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Title: Extending the known distributions of micro-tephra layers of the last glacial-interglacial transition age in Europe
Author: Davies, Siwan Manon.
Awarding Body: Royal Holloway, University of London
Current Institution: Royal Holloway, University of London
Date of Award: 2003
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A number of terrestrial stratigraphic sequences spanning the last glacial-interglacial transition from sites in Britain and continental Europe have been examined to assess the potential of tephrochronology as a precise correlation tool, and to contribute towards the construction of a tephrochronological framework for Europe. The distributions of four Icelandic tephras have been extended in Europe through the detection of micro-tephra horizons. These results include (i) the discovery of the Vedde Ash in the north-eastern Netherlands, (ii) the detection of the Borrobol Tephra and of the relatively unknown Askja 10.0 14Cka BP Tephra in south-eastern Sweden; and (iii) the discovery of the basaltic component of the Vedde Ash for the first time in two lake sequences in Britain, one being a visible horizon (I cm thick) and the other being a micro-tephra horizon. Potential areas in Europe that may have received tephras from more than one volcanic province are proposed based on the revised distributions of these tephras. Geochemical analyses by electron microprobe also point to the discovery of at least 4 previously undetected tephras, two of which are thought to have originated from the Icelandic volcanic province, while two are of unknown origin. Detailed investigations of one terrestrial site in the British Isles suggest that tephra horizons can be unevenly developed within lake basins, supporting the view that lake basin and catchment processes, as well as meteorological factors prevalent during tephra dispersal, influence the distribution and accumulation of tephra horizons. Methodological developments in detection techniques have enabled the extraction of a micro-tephra layer of basaltic geochemistry from minerogenic lake sediments, and experimentation with the determination of trace element composition of tephra samples by solution Inductively Coupled Plasma-Mass Spectrometry (lCP-MS) has highlighted a number of limitations associated with the analysis of very small samples. Recommendations for improved application of this technique in order to develop it as a diagnostic tool for the geochemical fingerprinting of tephra horizons are suggested. Results are also presented of investigations of micro-tephra horizons within the NordGRIP ice core (north of Greenland Summit). A possible total of six new tephra horizons have been detected. The geochemical results suggest that these shards may have originated from the Grimsvotn volcanic system (Iceland), although close similarity to the Saksunarvatn Ash, which has also been identified in this project, suggests the possibility of contamination within the filtration system employed. Recommendations for improvements to tephrochronological research in future work on the NordGRIP ice core are outlined.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available