | |
Unit of | Cederberg Formation, Table Mountain Group |
Underlies | Disa Siltstone |
Overlies | Pakhuis Tillite |
Thickness | 10–15 m (33–49 ft) |
Lithology | |
Primary | Shale |
Location | |
Coordinates | 33°00′S19°00′E / 33.0°S 19.0°E |
Approximate paleocoordinates | 28°30′S153°42′E / 28.5°S 153.7°E |
Region | Western Cape |
Country | South Africa |
The Soom Shale is a member of the Late Ordovician (Hirnantian) Cederberg Formation (Table Mountain Group) in South Africa, renowned for its remarkable preservation of soft-tissue in fossil material. [1] Deposited in still waters, the unit lacks bioturbation, perhaps indicating anoxic conditions. [1]
It overlies the Pakhuis tillite and is overlain by the Disa Siltstone. [1]
It contains typical Ordovician microfossils, such as chitinozoa, acritarchs and spores, and its shelly fauna is also typical of this time period. [1]
Its macrofauna comprises pelagic organisms that sank rapidly to a barren sea floor. [2] These include brachiopods, [3] eurypterids, conodonts, [4] nektaspids, trilobites and orthoconic cephalopods.
The environment of deposition is considered to be anoxic and occasionally euxinic cold bottom waters, as indicated by the lack of bioturbation and most epibenthic fauna, besides a small amount of transiently colonizing brachiopods during temporary oxic conditions. It was deposited in the immediate aftermath of the Hirnantian glaciation, the most likely primary cause of the Late Ordovician mass extinction. [5]
The preservation of fossils in the Soom Shale is the opposite of that of normal fossil deposits. Things that in typical preservation conditions are not preserved in the fossil record like soft tissue are preserved in exquisite detail. While hard parts (exoskeleton, etc.) that are normally preserved in the fossil record are demineralized, and are therefore by comparison poorly preserved, usually being preserved in the form of a mould. There is almost no taphonomic distortion, with little evidence of transport, current alignment and no evidence of scavenging. The process of preservation for soft tissues is under debate, but possibly could involve replacement by aluminosilicates, but this could just be an artifact of diagenesis and metamorphism. [5]
Color key
| Notes Uncertain or tentative taxa are in small text; |
Genus | Type of organism | Images |
---|---|---|
Promissum | Conodont | |
Notiodella | Conodont | |
Onychopterella | Eurypterid | |
Soomaspis | Liwiid Nektaspid | |
Mucronaspis | Dalmanitid Trilobite | |
Soomicaris | Archaeostracan Phyllocarid | |
Myodoprimigenia | Myodocope Ostracod | |
Palaeoglossa | Obolid Brachiopod | |
Trematis | Trematid Brachiopod | |
Kosoidea | Discinid Brachiopod | |
Plectothyrella | Rhynchonellid Brachiopod | |
Siphonacis | Incertae sedis | |
Undescribed Agnathan | jawless fish | |
An incertae sedis bilaterian genus, currently known from a pair of fossils, was discovered in 1998 in the Soom Shale by a team from Leicester University. [5] The specimens show a compressed, bilaterally symmetrical segmented body of around 38 cm (15 in) in length, surrounded by imbricating pairs of flaps on each of 45 segments, as well as wider lobe-like appendages of unknown purpose. The soft-bodied animal hasn't been formally described in the literature, and still remains without a valid name. [5] [6] This genus has been named “Keurbosia”, however it is a nomen nudum as this name was not published.
The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At 508 million years old, it is one of the earliest fossil beds containing soft-part imprints.
Conodonts are an extinct group of agnathan (jawless) vertebrates resembling eels, classified in the class Conodonta. For many years, they were known only from their tooth-like oral elements, which are usually found in isolation and are now called conodont elements. Knowledge about soft tissues remains limited. They existed in the world's oceans for over 300 million years, from the Cambrian to the beginning of the Jurassic. Conodont elements are widely used as index fossils, fossils used to define and identify geological periods.
The Maotianshan Shales (帽天山页岩) are a series of Early Cambrian sedimentary deposits in the Chiungchussu Formation, famous for their Konservat Lagerstätten, deposits known for the exceptional preservation of fossilized organisms or traces. The Maotianshan Shales form one of some forty Cambrian fossil locations worldwide exhibiting exquisite preservation of rarely preserved, non-mineralized soft tissue, comparable to the fossils of the Burgess Shale of British Columbia, Canada. They take their name from Maotianshan Hill in Chengjiang County, Yunnan Province, China.
A lagerstätte is a sedimentary deposit that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues. These formations may have resulted from carcass burial in an anoxic environment with minimal bacteria, thus delaying the decomposition of both gross and fine biological features until long after a durable impression was created in the surrounding matrix. Lagerstätten span geological time from the Neoproterozoic era to the present.
Neocephalopods are a group of cephalopod mollusks that include the coleoids and all extinct species that are more closely related to extant coleoids than to the nautilus. In cladistic terms, it is the total group of Coleoidea. In contrast, the palcephalopoda are defined as the sister group to the neocephalopoda.
Promissum is an extinct genus of conodonts, primitive chordates, that lived during the Upper Ordovician period.
Bromalites are the fossilized remains of material sourced from the digestive system of organisms. As such, they can be broadly considered to be trace fossils. The most well-known types of bromalites are fossilized faeces or coprolites. However, other types are recognised, including: regurgitalites ; cololites ; and gastrolites. Regurtitalites and coprolites are thus essentially known only after they have left the body of the producing organisms, whereas gastrolites and cololites are found in situ in their respective organs, but there are rare exceptions.
Onychopterella is a genus of predatory eurypterid, an extinct group of aquatic arthropods. Fossils of Onychopterella have been discovered in deposits from the Late Ordovician to the Late Silurian. The genus contains three species: O. kokomoensis, the type species, from the Early Pridoli epoch of Indiana; O. pumilus, from the Early Llandovery epoch of Illinois, both from the United States; and O. augusti, from the Late Hirnantian to Early Rhuddanian stages of South Africa.
Michelinoceras is the oldest known genus of the Michelinocerida, more commonly known as the Orthocerida, characterized by long, slender, nearly cylindrical orthocones with a circular cross section, long camerae, very long body chambers, and a central or near central tubular siphuncle free of organic deposits. Septal necks are straight; connecting rings cylindrical and thin. Cameral deposits are well developed. A radula has been found in one species, with seven teeth per row. It had ten arms, two of which formed longer tentacles.
The Burgess Shale of British Columbia is famous for its exceptional preservation of mid-Cambrian organisms. Around 69 other sites have been discovered of a similar age, with soft tissues preserved in a similar, though not identical, fashion. Additional sites with a similar form of preservation are known from the Ediacaran and Ordovician periods.
The Walcott–Rust quarry, in Herkimer County, New York, is an excellent example of an obrution Lagerstätte. Unique preservation of trilobite appendages resulted from early consolidation (cementation) of the surrounding rock, followed by spar filling of the interior cavity within the appendages. The presence of so many well preserved trilobites in one location alone qualifies the beds as an exceptional trilobite site, but the beds are further distinguished as the source of the first trilobites for which appendages were definitively described.
A megabias, or a taphonomic megabias, is a large-scale pattern in the quality of the fossil record that affects paleobiologic analysis at provincial to global levels and at timescales usually exceeding ten million years. It can result from major shifts in intrinsic and extrinsic properties of organisms, including morphology and behaviour in relation to other organisms, or shifts in the global environment, which can cause secular or long-term cyclic changes in preservation.
Prioniodontida, also known as the "complex conodonts", is a large clade of conodonts that includes two major evolutionary grades; the Prioniodinina and the Ozarkodinina. It includes many of the more famous conodonts, such as the giant ordovician Promissum (Prioniodinina) from the Soom Shale and the Carboniferous specimens from the Granton Shrimp bed (Ozarkodinina). They are euconodonts, in that their elements are composed of two layers; the crown and the basal body, and are assumed to be a clade.
Soomaspis is a genus of small to average size marine arthropods in the Liwiidae Family, that lived during the late Ordovician. Fossil remains of Soomaspis were collected from the Soom Shale Lagerstätte in Western Cape, South Africa. Soomaspis looks like a large, soft agnostid trilobite. It has a headshield wider than the tailshield (pygidium), and in between them three thoracic body segments (somites). The genus is monotypic, its sole species being Soomaspis splendida.
Balognathidae is an extinct conodont family.
Notiodella is an extinct conodont genus in the family Balognathidae. It has been described from a 17-element apparatus from the Soom Shale Lagerstätte in South Africa.
The Waukesha Biota is an important fossil site located in Waukesha County and Franklin, Milwaukee County within the state of Wisconsin. This biota is preserved in certain strata within the Brandon Bridge Formation, which dates to the early Silurian period. It is known for the exceptional preservation of soft-bodied organisms, including many species found nowhere else in rocks of similar age. The site's discovery was announced in 1985, leading to a plethora of discoveries. This biota is one of the few well studied Lagerstätten from the Silurian, making it important in our understanding of the period's biodiversity. Some of the species are not easily classified into known animal groups, showing that much research remains to be done on this site. Other taxa that are normally common in Silurian deposits are rare here, but trilobites are quite common.
The Winneshiek Shale is a Middle Ordovician (Darriwilian-age) geological formation in Iowa. The formation is restricted to the Decorah crater, an impact crater near Decorah, Iowa. Despite only being discovered in 2005, the Winneshiek Shale is already renowned for the exceptional preservation of its fossils. The shale preserves a unique ecosystem, the Winneshiek biota, which is among the most remarkable Ordovician lagerstätten in the United States. Fossils include the oldest known eurypterid, Pentecopterus, as well as giant conodonts such as Iowagnathus and Archeognathus.
The Tenjong Dendang Formation is a geologic formation in Malaysia. The band of graptolite- and trilobite-bearing shales interbedded in limestones preserves graptolite, brachiopod and trilobite fossils dating back to the Hirnantian stage of the Late Ordovician period. The sediments were deposited during the Late Ordovician glaciation.
Panderodus Is an extinct genus of jawless fish belonging to the order Conodonta. This genus had a long temporal range, surviving from the middle Ordovician to late Devonian. In 2021, extremely rare body fossils of Panderodus from the Waukesha Biota were described, and it revealed that Panderodus had a more thick body compared to the more slender bodies of more advanced conodonts. It also revealed that this conodont was a macrophagous predator, meaning it went after large prey.