Wednesday 6 March 2024

New lead isoscape map for archaeological provenance studies in Great Britain

 I was asked again about "Pigs from Scotland at Stonehenge" - the latest science says; "no".  For details see:



A contoured map of (A) 206Pb/204Pb isotope compositions. Superimposed over this contour map is the outcrop area of the Chalk Group. Chalk underlies much of southern Britain but it does not host much lead. Contains OS data © Crown copyright and database rights 2022. BGS © UKRI.


Links between Distant Monuments

Reviewing Richard Bradley's Antiquity Article: Beyond the bluestones: links between distant monuments in Late Neolithic Britain and Ireland http://dx.doi.org/10.15184/aqy.2024.3 I am struck by the concise way he sets out the long distance links. Whilst the degree of probability for each link that it actually existed varies I think taken together this paper establishes the long distance mindset of the prehistoric builders of monuments.

Well worth reading. 



I have scribbled his links onto the map in the paper to give a visual idea of the links he discusses: 


The table from the paper: 


Click to embiggen

 

Tuesday 20 February 2024

Antiquity Article: Beyond the bluestones: links between distant monuments in Late Neolithic Britain and Ireland

Richard Bradley writes: "Recent research has considered the relationship between Stonehenge and sites in south-west Wales, raising questions about whether the first monument at Stonehenge copied the form of an earlier stone circle at Waun Mawn and how the relationship between these sites was connected with the transport of bluestones between the different regions. But Stonehenge and Waun Mawn are not the only prehistoric sites in Britain and Ireland that share architectural elements and hint at social connections across vast distances of land and sea. This debate article explains how the questions raised about these Late Neolithic monuments can and should be applied to other monumental complexes to explore this insular phenomenon".   







Links:

Bradley, R. (2024) ‘Beyond the bluestones: links between distant monuments in Late Neolithic Britain and Ireland’, Antiquity, pp. 1–8. doi:10.15184/aqy.2024.3.

Monday 29 January 2024

What about the Bluestone pXRF studies?

The recent paper on Stonehenge Sarsen Debitage* ends with this conclusion:

"Our key message is that studies attempting to use surficial (pXRF) analysis to provenance any excavated artefact must demonstrate that weathering processes following burial did not significantly alter the primary chemical signature of the material before any meaningful provenance interpretations can be made."... "Any future attempts to provenance excavated dolerite fragments at the monument (likely derived from the in situ dressing of megaliths and/or the removal of flakes in more recent history) must consider differences in the weathering regime experienced by the buried fragments, exposed potential outcrops and standing stones. Due to its mineralogical composition, dolerite is more susceptible to chemical weathering than sarsen. Thus, one should expect differences in weathering to be much more significant between buried dolerite fragments exposed to subsoil weathering, and dolerite outcrops and megaliths exposed to differing intensities and durations of subaerial weathering."

This obviously could be thought to apply to the existing analysis of the bluestone dolerites, and any other non-sarsen stone.

So is there a problem?

Firstly, apart from the Newall boulder (https://www.sarsen.org/2023/07/the-erratic-that-came-in-from-cold.html), all the pXRF analysis has been on exposed Stonehenge stones comparing to exposed Welsh rocks, so they are like for like comparisons. And the Newall boulder was further analysed to show it was part of a broken monolith from Craig Rhos‐y‐Felin** 

Secondly the geochemistry revealed by xPDF is only part of the story. The recent Ixer, Bevins et al papers have also used petrology, understanding the matrix of the rock, to identify sources.

For instance in Bevins, Richard & Ixer, Robert & Webb, Peter & Watson, John. (2012). Provenancing the rhyolitic and dacitic components of the Stonehenge landscape bluestone lithology: New petrographical and geochemical evidence. Journal of Archaeological Science. 39. 1005–1019. 10.1016/j.jas.2011.11.020 the authors showed how Craig Rhos‐y‐Felin rhyolite had been misidentified as microtonalite, the geochemistry was very similar but the petrography different. This holistic approach to identification instills confidence. 

But the big difference is in the nature of the stones. Sarsen is over 99% silica, it is the white Wonderloaf of rocks. The various bluestones are complex rocks with other compounds in great abundance in them. So the presence of a small amount of chemical changes from weathering is important on Sarsen but not for bluestone. As Rob Ixer says; "A smear of marmite on plain buttered toast would be tasted but the same smear on jalapeno-anchovy toast would add nothing."

So the valuable lesson of the problems of using pXRF on Sarsen for sourcing studies doesn't cause worries about the reliability of the recent Bluestone papers, and is unlikely to be a problem in the future. 



David Nash responds:  Interesting thoughts but I wouldn’t be quite so confident about work on dolerite orthostats. These would have had fresh faces when quarried, and then slowly weathered at Stonehenge. The surfaces of comparator outcrops in Wales would have been weathering for much longer. This means that the Preseli outcrops are likely to be more altered by weathering than the comparatively fresh orthostats. Plus the weathering environment in wales will be different to that of Salisbury Plain. PXRF work needs to bear these differences in mind.

Local and exotic sources of sarsen debitage at Stonehenge revealed by geochemical provenancing,
T. Jake R. Ciborowski, David J. Nash, Timothy Darvill, Ben Chan, Mike Parker Pearson, Rebecca Pullen, Colin Richards, Hugo Anderson-Whymark,
Journal of Archaeological Science: Reports, Volume 53, 2024, 104406, ISSN 2352-409X,
https://doi.org/10.1016/j.jasrep.2024.104406.(https://www.sciencedirect.com/science/article/pii/S2352409X24000348)


**Lithological description and provenancing of a collection of bluestones from excavations at Stonehenge by William Hawley in 1924 with implications for the human versus ice transport debate of the monument's bluestone megaliths: DOI:10.1002/gea.21971
Richard Bevins  Rob Ixer  Nick Pearce  James Scourse  Tim Daw
https://onlinelibrary.wiley.com/share/author/YUUAUVRWBNTZTPSQVBGM?target=10.1002/gea.21971

Sunday 28 January 2024

Possible Stonehenge Debitage Sources

The two "exotic" sources Nash et al identify as possible sources for sarsen at Stonehenge are Stoney Wish near Ditchling Sussex and on the side of the A272 near Bramdean in Hampshire.

To help identify them here they are:



Click pictures to embiggen

For a source of monoliths the geochemistry, the petrography (the internal matrix of the stone) and the form of the natural rocks has to match. West Woods still has large boulders despite years of breaking and removal that are the size of some of Stonehenge's stones. Do these sites match up to this or as the paper suggests are they sources for small hammerstones or similar sized stones?  

There is a question mark over where the Bramdean stones originated as the circle of stones seems to date from about 1845   - https://pastrambles.wordpress.com/2015/02/22/the-bramdean-circle-of-stones/   erected by "Colonel George Greenwood of Brockwood (formerly Brookwood) House, a large property down the lane on the other side of the crossroads...there are two possible explanations of the Colonel’s motivation for building the it in 1845 or thereabouts: “One…is that he wished to see how long it would be before they were regarded as relics of the ancient past – this is commonly said of them today. The alternative is that they were a demonstration of the power of his tree-lifter”. The tree-lifter was the Colonel’s invention for transplanting trees up to 30 feet in height with their ball of earth intact, a feat the apparatus apparently made possible for a single individual to do at a rate of one tree per day. The somewhat aptly-named Colonel Greenwood was very enthusiastic about the importance of trees to the landscape and wrote a book in 1844 called The Tree-lifter, Or a new method of transplanting forest trees,....Colonel Greenwood is said to have excavated local archaeological sites and was a keen geologist referred to as ‘the father of subaerialism’, ascribing the greater inequalities in the earth’s surface to atmospheric influences. ..It was said in his obituary that “had he fallen amongst geologists in early life, instead of amongst ‘thoroughbreds’, he would doubtless have occupied a leading place among men of science”. ... Incidentally, the colonel is buried nearby at All Saints church, Hinton Ampner, his grave stone a recumbent sarsen which stands out pleasingly amongst all the more traditional ones.


 

A few thoughts on the 2024 Sarsen Debitage Paper

Local and exotic sources of sarsen debitage at Stonehenge revealed by geochemical provenancing

T. Jake R. Ciborowski, David J. Nash, Timothy Darvill, Ben Chan, Mike Parker Pearson, Rebecca Pullen, Colin Richards, Hugo Anderson-Whymark,
Journal of Archaeological Science: Reports, Volume 53, 2024, 104406, ISSN 2352-409X, https://doi.org/10.1016/j.jasrep.2024.104406. (https://www.sciencedirect.com/science/article/pii/S2352409X24000348)


An exciting addition to Stonehenge Research, identifying the sources of the stones not only satisfies the Stonehenge completist but also provides hints into the society that built it. The paper is very thorough and open and deserves study, even if the technicalities are beyond your ken.  

The authors have been admirably restrained in drawing conclusions about the sources of the debitage but it is worth emphasising the shortcomings they admit to. This is very much a preliminary paper and the tentative sources are just that.

The first problem is that they are using only twenty sample sites to compare with, the sites are detailed in David J. Nash et al. , Origins of the sarsen megaliths at Stonehenge. Sci. Adv.6,eabc0133(2020). DOI:10.1126/sciadv.abc0133  

Click to embiggen

There is much more work to be done in sampling and plotting the variations in Sarsens before there can be confidence that all potential sources or areas are known.

Secondly because of the well explained constraints they were working under the analysis had to be purely geochemical, whilst it isn't quite true that Coal and Diamonds are the same geochemically the principle that identification needs more than just the chemistry is valid.

These points are known and acknowledged by the authors but in the excitement of considering how and why sarsen may have come from across southern Britain to Stonehenge they need to be born in mind.

That long distance transport of stones and maybe even soil, Silbury?,  was a Neolithic practice is well known, but this study points to where new archaeology research may be fruitful.

There is one small inconsequential archaeological error I think I noticed in the paper. The position of excavation STH08 is erroneously plotted. I believe it is nearer the red rectangle I have overlain below.



As I blogged before it is a shame the excavation report* doesn't include a plan so it might be a problem if the plan becomes the record that is referred to in the future.

*(The Antiquaries Journal, 89,2009,pp1–19r The Society of Antiquaries of London, 2009 doi:10.1017⁄s000358150900002x. First published online 21 April 2009)   

Friday 26 January 2024

Local and exotic sources of sarsen debitage at Stonehenge revealed by geochemical provenancing,

David Nash et al have released a new paper on the Sarsen Sources of Stonehenge:



T. Jake R. Ciborowski, David J. Nash, Timothy Darvill, Ben Chan, Mike Parker Pearson, Rebecca Pullen, Colin Richards, Hugo Anderson-Whymark,

Local and exotic sources of sarsen debitage at Stonehenge revealed by geochemical provenancing,

Journal of Archaeological Science: Reports,  Volume 53, 2024, 104406, ISSN 2352-409X,

https://doi.org/10.1016/j.jasrep.2024.104406.

(https://www.sciencedirect.com/science/article/pii/S2352409X24000348)

Abstract: The application of novel geochemical provenancing techniques has changed our understanding of the construction of Stonehenge, by identifying West Woods on the Marlborough Downs as the likely source area for the majority of the extant sarsen megaliths at the monument. In this study, we apply the same techniques to saccharoid sarsen fragments from three excavations within and outwith the main Sarsen Circle to expand our understanding of the provenance of sarsen debitage present at the monument. Through pXRF analysis, we demonstrate that the surface geochemistry of 1,028 excavated sarsen fragments is significantly affected by subsurface weathering following burial in a way that cannot be overcome by simple cleaning. However, we show that this effect is surficial and does not have a volumetrically significant impact, thus permitting the subsequent use of whole-rock analytical methods. Comparison of ICP-AES and ICP-MS trace element data from 54 representative sarsen fragments with equivalent data from Stone 58 at Stonehenge demonstrates that none are debitage produced during the dressing of this megalith or its 49 chemical equivalents at the monument. Further inspection of the ICP-MS data reveals that 22 of these fragments fall into three distinct geochemical ‘families’. None of these families overlap with the geochemical signature of Stone 58 and its chemical equivalents, implying that sarsen imported from at least a further three locations (in addition to West Woods) is present at Stonehenge. Comparison of immobile trace element signatures from the 54 excavated sarsen fragments against equivalent data for 20 sarsen outcrop areas across southern Britain shows that 15 of the fragments can be linked to specific localities. Eleven of these were likely sourced from Monkton Down, Totterdown Wood and West Woods on the Marlborough Downs (25–33 km north of Stonehenge). Three fragments likely came from Bramdean, Hampshire (51 km southeast of Stonehenge), and one from Stoney Wish, East Sussex (123 km to the southeast). Technological analysis and refitting shows that one of the fragments sourced from Monkton Down was part of a 25.7 cm × 17.9 cm flake removed from the outer surface of a large sarsen boulder, most probably during on-site dressing. This adds a second likely source area for the sarsen megaliths at Stonehenge in addition to West Woods. At this stage, we can only speculate on why sarsen from such diverse sources is present at Stonehenge. We do not know whether the fragments analysed by ICP-MS were removed from (i) the outer surface of Stones 26 or 160 (which are chemically distinct to the other extant sarsen megaliths), (ii) one of the c.28 sarsen megaliths and lintels from the c.60 erected during Stage 2 of the construction of Stonehenge that may now be missing from the monument, or (iii) one of the dismantled and destroyed sarsen megaliths associated with Stage 1 of the monument. With the exception of the fragment sourced from Monkton Down, it is also possible that the analysed fragments were (iv) pieces of saccharoid sarsen hammerstones or their pre-forms, or (v) small blocks brought on-site for ceremonial or non-ceremonial purposes.

Keywords: Stonehenge; Sarsen; Silcrete; Geochemical provenancing; pXRF; ICP-AES; ICP-MS


David kindly explained the findings on X (née twitter) 


First, we analysed 1,028 sarsen fragments from 3 trenches dug at Stonehenge in 2008 using pXRF to see if there were differences within and between the trenches. In short, there weren't, due to subsoil weathering effects. Morale: don't bother using pXRF for this sort of thing.

Second, we analysed 54 sarsen fragments from the 3 trenches using ICP-MS. This is where it gets interesting. Comparison of the geochemistry of fragments against data for 20 sarsen outcrop areas across southern Britain shows that 15 fragments can be linked to specific areas.

Eleven sarsen fragments were likely sourced from Monkton Down, Totterdown Wood and West Woods on the Marlborough Downs (25–33 km N of Stonehenge). Three fragments likely came from Bramdean, Hampshire (51 km SE of Stonehenge), and one from Stoney Wish, East Sussex (123 km SE).

You might be thinking "Wow, Neolithic people dragged sarsen boulders all the way from Hampshire, East Sussex and other sites on the Marlborough Downs to build Stonehenge, not just from West Woods!" Not quite. Calm down, calm down.

We cannot tell if the fragments are from extant megaliths, or from stones from earlier phases of Stonehenge, or stones that have been removed. It is also possible the fragments were from saccharoidal sarsen hammerstones, or stone brought to Stonehenge for some other reason.

There is one exception - a sarsen fragment sourced from Monkton Down that we know (thanks to expert refitting by Ben Chan) was part of a 25.7 × 17.9 cm flake removed from the outer surface of a large sarsen boulder, most probably during on-site dressing.

We're pretty sure this boulder isn't on site today, unless it is stone 26 or 160, which have a different chemistry to the other extant sarsens. However, it adds a second likely source for the Stonehenge megaliths in addition to West Woods. I'll leave it there. Happy reading!