Hangenberg event

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The Hangenberg event (also known as the Hangenberg crisis ), named after the black slate sediments on the Hangenberg of the Rhenish Slate Mountains , marks a serious global change in the environment, including extensive mass extinction on the border between the geochronological periods of Devonian and Carboniferous 358.9 million years ago. According to recent findings, this biodiversity crisis led to a loss of species of up to 75 percent and thus reached dimensions similar to the five great waves of extinction (the so-called "Big Five") in the Phanerozoic , that is, during the last 541 million years.

The duration of the crisis is mostly estimated at around 100,000 to 300,000 years, with individual studies postulating a somewhat shorter time span. In the search for the causes, a large number of possible influencing factors are currently being considered in science, but an explanation for the extinction of species that covers all aspects is still pending.

The environmental situation in Devon

Skull of Dunkleosteus in the Queensland Museum (Australia)

The Devonian as the “Age of Fish” initially recorded a rapid increase in biodiversity in the oceans . This mainly affected the class of armored fish (Placodermi), with the Dunkleosteus measuring up to 9 meters as the most impressive representative. Numerous species also trained the spiny sharks , and the evolution of the coelacanth and lungfish also began . The first terrestrial vertebrates appeared towards the end of the Devonian , including the amphibious species Ichthyostega .

In terms of global temperature and the distribution of climatic zones, the Lower and Middle Devonian was similar to the previous Silurian . As a result of a relatively stable warm climate , the sea level remained high, and although parts of what was then the greater continent of Gondwana occupied a position in the immediate vicinity of the South Pole, extensive glaciers remained a rarity for the time being. In the Upper Devonian, the first forest landscapes arose - initially in the swamps and wetlands of the tropics - and the oxygen content rose relatively quickly to around 20 percent due to the increased rate of photosynthesis . In return, the carbon dioxide concentration steadily decreased. At the beginning of the Devonian Mountains, which were still in the vicinity of 2,000 ppm, considerable amounts of CO 2 were stored in the expanding belts of vegetation and thus withdrawn from the atmosphere.

The mass extinction

system series step ≈ age ( mya )
higher higher higher younger
Devon Upper Devonian Family 358.9
⬍
372.2
Frasnium 372.2
⬍
382.7
Middle Devon Givetium 382.7
⬍
387.7
Eifelium 387.7
⬍
393.3
Lower Devon Emsium 393.3
⬍
407.6
Pragium 407.6
⬍
410.8
Lochkovium 410.8
⬍
419.2
deeper deeper deeper older

By occurred in recent decades technical development of dating and detection methods which a fine resolution of certain stratigraphic layers allow a variety of more or less pronounced environmental changes was from the Devonian Emsium identified, sometimes sweeping under the name of the medium to Upper Devonian biocrisis firmierten . With increasing knowledge, research focused on two areas: firstly on the Big Five counting Kellwasser event before about 372 million years ago (Frasnian-Famennian transition) , named for the Upper Devonian limestone layers of Kellwassertals in the Upper Harz , as well as the least Hangenberg crisis of equal strength , divided into a lower, middle and upper interval.

While the Kellwasser event recorded several warming peaks, a clear and abrupt cooling on a geological scale began with the formation of extensive ice sheets in the southern and western regions of the greater continent of Gondwana, with a focus on today's South America and parts of Africa. The sea level sank by about 100 meters in the course of the glacial eustasia and subsequently led to the drying out of shallow tropical shelf seas and the collapse of several ecosystems. In connection with this, the atmospheric CO 2 concentration was reduced by around 50 percent due to the massive deposition of organic carbon in black shale horizons. Due to profound geochemical changes, the near-surface water layers of the oceans were increasingly subject to low-oxygen conditions, possibly linked to the formation of algal blooms and the release of highly toxic hydrogen sulfide . Ammonites , brachiopods , trilobites , conodonts , ostracods (mussel crabs), bazookas, the reef-building stromatopores and early land vertebrates ( tetrapods ) were particularly affected by the loss of their biotopes . The biodiversity of the severely damaged already during Kellwasser phase phytoplankton had reduced so much that the original biodiversity after nearly 200 million years in the Jurassic was reached again (phytoplankton blackout) .

Possible causes

The main cause of the Hangenberg event is often assumed in the specialist literature to be the influence of megavolcanism. There is a broad scientific consensus that so-called Magmatic Large Provinces ( Large Igneous Provinces ) were directly involved in a number of mass extinctions, such as at the Perm-Triassic border (252 mya ) or during the Triassic Jura -Transition (201 mya). In each case, it was a question of the large-volume escape of igneous rocks from the earth's mantle , predominantly in the form of flood basalts , which over the course of a hundred thousand years or longer sometimes spread over an area of ​​millions of square kilometers. A lasting volcanic impulse in the form of the Siberian Viluy Trapps is also being discussed for the Kellwasser strata based on the mercury anomalies discovered there . On the other hand, there is little evidence of the involvement of a Magmatic Greater Province in connection with the Hangenberg Crisis, especially since magmatic effusions of this magnitude did not cause any cooling, but often a pronounced global warming. As an alternative, a “volcanic belt” similar to today's Pacific Ring of Fire was proposed, the activities of which had a permanent impact on the global climate or cooled it off through the emission of sulfur dioxide and aerosols .

As additional mechanisms, further factors are put up for discussion in the specialist literature, such as a significantly increased effect of the orbital parameters due to the falling carbon dioxide concentration , especially with regard to the long-period eccentricity cycles , a sudden destabilization of the entire earth climate system when a certain tipping point is exceeded or the Radiation influence of a near-earth supernova that destroys the ozone layer . A relatively new aspect in the assessment of the mass extinctions in the Paleozoic (ancient times) is the realization that during these biological crises the extensive reduction of trace elements could have played a decisive role. The concentration of the vital element selenium in the Devonian period only reached a fraction of the current level. Various studies point to multi-causal explanatory approaches that include, among other things , the carbon cycle , vegetation cover, chemical weathering or plate tectonic processes . Possibly several large impact disasters such as the Australian Woodleigh impact (≈ 364 mya), the Alamo impact in today's Nevada (≈ 367 mya) or the Swedish Siljan impact structure (≈ 380–376 mya ) were associated with the extinction waves and climatic fluctuations in the Upper Devonian ) directly involved. Due to the relatively large uncertainties in the dating of these asteroid craters in particular , none of these events can be clearly assigned to the Hangenberg event.

Effects in carbon

The Tournaisium (358.9 to 346.7 mya), the first chronostratigraphic stage of the Carboniferous , which immediately followed the Hangenberg event , recorded a rise in sea level with a renewed expansion of shelf seas and the establishment of a warm climate, which, however, was not quite the level of the pre-crisis period reached. This warming tendency flattened out at the beginning of the Middle Tournaisian and gradually changed into the climatic state of the Permocarbon Ice Age .

A special feature of the early Carboniferous is the faunal situation with few fossils (Romer gap, in the specialist literature Romer's gap ) , which has long been considered puzzling and named after the paleontologist Alfred Romer (1894–1973 ). The species poverty, which extends well into the Lower Carboniferous for over 15 million years, could be a direct consequence of the previous Hangenberg extinction. Even if the gap has been partially closed by recent discoveries, the impression of a longer recovery phase remains. This assumption was confirmed by the evidence that many vertebrates ( vertebrates ) showed a sustained decrease in body size over a period of around 36 million years. Since the globally widespread short stature was apparently neither due to a lack of oxygen nor to temperature stress, this development was probably controlled by ecological factors, since a growth minimization as an evolutionary adaptation to a changed environment leads to higher reproduction rates, faster generation changes and larger populations .

Definition and GSSP

The Hasselbachtal in Hagen is one of the most striking geological outcrops on the Devonian-Carboniferous border in Germany . This location was discovered in 1900 by the geologist August Denckmann and was shortlisted as the official guiding profile ( type locality ). In 1990, the International Commission on Stratigraphy (ICS) chose the La Serre profile in France in the south-eastern Montagne Noire as a reference ( Global Stratotype Section and Point - GSSP for short ) . The stratigraphic profile is defined by the first appearance of the conodont species Siphonodella (Eosiphonodella) sulcata .

literature

  • George R. McGhee Jr: When the Invasion of Land Failed. The Legacy of the Devonian Extinctions. Columbia University Press, New York 2013, ISBN 978-0-231-16057-5

Web links

Individual evidence

  1. ↑ Hangenberg (NS = 51.39361, EW = 7.90442) near Arnsberg , cf. Friedrich Wilhelm Luppold, Claus-Dieter Clausen, Dieter Korn, Dieter Stoppel: Devon / Carbon border profiles in the area of ​​Remscheid-Altenaer Sattel, Warsteiner Sattel, Briloner Sattel and Attendorn-Elsper Doppelmulde (Rhenish Slate Mountains) . In: Geology and Paleontology in Westphalia . Issue 29. Landschaftsverband Westfalen-Lippe (LWL) , Münster 1994, ISBN 3-924590-40-0 , p. 7–69 ( download from LWL [PDF; 2.6 MB ; accessed on August 23, 2020]). Available under Download Geology and Paleontology in Westphalia. LWL Museum for Natural History .;
  2. ^ Paul M. Myrow, Jahandar Ramezani, Anne E. Hanson, Samuel A. Bowring, Grzegorz Racki, Michał Rakociński: High-precision U – Pb age and duration of the latest Devonian (Famennian) Hangenberg event, and its implications . (PDF) In: Terra Nova . 26, No. 3, June 2014, pp. 222–229. doi : 10.1111 / ter.12090 .
  3. ^ Grzegorz Racki: Understanding Late Devonian And Permian-Triassic Biotic and Climatic Events - Towards an Integrated Approach. Chapter 2: Toward understanding Late Devonian global events: few answers, many questions . (PDF) In: Developments in Palaeontology and Stratigraphy . 20, 2005, pp. 5-36. doi : 10.1016 / S0920-5446 (05) 80002-0 .
  4. ↑ Christopher M. Berry, John EA Marshall: Lycopsid forests in the early Late Devonian paleoequatorial zone of Svalbard . In: Geology . 43, No. 12, December 2015, pp. 1043-1046. doi : 10.1130 / G37000.1 .
  5. ↑ RT Becker, P. Königshof, CE Brett: Devonian climate, sea level and evolutionary events: an introduction . (PDF) In: Geological Society, London, Special Publications . 423, August 2016, pp. 1–10. doi : 10.1144 / SP423.15 .
  6. ^ "Middle to Upper Devonian biotic crisis", see Thomas J. Algeo, Stephen E. Scheckler: Terrestrial-marine teleconnections in the Devonian: links between the evolution of land plants, weathering processes, and marine anoxic events. In: Philosophical Transactions of the Royal Society of London B (Biological Sciences). 353, No. 1365, 1998, pp. 113–130, doi : 10.1098 / rstb.1998.0195 , PMC 1692181 (free full text)
  7. ↑ Leszek Marynowski, Michał Zatoń, Michał Rakociński, Paweł Filipiak, Slawomir Kurkiewicz, Tim J. Pearce: Deciphering the upper Famennian Hangenberg Black Shale depositional environments based on multi-proxy record . (PDF) In: Palaeogeography, Palaeoclimatology, Palaeoecology . 346-347, August 2012, pp. 66-86. doi : 10.1016 / j.palaeo.2012.05.020 .
  8. ^ A b Sandra Isabella Kaiser, Markus Aretz, Ralph Thomas Becker: The global Hangenberg Crisis (Devonian-Carboniferous transition): review of a first-order mass extinction . (PDF) In: Geological Society, London, Special Publications . 423, August 2016, pp. 387-437.
  9. ↑ Marina Kloppischː Organic-geochemical comparison of selected rocks of the Frasnium / Famennium border (Oberdevon) in the Bergisches Land and the Eifel (PDF). Reports from Forschungszentrum Jülich, Institute for Chemistry and Dynamics of the Geosphere, 2002.
  10. ^ 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) .
  11. ↑ Grzegorz Racki, Michał Rakociński, Leszek Marynowski, Paul B. Wignall: Mercury enrichments and the Frasnian-Famennian biotic crisis: A volcanic trigger proved? . (PDF) In: Geology . 46, No. 6, June 2018, pp. 543-546. doi : 10.1130 / G40233.1 .
  12. ↑ J. Ricci, X. Quidelleur, V. Pavlov, S. Orlov, A. Shatsillo, V. Courtillot: New 40 Ar / 39 Ar and K-Ar ages of the Viluy traps (Eastern Siberia): Further evidence for a relationship with the Frasnian-Famennian mass extinction . (PDF) In: Palaeogeography, Palaeoclimatology, Palaeoecology . 386, September 2013, pp. 531-540. doi : 10.1016 / j.palaeo.2013.06.020 .
  13. ↑ Olivia Paschall, Sarah K. Carmichael, Peter Königshof, Johnny A. Waters, Phuong H. Ta, Toshifumi Komatsu, Allison Dombrowski: The Devonian-Carboniferous boundary in Vietnam: Sustained ocean anoxia with a volcanic trigger for the Hangenberg Crisis? . (PDF) In: Global and Planetary Change . 175, April 2019, pp. 64–81. doi : 10.1016 / j.gloplacha.2019.01.021 .
  14. ^ David De Vleeschouwer, Micha Rakociński, Grzegorz Racki, David PG Bond, Katarzyna Sobień, Philippe Claeys: The astronomical rhythm of Late-Devonian climate change (Kowala section, Holy Cross Mountains, Poland) . (PDF) In: Earth and Planetary Science Letters . 365, March 2013, pp. 25-37. doi : 10.1016 / j.epsl.2013.01.016 .
  15. ^ Sarah K. Carmichael, Johnny A. Waters, Cameron J. Batchelor, Drew M. Coleman, Thomas J. Suttner, Erika Kido, LM Moore, Leona Chadimová: Climate instability and tipping points in the Late Devonian: Detection of the Hangenberg Event in an open oceanic island arc in the Central Asian Orogenic Belt . (PDF) In: Gondwana Research . 32, April 2016, pp. 213-231. doi : 10.1016 / j.gr.2015.02.009 .
  16. ↑ Brian D. Fields, Adrian L. Melott, John Ellis, Adrienne F. Ertel, Brian J. Fry, Bruce S. Lieberman, Zhenghai Liu, Jesse A. Miller, Brian C. Thomas: Supernova triggers for end-Devonian extinctions . In: PNAS . August 2020. doi : 10.1073 / pnas.2013774117 .
  17. ↑ John A. Long, Ross R. Large, Michael SY Lee, Michael J. Benton, Leonid V. Danyushevsky, Luis M. Chiappe, Jacqueline A. Halpin, David Cantrill, Bernd Lottermoser: Severe selenium depletion in the Phanerozoic oceans as a factor in three global mass extinction events . (PDF) In: Gondwana Research . 36, August 2016, pp. 209-218. doi : 10.1016 / j.gr.2015.10.001 .
  18. ↑ Julia Brugger, Matthias Hofmann, Stefan Petri, Georg Feulner: On the Sensitivity of the Devonian Climate to Continental Configuration, Vegetation Cover, Orbital Configuration, CO 2 Concentration, and Insolation . In: Paleoceanography and Paleoclimatology . 34, No. 8, August 2019, pp. 1375–1398. doi : 10.1029 / 2019PA003562 .
  19. Jump up ↑ Andrew J. Retzler, Leif Tapanila, Julia R. Steenberg, Carrie J. Johnson, Reed A. Myers: Post-impact depositional environments as a proxy for crater morphology, Late Devonian Alamo impact, Nevada . (PDF) In: Geosphere (Geological Society of America) . 11, February 2015, pp. 123-143. doi : 10.1130 / GES00964 .
  20. ↑ Benjamin KA Otoo, Jennifer A. Clack, Timothy R. Smithson, Carys E. Bennett, Timothy I. Kearsey, Michael I. Coates: A fish and tetrapod fauna from Romer's Gap preserved in Scottish Tournaisian floodplain deposits . In: Palaeontology . 62, No. 2, March 2019, pp. 225-253. doi : 10.1126 / science.aac7373 .
  21. ↑ Lauren Sallan, Andrew K. Galimberti: Body-size reduction in vertebrates following the end-Devonian mass extinction . In: Science . 350, No. 6262, November 2015, pp. 812-815. doi : 10.1126 / science.aac7373 .
  22. ^ Eva Paproth, Raimund Feist, Gerd Flajs: Decision on the Devonian – Carboniferous boundary stratotyp . (PDF) In: Episodes . 14, No. 4, 1991, pp. 331-336.