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A sedimentological study on the formation of a hummocky moraine at Törnåkra in Småland, southern Sweden

Thorbergsson , Gunnlaugur Brjánn (2011) In Dissertations in Geology at Lund University
Department of Geology
Abstract
A detailed sedimentological study was made on a section along the side of a moraine hummock at Törnåkra in Småland, south Sweden. Two sedimentary units, A and B, were identified, based on their sediment characteristics. Unit A, the lower one, was formed due to vertical stacking of sediment gravity flow deposits (diamict beds) in combination with melt water disaggregation of such beds, leaving residual lags and redeposited sorted sediment beds. This stacked sequence was laid down into a depression or a low in stagnant/dead ice. Syn- and post-depositional deformation as indicated from folds, faults and injection structures were also identified in unit A. Unit B overlies unit A and was formed due to continued deposition of debris flows.... (More)
A detailed sedimentological study was made on a section along the side of a moraine hummock at Törnåkra in Småland, south Sweden. Two sedimentary units, A and B, were identified, based on their sediment characteristics. Unit A, the lower one, was formed due to vertical stacking of sediment gravity flow deposits (diamict beds) in combination with melt water disaggregation of such beds, leaving residual lags and redeposited sorted sediment beds. This stacked sequence was laid down into a depression or a low in stagnant/dead ice. Syn- and post-depositional deformation as indicated from folds, faults and injection structures were also identified in unit A. Unit B overlies unit A and was formed due to continued deposition of debris flows. However, this unit is distinct from unit A by its lack of sorted sediments, suggesting that the melt water activity had ceased in the late stage of depression infilling. The overall bed configuration in the investigated section suggests that this was in an ice-proximal location; the sediment beds were both syn- and post-depositionally tilted towards the direction of the lost ice support. The section thus shows the sediment composition at the edge of a moraine hummock, and the sediment composition and architecture here might thus differ from that of the interior part. (Less)
Abstract (Swedish)
En detaljerad sedimentologisk studie har gjorts på en sektion längs med en moränkulle vid Törnåkra i Småland, södra Sverige. Två sedimentära enheter, enheterna A och B, identifierades baserat på deras sedimentologiska särdrag. Den understa enheten (A) bildades genom vertikal pålagring av gravitationsdrivna sedimentflöden (diamiktona lager), kombinerat med att smältvatten dissaggregerade en stor del av dessa gravitations-sediment. Detta resulterade dels i bildandet av residualavlagringar, dels att de diamikta sedimenten omformades till sorterade sedimentära lager av växlande kornstorlek. Denna pålagringssekvens byggdes upp i en sänka i omgivande dödis. Veck- och förkastningsstrukturer samt brant stående sedimentinjektioner av finkorniga... (More)
En detaljerad sedimentologisk studie har gjorts på en sektion längs med en moränkulle vid Törnåkra i Småland, södra Sverige. Två sedimentära enheter, enheterna A och B, identifierades baserat på deras sedimentologiska särdrag. Den understa enheten (A) bildades genom vertikal pålagring av gravitationsdrivna sedimentflöden (diamiktona lager), kombinerat med att smältvatten dissaggregerade en stor del av dessa gravitations-sediment. Detta resulterade dels i bildandet av residualavlagringar, dels att de diamikta sedimenten omformades till sorterade sedimentära lager av växlande kornstorlek. Denna pålagringssekvens byggdes upp i en sänka i omgivande dödis. Veck- och förkastningsstrukturer samt brant stående sedimentinjektioner av finkorniga sediment i de primärt avsatta sedimenten indikerar att avsättningen av dessa skedde under successiv ned- och tillbakasmältning av den omkringliggande dödisen. Enhet B ligger ovanpå enhet A och bildades under mer enhetliga förhållanden med ihållande deponering av massrörelse-avsatta sediment. Enhet B skiljer sig således från enhet A genom frånvaron av sorterat sediment. Detta tyder på att smältvattenaktiviteten börjat avta för att helt sluta under den senare delen af sekvensens bildning. Som helhet visar den undersökta sektionen att sedimenten avsattes i nära kontakt med is; de sedimentära lagern har fått en lutning mot den riktning där isen gradvis smälte ner och sedimenten tappade därmed successivt sitt isstöd. Sektionen representerar den sedimentologiska sammansättning av en yttre del av en moränkulle bildad i en dödismiljö; sedimentsammansättningen och sedimentarkitekturen här kan därför förväntas avvika från densamma i en mer central position inom moränkullen, där kanske med ännu högre frekvens av sorterade sedimentbäddar och mindre frekvens av diamikta bäddar. (Less)
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author
Thorbergsson , Gunnlaugur Brjánn
supervisor
organization
alternative title
En sedimentologisk studie av bildningen av kulliga moränformer vid Törnåkra i Småland, södra Sverige
year
type
H2 - Master's Degree (Two Years)
subject
keywords
smältvatten, kullformad moränterräng, glaciär, diamikton, dödis, Törnåkra, melt water, hummocky moraine, glacier, diamict, dead ice
publication/series
Dissertations in Geology at Lund University
report number
286
language
English
id
2277931
date added to LUP
2012-01-09 11:24:06
date last changed
2012-01-09 11:24:06
@misc{2277931,
  abstract     = {A detailed sedimentological study was made on a section along the side of a moraine hummock at Törnåkra in Småland, south Sweden. Two sedimentary units, A and B, were identified, based on their sediment characteristics. Unit A, the lower one, was formed due to vertical stacking of sediment gravity flow deposits (diamict beds) in combination with melt water disaggregation of such beds, leaving residual lags and redeposited sorted sediment beds. This stacked sequence was laid down into a depression or a low in stagnant/dead ice. Syn- and post-depositional deformation as indicated from folds, faults and injection structures were also identified in unit A. Unit B overlies unit A and was formed due to continued deposition of debris flows. However, this unit is distinct from unit A by its lack of sorted sediments, suggesting that the melt water activity had ceased in the late stage of depression infilling. The overall bed configuration in the investigated section suggests that this was in an ice-proximal location; the sediment beds were both syn- and post-depositionally tilted towards the direction of the lost ice support. The section thus shows the sediment composition at the edge of a moraine hummock, and the sediment composition and architecture here might thus differ from that of the interior part.},
  author       = {Thorbergsson , Gunnlaugur Brjánn},
  keyword      = {smältvatten,kullformad moränterräng,glaciär,diamikton,dödis,Törnåkra,melt water,hummocky moraine,glacier,diamict,dead ice},
  language     = {eng},
  note         = {Student Paper},
  series       = {Dissertations in Geology at Lund University},
  title        = {A sedimentological study on the formation of a hummocky moraine at Törnåkra in Småland, southern Sweden},
  year         = {2011},
}