Late Quaternary Climatic Oscillations are known to be intense, and in some cases too rapid to be resolved reliably using a radiocarbon chronology. Tephrochronology, the use of widespread and isochronous layers of volcanic ash is increasingly seen as a valuable tool in the inter-environmental correlation of proxy- palaeonclimatic indicators. A fundamental assumption that underpins tephrochronology in the North Atlantic is the acceptance that tephra horizons can be fingerprinted uniquely, by the major/minor element compositions of their vitric shards. This thesis concentrates on the analytical (Electron Probe Microanalysis) methodology required in the accurate and precise determination of this fingerprint, on factors which inhibit successful correlation using such fingerprints and on the application of geochemical signatures to the establishment of a meaningful regional tephrochronology. In addition, studies of tephra deposition and re-mobilisation have also been undertaken following the 1991 eruption of Hekla, with results indicating the need for caution in interpreting mass-loading and mapping of tephra isochrons. The principal tephrostratigraphy within this thesis relates to the Late Glacial and early Holocene, and is used in an attempt to achieve correlations between marine, terrestrial and ice-sheet environments. At least seven tephra isochrons are shown to be present in the North Atlantic region in the interval <I>ca. </I>14,000 <SUP>14</SUP>C yrs BP to <I>ca. </I>9,000 <SUP>14</SUP>C yrs BP, with one interpretation of evidence from the UK continental shelf suggestive of further horizons. Rigorous investigation of these tephras has revealed the potential inadequacies of major elements as unambiguous indices in the correlation and differentiation of Iceland-derived tephras. This is summarised by the term "geochemical equifinality", associated with higher eruption frequencies of known individual volcanic centres than previously recognised. It is apparent that, (i) geochemical data must be supplemented by more rigorous investigations of stratigraphical context; and (ii) new analytical techniques must be applied to the characterisation of potential trace elements signatures.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:652723 |
| Date | January 1996 |
| Creators | Hunt, Jonathan Brewster |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/12096 |
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