Article

Carn Goedog is the likely major source of Stonehenge doleritic bluestones: Evidence based on compatible element geochemistry and Principal Component Analysis

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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.

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... Of the 43 identified Welsh bluestones at Stonehenge, 30 are of dolerite (mostly spotted). These have long been recognised as coming from Preseli (Thomas 1923), although only recently has a large sample of them been pinpointed to three sources, most on the northern flank of Mynydd Preseli (Bevins et al. 2014): ...
... the Blue hard Stone also, ye same to some of the upright Stones in ye inner Circle atStonehenge" (Cunnington 1924). It is highly probable that this is the broken but un-dressed bluestone pillar fragment currently in Salisbury Museum (Figure 14;Pitts 2001: 198-204), now identified as spotted dolerite of Group 3 (Bevins et al. 2014). Given that British long barrows were constructed in the fourth millennium BC and Stonehenge was built in the third millennium BC, this discovery has proved something of a puzzle. ...
... The discovery that the dominant bluestone sources (so far provenanced) lie on the north side of Mynydd Preseli removes one of the main lines of evidence for the healing theory proposed to explain the bluestones' transportation, for as yet there is no convincing geological evidence that Carn Menyn provided pillars for Stonehenge (Bevins et al. 2014). Associations with medieval holy wells and healing-related springs on the south side of Preseli (Darvill 2007;Darvill & Wainwright 2009: 17-18;2014: 1112 are thus no longer sustainable on the current evidence. ...
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Article
The long-distance transport of the bluestones from south Wales to Stonehenge is one of the most remarkable achievements of Neolithic societies in north-west Europe. Where precisely these stones were quarried, when they were extracted and how they were transported has long been a subject of speculation, experiment and controversy. The discovery of a megalithic bluestone quarry at Craig Rhos-y-felin in 2011 marked a turning point in this research. Subsequent excavations have provided details of the quarrying process along with direct dating evidence for the extraction of bluestone monoliths at this location, demonstrating both Neolithic and Early Bronze Age activity.
... In this paper we first review previous descriptions of the dolerites and their spots and then present the results of a detailed mineralogical investigation of the spots and their host dolerite utilising standard optical microscopy including high resolution photomicrograph imagery, 'standard' scanning electron microscopy (SEM-EDS), automated scanning electron microscopy with linked energy dispersive analysis (automated SEM-EDS), and X-ray diffraction (XRD). Data obtained are used to interpret the genesis of the spots as well as to gain a greater understanding of the low-grade metamorphic mineralogy in two Preseli spotted dolerites, one from Carn Meini, considered by Thomas (1923) and Darvill and Wainwright (2016) to be one of the main sources of the Stonehenge spotted dolerites, and one from Carn Goedog, more recently proposed on geochemical grounds by Bevins et al. (2014) to be the source of the majority of the Stonehenge dolerites (comprising their geochemical Group 1; see Table 1 for an explanation of the classification scheme and proposed source outcrops). However, there are still unresolved dolerite sources, namely for geochemical Groups 2 and 3 of Bevins et al. (2014). ...
... Data obtained are used to interpret the genesis of the spots as well as to gain a greater understanding of the low-grade metamorphic mineralogy in two Preseli spotted dolerites, one from Carn Meini, considered by Thomas (1923) and Darvill and Wainwright (2016) to be one of the main sources of the Stonehenge spotted dolerites, and one from Carn Goedog, more recently proposed on geochemical grounds by Bevins et al. (2014) to be the source of the majority of the Stonehenge dolerites (comprising their geochemical Group 1; see Table 1 for an explanation of the classification scheme and proposed source outcrops). However, there are still unresolved dolerite sources, namely for geochemical Groups 2 and 3 of Bevins et al. (2014). As a consequence, we turn to other aspects of the dolerites to explore whether the sources of these other two groups can be identified. ...
... In his 1923 paper, Thomas compared loose rock samples from Stonehenge and Mynydd Preseli, although he provided no significant detail on the petrography of the dolerites or indeed the spots, despite their critical nature in comparing the two sample sets (Stonehenge and Preseli). He concluded (page 248) that the spotted dolerites could be matched 'especially in the outcrops of Carn Meini and Cerrigmarchogion' (see Fig. 1), although recently, on the basis of compatible element geochemistry, it has been suggested by Bevins et al. (2014) that the majority of the Stonehenge dolerites were sourced from Carn Goedog and to other, as yet unspecified, outcrops in the area. Harrison et al. (1979), in an unpublished Institute of Geological Sciences Technical Report, provided petrological descriptions of rock samples collected during excavations at Stonehenge by H. Cunnington between 1876 and 1886 and also from excavations by Gowland in 1901. ...
Article
Stonehenge is dominated by the large, locally derived sarsen stones which comprise the Outer Sarsen Circle and the Inner Sarsen Trilithon Circle. Lithologically they are a hard form of sandstone called silcrete. Less obvious are the smaller ‘bluestones’ which form the Outer Bluestone Circle and Inner Bluestone Horseshoe. The bluestone assemblage is composed of a variety of lithologies, including dolerite (almost all carrying small, cm scale, white to pink ‘spots’), rhyolites, volcanic tuffs and two different types of sandstone. The majority of the bluestones have been provenanced to the Mynydd Preseli area in west Wales some 200 km west of Stonehenge, and the distinctive spots in the dolerites were crucial evidence in making that link. However, despite the importance of the spots in that provenancing model, which provides evidence for one of the most remarkable feats of Neolithic time in north-west Europe, they have been little studied and are not fully characterized. One reason for this is the fact that they are difficult to study using standard optical microscopy because of the fine grain size of the component minerals. In order to gain a greater understanding of the mineralogy and origin of the spots we have used a range of alternative optical and analytical techniques, including high resolution photomicrography, ‘standard’ electron microscopy (SEM-EDS), automated scanning electron microscopy with linked energy dispersive analysis (automated SEM-EDS) and X-ray diffraction. These investigations, based primarily on samples from Carn Goedog and Carn Meini in the Mynydd Preseli, lead us to conclude that the spots result from a two-stage alteration history involving firstly saussuritization of primary igneous calcium-rich plagioclase phenocrysts/glomerocrysts. The saussuritization was probably a late-stage magmatic event, possibly occurring at ca. 400 ◦C, and led to the development of the secondary minerals clinozoisite, zoisite, albite and muscovite. Subsequently, the dolerites were affected by regional low-grade metamorphism at ca. 250–300 ◦C, at the transition from the prehnitepumpellyite to the greenschist facies. During this metamorphism the background (non-spot) areas of the samples were altered with the development of the secondary minerals chlorite, actinolite, epidote, quartz, titanite and further albite. Interpretation of these data shows that the Carn Goedog sample has a higher percentage of secondary minerals compared to the Carn Meini sample, suggesting that the former shows a higher degree of alteration. Further analyses of dolerite samples from the Mynydd Preseli should provide insight into the potential of the extent of rock alteration in the further refinement of understanding the source or sources of the Stonehenge bluestone dolerites.
... However, the Carn Goedog tor then attracted attention following suggestions by Thorpe et al (1991) that it might be the source of some Stonehenge rock fragments. Bevins et al (2014) went much further, and argued that at least five of the Stonehenge spotted dolerite monoliths might have come from here. They claimed to have done very accurate provenancing work, although no new fieldwork was involved. ...
... The igneous outcrops in this part of Preseli belong to the rocks of the Middle Ordovician Fishguard Volcanic Group (Bevins et al, 2014(Bevins et al, , 2017, around 464 million years old. The geological map (Fig. 2) reveals a suite of intrusive doleritic sills which were emplaced at a high level in the adjacent sedimentary sequence (referred to as the Abermawr Shales). ...
... Further complications arise because the area is structurally complex, with the rocks being deformed into a series of NE-SW oriented folds." During the geological attempts to unravel the complexities of these intrusions, scores of samples have been taken and analysed; of these, 46 were examined by Bevins et al (2014). ...
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This paper reports on new observations at the spotted dolerite tor of Carn Goedog on Mynydd Preseli, claimed by Parker Pearson and others to be the site of a Neolithic "bluestone monolith quarry" with links to Stonehenge. No evidence was found to support the contention of prehistoric quarrying, and indeed the claimed "engineering features" are all shown to be entirely natural and unexceptional. This work should be read alongside the two peer-reviewed papers by John, Elis-Gruffydd and Downes (2015 a and b) which show that the claims of Neolithic monolith quarrying at Craig Rhosyfelin (also excavated by Parker Pearson and his team) are similarly unfounded. It has to be concluded, on careful scrutiny of the evidence, that there are no Neolithic bluestone quarries in West Wales and that any blocks of local rock moved eastwards from Preseli to Salisbury Plain were most likely entrained and transported by glacier ice.
... Realising that standard transmitted and reflected light microscopy had essentially reached the limits of their application to advance our understanding of the character and provenance of the bluestones we have, over the last 10 years, employed a range of advanced analytical techniques in our investigations. Thorpe et al. (1991) and Bevins et al. (2012Bevins et al. ( , 2014 used whole-rock standard X-ray fluorescence spectrometry to some effect in provenancing some of the bluestone dolerites and one type of rhyolite. More recently we have used U-Pb zircon age determination, inductively coupled plasma-mass spectrometry, and automated scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) in our investigations of the bluestones, for example as in Bevins et al. (2020) for the Altar Stone, and Bevins et al. (2021) for further refinement of the provenance of the Group 2 dolerites of Bevins et al. (2014). ...
... Thorpe et al. (1991) and Bevins et al. (2012Bevins et al. ( , 2014 used whole-rock standard X-ray fluorescence spectrometry to some effect in provenancing some of the bluestone dolerites and one type of rhyolite. More recently we have used U-Pb zircon age determination, inductively coupled plasma-mass spectrometry, and automated scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) in our investigations of the bluestones, for example as in Bevins et al. (2020) for the Altar Stone, and Bevins et al. (2021) for further refinement of the provenance of the Group 2 dolerites of Bevins et al. (2014). ...
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Article
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.
... There are other sources in mid Wales and in the Welsh borders (Fig. 5). The more distant sources of dolerite, for example in the Cader Idris region, in Llyn, and in Snowdonia, have been considered as possible sources for the Stonehenge unspotted dolerite assemblage, but dismissed on the grounds that they are physically not well matched (Kokelaar et al, 1984;Williams-Thorpe et al, 2006;Bevins et al, 2014). The directions of ice movement in the Builth Wells and Llanwrtyd Wells area were broadly eastwards towards the Midlands and south-eastwards, but there is a slight chance that erratics from the Llanwrtyd Wells area might have travelled south-westwards along the Tywi trough during some glacial episodes. ...
... It is already well established through detailed petrological and geochemical research that almost all of the known spotted and unspotted dolerites in the Stonehenge bluestone assemblage have come from Preseli, although there is still doubt about precise provenances of analysed samples (Thomas, 1923;Ixer and Bevins, 2017;Bevins et al, 2014;Bevins, Pearce and Ixer, 2021). There is also an important association with rhyolite standing stones and debitage at Stonehenge, also apparently having come from the northern flanks of Mynydd Preseli. ...
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This interim report concerns the chance discovery of a very large igneous erratic on the foreshore of Limeslade Bay, Mumbles, Gower. In this position it must have been glacially transported from the west by the Irish Sea Glacier as it moved eastwards up the Bristol Channel. If the glacier was able to resist the pressure of Welsh ice coming from the north, it must have been a very powerful ice stream capable of reaching Somerset and Wiltshire. The significance of this research is discussed with respect to Quaternary studies and archaeology. There are major implications for the debate surrounding the mode of transport of the Stonehenge bluestones. Detailed provenancing work for the erratic is under way.
... Bluestones are actually a variety of rock types: spotted dolerite, unspotted dolerite, rhyolite, volcanics and sandstone. All derive from on and around the Preseli hills except for the sandstone Altar Stone, which comes from an as yet unidentified source (Ixer and Bevins 2011;Bevins et al. 2013Bevins et al. , 2020Ixer et al. 2017). ...
... In 2011 geologists Richard Bevins and Rob Ixer published their identification of an impressive rocky outcrop at Craig Rhos-y-felin, just north of the Preseli hills, as a source of one of the types of rhyolite at Stonehenge (Figure 2). Two years later their geochemical analysis sourced spotted and unspotted dolerite stones from Stonehenge to two less spectacular outcrops in these hills, one at Carn Goedog and the other at Cerrigmarchogion (Bevins, Ixer and Pearce 2013). This was something of a bombshell because, ever since Thomas's time, archaeologists had been focused on a different location, the impressive outcrop of Carn Menyn or Carn Meini (see, for example, Atkinson 1956, 36-9); yet none of Stonehenge's bluestones in the new analysis matched the geology of this more prominent outcrop. ...
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Article
Stonehenge is one of the world’s most famous prehistoric monuments, built 4,500–5,000 years ago during the Neolithic in a time long before written history. The recent dramatic discovery of a dismantled stone circle near the sources of some of Stonehenge’s stones in southwest Wales raises the fascinating possibility that an ancient story about Stonehenge’s origin, written down 900 years ago and subsequently dismissed as pure invention, might contain a grain of truth. This article explores the pros and cons of comparing the legend with the archaeological evidence.
... In the recent past, few archaeometric studies were carried out on European megalithic monuments, especially to investigate the technological properties and the provenance of their stone raw materials (e.g. Bevins and Ixer, 2013; Bevins et al., 2014; Pirson et al., 2002 Pirson et al., , 2003 Thorpe et al., 1991; Williams-Thorpe et al., 2006). Some of them specifically addressed a number of III–II millennium menhirs characterized by anthropomorphic features, often coming from Italy (Di Battistini et al., 2008; Rubinetto et al., 2013). ...
... This paper, in continuity with the recent European archaeometric works on megaliths (e.g. Bevins and Ixer, 2013; Bevins et al., 2014; Pirson et al., 2002 Pirson et al., , 2003 Thorpe et al., 1991; Williams-Thorpe et al., 2006), concerns a study of 34 menhirs coming from Laconi. The chosen approach aims to clarify the composition (elemental and mineralogical ), technological properties and geological and geographical origin of the raw materials used for the production of the local ancient menhirs. ...
Article
A multi-technique approach was carried out to investigate the provenance and technological properties of 34 anthropomorphic menhirs from Laconi (central Sardinia, Italy) dated back to the local Copper Age (III millennium BC). After visual inspection, geological materials coming from local ignimbritic outcrops were characterized by elemental and mineralogical analyses: portable X-Ray Fluorescence (pXRF), Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES), Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) and Powder X-Ray Diffraction (PXRD). Conversely, the menhirs were studied only by visual examination and non-destructive pXRF measurements. By means of a comparison between pXRF data collected on the menhirs and the lithological outcrops, it was possible to assign the prehistoric artifacts of Laconi to local geo-sources, taking into account geochemical intra- and inter-source variabilities. pXRF was demonstrated to be a useful tool for provenance studies while mineralogical analysis resulted fundamental for the technological aspects. The latter technique pointed out the main use of hardstones, probably owing to the durability they give to the menhirs.To the best of our knowledge, this is the first archaeometric study on Sardinian menhirs and one of the few recently developed on European megaliths.
... In the recent past, few archaeometric studies were carried out on European megalithic monuments, especially to investigate the technological properties and the provenance of their stone raw materials (e.g. Bevins and Ixer, 2013;Bevins et al., 2014;Pirson et al., 2002Pirson et al., , 2003Thorpe et al., 1991;Williams-Thorpe et al., 2006). Some of them specifically addressed a number of III-II millennium menhirs characterized by anthropomorphic features, often coming from Italy (Di Battistini et al., 2008;Rubinetto et al., 2013). ...
... This paper, in continuity with the recent European archaeometric works on megaliths (e.g. Bevins and Ixer, 2013;Bevins et al., 2014;Pirson et al., 2002Pirson et al., , 2003Thorpe et al., 1991;Williams-Thorpe et al., 2006), concerns a study of 34 menhirs coming from Laconi. The chosen approach aims to clarify the composition (elemental and mineralogical), technological properties and geological and geographical origin of the raw materials used for the production of the local ancient menhirs. ...
Article
A multi-technique approach was carried out to investigate the provenance and technological properties of 34 an-thropomorphic menhirs from Laconi (central Sardinia, Italy) dated back to the local Copper Age (III millennium BC). After visual inspection, geological materials coming from local ignimbritic outcrops were characterized by elemental and mineralogical analyses: portable X-Ray Fluorescence (pXRF), Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES), Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) and Powder X-Ray Diffraction (PXRD). Conversely, the menhirs were studied only by visual examination and non-destructive pXRF measurements. By means of a comparison between pXRF data collected on the menhirs and the lithological outcrops, it was possible to assign the prehistoric artifacts of Laconi to local geo-sources, taking into account geo-chemical intra-and inter-source variabilities. pXRF was demonstrated to be a useful tool for provenance studies while mineralogical analysis resulted fundamental for the technological aspects. The latter technique pointed out the main use of hardstones, probably owing to the durability they give to the menhirs. To the best of our knowledge, this is the first archaeometric study on Sardinian menhirs and one of the few recently developed on European megaliths.
... Since 2010, there has been an on-going extensive review of the petrography of the bluestones (Ixer and Bevins, 2010, 2011a,b, 2013, 2016Ixer et al., 2015Ixer et al., , 2017Ixer et al., , 2019Ixer et al., , 2020. Petrographic data have been combined with new geochemical data which has included laser ablation ICP-MS zircon chemistry (Bevins et al., 2011), a re-interpretation of whole rock XRF data for the dacites/rhyolites and the dolerites (Bevins et al., 2012(Bevins et al., , 2014 and application of U-Pb zircon radiometric dating of rhyolitic debris at Stonehenge and from the Mynydd Preseli in west Wales . Results from these studies have called into question many of the original sources proposed by Thomas (1923) and later proposals by Thorpe et al. (1991), as discussed in Bevins et al. (2014) and Bevins and Ixer (2018). ...
... Petrographic data have been combined with new geochemical data which has included laser ablation ICP-MS zircon chemistry (Bevins et al., 2011), a re-interpretation of whole rock XRF data for the dacites/rhyolites and the dolerites (Bevins et al., 2012(Bevins et al., , 2014 and application of U-Pb zircon radiometric dating of rhyolitic debris at Stonehenge and from the Mynydd Preseli in west Wales . Results from these studies have called into question many of the original sources proposed by Thomas (1923) and later proposals by Thorpe et al. (1991), as discussed in Bevins et al. (2014) and Bevins and Ixer (2018). ...
Article
A review of the provenance of the Altar Stone from Stonehenge and implications for transport of the bluestones to Stonehenge
... The geochemistry of stone has been used to identify provenance and it has been particularly successful when igneous rocks are involved, as in tying down the bluestones of Stonehenge to particular locations in the Preseli Mountains (Bevins et al. 2014). However, with carbonate rocks, there are several issues to consider. ...
... When more data are available, there will be a need for the application of multivariate statistics to determine which particular elements are useful in differentiating limestone types. Principal component analysis (PCA) can be applied to determine the correlations between elements and to suggest which groups are meaningful; PCA was successfully applied by Bevins et al. (2014) to the bluestones of Stonehenge and by Ashkanani et al. (2019) to Ubaid ceramics from Mesopotamia. Along with this approach, detailed petrographic work and microfacies analyses would be useful to ascertain primary differences between limestone units. ...
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Article
The Roman town of Bath (Aquae Sulis), renowned for its Temple to Minerva and thermal baths complex, is estimated here to have required around 500,000 m3 of stone for its construction. This huge amount of stone was likely to have been supplied from quarries within 5 km of the town, located towards the tops of the hills around Bath. Observations at the many old quarries show few features indicating Roman exploitation except for one Lewis bolt-hole and reports of chisel marks. The features of the majority of the stone in the Roman Baths-Temple Complex all suggest that the stone was sourced largely from the Combe Down Oolite Member (CDO; Jurassic, Bathonian stage), rather than the Bath Oolite Member (BO), of the Great Oolite Group. A portable X-Ray Fluorescence (pXRF) instrument, used to determine the trace element geochemistry of Bath Stone for comparison with the Roman stone, shows that the CDO and BO are very similar, except for different contents of Si, Al, Fe and Mn. These likely reflect variations in clay and organic matter content. However, with regard to the Roman stone and sculptures in the Baths-Temple Complex, all analyses of surfaces show enrichment in virtually all elements, but especially in P, Si, K, Al, S, Cl, Fe, Pb, Zn, Nb, and As. This contamination is largely attributed to the buried nature of the site (5�8 metres) from the 5th century AD until the end of the 19th century, during which time the stone would have been affected by groundwater, mostly derived from the hot-springs, with its high content of many elements. Analyses of cores cut into blocks of Roman stone show that the contamination is absent after 1�2 cm. This study demonstrates that care must be exercised in using geochemical analyses of ancient building materials for provenance studies, and that fresh surfaces of the material may well be required.
... In turn, the elaborate narrative concerning the Stonehenge bluestones, involving bluestone quarries at Craig Rhosyfelin and Carn Goedog and a "lost stone circle" at Waun Mawn (Parker Pearson et al, 2015;Bevins et al, 2013;Parker Pearson et al, 2021), is brought into question. This narrative, developed by Parker Pearson and his team over the last decade, has never been underpinned by evidence that withstands scrutiny (John, 2018), and must now be replaced with another, no less appealing story in which natural processes are accorded a modicum of respect. ...
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A brief analysis of the "Newall Boulder", recently rediscovered in Salisbury Museum after disappearing over 40 years ago. These notes follow a brief examination of the boulder on 14 June 2022. Its provenance at Stonehenge is undisputed, but it is not yet known where in the British Isles it originally came from. It has all of the characteristics of a glacially transported clast, and it is therefore suggested that it was carried to Stonehenge by glacier ice together with many of the Stonehenge bluestone monoliths and some of the "debitage" periodically exposed during excavations. The glacial transport hypothesis is enhanced, and further doubt must now be cast on the elaborate (but unsupported) archaeological narrative involving supposed bluestone quarries, "lost stone circles" and overland transport by Neolithic tribesmen. It is suggested that the boulder now needs a thorough "autopsy" involving specialists from a number of earth science disciplines.
... In contrast to this lack of interest or success in sarsen provenancing, research into the geochemistry and petrography of Stonehenge's Welsh bluestones has made huge strides in recent years. Recent work has established chemical matches with outcrops on the north side of the Preseli Hills in southwest Wales at Carn Goedog and its environs, and not the south side as previously thought (Bevins et al., 2014). Similarly, the source of the sandstone Altar Stone is not the Cosheston Beds of Milford Haven in southwest Wales, as once suggested, but the Senni Beds (Devonian) of south central Wales, perhaps from the Brecon Beacons (Ixer and Turner, 2006). ...
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Article
Anglo-Paris Basin silcretes are rarely observed in situ, particularly in the UK, do not form continuous layers, are mostly under a metre thick and are readily displaced in the surrounding soft sediments, moved by periglacial and/or subsequent human agencies (e.g. Stonehenge). Hertfordshire Puddingstone (HPS) was widely used in quern manufacture, mainly during the Romano-British period. New stratigraphic interpretations, and isotopic data presented here, are consistent with the HPS having formed at the Palaeocene–Eocene Thermal Maximum. The existing evidence is in favour of the HPS being a groundwater deposit, though other Tertiary silcretes in the Anglo-Paris Basin may be pedogenic.
... Until now, few studies have been carried out on European megaliths to investigate their source provenance and technological properties (Bevins and Ixer 2013;Bevins et al., 2014;Pirson et al., 2003;Williams-Thorpe et al., 2006) and only a small part of them concerns menhirs. Among these scientific researches, two addressed Italian menhirs characterised by anthropomorphic features (Di Battistini et al., 2008;Rubinetto et al., 2014), similar to the ones realised in Sardinia during the local Copper Age, probably from the first centuries of III millennium BC (Melis, 2009;Cocchi Genick, 2012). ...
Poster
In the 1990s a group of anthropomorphic menhirs were found into the walls of the Nuraghe Arasseda, in Allai (central-western Sardinia, Italy). They probably belonged to a Copper Age sanctuary of III millennium BC, and were reused as a building material by nuragic people during the II millennium BC. In modern times three of these megaliths were removed from the Nuraghe Arasseda and exposed at the Sardinian archaeological museum of Laconi. After testing the reliability of a non-destructive archaeometric approach, a study concerning the source provenance and the technological properties of the raw materials employed for the menhirs production were carried out. On eight geological samples (two of which come from an ancient quarry) collected from the Monte Ironi volcanic outcrop of Allai, visual examination and instrumental measurements were performed. Chemical analyses by portable X-Ray Fluorescence spectrometry (pXRF), Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) were carried out to determine the coherence between the analytical data collected by the different techniques [1], to characterise the stone raw material and to evaluate its chemical intra-source variability. On the three menhirs from Arasseda, in accordance with preservation of archaeological heritage, visual inspection and non-destructive pXRF measurements were achieved only. By means of a comparison between pXRF data collected on artefacts and geological samples, it was possible to indicate the Monte Ironi unit as the geo-source of two out of three Arasseda menhirs. Powder X-Ray Diffraction (PXRD) measurements were useful to recognize the technological properties of the Monte Ironi stone and to reconstruct the criteria adopted during Copper Age in selecting geo-materials for sculptural purposes. To the knowledge of the authors, this is the first research study on the Arasseda menhirs by means of chemical and physical methods (the second one on Sardinian menhirs [2]), and one of the few archaeometric studies recently developed on European megaliths. [1] D. Mitchell, P. Grave, M. Maccheroni, E. Gelman, Geochemical characterisation of north Asian glazed stonewares: a comparative analysis of NAA, ICP-OES and non-destructive Pxrf, Journal of Archaeological Science 39, 2921–2933, 2012. [2] M. Serra, V. Mameli, C. Cannas, Eneolithic menhirs of Laconi (central Sardinia, Italy): from provenance to technological properties, Journal of Archaeological Science: Reports 5, 197-208, 2016.
... 292?302, 2015), and also the smaller bluestones , a group comprising different geological types with sources identified, some to outcrop, to the Preseli Hills, Pembrokeshire in Wales (Thorpe et al. 1991, Darvill et al. 2012, Parker Pearson 2012, pp. 261?291, Bevins et al. 2014). Clear differences can be seen between groups of settings. ...
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Article
Studies of megalithic stone settings have tended to focus upon features perceptible above the ground, whereas sub-surface elements have received markedly less attention. Consideration of both as elements of assemblages provides opportunities for new understandings to emerge. Through re-examination of stone settings within the context of the Avebury monumental complex, the value of this approach is demonstrated. The existence of discrete material types with essential properties is undermined as new, fluid, contextually situated substances reveal themselves, enabling a reappraisal of other assemblages within the group.
... The Inca structures in Machu Picchu, Peru, were built from granite stone (Vilímek et al., 2007). The ancient Stonehenge in England is a group of stone monuments composed of various rock types but is principally bluestone, a volcanic rock (Bevins et al., 2014). ...
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Article
The Yokosuka Arsenal dry dock No. 1 is the oldest stone dock in Japan constructed from natural building stones. During the construction of the dock, Hakusen Hill, which comprised mainly Pleistocene sediments, was excavated. In this study, photogrammetric documentation and a non-invasive investigation were used to survey the dock site, evaluate its soundness, and assist in future preservation. Horizontal and vertical sections near the gate were successfully created using a photogrammetrically produced 3D surface model. The vertical sections of the south wall display greater deformation than those on the north wall. The water leakage on both walls was measured using rain gauges placed near the gate. The leakage was found to originate mainly from the mortar between the building stones and was correlated with sea level changes. The results indicate that rising sea level increased the water pressure leading to higher leakage inside the dock walls. The water leakage in the north and south walls peaked at different times, and the amplitude of the sea-level vs. water-leakage hysteresis loops also differed between the north and south walls. These differences may have been caused by the different permeability and storage coefficients of the wall mortar and the backfill materials behind the north and south walls. In addition, the different permeability and storage coefficients were likely caused by the deformation of the south wall due to lithological variations in the material underlying the north and south walls. These results contribute to future preservation plans regarding the soundness of the site. Ground stability is one of the main issues in engineering geology and related fields. Therefore, this study may also be helpful in similar cases worldwide.
... In Prehistory, PCA has been proposed as a method with which to characterize specific tool types, as was the case for the Noailles awl (Djindjian, 1991(Djindjian, , 1997 or, similar to our problematic, to individualize a chrono-culture, such as the Magdalenian of Eastern Languedoc (Bazile and Monnet-Bazile, 2000;Langlais, 2004). We must also mention the use of the PCA to characterize the dolerites of the site of Stonehenge (Bevins et al., 2014). ...
... So far, few studies investigated the source provenance and the technological properties of European megaliths (Bevins, and Ixer 2013;Bevins, Ixer, and Pearce 2014;Thorpe et al. 1991;Frèbutte 2002, 2003;Williams-Thorpe et al. 2006) and a small part of them concerns menhirs. Only two of the available research works addressed Italian standing stones characterised by anthropomorphic features (Di Battistini, Franzini, and Lezzerini 2008;Rubinetto et al. 2014) similar to those of Eneolithic Sardinia, probably produced from the first centuries of 3 rd millennium BC (Melis 2009;Cocchi Genick 2012;Perra 2012). ...
Article
During the 2nd millennium BC anthropomorphic menhirs belonging to a 3rd millennium BC sanctuary were reused as building material in the Arasseda Nuraghe (Sardinia, Italy). To analyse the Arasseda menhirs and the local Monte Ironi geological samples (presenting similar visual features), chemical (pXRF, ICP-OES, ICP-MS), mineralogical-chemical (PXRD) and physical (Mohs hardness) measurements were performed. Through the experimental data, the menhirs source provenance and the technological properties (workability, durability) of the raw material chosen for sculptural purposes during Copper Age were investigated. To the authors’ knowledge this is the first archaeometric study on the Arasseda menhirs (the third on Sardinian menhirs) and one between the few recently developed on European megaliths. © 2018, © 2018 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
... stonehenge/), also demonstrates the importance that neolithic communities placed on stone, and the effort undertaken to locate, quarry and transport the 'correct stone' to meet their ritual needs. In this case, doleritic 'bluestone' was extracted and brought some 225 km from Pembrokeshire in South Wales to construct part of the internationally renowned stone circles of Stonehenge (Bevins et al. 2014). ...
Article
Successful geoconservation increasingly depends on securing understanding and support from local communities and the decision makers within them. As most people do not understand geoscience, value geoheritage, or support geoconservation, it is extremely important that ways of raising awareness of geoheritage and building support for conservation are found. Connecting communities to their geoheritage is central to achieving this, and can be done in a variety of ways. Quarries and quarrying, including mines and mining, are perhaps the most effective means of engaging communities with their geoheritage as every quarry is ‘man-made’, and as such has a cultural connection with the community that worked it. Using examples from England, different connections between communities, quarries and geoheritage are described, and ways of making these connections are explored. Innovative approaches to making these links, such as those that involve physical engagement and activities with the community, and which contribute to a wider social agenda, are highlighted. The concept of an Anthropocene epoch, emphasising the links between society and its visible impact on the natural environment, including the geological record, provides a new context within which to use quarries to link communities to their geoheritage.
... At least five bluestone pillars (Stones 33,37,49,65 & 67) were taken from Carn Goedog, and probably many more (Bevins et al. 2013). The multiple and large recesses in the rock face are further evidence that pillar removal was extensive at this outcrop, even though quarrying in the early modern period has obscured evidence of pillar removal in the western part of the outcrop. ...
Full-text available
Article
Geologists and archaeologists have long known that the bluestones of Stonehenge came from the Preseli Hills of west Wales, 230km away, but only recently have some of their exact geological sources been identified. Two of these quarries—Carn Goedog and Craig Rhos-y-felin—have now been excavated to reveal evidence of megalith quarrying around 3000 BC—the same period as the first stage of the construction of Stonehenge. The authors present evidence for the extraction of the stone pillars and consider how they were transported, including the possibility that they were erected in a temporary monument close to the quarries, before completing their journey to Stonehenge.
... Another example of successful provenance is from the 'bluestones' of Stone Henge, which include dolerites, rhyolites and volcanic ashes, with some of these materials considered to originate from as far as southwest Wales (Thomas, 1923;Green, 1997). Petrology and geochemical provenance techniques applied to the volcanic rocks have been used to confirm these arguments, pinpointing the origins of the bluestones to specific outcrops at Mynydd Preseli in Wales (Bevins et al., 2011;Bevins et al., 2012Bevins et al., , 2014. ...
Article
Materials used in the construction of man-made structures can reveal information about societies, their environment , culture and mobility. Cultures throughout human history have used natural stone to construct fu-nerary monuments and tool technologies. Stone materials from igneous rocks can be provenanced by petro-graphic examination and geochemical methods that provide a direct link between the artefact and their source. For sedimentary sarsen stones, provenance is often complicated by diagenetic processes acting on source rocks. Here I use an example of stones used to build 6000-year-old earth and sarsen megalith structures from the River Medway valley (Kent, UK). These megalith structures lie on the strategic and pre-Neolithic North Downs migration route into Britain, but the provenance of the sarsens used in their construction has not been established. The highly competent sarsens are diagenetic groundwater silcretes, resulting from acid leaching of glauconitic clay components, and addition of a quartz cement. Heavy rare earth and high field strength element abundances and ratios are resistant to diagenetic effects and show a geochemical association with Paleogene sandstones from the Upnor Formation of the Lambeth Group at the 95% confidence limit. Detrital zircon and titanite grain compositions confirm this relationship. Preferential erosion and removal of the less competent sandstone around silcretes left large (> 2 m), durable and isolated sarsen blocks on top of the chalk downs that were subsequently exploited by Neolithic peoples. Use of local stone to construct the Medway megaliths is consistent with their distinct morphological characteristics that have been used to imply independence from continental European cultures at that time. Combined with careful field collection of possible source rocks and sarsen materials, provenance of stones of sedimentary origin that have been affected by diagenesis can be accurately assessed through a combination of petrography, bulk-rock heavy rare earth element and high field strength element abundances, and detrital mineral compositions.
... These stones-which include dolerites, tuffs, rhyolites, and sandstones-are clearly not local to Stonehenge, which stands in an area underlain by Chalk bedrock. Recent studies suggest that the igneous bluestones originated from the Preseli Hills in southwest Wales [e.g., (7)(8)(9)], over 200 km west of the monument, and that the sandstone Altar Stone came from east Wales (10). However, with the exception of work by Howard (11), no research has been published on the sources of the larger sarsens [a vernacular term for the duricrust silcrete; (12)], erected during the mid-third millennium BCE, that comprise the main architecture of Stonehenge (13,14). ...
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Article
The sources of the stone used to construct Stonehenge around 2500 BCE have been debated for over four centuries. The smaller “bluestones” near the center of the monument have been traced to Wales, but the origins of the sarsen (silcrete) megaliths that form the primary architecture of Stonehenge remain unknown. Here, we use geochemical data to show that 50 of the 52 sarsens at the monument share a consistent chemistry and, by inference, originated from a common source area. We then compare the geochemical signature of a core extracted from Stone 58 at Stonehenge with equivalent data for sarsens from across southern Britain. From this, we identify West Woods, Wiltshire, 25 km north of Stonehenge, as the most probable source area for the majority of sarsens at the monument.
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Article
How and why the bluestones arrived at Stonehenge, the UK's most revered ancient monument, has long held people's imagination. The key to understanding these questions relies heavily on the location of their sources. Following early studies in the late eighteenth and early nineteenth centuries, which proposed various places but in particular south-west England, H.H. Thomas, in 1923, suggested that they came from the Mynydd Preseli, in north Pembrokeshire, Wales. Thomas proposed a number of key locations for the geographical origin of the stones. However, recent investigations have called those locations into question, identifying different sources albeit from the same broad area in north Pembrokeshire. Identification of these proposed new sites has led to archaeological excavations and important new discoveries including new suggested routes for the transport of the bluestones from the Preseli Hills to Stonehenge some 230 km away.
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Conference Paper
Work that we undertook as part of the ‘Stonehenge Riverside Project’ illustrated that the late Neolithic (mid 3rd mill. BC) Stonehenge landscape attracted people from a wide geographic area. Strontium isotopic ratios from cattle tooth enamel – related to the nature of the rock substratum on which animals pastured –indicated that livestock from the site of Durrington Walls (Wiltshire) was diverse in terms of their geographic origins. This initial work was, however, undertaken on a relatively small sample size and required verification. The onset of the ‘Feeding Stonehenge’ project has broadened the Strontium isotope analysis programme, and preliminary results based on a much larger sample provide support to the initial results, as well as a more nuanced pattern of geographic variability. This work will also be interpreted in light of other – new – lines of isotopic analysis that we have undertaken as part of our current project, such as the ongoing investigation of carbon, nitrogen and particularly oxygen values. Parallel zooarchaeological work undertaken on the very large animal bone assemblage supports the idea of the site as a focus of imported livestock, with little or no evidence of on-site breeding having been found. The exogenous nature of much of the livestock (and, by proxy, people) provides an interesting contrast to the local origin of raw materials for the production of lithic tools and pottery, whilst the analysis of stone tools also provides insight into the composition of the communities that gathered at the site. The aggregation involved in both ceremonial practices and monument construction that took place in the area required both the introduction/importation of supplies but also the working of local resources by a diversity of communities. Thus a context was provided for the cultural transmissions of skills, the homogenisation of material culture and potentially for the exchange of goods and livestock.
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Article
Around 4500 years ago, some 80 large blocks of silcrete or 'sarsen' were erected at Stonehenge during its second stage of construction. Stonehenge is the only prehistoric stone circle to have its stones dressed, and debris from this stone-dressing has been found on the north side of the monument. Numerous locations have been proposed for the origin of these sarsens, from the immediate locality to more distant areas of east Somerset and north Wiltshire about 30. km (18 miles) away, but geological provenancing of Stonehenge's silcrete monoliths has so far been largely unsuccessful. The suspected sources are, however, much closer than those of Stonehenge's 'bluestones', over 200. km (125 miles) away in west Wales. That said, the sarsens are much heavier than the 1-2. tonne bluestones. For more than 300 years, researchers have suspected that the main sources of Stonehenge's sarsens were deposits of silcrete on the highest points of the Marlborough Downs, 30. km (18 miles) north of Stonehenge. Antiquarian records of a group of sarsens at Clatford Bottom, at the foot of the Downs, suggest that these may have been abandoned in transit to Stonehenge.
Article
This review describes advances in the XRF group of techniques published approximately between April 2014 and March 2015 and is therefore restricted to a selection of papers featuring developments in the XRF armoury. An active topic during this review period was that of imaging techniques and, more particularly of micro X-ray fluorescence spectrometry. Silicon-based semiconductor X-ray detectors such as SDD and Si(PIN) continue to reflect the maturity and widespread routine use of such devices. The significant expansion in studies evaluating the field use of portable XRF instrumentation in geological applications, often still proving the quality of the data, rather than adopting the technique in routine applications. New synchrotron beamlines offer previously unavailable spatial resolution and throughput for the characterisation of advanced energy materials and devices under varying temperatures and gas atmospheres. Nano-materials feature extensively this year such as the use of nanoparticles in cancer imaging and therapy. Synchrotron radiation has become a preferred technique for the analysis of a wide range of archeological samples, artwork, museum specimens and environmental studies. There has been a substantial rise in the number of Chinese researchers investigating objects of cultural heritage, especially porcelain, glazes and glass. Advances in TXRF and related techniques continue to feature with studies on thin films and nanomaterials. Feedback on this review is most welcome and the review coordinator can be contacted using the email address provided.
Article
Non-invasive survey in the Stonehenge ‘Triangle’, Amesbury, Wiltshire, has highlighted a number of features that have a significant bearing on the interpretation of the site. Geophysical anomalies may signal the position of buried stones adding to the possibility of former stone arrangements, while laser scanning has provided detail on the manner in which the stones have been dressed; some subsequently carved with axe and dagger symbols. The probability that a lintelled bluestone trilithon formed an entrance in the north-east is signposted. This work has added detail that allows discussion on the question of whether the sarsen circle was a completed structure, although it is by no means conclusive in this respect. Instead, it is suggested that it was built as a façade, with other parts of the circuit added and with an entrance in the south.
Article
Recent investigations at Stonehenge have been accompanied by new research on the origin of the famous ‘bluestones’, a mixed assemblage of rhyolites and dolerites that stand among the much taller sarsens. Some of the rhyolite debitage has been traced to a quarry site at Craig Rhosyfelin near the Pembrokeshire coast; but fieldwork on the upland outcrops of Carn Menyn has also provided evidence for dolerite extraction in the later third millennium BC, and for the production of pillar-like blocks that resemble the Stonehenge bluestones in shape and size. Quarrying at Carn Menyn began much earlier, however, during the seventh millennium BC, suggesting that Mesolithic communities were the first to exploit the geology of this remote upland location.
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The concept of distance between two compositions is important in the statistical analysis of compositional data, particularly in such activities as cluster analysis and multidimensional scaling. This paper exposes the fallacies in a recent criticism of logratio-based distance measures—in particular, the misstatements that logratio methods destroy distance structures and are denominator dependent. Emphasis is on ensuring that compositional data analysis involving distance concepts satisfies certain logically necessary invariance conditions. Logratio analysis and its associated distance measures satisfy these conditions.
Article
Stonehenge on Salisbury Plain is one of the most impressive British prehistoric (c. 3000–1500 BC) monuments. It is dominated by large upright sarsen stones, some of which are joined by lintels. While these stones are of relatively local derivation, some of the stone settings, termed bluestones, are composed of igneous and minor sedimentary rocks which are foreign to the solid geology of Salisbury Plain and must have been transported to their present location. Following the proposal of an origin in south-west Wales, debate has focused on hypotheses of natural transport by glacial processes, or transport by human agency. This paper reports the results of a programme of sampling and chemical analysis of Stonehenge bluestones and proposed source outcrops in Wales . Analysis by X-ray-fluorescence of fifteen monolith samples and twenty-two excavated fragments from Stonehenge indicate that the dolerites originated at three sources in a small area in the eastern Preseli Hills, and that the rhyolite monoliths derive from four sources including northern Preseli and other (unidentified) locations in Pembrokeshire, perhaps on the north Pembrokeshire coast. Rhyolite fragments derive from four outcrops (including only one of the monolith sources) over a distance of at least 10 km within Preseli. The Altar Stone and a sandstone fragment (excavated at Stonehenge) are from two sources within the Palaeozoic of south-west Wales. This variety of source suggests that the monoliths were taken from a glacially-mixed deposit, not carefully selected from an in situ source. We then consider whether prehistoric man collected the bluestones from such a deposit in south Wales or whether glacial action could have transported bluestone boulders onto Salisbury Plain. Glacial erratics deposited in south Dyfed (dolerites chemically identical to Stonehenge dolerite monoliths), near Cardiff, on Flatholm and near Bristol indicate glacial action at least as far as the Avon area. There is an apparent absence of erratics east of here, with the possible exception of the Boles Barrow boulder, which may predate the Stonehenge bluestones by as much as 1000 years, and which derived from the same Preseli source as two of the Stonehenge monoliths. However, 18th-century geological accounts describe intensive agricultural clearance of glacial boulders, including igneous rocks, on Salisbury Plain, and contemporary practice was of burial of such boulders in pits. Such erratics could have been transported as ‘free boulders’ from ‘nunataks’ on the top of an extensive, perhaps Anglian or earlier, glacier some 400,000 years ago or more, leaving no trace of fine glacial material in present river gravels. Erratics may be deposited at the margins of ice-sheets in small groups at irregular intervals and with gaps of several kilometres between individual boulders . ‘Bluestone’ fragments are frequently reported on and near Salisbury Plain in archaeological literature, and include a wide range of rock types from monuments of widely differing types and dates, and pieces not directly associated with archaeological structures. Examination of prehistoric stone monuments in south Wales shows no preference for bluestones in this area. The monoliths at Stonehenge include some structurally poor rock types, now completely eroded above ground. We conclude that the builders of the bluestone structures at Stonehenge utilized a heterogeneous deposit of glacial boulders readily available on Salisbury Plain. Remaining erratics are now seen as small fragments sometimes incorporated in a variety of archaeological sites, while others were destroyed and removed in the 18th century. The bluestones were transported to Salisbury Plain from varied sources in south Wales by a glacier rather than human activity.
Article
The source of the Stonehenge bluestones was first determined in the early 1920s by H.H. Thomas who was an officer with the Geological Survey of England and Wales. He determined that the so-called ‘spotted dolerites’ could be petrographically matched to a small number of outcrops in the Mynydd Preseli district in south-west Wales. The bluestones, however, comprise a number of additional lithologies, including rhyolite and ‘calcareous ash’, as well as various sandstones. Thomas was convinced that the volcanic lithologies in the bluestone assemblage were all sourced from a small area at the eastern end of the Mynydd Preseli, with the rhyolites originating from the prominent outcrop known as Carn Alw. Recently, provenancing of these rhyolites to Carn Alw has been questioned on the evidence of whole-rock geochemistry. This raised concerns over the original petrographical attribution. Accordingly a re-investigation was undertaken of the rhyolite petrography by re-examining the original specimens used by Thomas. Three of the original four thin sections studied by Thomas were re-examined, along with a newly made thin section from the fourth of Thomas' rock samples as the original thin section could not be located. The new petrographical evidence demonstrates convincingly that the two pairs of thin sections from the Preseli and Stonehenge as examined by Thomas do not match despite his contention and argues strongly that Carn Alw is not the source of the Stonehenge rhyolites which Thomas described. This reinforces the geochemical evidence presented recently and supports the contention that Craig Rhos-y-felin, to the north of Mynydd Preseli, is an important source of rhyolitic debris in the Stonehenge Landscape. Nevertheless, there remain uncertainties over the provenance of other Stonehenge rhyolites (and dacites), including four of the orthostats themselves.
Article
The source of the bluestone component found in the Stonehenge landscape has long been the subject of great interest and considerable debate. The bluestones are a mix of lithologies, the standing orthostats being predominantly dolerites, variably ‘spotted’, with only four of them being of dacitic and rhyolitic composition and the Altar Stone being sandstone. However in the 1920s the spotted dolerites were sourced to outcrops which comprise tors in the summit regions of the Mynydd Preseli in north Pembrokeshire, west Wales. There were also speculations about the possible sources of the dacitic and rhyolitic components, ideas which were elaborated on in the early 1990s when the original petrological provenancing was supplemented by whole-rock geochemical analysis. Most recently, new petrographical investigations have been combined with zircon geochemical data to determine the possible source of one type of rhyolite, the so-called ‘rhyolite with fabric’, found abundantly as débitage in the Stonehenge landscape (but not composing the four orthostats) to outcrops in the vicinity of Pont Saeson, especially a large craggy outcrop called Craig Rhos-y-felin, located in low ground to the north of the Mynydd Preseli. In order to test this provenance whole-rock geochemical analysis has been undertaken on samples of débitage from the Stonehenge landscape and from the Pont Saeson area, including Craig Rhos-y-felin. These data are then compared with other new and existing geochemical data for dacitic and rhyolitic lithologies recovered from the Stonehenge landscape, including the four orthostats, as well as geochemical data from outcrops of the same lithologies from the two main volcanic horizons exposed across north Pembrokeshire, namely the Fishguard Volcanic Group and the Sealyham Volcanic Formation, both of Ordovician age. This study concludes that previous, 20th century, attributions of provenance to a number of dacitic and rhyolitic outcrops in the north Pembrokeshire have been in error whilst the new data for the Pont Saeson rhyolite accords well with elemental contents recorded in the ‘rhyolite with fabric’ lithology from the Stonehenge landscape débitage. This study therefore endorses the proposal that the Pont Saeson area is indeed the source of the ‘rhyolite with fabric’ lithology recovered from numerous sites in the Stonehenge landscape, and is the only reliable provenance for any of the dacitic and rhyolitic bluestone material collected to date. It also serves to endorse the use of zircon chemistry as a provenancing tool in archaeopetrological investigations.
Article
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.
Article
A major doleritic and gabbroic sill complex, with minor microtonalitic components, cuts Ordovician strata to the east of Fishguard. Their age has long been equivocal. New geochemical data, combined with petrographic analyses, indicate that the intrusions represent an eastward extension of the Ordovician (Llanvirn) Fishguard Volcanic Complex lavas and high-level intrusions of the Strumble Head region. In addition similar doleritic intrusions crop out to the west of Strumble Head, as far as Traeth Llyfn. The data presented here confirm earlier conclusions that the FVC has tholeiitic affinities and that compositional variations largely result from low-pressure fractional crystallization. The petrogenetic relationships of the microtonalities are, however, as yet equivocal. Incompatible element discriminant diagrams indicate that the parental basic magmas were derived by melting of a slightly depleted mantle source similar to N-type MORB, to which had been added a minor supra-subduction zone LIL element component. The data are consistent with emplacement of the magmas in a marginal basin environment. -Authors
Article
Pearce, N. J. G., Bendall, C. A., Westgate, J. A. (2008). Comment on ?Some numerical considerations in the geochemical analysis of distal microtephra? by A.M. Pollard, S.P.E. Blockley and C.S. Lane. Applied Geochemistry, 23(5), 1353-1364.
Article
The use of Late Quaternary tephra horizons as isochronous markers for high resolution correlation between records is of growing importance in a number of scientific fields. Particular advancements have been made through the identification of microtephra deposits (very distal deposits of volcanic ash invisible to the naked eye). The successful correlation of ash layers and volcanic eruptions depends on the acquisition of the major element chemistries of a tephra layer, derived from microprobe analyses of individual glass shards. This is particularly important for microtephras where aeolian fractionation has removed much of the mineral phase of the ash deposit, which often aids tephra discrimination. There are, however, difficulties in distinguishing precisely between different eruptions of the same volcano using major element composition and this may not always be resolved by the use of trace elements. Given the potential of tephrochronology as a correlative tool in many disciplines it is important to resolve this difficulty. One way forward is to perform more robust statistical analyses on the geochemical data, as in general, analyses are confined to a series of bi-plots of major elements. Here the authors explore some of the problems associated with dealing with microprobe data generated for individual tephras and pay particular attention to the 'unit sum problem'. Using a subset of data generated as part of a EURODELTA project on tephra distribution in the Adriatic, the authors demonstrate that this problem is detectable in major element data from tephras and have consequently applied the logratio method before further analyses of the data. It is demonstrated that the use of logratios combined with discriminant functions analysis provides a more robust assessment of likely chemical correlations between tephras, and are superior to the use of bi-plots alone; and obviate the need for any data normalization, a particular point of contention between tephrochronologists. © 2006 Elsevier Ltd. All rights reserved.
Article
Abstract Mafic phyllosilicates in metabasites affected by low-grade regional metamorphism from Wales and eastern North Greenland show variations in their structure and chemistry. These variations are related to four mineral zones in these metabasites, which are recognized on the presence/absence of various key calc-silicate minerals and also actinolite. Zones 1 and 2 equate with the zeolite facies, zone 3 with the prehnite–pumpellyite facies (or prehnite–actinolite facies in rocks with appropriate bulk rock composition) and zone 4 with the greenschist facies. Whilst variations in Fe/(Fe + Mg) in chlorite correlate closely with Fe/(Fe + Mg) ratios in the whole-rock, other chemical variations are clearly unrelated to whole-rock compositions. Contents of Aliv are seen to increase systematically in samples from zone 1 through to zone 4, which relate to an increase in temperature. Calibration of alteration temperatures, calculated using the chlorite geothermometer (based on Aliv contents) developed for meta-andesites in the Los Azufres geothermal system (Mexico), against x values (an estimate of the proportion of chlorite to swelling component in the mafic phyllosilicates) shows a decrease in the swelling component in passing from zone 1 to zone 4, i.e. with an increase in temperature. Calculated temperatures compare favourably with published stability estimates for the various key calc-silicates and actinolite. These data indicate that the chlorite geothermometer, although developed for meta-andesites from a hydrothermal system, does show a correlation with temperatures estimated from calc-silicate assemblages in metabasites affected by low-grade metamorphism developed on a regional scale.
Article
The Fishguard Volcanic Complex represents an important volcanic episode which occurred within the Welsh sector of the British Caledonide region during early Ordovkian times. A variety of extrusive and contemporaneous intrusive rocks are present, ranging in composition from basic, through intermediate to acidic. Mineral and whole-rock chemical analyses have been determined on a representative suite of rocks from the complex and, despite secondary alteration effects, the original tholeiitic characteristics of the suite can be discerned. The variation observed is considered to result largely from low-pressure crystal fractionation, although the origin of the acidic magma remains speculative in view of subsequent extensive recrystallization. The rocks of the Fishguard Volcanic Complex formed in the Welsh Basin, which has been likened by earlier workers to a marginal basin. Comparison of the geochemical characteristics of the Fishguard Volcanic Complex with that of documented marginal basin rocks appears to favour this contention.
Article
Field-portable X-ray fluorescence (PXRF) instrumentation incorporating three radioisotope sources and a mercury (II) iodide detector has been evaluated in the non-destructive quantitative chemical analysis of lithic artefacts of archaeological interest. The method was tested by comparing PXRF analyses of 19 archaeological samples of fine- to medium-grained igneous rocks with laboratory wavelength-dispersive whole-rock XRF analyses of the same samples. Elements determined were K, Ca, Ti, Mn, Fe, Rb, Sr, Y, Zr, Nb, Ba, Cu, Zn and Pb, with detection limits for the most sensitively-determined elements of 6–14 ppm. PXRF analyses on fresh rock or artefact surfaces compare very well with the bulk WDXRF determinations, but weathered surfaces can give results significantly different from the corresponding bulk composition, especially for K, Ca, Ti and Fe. Seven British prehistoric stone implements (axes, axe-hammers and a mace-head) in the National Museum and Gallery, Cardiff, were analysed non-destructively by PXRF to assess the potential of this method in the provenancing of stone implements. Of four implements which had previously been assigned on petrographic grounds to Implement Petrology Committee (IPC) Group XIII (Preseli dolerite), two were confirmed as Group XIII and two have chemistry (and mineralogy) unlike Group XIII dolerite. Two implements previously assigned to IPC Group VIII (a rhyolite Group with suggested sources mainly in south Wales) have chemical characteristics which suggest sources respectively at an axe-manufacturing site near Carnalw in south-west Wales, and on the far west or north Pembrokeshire coast. The final implement, an axe, could not be assigned to any source with certainty either on petrographic or chemical grounds.
Article
An atypicality index has been used to compare the chemical compositions of 11 British prehistoric implements (axes and axe-hammers, and a mace) with previously suggested and likely sources in South Wales (Group XIII spotted dolerite from the Carnmenyn area, and Group VIII rhyolite from Carnalw). Atypicality indices together with mineralogy indicate that only two out of six supposed Group XIII implements are likely to be Group XIII, and only one of the five rhyolite implements is likely to originate from Carnalw. These results provide statistical support for earlier provenancing of seven of the implements, and provide the first geochemical source information for four implements. The results illustrate the usefulness of the atypicality index in archaeology, and support the idea that Groups XIII and VIII comprise a larger variety of chemical types than previously thought. Further work is now needed to determine how prevalent this variety is within these implement groups.
Article
Chemical compositions and magnetic susceptibility data were compared for 12 dolerite bluestone implements including axes, axe-hammers and battle-axes, 11 Stonehenge monoliths (chemical data only), and potential source outcrops in Preseli, South Wales. Most of the studied artefacts are of spotted dolerite, a small number being unspotted dolerite. Bivariate graphs, discriminant analysis and t-tests were used singly and in combination to show, respectively, that the implements found at sites in England are mainly similar to Stonehenge monoliths, while the implements found in Wales have a variety of compositions and are much less similar to Stonehenge monoliths. The dichotomy between English and Welsh dolerite bluestone implements could be explained by exploitation of different Preseli outcrops or erratic assemblages derived from them. A small number of spotted dolerite implements have previously been shown to have chemical compositions atypical of and marginal to Preseli, suggesting the possibility of a source of spotted dolerite outside Preseli. Previously published analytical data in combination with the new implement/outcrop comparisons presented in this paper support derivation of the majority of analysed Stonehenge monoliths at one particular outcrop within the group of four identified by Thorpe et al. 15 years ago. Analysis of all the extant bluestone monoliths at Stonehenge (now possible using non-destructive methods) would allow progress in identifying monolith outcrop sources, and in understanding the links with the bluestone axe trade.
Article
Eight dolerite outcrops in Preseli, south Wales were measured in situ using field-portable XRF analysis, in order to compare two different analysis (“sampling”) strategies, and to investigate geochemical variability within and between outcrops. A sampling strategy of two (neighbouring but independent) measurements at each of a maximal number of locations dispersed over an outcrop was the more effective in indicating the overall chemical variance of that outcrop. Analysis of variance indicated that much of the observed variance within individual outcrops stems from real geochemical variability rather than from sampling and analytical factors. Standard ANOVA F tests showed that several of the studied outcrops are heterogeneous at the 5% significance level for one or more elements. Geochemical distinctions between some outcrops were demonstrated using discriminant analysis. PXRF analysis offers an alternative approach to conventional characterisation of outcrops, which is often based on laboratory analysis of small numbers of samples. However, PXRF data are affected by rock weathering and may require correction for this if they are to be compared with analyses of fresh rock.
Article
The authors present a new procedure for discovering where stone artefacts come from without having to cut a slice through them. The method is tested on axes of spotted dolerite bluestone from Preseli in Wales, source of monoliths at Stonehenge.
Article
The Tal y Fan Intrusion is an altered olivine dolerite sheet emplaced into a coeval sequence of subaqueous volcanic rocks of Caradoc (Ordovician) age in NE Snowdonia, Wales. Primary mineral and chemical variations across the 110 m thick sheet suggest that the magma was drawn from a zoned magma chamber, although the intrusion consolidated predominantly as a single cooling unit. An horizon of ferrodolerite resulted from in situ fractionation. Secondary mineral assemblages are indicative of the prehnite-pumpellyite and prehnite-actinolite fades, suggesting metamorphic alteration conditions of approximately 310�C and 1-85 kb. Major elemental variation largely reflects primary mineral variations across the intrusion, although Ca, Al, and Na show limited mobility in the outermost 4-5 m, related to breakdown of plagioclase feldspar during metamorphism. The LIL elements Rb, Sr, K, and Ba were highly mobile, particularly in the marginal zones, whereas Th, in addition to the incompatible elements Zr, Y, Ti, P, Nb, Ta, Hf, and the REE, was immobile even in the marginal zones. Accordingly petrotectonic modelling based on discriminant diagrams using these immobile elements is considered most reliable. The Tal y Fan Intrusion has characteristics transitional between N-type and E-type MORB, similar to tholeiitic within plate basalts. In contrast with other Ordovician volcanic sequences of the Welsh Basin, no subduction component is identified in the Tal y Fan magma, the LIL element enrichment observed being related to alteration