Shallow Rock Pools at Winspit

Seashore life in shallow rock pools on a limestone ledge

The flat quarried limestone ledge on the water’s edge at Winspit in Dorset provides a slightly unusual substrate for seashore life. There are natural gullies and deep angular man-made inlets in the stone but the area is mostly characterised by an extensive network of very shallow rock pools. Although only capable of retaining a centimetre or two of salt water as the tide recedes, these shallow pans and the surrounding surfaces are intensely colonised by numerous marine organisms, The natural patchwork of seaweeds and seashore creatures resembles a vast multi-coloured carpet with predominating pink and green hues.

The depressions in the rock are caused by the differential erosion of the softer limestone and the more resistant black chert nodules liberally embedded in it. The chert is composed of hard quartz derived from the opaline silica of decomposing sea sponges millions of years ago. The exposed rock stratum belongs to the Portland Chert Member dating from the Jurassic Period. Physical wear and acid erosion affect the softer matrix by chipping away and dissolving the stone respectively. The result of these ongoing processes can be seen from the small pitting marks.

In addition to this, the colonising organisms contribute significantly to erosion processes. For example, encrusting lichens can penetrate the rock surface, and as limpets feed by scraping this and other types of biofilm from the surface, they incidentally remove minute particles of stone with the food. Over great periods of time this feeding behaviour, together with other natural phenomena, imperceptibly degrades and removes rock thereby increasing the depth of the depressions. Additionally, the limpets always return to a home base when the tide goes out, and the circular impressions left by the friction of the shell margin as the limpet suckers tight down to prevent moisture loss are evident everywhere. When a large limpet dies or is removed, the home base is frequently re-occupied by new generation small limpets.

The natural depressions retain water at low tide, sometimes just a few millimetres but enough to support continued activity and prevent dessication. The wet hollows and much of the surrounding rock are covered by a patchwork of black, green, pink and white encrusting lichens and algae with groups of sessile or acorn barnacles. Some of the encrusting algae are calcareous, and there are abundant short tufts of pink calcareous coral weed, branched and articulated. Soft, finely-branched and filamentous red algae also occur – sometimes  amusingly attaching themselves like decorative plumes to the shells of living limpets which often provide a home for dark brown encrusting algae, while dark red, almost black, beadlet anemones also glisten in the water.

Jellyfish and Japweed at Studland

Yesterday on Knoll Beach at Studland Bay in Dorset, the two most common things washed ashore were great clumps of Japweed (Sargassum muticum) and large barrel-mouthed or dustbin-lid jellyfish (Rhizostoma octopus). There were at least a dozen jellyfish on the stretch of sand that I walked. They varied in size from about 20 – 60 cm diameter across the dome. The colours varied from crystal clear to pink and blue. They all seemed very fresh and I think maybe some of them were still alive or just expiring. As they washed to and fro in the waves, sometimes entangled in the Japweed, they turned this way and that, upright then upside down, inside and out. This species is becoming an increasing feature on south-west coasts over the last couple of summers. I first encountered these seashore creature on the Gower Peninsula in South Wales where they have long been a frequent find on the beaches. Click here to learn more about the Rhizostoma octopus jellyfish on Jessica’s Nature Blog.

Rock Strata from Kimmeridge Cliffs – Part 2

Detail of cliff strata from Kimmeridge Bay

The second selection of photographs showing details of the rocks in the Upper Kimmeridgian Clay cliff mudstone and shale strata with iron staining on the east side cliffs of Kimmeridge Bay in Dorset, England on the World Heritage Jurassic Coast.

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

Rock Strata from Kimmeridge Cliffs – Part 1

Detail of cliff strata from Kimmeridge Bay

The first selection of photographs taken at Kimmeridge Bay in Dorset, England, yesterday (27 March 2015) showing details of the natural patterns, textures, and colours of the rocks. The rocks are described as rhythmically inter-bedded blocky, organic-poor mudstone and fissile, organic rich shale.

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

Detail of cliff strata from Kimmeridge Bay

For information about the geology of this location look at:

John C. W. Cope Geology of the Dorset Coast, Geologists’ Association Guide No. 22, Geologists’ Association, 2012, pp 159-167, ISBN978 0900717 61 1.

M. A Woods (compiler) Geology of south Dorset and south-east Devon and its World Heritage Coast, British Geology Survey, NERC, 2011, pp 61 – 67, ISBN 978 085272654 9.

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 – 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