Methanium

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In the course of the redefinition of the Precambrian , the methanium becomes the first period within the era of the Neo-Archean . It took 150 million years, from 2,780 to 2,630 million years BP .

designation

The name Methanium, engl. Methanian , is derived from the greenhouse gas methane . It was chosen because the methanotrophic bacteria multiplied strongly during this period .

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 methanium

The lower limit of methanium to the Mesoarchean is set by a GSSP at the base of Mount Roe Basalt in Western Australia . Mount Roe Basalt, deposited from 2,780 million years ago BP, belongs to the Fortescue Group and thus to the Mount Bruce Supergroup . The upper limit of the methanium to the overlying siderium is also defined by a GSSP. This is at the base of the Western Australian Marra Mamba Iron Formation , which belongs to the Hamersley Group of the Mount Bruce Supergroup. Their world's first, giant band ore deposits ( giant BIFs ) were sedimented from 2,630 million years BP.

meaning

According to Condie (2006), the age of new crust formation shows a clear maximum during methanium (Geon 27)

With the first occurrence of flood basalts at the lower limit of methanium, a cycle of magmatic activity began that was almost unique in the history of the earth , the peak of which, based on the frequency distribution of zirconia ages, came to be at 2,700 million years BP. As a result, there was enormous crust growth , which Taylor and McLennan (1985) estimate to be around 40% of today's crust. In the course of the methanium, according to them, the earth's crust expanded from 30% of its current value at 2700 million years BP to 70% at 2500 million years BP. The end result of this development is likely to have been the formation of one or more supercontinents ( Superia , Kenorland and / or Sclavia ).

Due to the increased volcanic activity of this so-called late Archaic Super event (Engl. Late Archean super event ) was including methane heavily in the atmosphere released which have virtually no free at this time oxygen could produce (the content of methane was at that time 1,000 ppm , the oxygen content less than 1% of today's level).

The formation of orogenic gold deposits , which usually took place somewhat later and which mineralized BP in greenstone belts around the world around 2,650 million years, is likely to be directly related to the late archaic super event . Known in English as the global gold event , huge gold deposits (English: giant gold deposits ) were created on several cratons at this time .

Icing

A total of 15 diamond horizons document glaciation in the more than 500 meters thick, around 2700 million year old Talya Conglomerate of the Vanivilas Formation in southern India . Simultaneous icing is also documented directly below the intrusion contact of the Stillwater Complex in Montana .

biosphere

Stromatolites settled on the newly formed, extensive continental shelf during the methanium , and in the interval 2780 and 2420 million years BP, microbes multiplied explosively , including in particular the methanogenic bacteria. These partly chaotic changes in the biosphere are reflected in geochemical proxies (substitutes), which for the methanium sometimes show very clear anomalies (or excursions).

Characteristic are, for example, very strongly negative δ 13 C values ​​(up to - 15 ‰ VPDB, in organic hydrocarbons even up to - 61 ‰ VPDB). At the same time, peak values ​​of + 4 ‰ VPDB already reach a somewhat higher level than in the previous Archean. The δ 56 Fe values ​​also fell very significantly, with minimum values ​​starting from - 1.5 ‰ at the beginning of the period finally reaching - 3.1 ‰. Similarly, δ 34 S, the minimum values ​​of which decreased from values ​​around 0 ‰ to - 20 ‰. In contrast to this, the Δ 33 S values ​​increased from 0 ‰ to + 8 ‰ in the younger section of methanium.

These proxies, which are provided with a very large spread for the methanium, clearly demonstrate the imbalance of the biosphere at that time in relation to geological processes and the reducing nature of the earth's atmosphere. Only around 2,450 million years BP should a new equilibrium be established with further cooling of the earth (falling mantle temperatures, see Archean-Proterozoic boundary ) and a gradual increase in oxygen in the earth's atmosphere.

stratigraphy

Significant sedimentary basins and geological formations

Deposits

Magmatism and Geodynamics

Individual evidence

  1. ^ JM Hayes: Global methanotrophy at the Archean-Proterozoic transition . In: S. Bengston (Ed.): Early Life on Earth, Nobel Symposium . tape 84 . Columbia University Press, New York 1994, pp. 220-236 .
  2. ^ Felix M. Gradstein et al .: On the Geologic Time Scale . In: Newsletters on Stratigraphy . tape 45/2 , 2012, p. 171-188 .
  3. ^ SR Taylor, SM McLennan: The Continental Crust: Composition and Evolution . Blackwell Scientific Publications, 1985, ISBN 0-632-01148-3 .
  4. ↑ DI Groves et al .: Secular changes in global tectonic processes and their influence on the temporal evolution of gold-bearing mineral deposits . In: Economic Geology . tape 100 , 2005, pp. 203-224 .
  5. ↑ RW Ojakangas et al: The Talya Conglomerate: an Archean (~ 2.7 Ga) Glaciomarine Formation, Western Dharwar Craton, Southern India . In: Current Science . tape 106 , N ° 3, 2014, p. 387-396 .
  6. ^ NJ Page: The Precambrian diamictite below the base of the Stillwater Complex, Montana . In: MJ Hambrey, NB Harland (Ed.): Earth's Pre-Pleistocene Glacial Record . Cambridge University Press, Cambridge 1981, pp. 821-823 .
  7. ↑ JM Hayes, JR Waldbauer: The carbon cycle and associated redox processes through time . In: Philosophical Transactions of the Royal Society, Series B, Biological Sciences . tape 361 , 2006, p. 931-950 .
  8. ^ MJ Van Kranendonk: A Chronostratigraphic division of the Precambrian: Possibilities and Challenges . In: FM Gradstein (Ed.): A Geological Time Scale 2012 . Elsevier, 2012.
  9. ↑ J. Farquhar, BA Wing: Multiple sulfur isotopes and the evolution of the atmosphere . In: Earth and Planetary Science Letters . tape 213 , 2003, p. 1-13 .