Columbium (period)

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The columbium is the third period within the eon Proterozoic and the third and final period within the era Paleoproterozoic . It follows the period of Jatuliums and its part of the period of Rodiniums replaced. The columbium lasted 280 million years and fills the period from 2060 to 1780 million years BP . It replaces the earlier Orosirium .

designation

The Columbium, English Columbian , was named after the supercontinent Columbia .

Redefinition of the Precambrian Periods

In the course of moving away from period boundaries determined purely by radiometry, the GSSP principle should now be applied as far as possible in the Precambrian, according to Gradstein et al. (2012) . The periods are thus defined on the basis of significant geological events and no longer on arbitrary, radiometric ages.

Definition of columbium

There are two GSSP locations to choose from for the lower limit of Columbium - the base of the Rooiberg Group of the Kapvaal Craton in South Africa , with which voluminous magmatism sets in, or the base of the Kolosjoki Formation or the Kuetsjärvi Formation in the Pechenga greenstone belt of the Baltic Shield . No GSSP has yet been considered for the upper limit (and thus the beginning of the Mesoproterozoic ). It is characterized by the first diversification of the eukaryotic acritars , discovered in the approximately 1800 million year old Changzhougou Formation in the People's Republic of China . It is here that reducing, sulphide-containing sediments, including huge sulphide deposits, are formed for the first time in the ocean (the so-called Canfield Ocean ) .

meaning

Chromitite outcrop in the Bushveld complex

In the history of the earth , after the Late Archaic super event, Columbium is likely to be the most important orogeny period that ultimately led to the formation of the supercontinent Columbia (or Nuna ) between 1880 and 1840 million years ago . The enormous crust growth , referred to by Condie (2002) as the 1.9-Ga superplume event , began around 2060 million years ago with the world's largest layer intrusion , the mafic-ultramatic Rustenburg Layered Suite in South Africa . It was associated with volcanic rocks and granitoids of the Rooiberg Group , which forms the base and roof area of ​​the igneous province of the intrusive bushveld . Generally (more than 90%) continental island arcs were accreted during the super event (exception: Ungava orogens with mostly oceanic crust) .

The reasons for the increased magmatic and tectonic activity are suspected to be either an increase in the upper mantle limit ( mantle superswell ) or a complete overturning of the earth's mantle ( mantle overturn ). For the location, at 1.9 billion years BP maximum of crustal growth Condie takes (1998) called a mantle Avalanche (Engl. Mantle avalanche ) as the triggering mechanism, which in turn several Manteldiapire sent up.

A consequence of the increased volcanic activity was the increase in the carbon dioxide concentration in the atmosphere and thus the return of reducing oceans with strip ores (BIF). The Komatiite, which had since disappeared, also reappeared in Columbium . The appearance of the first real ophiolites , which document the beginning of plate tectonics , is remarkable .

Shungite from Karelia

The Lomagundi-Jatuli isotope excursion and the associated red sediments (English redbeds) came to an end with the beginning of Columbian. The δ 13 C values ​​were reduced to their normal level again, which can be explained by the so-called shunga event - the first deposition of shungites that began in 2010 millions of years BP . Shungites are fine-grain sediments ( algae charcoal ) that are very rich in organic carbon . Their sedimentation suppressed the δ 13 C ratio. From the shungites, the world's first oil deposits formed in the southeast of the Baltic Shield with naturally emerging oil. A large part of the deposits was destroyed between 1920 and 1790 million years BP by the Svekofennische orogeny .

One consequence of the increasing oxygen concentrations was the mobilization of uranium from crateronic rocks . The dissolved uranium was able to accumulate along chemoclines in oxidized water masses . Occasionally, after reprecipitation, such high concentrations were achieved in the sediment that the nuclear fission chain reaction started and a natural nuclear reactor was set in motion in the host rock. Examples are Oklo and Bangombé in Gabon's Franceville Basin , which are dated to around 2000 million years BP.

Manganese deposits associated with uranium were also created by oxidative dissolution and reprecipitation in stratified water bodies.

Ribbon ores

As already mentioned, thick ribbon ore formations were again sedimented in the period 2000 to 1750 million years BP. In contrast to their beautifully banded, archaic predecessors, the formations of Columbium are granular iron formations, which are mainly composed of peloids and ooids . They have a thin, irregular stratification, are often obliquely stratified and contain stromatolites in places - signs of shallow water sedimentation. An investigation of the iron isotopes in the stromal parts suggests that iron-oxidizing microorganisms are involved in sediment formation. In sub-depths, sediment precipitation has very likely been facilitated by volcanic influx.

The oldest iron deposits are million years old in 2020 and come from the Wyoming Craton . The most recent formations are less than 1,800 million years old BP and were sedimented in two basins in Western Australia . Its very young age contradicts the theory that the Sudbury asteroid impact that occurred around 1850 million years BP brought about the global end of iron sedimentation through complete ocean overturning.

oceanography

A stratified ocean model is generally assumed for the Paleoproterozoic, which has a reducing layer containing a great deal of dissolved iron in the depths and an oxidizing cover layer above it. The model is based on phosphorites as well as uranium and manganese sediments, which require both reducing water masses and oxidizing layers for solution transport and precipitation. The iron formations prevailing in the course of the Columbium were mainly formed in the shallow water area. From this it can be concluded that the oxidizing cover layer was relatively thin and / or that the continental shelves were much wider compared to the Archean. The iron precipitation may have restricted the primary organic production, as phosphorus was simultaneously adsorbed onto iron oxides from the seawater.

Meteorite crater

Remnants of the Vredefort crater visible from the orbit of the space shuttle

The Vredefort Crater in South Africa (approx. 2023 ± 4 million years ago BP) and the Sudbury Basin (approx. 1849 million years ago BP) are formed in Columbium , caused by asteroid impact .

stratigraphy

Significant sedimentary basins and geological formations

Deposits

Platinum metals  :

  • Bushveld complex (Rustenburg Layered Suite) with 90% of world supplies and 80% of annual production

Copper :

  • Udokan in Siberia
  • Bushveld complex

Chromium , Titanium and Vanadium :

  • Bushveld complex

Iron :

Magmatism

Layer intrusion

  • Rustenberg Layered Suite (RLS) in South Africa - 2061 to 2052 million years BP

Komatiite

Ophiolites

Geodynamics

Orogenesis

Continental collisions:

Terran accretions in the period 1950/1900 to 1830 million years BP:

Due to all these numerous continent collisions and terranean dockings, the supercontinent Columbia forms towards the end of Columbium.

Individual evidence

  1. ^ Felix M. Gradstein et al .: On the Geologic Time Scale . In: Newsletters on Stratigraphy . tape 45/2 , 2012, p. 171-188 .
  2. ↑ Lamb, DM et al .: Evidence for eukaryotic diversification in the -1800 million-year-old Changzhougou Formation, North China . In: Precambrian Research . tape 173 , 2009, pp. 93-104 .
  3. ^ Van Kranendonk, MJ: Chapter 16. A Chronostratigraphic Division of the Precambrian: Possibilities and Challenges . In: The Geologic Time Scale 2012 . Elsevier BV, 2012, doi : 10.1016 / B978-0-444-59425-9.00016-0 .
  4. ^ Condie, KC: Supercontinents and superplume events: distinguishing signals in the geologic record . In: Physics of the Earth and Planetary Interiors . tape 146 , 2004, pp. 319 .
  5. ↑ Reddy, SM and Evans, DAD: Paleoproterozoic supercontinents and global evolution: correlations from core to atmosphere . In: Geological Society of London Special Publications . tape 323 , 2009, pp. 1-23 .
  6. ^ A b Condie, KC: Continental growth during a 1.9-Ga superplume event . In: Journal of Geodynamics . tape 34 , 2002, p. 249-264 .
  7. ↑ Schweitzer, JK et al .: Regional lithochemical stratigraphy of the Rooiberg Group, upper Transvaal Supergroup: a proposed new subdivision . In: South African Journal of Geology . tape 98 , 1995, pp. 245-255 .
  8. ^ Hoffman, PF: Speculations on Laurentias first gigayear (2.0-1.0 Ga) . In: Geology . tape 17 , 1989, pp. 135-138 .
  9. ↑ Davies, GF: Punctuated tectonic evolution of the Earth . In: Earth and Planetary Science Letters . tape 36 , 1995, pp. 363-380 .
  10. ^ Condie, KC: Episodic continental growth and supercontinents: a mantle avalanche connection? In: Earth Planet. Sci. Lett. tape 163 (1-4) , 1998, pp. 97-108 .
  11. ↑ Melezhik, VA et al: Paleoproterozoic evaporates in Fennoscandia: Implications for seawater sulfate δ13C excursions and the rise of atmospheric oxygen . In: Terra Nova . tape 17 , 2005, pp. 141-148 .
  12. ↑ Melezhik, VA et al.: A giant Paleoproterozoic deposit of shungite in NW Russia: genesis and practical applications . In: Ore Geology Reviews . tape 24 , 2004, pp. 135-154 .
  13. ↑ Gauthier-Lafaye, F. and Weber, F .: Natural fission reactors: Time constraints for occurrence, and their relation to uranium and manganese deposits and to the evolution of the atmosphere . In: Precambrian Research . tape 120 , 2003, p. 81-100 .
  14. ↑ Poulton, SW et al .: Spatial variability in oceanic redox structure 1.8 billion years ago . In: Nature Geoscience . tape 3 , 2010, p. 486-490 .
  15. ↑ Bjerrum, CJ and Canfield, DE: Ocean productivity before 1.9 Gyr ago limited by phosphorous adsorption onto iron oxides . In: Nature . tape 417 , 2002, pp. 159-162 .
  16. ↑ Rebekah Lundquist: Provenance Analysis of the Marquette Range Supergroup sedimentary rocks using U-Pb Isotope geochemistry on detrital zircons by LA-ICP-MS . In: 19th annual Keck Symposium . 2006.
  17. ^ Hanski, E. et al.: The Palaeoproterozoic komatiite-picrite association of Finnish Lapland . In: Journal of Petrology . tape 42 , 2001, p. 855-876 .
  18. ↑ Arndt, N. et al .: Geochemistry, petrogenesis and tectonic environment of circum-Superior Belt basalts, Canada . In: Pharaoh, TC ua Geochemistry and Mineralization of proterozoic volcanic suites (Ed.): Geological Society of London, Special Publication . tape 33 , 1987, pp. 133-145 .
  19. ↑ Scott, DJ et al .: Geology and chemistry of the Early proterozoic Portuniq ophiolite, Cape Smith belt, northern Quebec, Canada . Ed .: Peters, T. ua Ophiolite Genesis and Evolution of the Oceanic Lithosphere. Kluwer, Dordrecht 1991, p. 817-849 .
  20. ^ Kontinen, AT: An Early Proterozoic ophiolite - the Jormua mafic-ultramafic complex, northern Finland . In: Precambrian Research . tape 35 , 1987, pp. 313-341 .
  21. ↑ Lenoir, JL et al .: The Paleoproterozoic shear belt in Tanzania: geochronology and structure . In: J. African Earth Sci. tape 19 , 1994, pp. 169-184 .
  22. ^ Barley, ME: The Pilbara Craton . Ed .: De Wit, MJ and Ashwal, LD: Greenstone Belts. Clarendon Press, Oxford, New York 1997, pp. 657-663 .
  23. ^ O'Dea, MG et al.: Geodynamic evolution of the Proterozoic Mount Isa terrain . In: Geol. Soc. London, Spec. Public. tape 121 , 1997, pp. 99-122 .
  24. ↑ Mishra, DC, Singh, B., Tiwari, VW, Gupta, BS and Rao, MBSV: Two cases of continental collisions and related tectonics during the Proterozoic period in India - insight from gravity modeling constrained by seismic and magnetotelluric studies . In: Precambrian Res. Band 99,, 2000, pp. 149-169 .
  25. ↑ Ross, GM et al .: Tectonic entrapment and its role in the evolution of the continental lithosphere: an example of the Precambrian of western Canada . In: Tectonics . tape 19 , 2000, pp. 116-134 .
  26. ↑ Wilde, SA, Zhao, GC and Sun, M .: Development of the North China Craton during the late Archean and its final amalgamation at 1.8 Ga: some speculations on its position within a global Paleoproterozoic supercontinent . In: Gondwana Res. V. 5, 2002, p. 85-94 .
  27. ^ Rogers, JJW and Santosh, M .: Configuration of Columbia, a Mesoproterozoic Supercontinent . In: Gondwana Res. Band 5 , 2002, p. 5-22 .