Strange tale from the Mediterranean

Thanks to Dave for alerting me to this very strange and somewhat garbled article in The Independent — by David Keys,  one of our more gullible archaeological journalists:

https://www.independent.co.uk/news/science/archaeology/ancient-greece-archaeology-keros-aegean-sea-bronze-age-dhaskalio-bible-pyramids-crete-milos-a8997666.html

I have no ideas how serious or well-founded this may be — it may just be the latest hoax from a group of researchers desperate for some headlines.......

Will do some research and report back......... in the meantime, if anybody out there knows more, and would like to share info, please post your comments.

Giant marble pyramid-shaped island complex rising from sea uncovered, revealing secrets of ancient Greece’s origin

Exclusive: Thousands of years of history being unlocked in the Aegean isles which could provide groundbreaking knowledge of ancient civilisations.



Extracts:

Archaeologists now believe that, in order to construct the complex, early Bronze Age Greeks embarked on at least 3,500 maritime voyages to transport between 7,000 and 10,000 tonnes of shining white marble from one Aegean island to another.

Each return voyage would have required up to 24 crew members to paddle for around five hours.

“It is by far the largest prehistoric marine transport operation that has ever come to light anywhere in the world,” said Dr Julian Whitewright, a leading maritime archaeologist at the University of Southampton.

“It demonstrates quite clearly just how important, and integral to their culture, seafaring was to these early Bronze Age Aegean people.”

The voyages – totalling around 45,000 miles – allowed the architects to construct what is thought to have been a huge religious sanctuary consisting of up to 60 marble buildings, which were constructed specifically to glisten in the sun.

..........the architects “terra-formed” the pyramid-shaped island “mini-mountain”, known in recent centuries as Dhaskalio (possibly just meaning “islet”), to create around 1,000m of artificial terracing, arranged in six “steps” on its steep slopes.

These roughly six-metre wide terraces appear to have been built specifically to accommodate all the buildings. The summit itself was not initially built on – but instead had a small, probably sacred, open area where votive offerings may have been deposited.

More on ice gradients in the Celtic Sea arena

A winter photo of the Malaspina Glacier, the word's biggest piedmont glacier at the present time.

I have mulled over this topic before, because of the apparent mismatch between modelling work and "ground truthing" in which field evidence is crucial.  The diagram above shows assorted ice sheet long profiles, including some which accord reasonably well with the theoretical ice profile of an equilibrium glacier or ice sheet, and others (the red and green lines) which suggest that in some cases extremely low or "flat" profiles can be observed or deduced.  The diagram is from a 1973 article by Matthews, in which he wondered why glaciers with such low profiles could still move and be capable of eroding and transporting erratics and morainic materials.  See refs below.

The perfect piedmont glacier -- there are quite a few of them in North Greenland and Arctic Canada.  Generally the gradient of the feeder glacier is steeper, and the gradient on the piedmont part very flat..... 

The flat profiles come from the SW part of the Laurentide ice sheet and the "piedmont" glaciers flowing from the Cordilleran ice sheet. Lionel Jackson and colleagues have worked in areas affected by these glaciers, and have come to the view that gradients were often only about half as steep as those deduced by earlier researchers.  Without going into detail about shear stresses, basal sliding and internal deformation, there seems to be a rule that piedmont glaciers can have very low profiles as the ice spreads laterally across open country.  That makes sense,  and measured gradients are usually below 8m per kilometre and sometimes as low as 1m per kilometre.  

If we translate that into some crude figures for the Celtic Sea lobe, and if we assume for the moment that the long profile should be oriented from NE towards SW, as assumed by most researchers over the past 20 years, that means there could have been a grounded snout at -150m on the continental shelf edge and an ice surface at +250m about 400 km away in St George's Channel (if the gradient was 1m per km).  At the other extreme, with a gradient of 8m per km, the ice surface in St George's Channel would have been at +3050m -- more or less as I have previously assumed in earlier posts.   If we take a more modest figure of 4m per km, assuming the ice was dynamic enough to cross the Celtic Deep and still push southwards for 400 km, we get figures of -150m at the snout and +1,450m at the St George's Channel constriction point.

If the new suggestion from Scourse et al (2019) is to be taken seriously, glacially-forced isostatic depression on the shelf edge around 27,000 years ago must imply thicker rather than thinner ice, grounded over a substantial area.  No doubt the modelling people are hard at work on this issue as we speak...........

Whatever the models throw up, we have to explain the presence of a Devensian ice edge at about 300m on Carningli and about 250m on the north face of Mynydd Preseli -- and at assorted altitudes below 100m around the south Pembrokeshire coast.  Can these ice edge altitudes be accommodated in a scenario involving a very low long profile for the piedmont glacier in the Celtic Sea arena?  Watch this space......

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

References

W. H. Mathews (1974) Surface profiles of the Laurentide ice sheet in its marginal areas. Jnl of Glaciology,  Volume 13, Issue 67 1974 , pp. 37-43.  Published online: 30 January 2017.

DOI: https://doi.org/10.3189/S0022143000023352

Jackson, L.E., Jr., Little, E.C, Leboe, E.R., and Holme, P.J., 1996: A re-evaluation of the paleoglaciology of the maximum continental and montane advances, southwestern Alberta; in Current Research 1996-A; Geological Survey ofCanada, p. 165-173.

Abstract: 

Controversy over the age of the maximum known advances of continental and montane glaciers in southwestern Alberta rests largely on the paleoglaciology of the maximum montane piedmont glacier. Reconstruction of it, based upon features that mark the former glacier surface in the Foothills, indicate that the glacier had a maximum surface gradient of 0.4-0.6° - less than half the value assumed by previous workers. The continental ice sheet that was roughly coeval with the piedmont glacier and coalesced with it in the Foothills. Paleoglaciological evidence favours a Late Wisconsinan age for maximum extent of continental and montane ice.

Was there a Devensian ice stream in the Celtic sea arena?

Ice streams around the northern sector of the Laurentide Ice Sheet, shown with relation to reconstructed ice sheet edges.  The Hudson Bay Ice Stream appears to have flowed in a distinct channel while bounded by more sluggish ice.  The only ice stream that appears to have flowed as a lobe beyond the ice sheet edge was the McClure Ice Stream, but it too flowed through a highly constrained trough between islands like a great outlet glacier.  It was probably bounded by local ice caps. It does not provide a good analogue for the Celtic Sea arena.

On the matter of the name we should give to the 80,000 sq km ice mass that occupied the Celtic Sea arena in the Late Devensian, this very comprehensive article is of great interest and relevance.  Scourse et al  (2019) have suggested that the Hudson Bay ice lobe is a reasonable comparator for the BIIS that they consider pressed all the way out to the shelf edge — but the authors of this article suggest that nearly all of the identified ice streams around the edges of the Laurentide Ice Sheet were typographically constrained — in other words, they flowed in great troughs bounded by uplands.  The Hudson Bay Ice stream was no exception, and it did not apparently extend beyond the edge of the ice sheet itself at any stage.  

Reference (recommended reading!)

Margold, M., Stokes, C.s & Clark, C. (2015). Ice streams in the Laurentide Ice Sheet: Identification, characteristics and comparison to modern ice sheets. Earth-Science Reviews. 20. Volume 143, April 2015, Pages 117-146

10.1016/j.earscirev.2015.01.011.

ABSTRACT

This paper presents a comprehensive review and synthesis of ice streams in the Laurentide Ice Sheet (LIS) based on a new mapping inventory that includes previously hypothesised ice streams and includes a concerted effort to search for others from across the entire ice sheet bed. The inventory includes 117 ice streams, which have been identified based on a variety of evidence including their bedform imprint, large-scale geomorphology/topography, till properties, and ice rafted debris in ocean sediment records. Despite uncertainty in identifying ice streams in hard bedrock areas, it is unlikely that any major ice streams have been missed. During the Last Glacial Maximum, Laurentide ice streams formed a drainage pattern that bears close resemblance to the present day velocity patterns in modern ice sheets. Large ice streams had extensive onset zones and were fed by multiple tributaries and, where ice drained through regions of high relief, the spacing of ice streams shows a degree of spatial self-organisation which has hitherto not been recognised. Topography exerted a primary control on the location of ice streams, but there were large areas along the western and southern margin of the ice sheet where the bed was composed of weaker sedimentary bedrock, and where networks of ice streams switched direction repeatedly and probably over short time scales. As the ice sheet retreated onto its low relief interior, several ice streams show no correspondence with topography or underlying geology, perhaps facilitated by localised build-up of pressurised subglacial meltwater. They differed from most other ice stream tracks in having much lower length-to-width ratios and have no modern analogues. There have been very few attempts to date the initiation and cessation of ice streams, but it is clear that ice streams switched on and off during deglaciation, rather than maintaining the same trajectory as the ice margin retreated. We provide a first order estimate of changes in ice stream activity during deglaciation and show that around 30% of the margin was drained by ice streams at the LGM (similar to that for present day Antarctic ice sheets), but this decreases to 15% and 12% at 12 cal ka BP and 10 cal ka BP, respectively. The extent to which these changes in the ice stream drainage network represent a simple and predictable readjustment to a changing mass balance driven by climate, or internal ice dynamical feedbacks unrelated to climate (or both) is largely unknown and represents a key area for future work to address.

The Celtic Sea and its piedmont glacier

From a NASA animation of Antarctic ice flow.  Note the streamlines and the wide ice streams (coloured blue) transporting glacier ice towards the ice shelves.  All of these streams exist within landscapes almost completely submerged beneath glacier ice.

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

The Celtic Sea was affected by thick, dynamic and very extensive glacier ice during the Late Devensian.  But the ice was NOT contained within an ice stream.......

I’m returning to this one — the fascinating 2019 paper by James Scourse and many colleagues relating to the LGM advance of the Irish Sea Ice Stream (ISIS) between 27,000 and 24,000 years BP right out to the edge of the continental shelf and 150 km further our than previously estimated from marine floor sediments and bedforms.  The work is fastidious and the evidence presented by the authors looks solid enough — in line with former published work by Praeg and others.  So what this means is a substantial and rapid advance of ice across the Celtic Sea which was very early, and dramatically out of phase with events on other segments of the British and Irish Ice Sheet (BIIS).

One other point, to which I have not given much attention until now, is the conclusion that the advance (culminating around 25,000 yrs BP) took place at a time of falling global sea-level  but relatively stable relative sea-level on the shelf edge — and that retreat of the ice edge was triggered by "high relative sea-levels driven by significant glacio-isostatic depression, consistent with greater ice loads over Britain and Ireland than previously considered.”  That mean a very high crustal ice load in SW Britain — and that is not at all consistent with the idea that the ISIS was a narrow lobe pushing southwards from St George’s Channel towards the SW.  I have addressed that issue in many posts before……….

A much-reproduced eustatic sea-level curve covering the last two glacial episodes.  It's accepted that the lowest eustatic sea-level -- maybe below -130m -- occurred around 20,000 years ago.  This means that in the period around 27,000 - 25,000 yrs BP sea-level might have dropped by 3m. Could the crust in the Celtic Sea arena have been depressed isostatically by the weight of ice at an even greater rate, leading to a relative sea-level rise?

Then there is the name.  Was this really an ice stream in the normal sense of the word?  Scourse et al refer to it as having a width of c 100km, and they say: "A width of the order of 100 km places ISIS at the wider end of the phenomena (Margold et al., 2015) and comparable to the Hudson Strait Ice Stream of the Laurentide Ice Sheet and the Thwaites Ice Stream in Antarctica.”  But as I will never tire of saying, these and other ice streams flow, or flowed,  within landscapes completely inundated by glacier ice.  They are constrained laterally by flanking uplands, and their edges are seen to coincide with zones of shearing or intense crevassing on the contact between stagnant or slow-moving ice and the fast-moving ice within the ice stream.  The situation was nothing like that in the Celtic Sea — there are no topographic controls which might have prevented or constrained lateral spreading of the ice.  To the north of St George’s Channel, yes, that might have been the case, with an ice stream flanked by the Irish ice cap to the west and the Welsh ice cap to the east.  But to the south of St George’s Channel, no…….. in an “open landscape” with no deep troughs to direct the ice south-westwards, the ice MUST have spread laterally, and it MUST have spread well into the Bristol Channel and pressed against the coasts of Devon and Cornwall.  

It’s interesting that in the Ballum’s Bay article just published in QN, John Hiemstra and his colleagues now seem to accept that point.  And other authors are doing the same.  In the maps recently published by Glasser et al (2018) and Jenkins et al (2018) lobes are shown pressing well into Carmarthen Bay.  There is abundant empirical evidence in support of Devensian glacier ice affecting much of the south Pembrokeshire coast and also flowing across Caldey Island, as I have shown in many posts on this blog.. 

 

Glasser et al (2018).  An ice stream probably existed where the words are placed on the map, but the "outer" 400 km of the ice mass should be given a different label.  This was a vast Devensian piedmont glacier, covering 80,000 sq km.  Note that ice is shown pushing eastwards into the outer reaches of the Bristol Channel.

 

Jenkins et al (2018).  A similar Late Devensian ice edge is shown, but the ice flow arrows in the Celtic Sea are far too generalised.  Ice always flows perpendicular to the ice edge in unconstrained situations, so there must have been ice flow eastwards into the Bristol Channel. If the ice edge really did retreat from the shelf edge to the north Pembrokeshire coast (over a distance of 400 km) in 2,000 years, that represents a retreat rate of 200m per year at a time when glaciers were apparently expanding almost everywhere else.......

Glacier ice grounded right across the vast area of the Celtic Sea also provides a better explanation for the substantial ice load now required by Scourse et al in order to explain the isostatic depression and stratigraphic and bedform features at the edge of the continental shelf.  A rising relative sea level, at a time of a eustatic drop in global sea level, requires a lot of glacier ice, of considerable thickness!

So - thick ice in the Celtic Sea arena.  For 400 km from the constriction of St George's channel, there must have been a continuous gradient towards the south-west.  So what was the surface altitude of the ice in the middle of the Channel between Pembs and the SE coast of Ireland?   Let's assume, as I have done on many occasions, that the gradient was shallow -- consistent with a surging glacier on old sea-floor sediments, as modelled by many authors.  The ice must still have had a surface altitude of over 1500m in mid-channel c 27,000 years ago.  But why, in those circumstances, did the ice not overwhelm the whole of Pembrokeshire at the same time?  Maybe it did, and maybe we have just got our ice edge mapping all wrong?  I have been struggling with this issue for a long time, without having the skills or the tools for effective modelling.

My old map showing proposed ice masses and directions of ice movement at the time of the Anglian Glaciation.  Should we now be thinking of a similar situation during the Late Devensian?

My suggested ice contour map for the Anglian Glaciation.  How different might the ice contours have been

 in the Late Devensian?

This is all a bit of a glaciological puzzle, and I keep on coming back to this old map, which is so old that it is covered in cobwebs.  It looks crude, but I have sneaking feeling that all of the ice directions assumed by generations of geologists and geomorphologists are all wrong, and that this is what they were really like:

Does anybody have any evidence that this map is fundamentally wrong?  As far as I can see, it is the only one that fits the field evidence from a multitude of different sites around the edges of the Celtic Sea.

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

Anyway, here is a suggestion.  Can we please abandon the ice of the term “Irish Sea Ice Stream” for the area to the south of St George’s Channel, and use the term “Celtic Sea Ice Lobe” or “Celtic Sea Piedmont Glacier” instead?  

Relevant info:

James Scourse et al.   2019.  Advance and retreat of the marine-terminating Irish Sea Ice Stream into the Celtic Sea during the Last Glacial: Timing and maximum extent.  Marine Geology,  Volume 412, June 2019, pp 53-68

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

ABSTRACT 

The dynamics of the British-Irish Ice Sheet (BIIS) during the Last Glacial were conditioned by marine-based ice streams, the largest of which by far was the Irish Sea Ice Stream (ISIS) which drained southwest across the Celtic shelf. The maximum extent and timing of the ISIS have been constrained by onshore evidence from the UK and Ireland, and by glacigenic sediments encountered in a small suite of vibrocores from the UK-Irish continental shelf, from which a single radiocarbon date is available. These data have long supported ice advance to at least the mid-shelf, while recent results suggest the ISIS may have extended 150 km farther seaward to the shelf edge. The glacigenic sequences have not been placed within a secure seismic-stratigraphic context and the relationship between glaciation and the linear sediment megaridges observed on the outer shelf of the Celtic Sea has remained uncertain. Here we report results of sedimentological, geochemical, geochronological and micropalaeontological analyses combined with a seismic-stratigraphic investigation of the glacigenic sequences of the Celtic Sea with the aims of establishing maximum extent, depositional context, timing and retreat chronology of ISIS. Eight lithofacies packages are identified, six of which correlate with seismic facies. Lithofacies LF1 and LF2 correlate to a seafloor seismic facies (SF1) that we interpret to record the postglacial and Holocene transgressive flooding of the shelf. Lithofacies LF10 (till), LF3, LF4 and LF8 (glacimarine) correlate to different seismic facies that we interpret to be of glacigenic origin based on sedimentological, geotechnical and micropalaeontological evidence, and their distribution, supported by geochemical evidence from lithofacies LF8 and LF10 indicate extension of ISIS as far as the Celtic Sea shelf break. New radiocarbon ages on calcareous micro- and macrofauna constrain this advance to be between 24 and 27 cal ka BP, consistent with pre-existing geochronological constraints. Glacimarine lithofacies LF8 is in places glacitectonically contorted and deformed, indicating ice readvance, but the nature and timing of this readvance is unclear. Retreat out of the Celtic Sea was initially rapid and may have been triggered by high relative sea-levels driven by significant glacio-isostatic depression, consistent with greater ice loads over Britain and Ireland than previously considered.

Final section of text:

……………..While the existence of ISIS is well founded, its exact footprint remains ill-defined owing to few lateral geomorphological indicators such as a prominent edge to a field of mega-scale glacial lineations or shear margin moraines, and on the Celtic shelf there is a lack of obvious topography to constrain the margin. Nevertheless, a striking aspect is the large reconstructed width in comparison to other extant and palaeo ice streams from around the world. A width of the order of 100 km places ISIS at the wider end of the phenomena (Margold et al., 2015) and comparable to the Hudson Strait Ice Stream of the Laurentide Ice Sheet and the Thwaites Ice Stream in Antarctica. To maintain fast flow over such widths requires substantial feeder catchments that were probably unlikely from the BIIS. This suggests the ISIS could only exist as a transitory ice stream that rapidly drew down ice volumes. Our chronology of rapid advance and withdrawal is consistent with this, as are findings of numerical modelling investigations that struggle to simulate a steady state ice stream of this scale (Boulton and Hagdorn, 2006; Hubbard et al., 2009). It has also been a challenge for ice sheet models to simulate ice stream advance to the Isles of Scilly without building up ice elsewhere at locations more extensive than indicated by empirical evidence, such as mid and southern England (e.g. Patton et al., 2017). This problem is exacerbated by the Celtic Sea extent that we now report. Modelling investigations are underway to address this challenge. 

5. Conclusions 

Cored glacigenic sequences correlated to seismic stratigraphic units provide clear evidence of the advance and extent of the Irish Sea Ice Stream across the Celtic shelf during the Last Glacial. Overconsolidated subglacial diamicts (till) of ISIS origin have been recovered from close to the shelf break. Together with deformed and contorted proximal to distal glacimarine sequences containing distinctive cold water foraminiferal assemblages recovered from across the shelf, these diamicts indicate the advance of the ISIS into the Celtic Sea as far as the continental shelf break of the Irish and UK sectors of the Celtic Sea, and raises questions regarding the extent of ice into the French sector. The timing of this advance has been constrained by a series of new radiocarbon ages to between 27 and 24 cal ka BP. These ages are consistent with a single published radiocarbon determination from a glacimarine sequence recovered close to the shelf break, and with new geochronological data from the Isles of Scilly indicating ice advance at 25.5 ka. Comparison with ages for deglaciation farther north in the Irish Sea suggests that ice retreat across the Celtic shelf was initially rapid and then slowed, constrained by topographic controls, falling relative sea level and low tidal amplitudes in the vicinity of St George's Channel. Deglaciation on the outer shelf was probably initiated by high or rising sea level driven by glacio-isostatic depression during peak glaciation.

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

About ice streams (Bethan Davies):

Ice streams are corridors of fast flow within an ice sheet (ca. 800 metres per year). They discharge most of the ice and sediment from these ice sheets, flowing orders of magnitude faster than their surrounding ice. Their behaviour and stability is therefore essentially important to overall ice sheet dynamics and mass balance[1]. The Antarctic Ice Sheet currently discharges 90% of ice and sediment through ice streams. Antarctic Ice Streams are fed by complex tributaries that extend up to 1000 km into the interior of the ice sheet.

Ice streams can be constrained by topography or by areas of slow moving ice. They are called topographic ice streams or pure ice streams respectively. Both types show variations in behaviour (both through time and space), which indicates potential for instability and are therefore particularly interesting.

http://www.antarcticglaciers.org/glacier-processes/types-of-glacier-2/ice-streams/

According to this definition, th 80,000 sq kn of ice that filled the Celtic Sea arena should NOT be referred to as an ice stream,

The Flimston erratics — dumped by Devensian ice?

Not so long ago, I believed quite firmly that the erratic memorial stones in Flimston Churchyard (on the Castlemartin Peninsula, Pembs) had been introduced into the area during the Anglian Glaciation — since Devensian ice was assumed not to have affected the area.  Now I’m not so sure, following the discovery of apparently fresh till at numerous localities along the South Pembrokeshire coast.  My working assumption is that the Devensian ice came in from the west, pushing into Carmarthen Bay and probably covering Caldey Island.  At times it might have flowed ENE — indeed, this direction of movement is what seems to be indicated by the reddish (ORS) appearance of the Ballum’s Bay till, since the Devonian reddish sandstones are exposed on the southern part of the island, giving way to Carboniferous Limestone in the north.

My working assumption is that the rampart of cliffs was an efficient barrier to ice movement;  in places the ice overtopped the cliffs, and in places it did not.  South-facing cliffs were affected by ice, and east-facing cliffs may have been left ice-free.  The distribution of clifftop till seems to support this idea.  But.......

Might the Devensian ice have transgressed further inland?  There are abundant records of till and other deposits across the plateau landscape of the Castlemartin Peninsula.  I have always assumed that these are very old.  But if they are uncemented, I now think that they might be of Devensian age.

Back to the boulders.  From Adrian James’s description (below) we can see that the boulders were collected up for use as gravestones or memorial stones from locations up to 3.4 km from the chapel itself, in 1903.  But how heavily weathered are their surfaces?  Here we have a wonderful opportunity for cosmogenic dating.  Let’s assume that since emplacement these boulders have been exposed on the ground surface and not buried in other deposits or covered with vegetation — if they have been lying around since the Anglian glaciation there could be surface exposure ages of up to 450,000 years, but if they are Later Devensian erratics, abraded and modified during ice transport, there could be surface ages as young as 25,000 years BP.

Cosmogenic dating needed........

This map shows the putative Celtic Sea lobe of the Devensian Irish Sea Glacier or Ice Stream pushing eastwards into the Bristol Channel, flowing across Caldey and Lundy Islands and maybe almost reaching the coast of Gower.  Ice is shown just spilling over the cliffs of the South Pembrokeshire coast -- bud did it push much further inland?

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

Flimston Chapel churchyard (SR92399558). There is a substantial collection of erratics in this churchyard. Some have been used as headstones for the graves of members of the Lambton Family who died in military service. Others have been left sitting in one corner of the enclosure. All of these stones arrived in the churchyard when the chapel was renovated and re-consecrated in 1903. There are 7 of them. A pamphlet, which describes the features and memorials in the yard, printed at the time of the opening of the chapel in about 1914, gives us these vague details:

No. 1 Boulder, at the head of Lady Victoria Lambton's grave was taken from just opposite Flimston Cottage. A 'brecciated spherulite, albite, trachyte or rhyolite.' Many occur in Pembrokeshire. This one 'seems to fit best with those of Romans' Castle in the character of its spherulites and groundmass.'
[Flimston Cottage stood at SR927955, about 0.3 km ESE of the chapel and just north of the old clay pits.]
No. 2 Boulder, from Pwllslaughter, which stands in the opposite North corner. [Bullslaughter, SR942944 - approximately 2.25 km SE]
No. 3 Boulder from Bulliber Farm [About 2.25 km WNW, at SR905968]
No. 4 Boulder from Merrion pond. [ About 2 km NE].
No. 5 Boulder from Lyserry Farm
No. 6 Boulder from Lyserry Farm.
No.7 Boulder from Lyserry Farm.
[Lyserry is about 3.4 km ENE of Flimston chapel, at SR9556967]

Lydstep Point raised beach platform

The raised beach platform near Whitesheet Rock, on the flank of Lydstep Point, cut across steeply dipping strata of Carboniferous Limestone.  The platform site is open to wave attack from the SW.

This is one of the most impressive raised beach platforms in west Wales, tucked away behind Whitesheet Rock, near Lydstep Point.  Grid ref SS091975.  The remnant is over 100m long, and up to 30m wide — that’s much wider than any other old platform seen in this region.  The platform has a steeper gradient than many others, and it is severely broken up by gullies and solutional features -- the effects of current wave action are apparent at the outer edge of the platform.  In places it is actually quite dangerous to walk across the surface.  I have seen no raised beach cobbles here -- the only sediments are  solidly cemented slope deposits or scree, made entirely of limestone fragments.  At the back of the platform there are a number of old caves related to conduits within the limestone.  They would be worth investigating.......

Another view from platform level.  The platform is accessible -- with care -- from the slope above.

The distinct notch at the back of the platform.  Note that the platform has quite a steep gradient, and that its surface is very broken up -- an indicator of great age?

View to the NW, from near the southern edge of the platform.  At bottom left, we can see the current cliffs which are gradually eating into the platform.

Fine cemented limestone breccia on the platform surface

Coarse limestone breccia including large angular blocks resting on the highly 

dissected platform surface

Caldey Island — the Ballum's Bay till must be Late Devensian

Google Earth image of Ballums Bay, Caldey Island.  The till exposure is at the head of the gulley, top left.  The edge of the raised beach platform with cemented sediments coincides approximately with the black line.

 

 Ballums Bay from the east (from near Small Ord Point).  The beach, backed by the gully containing till, is right of centre. To left of centre we see remnants of raised beach platforms with cemented beach materials, breccia and sandrock, overlain by a terrace of more recent materials.

Following my note about the interesting QN article by John Hiemstra and others, I have been digging into my records of Caldey Island, and have found a number of photos that might be of interest.  I have several pics of the till exposure which has been investigated and now described in the QN piece, but we'll leave those to one side for the moment.  Of more interest to the debate about age are the photos of the cemented materials found on the old wave-cut platforms immediately to the south.

The platform is seriously broken up, cut by gullies and other inlets affected by ongoing wave action, and with steps and assorted vertical and overhanging sections.  Like the other wave-cut platforms on the limestone coasts of South Pembrokeshire, it appears to be a composite feature, representing erosion at a number of different levels between present HWM and +5m.  The raised beach platform is a mess -- appearing very old, with segments of many different ages.  Ipswichian?  My guess is that it is much older, and that it has been modified across several interglacials.  

                            

Raised beach platform remnants on steeply dipping Carboniferous Limestone strata on 

the south side of Ballums Bay

Cemented brecciated limestone debris incorporating raised beach boulders and cobbles on one of the highest rock platform remnants, Ballums Bay south.

Comparison with other platform remnants is instructive.  See these posts on Broad Haven South and Lydstep:

https://brian-mountainman.blogspot.com/2018/04/the-raised-beach-at-broad-haven-south.html

https://brian-mountainman.blogspot.com/2018/11/on-significance-of-cementation.html

Let's take a look at the cemented deposits.  There can be no doubt that these are all older than the Ballums Bay till.  The raised beach, limestone breccia and bedded sandrock are intimately associated, although they do not all appear in all exposures.  For example, in the extensive high raised beach platform near Lydstep Point cemented breccia and cemented sandrock are both found, but I have been unable to find any traces of cemented raised beach cobbles.

Key Quaternary locations on Lydstep Headland (note that there is a mistake on this map.  The raised beach platform is in the bay to the west, behind Whitesheet Rock.  To be corrected.....)

 

Complex cemented deposits on the limestone raised beach platform on the south side of Ballums Bay.   Here we see abundant raised beach cobbles, layers of sandrock, and masses of limestone rockfall debris and slope breccia. 

Bedded sandrock resting on slope breccia and raised beach cobbles., south side of Ballums Bay.   All cemented with carbonate cement -- with some traces of manganese oxide cement.

The South Pembrokeshire Quaternary regional stratigraphy (based on my own observations and those of Dixon and Leach) is as follows:

8. Sandy loam and blown sand
7. Upper head (uncemented)
6. Fluvioglacial sands and gravels -- traces
5. Till from Dewisland (Devensian) glaciation -- many coastal exposures
4c. Lower head (cemented in some localities)
4b. Cemented sands (sandrock)
4a. Head incorporating raised beach cobbles (cemented)
3. Cemented raised beach
2. Older glacial deposits -- mostly destroyed, but exposed at Lydstep (Black Mixen)
1. Raised beach platform (complex modifications over several interglacials?)

If, as suggested by John Hiemstra and his colleagues, the unconsolidated till at Ballums Bay is of Anglian age (but periglacially redistributed or redeposited), it must be older than the cemented raised beach deposits.  So why is it not cemented like deposits 2, 3 and 4 in the regional sedimentary sequence?  It does not make sense.  The authors seem to be suggesting that the original till is the same age as the ancient cemented till at Black Mixen -- that does not make sense either.  The fresh till at Ballums Bay lies in a limestone gully, just like the fresh till at Lydstep, so the two deposits must be related.

https://brian-mountainman.blogspot.com/2018/05/devensian-till-at-lydstep.html 

In addition, the Ballums Bay till looks like the fresh till exposed in many clifftop locations on the south Pembrokeshire coast -- and it lies in the same stratigraphic position, overlain only by unconsolidated blown sand or sandloess, as in the Isles of Scilly.  It must also be the same age as the till exposed near the Caldey landing stage, which is reddish in colour, sandy and gravelly in texture, matrix supported, and contains a similar mix of erratic cobbles.

Till exposure near the Caldey landing stage.  At the base, broken Carboniferous Limestone bedrock.  Above that, 1.3 m gravelly and sandy fresh unconsolidated till. Above 

that, c 1m of sandy loess and soil.

Brecciated limestone slope deposit or "head" above broken Carboniferous Limestone bedrock, near the Caldey landing stage.  This is uncemented, and appears to underlie the Devensian till.  It is probably of Early Devensian age, and correlated with many other slope deposits in West Wales which underlie till and fluvioglacial materials.

Here is the crucial discussion on the age of the till, from the QN article by John Hiemstra and his colleagues:

1) In situ Devensian till

This was the scenario we set out to test. Several features certainly favour this origin: (i) ‘foreign’ igneous erratics; (ii) dominance of sandstone clasts mostly probably from outcrops on the west of the island lying slightly south of Bullum’ Bay, which would tally with an ENE flow direction of ice as envisaged by Brian John; (iii) clast form characteristics; and (iv) probable loessic sediment overlying the diamicton without obvious hiatus, consistent with a Devensian origin. There are, however, several drawbacks to this scenario: (i) the very low content of any material that does not have a likely relatively local provenance: (ii) no observed far-travelled erratics or glacigenic diamicton in parts of the island we could access, and also very few such erratics on the beaches; (iii) flow structures atypical of till; and (4) no convincing striations. (The grain fabric evidence is equivocal, neither supporting nor ruling out a till origin.)

(2) Redistribution of pre-existing sediment including any residual Anglian glacigenic sediment during Devensian periglacial conditions

An in situ Anglian till origin is not feasible because raised Ipswichian sea level - probably at least c. +5 m OD (Dutton and Lambeck, 2012) - would have removed any existing sediment from the lower part of the gully where the diamicton lies. An origin by redistribution of regolith and soil as well as any Anglian glacial material by mass flow under Devensian periglacial conditions is, however, plausible. The igneous pebbles could have been derived from two possible transport directions and by two possible sequences of events. (In either case, mass flow would have moved sediment downslope from higher ground in the south of the island to the gully.) One alternative is that they could have been deposited on the island during the Anglian glaciation when many argue that ice from the Irish Sea Basin moved eastwards and southwards across this region. Mass flow processes would then have carried these clasts into the gully. The other alternative is that there is a possible source to the south of Bullum’s Bay of the igneous pebbles in conglomerates of the West Angle Formation of the upper ORS, which is said to be ‘rich’ in such clasts as well as those of some other lithologies (Howells, 2007). In this case, sediment containing clasts derived from mainland sources would have been transported to the island by glacial action, and during the Devensian any remnant glacigenic material would have been carried north(east)wards downslope to Bullum’s Bay by mass flow processes together with any locally eroded material including the igneous erratics. The flow structures, lack of striations, clay-rich texture and grain fabric evidence tally with an origin by periglacial slope processes. Clast rounding could be the result of one or a combination of long-term weathering, residual glacial modification or limited modification acquired during mass flow transport. The clast form characteristics of the igneous clasts would favour a glacial rather than fluvial (i.e. ORS conglomerate) origin, although reconstructing transport history from just four clasts must be treated with caution. Lack of angular clasts from the underlying limestone either in the diamicton or forming the main constituent of a discrete single-lithology periglacial diamicton might appear problematic given the frost susceptibility of this rock type. However, the lack of steep surrounding slopes with exposed bedrock that could act as the source of such material is the probable explanation. (Transport to Bullum’s Bay of the igneous erratics by northward-moving longshore drift during raised Ipswichian sea level is conceivable but their incorporation into the exposed diamicton seems unlikely given the lack of contained marine shells.)

On balance, therefore, we prefer the second scenario to explain the Bullum’s Bay diamicton as it provides a better explanation of the evidence.

In my view, as indicated earlier, the discussion by the authors is not at all convincing, and includes a good deal of special pleading.  The till is not unusual or unique in any way, and like most of the related deposits in South Pembrokeshire, if it looks like a till it probably is a till.  One gets the impression that the authors are rather desperate to demonstrate that the deposit is not an in situ till, and their suggested "drawbacks" are perhaps based on the fact they are not familiar with related deposits, their lithologies and their stratigraphic relationships.  The low content of foreign materials is not at all unusual in Pembrokeshire tills, as I demonstrated in my 1965 thesis. There ARE far-travelled erratics and other tills on the island, as I have shown above.  There are erratics on the beaches.  There are scratches on cobbles which I have interpreted as striations.  And they have not demonstrated that the flow structures seen are "atypical of till" -- this is not a lodgement till or a true flow till, but a till laid down in a wasting ice environment, which was mobile during deposition and then subject to a degree of remobilisation or rearrangement following ice wastage. In that respect it is typical of most of the till exposures of West Wales.

The "preferred explanation" of the till -- namely that it is "a discrete single-lithology periglacial diamicton"  is so convoluted that it is slightly embarrassing!  Is this how the authors would explain the other clifftop diamictons on the south Pembrokeshire coast, or the similar diamictons on the north coasts of the Isles of Scilly?  In my view, if there had been Anglian or other ancient tills littering the ground surface of the Caldey limestone plateau, they would have been "locked in" by interglacial carbonate cementation processes and would not have been available for periglacial redistribution.

Unfortunately, the authors appear to have been so concerned about the implications of fresh Devensian till in this part of the Bristol Channel that they have refused to believe the evidence of their own eyes!  Occam's Razor, chaps.  This looks like a fresh till and it is a fresh till -- and there was Devensian Irish Sea ice in this part of the Bristol Channel around 20,000 years ago.

Finally, this is where some work needs to be done -- in Drinkim Bay, south of Ballums Bay.  I was not able to look at it last time because of tidal and time constraints, but it looks as if there are exposed sediments and platform traces there........