Outwash gravel sheets in Central Pembrokeshire

 

Did a braided river like this once flow from the Trefgarn Gorge exit and then southwards across the site of Haverfordwest?

Extract from the geology map showing the main gravel occurrences in pink.  The present course of the Western Cleddau river can be picked out by the yellow band on the image, showing where the present flood plain is located.

I have long been intrigued by the extensive sheets of glaciofluvial gravel found in the Haverfordwest area, especially on the "plateau" incorporating Prendergast, on the NE edge of the town, and running up through the site of the Withybush Aerodrome (where of course they are massively disturbed) towards Rudbaxton and thence towards the southern exit of the Trefgarn Gorge.

There was an outcrop of these gravels on the bank that dropped away beneath Cherry Grove, where I lived as a child, and I was intrigued by them even at that tender age! 

But why does this "gravel sheet" not run along the present route of the Western Cleddau river and to the west of the A40 road?  Was there a braided outwash river to the east of the road?  That would have been a strange situation, since much of the land to the east of the road is above the 50m contour whereas much of the land to the west of the road is below 50m.  Or might the river have migrated westwards and removed vast quantities of glaciofluvial material in the process?

Various attempts have been made to recognize river terraces in the Haverfordwest area, but they have never been very successful, partly because of the extent of the built-up area and partly because terrace remnants are small and difficult to identify.  Traditionally, the gravels in the Haverfordwest area have been interpreted either as pre-glacial river gravels laid down at a time of higher sea-level, or as glaciofluvial gravels associated with one of the earlier glaciations (Anglian?).  This would make sense, if the Gwaun-Jordanston channels are assumed to have been formed by vast torrents of meltwater flowing under the ice and flowing first westwards and then southwards, through Trefgarn Gorge and towards Milford Haven.  This too makes sense, with an ice surface gradient sloping down from NW towards SE.   If the gravels are stained and even rotten -- and hence very old -- this would support the Anglian glacial hypothesis........ and the assumption that Devensian or LGM ice could not have affected central Pembrokeshire.

On the other hand, I have been thinking for some time that Devensian ice did not simply skid to a halt along the coast of St Bride's Bay, but pushed well inland.  To his credit, Prof Dai Bowen was the only person to have suggested this in his Devensian / Weichselian ice limits maps:

Recently some big exposures have been opened up in association with the building of a new Haverfordwest High School on the site of the old Sir Thomas Picton School.  Near Prendergast Cemetery and the County Archives building there is a huge mound of excavated gravels, incorporating large boulders which suggest to me either a very powerful meltwater torrent or the close proximity of glacier ice.  Sadly, I have not been able to examine any in situ gravels which might indicate the direction of meltwater flow.........

Another braided river plain (sandur), showing the complexity of anastomosing channels and suggesting the frequent lateral displacement of the dominant water routes.  We should not strictly refer to this as a "flood plain" since the "flooding" is going on for much of the time during the melting season, here, there and almost everywhere........  Multi-channel rivers like this are a nightmare to cross on foot with a heavy pack!

Kaldalon braided river and sandur in NW Iceland.  We crossed this one many times in 1960, usually in the middle of the "night" when the water level was low.

When I examined the apparently fresh glaciofluvial gravels at Picton Point, I became convinced that they were Devensian in age, and that they were laid down nor far from an ice edge:

https://brian-mountainman.blogspot.com/2018/11/fluvioglacial-gravels-exposed-at-picton.html

It would be logical for the gravel sheet north of Haverfordwest to be the same age, and to have formed in similar circumstances.

If we look at the topographic map of north Pembrokeshire we can see where the main drainage routes are.  The Gwaun-Jordanston meltwater channel system has flummoxed researchers for well over a hundred years, but most people nowadays accept that they are very old, having been cut (and then modified) by sublgacial meltwater during several glacial episodes.  But they must have been used by huge torrents of meltwater at the end of the Devensian (LGM) glaciation as well.  If Lake Teifi and the other features in the Teifi Valley were created in the WAXING phase of the LGM ice advance, that makes it quite likely that meltwater escaped westwards through Cwm Gwaun and the other big rock-cut channels prior to the LGM and after it as well.  All very confusing.  That means a complex history of meltwater flow and landform development, between 30,000 and 20,000 years ago.

Main meltwater routes used during the Late Devensian.  It is assumed that meltwater flowed westwards and then southwards through Trefgarn Gorge when the ice was far advanced, and then escaped northwards into Cardigan Bay once the ice edge had retreated to the north of the present coastline.

So where should we draw the Devensian ice edge at the time of the LGM?  I am inclined to think we are talking of retreat phases here, rather than a terminal of "end moraine" position.  Watch this space.......

Rock avalanche

A fabulous image.  A rock avalanche onto the surface of Scud Glacier, British Columbia, June 2020.

 

The isotope analysis debate gets vicious

 

Thanks to Jon for drawing attention to this, published just a few days ago.  

A veritable confusion: use and abuse of isotope analysis in archaeology
Richard Madgwick, Angela Lamb, Hilary Sloane, Alexandra Nederbragt, Umberto Albarella, Mike Parker Pearson & Jane Evans

Archaeological Journal, 18 May 2021

https://doi.org/10.1080/00665983.2021.1911099

https://www.tandfonline.com/doi/full/10.1080/00665983.2021.1911099

ABSTRACT
The expansion of isotope analyses has transformed the study of past migration and mobility, sometimes providing unexpected and intriguing results. This has, in turn, led to media attention (and concomitant misrepresentation) and scepticism from some archaeologists. Such scepticism is healthy and not always without foundation. Isotope analysis is yet to reach full maturity and challenging issues remain, concerning diagenesis, biosphere mapping resolution and knowledge of the drivers of variation. Bold and over-simplistic interpretations have been presented, especially when relying on single isotope proxies, and researchers have at times been accused of following specific agendas. It is therefore vital to integrate archaeological and environmental evidence to support interpretation. Most importantly, the use of multiple isotope proxies is key: isotope analysis is an exclusive approach and therefore single analyses provide only limited resolution. The growth in isotope research has led to a growth in rebuttals and counter-narratives. Such rebuttals warrant the same critical appraisal that is applied to original research, both of evidence for their assertions and the potential for underlying agendas. This paper takes a case study-based approach focusing on pig movements to Neolithic henge complexes to explore the dangers encountered in secondary use of isotope data.

The abstract looks innocuous enough, since it does not mention anybody by name, but it is actually a full-on and rather vicious attack on the authors of this paper:

Barclay, G. J., and K. Brophy. 2020. “‘A Veritable Chauvinism of Prehistory’: Nationalist Prehistories and the ‘British’ Late Neolithic Mythos.” Archaeological Journal 1–31. doi:10.1080/00665983.2020.1769399.

.... and a forthright defence of this one:

Madgwick, R., A. L. Lamb, H. Sloane, A. J. Nederbragt, U. Albarella, M. Parker Pearson, and J. A. Evans. 2019a. “Multi-isotope Analysis Reveals that Feasts in the Stonehenge Environs and across Wessex Drew People and Animals from Throughout Britain.” Science Advances 5 (3)

doi:10.1126/sciadv.aau6078.

I have read through the new article, and am intrigued.  I guess a "robust defence" of the isotope analysis research was inevitable — and Barclay and Brophy would have expected it.  MPP, Madgwick and Co have clearly worked long and hard on this — but it's far nastier than I anticipated! On a quick reading, it's a classic defence based on a lot of selective citations and much nit-picking on the minor details of phraseology.  It sometimes assumes meanings or intentions that were not necessarily there. It pulls in a lot of additional isotope analytical detail, claiming that it supports the points originally made by Madgwick, Evans and others (and then questioned by Barclay and Brophy) but it is difficult here to see the wood for the trees, and does not invalidate the point made by the Scottish duo that the presented evidence of "feasting connections" did not support the 2019 conclusions.

It is clearly the intention of the authors of this new article to demonstrate that Barclay and Brophy have "abused" the isotope analyses done by Madgwick, Evans, Lamb and others.  In other words, they are accused of not really understanding it.  Well, that's a bit rich, since in my view the actual evidence presented in the "isotope analyses" papers was abused by the researchers themselves when they over-interpreted and misrepresented what it was showing.  They claim that they simply "used" the evidence --  but that's not the way I saw it!

The whole article seems to me rather disingenuous, and fails to properly address the central point of Barclay and Brophy’s paper, which was that the isotope dating specialists have been seeing everything through a Stonehenge-centred lens instead of seeing the island of Great Britain as one with a high-density traffic map, with multiple centres generating and accepting traffic from elsewhere. And I think it’s a bit rich for Madgwick et al to now claim that the media has “inflated” or misinterpreted their ideas and their press releases. One’s heart bleeds for them! They need to get real. They are the ones who write the press releases, designed for maximum media impact and coverage. They manipulate the media and manufacture myths, and know exactly what they are doing…….

Richard Madgwick, the lead author of the new article

As readers of this blog will know, I have had a go at Richard Madgwick and his friends a few years ago,  2017 - 2019:

https://brian-mountainman.blogspot.com/2020/06/isotope-evidence-not-so-spectacular.html

https://brian-mountainman.blogspot.com/2019/03/neolithic-feasts-and-far-travelled-pigs.html
https://brian-mountainman.blogspot.com/2019/04/was-there-neolithic-mass-exodus-from.html
https://brian-mountainman.blogspot.com/2018/01/affinities-of-sampled-animal-remains-at.html
https://brian-mountainman.blogspot.com/2018/08/could-cremated-foreigners-have-come.html
https://brian-mountainman.blogspot.com/2016/06/stonehenge-cremated-remains-from-west.html
https://brian-mountainman.blogspot.com/2019/03/strontium-isotope-results-may-be-deeply.html
https://brian-mountainman.blogspot.com/2018/10/dem-crem-bones-ca-overwhelmed-and-ba.html
https://brian-mountainman.blogspot.com/2018/10/more-on-strontium-isotope-west-wales.html
https://brian-mountainman.blogspot.com/2018/09/current-archaeology-too-much-marketing.html
https://brian-mountainman.blogspot.com/2018/08/the-mythologising-of-west-wales-role-of.html
https://brian-mountainman.blogspot.com/2018/08/could-cremated-foreigners-have-come_4.html
https://brian-mountainman.blogspot.com/2018/08/now-smithsonian-goes-completely-bonkers.html
https://brian-mountainman.blogspot.com/2018/08/strontium-levels-in-cremated-bone-what.html
https://brian-mountainman.blogspot.com/2017/05/strontium-isotope-ratios-in-stonehenge.htm

I found most of the isotope analysis work deeply unsatisfactory and unconvincing, and I was not alone in saying this. I also thought that the points made by Barclay and Brophy (with reference to Scotland) were eminently sensible -- although I was more concerned about some of the dodgy things being said about the "Welsh connection" by the isotope analysis team.  See here:

https://brian-mountainman.blogspot.com/2020/06/the-politicisation-of-neolithic.html

https://brian-mountainman.blogspot.com/2020/07/bluestones-and-interpretative-inflation.html

https://brian-mountainman.blogspot.com/2020/08/the-stonehenge-myth-machine-high-time.html

https://brian-mountainman.blogspot.com/2020/06/the-origins-of-british-neolithic-mythos.html

This one will run and run….

Sheffield Archaeology Dept under threat?

There's a strange article in The Guardian about the threat of closure hanging over the Sheffield University Archaeology Dept:

 https://www.theguardian.com/science/2021/may/21/stonehenge-research-in-jeopardy-if-sheffield-university-archaeology-unit-closes?

It looks like a bit of a rearguard action initiated by Mike Parker Pearson and other "experts" (don't you just love that word?) who have -- or who had in the past -- links with the Department. Of course one is sad to read of the closure -- or possible closure -- of any university department. But as we know, the Sheffield Archaeology Dept has not helped itself through its association with some very dodgy "bluestone" research at Stonehenge, "Bluestonehenge" and in West Wales -- demonstrating rather too much interest in perpetrating elaborate myths of bluestone quarrying and transport, and rather too little interest in sound science. 

Quote:
"Important research on Stonehenge could be put in jeopardy if the threatened closure of one of the UK’s most renowned university archaeology departments goes ahead, leading experts on the prehistoric monument have warned."

Quote:

Parker Pearson directed the Stonehenge Riverside Project, which has made some of the most impressive discoveries about the monument of modern times, including finding evidence of a second Stonehenge a mile away from the great stone circle.

He said: “Colleagues at Sheffield are working right now on material from my project at Stonehenge and if they lose their jobs it jeopardises completion of this project which has grabbed the world media’s attention over the last 15 years.”

There, in a nutshell, we have it.  A second Stonehenge?  Well, "Bluestonehenge" was claimed ten years ago to hold fragments of bluestones in its supposed stone sockets -- and that was shown to be incorrect. But it is still marketed by MPP and others, regardless of the dodgy nature of their claims.  And as for grabbing the attention of the world's media,  that's something MPP knows all about -- promoting completely outrageous theories and myths that are essentially unsupported by any evidence that can withstand scrutiny.  If that is still one of the priorities of the Sheffield University Archaeology Dept, with myth making in the foreground and sound science pushed into the background, how sound is its claim that it should be taken seriously, and spared from the axe?

Of course, the size and success of a university department can always be measured by the size of the student demand for its courses and its degrees.  This is a more effective measure than the size of banner headlines in the tabloid press.

Reputations are hard to come by, and are all too easily destroyed.........

See also:

https://thetab.com/uk/sheffield/2021/05/21/uni-of-sheffield-archaeology-department-set-up-to-fail-faces-possible-closure-48150

https://www.bbc.co.uk/news/uk-england-south-yorkshire-57199118

PS.   27 May 2021

It looks as if the department's fate is sealed.  The real issue was clearly the lack of student demand.  Without students, no university department can survive, even if it specialises in developing elaborate myths and capturing the attention of the media........

New dating for LGM Irish Sea Ice Stream

Maximum extension of the Irish Sea Ice Stream (ISIS) at the time of the Last Glacial Maximum, 

with dated retreat stages.

Here is a big new paper from the BRITICE-CHRONO project, reporting on new dates for the retreat (with occasional readvances) of the ISIS through St Georges Channel and the Celtic Sea and the "Irish Sea Glacier" which is deemed to have pressed through the Cheshire Gap and into the Midlands of England. This new terminology is a bit confusing -- but no matter. This is a very intreresting and useful paper.

Maximum extent and readvance dynamics of the Irish Sea Ice Stream and Irish Sea Glacier since the Last Glacial Maximum
J. D. Scourse, R. C. Chiverrell, R. K. Smedley, D. Small, M. J. Burke, M. Saher, K. J. J. Van Landeghem, G. A. T. Duller, C. Ó Cofaigh, M. D. Bateman, S. Benetti, S. Bradley, L. Callard, D. J. A. Evans, D. Fabel, G. T. H. Jenkins, S. McCarron, A. Medialdea, S. Moreton, X. Ou, D. Praeg, D. H. Roberts, H. M. Roberts, C. D. Clark
Jnl of Quaternary Science, 7 May 2021 (special issue article)

https://onlinelibrary.wiley.com/doi/10.1002/jqs.3313?af=R

https://doi.org/10.1002/jqs.3313

ABSTRACT

The BRITICE-CHRONO Project has generated a suite of recently published radiocarbon ages from deglacial sequences offshore in the Celtic and Irish seas and terrestrial cosmogenic nuclide and optically stimulated luminescence ages from adjacent onshore sites. All published data are integrated here with new geochronological data from Wales in a revised Bayesian analysis that enables reconstruction of ice retreat dynamics across the basin. Patterns and changes in the pace of deglaciation are conditioned more by topographic constraints and internal ice dynamics than by external controls. The data indicate a major but rapid and very short-lived extensive thin ice advance of the Irish Sea Ice Stream (ISIS) more than 300 km south of St George's Channel to a marine calving margin at the shelf break at 25.5 ka; this may have been preceded by extensive ice accumulation plugging the constriction of St George's Channel. The release event between 25 and 26 ka is interpreted to have stimulated fast ice streaming and diverted ice to the west in the northern Irish Sea into the main axis of the marine ISIS away from terrestrial ice terminating in the English Midlands, a process initiating ice stagnation and the formation of an extensive dead ice landscape in the Midlands.

In the dating, using a variety of techniques, there are a few anomalies (as one might expect) but the pattern and timing of ice retreat now seems pretty well established, following a rapid advance of thin ice right out to the Celtic Sea shelf edge at about 25,500 BP.  the authors say "this may have been preceded by extensive ice accumulation plugging the constriction of St George's Channel."  I'm not sure how strong the evidence is for this, and I'm not sure how this "plugging" might have worked, but that's a minor point.

Some of the dates now published are around a thousand years adrift from those published by the same team of researchers a couple of years ago, but there is now a much more sophisticated analysis of the data.   As we can see from the map, the ice edge retreat was remarkably rapid, progressing across terrain which is now mostly sea floor over a distance of more than 700 km from shelf edge to the Isle of Man in little more than 5,000 years.  That's extraordinary if correct -- a rate of around 7 km per year.  The key positions were:

Shelf edge  25,500 yrs BP

West of Scilly 25,300

Outer Bristol Channel  25,000

Outer St Brides Bay (off Pembrokeshire) 24,700

North Pembs coast  24,300

Cardigan Bay  24,000

North Cardigan Bay  22,700

Llyn Peninsula 21,000

Anglesey 20,900

Isle of Man c 19,000

One interesting thing is that all of these speculative ice edge positions are convex.  That means they are all interpreted as land-based.  If they had been calving bays with ice breaking free off a floating ice front, as suggested by Ed Lockhart, they would have been concave, like the ice fronts shown in the Irish Sea in the latter phases of deglaciation.  This means -- or so the current authors think --  that the ice occupying the Celtic Sea arena was not an ice shelf but a grounded glacier; and it must have followed the rules of ice physics, with a gradual (if shallow) ice gradient from source to ice front.  I have discussed this before on this blog:

https://brian-mountainman.blogspot.com/2020/10/on-lateral-spreading.html

https://brian-mountainman.blogspot.com/2019/07/the-celtic-sea-and-its-piedmont-glacier.html

This brings me to my next point, concerning the eastern edge of the Irish Sea Ice Stream.  As shown on the maps in this article, I don't think it makes sense.  it would have been nice to have more information on the interactions between the ice of the ISIS and that of the Welsh Ice Cap, both in Cardigan Bay and on the south Wales coast; maybe that will be forthcoming in future articles from the BRITICE-CHRONO group.   But let's look at the outer reaches of the Bristol Channel, where the authors show streaming ice travelling broadly NE >>SW from the constriction of St Georges Channel towards the shelf edge:

As I have pointed out to the researchers on this team many times before, this is not how ice flows when it is grounded.  Ice always flows perpendicular to the ice edge in situations unconstrained by topography, and if the ice surface was high enough (probably in excess of 350m) off the Pembrokeshire coast to maintain a flow all the way to the shelf edge at -200m, 400 km away, it must also have pushed ice much further to the east across Carmarthen Bay and up the Bristol Channel.  I have discussed this with respect to Ed Lockhart's thesis, here:

https://brian-mountainman.blogspot.com/2020/04/late-devensian-glaciation-of-celtic-sea.html

I'm gratified that the authors of this new paper have accepted my point that Caldey Island and the South Pembrokeshire coast were glaciated during the LGM, but they have not gone so far as to accept my contention that the ice reached the coasts of west Cornwall and west Devon, and that the Scilly Islands archipelago was a nunatak:

https://brian-mountainman.blogspot.com/2018/08/south-pembrokeshire-devensian-till.html

https://brian-mountainman.blogspot.com/2020/10/the-late-devensian-ice-edge-and.html

https://brian-mountainman.blogspot.com/2020/04/the-scilly-nunatak.html

https://brian-mountainman.blogspot.com/2020/04/the-ice-edge-on-scilly-nunatak.html

I repeat here that the Bristol Channel ice edge as shown by the authors in this paper is not supported by sound published evidence.  I would have liked more geomorphology in this paper.

But these large research teams are often very reluctant to abandon their working hypotheses.  They will get there in the end........

One of my recent reconstructions of the relationships between the ISIS and the Welsh Ice Cap.  

Here I am suggesting that Preseli was completely inundated by the ISIS; in reality 

it might be that there was a small cold-based ice cap on Preseli which protected it from 

intensive scouring or other glacial effects.  On the north flank of Preseli it is clear that there are traces of Irish Sea ice at least up to the 340m contour.

Byers Peninsula in focus

 

I came across a novel the other day -- called "The Killing Ship" and written by two anonymous academics under the pseudonym Simon Beaufort.  It's set on Livingston Island at the western end of the South Shetlands group in west Antarctica, with the Byers Peninsula at the heart of the story.  Well, this is where I was based with three colleagues for a whole month in late 1965 -- so we got to know it rather well after many miles of trudging back and forth across what was essentially a snow-covered landscape in the early summer season.

So I bought the book and read it -- and it was a massive disappointment.  It was obvious from the outset that the authors had not the faintest idea what the environment was like or what the landscape looked like.  And even less idea of what the practicalities of living and working on the peninsula are or were in recent decades.  The book is flagged up as a thriller, but almost every incident was laughably ridiculous, with cardboard characters who elicited no sympathy from the reader, and dialogue that was unbelievably unlike anything that goes on in real life.  The whole thing was simply a catalogue of absurdities.  How on earth did it ever manage to get into print?  One star out of five, if I'm being generous.  The ending was replete with hints of a sequel.  Oh dear -- if it ever does appear, I for one will not be reading it......

Three recent photos of Byers Peninsula, which is now a protected area frequently visited by research scientists and also by tourists.  When we were there, the landscape was completely unaffected by human activity apart from some small traces of sealing activities on the beaches in the 1800's -- one of the celebrated "last great wildernesses".........

See also:

https://brian-mountainman.blogspot.com/2019/01/archaeology-on-byers-peninsula-or-maybe.html

3,000 reads of Waun Mawn article

I got a message from Researchgate to tell me that my Waun Mawn article entitled "Waun Mawn and the search for Proto-Stonehenge" has now had more than 3,000 reads.  This is an extraordinary figure for an article which was initially published on Researchgate (rather than in the pages of a specialist journal) just six months ago.  

https://www.researchgate.net/publication/345177590_Waun_Mawn_and_the_search_for_Proto-_Stonehenge 

A lot of the readers must be archaeologists -- and I will be quite pleased if just some of them, after reading it, come to the same view as me, namely that the MPP insistence on a "giant circle" at Waun Mawn, dismantled and shipped off to Stonehenge, is a wild theory unsupported by the evidence.  In short, it is nothing more than a gigantic hoax.