5 results on '"Pearce, Nick"'
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2. Investigating the Secrets of Stonehenge with Raman Spectroscopy: Provenance of the Ancient Altar Stone.
- Author
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Andò, Sergio, Barbarano, Marta, Diniz, Jorge, Bevins, Richard E, and Pearce, Nick J G
- Subjects
RAMAN spectroscopy ,BUILDING stones ,RELICS - Abstract
In-field compositional analysis of large prehistoric relics, such as the Altar Stone at Stonehenge (England), is limited due to the size of the relics and difficulty in obtaining samples that can be analyzed in a laboratory. In this study, a portable Raman spectroscopy system was used to analyze the Altar Stone to help determine its origin and classification, which appears to differ from other bluestones at Stonehenge. While the study is ongoing and the definitive origin of the Altar Stone is not yet known, this study demonstrates the applicability of a portable Raman spectroscopy system in the compositional analysis of large samples in the field. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
3. Linking derived debitage to the Stonehenge Altar Stone using portable X-ray fluorescence analysis.
- Author
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Bevins, Richard E., Pearce, Nick J.G., Ixer, Rob A., Hillier, Stephen, Pirrie, Duncan, and Turner, Peter
- Subjects
- *
X-ray fluorescence , *X-ray spectroscopy , *RAINFALL , *PORE water - Abstract
The Altar Stone at Stonehenge in Wiltshire, UK, is enigmatic in that it differs markedly from the other bluestones. It is a grey–green, micaceous sandstone and has been considered to be derived from the Old Red Sandstone sequences of South Wales. Previous studies, however, have been based on presumed derived fragments (debitage) that have been identified visually as coming from the Altar Stone. Portable X-ray fluorescence (pXRF) analyses were conducted on these fragments (ex situ) as well as on the Altar Stone (in situ). Light elements (Z<37) in the Altar Stone analyses, performed after a night of heavy rain, were affected by surface and pore water that attenuate low energy X-rays, however the dry analyses of debitage fragments produced data for a full suite of elements. High Z elements, including Zr, Nb, Sr, Pb, Th and U, all occupy the same compositional space in the Altar Stone and debitage fragments, and are statistically indistinguishable, indicating the fragments are derived from the Altar Stone. Barium compares very closely between the debitage and Altar Stone, with differences being related to variable baryte distribution in the Altar Stone, limited accessibility of its surface for analysis, and probably to surface weathering. A notable feature of the Altar Stone sandstone is the presence of baryte (up to 0.8 modal%), manifest as relatively high Ba in both the debitage and the Altar Stone. These high Ba contents are in marked contrast with those in a small set of Old Red Sandstone field samples, analysed alongside the Altar Stone and debitage fragments, raising the possibility that the Altar Stone may not have been sourced from the Old Red Sandstone sequences of Wales. This high Ba 'fingerprint', related to the presence of baryte, may provide a rapid test using pXRF in the search for the source of the Stonehenge Altar Stone. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
4. Stonehenge rhyolitic bluestone sources and the application of zircon chemistry as a new tool for provenancing rhyolitic lithics
- Author
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Bevins, Richard E., Pearce, Nick J.G., and Ixer, Rob A.
- Subjects
- *
ZIRCON , *PETROLOGY , *RHYOLITE , *PRINCIPAL components analysis , *OUTCROPS (Geology) - Abstract
Abstract: The source of the bluestones at Stonehenge has long been debated, and while there is general consensus that the so-called spotted dolerites are derived from a relatively small number of outcrops exposed in the highest parts of Mynydd Preseli, in southwest Wales the source of the rhyolitic component has attracted relatively little detailed attention. This is largely because unlike the uniqueness of the spots in the coarser grained doleritic rocks, the rhyolites are fine-grained in character and lack any obvious distinctiveness, especially in hand specimen. This makes their provenancing difficult. A recent study, however, suggested that there was a close lithological similarity between the informally-termed ‘rhyolite with fabric’ bluestone component and rhyolitic rocks from the Ordovician Fishguard Volcanic Group exposed in the Pont Saeson area of north Pembrokeshire. This study aims to see if the chemistry of zircons, which are present in both sets of samples, could be used to support the petrographical association. Analyses for certain high field strength elements (including the rare earth elements) obtained by LA-ICP-MS showed that indeed the analyses were nearly identical when compared using a range of statistical approaches, including similarity coefficients, statistical distance, and principal component analysis, while showing clear differences to sample sets which had no reason to be correlated with the Pont Saeson samples. There are two important conclusions arising from this study. Firstly, the identification of the Pont Saeson source of the ‘rhyolite with fabric’ bluestone from outcrops in low ground to the north of the Mynydd Preseli will without doubt lead to fresh debates about the mechanisms of transport of this component of the bluestones to the Stonehenge site. Secondly, the chemistry of zircons may well prove to have a wider application in the provenancing of fine-grained rhyolitic rocks which have an archaeological context. [Copyright &y& Elsevier]
- Published
- 2011
- Full Text
- View/download PDF
5. Carn Goedog is the likely major source of Stonehenge doleritic bluestones: evidence based on compatible element geochemistry and Principal Component Analysis.
- Author
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Bevins, Richard E., Ixer, Rob A., and Pearce, Nick J.G.
- Subjects
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GEOCHEMISTRY , *DIABASE , *PRINCIPAL components analysis , *OUTCROPS (Geology) , *CRYSTALLIZATION - Abstract
Abstract: The Stonehenge bluestones were first sourced to outcrops in the high parts of the eastern Mynydd Preseli in SW Wales by H.H. Thomas in the early 1920s. He recognised the distinctive ‘spotted dolerite’ from his fieldwork in that area and suggested that the tors of Carn Meini (also known as Carn Menyn) and Cerrigmarchogion were the most likely sources. In the early 1990s, in a major contribution to our understanding of the Stonehenge bluestones, the geochemistry of a set of samples from Stonehenge monoliths and debitage was determined and compared against the geochemistry of dolerites from the eastern Mynydd Preseli by a team from the Open University led by R.S. Thorpe. They argued that the majority of the Stonehenge dolerites could be sourced from outcrops in the Carn Meini-Carn Gyfrwy area, based on the concentrations of the so-called ‘immobile’ elements (elements which are not affected by rock alteration processes), in particular TiO2, Y, and Zr. However, these elements are incompatible during crystallization of mineral phases in basaltic systems (that is they do not enter into the mineral phases which are crystallizing but are concentrated in the residual liquid) which severely hampers their use in discriminating between different pulses of an evolving magma (as is the case of the doleritic sills emplaced high in the crust and now exposed in the Mynydd Preseli). An alternative strategy in this study re-examines the data set of Thorpe's team but investigates the concentration of elements which are compatible in such basaltic systems (that is elements which do enter into the crystallizing mineral phases), namely MgO, Ni, Cr and Fe2O3. On the basis of the abundances of these elements on bivariate plots and also by using Principal Component Analysis on the dataset available and various sub-sets we identify three compositional groupings for the Stonehenge doleritic monolith and debitage samples and conclude that the majority of them (Group 1 of this paper) can be sourced to the prominent outcrop in the eastern Mynydd Preseli known as Carn Goedog. We also offer potential sources (with one exception) for those Stonehenge dolerites which appear not to relate to Carn Goedog. [Copyright &y& Elsevier]
- Published
- 2014
- Full Text
- View/download PDF
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