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Tephrochronological Studies in Scotland and Sweden
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. (Kvartärgeologi)
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The study of palaeoclimates, especially the rapid climate changes during the Last Glacial-Interglacial Transition (LGIT ca. 15-8 ka BP), requires precise dating as well as the ability to link climate records over large regional areas. As has recently been demonstrated by the Eyjafjallajökull eruption, volcanic ash (tephra) has the possibility of a widespread geographical distribution which for geological purposes is instantaneous. Tephrochronology, the study of volcanic ash as a geochronological method, has over the past few decades developed methods to identify distal cryptotephras, tephras invisible to the naked eye. This has expanded the number of maker horizons as well as the areas in which they can be found. The studies presented here expand the geographical extent of one marker horizon, the Hässeldalen Tephra, in Southern Sweden. At the same time, some of the problems of the method are examined. The method builds on horizons being distinct and geochemically fingerprinted. The Borrobol Tephra has been found in Scotland and Sweden but with widely differing dates leading to the possibility of there actually being two geochemically identical horizons in close stratigraphic proximity. The present studies provide new results from the original type-site as well as reanalysis of the geochemistry of shards from the first Swedish findings. The major element analysis used here reflects improvements in Electron Probe Microanalysis (EPMA) settings which provides more robust data with slightly altered values from those previously published. These altered values must be taken into account when making inter-site comparisons. Trace element data for the Borrobol type-site and for the two original Swedish sites are also published. Results remain inconclusive as no differences were found between the Swedish and Scottish horizons. Even some problems with confusing the Hässeldalen Tephra with another horizon, the Askja-S Tephra, in Swedish sites are considered. 

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography and Quaternary Geology, Stockholm University , 2013. , 19 p.
National Category
Geology
Research subject
Geology
Identifiers
URN: urn:nbn:se:su:diva-90039OAI: oai:DiVA.org:su-90039DiVA: diva2:622164
Presentation
2013-06-10, De Geer-salen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 10:15 (English)
Opponent
Supervisors
Available from: 2013-05-22 Created: 2013-05-20 Last updated: 2013-05-23Bibliographically approved
List of papers
1. A Lateglacial-early Holocene tephrochronology for SW Sweden
Open this publication in new window or tab >>A Lateglacial-early Holocene tephrochronology for SW Sweden
2013 (English)In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 42, no 3, 544-554 p.Article in journal (Refereed) Published
Abstract [en]

Four cores from southwestern Sweden are presented together with their tephra geochemistry. Two cryptotephra horizons were confirmed geochemically in the cores, the Vedde Ash and the Hässeldalen Tephra. The Lateglacial Hässeldalen Tephra (11 360–11 300 cal. a BP) offers great potential as a regional isochrone to add a new degree of certainty to the deglaciation chronology of southern Sweden, including the extent of glacial Lake Bolmen. In addition, the geographical distribution of the Hässeldalen Tephra has recently been extended outside of Sweden, making it an important time-marker horizon in northern Europe. There are potential difficulties, however. Proper identification of the actual isochrone is complicated by the vertical pattern of shard distribution, which could be the result of several eruptive events, as well as by the fact that shards from the 10-ka Askja horizon (10 500–10 350 cal. a BP) were found in close stratigraphical proximity. The geochemical data presented are the result of improved EPMA methodology, which significantly reduces sodium mobilization. The results therefore have slightly altered values, which has consequences for classifying new finds when they are compared with previous data for geochemically similar tephras. Finally, potential indications of the Borrobol/Penifiler horizon are presented, although the existence of the horizon could not be confirmed geochemically. This highlights the need to retrieve cores from different locations within a basin based on an analysis of basin morphology if horizons are to be located.

National Category
Geology Physical Geography
Identifiers
urn:nbn:se:su:diva-90103 (URN)10.1111/j.1502-3885.2012.00296.x (DOI)000320782800005 ()
Available from: 2013-05-22 Created: 2013-05-22 Last updated: 2017-12-06Bibliographically approved
2. Revisiting the Borrobol Tephra
Open this publication in new window or tab >>Revisiting the Borrobol Tephra
(English)Manuscript (preprint) (Other academic)
Abstract [en]

New results are presented from the Borrobol type-site, northern Scotland, as well as from the two Swedish sites, Hässeldala port and Skallahult, where a Borrobol-like horizon has previously been found. New major element geochemistry data is reported reflecting improved EPMA (Electron Probe Micro-analysis) methodologies. These newer methodologies slightly alter the geochemistry which should be considered when making comparisons between sites. Trace element data is also presented for the Borrobol-like horizons found in Sweden and the Borrobol site. Initial findings indicate that there is no difference between the trace element geochemistry of the Swedish sites and the Scottish Borrobol horizon

National Category
Geology
Identifiers
urn:nbn:se:su:diva-90104 (URN)
Available from: 2013-05-22 Created: 2013-05-22 Last updated: 2013-05-23

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