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Record of the end-Triassic mass extinction in shallow marine carbonates: the Lorüns section (Austria)

Brakebusch, Linus LU (2022) In Dissertations in Geology at Lund University GEOR02 20222
Department of Geology
Abstract
The end-Triassic mass extinction (ETE) was one of the five big mass extinctions of the Phanerozoic and occurred ~201 Ma ago. Research agrees that the main triggering factor for the ETE was the eruptions of the Central Atlantic Magmatic Volcanic Province (CAMP), linked to the break-up of the supercontinent Pangaea. The large amounts of CO2 and SO2 released from the volcanic eruptions had a series of consequences such as climatic changes and ocean acidification, all possibly contributing to an extinction of a large number of taxa in the marine and terrestrial realm.

The Lorüns section constitutes a shallow-marine carbonate succession located in the Northern Calcareous Alps (NCA), Austria, and is a key section for studying the ETE because... (More)
The end-Triassic mass extinction (ETE) was one of the five big mass extinctions of the Phanerozoic and occurred ~201 Ma ago. Research agrees that the main triggering factor for the ETE was the eruptions of the Central Atlantic Magmatic Volcanic Province (CAMP), linked to the break-up of the supercontinent Pangaea. The large amounts of CO2 and SO2 released from the volcanic eruptions had a series of consequences such as climatic changes and ocean acidification, all possibly contributing to an extinction of a large number of taxa in the marine and terrestrial realm.

The Lorüns section constitutes a shallow-marine carbonate succession located in the Northern Calcareous Alps (NCA), Austria, and is a key section for studying the ETE because it records continuous sedimentation from the late Rhaetian to the Sinemurian. In this study, the Rhaetian Kössen Formation, the Schattwald Beds, and the Hettangian Lorüns oolite have been petrographically analysed. Geochemical analyses with laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) were also performed, mainly on the recovery facies from the Lorüns oolite. This study aims to offer a detailed description of the geological, geochemical and palaeoenvironmental conditions at Lorüns in the aftermath of the ETE and to compare the results with other Triassic-Jurassic boundary sections around the world.

The lack of calcareous fossils and the deposition of the siliciclastic Schattwald Beds during the “Extinction interval” together with the formation of coated grains in the post-extinction Lorüns oolite indicate that ocean acidification occurred in this area, especially affecting acid-sensitive organisms. Seawater was oxygenated during the early Hettangian. However, dysoxia occurred in the sediments during this period and is ascribed to the loss of biogenic sediment mixing due to the extinction of infaunal taxa. Analysis of the weathering proxies Si, Al, and Ti shows that weathering decreased continuously during the Hettangian. This could be explained by the marine transgression in the Lorüns area, a greater distance to the siliciclastic input zone, or because of a shift towards a less humid and hot climate after the extreme greenhouse conditions caused by volcanism around the ETE. Contrarily to the models from Hardie (1996) and Stanley & Hardie (1998), who propose an “aragonite” sea in the Late Triassic and Early Jurassic, the sea was found to be low-Mg calcitic at the time of deposition of the Schattwald Beds and Lorüns oolite. Triassic-Jurassic boundary sections in the Arab Emirates also imply a low-Mg calcitic sea, suggesting that the signal recorded at Lorüns was global, or at least Tethys-wide. Hence, the shift from an “aragonite” to “calcite” sea might have occurred earlier than previously believed. (Less)
Abstract (Swedish)
Det sen-Triassiska massutdöendet (STM) var ett av de fem stora massutdöenden i Fanerozoikum och inträffade för omkring 201 miljoner år sedan. Forskningen är enig om att utdöendet orsakades av vulkanutbrotten associerade med bildandet av den Centralatlantiska magmatiska provinsen (CAMP), som är kopplade till uppbrottet av superkontinenten Pangea. De omfattande vulkaniska utsläppen av CO2 och SO2 ledde till miljöpåverkan i form av klimatförändringar och havsförsurning, vilket i sin tur bidrog till att många arter i havet och på land dog ut.

Lorünsblottningen är en kalkstensavlagring från de Norra Kalkalperna i Österrike. Det är en viktig blottning för att studera det sen-Triassiska massutdöendet eftersom den representerar kontinuerlig... (More)
Det sen-Triassiska massutdöendet (STM) var ett av de fem stora massutdöenden i Fanerozoikum och inträffade för omkring 201 miljoner år sedan. Forskningen är enig om att utdöendet orsakades av vulkanutbrotten associerade med bildandet av den Centralatlantiska magmatiska provinsen (CAMP), som är kopplade till uppbrottet av superkontinenten Pangea. De omfattande vulkaniska utsläppen av CO2 och SO2 ledde till miljöpåverkan i form av klimatförändringar och havsförsurning, vilket i sin tur bidrog till att många arter i havet och på land dog ut.

Lorünsblottningen är en kalkstensavlagring från de Norra Kalkalperna i Österrike. Det är en viktig blottning för att studera det sen-Triassiska massutdöendet eftersom den representerar kontinuerlig sedimentation från sen rät till sinemur. I detta projekt har Kössen Formationen från rät, samt Schattwaldlagren och Lorünsooliten från hettang analyserats petrografiskt. Geokemiska analyser av framförallt de lager som avsattes direkt efter utdöendet utfördes genom laser-spektroskopi (LA-ICP-MS). Syftet med projektet är att ge en detaljerad beskrivning av de geologiska och geokemiska förhållandena samt miljön i Lorüns under återhämtningsfasen av STM och jämföra resultaten med andra likåldriga sektioner globalt.

Avsaknaden av kalkhaltiga fossil och avlagringen av de siliciklastiska Schattwaldlagren under STM tillsammans med bildandet av abiotiska karbonatkorn i Lorünsooliten tyder på att havsförsurning skedde i Lorüns. Särskilt påverkade av detta var syrakänsliga organismer. Havsvattnet var syresatt under hela återhämtningsfasen efter utdöendet. Under tidig hettang rådde syrefattiga förhållanden i sedimenten, vilket kan förklaras genom förlusten av bioturbation på grund av att infaunan dog ut. Vittringsproxys som Si, Al och Ti indikerar att vittringen minskade under hela hettang. Detta kan bero på att havsnivån steg, att avståndet till det siliciklastiska källområdet ökade eller på grund av att klimatet blev mindre fuktigt och varmt efter de extrema växthusförhållandena orsakade av vulkanism i samband med massutdöendet. I motsats till modellerna från Hardie (1996) och Stanley & Hardie (1998), som föreslog ett aragonitiskt hav i sen trias och tidig jura, var havet låg-Mg kalcitiskt i de sen-rätiska till tidig-hettangiska Schattwaldlagren och Lorünsooliten. Trias-jura gränsavlagringar från Förenade Arabemiraten visar också på ett låg-Mg kalcitiskt hav vilket tyder på att förhållandena i Lorüns var globala eller åtminstone förekommande över hela Tethyshavet. Övergången från ett aragonitiskt till kalcitiskt hav kan därför ha skett tidigare än vad man har trott tidigare. (Less)
Please use this url to cite or link to this publication:
author
Brakebusch, Linus LU
supervisor
organization
course
GEOR02 20222
year
type
H2 - Master's Degree (Two Years)
subject
keywords
sedimentology, geochemistry, ooids, oolites, oncoids, oncolites, Triassic, Jurassic, Rhaetian, Hettangian, ocean acidification
publication/series
Dissertations in Geology at Lund University
report number
645
language
English
id
9103603
date added to LUP
2022-11-28 15:17:25
date last changed
2022-11-29 10:41:26
@misc{9103603,
  abstract     = {{The end-Triassic mass extinction (ETE) was one of the five big mass extinctions of the Phanerozoic and occurred ~201 Ma ago. Research agrees that the main triggering factor for the ETE was the eruptions of the Central Atlantic Magmatic Volcanic Province (CAMP), linked to the break-up of the supercontinent Pangaea. The large amounts of CO2 and SO2 released from the volcanic eruptions had a series of consequences such as climatic changes and ocean acidification, all possibly contributing to an extinction of a large number of taxa in the marine and terrestrial realm.

The Lorüns section constitutes a shallow-marine carbonate succession located in the Northern Calcareous Alps (NCA), Austria, and is a key section for studying the ETE because it records continuous sedimentation from the late Rhaetian to the Sinemurian. In this study, the Rhaetian Kössen Formation, the Schattwald Beds, and the Hettangian Lorüns oolite have been petrographically analysed. Geochemical analyses with laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) were also performed, mainly on the recovery facies from the Lorüns oolite. This study aims to offer a detailed description of the geological, geochemical and palaeoenvironmental conditions at Lorüns in the aftermath of the ETE and to compare the results with other Triassic-Jurassic boundary sections around the world.

The lack of calcareous fossils and the deposition of the siliciclastic Schattwald Beds during the “Extinction interval” together with the formation of coated grains in the post-extinction Lorüns oolite indicate that ocean acidification occurred in this area, especially affecting acid-sensitive organisms. Seawater was oxygenated during the early Hettangian. However, dysoxia occurred in the sediments during this period and is ascribed to the loss of biogenic sediment mixing due to the extinction of infaunal taxa. Analysis of the weathering proxies Si, Al, and Ti shows that weathering decreased continuously during the Hettangian. This could be explained by the marine transgression in the Lorüns area, a greater distance to the siliciclastic input zone, or because of a shift towards a less humid and hot climate after the extreme greenhouse conditions caused by volcanism around the ETE. Contrarily to the models from Hardie (1996) and Stanley & Hardie (1998), who propose an “aragonite” sea in the Late Triassic and Early Jurassic, the sea was found to be low-Mg calcitic at the time of deposition of the Schattwald Beds and Lorüns oolite. Triassic-Jurassic boundary sections in the Arab Emirates also imply a low-Mg calcitic sea, suggesting that the signal recorded at Lorüns was global, or at least Tethys-wide. Hence, the shift from an “aragonite” to “calcite” sea might have occurred earlier than previously believed.}},
  author       = {{Brakebusch, Linus}},
  language     = {{eng}},
  note         = {{Student Paper}},
  series       = {{Dissertations in Geology at Lund University}},
  title        = {{Record of the end-Triassic mass extinction in shallow marine carbonates: the Lorüns section (Austria)}},
  year         = {{2022}},
}