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Saturday, 8 June 2024

The Stonehenge sarsens probably did NOT come from West Woods


Stonehenge revisited: A geochemical approach to interpreting the geographical source of sarsen stone #58
Archaeometry, June 2024
DOI:  10.1111/arcm.12999
by Ronald G V Hancock,  Michael P Gorton,  William C Mahaney, Suzanne Aufreiter and Kostalena Michelaki

ABSTRACT


It is tempting in material sourcing analyses to treat chemical data primarily as numbers to be sorted, while disregarding their interlinked geochemistries. Consideration of geochemistry, however, often leads to the drawing of more nuanced and reliable conclusions. In this paper we re-examine data published in 2020, related to the sourcing of stone #58 at Stonehenge, paying attention to geochemistry. We question the potential single-source interpretation of these data and suggest instead that three to six sources cannot be ruled out.

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Well well -- this is a surprise.  I knew that some new research was under way involving the Altar Stone, but I was unaware that new geochemistry work was also going on with regard to Sarsen 58 and the West Woods connection.  Readers of this blog will recall that I had a vigorous spat with David Nash a few years ago, in 2020, on the grounds that I was not convinced that his analytical plots did actually show a strong connection between West Woods and Stonehenge.  I thought that there was "over interpretation" going on, particularly with regard to the visual messages coming out of scatter diagrams etc.


See also:

Quote from the new article:


........the Nash et al. (2020) proposal of West Woods as a possible source for stone #58 from Stonehenge was taken to be more certain by Ixer and Bevins (2021) and Worsley (2021), and by 2024 it was treated as a given by Ciborowski et al. (2024).


In fairness to all concerned, the original stark proposition which got the full media treatment in 2020 ("Stonehenge sarsen mystery solved" and so forth)  has subsequently been abandoned and replaced by something more nuanced, with multiple sarsen sources for Stonehenge now broadly accepted.  Unfortunately, the media do not do subtlety and truth -- they just want spectacular discoveries and banner headlines -- and so the developments since 2020 have been largely ignored.  That's the way of the world, and those who rush into print should perhaps be more mindful of the fact.....

Anyway, the other thing that is interesting about this article is that it cites Lionel Jackson and myself (2009) as the authorities on glacial transport, ignoring the fact that there has been a vast literature since then.  As authors based in North America, I am not sure that they are up to speed on the different arguments involving sarsen origins and bluestone origins, but they say:

"........... two samples (MD2 and TF2) severely question the assumption that all three chosen stones are always geochemically similar at each geographic location. Their presence at their find-spots may contribute to the idea of John and Jackson (2009), and others (e.g., Briggs, 2009; Burl, 2006; Kellaway, 1971), that the huge stones of Stonehenge were moved naturally over long distances and were deposited by ice during the last glacial maximum (LGM),  20 ka ago. This does not preclude them from being removed from their find-spots at Lenham Quarry and Totterdown Wood and taken to Stonehenge."

and also:

"Given the range of chemistries from the limited sample selection available, the data reveal a broad sweep of source rocks. Some of the data may support the importation of rock to southern England by glacial transport, an idea first proposed by Kellaway (1971) and later fine-tuned by John and Jackson (2009). Sarsen stone #58 does not closely correlate well with the sampled sarsens. If the current sampling of sarsens from southern England is representative of the total geochemical variability to be found in southern sarsens, then stone #58 may have come into southern England by glacial transport. This would make it a megalith erratic derived from glacial plucking of bedrock or derived from a nunatak upstream all the way to Scandinavia. Glacial plucking is often related to regelation, a process causing mechanically induced melting and refreezing at the base of the ice, producing joint blocks up to 3–4 m that can be “plucked” and deposited or thrust to the surface of the ice. Glacial plucking both exploits pre-existing fractures in the bedrock and is most proficient where rock surfaces are well jointed or fractured or where exposed bedding planes allow meltwater to penetrate more easily. For an example of such glacial transport, see Stalker (1956, 1975). A similar situation may have occurred in southern
England as the last Pleistocene ice melted, as documented by John and Jackson (2009). While the sources of sarsen stones remain controversial, glacial transportation should be considered seriously in the explanation of the source of silicified sandstones used to form Stonehenge."

So it's good to see the glacial theory applied to both sarsens and bluestones, although many of their statements relating to dating and ice movement directions are rather unreliable.







2 comments:

David Nash said...

Hi Brian. I just stopped by to see your thoughts on the recent Altar Stone paper. Needless to say, you didn’t disappoint. I wondered if you had picked up on the publication by Hancock and I see now that you have. I won’t comment any further on your post other than to say that we have submitted a response paper to Archaeometry. This is still in review. However, to summarise our argument, the analysis by Hancock and colleagues is fundamentally flawed. There are no new data. Without getting too technical, they simply re-analyse our published chemical data as raw numbers rather than using ratios (absolutely essential to take into account the different proportions of silica cement between our different samples). As a result, all of their discussion about various elements being present in too high or too low concentrations is nonsense. I’m not sure how it got through peer review - and that’s before you get to the sections about sarsen stones being transported from Scandinavia. The Hancock paper is still only available as “Early view” on the journal pages but will eventually be published in print along with our comment and any response from Hancock. This may take a little time. However, in the meantime, West Woods is still very much the most likely source for the majority of the extant Stonehenge sarsens based on current data.

BRIAN JOHN said...

Thank you David -- good to hear from you! Interesting points -- I look forward to seeing more info when it is available. You will have picked up on my concerns about the Hancock article..........