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Paleomagnetic dating of a mysterious lake record from the Kerguelen archipelago by matching to paleomagnetic field models

Teilmann, Kim LU (2016) In Dissertations in Geology at Lund University GEOL01 20161
Department of Geology
Abstract (Swedish)
Kerguelenöarna är en vulkanisk ögrupp belägen i det södra Indiska oceanen. Öarna ligger på polarfronten samt inom den cirkumpolära Antarktiska strömmen och södra halvklotets västvindsbälte. Detta gör Kerguelenöarna till en intressant plats för klimatstudier. Av denna anledning erhölls en tre meter lång sekvens av sediment från en sjö på ögruppen 2013. Kol-14 datering av sjösedimenten gav ett gåtfullt resultat med förekomst av flera åldersomkastningar. Denna studie syftar till att förbättra förståelsen av sedimentens kronologi genom att skapa en ålders-djup-modell baserad på jämförelse av sedimentens karakteristiska remanenta magnetisering med de pa-leomagnetiska modellerna pfm9k.1a och A_FM.
Avmagnetisering av 153 prover med alternerande... (More)
Kerguelenöarna är en vulkanisk ögrupp belägen i det södra Indiska oceanen. Öarna ligger på polarfronten samt inom den cirkumpolära Antarktiska strömmen och södra halvklotets västvindsbälte. Detta gör Kerguelenöarna till en intressant plats för klimatstudier. Av denna anledning erhölls en tre meter lång sekvens av sediment från en sjö på ögruppen 2013. Kol-14 datering av sjösedimenten gav ett gåtfullt resultat med förekomst av flera åldersomkastningar. Denna studie syftar till att förbättra förståelsen av sedimentens kronologi genom att skapa en ålders-djup-modell baserad på jämförelse av sedimentens karakteristiska remanenta magnetisering med de pa-leomagnetiska modellerna pfm9k.1a och A_FM.
Avmagnetisering av 153 prover med alternerande fält upp till 80 mT avslöjade en viskös komponent som av-lägsnades efter avmagnetiseringssteg på 10 till 15 mT. Undersökning av sedimentstratigrafin och den karaktärist-iska remanenta magnetiseringen tyder på att delar av sekvensen har avsatts i samband med massflöden. Deklinat-ionen och inklinationen i de sedimenten som antas vara in situ uppvisar likheter med A_FM, och en simpel ålders-djup-modell för den nedre halvan av sekvensen har konstruerats genom korrelation av utmärkande deklinations- och inklinationshändelser.
Den etablerade ålders-djup-modellen visar skillnader på upp till ett par hundra år jämfört med kol-14 date-ringarna. Avvikelserna kan möjligvis förklaras av begränsningar av de paleomagnetiska modellerna, eftersom dessa huvudsakligen är baserade på paleomagnetisk data från norra halvklotet, men svårigheter vid tolkningen av sedi-mentetstratigrafin kan också vara en medverkande faktor. Ytterligare kol-14-dateringar av strategiskt utvalda delar av sedimentsekvensen rekommenderad för att förbättra förståelsen av kronologin. (Less)
Abstract
The Kerguelen archipelago is a volcanic island group in the southern Indian Ocean. It is located on the polar front as well as within the Circumpolar Antarctic Current and the Southern Hemisphere Westerly Wind Belt. This makes it an interesting location for paleoclimate studies. For this reason, a three meter long sediment sequence from a lake on the archipelago was retrieved in 2013. Radiocarbon dating of the lake record revealed a puzzling result with the occurrence of several age reversals. This study aims at improving the understanding of the chronology of the sequence by establishing an age-depth model based on comparison of the characteristic remanent magnetization of the sediment with the pfm9k.1a and A_FM paleomagnetic models.
... (More)
The Kerguelen archipelago is a volcanic island group in the southern Indian Ocean. It is located on the polar front as well as within the Circumpolar Antarctic Current and the Southern Hemisphere Westerly Wind Belt. This makes it an interesting location for paleoclimate studies. For this reason, a three meter long sediment sequence from a lake on the archipelago was retrieved in 2013. Radiocarbon dating of the lake record revealed a puzzling result with the occurrence of several age reversals. This study aims at improving the understanding of the chronology of the sequence by establishing an age-depth model based on comparison of the characteristic remanent magnetization of the sediment with the pfm9k.1a and A_FM paleomagnetic models.
Alternating field demagnetization up to 80 mT applied to 153 discrete samples revealed the presence of a viscous component that was removed after demagnetization steps of 10 to 15 mT. Investigation of the sediment stra-tigraphy and the characteristic remanent magnetization indicates that part of the lake sequence consists of slump deposits. The declination and inclination of the sediment presumed to be in situ shows similarities with the A_FM model, and a simple age-depth model for the lower half of the sequence has been constructed by correlation of inclination and declination features.
The established age-depth model shows discrepancies of up to a couple of hundred years when compared with the radiocarbon dates. The discrepancies might be explained by limitations of the paleomagnetic models, as these are mainly based on paleomagnetic data from the northern hemisphere, but difficulties in the interpretation of the sediment stratigraphy might play a role as well. Radiocarbon dating of samples from a few identified key horizons is suggested to improve the understanding of the chronology of the sediment sequence. (Less)
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author
Teilmann, Kim LU
supervisor
organization
course
GEOL01 20161
year
type
M2 - Bachelor Degree
subject
keywords
lake sediment, Kerguelen archipelago, paleomagnetic secular variation, paleomagnetism, paleomagnetic field models, slump deposits
publication/series
Dissertations in Geology at Lund University
report number
480
language
English
id
8879217
date added to LUP
2016-06-09 14:37:03
date last changed
2016-06-09 14:37:03
@misc{8879217,
  abstract     = {The Kerguelen archipelago is a volcanic island group in the southern Indian Ocean. It is located on the polar front as well as within the Circumpolar Antarctic Current and the Southern Hemisphere Westerly Wind Belt. This makes it an interesting location for paleoclimate studies. For this reason, a three meter long sediment sequence from a lake on the archipelago was retrieved in 2013. Radiocarbon dating of the lake record revealed a puzzling result with the occurrence of several age reversals. This study aims at improving the understanding of the chronology of the sequence by establishing an age-depth model based on comparison of the characteristic remanent magnetization of the sediment with the pfm9k.1a and A_FM paleomagnetic models.
Alternating field demagnetization up to 80 mT applied to 153 discrete samples revealed the presence of a viscous component that was removed after demagnetization steps of 10 to 15 mT. Investigation of the sediment stra-tigraphy and the characteristic remanent magnetization indicates that part of the lake sequence consists of slump deposits. The declination and inclination of the sediment presumed to be in situ shows similarities with the A_FM model, and a simple age-depth model for the lower half of the sequence has been constructed by correlation of inclination and declination features.
The established age-depth model shows discrepancies of up to a couple of hundred years when compared with the radiocarbon dates. The discrepancies might be explained by limitations of the paleomagnetic models, as these are mainly based on paleomagnetic data from the northern hemisphere, but difficulties in the interpretation of the sediment stratigraphy might play a role as well. Radiocarbon dating of samples from a few identified key horizons is suggested to improve the understanding of the chronology of the sediment sequence.},
  author       = {Teilmann, Kim},
  keyword      = {lake sediment,Kerguelen archipelago,paleomagnetic secular variation,paleomagnetism,paleomagnetic field models,slump deposits},
  language     = {eng},
  note         = {Student Paper},
  series       = {Dissertations in Geology at Lund University},
  title        = {Paleomagnetic dating of a mysterious lake record from the Kerguelen archipelago by matching to paleomagnetic field models},
  year         = {2016},
}