Ian West
Romsey, Hampshire

and Visiting Scientist at:
Southampton University,
Website hosted by courtesy of iSolutions, Southampton University
Aerial photographs by courtesy of The Channel Coastal Observatory .
Website archived at the British Library
N.B. This webpage has much reliance on the classic work of the Kimmeridge Clay specialist: Ramues Gallois.

Home and Contents |Kimmeridge - Kimmeridge Bay |Kimmeridge - Fossils |Kimmeridge - West of Kimmeridge Bay |Kimmeridge - Hen Cliff, Cuddle and Yellow Ledge |Kimmeridge - Blackstone, Oil Shale at Clavell's Hard |Kimmeridge - Burning Beach, Burning Cliffs |Kimmeridge - Rope Lake Head to Freshwater Steps |Kimmeridge - Egmont Bight to Chapman's Pool |Kimmeridge Clay Boreholes at Swanworth Quarry
|Kimmeridge - Bibliography - Start |Lulworth Area, - Lulworth Cove |Kimmeridge - Bibliography Continued |Channel Coastal Observatory, National Oceanography Centre.

| Selected external links: | Jurassic Coast (DCC) | Exmouth to Milford-on-Sea 1800-2000, Kimmeridge section - old photographs collected by Doreen Smith Click here for the full LIST OF WEBPAGES

(You can download this educational site to SurfOffline, WebCopier or similar software to keep a safe permanent offline copy, but note that at present there is periodic updating of the live version.)

GO EAST? - KIMMERIDGE - CLAVELL'S HARD AND OIL SHALE ; - GO WEST? - KIMMERIDGE BAY

Click on images for large, high resolution versions!
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INTRODUCTION:

Topographic Maps and Location Aerial Photographs

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This map, modified after Cox and Gallois (1981) shows the solid geology of the Kimmeridge area in particular and locations referred to in this and associated Kimmeridge field trip guides. More initial information is in the Introduction to Kimmeridge Bay and the Kimmeridge Clay webpage.

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INTRODUCTION:

Safety; the Hazards of Kimmeridge Cliffs

Note that there is some significant danger with regard to the Kimmeridge cliffs. One danger, the main one, is risk of rock fall; the second hazard is that of being cut off by the tide. This applies particularly to the cliffs east of Kimmeridge, although it could also happen at Brandy Bay and elsewhere. In general, keep out as far from the cliffs as possible. Some debris falls every day and if you are close to the cliff you are at risk of being hit by a rock-fall.

Because of the hazard of rock falls and it is a dangerous place to visit unless it is well-understood and proper precautions are undertaken. The cliffs are vertical and high and subject to erosion by the sea at the base. The shale and mudstone is full of joints and fissures and not stable. Small pieces will tumble off from time to time as you walk along.

More serious are substantial falls like the one shown above. These may occur without warning; suddenly there will be a loud crash and a plum of debris and dust. These happen particularly in certain weather conditions, such as when there is frost or rain and sometimes when the shale has dried in the hot sun. If you are out on the low-tide ledges falling debris would not usually reach you but there is no guarantee of safety. The risk is greatest where the cliffs are highest, where there is joint-separated shale above and where there is evidence of a recent fall in the form of shattered debris.

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Kimmeridge Safety Addendum:

Photographs shown on this website have been taken over a period of many years by the author and various other people. Some photographs are from organised field-trips, which may be those of the present author or of other geologists. Many, though are from informal, private coastal walks, or from private, research field-trips. The photographs are for geological purposes only and are there to show rocks, not people or techniques. They are not intended to show safety procedures and no activities shown are necessarily intended to be copied. This website is about geology for geologists. The cliff, sea, tide and weather conditions vary greatly so always make your own assessment of the cliffs and conditions on the day, and arrange your coastal procedures in accordance. Always consult tide tables before field work at or near Kimmeridge. No responsibility at all is taken for any activities of field parties or individuals going to the Kimmeridge coast for their own purposes or objectives. As at other geological sites a risk is present and the possibility of an accident, although a rare occurrence, cannot be eliminated.

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INTRODUCTION:

Geological Maps

Geology of the Isle of Purbeck shown on an old map (part of a map modified from Damon, 1884). Modern changes in the geological mapping of the area have only been of detail. Some place names have changed since Victorian times and Clavell's Hard has been added by the present author. Note an older spelling of "Kimeridge" with one "m".

STRATIGRAPHY - INTRODUCTION

More Information - Go to Kimmeridge Bay Webpage

For more on Kimmeridge Clay stratigraphy, zones and cliff section etc, please go to:

Kimmeridge Bay - Kimmeridge Clay - Stratigraphy Introduction.

Be sure to have at hand a copy of the above publication by Cox and Gallois (1981). This is essential for field work at Kimmeridge.

STRATIGRAPHY:

Cliff Section

A cliff section is shown here for a large part of the Kimmeridge Coast. This is based on Arkell (1933), Cox and Gallois (1981) and other information. Amongst other features, it shows the position of the Kimmeridge oil-shale, Clavell's Hard and the location of the mining in the cliffs.

INTRODUCTION: General Introduction - East of Kimmeridge Bay

At Kimmeridge Bay the lower Kimmeridge Clay with dolomite beds, crushed ammonites and cycles of sedimentation is seen. By walking along the coast eastward from the bay progressively higher parts of the Kimmeridge Clay are seen. Hen Cliff shows the junction of the Lower and Upper Kimmeridge Clay. The shale debris at the foot of this cliff contains good fossil bivalves and some crushed ammonites. Yellow Ledge is a notable feature a little further east and the Yellow Ledge Dolomite Bed provides the fallen blocks on the beach which can be walked on like stepping stones. This is a good example of an extensional fault just here. Beyond to the east are the cliffs of Cuddle and a shallow embayment. The oil shale is in the upper part of the cliff and descends eastward to the Clavell Hard area, discussed in the separate Kimmeridge Oil Shale or Blackstone webpage. Fallen debris from the oil shale has caught fire in the bay between Cuddle and Clavell's Hard. This topic is described in a separate webpage on beach fires and cliff fires in the Kimmeridge oil-shale .

INTRODUCTION:

Safety

From the east side of Kimmeridge Bay it is possible to walk eastward by the cliff top, but there is no route down to the beach. At beach level it is possible to proceed east but only providing the tide is low and conditions are favourable. It is easy to be cut off on the beach here and only if the tide and weather conditions are safe should one proceed along the beach. The danger of falling rock is great and cannot be over-emphasised. Safety helmets are useful, especially for parties, and much care should be taken to keep out as far from the cliffs as possible.

Always check the tides in advance by using tide tables. Local tide tables are usually on sale in the marine centre at Kimmeridge Bay. On the stretch described here, please examine the ledges instead of the cliffs whenever this can be done.

Several people have been cut off by the tide and have had to have been rescued. It was once possible to ascend and descend the cliff at Clavell's Hard. Erosion of the steps has now made this impossible (without a rope). At Freshwater Steps, further east, a ladder was once present but there is now no access here, and thus no escape from the beach to the east. This is, therefore, a coast which requires great care and full attention to safety precautions. It is, nevertheless, a place of great geological interest.

The stretch discussed in this particular webpage is only from Kimmeridge Bay to Cuddle and adjacent cliffs. It does not extend to Clavell's Hard or beyond. Thus the risk of being cut off by the tide is rather less than for the beach further east. Nevertheless, you can be cut off by a rising tide at Yellow Ledge, and the cliffs beyond Yellow Ledge are particularly prone to rock falls.

LOCATION:

Hen Cliff

Directly east of Kimmeridge Bay is Hen Cliff. This is easy to get to during most tide conditions. The following images explain the general geology here.

The lowermost part of the Upper Kimmeridge Clay as exposed in Hen Cliff. The cliff is suprisingly steep, almost vertical, and presumably this is the result of rapid sea erosion and the low angle of dip. Elsewhere (near Osmington and Ringstead) the Kimmeridge Clay is present not as vertical cliffs but as slumped and landslipping cliffs with mudslides (mudflows). Notice the gentle dip towards the east and the several small faults which generally trend north-south. Because these faults are extensional and cut only Jurassic strata here, they are mostly likely to be of Late Kimmerian or Cretaceous origin. They are probably from the phase of extensional faulting that occurred just prior to the development of the North Atlantic Ocean.

Notice how the Yellow Ledge Dolomite Bed affects coast erosion, both by forming a ledge, the Yellow Ledge itself, and by supplying large rectangular blocks to the beach which form natural sea defences. The Yellow Ledge Stone Band is a dolomite with a low clay content and is ferroan. Weathering of the originally reduced iron to ferric oxide produces the characteristic yellowish colour. The Cattle Ledge and the Grey Ledge have higher clay contents, are less resistant to erosion and fracture with a characteristic blocky fabric. This type of weathering fracture is best developed in the Basalt Stone, another argillaceous dolomite seen further east. (This image may be of use for student exercises, for sketching and indicating faults and answering questions. Note that the image is constructed from three joined photographs and there are minor defects at the two vertical joins.)

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The features seen in the photographs can be tied in to this old cliff section drawn in late Victorian times. The oil shale mining and the working of argillaceous dolomites for cement was still taking place.

Near the top of Hen Cliff, in its western part, the Grey Ledge Dolomite Bed appears to double at a particular place. You can find the location in the large image of Hen Cliff above. The light brown staining of the carbonate bed on surfaces and joints is the result of Fe substitution in the dolomite and subsequent oxidation of the ferrous iron on weathering. The white surface in this inaccessible section may be calcite on veins.
For comparison, similar features are shown in the Blue Lias at Lyme Regis, except this is an argillaceous limestone rather than an argillaceous dolomite (dolomite occurs in the Shales-with-Beef above).
Carbonate beds in British Jurassic shales often contain burrows which show that there was some primary sedimentary difference, usually higher carbonate. There is, however, often in addition a major overprint of concretionary or diagenetic processes so as to produce carbonate beds which are effectively extended nodules (and sometimes septarian). They can be continuous for kilometres in some cases but are prone to come to an end abruptly. Instead they can, as shown here, suddenly develop, giving an appearance of doubling up. Gallois (2000) has provided instances of this in records of a borehole and the cliff section at Kimmeridge. For more detail on Kimmeridge carbonate diagenesis please see Bellamy (1977; 1980). Note that the lateral variation in the largely diagenetic, stone bands has to be taken into account when studies are made of cyclicity.

LOCATION:

Hen Cliff - Blakes Bed No. 42

With the somewhat cumbersome name of Blake's Bed No.42 (named by the Reverend Blake) this dolomite is important. It marks the base of the Upper Kimmeridge Clay, of the Bolonian Stage. In France the strata equivalent to the Upper Kimmeridge Clay are of shallower water facies; they are largely carbonates. Blakes Bed 42 at Kimmeridge shows evidence of a temporary regression. The bed is a very ferroan dolomite or an ankerite and it contains not only small quartz sand grains but also common glauconite (glauconie) grains. Glauconite is not present in the other dolomites and its usual origin in the Mesozoic is on current-swept sea-floors, where conditions are appropriate both for ferrous and ferric iron. It is not normal in the deeper and suboxic to anoxic Kimmeridge Clay sea floors.

Pari White, in a geoarchaeological project, found that this bed had been quarried by the Romans to provide dark grey tesserae for their mosaic floors at Fishbourne, near Chichester. Because of the glauconite and other petrographic features it is easy to recognise.

LOCATION:

Hen Cliff - Fossiliferous Shales

At the foot of Hen Cliff pieces of fossiliferous shale are commonly lying around. These have fallen from the cliff. They usually contain bivalves, such as Protocardia and, in some cases, ammonites. It is important to note that strata of the Aulacostephanus autissiodorensis Zone (Lower Kimmeridge Clay) and of the Pectinatites elegans Zone (Upper Kimmeridge Clay) are present in Hen Cliff, so fallen pieces might be from either zone.

LOCATION:

Hen Cliff - Clavell Tower on Cliff Top

(See also:
Landmark Trust - Clavell Tower.)

Shown for general interest are some photographs of Clavell Tower on the Cliff Top at Hen Cliff to the east of Kimmeridge Bay. This tower was built in 1831 by the Rev. John Richards who assumed the name Clavell when he inherited the Smedmore Estate (Legg, 1984) . It was used as a coastguard lookout and had a flagpole, held in position by several old cannon buried in the ground at angles. It has historic connections with Thomas Hardy and was apparently the inspiration for James' novel - The Black Tower.

It is of interest geologically as being probably the only large building constructed of Kimmeridge dolomite. This is exposed in places where the the stucco has broken away. The dolomite is very yellow and is therefore weathered. It is Yellow Ledge dolomite possibly from the beach but, more likely, from a small cliff quarry immediately to the west. It is likely that blocks that were already weathered were used, rather than weathering having taken place in the tower. Unless there has been some degree of weathering to produce ferric iron the dolomite should be grey, the natural fresh colour, not yellow.

Plans were made by Landmark Trust to move this tower away from the cliff edge because of the threat from coast erosion and, in any case, its progressive collapse. It has recently been taken apart and rebuilt it further down the northeast slope, about 25 metres inland from the cliff. The interior is to be used as holiday flats. The tower seems to have been solidly constructed, even though the underlying clay is not in good condition.

The uppermost 2 metres or more of Kimmeridge Clay material below the organic-rich soil has disintegrated into a grey, soft, debris of shale and clay fragments, that has very little strength. This material shows evidence of soil creep and is, to some extent, moving down the slope in a series of very small-scale slumps. Probably the tower has deep and solid foundations.

The photograph above shows a stage of work in progress in dismantling the tower. The stones were laid out and numbered ready for rebuilding in the new location. Notice the pillars or columns which are of Portland Stone from the Isle of Purbeck.

By 2008 Clavell Tower had been rebuilt a short distance further inland. It does not look very different apart from the glazed windows and the fact that it is in use for holiday appartments.

LOCATION:

Yellow Ledge
(basal scitulus Zone of the Upper Kimmeridge Clay)

Yellow Ledge is the prominant Kimmeridge ledge formed by a stone band at the eastern end of Hen Cliff, at Cuddle. There is an excellent exposure of the Yellow Ledge Dolomite Bed. It is seen in one photograph here at the time of a oil-shale fire on the beach. Another image shows it rising westward in the cliff. It extends to quay at the eastern side of Kimmeridge Bay, and was once quarried in the old cliff above (just round the corner, and near to Clavell's Tower). The stone was used for the old pier at the point here.

The Yellow Ledge Dolomite Bed is a useful marker for the base of the Pectinatites scitulus Zone of the Upper Kimmeridge Clay. See Cox and Gallois (1981) for stratigraphic details. The Cattle Ledge Stone Band is just under the top of the scitulus Zone, so for simplicity the scitulus Zone can be regarded as extending from Yellow Ledge dolomite bed to Cattle Ledge Stone Band, and both of these are obvious in the cliff section.

The Yellow Ledge Dolomite Bed is a kerogenous dolostone or dolomite according to Bellamy (1980) (that is it consists of calcium and magnesium carbonate with kerogen, waxy brown organic matter which when heated for a long period during deep burial can generate oil). The technical data is that it consists of 80%% ferroan dolomite, 4%% calcite with kerogen and clay. Stable isotope analysis gives -1.5 C18 and +1.8 C13. The oxidation of the ferrous iron in the ferroan dolomite is responsible for the yellow surface. It is dark grey internally.

In the field occasional ammonites can be seen on the top surface, and these are not completely crushed as is usually the case with Kimmeridge ammonites. This is evidence of some early cementation. Cross-sectional surfaces show some interesting early compaction structures resulting from vertical compression (vertical sigma one) and some miniature extensional faults. Some evidence of a concretionary-type origin can also be seen.

Where the Yellow Ledge reaches the shore there is a fault, and the bed is extensively jointed in an almost rectangular pattern. Some barite has found in the fault plane together with the more abundant calcite.

LOCATION:

Cuddle and towards Clavell's Hard:
Introduction

(There has been a small oil shale fire in this bay. For more information on this please go to Burning Beach website.)

Aerial view of the cliffs, with the ledges of dolomite clearly shown in the sea. Yellow Ledge is the most conspicuous, and this fixed the position in relation to the photograph on the right. Notice the faulting of the stone bands, visible in the sea. Traces of the old tramways etc. of the old Blackstone working are visible on the land. For details of the old workings and tramways see the map in Legg (1984). It is interesting to compare the map with aerial photograph. I think that you will find the location of the Manfield Shaft of 1883. The route of the old tramway of 1884 can be seen on the aerial photograph near Cuddle.

Looking east towards Yellow Ledge from within the bay. The ledge is at the headland in the distance but the tide is relatively high, so it is not prominant as in the aerial photograph. This was taken at the time of an oil-shale fire on the beach.

The Blackstone is present in the cliff between Cuddle and Clavell's Hard. However there has been extensive oil shale mining in the vicinity of No. 1 Level (at about the middle of this bay) and, thus, much has been worked out. This is easily visible from the beach.

DIAGENESIS OF THE DOLOSTONES (DOLOMITES)

Cattle Ledge and Grey Ledge:
(within Scitulus and Wheatleyensis Zones)
Fermentation Dolomites at Cuddle, East of Kimmeridge Bay

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Some of the illustrations above are based on work by Bellamy (1980) and parts of a graphic log by Coe et al. (1999). The above diagrams show that dolomite beds of fermentation type (fermentation zone diagenesis) as recognised as such by Bellamy (1980) and Irwin et al. (1977 ) can be clearly observed on the magnetic susceptibility log and gamma ray log of Coe et al. (1999). There is symmetry of composition, presumably resulting from most Fe at the top and bottom of the bed. This produces a double peak. In the field the symmetry above and below is not obvious in the Cattle Ledge and the Grey Ledge. However, it is easily seen in the field in Washing Ledge (conveniently near the car park), and accounts for the development of thrust structures in the Flats Stone Band. Unmixing would have involved migration in solution of carbonate and Fe towards a very thin, pre-existing limestone or dolomite.

The depositional carbonates in the Kimmeridge Clay, such as the White Stone Band etc do not show this fish tail pattern of magnetic susceptibility. In fact they show very low magnetic susceptibility, and quite distinctive from the diagenetic, unmixing dolomite.

In terms of general composition, a sample of Cattle Ledge dolomite gave 83%% dolomite, Sr of 299 ppm and dolomite composition of Ca51.23 Mg43.15 Fe5.54 Mn 0.08 CO ₃ according to Bellamy (1980). That author noted that like the other dolomites there is an excess of Ca and Fe but the iron content does not exceed 10mol%% FeCO ₃ . However, note that the magnetic susceptibility log and the gamma ray log suggest the bed is not uniform, so that this is just an example composition. It is unlikely to be exactly the same for the whole thickness of the bed.

CATTLE LEDGE AND GREY LEDGE continued

Grey Ledge argillaceous dolomite bed descends to the shore just west of the fire site, shown above, but is not conspicuous in that photograph. Both of these were worked for cement in the 19th century.

Here, near the middle of the bay the Grey Ledge Dolomite Bed can be seen at the foot of the cliffs. Detailed mineralogical or geochemical information is not available for this bed but it is probably similar to the Cattle Ledge Dolomite Bed, which it much resembles.

Higher in the cliff is the Blackstone. Note that this has a similar jointing pattern to the Rope Lake Head Dolomite Bed. Two sets of joints are almost at right-angles but are oblique to the cliff. The Rope Lake Head Dolomite Bed shows the brown surface colour that results from the oxidation of ferrous iron in the dolomite. The Blackstone, in contrast, has white surfaces of vein-calcite on joints in the black oil-shale. This gives it the characteristic black and white appearance. It is a common circumstance for later tectonic veins and joints to be of calcite rather than dolomite. It is interesting that the oil-shale, although consisting of the waxy substance - kerogen, shows more brittle fracture than does the shale above and below.

Notice the type of erosion on the beaches here. At times, the sea erodes the base of the cliffs, removing any loose shale debris. It partially rounds the fallen blocks of dolomite on the beach. The sea steepens the cliff profile from the base and material falls from above. The shale falls as small fragments, but the dolomites, calcareous mudstone and the oil shale descend as large (and dangerous) angular pieces, the shape of these being defined by the joints. The photograph shows Pectinatitid ammonites in a large fallen block of calcareous mudstone.

The beach material is almost entirely local. There is much dolomite and hard shale from the Kimmeridge Clay and some chert from the Portland Stone (which forms the hills at the back). There is a great rarity of flint and extraneous material, unlike for example the beach at Lulworth Cove. More effective at Kimmeridge in producing a characteristic odour than the oil shale is the large amount of seaweed present. Why is seaweed, which in turn leads to an abundance of sand-hoppers and flies, in such quantities here?

LOCATION:

Cuddle towards Clavell's Hard continued:
More on Grey Ledge

Cattle Ledge and Grey Ledge have been worked for hydraulic cement in the past (I am grateful to Steve Etches for helpful information on this topic).

Cuddle Towards Clavell's Hard
More Ammonites

LOCATION:

Cuddle towards Clavell's Hard continued:
Beach Pebbles

The slippery, beach pebbles of shale are interesting as being oligomict (mostly one type) and mostly of a particular shape. Apart from some Portland chert in thin head (hillwash) deposits at the top of the cliff there is no source of rock material for pebbles other than the Kimmeridge Clay. The mudstones probably break down into dispersed clay. The harder, bituminous shales seem to provide most beach clasts. These are bladed pebbles of bituminous shale, dark grey in colour. In addition, on the beach in places, are larger clasts of more brownish ("chocolate-coloured")shale of low density. These are fragments of the Blackstone oil shale or of a similar bed such as the Bubbicum. They are quite distinctive.

FURTHER INFORMATION:

Continue East to Clavell's Hard?

Continue on to Clavell's Hard with oil shale (Blackstone). Note, that is indicated but the photograph above, a good low tide is required. There is real risk of being cut off if care is not taken when proceeding east of this locality!

ACKNOWLEDGEMENTS

I am very grateful to the many geologists and students who have discussed the cliffs on field trips to this locality. I am very grateful to the well-known palaeontologist and fossil collector Steve Etches for information on the history of cliff quarrying here and other help. There is much reliance in this webpage on the classic work of Ramues Gallois and other Kimmeridge Clay specialists, and this source information is gratefully acknowledged. Ramues Gallois has kindly supplied an excellent photograph of the cliff at Yellow Ledge and this much appreciated. I would like to thank radio presenter David Dodd for acompanying me and recording a programme for BBC Radio 4 in July 2010. I much appreciate the advice and help of my daughter, Tonya Loades of Bartley West, Chartered Surveyors.

Copyright © 2014 Ian West, Catherine West, Tonya Loades and Joanna Bentley. All rights reserved. This is a purely academic website and images and text may not be copied for publication or for use on other webpages or for any commercial activity. A reasonable number of images and some text may be used for non-commercial academic purposes, including field trip handouts, lectures, student projects, dissertations etc, providing source is acknowledged. Images shown on this website are reduced and compressed versions, and not identical to the original master copies held in different formats by Ian West.

Disclaimer: Geological fieldwork involves some level of risk, which can be reduced by knowledge, experience and appropriate safety precautions. Persons undertaking field work should assess the risk, as far as possible, in accordance with weather, conditions on the day and the type of persons involved. In providing field guides on the Internet no person is advised here to undertake geological field work in any way that might involve them in unreasonable risk from cliffs, ledges, rocks, sea or other causes. Not all places need be visited and the descriptions and photographs here can be used as an alternative to visiting. Individuals and leaders should take appropriate safety precautions, and in bad conditions be prepared to cancell part or all of the field trip if necessary. Permission should be sought for entry into private land and no damage should take place. Attention should be paid to weather warnings, local warnings and danger signs. No liability for death, injury, damage to, or loss of property in connection with a field trip is accepted by providing these websites of geological information. Discussion of geological and geomorphological features, coast erosion, coastal retreat, storm surges etc are given here for academic and educational purposes only. They are not intended for assessment of risk to property or to life. No liability is accepted if this website is used beyond its academic purposes in attempting to determine measures of risk to life or property.

Webpage - written and produced by:

Ian West, M.Sc. Ph.D. F.G.S.

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at his private address, Romsey, Hampshire, kindly supported by Southampton University,and web-hosted by courtesy of iSolutions of Southampton University. The website does not necessarily represent the views of Southampton University. The website is written privately from home in Romsey, unfunded and with no staff other than the author, but generously and freely published by Southampton University. Field trips shown in photographs do not necessarily have any connection with Southampton University and may have been private or have been run by various organisations.