Comment on “Some numerical considerations in the geochemical analysis of distal microtephra” by A.M. Pollard, S.P.E. Blockley and C.S. Lane

Pearce, Nick; Bendall, Charles A.; Westgate, John A.

doi:10.1016/j.apgeochem.2008.01.002

Cited by 43 publications

(51 citation statements)

References 23 publications

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“…comm., 2010). On the other hand, others have maintained that normalization is essential (e.g., Stokes et al, 1992;Shane, 2000;Pearce et al, 2008a) because it results in consistent elemental abundances, suggesting that the water is accommodated within the glass structure without chemical alteration (Shane, 2000). Also, discriminant function analysis undertaken by Stokes et al (1992) showed that such normalization provides statistically valid results.…”

Section: Electron Probe Microanalysis Of Glassmentioning

confidence: 99%

“…There is no consensus as to the optimum specific elements for SC calculations (Froggatt, 1992;Stokes et al, 1992;Hillenbrand et al, 2008). Consequently, various multivariate statistical methods have been applied including Euclidian distance analysis (which involves analysis of means), statistical distance analysis (which involves analysis of means and standard deviations), cluster analysis, ttest comparisons of means, discriminant function analysis (DFA), and principal components analysis (PCA) (Preece et al, 2000, in press;Keenan, 2003;Pollar et al, 2006;Kurbatov et al, 2006;Lowe et al, 2007;Pearce et al, 2007Pearce et al, , 2008aHillenbrand et al, 2008;Turner et al, 2009). …”

Section: Numerical and Statistical Techniquesmentioning

confidence: 99%

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Tephrochronology and its application: A review

Lowe

2011

Quaternary Geochronology

642

535

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Tephrochronology (from tephra, Gk "ashes") is a unique stratigraphic method for linking, dating, and synchronizing geological, palaeoenvironmental, or archaeological sequences or events. As well as utilizing the Law of Superposition, tephrochronology in practise requires tephra deposits to be characterized (or "fingerprinted") using physical properties evident in the field together with those obtained from laboratory analyses. Such analyses include mineralogical examination (petrography) or geochemical analysis of glass shards or crystals using an electron microprobe or other analytical tools including laser-ablation-based mass spectrometry or the ion microprobe. The palaeoenvironmental or archaeological context in which a tephra occurs may also be useful for correlational purposes. Tephrochronology provides greatest utility when a numerical age obtained for a tephra or cryptotephra is transferrable from one site to another using stratigraphy and by comparing and matching inherent compositional features of the deposits with a high degree of likelihood. Used this way, tephrochronology is an age-equivalent dating method that provides an exceptionally precise volcanic-event stratigraphy. Such age transfers are valid because the primary tephra deposits from an eruption essentially have the same short-lived age everywhere they occur, forming isochrons very soon after the eruption (normally within a year).As well as providing isochrons for palaeoenvironmental and archaeological reconstructions, tephras through their geochemical analysis allow insight into volcanic and magmatic processes, and provide a comprehensive record of explosive volcanism and recurrence rates in the Quaternary (or earlier) that can be used to establish time-space relationships of relevance to volcanic hazard analysis.The basis and application of tephrochronology as a central stratigraphic and geochronological tool for Quaternary studies are presented and discussed in this review. Topics covered include principles of tephrochronology, defining isochrons, tephra nomenclature, mapping and correlating tephras from proximal to distal locations at metre-through to sub-3 millimetre-scale, cryptotephras, mineralogical and geochemical fingerprinting methods, numerical and statistical correlation techniques, and developments and applications in dating including the use of flexible depositional age-modelling techniques based on Bayesian statistics.Along with reference to wide-ranging examples and the identification of important recent advances in tephrochronology, such as the development of new geoanalytical approaches that enable individual small glass shards to be analysed near-routinely for major, trace, and rare-earth elements, potential problems such as miscorrelation, erroneous-age transfer, and tephra reworking and taphonomy (especially relating to cryptotephras) are also examined. Some of the challenges for future tephrochronological studies include refining geochemical analytical methods further, improving understanding of cryptotephra dis...

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Section: Electron Probe Microanalysis Of Glassmentioning

confidence: 99%

Section: Numerical and Statistical Techniquesmentioning

confidence: 99%

Tephrochronology and its application: A review

Lowe

2011

Quaternary Geochronology

642

535

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“…Whilst it has been suggested data with oxide totals of less than 95% should be omitted from analyses (Hunt and Hill, 1993), totals exceeding this are not always consistently obtainable, owing frequently to the primary magmatic and/or post-depositional hydration of shards (Pearce et al 2008) and lower minimum oxide totals (e.g. ≥93%, Eiríksson et al, 2000, Bergman et al, 2004 have been imposed.…”

mentioning

confidence: 99%

Was there a ‘4.2 ka event’ in Great Britain and Ireland? Evidence from the peatland record

Roland

Caseldine

Charman

et al. 2014

Quaternary Science Reviews

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palaeohydrological proxy data generated during this study (peat humification, plant macrofossil and testate amoebae analyses) supported by a high-resolution chronology (including comprehensive AMS 14 C and tephrochronology). The inter-site testate amoebae reconstructions appear coherent and were combined to produce a regional climatic record, in marked contrast to the plant macrofossil and peat 20 humification records that appear climatically complacent. The testate amoebae reconstruction, however, provides no compelling evidence for a 4.2 kyr event signal and is consistent with previously reported studies from across northwest Europe, suggesting the origin and impact of this event is spatially complex.

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“…Prior probabilities were weighted proportionately due to group size differences within our sample. Untransformed data are used here due to the higher posterior probabilities of group membership relative to data transformed by normalization or the centered log ratio method of Aitchison (1986), the latter used in some provenance studies based on geochemical data with varying degrees of success (see discussions in Stokes et al, 1992;Baxter et al, 2005;Pearce et al, 2008;Pollard et al, 2006). This classificatory model was used to assign distal tephra deposits from archaeological sites to one of the volcanic sources or eruptive phases within the reference set: Erciyes Dağ, Hasan Dağ, Göllü Dağ, or the syn-caldera or post-caldera deposits from Acigöl.…”

Section: Multivariate Statistical Methodsmentioning

confidence: 99%

“…Because of minimal intragrain variation and to facilitate multivariate analyses of the data, each grain is characterized by the average value for each element oxide. The dataset was further culled by removing analyses with analytical totals < 90%, following the range of acceptable values noted by Froggatt (1992; see also Pearce et al, 2008). Data are not normalized except where required for comparison with whole-rock analyses (e.g., when plotted on the total-alkali-silica diagram), in part because of some of the unwarranted assumptions this makes about the parent magma, but more importantly because such treatment of the data has little to no effect on the discriminant analyses used here (see discussions in Brown et al, 1992;Hunt and Hill, 1993;Charman and Grattan, 1999;Pearce et al, 2007).…”

Section: Data Reductionmentioning

confidence: 99%