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Wednesday, 21 December 2016

Sarsens and the solution hollow dilemma



A few months ago I did a post on the 'honeycomb' characteristics of the solid chalk surface beneath Stonehenge -- or at least, beneath the bits that we know about.   I referred to the pits, hollows, sockets and solution features which are almost universally interpreted by archaeologists as being man-made -- the assumption being that the bluestones -- and maybe the sarsens as well -- have been moved about from one setting to another during the various "stone phases" of the monument.   This has been remarked upon by Anthony Johnson in his book on Stonehenge, and by many others as well.

Anthony Johnson says on page 157:  "... the maze of holes, hollows, abandoned settings and residual stone fragments in the centre of the monument has left the underlying chalk resembling a very badly mauled Swiss cheese which, compounded by extensive disturbance from rabbit burrows, has made the disentangling of the various periods of activity almost impossible, leading Hawley to conclude:  "I frankly confess that I have no explanation to offer in elucidation of this tangle, and I doubt whether anybody will ever be able to explain it satisfactorily."

I wondered whether some of the pits might actually be "extraction pits" from which embedded monoliths had been collected -- and I cited Nick Snashall, who is quite convinced that she can tell exactly which pits are man-made and which ones are not........  

https://brian-mountainman.blogspot.co.uk/2016/08/extraction-pits-solution-hollows-post.html

We have discussed the nature of the  chalk bedrock surface in other posts, including many on the so-called "periglacial stripes" within the Avenue near Stonehenge.  Here is another of my posts:

https://brian-mountainman.blogspot.co.uk/2013/04/the-chalk-surface-grooves-everywhere.html

I would hazard a guess that at least a part of the pitted surface we see in the image above is natural, revealed when the archaeologists carefully scraped away everything rotten or loose.

Some more guidance on the nature of the bedrock / regolith interface is found in the booklet on Fyfield Down written by Mike Clark and published by NCC in 1976.  This is a revealing and perhaps surprising diagram from page 16:

 It shows a section cut alongside one of the recumbent large sarsens found in Clatford Bottom.  It shows that the sarsen is embedded in a layer of brown flinty  loam which extends for about a metre beneath the stone base, with combe rock beneath that, and then with almost a metre of strongly weathered chalk above largely unaltered chalk bedrock.  The brown loam is presumably the periglacial material that has moved downslope, maybe carrying or rafting the sarsen along as it accumulated.  But what interested Clark and his colleague was the evidence that in ten pits examined under and adjacent to recumbent sarsens, there was increased soil acidity as compared with soils where no sarsens were present.  There was also a tendency for solution pipes to occur beneath sarsens of various sizes in the combe rock, penetrating into the weathered chalk beneath.  One of these pipes can be seen in the illustration above.  Conclusion:  the presence of sarsens in one position for many thousands of years leads to enhanced solution in the regolith and rotten chalk beneath.
  
Result: a highly irregular and pitted bedrock surface.

---------------------

Fast forward to another paper, kindly brought to my attention by Alex.  This one is from 1996, by Julian Murton.  Details:

Julian B. Murton:  Near-Surface Brecciation of Chalk, Isle of Thanet, South-East England - a Comparison with Ice-Rich Brecciated Bedrocks in Canada and Spitsbergen
Permafrost and Periglacial Processes,Vol. 7: 153-164 (1996)

ABSTRACT

Chalk on the Isle of Thanet, Kent, is brecciated to depths of a few metres beneath the ground surface. The brecciation commonly comprises (i) an undeformed layer of angular, platy blocks more or less parallel to the surface overlain by (ii) a deformed layer containing small open folds, typically with vertical axial planes. Above the brecciated chalk is an involuted layer (-0.5 to 2.0 m thick) of chalk diamicton and brickearth.
By analogy with brecciated ice-rich limestones, arkoses and shales in areas of continuous permafrost in Arctic Canada and Spitsbergen, it is suggested that brecciation of the Chalk resulted primarily from ice segregation in perennially frozen bedrock, and repeated segrega- tion formed an ice-rich layer just beneath the former permafrost table. Subsequent thaw consolidation of this layer is thought to have formed an involuted layer through soft-sediment deformation.
Three implications arise from this study: (i) near-surface brecciation of the Chalk probably took place during conditions of continuous permafrost; (ii) the growth and thaw of the ice-rich layer in chalk was probably an important element in the geomorphological evolution of the English Chalklands, heaving and brecciating the Chalk during permafrost conditions, and deforming or redepositing the overburden during periods of active layer deepening; and (iii) repeated ice segregation near the top of permafrost may have brecciated other bedrocks in the British Isles.

The paper illustrates how, under conditions of continuous permafrost such as those which prevailed for lengthy periods on Salisbury Plain, brecciation of the bedrock combined with frost-heave processes led to the creation of both involutions and a highly complex bedrock - combe rock interface.
  
Result: a highly irregular and pitted bedrock surface.

-------------------------------- 



Fast forward to another paper brought to our attention by Alex. This one is from a group of Polish researchers, published in 2012:

Radosław Dobrowolski, Andrzej Bieganowski, Przemysław Mroczek and Magdalena Ryżak:
Role of Periglacial Processes in Epikarst Morphogenesis: A Case Study from Chełm Chalk Quarry, Lublin Upland, Eastern Poland
Permafrost and Periglac. Process., 23: 251–266 (2012) 
DOI: 10.1002/ppp.1750

ABSTRACT

Pocket forms several decimetres in diameter, 0.5–1.5 m deep and infilled mainly with glaciogenic sands, silts and clays of Saalian age are commonly developed on the top of the karstified chalk massif of the Lublin Upland, eastern Poland. Analysis of lithofacies, particle-size distribution and micromorphology of three pocket infills in the Chełm chalk quarry reveals a prominent clay cortex between the host chalk and the glaciogenic infill and suggests that periglacial processes have played a considerable role in the formation of the pockets and in the redistribution of their primary glaciogenic infill. A conceptual model for epikarst morphogenesis for the chalk karst of Lublin Upland is proposed, involving three stages. Stage I: In the absence of permafrost, precipitation water infiltrates unconsolidated glaciogenic deposits. Stage II: Periglacial transformation with underlying permafrost. Primary cryoturbation structures became protokarst forms, and then epikarst forms. Stage III: Degradation of the permafrost, with increased carbonate dissolution and development of a clay karst cortex.

This is a highly technical paper, and a convincing one, arguing that karstification and the creation of deep "pockets" can occur in chalk landscapes under a periglacial / permafrost regime, with physical and chemical (solutional) processes operating together.  We are talking about pockets here, and not solutional rills or runnels.

Result: a highly irregular and pitted bedrock surface.

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 I suspect that if you were to let loose groups of archaeologists with brushes, pans, buckets and trowels in any of the areas described in these three research publications, they would eventually reveal a chalk surface looking very much like the one shown from Stonehenge, at the top of this post.

16 comments:

Richard said...

Hi,

I find your posts about Stonehenge very informative. Would love your thoughts on this analysis of Stonehenge, which claims that it was most likely built originally for a burial site or sun worship. Thanks!

The source: https://www.rootclaim.com/claims/why-was-stonehenge-built-13169

Jon Morris said...

That sounds fun Richard. Have put a claim in!

Alex Gee said...

Brian : Well done, glad to see the post up.

Looking at the top picture with hindsight, its quite incredible that none of the Archeos

considered "Why would any one dig holes of that odd shape?

I suppose the main problem is that the chalky loam of the involuted layer looks identical to

that of backfilled manually disturbed ground?

Be interested to see which of the archeos will be quickest to seize on this and produce a paper?





TonyH said...

Definitely worth a Chapter to itself in your eagerly - awaited revised edition of your "Bluestone Enigma" book. Perhaps you'll have a sub - title referring to the Sarsens.

Jon Morris said...

Thought that this looked like an interesting website start-up Richard.

I've contributed two evidence referenced features to see what they do with it (there's well over 100 evidentiary items I have logged which largely indicate one particular hypothesis, but would be a lot of work to do all of them).

There's a number of criticisms I would have of the site, but it looks like a start-up, so can't be too critical.

Alex Gee said...

Perhaps it might even be seized on by some brain dead undergrad as an original idea of

theirs? Lets keep a close eye on the literature!

Although what might be most interesting is to run a book on how long the Archaeos who visit

this blog can resist the temptation to achieve fame and ever lasting glory by destroying

the Stonehenge orthodoxy by publishing a paper claiming the idea as their own.

I'll have a fiver on 6 months at evens?

chris johnson said...

Interesting site to browse when I have time - tonight with a Christmas Eve whisky maybe.

My conviction is that monuments built in the megalithic times display an awareness of star movements, not simply solar events. In this respect I like Jon's "New Theory" and it will be interesting to see if it attracts contributions. The star gazers tend to be very secretive - I know a big secret but I am not going to share it with you just yet - you know the type.

For Brian's house near Newport you want to google the kings quoit in manorbier/deneb/alignments or some such. A researcher makes a convincing case for the alignment various megalithic/bronze age features with an alignment that runs through Newport Pembs. (Tongue in cheek). The theory is that winter solstice saw deneb setting and rising across the ridgeway. The observation place is the Quoit and the rising and setting occur over the bronze age barrows - or did in the late third century BC. It is a fun read - if you can't find it I'll look up the link or mail you the paper. And, by the way, the Egyptian beliefs were that souls migrated north, hence the interest in the Swan constellation of which Deneb is a part and was certainly used by navigators to point to the North.

Happy Christmas all!!

Jon Morris said...

Thanks Chris. I'm not sure about that site: It's not very transparent who making decisions about what. The evidence section seems to require the manual intervention of a moderator, which strikes me as putting too much burden on the moderator. It has a few other problems with the way it ranks the importance of evidence. So as it stands, I anticipate that the concept will fail. Nevertheless, I've added a few pieces of evidence to see what happens.

The star gazers are very secretive. Archaeology is very much a minority interest and there's very little interest from academia in new interpretation (there's no money in it). So being "publicly secretive" about it is very counter-productive. In my opinion, it would be better for them to keep completely silent if they haven't got the time to fully explain whatever it is that they think they have.

BRIAN JOHN said...

Yes -- this is an issue. For example, I cannot see why the "evidence" (very selectively presented) has any real bearing on the debate about the PURPOSE of the site......

chris johnson said...

The bit about the "many" dead at Stonehenge struck me. 200-300 over 1500 years does not strike be a being "many".

Jon Morris said...

is an issue. For example, I cannot see why the "evidence" (very selectively presented) has any real bearing on the debate about the PURPOSE of the site......

Agreed with you both. The evidence that has been listed is a bit lightweight and selective.

The past and purpose of a structure can give a lot of clues on how to reduce costs of modification, so there is a definite economic advantage to having a structured assessment based on limited evidence: The savings can be quite large relative to costs of investigation.

However, there do not seem to be any economic or social benefits to finding out what purpose Neolithic monuments served, so there's perhaps very little incentive to develop the sort of methods used by industry. The other subjects that the website deals with might provide some sort of benefit and this could, possibly, allow the developers to get a format that will work.

Neil Wiseman said...

To the original point:
I think the evidence for tooled sockets outweighs the evidence for any natural characteristics in the chalk bed - the excellent papers submitted notwithstanding.

Notice that the sockets for the West Trilithon are immutable, meaning they were never adjusted after erection, while there's any number of cuts and re-cuts for the Bluestones. I agree with Tony Johnson on that one, that is: We'll probably never be able to either date and sequence them, or even untangle the mess.
But it's clear which ones are man-made and which are not.

Neil

BRIAN JOHN said...

Thanks Neil -- so what is the evidence for "tooled sockets"? And have all -- or even many -- of the sockets/ pits / solution hollows / periglacial pockets been carefully examined for evidence of tooling or digging? Or is there just a prevailing assumption.....?

Neil Wiseman said...

Hi Chris,
Just to clarify: 2-300 cremation depositions over 500 years - not 1,500.
Which, with some dating forgiveness, is about one a month. So it was a pretty busy place before the stones went up.
This plus/minus allows that some of the deposits were curated - older than the ditch itself. Apparently it was quite a special cemetery until the Beakers came along and changed everything.

Neil

chris johnson said...

Hi Neil,
On your estimation of one "burial" per month the monument was used as a cemetary for some 20 years only (20x12=240). This is a very short period in the very long life of Stonehenge as a monument - my estimate of 1500 years is very rough of course as we do not know with certainty when usage started and stopped in pre-history.

I fear the certainty of experts when talking about this reflects a conviction on their part more than any weighting of evidence. Where do you get the one a month figure from by the way? I don't follow these aspects as closely as yourself.

Neil Wiseman said...

Hi Chris,

Oops ...
My arithmetic is obviously flawed. LOL
500 years is the baseline for burials, not one per month.

1,500 years is almost the entire working life of the monument, and we know interments were over by the time the Sarsens went up. There's about 500 years between the ditch and the stones, so this is where that number comes from. (The figure: '200 or 300 burials' is an extrapolation because only 32 of the 56 Aubreys have been excavated).

The monument was almost certainly a moon-governed cemetery when it was established - though it did have a few solar references. (The central Axis being the most obvious). Following this it was abandoned for about a hundred years and it was during this time that the Beaker influence began to flourish.
Upon return, they re-fitted the place and reversed the emphasis to solar, switching the purpose from death to life. We see a substantial bloom in the number of Barrows built at this time because they'd become much more popular for the big-wigs, while cremations - though not extinct - weren't used at Stonehenge from that point because it was no longer a cemetery.

When the lunar sightline posts were removed (or rotted away) from the entrance and the Heelstone re-situated from the S-97 position, the moon lost its influence and the Aubreys were no longer relevant. Were they forgotten altogether? No idea - but they couldn't have been used as a calendar anymore because all the cross-henge sightlines were interrupted by the stones, while the axis and cardinals had been re-calibrated.

They put up the Trilithons and a little later the Stone Circle, while shifting the Blues around in the interim to accommodate the new symmetry. Dates for the cessation of use at the West Amesbury Henge tend to bolster the thinking on re-establishing its Bluestone oval within the Trilithons, in addition to its now-redundant use as a cremation facility for the big site. (Admittedly, there's some vacancies in this rationale; the much later Avenue being a glaring example.)

Anyway, 4- or 500 years for use as a cemetery, and forget about my error of one burial per month.

With regard to what the 'Experts' think: None of this is particularly codified, and nothing is Certain - but based on evidence it's the rough scenario used at present until additional information comes along to contradict it. The learning curve is fluid and very little is cast in stone. (pun intended) Though I'm considered to be slightly out-on-a-limb with some ideas, my focus is intent, while the currently established timeline tends to corroborate it.

Best,
Neil