Triassic-Jura border

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The Triassic-Jura border around 201 million years ago was accompanied by the fifth largest mass extinction in the history of the earth, to which the conodonts and many other taxa fell victim. Several theories exist to explain it, but the evidence is growing towards enormous volcanic activity.

Effects on the living world

Intensity of the mass extinction of marine genera during the Phanerozoic . The peak is clearly visible at the Triassic-Jura border (at 200 million years).

Affected groups of fauna

Most affected by the mass extinction at the Triassic-Jurassic extinction event ( English Triassic-Jurassic extinction event ) was the class of marine conodonts , which disappeared completely. In addition, a fifth of the families living in the sea at that time were wiped out. The entactinaria were reduced very drastically in the radiolarians and the spumellaria lost over two thirds of their taxa. The Albaillellaria were previously extinct in the Upper Triassic.

With the exception of the crocodiles, all large crurotarsi ( archosaurs that do not belong to the dinosaurs ) were destroyed on the mainland . It went out:

Postosuchus , a Rauisuchidae that died out on the Triassic-Jura border

Also many of the large amphibians such as the temnospondylum superfamilies

as well as some Therapsida did not survive the turn of the Triassic Jura. The diapsid Endennasauridae and the mammalian precursors of the Traversodontidae also became extinct . The overall balance of the mass extinction was devastating - it is believed that up to 70 percent of the species at that time died out in this event within a relatively short period of time.

Newly published groups of fauna

The temporal distribution of tetrapod families during the Upper Triassic and Lower Jurassic

The decimation of the Archosauria freed up a large number of ecological niches , which in the further course of the Jura were mainly occupied by the dinosaurs and which then advanced to a dominant position on the mainland.

The following taxa appeared for the first time after the Triassic-Jura border:

Causes of mass extinction

The following theses are used to explain the evolutionary turning point at the Triassic-Jura border:

Sea level and climate changes

Significant sea level and climate changes usually take place over longer geological periods. The mass extinction at the Triassic-Jura border, on the other hand, was a sudden cut that took about 10,000 to a maximum of 50,000 years.

The sea level at the Triassic-Jura border was at a worldwide eustatic low ( regression He1 ). Then the transgression of the hettangium began.

Impact of an asteroid

The Wells Creek Crater and the Red Wing Crater in the United States and the Rochechouart-Chassenon Crater in France are quite close in time to the Triassic-Jura boundary . However, these impact craters are relatively small and are hardly a possible cause of global mass extinction. The Manicouagan impact structure in Canada has much larger dimensions (originally around 100 km), but it was formed around 13 million years before the Triassic-Jurassic border.

Intense volcanism

Changes in CO 2 concentration during the Phanerozoic , i.e. during the last 542 million years. More recent data is on the right side of the graph. The graph begins on the left in the time before plant life existed on land and during which the sun's output was 4% lower than today. The current CO 2 levels are shown on the far right of the graphic .

Towards the end of the Triassic, a geological upheaval was heralded with the beginning of the disintegration of the Pangea supercontinent, which had existed since the late Carboniferous . Along the plate edges of today's North America and Europe, extensive rift fractures (rift systems) with the first marine ingresses arose . This development, towards the gradual opening of the later Central Atlantic-Jurassic boundary Triassic resulted in the emergence of 11 million km² Central Atlantic magmatic province (English Central Atlantic Magmatic Province , abbreviated CAMP ), including their Magmaausflüsse of the richest of the known geological history . The intense volcanism released enormous amounts of the greenhouse gas carbon dioxide (CO 2 ) and the aerosol-forming gas sulfur dioxide (SO 2 ), had serious consequences for the atmosphere, climate and biosphere and is considered the primary cause of mass extinction in current research. In addition to the climatic effects, ocean acidification through the uptake of volcanic carbon dioxide and sulfur dioxide also played an important role in the marine mass extinction .

The main phase of flood basalt volcanism lasted approximately 600,000 years and probably had several very pronounced activity peaks. In this context, a work published in 2020 postulates a pulsed CO 2 release from deep carbonaceous "bubbles" which, in the course of the CAMP event, gassed their contents within a short period of time and developed an eruptive effect similar to a propellant.

Geochemical investigations on intermediate soil profiles within the CAMP basalts in eastern North America found strong negative anomalies in the carbon isotope 13 C ( negative carbon isotope excursion ), which indicate rapid warming from +4 to +6 ° C. This finding comes from the lignin found in the paleo soils and the wax of leaves. Two enclosed lake sediment profiles were also examined. The δ 13 C curves obtained in this way from n-alkanes with their negative deflections were almost identical and could also be correlated with the largely marine profile of Saint Audrie's Bay in Somerset ( England ). From this it was concluded that both terrestrial and marine areas were affected by the Triassic Jurassic event. An additional aspect is the possible destabilization and release of extensive amounts of methane hydrate from oceanic deposits, as is also assumed for the previous mass extinction at the Permian-Triassic border .

Some recent studies come to the conclusion that the focus of mass extinction is to be set around 100,000 years before the effusive flood basalt phase of the CAMP event. According to these analyzes, activity in the Central Atlantic Magmatic Province began at an intrusive stage . In the course of this, large amounts of magma flowed into evaporite and carbonate deposits and over periods of several thousand or ten thousand years caused the outgassing of carbon dioxide in the five-digit gigaton range through contact metamorphosis .

Age

In previous analyzes, the age of the Triassic-Jurassic boundary was given as 199.6 million years BP . The current chronostratigraphic time table of the International Commission for Stratigraphy (ICS) currently states a radiometrically determined age of 201.3 million years.

See also

literature

Individual evidence

  1. ^ David PG Bond, Paul B. Wignall: Large igneous provinces and mass extinctions: An update . (PDF) In: The Geological Society of America (GSA) Special Paper . 505, September 2014, pp. 29-55. doi : 10.1130 / 2014.2505 (02) .
  2. ↑ Royer: CO 2 -forced climate thresholds during the Phanerozoic . (PDF) In: Geochimica et Cosmochimica Acta . 70, No. 23, 2006, pp. 5665-5675. bibcode : 2006GeCoA..70.5665R . doi : 10.1016 / j.g approx . 2005.11.031 .
  3. ↑ Guinan, Ribas: Our Changing Sun: The Role of Solar Nuclear Evolution and Magnetic Activity on Earth's Atmosphere and Climate . In: Montesinos, Benjamin; Gimenez, Alvaro; Guinan, Edward F. (Ed.): The Evolving Sun and its Influence on Planetary Environments  (= ASP Conference Proceedings), Volume 269. Astronomical Society of the Pacific, San Francisco 2002, ISBN 1-58381-109-5 , pp. 85.
  4. ^ Tran T. Huynh, Christopher J. Poulsen: Rising atmospheric CO 2 as a possible trigger for the end-Triassic mass extinction . (PDF) In: Palaeogeography, Palaeoclimatology, Palaeoecology . 217, No. 3-4, February 2005, pp. 223-242. doi : 10.1016 / j.palaeo.2004.12.004 .
  5. ↑ Jessica H. Whiteside, Paul E. Olsen, Timothy Eglinton, Michael E. Brookfield, Raymond N. Sambrotto: Compound-specific carbon isotopes from Earth's largest flood basalt eruptions directly linked to the end-Triassic mass extinction . (PDF) In: PNAS . 107, No. 15, April 2010, pp. 6721-6725. doi : 10.1073 / pnas.1001706107 .
  6. ↑ Michael Hautmann: Effect of end-Triassic CO2 maximum on carbonate sedimentation and marine mass extinction . In: Facies . tape 50 , no. September 2 , 2004, ISSN  0172-9179 , doi : 10.1007 / s10347-004-0020-y ( springer.com [accessed May 25, 2020]).
  7. ^ Michael Hautmann, Michael J. Benton, Adam Tomašových: Catastrophic ocean acidification at the Triassic-Jurassic boundary . In: New Yearbook of Geology and Paleontology - Treatises . tape 249 , no. 1 , July 1, 2008, p. 119–127 , doi : 10.1127 / 0077-7749 / 2008 / 0249-0119 ( ingenta.com [accessed May 25, 2020]).
  8. ↑ Terrence J. Blackburn, Paul E. Olsen, Samuel A. Bowring, Noah M. McLean, Dennis V. Kent, John Puffer, Greg McHone, E. Troy Rasbury, Mohammed Et-Touhami: Zircon U-Pb Geochronology Links the End -Triassic Extinction with the Central Atlantic Magmatic Province . (PDF) In: Science . 340, No. 6135, May 2013, pp. 941-945. doi : 10.1126 / science.1234204 .
  9. ↑ Manfredo Capriolo, László E. Aradi, Sara Callegaro, Jacopo Dal Corso, Robert J. Newton, Benjamin JW Mills, Paul B. Wignall, Omar Bartoli, Don R. Baker, Nasrrddine Youbi, Laurent Remusat, Richard Spiess, Csaba Szabó: Deep CO 2 in the end-Triassic Central Atlantic Magmatic Province . In: Nature Communications . April 11, 2020. doi : 10.1038 / s41467-020-15325-6 .
  10. ↑ Jessica H. Whiteside, Paul E. Olsen, Timothy Eglinton, Michael E. Brookfield, Raymond N. Sambrotto: Compound-specific carbon isotopes from Earth's largest flood basalt eruptions directly linked to the end-Triassic mass extinction . In: PNAS . tape 107 , no. 15 , 2010, p. 6721-6725 .
  11. ^ MHL Deenen, M. Ruhl, NR Bonis, W. Krijgsman, W. Kuerscher, M. Reitsma, MJ van Bergen: A new chronology for the end-Triassic mass extinction . In: EPSL . 2010.
  12. ↑ JHFL Davies, H. Bertrand, N. Youbi, M. Ernesto, U. Schaltegger: End-Triassic mass extinction started by intrusive CAMP activity . In: Nature Communications . May 8, 2017. doi : 10.1038 / ncomms15596 .
  13. ↑ Thea H. Heimdal, Henrik. H. Svensen, Jahandar Ramezani, Karthik Iyer, Egberto Pereira, René Rodrigues, Morgan T. Jones, Sara Callegaro: Large-scale sill emplacement in Brazil as a trigger for the end-Triassic crisis . (html) In: Nature Scientific Reports . January 8, 2018. doi : 10.1038 / s41598-017-18629-8 .
  14. ↑ International Commission on Stratigraphy: International Stratigraphic Chart . In: ICS Chart / Time Scale . .