Sheep skull on a signpost along the Welsh Coastal Path, at Whiteford Sands, Gower, South Wales.
The shape of natural abstract sand sculptures, like these ripples on the seashore, result from complex interactions of water and substrate which are the subject of much research in the field of fluid mechanics. They are described as “small-scale three-dimensional bedforms due to interactions of an erodible bed with a sea wave that obliquely approaches the coast, being partially reflected at the beach” (Roos & Blondeaux 2001). Different combinations of three main perturbation agencies create different ripple designs.
Roos, P.C. and Blondeaux, P. (2001) Sand ripples under sea waves. Part 4. Tile ripple formation, J. Fluid Mech. vol. 447, pp. 227-246.
Yesterday I posted pictures of a massive tree trunk that is being washed out of the peat on the beach at Whiteford Sands. It is lying on its side. Next to it are the remains of a clump of smaller trees. [I have indicated their positions with arrows in a context shot below]. The trees were growing close together. Only the stumps survive but they are preserved upright in their life position, complete with root systems penetrating downwards through the peat. I noticed for the first time in preparing these photographs for the post that someone has very neatly and professionally cut off one of the tree roots; this may substantiate my assumption that someone is in fact carrying out research on the newly emerging trees of this submerged forest.
Some of the ancient wood that has long been buried in peat and clay deposited after the last ice age has wonderful textures and woodgrain patterns. Whole recumbent tree trunks have been emerging from the peat as a result of recent beach erosion at Whiteford on the Gower Peninsula in South Wales. This wood is not fossilised but is preserved in its original state by the anaerobic conditions in which it was buried – in the same way that the bodies of the so-called Bog People were preserved.
You don’t exactly have to keep your nose to the ground to see them but you do have to be a keen observer to notice all the different tracks and trails left on the soft wet sediments of the beach at low tide. Larger marks left by people and vehicles are the first ones you see. Bird footprints are every where. The birds are feeding on all sorts of invertebrate seashore creatures like worms, small crustacea and molluscs – all of which leave holes, burrows and furrows as they move in and out of the sand and across the surface. Some of the pictures shown here simply aim to give the general context for the area of Whiteford Sands that I was walking across. If you look closely the other images, you will see not only the ripples in the sand but also the intricate network of traces left by the virtually invisible organisms that inhabit this ecosystem. The larger furrows in photos 1, 12 and 13 are made by the common winkle (Littorina littorea Linnaeus). I cannot name each animal that is responsible for each of the other types of trace. However, I am sure that there will be some specialists out there who could, especially those researchers concerned with the interpretation of trace fossils (the ichnologists).
Click images to view full size.
At low tide many thousands of common winkles or periwinkles (Littorina littorea Linnaeus) seek shelter from dessication and predation by clustering together in the few hiding places available on the beach. At Whiteford Sands these niches include the overhung bases of larger stones, crevices in ancient timbers from the rapidly emerging submerged forest, and nooks and crannies in the recently exposed ancient peat. Alternating layers of peat and clay, overlain by rocks from glacial till, provide algae-covered surfaces on which gastropods can feed, and islands of low tide refuge in the vast expanses of sand on this sea shore.
Crisp and cold, bright and sunny, just right for blowing away the cobwebs with a walk along the strand at Whiteford Sands. On this particular winter’s day the tide had brought ashore lots of flotsam – fishing nets, buoys, floats, and crates, shoes, hard hats, and miscellaneous plastic rubbish that rested on a driftline of sand, pebbles or shells. Here are some of the things that caught my eye as I strolled the high water mark from Cwm Ivy Tor to the spit beyond Whiteford Point on Boxing Day 2013. Click on any of the images in the gallery below to view in a larger format and slideshow.
Shorelines evolve. Changes happen – sometimes slowly and sometimes quickly. The winter of 2013 to 2014 brought severe storms and winds that impacted on all our British coastlines. Whiteford Sands on the north shore of the Gower Peninsula in South Wales was no exception. By May 2014 a dramatic change in the long line of dunes bordering the sands was clear to see. The dunes have been fixed for a long time with the outer slopes stabilised with marram grass, and a turf covering further inland. Small changes had been occurring steadily for many years with a gradual wearing away of the dunes. High tides and extreme weather events had been nibbling at the seaward faces. The erosion process has not been continuous but interspersed with periods of accretion both by water-borne and wind-borne sand.
The sand was originally deposited by a melting ice sheet in Carmarthen Bay, including the Loughor estuary on which Whiteford Sands is situated, and at Pendine Sands and Rhossili Bay. The first direct evidence for glaciation on Wales dates to 480,000 years ago in the Anglian Stage of the Pleistocene in the Quaternary Period when ice sheets enveloped Wales and the adjacent sea. The last ice coverage in the region was the Late Devensian Era about 24,000 years ago. There seem to be only minimal additions to the sand deposits from local sources since then because the Carboniferous limestones of the area dissolve rather than disintegrate into particles or grains. The sand is a therefore a finite resource albeit one that is controversially exploited locally by dredgers on the Helwick Bank just off the tip of Gower.
The sand is basically mobile within the area on the shorter and longer timescales. A useful and interesting research report on this subject is that by V J May on Carmarthen Bay in the Geological Conservation Review in which the sediment transport around the region is discussed. Figure 11.12 presents a sketch map of the key geomorphological features and sediment transfers of Carmarthen Bay. Figure11.13 depicts variations in accretion and erosion since 1950 in Carmarthen Bay. Figure 1.17 illustrates geomorphological features of Rhossili bay and Whiteford Burrows. The report records how and in which directions the sand is being shifted by river/estuarine currents, onshore and longshore drift; and where attrition and accumulation of sand is most marked. It is an intriguing read and gives much to elucidate the field observations I have been making in the area over the last decade.
The photographs in this post illustrate the way that vast quantities of wind- and wave-borne sand at Whiteford Sands on the Gower Peninsula move around the shore over time. I have taken one fixed object, a piece of ancient timber with an unmistakable shape that projects from the early to post Holocene deposits of peat and clay, and taken shots of it on every visit to the beach over the past ten years or so. The following images show how the sand level changes periodically to reveal or conceal the underlying layers with the surface scattering of rocks that were dumped by the melting ice during the last glacial event. Beaches like Whiteford are incredibly dynamic. Click on any image in the gallery below to view as a slideshow in chronological order.
Fossils can include not only the actual preserved remnants of organisms from times long past (like shells and bones), and the replacements of such organisms (such as infilled moulds and casts), but also the evidence of their existence – for example their modified habitats, trails, burrows, tubes, marks and structures left by their feeding activities. Such evidence of long dead creatures is referred to as trace fossilisation; and the study of fossil traces is termed ichnology.
Part of the process of identifying the exact nature of trace fossils and reaching an understanding of their significance, involves making observations of the behaviour of related or similar present day organisms. This includes a study of their activities and the impact of them on their immediate environment in life. It also involves making records of the way in which the organisms change – what happens to them and their habitat after death (taphonomy).
Many of the trace fossils which I have discovered while walking along seashores and looking at cliffs, outcrops and boulders on beaches were made by various invertebrate seashore creatures in soft intertidal sediments that have later been buried, compressed, and hardened into rock. Recent marine worm tubes of various kinds are a fairly common occurrence on beaches and also as fossils in the sedimentary rocks of, for example, the Dorset coast in England. A short while ago I posted some photographs of fossil worm tubes that I found at Winspit.
For these reasons I was particularly interested to see the millions of sand grain tubes of marine polychaete worms on the low tide beach at Whiteford Sands on the north coast of the Gower Peninsula in South Wales. Many could be seen in situ, no doubt with worms in residence, projecting from the surface of the wet sand like some kind of stunted crop with seashells scattered among them. On the shallow bank created by a beach stream wending its way seawards, it was fascinating to see how far down into the sediments the tubes extended, a thick layer of unknown depth. It reminded me of a fantastic illustration in a book I recently acquired by Wilhelm Schäfer called Ecology and Palaeoecology of Marine Environments, originally published in Edinburgh by Oliver & Boyd in 1972. Copyright considerations mean the book is not old enough for me to reproduce the drawing here for you without written permission but Figure 190 on page 326 shows a cross-section through bedded sands and muds and shell deposits with many-branched and frequently extended dwelling tubes of Lanice conchilega cutting across the layers – just like the deposits on Whiteford Sands. Even though the book is old it is still widely available secondhand and is a wonderful repository of information.