Rusty Pebbles at Whiteford

Rusty Pebbles at Whiteford (1) - View looking across to Llanmadoc Hill showing pebbles on the beach at Whiteford Sands, Gower, South Wales, some of which are covered with a rusty deposit thought to derive from the break up of an iron-pan associated with a Holocene peat layer.

Vast swathes of pebbles on the beach at Whiteford in Gower are coloured orange – or at least they were the last time I looked. (The beach sediments there are very mobile so it cannot be guaranteed that you will see exactly the same thing on each visit). These coloured pebbles are found in a band stretching from the base of the sand dunes at the eastern end of the beach towards the disused Victorian Whiteford Lighthouse.

The pebbles seem to be coated in rust rather than rusty because of their intrinsic composition. I guess the first couple of times that I noticed the orange pebbles I vaguely thought that they were stained by rust emanating from the decomposing remains of the old iron causeway that linked the lighthouse to the shore. You can often find pieces of the iron framework of the walkway – sometimes supports still in situ and other times single pieces of the structure lying free.

However, lately, I have been discovering more and more about the Quaternary geology of the Gower – a relatively recent geological period dating from about 2.5 million years ago to the present. This includes the Pleistocene with a variety of glacial, peri-glacial and inter-glacial deposits; and the recent Holocene (from 11,800 years ago) with peat and submerged forests, marsh, dune, beach and alluvial deposits. As I read more, I am gradually reaching something of an understanding about some of the natural phenomena that I observe and photograph on Gower beaches. So I now tentatively consider that the rusty pebbles are not related to the dilapidation of the old lighthouse but are the result of a much older natural geological process.

I have already mentioned in Jessica’s Nature Blog the remains of the submerged forest at Broughton Bay which lies to the west and adjacent to Whiteford Sands. These ancient tree trunks are embedded in peat deposits. While I was reading George (2008), I learnt that the peat decomposes to form a hard ferruginous layer called an iron-pan or hardpan. This has led me to wonder if the iron compounds that coat the pebbles at Whiteford are derived from an iron pan layer.

Supporting evidence for this idea comes from the presence of ancient tree trunks emerging from black peat deposits close to the rusty pebbles – similar to those stumps found at Broughton. The old waterlogged wood is also stained with rust – as you will see from the photographs below. Additionally, slightly higher on the beach, closer to the dunes, the shore is strewn with pebbles around which orange-coloured watery ‘tears’ rise to the surface and weep across the surface of the sand – making me think they might originate from a concealed ferruginous hardpan below.

Then again, I suppose the rust could come from buried decomposing munitions as the beach was used for firing practice in the Second World War!

Reference:

George, Gareth T. (2008) The Geology of South Wales – A Field Guide, G.T.George at gareth@geoserve.co.uk , ISBN 978-0-9559371-0-1, p 70.

Rusty Pebbles at Whiteford (2) - View looking across to Llanmadoc Hill showing pebbles on the beach at Whiteford Sands, Gower, South Wales, some of which are covered with a rusty deposit thought to derive from the break up of an iron-pan associated with a Holocene peat layer.

Rusty Pebbles at Whiteford (3) - Pebbles on the beach at Whiteford Sands, Gower, South Wales, some of which are covered with a rusty deposit thought to derive from the break up of an iron-pan associated with a Holocene peat layer.

Rusty Pebbles at Whiteford (4) - Pebbles on the beach at Whiteford Sands, Gower, South Wales, some of which are covered with a rusty deposit thought to derive from the break up of an iron-pan associated with a Holocene peat layer.

Rusty Pebbles at Whiteford (5) - View looking across towards Whiteford Lighthouse showing pebbles on the beach at Whiteford Sands, Gower, South Wales, some of which are covered with a rusty deposit thought to derive from the break up of an iron-pan associated with a Holocene peat layer. Ancient waterlogged wood from the submerged forest is also visible.

Rusty Pebbles at Whiteford (6) - Ancient iron-stained log embedded in peat from a submerged post-glacial forest - associated with pebbles on the beach at Whiteford Sands, Gower, South Wales, some of which are also covered with a rusty deposit thought to derive from the break-up of an iron-pan associated with the disintegration of the Holocene peat layer.

Rusty Pebbles at Whiteford (7) - Ancient iron-stained log embedded in peat from a submerged post-glacial forest - associated with pebbles on the beach at Whiteford Sands, Gower, South Wales, some of which are also covered with a rusty deposit thought to derive from the break-up of an iron-pan associated with the disintegration of the Holocene peat layer.

Rusty Pebbles at Whiteford (8) - Pebbles scattered on the surface of the sand with 'tears' of rusty water, possibly rising from a buried Holocene iron-pan layer below the sand, weeping across the beach.

Rusty Pebbles at Whiteford (9) - Pebbles scattered on the surface of the sand with 'tears' of rusty water, possibly rising from a buried Holocene iron-pan layer below the sand, weeping across the beach.

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An odd ball from Ringstead Bay

Clay ball from Ringstead Bay: Pebble-studded clay ball from Ringstead Bay, Dorset, UK - part of the Jurassic Coast. 

A naturally-occurring pebble-studded ball of Kimmeridge Clay. It was found rolling around on the water’s edge at Ringstead Bay in Dorset. I like the shape of this beachcombed object. It’s quite decorative. The pattern of the bright orange and lighter-coloured stones looks attractive against the blue-grey clay.

The main body of the clay outcrops high on the seashore and has a very glutinous texture when wet. Sometimes pieces of this clay crack off in dry conditions or may be loosened by wave action. When wet, these lumps of clay stick to anything they come into contact with.

The seashore at this point is mostly flint shingle with smaller pebbles and finer gravel at low tide level. The strong currents and crashing waves have moved the clay around until it has become this interesting rounded shape and texture. It has acquired the pebble coating in much the same way that a soft sweet acquires its finish of “hundreds and thousands”.

Revision of a post first published 23 June 2009

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Waves at Lyme Regis

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How many ways are there for the waves to break on the seashore? Each beach, each tide, is different. Have you ever noticed how the circular motion of waves means that waves are retreating and advancing at the same time? No sooner has a wave crashed on the shore creating millions of salty bubbles, than it is being dragged back seawards under the sediments, while the next wave builds and advances above. The whole cyclical dynamic process generating  hypnotic movement and sound accompanied by changing lacey patterns of seafoam on water and shingle.

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Pebbles from Corsica

Pebbles of many colours and patterns from Corsica arranged in a blue bowl (1)

Many years ago, I picked up these wonderfully patterned and coloured pebbles on a beach in Corsica.  They remind me of the warm sunny day that I saw the fantastic sight of an entire seashore covered with pebbles just like them.

I have to confess that I know very little about them except that they are extremely beautiful and varied in many ways: geological origin and structure; pattern (plain, spotted, marbled and striped); texture and shape (smooth, rounded or flattened); and colour (yellow, orange, red, black and white). The rocks from which these stones were derived must to be volcanic or igneous in origin. I remember that in Corsica the whole mountainsides are pink and red. 

Pebbles from Corsica: A grey-green pebble with stripes and dots from Corsica (2)

Pebbles from Corsica: An orange and black patterned pebble from Corsica (3)

Corsican pebbles: Spotted pebbles from Corsica (4)

Pebbles from Corsica: Black and white spotted pebble from Corsica (5)

Corsican pebbles: Red and white spotted pebble from Corsica (6)

Pebbles from Corsica: Stripes and dots in a pebble from Corsica (7)

Pebbles from Corsica: Orange and black pebble from Corsica (8)

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Some pebbles from Eype

Eype in Dorset has an interesting beach. Mostly it is shingle – orange and grey rounded pebbles of various sizes. However, there are large boulders of different geological types that have fallen from the cliff and are now scattered across the shore. When the tide comes in, it sometimes washes the pebbles high over the boulders so that, when the tide goes out, groups of small pebbles remain in nooks and crannies on the surface of the larger rocks – looking like odd eggs in a strange stony nest. 

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Lots more pebbles from Eype

Pebbles on the beach at Eype, Dorset, UK on the Jurassic Coast. Photographs of shingle – wet, dry, big, small, assorted sizes, graded sizes, various shapes, different colours, orange pebbles, grey pebbles, black pebbles, pebbles with sand, pebbles washed by white seafoam, pebbles with a measuring scale, millions of pebbles in all.

If this is not enough for you pebble lovers, click here for more PEBBLES.

 
 
 
 
 
 
 
 

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