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Wednesday, 24 April 2013

The Stonehenge rock types -- time for an update?


These two diagrams, courtesy Rob Ixer, show the composition of rock types from part of the Stonehenge Layer.  The diagrams probably need to be updated.   Note -- they do not represent the WHOLE of the Stonehenge Layer, most of which has never been properly examined.  Who knows what treasures there are, still to be uncovered?

Last year, in October, I published the following information, some of which probably needs to be updated.  There has been such a flood if geological information in recent years that it's difficult to keep up -- the geologists are rolling together some of the rock types which were previously differentaited, and finding petrographic reasons for differentiating others that were previously assumed to be the same,  such is the way with science.  All updates gratefully received -- I will amend the list as necessary and then publish it again.

So here goes:

1.  There are 31 dolerite orthostats, of which 14 have been sampled in 1991 and 2008.  Some are standing stones and some are stumps.  Some are spotted and some are unspotted. (I am a bit mystified as to why the unspotted dolerites do not appear on the diagrams above -- stones 45 and 62 are made of unspotted dolerite.)  Rob has made the point that the differences between the spotted and unspotted dolerites are "a chimera" -- presumably on the basis that there are wide variations within the Preseli tors and other outcrops.  But the latest thinking is that Carn Meini is probably NOT a source....

2.  There are five crystal vitric ash flow tuffs represented in the orthostat collection.  (Stones 40, 48, 46, 38, 52c.  (Four distinct types?)  There is not much debris to match these in the Stonehenge debitage, but similar fragments are found in the great cursus field.  Research is ongoing, but they may come from the Preseli area. In the latest paper by B+I, Carn Alw is ruled out as a source location, but it is suggested that there are four other locations for similar broadly similar rock types -- as yet unidentified.

3.  There are four volcanic ashes -- stumps 32c, 33e, 33f, 41d. (These are not sampled, and so all we can do is speculate...)

4.  There is one calcareous volcanic ash stump -- number 40c (Again not sampled?)

5.  There are 2 micaceous sandstone stumps -- numbered 40g and 42c.  (More info is eagerly awaited on these......)  There are also lumps of Lower Palaeozoic sandstone scatterd about in the debitage -- the largest lump weighing c 8.5 kgs.  From SW Wales? Work is apparently in progress in an attempt to find the source areas for these samples.

6.  There is another calcareous sandstone -- the Altar Stone (stone 80).  sampled more than a hundred years ago, but not since.  Probably from the Senni Beds of Carmarthenshire or Powys? (Not from Milford Haven)  Interestingly, no debitage has been recognized in recent digs from this stone or from anything like it.

7.  In the debitage there are lots of fragments of volcanics with sub-planar cleavage -- matching the Rhosyfelin rocks?  The "rhyolite with fabric" is not all the same -- but most appears to be from the Pont Saeson area.  There are NO matching orthostats.

8.  There are also some basic tuffs in the collection of fragments from the debitage -- two lithologically different types.  From the Fishguard Volcanics?

9.  Other lithics in the stone collections from the debitage -- some stones are adventitious / introduced / modern, but some (eg haematite, greensand, slate, Mesozoic sandstones and gabbros) appear genuine, and need further research.

10.  In the course of the recent geological research, 6,368 rock samples have been examined and classified -- and organized by archaeological context.  the total weight of samples thus far is in excess of 70 kg.  Most fragments are very small, weighing on average about 11 grams.

11.  Almost half of the material in the debitage is sarsen -- I suppose we should not be surprised by that, but it would be good to know how many types of sarsen there are, and where they came from.....

12.  This recent research matches pretty well with what I said in my post dated 3 December 2011:
http://brian-mountainman.blogspot.co.uk/2011/12/bluestone-rock-types.html

I reckoned then that there are about 30 different rock types represented in the "bluestone assemblage" -- and unlike Rob, I give significance to the small bits as well as the orthostats, since I am interested in glacial and other processes and want to know where they came from and how they got here.

======================

Stonehenge Bluestone Types

1.  Unspotted dolerite ---- monoliths  45 and 62.  Carn Ddafad-las?

2,  Spotted dolerite -- densely spotted.  Monolith 42  -- Carnbreseb? 43?

3.  Boles Barrow dolerite -- spotted?  But similar to stones 44 and 45? From Carnmeini / Carngyfrwy area?

4.  Rhyolite  -- stones 38, 40, ignimbrite character.  Ash-flow tuffs (dacitic). Not Carnalw ? May be from different sources?

5.  Rhyolite --  stones 46 and 48, rhyolitic ash-flow tuffs.  Carnalw area?  Same source?

6.  Rhyolite fragment from a different source from the above types

7.  Laminated calcareous ash -- stumps 40c, 33f,  41d

8.  Altered volcanic ash -- stump 32c, 33e?

9.  Rhyolite -- another type -- stump 32e.  Related to Pont Saeson / Rhosyfelin samples?

10.  Micaceous sandstone -- stumps 42c, 40g (Palaeozoic -- South Wales origin?)

11.  Rhyolite -- lava -- stone 46

12.  Rhyolite -- flinty blue -- different lava?  stone 48

13.  Spotted dolerite with whitish spots --stones 33, 65, 68, stump 70a?, stump 71?, 72

14.  Spotted dolerite with few spots -- stone 31, 66?

15.  Spotted dolerite with pinkish spots -- stones 150, 32, 34, 35A, 35B (one stone), 39 (?), 47, 49, 64, 67, 69, 70

16. Spotted dolerite -- moderate spots -- stone 37, 61, 61a?

17.  Unspotted dolerite -- stone 44 -- different from stones 45 and 62

18.  Very fine-grained unspotted dolerite -- stone 62

19.  Silurian sandstone -- Cursus -- fragments

20.  Devonian sandstone -- Altar Stone -- Devonian Senni Beds -- Carmarthenshire or Powys

21.  Sarsen sandstones -- various types -- packing stones and mauls

22.  Jurassic oolitic ragstone -- Chilmark?

23.  Jurassic glauconitic sandstone -- Upper Greensand?

24.  Gritstone unspecified fragments (Maskelyne, Judd)

25.  Quartzite unspecified fragments (Maskelyne, Judd)

26.  Greywacke unspecified fragments (Maskelyne, Judd)

27.  Granidiorite -- Amesbury long barrow 39

28.  Quartz diorite -- ditto

29.  Hornblende diorite -- ditto

30  Flinty rhyolite -- fragments from Pont Saeson (see 9, 11 and 12 above.  same source?)

31.  Rhyolite fragments -- with titanite-albite intergrowths (source unknown) 

37 comments:

TonyH said...

Interesting there is slate fragment in the debitage. Any likelihood of this being examined more closely and categorised more precisely? The Open University dig's finding of a shaped? piece of metamudstone ought to make having a good look at the slate Stonehenge debitage of more relative pressing importance in the overall scheme of analysis.

TonyH said...

Your Heading: Stonehenge Bluestone Types, 4 Rhyolite:- mentions Ignimbrite - have you any updated information about Colonel Hawley's alleged finding of an ignimbrite boulder in the 1920's or '30's when he was in sole charge of excavations at the Monument? I believe Kellaway made comment upon it.

BRIAN JOHN said...

I did a post about that ignimbrite some time ago -- no new information since then.......

Alex Gee said...

Brian
Do you know of any studies that have recorded the stratigraphy of the sections the debitage samples have been removed from and the position of the samples within the section?

Cheers
Alex

GCU.intwominds said...

Try Ixer and Bevins 2013!
Their most recent Ferret Club Mag has EXACTLY what you need due to Mike Pitts' contribution.
When the May 2008 Stonehenge excavation is published all of hundreds of bluestone will be contested etc.
The data are all there most of it published. It just needs a bit off effort to find it.
M

TonyH said...

Alex

M is referring to WANHS Studies 2013 when he says "their most recent Ferret Club Mag". This is Wiltshire Studies, vol 106 (2013), pp 1-15. 'A re-examination of rhyolitic bluestone "debitage".....'

GCU.intwominds said...

Bloody Kindle and my not proofing.
Contexted not contested.
M

BRIAN JOHN said...

Nice mistake!! I will take it that my list is essentially correct, at least for the moment, since nobody can be bothered to criticise or question anything on it.....

Alex Gee said...

Thanks Chaps.

What if erratic material were to be found within undisturbed small scale deformation structures; that were agreed to be cryogenic involutions(cryoturbations)?

Given that such involutions could only have formed during the Younger Dryas; more probably during the LGM?

The erratic material would have to have been present, to be incorporated into these structures?

Would this not also invalidate claims of human transport?

Cheers
Alex


GCU:Intwominds said...

Nice try! but no ice-lolly this time
M

Constantinos Ragazas said...

Alex,

Would the rhyolitic debitage at Stonehenge be such erratic material you speak of?

I have puzzled for a long time why debris in the Stonehenge Layer is so uniformly mixed in the soil (according to the Atkinson excavation photos). There is only one process I can think of that can account for this. Alluvial deposits in water retaining basins. Have any other explanations?

Kostas

BRIAN JOHN said...

Nonsense, Kostas. Alluvial deposits in water retaining basins would NOT look like this. Kindly move on from this absurd obsession of yours, and pay some attention to the evidence and to the laws of physics.

BRIAN JOHN said...

Alex, there are various types of frozen ground phenomena. If cryoturbations exist in southern England, they could date from any of the cold phases -- the stratigraphy shoulkd show which one we are dealing with. I agree that big cryoturbations might be Devensian (around 20,000 BP) and smaller ones might be Younger Dryas (c 10,500 BP)and that if there is erratic material contained within them, that material cannot have arrived any later than the time of the frozen ground conditions. Ice wedge casts could involve a different scenario -- if there is an ice wedge in permafrost, it could take a long time to melt, and then debris falls into it from above -- or from the slumping of the sides. So the debris is later than the wedge -- but probably not by very much........

Do I sense an interesting contribution coming our way?

Constantinos Ragazas said...

Brian,

“Alluvial deposits in water retaining basins would NOT look like this”.

I agree! If the “look like this” refers to “cryoturbations”.

But this does not answer the larger question. Does the Stonehenge Layer look like alluvial deposits in the bottom of a retaining basin?

How else do you explain the uniform mixture of the debris in it?

Kostas

BRIAN JOHN said...

(a) the Stonehenge Layer appears quite variable -- it is not uniform.

(b) deposits in the bottom of lakes or the sea are stratified and arranged in beds with more or less uniform particle sizes.

Constantinos Ragazas said...

Brian,

In a good discussion ideas take on a life of their own … and ask for thoughtful response. But I will understand if you are fed up and do not want to pursue this further. For whatever it is worth.

I am going entirely by the Atkinson excavation photos you have posted earlier. Your points a) and b) are 'falsifiable', along with my observation re: Stonehenge Layer.

I think we can agree with Richard Atkinson the Stonehenge Layer holds the key to the Stonehenge Enigma. Can you post on this along with some Atkinson photos showing trench cross-sections of the Layer?

Kostas

GCU.intwominds said...

The Stonehenge Layer has much struck material, both Preselite and rhyolite and many pottery sherds.
It is anthropogenic.

Whence this Narcissistic desire to see all in limpid waters. An Echo of our late Spring?
M.

Constantinos Ragazas said...

M of twominds,

If Neolithic men used stone to strike stone, why can't stone strike stone in meltwater streams? As for many pottery sherds, any whole pottery found? Even in pieces? This would prove “anthropogenic”. But pottery sherds and knock-outs do not.

Furthermore, why should any of this debris be more or less uniformly mixed-in the soil meters deep as the Atkinson photos clearly show? Wont “anthropogenic” debris from stone dressing be in distinct layers closer to the surface and at the base of the stones being dressed?

Nothing Narcissistic about any of this! Unless you call passion for truth Narcissistic.

Kostas

Alex Gee said...

Brian: glad you grasped my point.

Younger Dryas or LGM cryoturbations are extant along the north and south flanks of the Mendip Hills; at near sea level.

I wasn't referring to the Stonehenge layer. But the sub- surface morphology of Salisbury Plain.

I merely wished to know how detailed the excavators studies of micro and macro structures in the unconsolidated sediment and weathered chalk layer have been?.

Just a single erratic would need to be found intact in an undisturbed cryoturbation, for human transport to be consigned to the history books.

I think the idea is worth pursuing. I will send you some piccies and data this week:if you wish? I Think it would make a good post.

Whilst I now have the utmost respect for our port dwelling itinerant ice cream seller!

I can't help thinking that Myris has missed the boat on this occasion, and would find more profit,in a return to doing favours for sailors down the docks!

Cheers
Alex






GCU.intwominds said...

Ah Mr Gee my comment was for Brian whom I respect as an academic not you.
M

BRIAN JOHN said...

Ah yes, a lot of people talk in riddles on this site -- some intentionally, and some not.....

TonyH said...

Well, I admit it, I may have studied Undergraduate level geomorphology many geological moons ago, but no little about cryoturbations........... but,however, I was transfixed over the "Handbags At Dawn" dispute between, in the blue corner, the DreamTeam of GeoffW & TimD, and in the red, blustering corner, MPP, over the political Hot Potato that is:-
'Bioturbation at Stonehenge', involving the HUMBLE EARTHWORM & Mr DARWIN [1881].Mr Parker Pearson devotes the whole of chapter 19 to this wriggly problem.

Alex Gee said...

Thanks for the waffle chaps, but still awaiting enlightenment, as to which published papers contain detailed sections of structures within the unconsolidated sediment and weathered chalk layer?

As I said, any erratic contained within cryoturbation structures, immediately bins the Human transport theory.

It wasn't a spurious request!

My fear is that no such studies of these structures have been done prior to removal of erratics, and that erratic samples have simply been removed from upper stratigraphic layers, idly labelled brickearth /Loessic soils.

Thereby destroying vital evidence.A
case of grab the goodies and run?

Be most delighted to be proved wrong!


Cheers
Alex



GCU.intwominds said...

Finally finished relooking at the May 2008 lithics.
The original Ixer-Hilton diagrams are but little altered.
No vast numbers of exotic lithics.
More greensand less saccharoidal sarsen, more group c rhyolite far less group a.
That little unwashed/unwatered outcrop has shelled out more than its fair share.
M

BRIAN JOHN said...

So one or maybe two orthostats made of Rhosyfelin rhyolite and now broken up into lots of little pieces because the rock was just too flaky and friable -- leaving behind those two stumps about which you have often speculated? Can you indicate on a map exactly where this group C rhyolite debitage has been found?

Constantinos Ragazas said...

M in clear and simple terms...

...have you now matched the Rhosyfelin rhyolite fragments in the SH debitage with stump or standing orthostats at SH?

Brian wants to know where the debitage lies. I want to know what these matched orthostats are.

Kostas

BRIAN JOHN said...

Kostas -- we have all complained that those two stumps that look as if they might be the right sort of rhyolite have NOT been sampled. All of us would like that to be done, and I dare say EH have been asked for their consent over and again........ what remains is educated guesswork. But don't blame the geologists.

Constantinos Ragazas said...

Brian,

As long as the Rhosyfelin rhyolites in the debitage are NOT MATCHED to any SH stones, all claims by MPP and others of a “Rhosyfelin quarry” are totally meaningless.

These claims should contain disclaimers in bold: NO MATCH MADE. Let MPP figure out sensible explanations of how these fragments found in SH got to SH. And WHY!

Any sight of any Rhosyfelin RC-dates from samples taken by MPP many moons ago, Myris? What does sublime Apollo say about such human frailties?

Kostas

GCU.intwominds said...

Dear Kostas
The mismatch between the extant orthostats and debitage has been highlighted by Ixer and I and B since 2008 and is in everyone of their publications. Have you ever read even an abstract of those carefully crafted papers.
Read the last sentence of their most recent B and I 2013.
C14 dates are very very very slow and I fear may be given by the spurning fiancee of Sublime Apollo.
Re reexcavation of Atkinson's trench about SH 33 it is early days but there is interest in such a project. It is so obvious a thing too do.
The Nile is rising nicely so perhaps the harvest will be grand this year.
M.

GCU:Intwominds said...

Nevertheless, there remain uncertainties over the provenance of other Stonehenge rhyolites (and dacites), including four of the orthostats themselves.

B and I 2013.

M

Constantinos Ragazas said...

Dear M,

My comments were more directed to the likes of MPP who are using your good science for their shoddy stories. Meant no offense to you.

Will the mystery demolished orthostats “producing” the rhyolite fragments in the debitage at SH also explain the other Rhosyfelin knock-offs at the Avenue and at the Cursus area?

As for the RD-dates ... I know a lab in Miami that would have this done in just two weeks, guaranteed. And that is normal time. If you are at a hurry, can get these dates done in days.

You are not looking good to Apollo apologizing for MPP's sins.

Kostas

BRIAN JOHN said...

Tend to agree with Kostas here -- there are so many labs around these days that C14 dates -- even for a sizeable batch of samples -- should be ready in a couple of weeks. MPP probably had the dates in his pocket by the end of October.......

two theories. Either the dates are extremely embarrassing in that they support my dating ideas rather than his -- or else National Geographic has such control over the project that there is an embargo on releasing the dates until they are announced in a blaze of glory in the next TV spectacular. Don't laugh -- I have a note in front of me (from MPP's talk in Brynberian last September) saying that nothing can be released without Nat Geog Mag's consent.

Constantinos Ragazas said...

Brian,

You are to quick to excuss MPP's reluctance to release the RC-dates for Rhosyfelin.

Clearly, if National Geographic is behind this, why didn't National Geographic saved the blockbuster boast Rhosyfelin was the “bluestone quarry” for a must-see TV spectacular?

A curiosity. When did MPP made his comment about needing NG approval for the release of the RC-dates? Perhaps at a time when he already had these dates “in his pocket”?

National Geographic may have provided an easy alibi to avoid embarrassment. Or excuse to deliberately keep the dates hidden from the world?

Kostas

TonyH said...

I think National Geographic may well have trumpeted Rhosyfelin in the way Kostas describes, but just in its well- circulated Magazine, with its world-wide sales, thus far.

It could be that any N.G. TV spectacular is hanging fire for the time being, until/ if Rhosyfelin, and other MPP ventures, comes up with a sufficiently adventurous tale to "justify" such a TV extravaganza. MPP may be putting more of his eggs in another basket, namely, that he "discovers" the route along which he reckons the Wiltshire sarsens were moved overland from, he thinks, the area to the east of Avebury and west of Marlborough. He is hoping he has a Neolithic "road" but needs another season to confirm his notion. Personally, I think the jury is out on that one. We may need Myris/ Apollo to establish the provenance of the Stonehenge sarsens, since it still may be that many were obtained much closer to Stonehenge than the 20th Century Legends from Atkinson would have us believe? Are you listening, Myris/ Apollo and others?

Constantinos Ragazas said...

Tony,

Thanks for the scoop inside. Leaves me more bewildered and more convinced MPP is purposely hiding his dates! Afraid truth will catch him in an illicit affair. Can't use his pal NG to hide behind any more.

Kostas

TonyH said...

Mike PP would, of course, ideally like to produce an ultra-mega-scoop of his own, telling of how those hyper-cooperative Arnie-muscled guys moved stones here, there, and everywhere, be they quaint little blue ones or truly monstrous mega-sarsens. So if the Rhosyfellin etc side of the equation should prove pointless, then he may at least be hoping to cobble together something from his Marlborough Downs investigations. Watch this space.

Constantinos Ragazas said...

Tony,

MPP may be following a strategy of never looking back and never admitting failure. If he brings to his Marlborough Downs investigations the same mindset of playing loose with the facts and peddling made up stories as explanations, he may get rich in the process but not get any closer to the truth of Stonehenge. The poor public eager to know will be that much the poorer.

Serves us right? NO! We must expect more from 'experts'. Like the Rhosyfelin RC-dates which MPP is keeping from us.

Kostas