Major Glacial period
49°40′58″N 57°57′55″W / 49.6829°N 57.9653°W
The Cambrian Period (
The Cambrian marked a profound change in
The Cambrian Period followed the Ediacaran Period and was followed by the Ordovician Period.
The base of the Cambrian lies atop a complex assemblage of
The Cambrian is divided into four
Because the international stratigraphic subdivision is not yet complete, many local subdivisions are still widely used. In some of these subdivisions the Cambrian is divided into three epochs with locally differing names – the Early Cambrian (Caerfai or Waucoban, 538.8 ± 0.2 to 509 ± 1.9 mya),Trilobite zones allow biostratigraphic correlation in the Cambrian. Rocks of these epochs are referred to as belonging to the Lower, Middle, or Upper Cambrian.
Each of the local series is divided into several stages. The Cambrian is divided into several regional
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*Most Russian paleontologists define the lower boundary of the Cambrian at the base of the Tommotian Stage, characterized by diversification and global distribution of organisms with mineral skeletons and the appearance of the first Archaeocyath bioherms.
Dating the Cambrian
The International Commission on Stratigraphy lists the Cambrian Period as beginning at 538.8 million years ago and ending at 485.4 million years ago.
The lower boundary of the Cambrian was originally held to represent the first appearance of complex life, represented by
Despite the long recognition of its distinction from younger
This formal designation allowed radiometric dates to be obtained from samples across the globe that corresponded to the base of the Cambrian. Early[when?] dates of 570 million years ago quickly gained favour, though the methods used to obtain this number are now considered to be unsuitable and inaccurate. A more precise date using modern radiometric dating yield a date of 538.8 ± 0.2 million years ago. The ash horizon in Oman from which this date was recovered corresponds to a marked fall in the abundance of carbon-13 that correlates to equivalent excursions elsewhere in the world, and to the disappearance of distinctive Ediacaran fossils (Namacalathus, Cloudina). Nevertheless, there are arguments that the dated horizon in Oman does not correspond to the Ediacaran-Cambrian boundary, but represents a facies change from marine to evaporite-dominated strata – which would mean that dates from other sections, ranging from 544 or 542 Ma, are more suitable.
Plate reconstructions suggest a global supercontinent, Pannotia, was in the process of breaking up early in the Cambrian, with Laurentia (North America), Baltica, and Siberia having separated from the main supercontinent of Gondwana to form isolated land masses. Most continental land was clustered in the Southern Hemisphere at this time, but was drifting north. Large, high-velocity rotational movement of Gondwana appears to have occurred in the Early Cambrian.
With a lack of sea ice – the great glaciers of the Marinoan Snowball Earth were long melted – the sea level was high, which led to large areas of the continents being flooded in warm, shallow seas ideal for sea life. The sea levels fluctuated somewhat, suggesting there were "ice ages", associated with pulses of expansion and contraction of a south polar ice cap.
Glaciers likely existed during the earliest Cambrian at high and possibly even at middle palaeolatitudes, possibly due to the ancient continent of Gondwana covering the South Pole and cutting off polar ocean currents. Middle Terreneuvian deposits, corresponding to the boundary between the Fortunian and Stage 2, show evidence of glaciation. However, other authors believe these very early, pretrilobitic glacial deposits may not even be of Cambrian age at all but instead date back to the Neoproterozoic, an era characterised by numerous severe icehouse periods. The beginning of Stage 3 was relatively cool, with the period between 521 and 517 Ma being known as the Cambrian Arthropod Radiation Cool Event (CARCE). The Earth was generally very warm during Stage 4; its climate was comparable to the hot greenhouse of the Late Cretaceous and Early Palaeogene, as evidenced by a maximum in continental weathering rates over the last 900 million years and the presence of tropical, lateritic palaeosols at high palaeolatitudes during this time. The Archaecyathid Extinction Warm Event (AEWE), lasting from 511 to 510.5 Ma, was particularly warm. Another warm event, the Redlichiid-Olenid Extinction Warm Event, occurred at the beginning of Stage 5. It became even warmer towards the end of the period, and sea levels rose dramatically. This warming trend continued into the Early Ordovician, the start of which was characterised by an extremely hot global climate.
The Cambrian flora was little different from the Ediacaran. The principal taxa were the marine macroalgae Fuxianospira, Sinocylindra, and Marpolia. No calcareous macroalgae are known from the period.
The Cambrian explosion was a period of rapid multicellular growth. Most animal life during the Cambrian was aquatic. Trilobites were once assumed to be the dominant life form at that time, but this has proven to be incorrect. Arthropods were by far the most dominant animals in the ocean, but trilobites were only a minor part of the total arthropod diversity. What made them so apparently abundant was their heavy armor reinforced by calcium carbonate (CaCO3), which fossilized far more easily than the fragile chitinous exoskeletons of other arthropods, leaving numerous preserved remains.
The period marked a steep change in the diversity and composition of Earth's biosphere. The Ediacaran biota suffered a mass extinction at the start of the Cambrian Period, which corresponded with an increase in the abundance and complexity of burrowing behaviour. This behaviour had a profound and irreversible effect on the substrate which transformed the seabed ecosystems. Before the Cambrian, the sea floor was covered by microbial mats. By the end of the Cambrian, burrowing animals had destroyed the mats in many areas through bioturbation. As a consequence, many of those organisms that were dependent on the mats became extinct, while the other species adapted to the changed environment that now offered new ecological niches. Around the same time there was a seemingly rapid appearance of representatives of all the mineralized phyla, including the Bryozoa, which were once thought to have only appeared in the Lower Ordovician. However, many of those phyla were represented only by stem-group forms; and since mineralized phyla generally have a benthic origin, they may not be a good proxy for (more abundant) non-mineralized phyla.
While the early Cambrian showed such diversification that it has been named the Cambrian Explosion, this changed later in the period, when there occurred a sharp drop in biodiversity. About 515 million years ago, the number of species going extinct exceeded the number of new species appearing. Five million years later, the number of genera had dropped from an earlier peak of about 600 to just 450. Also, the speciation rate in many groups was reduced to between a fifth and a third of previous levels. 500 million years ago, oxygen levels fell dramatically in the oceans, leading to hypoxia, while the level of poisonous hydrogen sulfide simultaneously increased, causing another extinction. The later half of Cambrian was surprisingly barren and showed evidence of several rapid extinction events; the stromatolites which had been replaced by reef building sponges known as Archaeocyatha, returned once more as the archaeocyathids became extinct. This declining trend did not change until the Great Ordovician Biodiversification Event.
Some Cambrian organisms ventured onto land, producing the trace fossils
In contrast to later periods, the Cambrian fauna was somewhat restricted; free-floating organisms were rare, with the majority living on or close to the sea floor;
Many modes of preservation are unique to the Cambrian, and some preserve soft body parts, resulting in an abundance of Lagerstätten. These include Sirius Passet, the Sinsk Algal Lens, the Maotianshan Shales, the Emu Bay Shale, and the Burgess Shale,.
The United States Federal Geographic Data Committee uses a "barred capital C" ⟨Ꞓ⟩ character to represent the Cambrian Period. The Unicode character is U+A792 Ꞓ LATIN CAPITAL LETTER C WITH BAR.
Stromatolites of the Pika Formation (Middle Cambrian) near Helen Lake, Banff National Park, Canada
Trilobites were very common during this time
Anomalocaris was an early marine predator, among the various arthropods of the time
Opabinia was a creature with an unusual body plan; it was probably related to arthropods
Pikaia was a stem-chordate from the Middle Cambrian
Protichnites were the trackways of arthropods that walked Cambrian beaches
Hallucigenia sparsa was a member of group lobopodian, that is considered to related to modern velvet worms.
Cambroraster falcatus was a large arthropod for the era
- Cambrian–Ordovician extinction event – circa 488 mya
- Dresbachian extinction event—circa 499 mya
- End Botomian extinction event—circa 513 mya
- List of fossil sites (with link directory)
- Type locality (geology), the locality where a particular rock type, stratigraphic unit, fossil or mineral species is first identified
- ^ "Chart/Time Scale". stratigraphy.org. International Commission on Stratigraphy.
- ^ Brasier, Martin; Cowie, John; Taylor, Michael. "Decision on the Precambrian-Cambrian boundary stratotype" (PDF). Episodes. 17. Archived (PDF) from the original on 9 October 2022. Retrieved 6 December 2020.
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- ^ a b c Howe 1911, p. 86.
- ^ a b "Stratigraphic Chart 2022" (PDF). International Stratigraphic Commission. February 2022. Archived (PDF) from the original on 9 October 2022. Retrieved 5 April 2022.
- ^ Sedgwick and R. I. Murchison (1835) "On the Silurian and Cambrian systems, exhibiting the order in which the older sedimentary strata succeed each other in England and Wales," Notices and Abstracts of Communications to the British Association for the Advancement of Science at the Dublin meeting, August 1835, pp. 59–61, in: Report of the Fifth Meeting of the British Association for the Advancement of Science; held in Dublin in 1835 (1836). From p. 60: "Professor Sedgwick then described in descending order the groups of slate rocks, as they are seen in Wales and Cumberland. To the highest he gave the name of Upper Cambrian group. ... To the next inferior group he gave the name of Middle Cambrian. ... The Lower Cambrian group occupies the S.W. coast of Cærnarvonshire,"
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- ^ "Discovery of possible earliest animal life pushes back fossil record". 17 August 2010.
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- ^ a b Schieber et al. 2007, pp. 53–71.
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- ^ Collette, Gass & Hagadorn 2012.
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- ^ A. Knoll, M. Walter, G. Narbonne, and N. Christie-Blick (2004) "The Ediacaran Period: A New Addition to the Geologic Time Scale." Submitted on Behalf of the Terminal Proterozoic Subcommission of the International Commission on Stratigraphy.
- ^ M.A. Fedonkin, B.S. Sokolov, M.A. Semikhatov, N.M.Chumakov (2007). "Vendian versus Ediacaran: priorities, contents, prospectives. Archived 4 October 2011 at the Wayback Machine" In: edited by M. A. Semikhatov "The Rise and Fall of the Vendian (Ediacaran) Biota. Origin of the Modern Biosphere. Transactions of the International Conference on the IGCP Project 493, August 20–31, 2007, Moscow. Archived 22 November 2012 at the Wayback Machine" Moscow: GEOS.
- ^ A. Ragozina, D. Dorjnamjaa, A. Krayushkin, E. Serezhnikova (2008). "Treptichnus pedum and the Vendian-Cambrian boundary Archived 4 October 2011 at the Wayback Machine". 33 Intern. Geol. Congr. 6–14 August 2008, Oslo, Norway. Abstracts. Section HPF 07 Rise and fall of the Ediacaran (Vendian) biota. p. 183.
- S2CID 128128572.
- doi:10.18814/epiiugs/1984/v7i1/004. Archived from the original(PDF) on 25 March 2009.
- ^ V. V. Khomentovskii; G. A. Karlova (2005). "The Tommotian Stage Base as the Cambrian Lower Boundary in Siberia". Stratigraphy and Geological Correlation. 13 (1): 21–34. Archived from the original on 14 July 2011. Retrieved 15 March 2009.
- ^ S2CID 133538050.
- Eos, Transactions, American Geophysical Union. 76: 46–72.
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- . Retrieved 17 December 2022.
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- ^ "Greening of the Earth pushed way back in time". Phys.org. University of Oregon. 22 July 2013.
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- ^ Paselk, Richard (28 October 2012). "Cambrian". Natural History Museum. Humboldt State University.
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- ^ Perkins, Sid (23 October 2009). "As the worms churn". ScienceNews. Archived from the original on 25 October 2009.
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- ^ "The Ordovician: Life's second big bang". Archived from the original on 9 October 2018. Retrieved 10 February 2013.
- ^ Marshall, Michael. "Oxygen crash led to Cambrian mass extinction".
- ^ Collette & Hagadorn 2010; Collette, Gass & Hagadorn 2012.
- ^ Yochelson & Fedonkin 1993; Getty & Hagadorn 2008.
- ISSN 0091-7613.
- . Retrieved 12 November 2022.
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- ^ Federal Geographic Data Committee, ed. (August 2006). FGDC Digital Cartographic Standard for Geologic Map Symbolization FGDC-STD-013-2006 (PDF). U.S. Geological Survey for the Federal Geographic Data Committee. p. A–32–1. Archived (PDF) from the original on 9 October 2022. Retrieved 23 August 2010.
- ^ Priest, Lorna A.; Iancu, Laurentiu; Everson, Michael (October 2010). "Proposal to Encode C WITH BAR" (PDF). Archived (PDF) from the original on 9 October 2022. Retrieved 6 April 2011.
- ^ Unicode Character 'LATIN CAPITAL LETTER C WITH BAR' (U+A792). fileformat.info. Retrieved 15 June 2015
- Amthor, J. E.; Grotzinger, John P.; Schröder, Stefan; Bowring, Samuel A.; Ramezani, Jahandar; Martin, Mark W.; Matter, Albert (2003). "Extinction of Cloudina and Namacalathus at the Precambrian-Cambrian boundary in Oman". Geology. 31 (5): 431–434.
- Collette, J. H.; Gass, K. C.; Hagadorn, J. W. (2012). "Protichnites eremita unshelled? Experimental model-based neoichnology and new evidence for a euthycarcinoid affinity for this ichnospecies". Journal of Paleontology. 86 (3): 442–454. S2CID 129234373.
- Collette, J. H.; Hagadorn, J. W. (2010). "Three-dimensionally preserved arthropods from Cambrian Lagerstatten of Quebec and Wisconsin". Journal of Paleontology. 84 (4): 646–667. S2CID 130064618.
- Getty, P. R.; Hagadorn, J. W. (2008). "Reinterpretation of Climactichnites Logan 1860 to include subsurface burrows, and erection of Musculopodus for resting traces of the trailmaker". Journal of Paleontology. 82 (6): 1161–1172. S2CID 129732925.
- ISBN 9780393027051.
- Howe, John Allen (1911). Encyclopædia Britannica. Vol. 05 (11th ed.). Cambridge University Press. pp. 86–89. . In Chisholm, Hugh (ed.).
- Ogg, J. (June 2004). "Overview of Global Boundary Stratotype Sections and Points (GSSPs)". Archived from the original on 23 April 2006. Retrieved 30 April 2006.
- Owen, R. (1852). "Description of the impressions and footprints of the Protichnites from the Potsdam sandstone of Canada". Geological Society of London Quarterly Journal. 8 (1–2): 214–225. S2CID 130712914.
- Peng, S.; Babcock, L.E.; Cooper, R.A. (2012). "The Cambrian Period" (PDF). The Geologic Time Scale. Archived from the original (PDF) on 12 February 2015. Retrieved 14 January 2015.
- Schieber, J.; Bose, P. K.; Eriksson, P. G.; Banerjee, S.; Sarkar, S.; Altermann, W.; Catuneau, O. (2007). Atlas of Microbial Mat Features Preserved within the Clastic Rock Record. Elsevier. pp. 53–71. ISBN 9780444528599.
- Yochelson, E. L.; Fedonkin, M. A. (1993). "Paleobiology of Climactichnites, and Enigmatic Late Cambrian Fossil". Smithsonian Contributions to Paleobiology. 74 (74): 1–74.
- Cambrian period on In Our Time at the BBC
- Biostratigraphy – includes information on Cambrian trilobite biostratigraphy
- Dr. Sam Gon's trilobite pages (contains numerous Cambrian trilobites)
- Examples of Cambrian Fossils
- Paleomap Project
- Report on the web on Amthor and others from Geology vol. 31
- Weird Life on the Mats
- Chronostratigraphy scale v.2018/08 | Cambrian