Rocks at Redend Point in Studland Bay – 4

Orange cliff rocks on the north side of Redend Point in Studland Bay, Dorset, England.

I revisited Redend Point at Studland in Dorset yesterday for the first time in several years. Here are some of the pictures I took. I was only able to look at the north side of the Point because of the state of the tide. The colours seem different from my last trip there. This could be to do with how much rain there has been but also possibly to do with the weathering affect on the iron. [The part of the Point with the wonderful pink and yellow stripes and patterns was further on – to the south of the Point which I could not reach].

More rocks have fallen from the ferruginous sandstone and from the overlying clays. This has brought down a large tree which now lies across the beach. In some areas the sea has undercut the sandstone to produce small caves. These have floors composed of a mixture very fine pale sand, rust-stained flints from the nearby chalk strata around the corner, and bright orange sandstone with pot-holes and eroded channels draining seawards. In this northern part of the Point the colours manifest by the Redend Sandstone seemed less varied than four years ago, and the carved graffiti was much greater than previously noted. Such a shame that almost every surface was disfigured.

Beach boulder and pebbles on the north side of Redend Point in Studland Bay, Dorset, England.

Flint pebbles and boulders on the north side of Redend Point at Studland Bay in Dorset, England.

Flint pebbles on the north side of Redend Point at Studland Bay in Dorset, England.

Beach boulder and pebbles on the north side of Redend Point in Studland Bay, Dorset, England.

Cliff rocks on the north side of Redend Point in Studland Bay, Dorset, England.

Beach boulder and pebbles on the north side of Redend Point in Studland Bay, Dorset, England.

Lower cliff rocks on the north side of Redend Point in Studland Bay, Dorset, England.

Lower cliff rocks on the north side of Redend Point in Studland Bay, Dorset, England.

Lower cliff rocks on the north side of Redend Point in Studland Bay, Dorset, England.

 Boulder and cliff on the north side of Redend Point in Studland Bay, Dorset, England.

Beach boulder on the north side of Redend Point in Studland Bay, Dorset, England.

Boulder and cliff on the north side of Redend Point in Studland Bay, Dorset, England.

Rocks at Redend Point in Studland Bay – 3

Rock colour, pattern, and texture in Creekmoor Sand (Redend Sandstone) at Studland Bay

Several years ago I first posted some of these photographs of Studland Bay rocks but I think it is still worth posting some more now, as it is not every one who will have had the time and patience to burrow through the archives of rock postings on this web log. I never cease to be amazed by the stripe patterns, and the red, yellow, and purple colours of the Redend Sandstone (Creekmoor Sand) at Studland Bay. They are incredible.

Rock colour, pattern, and texture in Creekmoor Sand (Redend Sandstone) at Studland Bay

Rock colour, pattern, and texture in Creekmoor Sand (Redend Sandstone) at Studland Bay

Rock colour, pattern, and texture in Creekmoor Sand (Redend Sandstone) at Studland Bay

Rock colour, pattern, and texture in Creekmoor Sand (Redend Sandstone) at Studland Bay

Rock colour, pattern, and texture in Creekmoor Sand (Redend Sandstone) at Studland Bay

Rock colour, pattern, and texture in Creekmoor Sand (Redend Sandstone) at Studland Bay

Rock colour, pattern, and texture in Creekmoor Sand (Redend Sandstone) at Studland Bay

Rock colour, pattern, and texture in Creekmoor Sand (Redend Sandstone) at Studland Bay

Rocks at Redend Point in Studland Bay – 2

Rock colour, pattern, and texture in Creekmoor Sand (Redend Sandstone) at Studland Bay

Pink and yellow patterned sandstone with Liesegang rings resulting from the dispersion of iron minerals dissolved in river water percolating through the rock. Photographed at Studland Bay in Dorset, England, in outcrops of Eocene-dated Redend Sandstone (Creekmoor Sand) of the Poole Formation in the Bracklesham Group. These soft sandstones in the low cliffs at the south end of the bay seem to be an irresistible  “canvas” for graffiti artists.

Rock colour, pattern, and texture in Creekmoor Sand (Redend Sandstone) at Studland Bay

Rock colour, pattern, and texture in Creekmoor Sand (Redend Sandstone) at Studland Bay

Rock colour, pattern, and texture in Creekmoor Sand (Redend Sandstone) at Studland Bay

Rock colour, pattern, and texture in Creekmoor Sand (Redend Sandstone) at Studland Bay

Rock colour, pattern, and texture in Creekmoor Sand (Redend Sandstone) at Studland Bay

Rocks at Redend Point in Studland Bay – 1

Rock texture, colour, and pattern in Redend Sandstone  at Studland Bay

Examples of rock texture, colour and pattern in Redend Sandstone (also known as Creekmoor Sand) which is a basal member of the Poole Formation (formerly referred to as the Bagshot Formation), of the Bracklesham Group. The pastel almost rainbow colours are caused by iron staining. Hollow pipes (as in the shot immediately below), which can be up to 15 cm diameter and sometimes extend as much as 4 m through the strata, are of unknown origin. The sandstones were laid down in the Eocene.

REFERENCE

Cope, J. C. W., 2012, Geology of the Dorset Coast, Geologists’ Association Guide No. 22, 191-194, ISBN 978-0900717-61-1.

Rock texture, colour, and pattern in Redend Sandstone at Studland Bay

Rock texture, colour, and pattern in Redend Sandstone at Studland Bay

Rock texture, colour, and pattern in Redend Sandstone at Studland Bay

Permian Red Beds at Lord Selkirk Park, PEI

View along the shoreline at Lord Selkirk Provincial Park in Prince Edward Island, Canada, with lush green early summer vegetation and red Permian rocks.

Views along the shoreline at Lord Selkirk Provincial Park, on the south coast of Prince Edward Island in Canada, show the red Permian sedimentary rock layers in low cliffs, and as mud beneath the water of the Northumberland Strait. The lush vibrant green of the new season’s vegetation makes a striking contrast to the outcropping red beds.

The whole of Prince Edward Island is underlain by Permian rocks which also extend outwards to New Brunswick and Nova Scotia. They date from around 255 million years ago and were laid down between the Carboniferous period which came before it and the Triassic period which followed it. Towards the end of the Carboniferous, the climate started to warm up and dry out; and this marked the end of the vast wetland forests and swamps that had been so characteristic of the Carboniferous and that are recorded by numerous plant fossils and extensive coal measures.

The plants and trees that continued to grow in the Permian Period were mainly those which were resistant to drought, like conifers, although some plants such as tree ferns persisted in the wetter ares.  Remains of these plants have been preserved as fossils in the Permian rocks. The terrestrial red beds of Prince Edward Island have also preserved the bones of vertebrates, reptiles, that were washed down rivers in monsoon flash floods and became buried in pebbles and debris. At Point Prim, very close to Lord Selkirk Provincial Park, trace fossils of one of these mammal-like reptiles has been found. We were not lucky enough to find fossils of any kind while we were there as our visit was so fleeting.

Stephanian to late Early Permian rocks occur in and under PEI. The fields, so famous for their potato crops, are a distinctive red colour, indicating the rock type from which the soil is derived. The rocks themselves are best seen outcropping along the coast – in fact one of the first things you notice as you cross the Confederation Bridge to get to the island is the continuous thin red rocky line along the miles of southern shore.

The Permian strata on PEI are divided into different phases, and those shown in the photographs here, from Lord Selkirk Park near Point Prim, belong to the Wood islands Member, which together with the Malpeque Member to its west, comprise the relatively recently-designated Hillsborough River Formation, that belongs to the Northumberland Strait Supergroup. The rocks are made up of conglomerates, sandstones, and mudstones.

REFERENCES

van de Poll, H. W., 1989, Lithostratigraphy of Prince Edward Island redbeds, Atlantic Geology, 25, 23-35.

Atlantic Geoscience Society, 2001, The Last Billion Years: A Geological History of the Maritime Provinces of Canada, Nimbus Publishing, ISBN1-55 109-351-0, Atlantic Geoscience Society Special Publication No 15.

Caswell Bay Mudstone Formation

These three galleries show pictures of rock texture and pattern in strata of Caswell Bay Mudstone Formation (CBMF) at Caswell Bay on the Gower Peninsula in South Wales. This is the type location for the CBMF – the place from which the rocks were first described and named. The rocks are part of the Pembroke Limestone Group of the Tournasian/Visean epoch of the Mississipian subdivision of the Carboniferous Period. The Carboniferous Period lasted from 359 to 299 million years ago (mya) but the Tournasian/Visean part only lasted from 359 to 326 mya. The CBMF were deposited around the middle of that period. The total thickness of rocks deposited during the Tournasian/Visean epoch was around 750 metres but the CBMF is just a narrow band – with estimates of its thickness varying from 0-14 metres (George, 2008) to 3 – 7.5 metres thick (Barclay, 2011). The CBMF is sandwiched between the Gully Oolite Formation limestone below and the High Tor Limestone Formation above.

Barclay (2011) says that: the Caswell Bay Mudstone Formation is composed of thinly bedded calcitic and dolomitic mudstones and micritic limestones (George, 1978; Ramsay, 1987). The basal bed is a calcrete (Heatherslade Geosol of Wright, 1987b), with beds of algal laminate and oncoid limestone. The rocks are pale grey to greenish grey, buff, brown and yellow, locally with some red staining.

Barclay says there are some but not many fossils. Also that: the rocks formed in shallow water environments referred to as “lagoon phase” by Dixon and Vaughan (1912). They are interpreted as shallow-water, peritidal deposits formed in a tidal flat lagoon complex behind a beach barrier in a humid climate, with abundant evidence of sub-aerial exposure in the form of dessication cracks (Riding and Wright, 1981; Wright, 1986; Ramsay, 1987).

The Caswell Bay Mudstone Formation lies unconformably on top of of the sub-aerially weathered palaeo-karst surface of the Gully Oolite Formation limestone. It means that there was a time lag between the deposition of the limestone and the next phase of deposition of the mudstones. The palaeo-karst surface is full of dissolved pot-holes. These pot-holes are a common karstic feature on Gower south coast beaches – with Mewslade Bay and the Worms Head Causeway exhibiting some good examples.

The Gully Oolite Formation limestone was deposited in warm tropical seas at a time when sea-level was standing still or slowly falling. The extended period of sub-aerial weathering that created the palaeo-karst surface occurred during a significant relative fall in sea-level (George, 2008, 85). The Caswell Bay Mudstone Formation was formed during a subsequent phase of slow sea-level rise.

References

Barclay, W. J. (2011) Geology of the Swansea District: a brief explanation of the geological map Sheet 247 Swansea,  British Geological Survey, Natural Environment Research Council,  ISBN 978-085272581-8, pp 4-6.

Dixon, E. E. L., and Vaughan, A. (1912) The Carboniferous succession in Gower (Glamorgan) with notes on its fauna and conditions of deposition. Quarterly Journal of the Geological Society of London, Vol. 67, pp 477-571.

Geological Society Field Guide to Caswell Bay.

George, G.T. (2008) The Geology of South Wales: A Field Guide, published by gareth@geoserve.co.uk, ISBN 978-0-9559371-0-1,  pp 82- 86.

George, T. N. ((1978) Mid Dinantian (Chadian) limestones in Gower. Philosophical Transactions of the Royal Society, Vol. B282, pp 411-462.

Ramsay, A. T. S. (1987) Depositional environments of Dinantian limestones in Gower, 265-308 in European Dinantian environments, Miller, J., Adams, A. E. and Wright, V. P. (editors). (Chichester: John Wiley & Sons Ltd.)

Riding, R. and Wright, V. P. (1981) Palaeosols and tidal flat/lagoon sequences on a Carboniferous carbonate shelf: sedimentary associations of triple disconformities. Journal of Sedimentary Petrology, Vol. 51, pp 275-293.

Wright, V. P. (1986) Facies sequences on a carbonate ramp: the carboniferous Limestone of south Wales. Sedimentology, Vol. 33, pp 221-241.

Wright, V. P. (1987b) The ecology of two early Carboniferous palaeosols, 345-358 in European Dinantian environments. Miller, J., Adams, A. E. and Wright, V. P. (editors). (Chichester: John Wiley & Son.)

Shingle Banks at Pwll Du

View looking east across the water's edge at Pwll Du Bay

Long before the beach was actually visible, the thunder of the waves crashing on the shore, and the grinding of the pebbles against each other on the water’s edge, could be heard as I followed the signpost from Pwll Du Head, down the steep path through the tree-clad valley side to the shore below.

Stretched across the mouth of the valley below lies a massive bank of cobbles and pebbles, or more accurately three successive banks. Unusually for this type of beach, almost all the rocks that make up the banks are the waste product of quarrying activity. Certain privileged farming tenants up until the beginning of the 20th century were granted rights of “cliffage” that allowed them to quarry limestone from the valley sides and the eastern cliff face of Pwll Du Head. The quarry on the Head ceased operation in 1884. The workings are now mostly overgrown.

Boulders from the quarries were placed in heaps marked with wooden stakes on the beach. Ships came over from the north Devon coast to collect the stone to be burnt for lime that would fertilise the fields. Apparently, when the boats arrived, they would scupper in the shallow water at high tide next to the marker posts. Once they were in position on the bottom, the sea-cocks were closed again, with the boat remaining full of water as the tide went out. This technique meant that the bottom of the boat would not be damaged because the water cushioned the fall as the first of the quarried boulders were thrown aboard. Once the cargo was loaded, the sea-cocks were opened to drain away excess water, then closed so that the boat could float on the next high tide ready for the return trip to Devon. Small pieces of rock were too bothersome to load and remained on the shore, gradually building up over the years into the banks.

The shingle banks block the flow of the small river known as Bishopston Pill. The barrier of the shingle banks forms a dam. A small lake lies behind the banks. Beyond the pooled water in the pictures below, two white buildings are tucked into the western valley side at the back of the shingle; these were once public houses that catered for the workmen labouring in the quarries – it must have been thirsty work.

In summer when flow is reduced the water seeps gently from the base of the banks and spreads out across the shore, usually at the eastern end of the beach. When I visited in October after heavy rain, the water was emerging in two fast-flowing streams that were cutting embryo channels through the shingle at the seaward face. In winter when flow is greatest it seems that the banks are breached completely by the flow.

The pebbles nearest to the shore, where they are constantly moved against each other by the waves, tend to be the smallest and smoothest. Most of them are the local Carboniferous limestone but some “foreign” pebbles are included and these originated as jettisoned ballast from ships plying trade in the Pwll Du quarried limestone.

As you walk inland across the shingle, the nature of the stones beneath your feet changes. Whereas on the shore small rounded pebbles tend to predominate, further inland the stones increase to cobble size and they become progressively less rounded and more angular. The shingle bank is always a dynamic structure. However, for many years the innermost couple of the three terraces or ridges, storm beaches, were relatively stable. The stability partly enabled and partly resulted from vegetative colonisation.

I have read accounts of lichen-covered pebbles on the inner banks but none were visible when I visited. Although this was my first visit, I have seen earlier accounts of this locality, and I think that last winter’s storms may well have had a profound effect on the shingle banks. It seemed to me that there had been a great churning up of the stones, resulting in a greater mixing of size and shape, possibly a partial reconstruction of the ridges, destruction of some of the patches formerly stabilised by rooted plants, and removal of lichen encrustations or burial of lichen coated pebbles.

REFERENCES

Gillham, M. E. (1977) The Natural History of the Gower, South Wales, D. Brown and Sons Ltd, Cowbridge, ISBN 0 905928 00 8.

Mullard, J (2006) Gower, New Naturalist Series, Collins, ISBN 0 00 716066 6.

Pwll-Du and the quarrymen of Gower The Geological Society Website

Sea-washed Carboniferous limestone pebbles at Pwll Du Bay