In the top caption I refer to the clay-rich blue-grey deposit as a "diamicton" -- but there is really not much doubt as to what it is. If I was to see this in Greenland or Iceland it would be accepted instantly as a clay-rich till laid down at the base of a glacier where lodgement processes were at work. It is certainly not a river or shoreline deposit, and it is not a brecciated slope deposit or a turbidite. It has all of the characteristics of a true till -- highly varied stone shapes and sizes, many different lithologies, faceted faces, and no sign of layering or other arrangement. Are there striations on any of the pebbles? That could be a clincher......... (There may of course be signs of layering at the top of this bed, where the material becomes richer in organic materials and grades up into the peaty layers of the submerged forest.)
At the moment I see no reason why this deposit should not be interpreted as Irish Sea Till, laid down by the Irish Sea Glacier as it pressed eastwards into Carmarthen Bay. There are clear similarities with the deposits exposed in Freshwater West and West Angle....... It is uncemented and fresh-looking, and so my provisional interpretation is that it is of Late Devensian age, like all of the other unconsolidated tills of West Wales.
Gary thinks that the limestone fragments in the Amroth exposures look as if they might have come from Ludchurch, a few miles to the north. I'm not very convinced about that, as they could equally well have come from the limestone outcrops of the South Pembrokeshire coast. The local rocks in Amroth all belong to the Coal Measures -- sandstones, shales and mudstones, and coal bands as well. That having been said, erratics can be moved about in different directions in different glaciations, and it is known that many erratics rom North and mid Pembrokeshire were indeed transported southwards and eastwards during the Anglian glaciation. Erratics from Ludchurch could have been introduced to the Amroth area 450,000 years ago and then redistributed during the Late Devensian glaciation.
What does all this mean?
This is all rather provisional, until the "Devensian till" and other deposits have been properly examined, but all of our assumptions about the extent of Devensian ice now have to be subjected to intense scrutiny. Readers of this blog will know that I have wrestled endlessly with the concept of the "South Pembrokeshire enclave" -- hemmed in by ice from the east, north and west. But now we are seeing increasingly convincing evidence of ice coming from the south as well, to the point where it becomes ludicrous (ice does not like flowing in a direction opposite to that from whence it came.......).
But now are we needing to extend this line right up into Saundersfoot Bay and suggest that the ice of the Irish Sea Glacier travelled NORTHWARDS to reach the coast at Amroth? What other evidence is there for glacial action on this stretch of coast? I have to admit that it is the part of Pembrokeshire that I know least well.
But the idea of an enclave pretty well encircled by active glacier ice looks increasingly untenable, especially in a lowland location like this. This is no upland nunatak. So did the ice of the Devensian Irish Sea Glacier affect the WHOLE of Pembrokeshire?
Watch this space ..........
This is a nice image (courtesy Pembs Coastal Photography) showing just how extensive the Amroth submerged forest is, when exposed:
In this surface exposure the peat is very thin, and we can see that it grades down into
a sticky blue clay
"Amroth, Site B2. -- Below the western end of this village evidence of flint-working abounds on a site first noted in August, 1912, and examined each summer and winter since. The sea washes away the soft blue silt, leaving the flakes projecting more or less noticeably. On each occasion I removed all visible flints and by the time of the next visit a fresh crop had become exposed. In August, 1917, for the first time in my experience, the whole site lay buried under several inches of sand. Objects in flint and chert collected inclued: one hollow scraper, one long flake, ridge-backed and serrated (saw); two shorter flint saws, two conical cores, one core trimmed to yield small flakes, three contiguous flakes, three long cores of cherty flint, two cores of black glossy flint, ten flint pebbles partly chipped into cores, fourteen small blades, twelve large flakes, two calcined flints, some scores of roughly chipped and broken fragments.”
See also Royal Commission Inventory for Pembs 1925.
One locality near Amroth, in Carmarthen Bay, yielded cores and flakes in abundance; the circumstances indicate the existence of a chipping-floor or implement-factory on this part of the submerged land-surface, which now, during spring tides, is covered by not less than 20 ft. of water. In the patch of submerged forest recently exposed at Fresh-water West, in southern Pembrokeshire (see NATURE, March 28, 1912), a few small flint implements were also found.
Ref: Antiquity of Neolithic Man. A. L. LEACH — Nature volume 90, page134 (1912)