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The Cambrian Period was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago (mya) to the beginning of the Ordovician Period 485.4 mya. Its subdivisions, and its base, are somewhat in flux. The period was established as "Cambrian series" by Adam Sedgwick, who named it after Cambria, the Latin name for 'Cymru' (Wales), where Britain's Cambrian rocks are best exposed. Sedgwick identified the layer as part of his task, along with Roderick Murchison, to subdivide the large "Transition Series", although the two geologists disagreed for a while on the appropriate categorization. The Cambrian is unique in its unusually high proportion of lagerstätte sedimentary deposits, sites of exceptional preservation where "soft" parts of organisms are preserved as well as their more resistant shells. As a result, our understanding of the Cambrian biology surpasses that of some later periods.
The Ediacaran Period is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and the beginning of the Phanerozoic Eon. It is named after the Ediacara Hills of South Australia.
The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago.
The Snowball Earth hypothesis proposes that, during one or more of Earth's icehouse climates, the planet's surface became entirely or nearly entirely frozen. It is believed that this occurred sometime before 650 M.Y.A. during the Cryogenian period. Proponents of the hypothesis argue that it best explains sedimentary deposits that are generally believed to be of glacial origin at tropical palaeolatitudes and other enigmatic features in the geological record. Opponents of the hypothesis contest the implications of the geological evidence for global glaciation and the geophysical feasibility of an ice- or slush-covered ocean, and they emphasize the difficulty of escaping an all-frozen condition. A number of unanswered questions remain, including whether Earth was a full snowball or a "slushball" with a thin equatorial band of open water. The snowball-Earth episodes are proposed to have occurred before the sudden radiation of multicellular bioforms known as the Cambrian explosion. The most recent snowball episode may have triggered the evolution of multicellularity.
Rodinia was a Neoproterozoic supercontinent that assembled 1.1–0.9 billion years ago and broke up 750–633 million years ago. Valentine & Moores 1970 were probably the first to recognise a Precambrian supercontinent, which they named 'Pangaea I'. It was renamed 'Rodinia' by McMenamin & McMenamin 1990 who also were the first to produce a reconstruction and propose a temporal framework for the supercontinent.
The Doushantuo Formation is a geological formation in western Hubei, eastern Guizhou, southern Shaanxi, central Jiangxi, and other localities in China. It is known for the fossil Lagerstätten in Zigui in Hubei, Xiuning in Anhui, and Weng'an in Guizhou, as one of the oldest beds to contain minutely preserved microfossils, phosphatic fossils that are so characteristic they have given their name to "Doushantuo type preservation". The formation is of particular interest because a part of it appears to cover the boundary between the enigmatic organisms of the Ediacaran geological period and the more familiar fauna of the Cambrian explosion where lifeforms recognizable as ancestors of later and recent lifeforms first emerged. Taken as a whole, the Doushantuo Formation ranges from about 635 Ma at its base to about 551 Ma at its top, predating by perhaps five Ma the earliest of the 'classical' Ediacaran faunas from Mistaken Point on the Avalon Peninsula of Newfoundland, and recording conditions up to a good forty to fifty million years before the Cambrian explosion.
The Cryogenian is a geologic period that lasted from 720 to 635 million years ago. It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by the Ediacaran.
The Adelaide Superbasin is a major Neoproterozoic to middle Cambrian geological province in central and south-east South Australia, western New South Wales, and western Victoria.
Namacalathus is a problematic metazoan fossil occurring in the latest Ediacaran. The first, and only described species, N. hermanastes, was first described in 2000 from the Nama Group of central and southern Namibia.
The Ediacaranbiota is a taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period. These were composed of enigmatic tubular and frond-shaped, mostly sessile, organisms. Trace fossils of these organisms have been found worldwide, and represent the earliest known complex multicellular organisms.
Evidence suggesting that a mass extinction occurred at the end of the Ediacaran period, 539 million years ago, includes:
The small shelly fauna, small shelly fossils (SSF), or early skeletal fossils (ESF) are mineralized fossils, many only a few millimetres long, with a nearly continuous record from the latest stages of the Ediacaran to the end of the Early Cambrian Period. They are very diverse, and there is no formal definition of "small shelly fauna" or "small shelly fossils". Almost all are from earlier rocks than more familiar fossils such as trilobites. Since most SSFs were preserved by being covered quickly with phosphate and this method of preservation is mainly limited to the late Ediacaran and early Cambrian periods, the animals that made them may actually have arisen earlier and persisted after this time span.
The Marinoan glaciation was a period of worldwide glaciation that lasted from approximately 650 to 632.3 ± 5.9 Ma during the Cryogenian period. This glaciation possibly covered the entire planet, in an event called the Snowball Earth. The end of the glaciation might have been hastened by the release of methane from equatorial permafrost.
John P. Grotzinger is the Fletcher Jones Professor of Geology at California Institute of Technology and chair of the Division of Geological and Planetary Sciences. His works primarily focus on chemical and physical interactions between life and the environment. In addition to biogeological studies done on Earth, Grotzinger is also active in research into the geology of Mars and has made contributions to NASA's Mars Exploration Program.
Al-Hajar Mountains in northeastern Oman and also the eastern United Arab Emirates are the highest mountain range in the eastern Arabian peninsula. Also known as "Oman Mountains", they separate the low coastal plain of Oman from the high desert plateau, and lie 50–100 km (31–62 mi) inland from the Gulf of Oman.
The Nama Group is a 125,000 square kilometres (48,000 sq mi) megaregional Vendian to Cambrian group of stratigraphic sequences deposited in the Nama foreland basin in central and southern Namibia. The Nama Basin is a peripheral foreland basin, and the Nama Group was deposited in two early basins, the Zaris and Witputs, to the north, while the South African Vanrhynsdorp Group was deposited in the southern third. The Nama Group is made of fluvial and shallow-water marine sediments, both siliciclastic and carbonate. La Tinta Group in Argentina is considered equivalent to Nama Group.
The Sturtian glaciation was a glaciation, or perhaps multiple glaciations, during the Cryogenian Period when the Earth experienced repeated large-scale glaciations. The duration of the Sturtian glaciation has been variously defined, with dates ranging from 717 to 643 Ma. Stern et al. place the period at 715 to 680 Ma.
The Hormuz Formation, Hormuz Series, Hormuz Evaporites or Hormuz Group is a sequence of evaporites that were deposited during the Ediacaran to Early Cambrian, a period previously referred to as the Infra-Cambrian. Most exposures of this sequence are in the form of emergent salt diapirs within anticlines of the Zagros fold and thrust belt. As a result of their involvement in post-depositional salt tectonics, the internal stratigraphy of the sequence is relatively poorly understood. They are the lateral equivalent of the evaporite-bearing Ara Group in the South Oman Basin.
The South Oman Salt Basin or SOSB is a sedimentary basin located in the Sultanate of Oman, at the southeastern edge of the Arabian Peninsula. The basin is well-known for being one of the oldest commercial deposits in the world. Oil in SOBS is associated with source rocks of the Neoproterozoic to Cambrian Huqf Supergroup. In 1937, the first operating license in South Oman was awarded to Petroleum Development Oman and Dhofar. In 1976, the discovery of moveable oil in Nasir-1 boost the carbonate intrasalt stringer exploration. However, as the difficulty in delivering expected reserves was greater than expected, the deposits became dormant in 1986.
The Abu Mahara Group is a geologic group of formations that are spread across northern Oman, east-central Oman, and southern Oman. It belongs to the Huqf Supergroup.
References
- 1 2 Allen, Philip A. (October 2007). "The Huqf Supergroup of Oman: Basin development and context for Neoproterozoic glaciation". Earth-Science Reviews. 84 (3–4): 139–185. Bibcode:2007ESRv...84..139A. doi:10.1016/j.earscirev.2007.06.005 . Retrieved 15 December 2021.
- 1 2 Butterfield, Nicholas J.; Grotzinger, John P. (2012). "Palynology of the Huqf Supergroup, Oman". Geological Society, London, Special Publications. 366 (1): 251–263. Bibcode:2012GSLSP.366..251B. doi:10.1144/SP366.10. S2CID 128599229.
- ↑ Bowring, Samuel A.; Grotzinger, John P.; Condon, Daniel J.; Ramezani, Jahandar; Newall, Mark J.; Allen, Philip A. (1 December 2007). "Geochronologic constraints on the chronostratigraphic framework of the Neoproterozoic Huqf Supergroup, Sultanate of Oman" (PDF). American Journal of Science. 307 (10): 1097–1145. Bibcode:2007AmJS..307.1097B. doi:10.2475/10.2007.01. S2CID 14128896.
- ↑ Allen, Philip A.; Leather, Jonathan; Brasier, Martin D.; Rieu, Ruben; McCarron, Margaret; Guerroué, Erwan le; Etienne, James L.; Cozzi, Andrea (2011). "Chapter 20 The Abu Mahara Group (Ghubrah and Fiq formations), Jabal Akhdar, Oman". Geological Society, London, Memoirs. 36 (1): 251–262. doi:10.1144/M36.20. S2CID 130493080.
- ↑ Grosjean, E.; Love, G. D.; Stalvies, C.; Fike, D. A.; Summons, R. E. (1 January 2009). "Origin of petroleum in the Neoproterozoic–Cambrian South Oman Salt Basin". Organic Geochemistry. 40 (1): 87–110. doi:10.1016/j.orggeochem.2008.09.011 . Retrieved 15 December 2021.
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