Eype Beach Stream 3

Little pebble bridges over a beach stream

On the western half of the shore at Eype in Dorset, England, the cliff is basically made up of porous yellow sandstones and limestones, belonging to the Middle Jurassic Down Cliff Sand Member and Thorncombe Sand Member, overlying the pale, blue-grey micaceous silty mudstone and shale known as the Eype Clay Member. All three members belong to the Dyrham Formation.  Rainwater soaks down through the upper porous rocks but, when it reaches the lower clay-based strata, it seeps out to the surface and drains away down the cliff face to the shore in numerous small streams.

The picture above, and the short video clip below, show one of these little streams running over the clay where someone has artistically constructed small pebble bridges over the flow. The last image in the post illustrates the general appearance of the cliff face with the small streams issuing from the lower layers.

Blue-grey clay and yellow sandstone strata at Eype Beach

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved

Lyme 8

 

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved

Lyme 7

 

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved

Rock Textures at Eype 1

View of the cliff on the western shore at Eype showing stratification

View of the cliff on the western shore at Eype showing stratification

The interesting thing about Eype Beach is that you don’t have to climb the cliffs to see the rocks in detail – the rocks come to you! Boulders of sandstone and limestone from high in the cliffs regularly collapse to the beach, which becomes strewn with them, and affords an opportunity to examine the composition of, and the fossil content of, the variety of rock types represented in the strata above shore level. Even the low, thick band of softer mudstones and shales slips down on a fairly regular basis, and liquified by small streams, oozes over the shingle of the upper beach.

It’s going to take me a while to work out which rock is which. However, I can say that Eype Beach has two different geologies more or less separated at Eypesmouth where a small stream cuts its way down a steep-sided valley through the predominantly soft rocks. If you turn right and westwards where the stream breaks through to the shore, and walk towards Thorncombe Beacon as I did, then on your right-hand side are cliffs made up of several virtually horizontal rock strata of different types of sedimentary rock. The lowermost layer, nearest to the level of the shingle beach, is a 55 foot depth of blue-grey Eype Clay Member made up from micaceous silty mudstone and shale – also called  the Micaceous Beds – from the Middle Jurassic Period.

Above the blue-grey mudstone, are the yellow layers of silts and sandstones of the Down Cliff Sand Member and the Thorncombe Sand Member – with sporadic fossil beds, and thinner bands of calcareous sandstone and ironshot limestone. You can easily see the contrasting colours of the different rocks in the cliff face.

I had hoped to find some brittle star fossils, that was the main aim of the visit, but I wasn’t lucky on this occasion. It was rather hot on the day and I don’t think I walked far enough along the shore to be in the most likely location. The Starfish Bed with Palaeosoma egertoni is at the very base of the Down Cliff Sand Member which itself overlies the Eype Clay Member. Large blocks of this rock fall to the beach – but you have to hope that the block has fallen the right way up for you to see the brittle star fossils, and also hope that a professional fossil hunter has not got there before you! I’ll have to keep on keep searching.

View looking west toward Thorncombe Beacon from the base of the cliff at Eype

View looking west toward Thorncombe Beacon from the base of the cliff at Eype

It was clear that many types of rock were identifiable on the beach; even the modern mud-slicks and clay seepages were interesting because they demonstrate and replicate the same  processes that would have contributed to the textures and patterns of the ancient rocks. As the soft muds dried out in the sun, the surfaces were beginning to form a crazy paving patchwork of cracks – the same as could be observed in nearby slabs of rock. As the liquified clays dribbled outward from the base of the cliff rock exposure, they incorporated assemblages of small pea-sized pebbles and who-knows-what man-made objects that might end up in rock strata of the future.

So the gallery of pictures today just shows details of a small selection of the rocks and sediments to be found on Eype Beach with a range of the natural textures and patterns they exhibit. It’s the starting point for the Eype geological learning journey.

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved.

Eype Beach Stream 1

Lyme 4

Large Jurassic ammonite fossil in a beach boulder

An abundance of Jurassic ammonites – seen on a single walk along the shore at Monmouth Beach in Dorset, England, a few years back. There were large ones and small ones; embedded in beach boulders and forming rock pavements; in limestone and shale; some crystallised and others just impressions; some with other fossils preserved alongside or even inside the chambers.

Large Jurassic ammonite fossils embedded in a rock platform on the beach

Small ammonite fossil in Jurassic limestone

Impression of a small ammonite fossil

Large Jurassic ammonite fossil in a beach boulder

Large Jurassic ammonite fossils embedded in a rock platform on the beach

Large Jurassic ammonite fossils embedded in a rock platform on the beach

Large Jurassic ammonite fossil in a beach boulder

Ammonite fossil on Monmouth Beach at Lyme Regis

Ammonite fossil on Monmouth Beach at Lyme Regis

Large Jurassic ammonite fossil in a beach boulder

Large Jurassic ammonite fossil in a beach boulder

Monmouth Beach at low tide

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved

Ringstead Sea Kale

Young curly leaf of Sea Kale just opening

Close-up of a young red and purple leaf of Sea Kale

Sea Kale, Crambe maritima Linnaeus, grows on the shingle beaches in Dorset, England. When the leaves first sprout, they are a delectable colour of purple but as the plant matures the leaves become grey-green. However, the leaf veins and the curly edges of the leaves remain pink/purple but not as intense a colour as in the young shoots.

Sea Kale leaf becoming greener as it develops but with purple veins and edges

Close-up of a semi-mature Sea Kale leaf with leaf veins and curly edges still coloured purple or deep pink

Close-up of well developed Sea Kale leaf showing pink/purple leaf edges

Close-up of well developed Sea Kale leaf with grey-green blade and just the edges pink

Sea Kale (Crambe maritima) growing on the beach

A Sea Kale plant growing on seashore shingle at Ringstead Bay

Sea Kale (Crambe maritima) growing on the beach

Sea Kale (Crambe maritima) growing on the beach

Young purple shoots at the base of Sea Kale (Crambe maritima) growing on the beach

Young purple shoots sprouting at the base of Sea Kale (Crambe maritima) growing on the Ringstead Beach

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved

 

Lyme 3

 

Large ammonite fossil in a boulder on Monmouth Beach

Large ammonite fossil in a boulder on the beach

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved

Pictures from an Isle of Portland walk – Part 5

 

The rocks and soils above and below the raised beaches at the southern tip of the Isle of Portland in Dorset, England, exhibit features that are believed to be associated with freeze-thaw  periglacial conditions. These photographs show interesting rock features in the Upper Jurassic limestone that I think may possibly relate to the cold period prevailing prior to the interglacial period in which the younger of the two raised beaches known as Portland East Beach (as shown in the previous post) were formed.  Pugh & Shearman (1967) first described these cryoturbation features on the Isle of Portland, and later  (Goudie & Brunsden, 1997) stated that:

At the base of the raised beach gravels, the shore platform is heaved, cracked, and warped to a depth of up to 3m.  The meticulous observer will also be able to reconstruct crude polygons of angular boulders which stand on edge. Such features are thought to be caused by frost action under cold conditions and are commonly known as periglacial (tundra) patterned ground and, more specifically as rock blisters.

REFERENCES

Goudie, A. and Brunsden, D. (1997) Classic Landforms of the East Dorset Coast, Series Editors Rodney Castleden and Christopher Green, The Geographical Association, ISBN 1 899085 28 9.

Pugh, M. E. and Shearman, D. J. (1967) Cryoturbation structures at the south end of the Isle of Portland in Proceedings of the Geologists’ Association, 78, pp 463 – 471.

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved

Pictures from an Isle of Portland Walk – Part 4

On the southern tip of the Isle of Portland, in Dorset, England, raised beach deposits provide evidence of higher sea levels at some periods during the Quaternary. There are two separate raised beaches, the more publicised Portland West Beach just to the west of Portland Bill Lighthouse – and another 200 metre long section of Portland East Beach to the east of the lighthouse and behind the Lobster Pot Café.

The Portland East Beach raised beach deposits are shown in these photographs. They sit on top of layers of limestone and are made up of pebbles, larger beach stones, and boulders of Portland and Purbeck limestone, flint and chert – intermixed with seashells. The shells in the images here are all marine gastropod shells of the common periwinkle. All the beach material is bound together in a cement-like matrix of high calcium content, the whole being frequently stained rusty by iron from percolating water. It is interesting to note how many of these ancient beach stones were already riddled with small holes and burrows made by sea creatures, such as Polydora-type worms and boring bivalve molluscs like piddocks, before being isolated and consolidated into the solid layer of beach deposits when the sea levels went down. If you look closely, you can actually see the piddock shells retained within the bore holes of some of the stones..

The whole raised beach layer is up to 0.45 metres thick but is mostly patchy in its distribution. Amino-acid analysis of the mollusc shells suggests that they date from the Ipswichian period of 125,000 years before present, which was the last interglacial. The sea level at that time would have been about 6.95 – 10.75 metres above present sea level. The Portland East Beach is a more recent deposit than the Portland West Beach that has been dated by the same method to 210,000 BP, at which time the shoreline would have been about 14.5 metres above present levels. The higher sea levels are thought to have resulted from the melting of the ice caps in these warmer interludes in the Ice Age, and it is also possible that some local tectonic uplift of the land mass may have played a part.

REFERENCES

Barton, C. M.; Woods, M. A.; Bristow, C. R.; Newell, A. J.; Westhead, R. K.; Evans, D. J.; Kirby, G. A.; Warrington, G. (2011) Geology of south Dorset and south-east Devon and its World Heritage Coast, Special Memoir for 1:50 000 geological sheets 328 Dorchester, 341/342 west Fleet and Weymouth and 342/343 Swanage, and parts of sheets 326/340 Sidmouth, 327 Bridport, 329 Bournemouth and 339 Newton Abbot, Compiled by M. A. Woods, British Geological Survey, Keyworth, Nottingham.

Davis, K. H. and Keen, D. H. (1985) The age of Pleistocene marine deposits at Portland, Dorset, Proceedings of the Geologists’ Association, 96, pp 217 – 225.

Goudie, A. and Brunsden, D. (1997) Classic Landforms of the East Dorset Coast, Series Editors Rodney Castleden and Christopher Green, The Geographical Association, ISBN 1 899085 28 9.

Keen, D. H. (1995) Raised beaches and sea levels in the English Channel in the Middle and late Pleistocene: problems of interpretation and implications for the isolation of the British Isles, in Island Britain: a Quaternary perspective, Preece, R. C. (editor). Geological Society of London Special Publication, No. 96, pp63 – 74.

Keen, D. H. (1985) Late Pleistocene deposits and mollusca from Portland, Dorset, Geological Magazine, 122, pp 181 – 186.

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved