Dasberg Event

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The Dasberg Event was a minor extinction event that occurred during the Famennian, the final stage of the Devonian period. It is often considered to be one of the events contributing to the Late Devonian extinction, which is believed by many palaeontologists to have been a protracted event that took place over millions of years.

Contents

Timing

The Dasberg Event occurred during the late Famennian in the Palmatolepis gracilis expansa conodont biozone, near the boundary between the lower and middle parts of the expansa biozone. [1]

Causes

Anoxia has been implicated as the main cause of the Dasberg Event. In the deep-shelf Kowala site in the Holy Cross Mountains of Poland, possible evidence of either intermittent anoxia throughout the water column or of prevalent anoxia in surficial waters concurrent with oxygenated bottom water in the lower Dasberg shale comes from low ratios of uranium to thorium, the dominance of small framboids combined with the presence of large framboids, and the presence of green sulphur bacterial biosignatures. No evidence of anoxia exists in the sedimentary layers sandwiched in between the lower and upper Dasberg shale layers. During the deposition of the upper Dasberg shale, both bottom waters and the water column were anoxic. Both of the two intervals of anoxia are linked to marine transgressions and microbial blooms of primary producers. [2]

Volcanic activity from the Yakutsk-Vilyuy Large Igneous Province or the Kola-Dnieper Large Igneous Province has been put forward as an explanation for the occurrence of anoxia. Pulses of activity from these large igneous provinces have been suggested as causes for other Late Devonian biotic crises. However, this association is highly tentative, as there exist no estimates precise enough for the timing of these pulses to conclusively prove their responsibility for causing the Dasberg Event. [3]

Effects

The Dasberg Event caused the extinction of many pelagic species, particularly ammonoids. [1] One of its other consequences was the appearance of the Etroeungt fauna, an unusual faunal assemblage consisting of very large brachiopods and solitary rugose corals; this short-lived fauna died out a few million years later in the much more severe Hangenberg Event. [4]

This event, like many anoxic events, resulted in the widespread deposition of black shales. [5] In addition to black shales, widespread organic-rich limestones were also deposited during the event. [6]

See also

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References

  1. 1 2 Hartenfels, Sven; Becker, R. Thomas (December 2009). "TIMING OF THE GLOBAL DASBERG CRISIS – IMPLICATIONS FOR FAMENNIAN EUSTASY AND CHRONOSTRATIGRAPHY". Palaeontographica Americana (63): 71–97. Retrieved 24 March 2023.
  2. ↑ Marynowski, Leszek; Filipiak, Paweł; Zatoń, Michał (15 January 2010). "Geochemical and palynological study of the Upper Famennian Dasberg event horizon from the Holy Cross Mountains (central Poland)". Geological Magazine . 147 (4): 527–550. doi:10.1017/S0016756809990835 . Retrieved 24 March 2023.
  3. ↑ Rakociński, Michał; Pisarzowska, Agnieszka; Corradini, Carlo; Narkiewicz, Katarzyna; Dubicka, Zofia; Abdiyev, Nuriddin (11 March 2021). "Mercury spikes as evidence of extended arc-volcanism around the Devonian–Carboniferous boundary in the South Tian Shan (southern Uzbekistan)". Scientific Reports . 11: 1–15. doi:10.1038/s41598-021-85043-6 . Retrieved 24 March 2023.
  4. ↑ Stock, Carl W.; Sandberg, Charles A. (15 November 2019). "Latest Devonian (Famennian, expansa Zone) conodonts and sponge-microbe symbionts in Pinyon Peak Limestone, Star Range, southwestern Utah, lead to reevaluation of global Dasberg Event". Palaeogeography, Palaeoclimatology, Palaeoecology . 534: 1–44. doi:10.1016/j.palaeo.2019.109271 . Retrieved 24 March 2023.
  5. ↑ Zhang, Xinsong; Joachimski, Michael M.; Over, D. Jeffrey; Ma, Kunyuan; Huang, Cheng; Gong, Yiming (November 2019). "Late Devonian carbon isotope chemostratigraphy: A new record from the offshore facies of South China". Global and Planetary Change . 182: 1–38. doi:10.1016/j.gloplacha.2019.103024 . Retrieved 24 March 2023.
  6. ↑ Becker, R. Thomas; Hartenfels, Sven (September 2007). "THE DASBERG EVENT IN THERHENISH MASSIVE, CARNIC ALPS,AND ANTI-ATLAS (TAFILALT,MAIDER) – IMPLICATIONS FOR FAMENNIAN EUSTATICS AND CHRONOSTRATIGRAPHY": 40–45. Retrieved 24 March 2023.{{cite journal}}: Cite journal requires |journal= (help)
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