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An interpretation of oncoid mass-occurrence during the Late Silurian Lau Event, Gotland, Sweden

Qvarnström, Martin LU (2012) In Dissertations in Geology at Lund University GEOL01 20122
Department of Geology
Abstract
The geological significance of the microbial-formed oncoid is not as well understood as the recognized, analogous stromatolite but can, as well be used as an environmental indicator. In association with the larger Phanerozoic mass extinctions, a resurgence of microbialites as a disaster fauna is at present an accepted view. The same model, however, is under debate concerning whether or not it can be applied to minor extinction events such as the Lau Event, a coupled extinction-isotopic event recorded from Late Silurian. The Lau Event displays one of the largest positive carbon isotope excursions (CIE) during the entire Phanerozoic with detrimental effects on various marine fauna. The last appearance datum (LAD) of the conodont species P.... (More)
The geological significance of the microbial-formed oncoid is not as well understood as the recognized, analogous stromatolite but can, as well be used as an environmental indicator. In association with the larger Phanerozoic mass extinctions, a resurgence of microbialites as a disaster fauna is at present an accepted view. The same model, however, is under debate concerning whether or not it can be applied to minor extinction events such as the Lau Event, a coupled extinction-isotopic event recorded from Late Silurian. The Lau Event displays one of the largest positive carbon isotope excursions (CIE) during the entire Phanerozoic with detrimental effects on various marine fauna. The last appearance datum (LAD) of the conodont species P. siluricus in the uppermost Hemse Group on Gotland marks the commencement of the event and the superimposing Eke Formation is extremely rich in oncoids. To analyze the specific controlling determinants and the potential for oncoids as environmental indicators, I measured size and shape for over one hundred oncoids deriving from Gotland and Bjärsjölagård, Sweden. Thin sections and cross-sections of oncoids were produced and Rothpletzella was by far the most abundant calcimicrobe in oncoid cortex, often associated with Wetheredella. Results herein strengthen the theory of the mass abundant oncoids constituting an anachronistic facies. Furthermore, oncoid- shape and morphology are concluded herein to, with caution, be used as indicators of water energy which sets the deposition of the Eke Formation under a phase of transgression. (Less)
Abstract (Swedish)
Den geologiska signifikansen av onkoider, mikrobialiter uppbyggda av calcifierande mikroorganismer, är varken lika studerad eller vedertagen som för de likartade stromatoliterna. I samband med de större fanerozoiska utdöenderna är ett uppsving av dessa mikrobialiter ett accepterat bevis för en krisfauna vilken utgör ett anarchronistiskt facies. Desto mer omdebatterad är möjligheten att applicera denna modell även på mindre utdöenden som Lau Event, ett event kopplat till ett udöende samt till en av de största kolisotop anomalierna under hela Fanerozoikum. Utdöendet av konodonten P.siluricus markerar eventets början och den överlagrande Eke Formationen är väldigt rik i onkoider. För att analysera biologisk determinism och onkoidernas... (More)
Den geologiska signifikansen av onkoider, mikrobialiter uppbyggda av calcifierande mikroorganismer, är varken lika studerad eller vedertagen som för de likartade stromatoliterna. I samband med de större fanerozoiska utdöenderna är ett uppsving av dessa mikrobialiter ett accepterat bevis för en krisfauna vilken utgör ett anarchronistiskt facies. Desto mer omdebatterad är möjligheten att applicera denna modell även på mindre utdöenden som Lau Event, ett event kopplat till ett udöende samt till en av de största kolisotop anomalierna under hela Fanerozoikum. Utdöendet av konodonten P.siluricus markerar eventets början och den överlagrande Eke Formationen är väldigt rik i onkoider. För att analysera biologisk determinism och onkoidernas potential som miljöindikatorer har storlek och form på över hundra onkoider analyserats från södra Gotland och Bjärsjölagård i centrala Skåne. Ett representativt urval gjordes för vidare analys i form av bland annat genomskärning, isotopprov och tunnslipsframställning. Resultaten styrker teorin att onkoiderna utgör en krisfauna. Genom studier av tunnslip visas Rothpletzella vara den dominerande mikroorganismen i onkoidkortex. Fortsättningsvis, kontateras att onkoiders form och storlek är lämpliga parametrar för att i större utsträckning användas som indikatorer för vattenenergi. Detta sätter depositionen av Eke Formationen under en fas av trangression. (Less)
Please use this url to cite or link to this publication:
author
Qvarnström, Martin LU
supervisor
organization
alternative title
En redogörelse för massförekomsten av onkoider associerad till Lau Event, en ekologisk kris från sen Silur
course
GEOL01 20122
year
type
M2 - Bachelor Degree
subject
keywords
Bjärsjölagård, Gotland, microbialites, Silurian, Oncoids, Lau Event, ecological crisis, Onkoider, Silur, microbialiter, ekologisk kris
publication/series
Dissertations in Geology at Lund University
report number
326
language
English
id
3410111
date added to LUP
2013-01-25 13:14:16
date last changed
2013-01-25 13:14:16
@misc{3410111,
  abstract     = {The geological significance of the microbial-formed oncoid is not as well understood as the recognized, analogous stromatolite but can, as well be used as an environmental indicator. In association with the larger Phanerozoic mass extinctions, a resurgence of microbialites as a disaster fauna is at present an accepted view. The same model, however, is under debate concerning whether or not it can be applied to minor extinction events such as the Lau Event, a coupled extinction-isotopic event recorded from Late Silurian. The Lau Event displays one of the largest positive carbon isotope excursions (CIE) during the entire Phanerozoic with detrimental effects on various marine fauna. The last appearance datum (LAD) of the conodont species P. siluricus in the uppermost Hemse Group on Gotland marks the commencement of the event and the superimposing Eke Formation is extremely rich in oncoids. To analyze the specific controlling determinants and the potential for oncoids as environmental indicators, I measured size and shape for over one hundred oncoids deriving from Gotland and Bjärsjölagård, Sweden. Thin sections and cross-sections of oncoids were produced and Rothpletzella was by far the most abundant calcimicrobe in oncoid cortex, often associated with Wetheredella. Results herein strengthen the theory of the mass abundant oncoids constituting an anachronistic facies. Furthermore, oncoid- shape and morphology are concluded herein to, with caution, be used as indicators of water energy which sets the deposition of the Eke Formation under a phase of transgression.},
  author       = {Qvarnström, Martin},
  keyword      = {Bjärsjölagård,Gotland,microbialites,Silurian,Oncoids,Lau Event,ecological crisis,Onkoider,Silur,microbialiter,ekologisk kris},
  language     = {eng},
  note         = {Student Paper},
  series       = {Dissertations in Geology at Lund University},
  title        = {An interpretation of oncoid mass-occurrence during the Late Silurian Lau Event, Gotland, Sweden},
  year         = {2012},
}