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Climate archives and the Late Ordovician Boda Event

Olsson, Håkan (2009) In Dissertations in Geology at Lund University
Department of Geology
Abstract
Climate change has become an increasingly important subject in geological research as past climates can
teach us about the global climate systems. This thesis is a literature study on natural climate archives with examples
from the Late Ordovician Boda Event. The Ordovician Period represented a greenhouse world with atmospheric
CO2 levels almost twenty times higher then today. The climate became cooler in the Late Ordovician and the period
was terminated by a global ice-age in the Hirnantian. Much of the studies of Ordovician climate have focused on
this glaciation. Recent studies have, however, revealed another drastic climatic change preceding the terminal Ordovician
glaciation. In the pre-Hirnantian (latest Katian) there was an... (More)
Climate change has become an increasingly important subject in geological research as past climates can
teach us about the global climate systems. This thesis is a literature study on natural climate archives with examples
from the Late Ordovician Boda Event. The Ordovician Period represented a greenhouse world with atmospheric
CO2 levels almost twenty times higher then today. The climate became cooler in the Late Ordovician and the period
was terminated by a global ice-age in the Hirnantian. Much of the studies of Ordovician climate have focused on
this glaciation. Recent studies have, however, revealed another drastic climatic change preceding the terminal Ordovician
glaciation. In the pre-Hirnantian (latest Katian) there was an episode of increased carbonate deposition
worldwide. Reefs and carbonate mud-mound developed in high latitudes in several areas that were previously associated
with siliciclastic sedimentation. There was a contemporaneous pole-ward migration of marine faunas, resulting
in a breakdown of climatically controlled endemism. These drastic changes have been termed as the Boda
Event by Fortey and Cocks (2005) who interpreted this as an episode of global warming. They argue that higher
ocean temperatures would allow carbonate producers to spread into higher latitudes. Cherns and Wheeley (2007) on
the other hand, suggested that the Boda Event represented a cooling event, resulting in lowering of global sea-level
and increased oceanic circulation and overturn. This would oxygenise bottom waters and allow carbonate production
and faunal migration. In this thesis the contradicting theories are evaluated and exemplified by the Swedish
Boda Limestone that formed during this time interval. (Less)
Abstract (Swedish)
Klimatförändringar har under de senaste decennierna blivit ett allt hetare forskningsämne och man har då även studerat hur klimatet förändrats genom årmiljonerna. Ett spännande kapitel i jordens historia är ordovicium som karaktäriserades som en växthusvärld med koldioxidhalter nära tjugo gånger dagens. Denna varma period avslutades med en global istid som resulterade i ett av de största massutdöendena i Jordens historia där över 80 % av alla arter dog ut. Mycket av klimatstudierna har fokuserat på denna del av ordovicium. Lika fascinerande är tidsavsnittet precis innan Hirnantian. Då skedde en klimatförändring som resulterade i uppkomsten av kalkstenar och rev världen över, t o m på höga latituder nära sydpolen, i dagens Nordafrika och... (More)
Klimatförändringar har under de senaste decennierna blivit ett allt hetare forskningsämne och man har då även studerat hur klimatet förändrats genom årmiljonerna. Ett spännande kapitel i jordens historia är ordovicium som karaktäriserades som en växthusvärld med koldioxidhalter nära tjugo gånger dagens. Denna varma period avslutades med en global istid som resulterade i ett av de största massutdöendena i Jordens historia där över 80 % av alla arter dog ut. Mycket av klimatstudierna har fokuserat på denna del av ordovicium. Lika fascinerande är tidsavsnittet precis innan Hirnantian. Då skedde en klimatförändring som resulterade i uppkomsten av kalkstenar och rev världen över, t o m på höga latituder nära sydpolen, i dagens Nordafrika och Sydeuropa. Även i Sverige, som vid denna tid låg precis söder om ekvatorn, hade vi flera revliknande miljöer i både Siljansområdet och på Gotland. Förutom ökad karbonatproduktion skedde en drastisk förändring i havens faunasammansätting. Faunor som dittills varit endemiska för enskilda regioner i låga latituder spreds plötsligt till höglatitudsområden. Den bakomliggande orsaken till dessa händelser var enligt Fortey och Cocks (2005) en global uppvärmning som höjde havets temperaturer nära sydpolen. De namngav detta som Boda Event. Cherns och Wheeley (2007) hävdade det motsatta, att det var en kall episod innan Hirnantian-glaciationen som genom ökad cirkulation och syresättning i haven globalt främjade artspridning och kalkavsättning. I detta arbete diskuteras de två teorierna, bl.a. med exempel från Bodakalkstenen i Siljansområdet. (Less)
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author
Olsson, Håkan
supervisor
organization
alternative title
Klimatarkiv och det sen-ordoviciska Boda Event
year
type
M2 - Bachelor Degree
subject
keywords
Climate, Boda Event, Late Ordovician, Siljan district, Carbonate mud-mounds, klimat, Siljanområdet, sen-ordovicium, rev
publication/series
Dissertations in Geology at Lund University
report number
244
language
English
id
2302131
date added to LUP
2012-01-25 15:00:30
date last changed
2012-01-25 15:00:30
@misc{2302131,
  abstract     = {Climate change has become an increasingly important subject in geological research as past climates can
teach us about the global climate systems. This thesis is a literature study on natural climate archives with examples
from the Late Ordovician Boda Event. The Ordovician Period represented a greenhouse world with atmospheric
CO2 levels almost twenty times higher then today. The climate became cooler in the Late Ordovician and the period
was terminated by a global ice-age in the Hirnantian. Much of the studies of Ordovician climate have focused on
this glaciation. Recent studies have, however, revealed another drastic climatic change preceding the terminal Ordovician
glaciation. In the pre-Hirnantian (latest Katian) there was an episode of increased carbonate deposition
worldwide. Reefs and carbonate mud-mound developed in high latitudes in several areas that were previously associated
with siliciclastic sedimentation. There was a contemporaneous pole-ward migration of marine faunas, resulting
in a breakdown of climatically controlled endemism. These drastic changes have been termed as the Boda
Event by Fortey and Cocks (2005) who interpreted this as an episode of global warming. They argue that higher
ocean temperatures would allow carbonate producers to spread into higher latitudes. Cherns and Wheeley (2007) on
the other hand, suggested that the Boda Event represented a cooling event, resulting in lowering of global sea-level
and increased oceanic circulation and overturn. This would oxygenise bottom waters and allow carbonate production
and faunal migration. In this thesis the contradicting theories are evaluated and exemplified by the Swedish
Boda Limestone that formed during this time interval.},
  author       = {Olsson, Håkan},
  keyword      = {Climate,Boda Event,Late Ordovician,Siljan district,Carbonate mud-mounds,klimat,Siljanområdet,sen-ordovicium,rev},
  language     = {eng},
  note         = {Student Paper},
  series       = {Dissertations in Geology at Lund University},
  title        = {Climate archives and the Late Ordovician Boda Event},
  year         = {2009},
}