Eype Beach Stream 4

Beach Boulders at Eype 2

Sedimentary rock boulders on the seashore extending into the sea

Another gallery depicting the amazing rock boulders on the seashore at Eype in Dorset, England, and the contexts in which they are found on the beach.

The cliffs at Eype, and the boulders on the beach below them, are made of Middle Lias sedimentary rocks from the Jurassic Period. It is difficult to judge the scale of the cliffs from looking at the photographs, so you might like to know that the silty sand and hard sandstone bands of the Three Tiers layers at the base can reach a maximum of 9m thick (although much of that is buried in this location); the clays and sandstones of the Eype Clay Member above that are 60 metres deep; on top of that the soft sands of the Downcliff Sands Member are 30 metres deep; and above that the soft sandstones of the Thorncombe Sands Member are 21 metres thick. This makes for a sequence of rock strata measuring a potential 120 metres (390 feet) in height – the measurements are approximate as the depth of the layers varies a lot.

In their book Classic Landforms of the West Dorset Coast, Brunsden and Goudie state that

The coastal cliffs of West Dorset owe their shape to the relief and orientation of the coastline, the variable properties or lithology of the rocks, the geological structure, the history of relative land and sea movements, the sequences of environmental change, the difference in erosional energy of the sea between the more exposed and sheltered parts of Lyme Bay, and to the complex sub-aerial processes which currently act on the cliffs themselves.

At Eype, the boulders on the beach demonstrate not only the variable lithology of the rocks in the cliffs above but also their structure. The alternating bands of different rock composition and colour are evidence for the cyclical nature of changing environmental conditions throughout geological history, including changes in sea level relative to land; while their presence on the seashore illustrates the ongoing erosional processes affecting the coastline to this day.

COPYRIGHT JESSICA WINDER 2014

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Beach Boulders at Eype 1

Stratification in a beach boulder

As the soft rocks of the exposed Eype Clay Member mudstones in the cliffs at Eype are eroded, the harder sandstone and limestone rocks (that were laid down at a later date above them) are under-mined. The unsupported rocks then break under their own weight, slide down the cliff and eventually come to rest on the orange gravel and pebbles of the shore. At the western end of Dorset’s Eype beach, part of the Jurassic Coast World Heritage Site, the boulders extend continuously from the base of the cliff out into the sea. Elsewhere along the shore, the boulders are clustered at the cliff foot adjacent to the soft micaceous mudstone layer. Most of the images shown here were photographed in a stretch of shore just a couple of hundred metres long.

The boulders tend to be very large, some about two metres in height and width. Their shapes are endlessly variable and their colours are generally complementary shades of yellow and grey. They can be patterned by layers of contrasting width, colour, and composition; or by scattered fossils and iron nodules. This is the first of several posts showing the fascinating variety of composition and form of these boulders, and the contexts in which they can be found. The boulders in these photographs are the same ones from which I photographed the rock textures in an earlier post. Every boulder seems unique in its appearance.

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved

Eype Beach Stream 2

Rock Textures at Eype 2

 

View of the beach at Eype in DorsetThe shore at Eype is littered with large boulders, several tons in weight, that have broken from the strata high on the cliff and then slip-slided down the lower mudstones and clays to the beach. They are all rocks belonging to the Jurassic Dyrham Formation. that includes a fascinating assortment of mudstones, sandstones, and limestones, some with ironstone nodules or carbonate concretions, and lots with fossils. I cannot with confidence identify the specific rock types illustrated in all the close-up photographs I took. It is quite a complicated geology at this coastal location. However, a general picture of the represented rock types follows. Fossils are found in more or less all the strata, ammonites are said to be common, but the ones I saw were mostly fragmentary shells and bullet-shaped belemnites

An accurate and up-to-date source of information about the geology of this locality is the British Geological Survey’s Geology of south Dorset and south-east Devon and its World Heritage Coast, published in 2011 by the Natural Environment Research Council. All the information that follows has been obtained from this book.

The Dyrham Formation is comprised of three members. At the base of the cliff is the Eype Clay Member which is a pale, blue-grey micaceous silty mudstone and shale. The base of the Eype Clay Member is marked by The Three Tiers  about a metre thick with three prominent sandstone beds separated by shales and mudstones. Higher up is a band of calcareous nodules, the Eype Nodule Bed. At the top of the band is Day’s Shell Bed with a rich fauna of juvenile bivalves and gastropods.

Above the Eype Clay member is the Down Cliff Sand Member made up of silts and fine sands with thin lenticles of hard calcareous sandstone. At its base is a fossil-rich layer known as the Starfish Bed, with abundant brittle-stars. At its top is the Margaritatus Stone which is hard, grey, iron-shot limestone.

At the top of the Dyrham formation is the Thornecombe Sand Member, sitting on the Down Cliff Sand Member. The bottom-most layer is the blue-grey Margaritatus Clay, above which are yellow-weathering, heavily bioturbated sands, with several horizons of large rounded calcareously cemented concretions. There is an impersistent band of limestone running through the middle of this, and a shelly Thornecombiensis Bed sealed by sandy mudstone atop it.

So you can see that there are many different rock layers and types in the stratified cliff, often obscured by land slips, and it is quite difficult for an amateur like myself to correctly identify pieces of these strata when they are lying on the shore.

However, one noticeable feature in the beach boulders was the occurrence of bioturbation: this is defined as a disruption of sediment by organisms, seen either as a complete churning of the sediment that has destroyed depositional sedimentary structures, or in the form of discrete and clearly recognisable burrows, trails, and traces (trace fossils). The most easily recognisable trace fossils are the largish burrows of Crustacean Thalassinoides – which you can see in images 4 and 9.

View of the beach at Eype in DorsetAnother phenomenon that is responsible for some of the more unusual colouration and patterning of the rocks, is the transformation of blue-grey rock to yellow by the weathering process on exposure to air, which oxidises iron minerals in the stone. Iron staining, iron nodules (often in association with fossil fragments), and veins of iron, also contribute to rich colour patterns both within and on the surface of the boulders. Sometimes the colours are exhibited as a thin outer layer that is exfoliating into abstract patterns of contrasting hues on the rock.

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved

The Barnacle Zone on Waterfront Structures

Barnacles and mussels above the waterline on a wooden pier piling.

Barnacles often settle higher on the shore than most other organisms. They are adapted to live part of their life, sometimes most of it, actually out of water – being able to get by on splashes of water that extend beyond the high-tide line.

The way that animals and plants are distributed across the shore is known as zonation. Zonation is generally accepted as meaning a vertical separation of different groups of organism, often into distinct bands of different colour when living on hard substrates, resulting from the tolerances of individual species to dessication, temperature, and wave action – otherwise termed ‘exposure’. The barnacles and mussels occupy the mid-shore level. Around the world, although the species differ, the same phenomenon is found, with zonation more clearly visible to the casual observer on steep exposed rocky shores.

An extreme example of this zonation can often be seen on the artificial structures of a waterfront harbour where wooden wharf-sides, timber pier pilings, and metal revetments substitute for rock surfaces on which organisms can settle. Many of these artificial substrates are vertical and therefore the zoning of the organisms may be exaggerated and clearer to see.

The pictures in this post show a pale band or stripe, made up almost entirely of cream-coloured sessile or acorn barnacles, naturally cemented onto harbour-side structures, sometimes wholly encircling them. A few common periwinkle gastropod molluscs move around the barnacles, feeding on the bio-film that accumulates on their shells.  Fronds of spiral wrack and sea lettuce type of seaweed, both also fairly tolerant of exposure out of water, are sometimes scattered over the barnacle zone. The barnacles have special adaptations that allow them to survive dehydration at low water but they are none-the-less vulnerable to predating dog whelks at all stages of the changing tides.

Below the barnacle zone, a darker, almost black band, is composed of edible mussels attached by byssus threads. Mussels are less tolerant to air exposure than the barnacles so they survive best lower down where they are not out of the water for so long. They are a sitting target, though, for starfish which use their tube feet to sucker onto these bivalves, forcing them to open, and then everting and inserting their starfish stomach into the mollusc so that they can feed upon the living contents.

All these photographs were taken on the waterfront in Halifax, Nova Scotia. Most of the piers and jetties are still traditionally made of timber because it is such an abundant commodity in Canada. There are generations of timber structures: new; old and decaying; and derelict examples. All of these show the barnacle banding. So do the more recently built rusting metal revetments to the edges of the renovated wharves in the more developed areas.

Interestingly, many modern high-rise buildings in that location have been constructed right on the water’s edge where they are supported by foundations of steel piles driven deep down into the very hard metamorphosed bed-rock. The pilings can be seen projecting below the buildings on the waterside elevations, disappearing into the harbour water. Each white-painted column displays at its base a lower ring of black mussels and a higher ring of paler barnacles – the structures themselves being reflected in the seawater with an odd abstract effect.

 COPYRIGHT JESSICA WINDER 2014

All Rights Reserved

Glimpses of Montreal Biodome

We know there is Nature in the city but in Montreal this can be experienced on a large scale in the Biodôme which is a unique museum of environment. Live collections with more than 4,800 animals from 230 species and 750 plants species in four ecosystems from the Americas, each with a different climate – all under one roof.

To quote from the Lonely Planet guide to Montreal and Quebec City:

you can amble through a rainforest, explore Antarctic islands, view rolling lowlands or wander along the raw Atlantic oceanfront – all without ever leaving the building.

Penguins frolic in the pools…the tropical chamber is a cross-section of Amazonia with mischievous little monkeys teasing alligators in the murky waters below. The Gulf of St Lawrence has an underwater observatory where you can watch cod feeding alongside lobsters and sea urchins in the tidal pools. The appearance of the Laurentian Forest varies widely with the seasons, with special habitats for lynx, otters and around 350 bats.

 [These pictures from the visit to the Biodôme are also shown on my other WordPress site along with more postings of photographs taken in Montreal during my trip to Canada last year].