A new and less destructive laboratory procedure for the physical separation of distal glass tephra shards from sediments

S P E Blockley, S D F Pyne-O'Donnell, J J Lowe, I P Matthews, A Stone, A M Pollard, C S M Turney, Elizabeth Molyneux

Research output: Contribution to journalArticle

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Abstract

Tephrochronology, a key tool in the correlation of Quaternary sequences, relies on the extraction of tephra shards from sediments for visual identification and high-precision geochemical comparison. A prerequisite for the reliable correlation of tephra layers is that the geochemical composition of glass shards remains unaltered by natural processes (e.g. chemical exchange in the sedimentary environment) and/or by laboratory analytical procedures. However, natural glasses, particularly when in the form of small shards with a high surface to volume ratio, are prone to chemical alteration in both acidic and basic environments. Current techniques for the extraction of distal tephra from sediments involve the 'cleaning' of samples in precisely such environments and at elevated temperatures. The acid phase of the 'cleaning' process risks alteration of the geochemical signature of the shards, while the basic phase leads to considerable sample loss through dissolution of the silica network. Here, we illustrate the degree of alteration and loss to which distal tephras may be prone, and introduce a less destructive procedure for their extraction. This method is based on stepped heavy liquid flotation and which results in samples of sufficient quality for analysis while preserving their geochemical integrity. In trials, this method out-performed chemical extraction procedures in terms of the number of shards recovered and has resulted in the detection of new tephra layers with low shard concentrations. The implications of this study are highly significant because (i) the current database of distal tephra records and their corresponding geochemical signatures may require refinement and (ii) the record of distal tephras may be incomplete due to sample loss induced by corrosive laboratory procedures. It is therefore vital that less corrosive laboratory procedures are developed to make the detection and classification of distal glass tephra more secure. (c) 2005 Elsevier Ltd. All rights reserved.

Original languageEnglish
Pages (from-to)1952-1960
Number of pages9
JournalQuaternary Science Reviews
Volume24
Issue number16-17
Early online date31 Mar 2005
DOIs
Publication statusPublished - Sep 2005

Keywords

  • vedde ash
  • early Holocene
  • radiocarbon
  • Scotland
  • microtephra
  • stability
  • precision
  • protocol
  • Europe
  • Sweden

Cite this

Blockley, S. P. E., Pyne-O'Donnell, S. D. F., Lowe, J. J., Matthews, I. P., Stone, A., Pollard, A. M., ... Molyneux, E. (2005). A new and less destructive laboratory procedure for the physical separation of distal glass tephra shards from sediments. Quaternary Science Reviews, 24(16-17), 1952-1960. https://doi.org/10.1016/j.quascirev.2004.12.008

A new and less destructive laboratory procedure for the physical separation of distal glass tephra shards from sediments. / Blockley, S P E ; Pyne-O'Donnell, S D F ; Lowe, J J ; Matthews, I P ; Stone, A ; Pollard, A M ; Turney, C S M ; Molyneux, Elizabeth.

In: Quaternary Science Reviews, Vol. 24, No. 16-17, 09.2005, p. 1952-1960.

Research output: Contribution to journalArticle

Blockley, SPE, Pyne-O'Donnell, SDF, Lowe, JJ, Matthews, IP, Stone, A, Pollard, AM, Turney, CSM & Molyneux, E 2005, 'A new and less destructive laboratory procedure for the physical separation of distal glass tephra shards from sediments', Quaternary Science Reviews, vol. 24, no. 16-17, pp. 1952-1960. https://doi.org/10.1016/j.quascirev.2004.12.008
Blockley, S P E ; Pyne-O'Donnell, S D F ; Lowe, J J ; Matthews, I P ; Stone, A ; Pollard, A M ; Turney, C S M ; Molyneux, Elizabeth. / A new and less destructive laboratory procedure for the physical separation of distal glass tephra shards from sediments. In: Quaternary Science Reviews. 2005 ; Vol. 24, No. 16-17. pp. 1952-1960.
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AU - Pyne-O'Donnell, S D F

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AU - Matthews, I P

AU - Stone, A

AU - Pollard, A M

AU - Turney, C S M

AU - Molyneux, Elizabeth

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N2 - Tephrochronology, a key tool in the correlation of Quaternary sequences, relies on the extraction of tephra shards from sediments for visual identification and high-precision geochemical comparison. A prerequisite for the reliable correlation of tephra layers is that the geochemical composition of glass shards remains unaltered by natural processes (e.g. chemical exchange in the sedimentary environment) and/or by laboratory analytical procedures. However, natural glasses, particularly when in the form of small shards with a high surface to volume ratio, are prone to chemical alteration in both acidic and basic environments. Current techniques for the extraction of distal tephra from sediments involve the 'cleaning' of samples in precisely such environments and at elevated temperatures. The acid phase of the 'cleaning' process risks alteration of the geochemical signature of the shards, while the basic phase leads to considerable sample loss through dissolution of the silica network. Here, we illustrate the degree of alteration and loss to which distal tephras may be prone, and introduce a less destructive procedure for their extraction. This method is based on stepped heavy liquid flotation and which results in samples of sufficient quality for analysis while preserving their geochemical integrity. In trials, this method out-performed chemical extraction procedures in terms of the number of shards recovered and has resulted in the detection of new tephra layers with low shard concentrations. The implications of this study are highly significant because (i) the current database of distal tephra records and their corresponding geochemical signatures may require refinement and (ii) the record of distal tephras may be incomplete due to sample loss induced by corrosive laboratory procedures. It is therefore vital that less corrosive laboratory procedures are developed to make the detection and classification of distal glass tephra more secure. (c) 2005 Elsevier Ltd. All rights reserved.

AB - Tephrochronology, a key tool in the correlation of Quaternary sequences, relies on the extraction of tephra shards from sediments for visual identification and high-precision geochemical comparison. A prerequisite for the reliable correlation of tephra layers is that the geochemical composition of glass shards remains unaltered by natural processes (e.g. chemical exchange in the sedimentary environment) and/or by laboratory analytical procedures. However, natural glasses, particularly when in the form of small shards with a high surface to volume ratio, are prone to chemical alteration in both acidic and basic environments. Current techniques for the extraction of distal tephra from sediments involve the 'cleaning' of samples in precisely such environments and at elevated temperatures. The acid phase of the 'cleaning' process risks alteration of the geochemical signature of the shards, while the basic phase leads to considerable sample loss through dissolution of the silica network. Here, we illustrate the degree of alteration and loss to which distal tephras may be prone, and introduce a less destructive procedure for their extraction. This method is based on stepped heavy liquid flotation and which results in samples of sufficient quality for analysis while preserving their geochemical integrity. In trials, this method out-performed chemical extraction procedures in terms of the number of shards recovered and has resulted in the detection of new tephra layers with low shard concentrations. The implications of this study are highly significant because (i) the current database of distal tephra records and their corresponding geochemical signatures may require refinement and (ii) the record of distal tephras may be incomplete due to sample loss induced by corrosive laboratory procedures. It is therefore vital that less corrosive laboratory procedures are developed to make the detection and classification of distal glass tephra more secure. (c) 2005 Elsevier Ltd. All rights reserved.

KW - vedde ash

KW - early Holocene

KW - radiocarbon

KW - Scotland

KW - microtephra

KW - stability

KW - precision

KW - protocol

KW - Europe

KW - Sweden

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VL - 24

SP - 1952

EP - 1960

JO - Quaternary Science Reviews

JF - Quaternary Science Reviews

SN - 0277-3791

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ER -