Cemented till, Traeth Mawr, Newport

Two exposures of cemented till on Traeth Mawr beach, Newport.  To some degree the exposure is masked by limpets and other marine creatures including seaweeds and the casts made by the honeycomb worm.

Traeth Mawr, Newport, there is a little patch of cemented till, broken up into a number of small outcrops, sticking up through the sand directly in front of the car park.  It is only visible at low tide, and sometimes, when the sand beach has been aggrading (as in the summer months) it may not be visible at all.  It is clearly a till, with rounded and faceted stones up to 30 cm in diameter visible in small cuttings and on the upper surface of the outcrop -- but there is a crust of what look like corals or large barnacles which attracts the immediate attention.  They are in fact worm casts --created in certain conditions on beaches in western Britain by colonies of the worm called Sabellaria.

In the vicinity of the outcrops I have in the past seen fragments of the submerged forest, and I have assumed (because of the apparent association between the two) that the till is late Devensian in age, and that the submerged forest is Holocene.  Now I am not so sure.  In recent months I have been finding cemented till in a number of locations (as at Lydstep, Ceibwr and Witches Cauldron), and I am becoming more convinced that it is possibly Anglian in age -- partly because in those locations there is also nearby fresh till with no trace of cementation.  There is fresh Devensian till at the head of the main beach, occasionally exposed and overlain by blown sand, and on the adjacent clifftops.  It is also seen in the Nevern Estuary, behind the protective promontory of sand dunes, on the shore where it is covered at high tide -- and it is slippery, mucky and soft enough to dig out with ease. Conditions inside the estuary are not dissimilar to those on the outer beach -- apart maybe for reduced salinity in the water that covers the deposits twice a day.

For the moment, I shall go with the thesis that there are TWO tills in Pembrokeshire -- the older one cemented (maybe not everywhere?) and the younger one fresh and soft.

Watch this space........

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A colony of Sabellaria worms on the outcrop

Note:
Honeycomb worms (Sabellaria spp.) are tiny worms that live around the low tide area of the beach. They build tubes, attached to the rock to live in and the structures we see on the beach are dense colonies made up of thousands of individual worms. Fully grown, each individual worm is around 3-4cm. The colonies however can often cover large areas of rock, forming solid reefs.