West, Ian M. 2016. Kimmeridge, - Kimmeridge Clay and Kimmeridge Bay; Geology of the Wessex Coast. Geological field guide. Internet site: www.southampton.ac.uk/~imw/Kimmeridge-Bay.htm. Version: 8th December 2016

by: Ian West
Romsey, Hampshire, and:
a Visiting Scientist at the:
Faculty of Natural and Environmental Sciences
Southampton University,
Webpage hosted by courtesy of iSolutions, Southampton University
Aerial photographs by courtesy of The Channel Coastal Observatory , National Oceanography Centre, Southampton.
Website archived at the British Library

Click here for the full LIST OF WEBPAGES
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THIS IS THE INTRODUCTORY WEBPAGE TO THE KIMMERIDGE CLAY CLIFF SECTION - OTHER KIMMERIDGE WEBPAGES, LISTED BELOW, ARE ON SPECIFIC LOCATIONS EAST AND WEST OF KIMMERIDGE.
FOR OIL SHALE GO TO:
KIMMERIDGE BLACKSTONE, OIL SHALE at Clavell's Hard

GO EAST? - KIMMERIDGE - EAST TO YELLOW LEDGE; GO WEST? - KIMMERIDGE BAY TO BRANDY BAY AND GAD CLIFF

Kimmeridge Field Guides

Kimmeridge Bay and Introduction
Kimmeridge - Fossils
Kimmeridge - Kimmeridge Bay to Brandy Bay and Gad Cliff
Kimmeridge - Kimmeridge Bay to Gad Cliff
Kimmeridge - East - Hen Cliff, Yellow Ledge and Cuddle
Kimmeridge Bay - Westward
Kimmeridge - BLACKSTONE, OIL SHALE at Clavell's Hard
Kimmeridge - Burning Beach, Burning Cliffs
Kimmeridge - Rope Lake Head to Freshwater Steps
Kimmeridge - Egmont Bight, Houns-tout Cliff and Chapman's Pool
Kimmeridge - Kimmeridge Bay to Gad Cliff
Kimmeridge Clay Boreholes at Swanworth Quarry
Kimmeridge - Bibliography - Start
Kimmeridge - Bibliography Continued
Petroleum-Geology-Kimmeridge Clay - Weald
Petroleum Geology of the South of England

| Selected external links: | Jurassic Coast (DCC) | Exmouth to Milford-on-Sea 1800-2000, Kimmeridge section - old photographs collected by Doreen Smith

(You can download this educational site to SurfOffline or similar software to keep an offline copy, but note that updating of the live version takes place periodically.)


Click on images for large, high resolution versions!
(do not use browser zoom on the low resolution versions)

 Kimmeridge Bay, Dorset, seen by Ian West from the cliff top above Washing Ledge, on a tranquil day

Kimmeridge Bay in stormy weather, seen from the approach road, 4th February 2011

 Kimmeridge Bay, Dorset, in a southwesterly gale, 24th September 2012

Kimmeridge Bay, Dorset, seen from the hill with Clavell Tower, in stormy weather, 4th February 2011

 Kimmeridge Bay, Dorset, seen from across Egliston Gwyle. View eastward

A general view of Kimmeridge Bay, Dorset at high tide, as seen from near Clavell's Tower, 9 Oct 2005

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CONTENTS
(Click on an item to go there!)

KB-1. LOCATION - En Route to Kimmeridge
KB-2. LOCATION - General


KB-3. INTRODUCTION - Safety - Kimmeridge Hazards
KB-4. INTRODUCTION- Safety continued
KB-5. INTRODUCTION - Safety Addendum
KB-6. INTRODUCTION - Industrial History
KB-7. INTRODUCTION - Some General Views
KB-8. INTRODUCTION - Geological Maps
KB-9. INTRODUCTION - Multibeam Bathymetry Images
KB-10. INTRODUCTION - Access to Cliffs
KB-11. INTRODUCTION - General - Kimmeridge Bay
KB-12. INTRODUCTION - Aerial Photos - General
KB-13. INTRODUCTION - Aerial Photos - Kimmeridge Bay
KB-14. INTRODUCTION - Seaweed Flies
KB-15. ---
KB-16. INTRODUCTION - Commencing Fieldwork
KB-17. INTRODUCTION - Kimmeridge Bay History


KB-18. STRATIGRAPHY - Introduction
KB-19. STRATIGRAPHY - Introduction, General
KB-20. STRATIGRAPHY - Key Publications
KB-21. STRATIGRAPHY - Stages and Zones


KB-22. STRUCTURE - Cliff Section
KB-22a STRUCTURE - ??
KB-22ba STRUCTURE - Corner Fault
KB-22bb STRUCTURE - Maple Ledge Fault


KB-22e EROSION - General (to be added)

KB-23. CYCLOSTRATIGRAPHY - Cycles of Sedimentation
KB-24. CYCLOSTRATIGRAPHY - Cycles - More
KB-25. CYCLOSTRATIGRAPHY - Cycles - Update


KB-26. SEDIMENTOLOGY - Clay Mineralogy
KB-27. SEDIMENTOLOGY - Dolomite - Introduction
KB-28. SEDIMENTOLOGY - Dolomite - Flats Dolostone
KB-29. SEDIMENTOLOGY - Petrography of Flats
KB-30. SEDIMENTOLOGY - Washing Ledge Dolostone
KB-31. SEDIMENTOLOGY - Maple Ledge Dolostone
KB-32. SEDIMENTOLOGY - Maple Ledge Shales
KB-32c. SEDIMENTOLOGY - Pyrite Diagenesis

KB-32ePALAEONTOLOGY - Fossil Collecting
KB-33. PALAEONTOLOGY - Ammonites
KB-34. PALAEONTOLOGY - Lower Kimmeridge Ammonites

KB-35. PETROLEUM GEOLOGY - Kimmeridge Oil Well
KB-36. PETROLEUM GEOLOGY - The Kimmeridge Wells

KB-36d QUATERNARY - Weathered Brown Clay

KB-37. SPECIFIC LOCATION - The Oil Shale Port
KB-38. SPECIFIC LOCATION - Clavell Tower

KB-39. GEOARCHAEOLOGY - The Flats Stone Band
KB-40. GEOARCHAEOLOGY - Oil Shale Armlet Factory

KB-41. MISCELLANEOUS - Odd Fish of Kimmeridge

KB-42. BIBLIOGRAPHY - Redirection to Bibliography Webpage

KB-43. ACKNOWLEDGEMENTS

KB-44. THE AUTHOR

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KB-1 - LOCATION:

En Route to Kimmeridge

The road up the Purbeck Hills of vertical Chalk, south of Creech Grange, en route to Kimmeridge Bay, Dorset, March, 2012

Creech Grange, passed en route by car to Kimmeridge Bay, Dorset, 11th March 2012

The quickest route to Kimmeridge is by the minor road south of Stoborough. This passes Creech Grange, shown above, and ascends the Purbeck hills with a steep gradient.

The tollkeeper and tollhouse at the road to Kimmeridge Bay, Dorset, 2012

At Kimmeridge, within the Smedmore Estate, there is a toll road to the cliff-top car park. I have stopped here at the toll gate this since I was boy in the 1950s. I do not know how long before this there was a tollhouse and tollkeeper here. At present the toll for a car is only about 5 pounds sterling.

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KB-2 - LOCATION:

General

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A modified old map,1900, of Kimmeridge Bay, Dorset, and the adjacent Kimmeridge coast, the site of old oil shale workings

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KB-3 - INTRODUCTION:

Safety; the Hazards of Kimmeridge Cliffs

A small rock fall from Kimmeridge Clay cliffs, Kimmeridge coastline, Dorset, 2011

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.

Cliff collapse at the old No. 2 Level of 1890 Blackstone workings, just west of Clavell's Hard, Kimmeridge, Dorset

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 plume 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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A photograph of Maple Ledge Fault (below), illustrates the risk even in fine, dry weather. Geologists should keep out from the cliffs as far as possible, although geological study does require close examination of the cliff at intervals. These should be kept short and only take place after examination of the cliff above. Geologists, although by the nature of their interests and activities are not free from risk. However, they would not generally do what some holiday-makers do, that is sit at the foot of a Kimmeridge Clay or other vertical cliff. This is very unwise. If you want to sit for a lunch break, perhaps, then sit out on a ledge away from the cliff. The worst cliff accident on the Dorset coast took place at Lulworth Cove in the 1970s to a group that was sitting at the foot of a cliff.

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KB-4 - INTRODUCTION continued:

Safety Continued

Safety notice at  Kimmeridge Bay, Dorset

Dangerous cliffs sign at  Kimmeridge Bay, Dorset

The cliffs in the Kimmeridge area are mostly vertical and from time to time shed debris which descends at high velocity. At all localities beware of falling debris and do not hammer or dig out the cliffs. This is very hazardous because the falling shale or dolomite could easily have fatal consequences. Keep away from the foot of the cliff and wear safety helmets. Do not sit at the foot of the cliffs, although, unfortunately, this is sometimes foolishly undertaken by non-geological visitors to Kimmeridge Bay. The higher cliffs to the east are even more dangerous than those in Kimmeridge Bay. You can walk some way westward in Kimmeridge Bay and you can study ledges of the Flats Stone Band. The western extremity of the bay though is in the Army firing ranges and you should abide by the army safety warning notices.

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The tidal trap just west of Clavell's Hard, Kimmeridge, Dorset

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You need low tide to travel far along the cliffs to the east and there is danger of being cut off there if care is not taken. There is a tidal trap just west of Clavell's Hard and you can easily go beyond this at a low spring tide. You may have about two hours maximum to explore east of Clavell's Hard. It is also worth noting that low tide is preferable on all the Kimmeridge coast because not only does it reveal more of the ledges but it allows the visitors to keep further out from the cliffs. High tide may push them back too close to the foot of the cliff and into the hazard zone.

Take care on the beach and ledges because the shale can be very slippery. Obviously when above the cliffs one should not approach the cliff edge which is quite abrupt. Do not handle or interfere with any metal objects that might be connected with the army firing activities. Do not attempt to climb the shale cliffs; there is no route up except at the obvious footpath access points. Because this website is on geology, safety regarding marine activities is a separate matter not dealt with here.

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KB-5 - INTRODUCTION continued:

Safety Addendum

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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KB-6 - INTRODUCTION:

Kimmeridge and Kimmeridge Bay,
Note on Industrial History and Smedmore Estate

Smedmore House, Kimmeridge, Dorset, once the home of Sir William Clavell, but since extended

Kimmeridge Bay is within part of the large Smedmore Estate. The house is not on the route to the bay which is through Kimmeridge Village. Kimmeridge Bay has been modified on the eastern side by previous industry and Smedmore House is relevant to this. It is of particular interest in that it was the home of Sir William Clavell who built the first house in 1620 (it has been much enlarged since).

A waste tip of burnt Kimmeridge oil shale, probably from the 17 century works of Sir William Clavell, southeastern corner of Kimmeridge Bay, Dorset, photo 2006

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Erosion at the former industrial port of eastern Kimmeridge Bay, Dorset, has shown a stratified sequence, including burnt shale, 16th April 2014

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Layers of burnt oil shale and of clay at the former industrial area of Kimmeridge Bay, Dorset, shown by coast erosion in 2014

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Sir William Clavell organised the working of the Kimmeridge oil shale and used it as fuel for glass-making and for boiling sea-water to manufacture salt. He was also involved in the production of alum. Clavell's Hard is an oil-shale mining site on the cliffs to the south of Smedmore House House, and this is a familiar to many geologists. The oil shale or Kimmeridge Coal used in the industry may have come from the cliff top near Cuddle or it may been quarried by Clavell's workers from Clavell's Hard (as it was mined there in the 19th century).

For more on the oil-shale and its use in the production of alum and information on Clavell's Hard see my associated webpage on:
Kimmeridge Oil Shale.

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KB-7 - INTRODUCTION:
Some General Views of Kimmeridge Bay

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Kimmeridge ledges of dolomite and bituminous shale of the Lower Kimmeridge Clay in Kimmeridge Bay, Dorset, low tide

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Washing Ledge seen from the Kimmeridge Bay cliff edge, Dorset, in very calm conditions, March 2012

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A wide angle photograph of eastern Kimmeridge Bay, taken by Ian West from the end of Washing Ledge, Kimmeridge Bay, Dorset, 16th April 2014

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The eastern part of  Kimmeridge Bay, Dorset, with Maple Ledge, the Maple Ledge Fault, the Head deposits and the car park above, seen from the end of Washing Ledge at low tide, 16th April 2014

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The western part of  Kimmeridge Bay, Dorset, March 2012, seen in very calm conditions and at low tide

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Path into Kimmeridge Bay

The beach and cliffs at Gaulter's Gap

An old gun emplacement from the 1940s at Gaulter Gap, Kimmeridge Bay, Dorset

Kimmeridge Bay, Dorset

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KB-8 INTRODUCTION

Geological Maps

The Kimmeridge Clay outcrop and subcrop under England, modified and redrawn after Gallois (2012)

Geology of the Kimmeridge coast, Dorset, partly redrawn after a modern BGS geological map

Map - Geology of the Isle of Purbeck

A very simplified location and geological map of the Kimmeridge Bay area and adjacent coast, Dorset, southern England

Geology of the Isle of Purbeck is 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".

A map above shows the simplified solid geology of the Kimmeridge area and locations referred to in this and associated Kimmeridge field trip guides. The area shown on the map is one in which Upper Jurassic and Lower Cretaceous strata generally dip northward within the Purbeck Monocline. The major, regional, anticlinal axis is east-west, offshore south of Kimmeridge, although a local complication is the Broad Bench anticlinal axis which is at an appreciable angle to the main fold axis. Structure is also complicated by a general plunge of the Purbeck Monocline to the east. The positions of most of the cliffs near the axis results in a low dip for much of the stretch of coast. The dip steepens (northward) in Brandy Bay and also inland around the villages of Kimmeridge, Steeple and Kingston. The oldest strata visible, part of the Lower Kimmeridge Clay Formation, is exposed on the west side of Kimmeridge Bay . By walking along the coast eastward from here progressively higher parts of the Kimmeridge Clay are seen. The highest beds are seen at Egmont Bay, Hounstout Cliff and Chapmans Pool. West of Kimmeridge Bay progressively higher parts of the Kimmeridge Clay occur in a northwestward direction in Brandy Bay. This is within the Army Firing Ranges and the foot of the cliffs is not normally accessible. When the ranges are open, however, the cliffs can be seen to some extent from a footpath above.

Old topographic map of the area around Kimmeridge Bay, Dorset, 1890

The lithological succession, using traditional names, in the Kimmeridge area, Dorset, based on old geological survey maps, with a minor correction on the Jurassic-Cretaceous boundary

Old geological map of the Kimmeridge Area, Dorset, based on 1895 and 1904 editions

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KB-9 - INTRODUCTION

Multibeam Bathymetry Images

A multibeam bathymetry image of the sea floor south of Kimmeridge, Dorset, courtesy of the Channel Coastal Observatory

Plunging anticlines with faults offshore from Kimmeridge and Gad Cliff, Dorset, multibeam bathymetry image of the Channel Coastal Observatory

The multibeam bathymetry image and the geological map of the coast between Kimmeridge Bay and St. Aldhelm's Head, Dorset, linked to show sea floor geology

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KB-10 - INTRODUCTION continued:

Access to Kimmeridge Bay and Adjacent Coast

Car or minibus access is easy, through a private toll road of the Smedmore Estate. Bringing coaches to Kimmeridge is possible but requires written permission from Dorset County Council in advance, with details and time of the specific visit. The road is narrow and has width restrictions. The pass must be in the possession of the coach driver when arriving.

Note that the Army Range starts west of Kimmeridge Bay and access to this is only on the Range Walks, which are open most weekends and at some other times. Obviously do not touch any shells or other dubious metal objects.

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KB-11 - INTRODUCTION continued:

General - Kimmeridge Bay

Kimmeridge Bay, Dorset

Location of oil well and Gaulter Gap at Kimmeridge Bay, Dorset

Maple Ledge and eastern  Kimmeridge Bay, Dorset

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Above Gaulter Gap looking westward in Kimmeridge Bay, Dorset, at high tide, 16th April 2014

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Geologists on the beach at Gaulter Gap, Kimmeridge Bay and in front of cyclical bituminous shale cliffs, 16th April 2014

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On Maple Ledge in the Lower Kimmeridge Clay,  Kimmeridge Bay, Dorset, 2012

The waterfall at Kimmeridge Bay, Dorset, flows over a ledge of bituminous shale in the Lower Kimmeridge Clay, 2012

Waterfall in eastern Kimmeridge Bay, Dorset

Rapid erosion in the northeastern part of Kimmeridge Bay, Dorset, has caused recession of the cliff and the truncation of a small stream so that it now flows over the cliff in a waterfall

The approach is through Kimmeridge village and on to the beginning of a narrow, private, toll-road belonging to the Smedmore Estate. The narrow road is suitable for cars and mini-buses but there is no access for full-size coaches or buses (although in special cases application can be made to Dorset County Council and also to the Smedmore Estate for a coach permit). Payment is at a hut at the entrance to the toll road, although there not always a toll-collector present in winter. You can park in the central car park shown and descend to the beach at the ravine at Gaulter Gap. You can almost always walk down onto the beach of Kimmeridge Bay but low tide is preferably.

As mentioned above, you will need low tide to travel far along the cliffs to the east and there is danger of being cut off. You can walk some way westward in Kimmeridge Bay and you can study the Flats Stone Band. The western extremity of the bay though is in the Army firing ranges and there is no access along the beach west of the bay. There is, however, a cliff-top path which is open when the Range Walks are open (usually at weekends and certain holiday periods).

Marine Centre at Kimmeridge Bay, Dorset

Although this is a geological field guide, it is worth mentioning that there is a well-known marine nature reserve at Kimmeridge (see website: Purbeck Marine Wildlife Reserve). You can visit the Marine Centre which is amongst the black fishermen's huts at the southeastern corner of Kimmeridge Bay. Boat and diving enthusiasts congregate here, and there is separate parking at this end for boat owners.

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KB-12 - INTRODUCTION:

Aerial Photographs - General

A general aerial photograph overview of Kimmeridge Bay, Dorset, for location purposes

Aerial photograph index map for Kimmeridge Bay to Freshwater Steps, Dorset, based on a Channel Coastal Observatory image

Location aerial photograph of  Kimmeridge Bay and the cliffs to the east as far as Freshwater Steps, Dorset

An aerial photograph of the coast from Clavell's Hard to Freshwater Steps with some zonal information, east of  Kimmeridge, Dorset

A small-scale, location aerial photograph of the cliffs west of Kimmeridge Bay, Dorset, to Gad Cliff

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KB-13 - INTRODUCTION:

Aerial Photographs - Kimmeridge Bay

The northwestern part of Kimmeridge Bay, Dorset, as shown in a modified aerial photograph of the Channel Coastal Observatory, 2005

Aerial view, by the Channel Coastal Observatory, of southeast Kimmeridge Bay, Dorset, showing reefs of Lower Kimmeridge Clay

 Hen Cliff and Kimmeridge Bay, Dorset, from the air

Aerial photographs above show Kimmeridge Bay and adjacent area. These and other images provide general views of the bay to set the geography and perspective. Other specific and detailed aerial photographs, courtesy of the The Channel Coastal Observatory are given elsewhere.

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KB-14 - INTRODUCTION continued:

Seaweed Flies and Rotting Seaweed at Kimmeridge

Seaweed Flies or Kelp Flies at Kimmeridge Bay, Dorset, 23rd October 2009

An interesting aspect of Kimmeridge Bay is that in the past (up to about the 1990s) there were very large accumulations of rotting seaweed. The reason for this is that there are many offshore ledges or reefs of dolomite and hard bituminous shale, and the seaweed grows on these. In 2011 there now seems to be much less accumulated dead seaweed. This has been noticed elsewhere, as in the Torquay region.

When there is abundant rotting seaweed, it gives off a characteristic odour that some people think is a smell of oil from oil shale (there is a minor smell from oil shale, but it is far exceeded by the seaweed). The seaweed smell is not particularly unpleasant or particularly noticeable to everyone, but some local people have an impolite name for the northeast corner of Kimmeridge Bay. When the seaweed is trodden on in summer or autumn large swarms of seaweed flies (Coelopa frigida) rise from the beach. This is a harmless fly of rather crab-like appearance that is of little inconvenience to geologists. The soft rotting seaweed and flies also can also occur in abundance to the east of Kimmeridge Bay, particularly in the Cuddle area. Occasionally when walking in this area on a hot day the flies are a minor nuisance and it is good to get onto hard rock. In general the flies add interest and character to the Kimmeridge coast and their worm-like larvae help in the decomposition of the seaweed. I am not aware of any harm having occurred at Kimmeridge from the rotting seaweed, but it should be noted that on the French coast a horse has been killed by H2S from rotting seaweed and a rider taken to hospital. In cold, windy or stormy weather you will encounter no problem with flies. In general the flies are a good safety factor because they deter summer holiday-makers from sitting on the beach beneath the hazardous cliffs.

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KB-16 INTRODUCTION continued:

Commencing Field Work at Kimmeridge Bay

To commence a general field trip, park the car in the main car park on the cliff top. Have a look over the cliff, without going too close to the edge (unstable shale). Dark cliffs of shale, and ledges of stone projecting into the sea. You may notice the smell of seaweed, and sometimes in summer an odour of warm oil-shale. You can commence study of the bay by looking at the notice boards and then walking down the steps into the Gaulter Gap ravine (centre of the bay), across the little bridge and down onto the beach. A small part of the bay is often accessible even at high tide, but low tide conditions are much better and tide tables should be consulted prior to a field trip.

Gaulters Gap in central  Kimmeridge Bay, Dorset

Path into Kimmeridge Bay

Coastal recession at Gaulter's Gap in the centre of Kimmeridge Bay, Dorset, as seen on 4 March 2007

Burial diagenesis dolomite, the Washing Ledge Dolomite Bed, near Gaulter Gap, Kimmeridge Bay, Dorset, on 4 October 2005

These photographs show Gaulter Gap, where the Lower Kimmerige Clay is exposed. The path into Kimmeridge Bay from the car park on the cliff top at the centre is alongside a small ravine with a stream. Rejuvenation of the stream valley has occurred as a result of rapid cliff retreat and this has formed the ravine within the broader valley. In the distance is Clavell's Tower above Hen Cliff. At the mouth of the ravine you can see the Lower Kimmeridge Clay (of the Aulacostephanus autissiodorensis ammonite zone - see Cox and Gallois, 1981). If you turn right at the bottom you will see the cycles of sedimentation shown in the next image and also the Washing Ledge Stone Band.

Some erosion of the shale has been taking place here (compare older and newer photographs). The concrete "Dragon's Teeth" were placed here to prevent invasion by German tanks from landing craft during the Second World War. There would have been barbed wire and mines here too then. Although erosion is taking place, the survival of the "Dragon's Teeth" from the 1940s shows that it not at a very high rate just here. The Kimmeridge Clay is always crumbling in the cliffs and the calcareous, less bituminous parts break into small pieces. The bituminous shale is rather more resistant but a major feature are ledges of stone band dolomite, the Kimmeridge Ledges, extending some way out to sea (many ships have been wrecked on them). These ledges break the waves and protect the coast to some extent. Unfortunately, the tide was fairly high at the time of the photograph so they are not visible (but can be seen in the left image). This particular location at the back of the back of the bay is also less exposed than elsewhere.

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KB-17 - INTRODUCTION continued:

Kimmeridge Bay, History - in 1882.

In Victorian times Kimmeridge was hardly any different, apart from the absence then of the oil-well, and the presence of an unpleasant odour of some drifting sulphurous smoke from the cottages, which were burning oil-shale . Fortunately, it has been spared the rather urban development that is seen at Lulworth Cove. The barrister and poet, Mr C.E. Robinson guides us along the cliff-top in 1882 from the east into Kimmeridge Bay.

west side of Kimmeridge Bay and Gad Cliff

"Presently a little open 'coombe' gives a glimse inland of some ugly coastguard houses, partly screened by a grove of straggling trees, and turning this way, but keeping on the turfy hillside, we open Kimmeridge Bay itself. The view is very quaint: its foreground composed of the sloping down, near the foot of which lie the objectionable houses [at Gaulter Gap], while on the summit stands a curious circular tower [Clavell's Tower] of dark stone [Kimmeridge dolomite], with a parapet of lighter tint, and encircled at its base with a colonnade supporting a balcony, whence a charming and extended landscape is visible, for the sake of which, no doubt, this not ill-designed Belvedere was erected. Northward, a mile or more away, in a vast curve receding by hollow slopes from the sea edge, rises a lofty range of hills, grassed over to the very crest. Hill and dale, nearly treeless, are vested in a garment of brilliant emerald, only blue-green glimmering waters of the miniature bay, fringed with low but steep shores of dingy shale, and more distant, the magnificent stone-yellow precipices of Gad Cliff, with the chalken heights round Worbarrow Bay break the verdant mononoty of hue."

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KB-18 KIMMERIDGE STRATIGRAPHY - INTRODUCTION

(also applicable to the other Kimmeridge Webpages)




KB-19 STRATIGRAPHY:

General Succession

The Kimmeridge Clay Formation is largely, but not completely exposed at the surface at Kimmeridge (Arkell, 1947). Thus the thickness cannot be directly measured. Seismic reflection profiles by British Petroleum Ltd have shown that the full thickness is between 535m and 585m in this area (Gallois, 2000). Measurement is further complicated by lateral changes in thickness. Cox and Gallois (1981) should be consulted as the key publications on the stratigraphy, with valuable additional data coming from the new borehole investigations of the RGGE (Rapid Global Geological Events special research project of NERC) as described by Gallois (2000). This new work, in addition to providing detailed data for cyclicity studies, has revealed what strata lie unexposed beneath Kimmeridge Bay and it has also clarified the details of the upper part of the succession.

The Kimmeridge Clay represents the clays sediments of the sea for approximately 8.5 million years (Gradstein et al., 1994).

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KB-20 - STRATIGRAPHY continued:

Key Publications on the Kimmeridge Clay of Kimmeridge

The Key Publication on the Kimmeridge Cliff Sections, Dorset, by Cox and Gallois, 1981

Generalised sequence of the Upper Kimmeridge Clay in Dorset after Cox and Gallois (1981)

Generalised sequence of the Lower Kimmeridge Clay in Dorset after Cox and Gallois (1981)

If visiting Kimmeridge and studying the Kimmeridge Clay you will need to have a copy at hand of the key publication by B.M. Cox and Ramues Gallois, the Kimmeridge Clay expert. This is needed to find the stratigraphical and zonal position of any cliff exposure.

Cox, B.M. and Gallois, R.W. 1981. Stratigraphy of the Kimmeridge Clay of the Dorset type area and its correlation with some other Kimmeridgian sequences. Report of the Institute of Geological Sciences, No. 80/4, 144. [obtainable from the British Geological Survey].

Serious researchers on the Kimmeridge Clay will need, in addition, the following publication. However, when printed out it is too large (two or three metres in length) to open out on a windy beach. It is best used for reference purposes in the study, but perhaps the pdf could be used on a sturdy, water-resistant, hand computer in the field.

Coe , A.L., Hesselbo, S.P., Jenkyns, H.C., Morgans Bell, H. and Weedon, G.P. 2001. Kimmeridge Clay Formation composite graphic log for coastal exposures, near Kimmeridge, Dorset. Part of Supplementary Publication No. SUP 90490, British Library. Associated with paper by Morgans-Bell, Coe, Hesselbo, Jenkyns, Weedon, Marshall, Tyson and Williams (2001). By Angela L. Coe of the Open University and others.

See also the classic, original ammonite stratigraphy of Cope.

These publications mentioned above are the starting points for study of the Kimmeridge Clay in the field in Dorset, but, of course, there are numerous other papers on the Kimmeridge Clay, most of which are listed in the associated Kimmeridge and Kimmeridge Clay Bibliography.

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KB-21 - STRATIGRAPHY continued

Kimmeridge Clay - Stages and Ammonite Zones

Over the years since Salfeld established the Kimmeridge ammonite zones in 1913 there have been a number of changes. Salfeld classified the whole sequence as Kimmeridgian Stage. The Kimmeridge Clay is now considered to be the equivalent of two stages, the Kimmeridgian and the Bolonian Taylor et al. (2001). The zonal scheme shown here is that of Cope (1978), as used by Taylor et al. (2001).

STAGE CHRONOZONE ZONAL AMMONITE
Bolonian

(Upper part of broader "Kimmeridgian" according to some previous authors. At Kimmeridge, the Upper Kimmeridge Clay, in the cliffs east of Kimmeridge Bay, and also west in part of Brandy Bay, corresponds to this. Includes Yellow Ledge, Kimmeridge oil shale, Rope Lake Head SB, White Band and associated shales etc.)

Fittoni Virgatopavlovia fittoni
Rotunda Pavlovia rotunda
Pallasioides Pavlovia pallasioides
Pectinatus Pectinatites pectinatus
Hudlestoni Pectinatites hudlestoni
Wheatleyensis Pectinatites wheatleyensis
Scitulus Pectinatites scitulus
Elegans Pectinatites elegans
Kimmeridgian

(Lower part of the broader "Kimmeridgian" as used by some previous authors. At Kimmeridge the Lower Kimmeridge Clay, within Kimmeridge Bay, corresponds to this. Includes the Flats , Washing Ledge, Maple Ledge Dolomite Beds and associated shales etc.)

Autissiodorensis Aulacostephanus autissiodorensis
Eudoxus Aulacostephanus eudoxus
Mutabilis Aulacostephanus mutabilis
Cymodoce Rasenia cymodoce
Bayliei Pictonia baylei

Here at Kimmeridge Bay we are dealing with Eudoxus and Autissiodorensis Zones. We do not see Bayliei, Cymodoce and Mutabilis. Generally within the bay the matter is not complicated; just remember that Autissiodorensis commences at the top of the Flats Dolomite Bed. The top of the Autissiodorensis is out of the bay and not so obvious. It is the base of Blake's Bed 42 which is in Hen Cliff, just to the east of Kimmeridge Bay. It is in the cliff well below Yellow Ledge and not conspicuous. You will need to have a copy of Cox and Gallois (1981) at hand to find it.

For more on the perisphinctid ammonite Aulacostephanus and other members of the Aulacostephanidae (Spath, 1924) see Fossiles - Ammonites du Jurassique. See also Aulacostephanus autissiodorensis (Cotteau). See also the paper by Geyssant et al. on the Kimmeridgian of the Boulonnais, France.

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[END OF STRATIGRAPHY]

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STRUCTURE
KB-22 - STRUCTURE:

Cliff Section

Section of the Kimmeridge cliffs from Broad Bench eastward to Houns-tout, near Chapmans Pool,  Dorset

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 things, it shows the position of the Kimmeridge oil-shale, Clavell's Hard and the location of the mining in the cliffs.

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KB-22a - STRUCTURE (continued)

More Details (to be added)

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KB-22ba - STRUCTURE continued:

Faults of Kimmeridge Bay - Corner Fault

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Corner Fault, an extensional fault, with a damage zone, in bituminous shales of the uppermost part, the Autissiodorensis Zone, of the Lower Kimmeridge Bay, Dorset, 1st May 2014

Above is shown Corner Fault, near the eastern corner of Kimmeridge Bay. This is approximately parallel to Maple Ledge, but is about 15 metres or so to the east of the ledge. It is about 50 metres from Corner. The original name for this place, used by Gallois (2012), is impolite and takes its local name because an odour originated in an accumulation of rotting seaweed. This seaweed pile, and its effects, does not seem to have been developed so much in recent years. The name here is shortened to "Corner Fault". The thin hard band in the Maple Ledge Mudstone Member is shortened to "Corner Rib". For a map and aerial photograph of this area, with appropriate labels see: Gallois (2012) - A Revised Description of the Lithostratigraphy etc..., Fig 3 on p. 11.

In general, almost all the faults in the Kimmeridge cliff sections are extensional and they generally cut the cliff in a roughly north-south direction (of course the coast is predominantly east-west so this may be expected). They mostly have small throws of a few metres at most, but there are exceptions. The throws for all but the very small faults have a negative power law distribution (Hunsdale and Sanderson (1998)). They occur almost every few hundred metres along the cliffs both within Kimmeridge Bay and along the coastal exposures east and west. An interest aspect is the presence of damage zones in the sequences of cyclical bituminous shales, but not in the more homogeneous, calcareous mudstones. For more information on this topic see: Hunsdale and Sanderson (1998) and Guerrero-Munoz (2001).

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KB-22bb - STRUCTURE continued:

Faults of Kimmeridge Bay contin. - Maple Ledge Fault

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Geologists walk past the Maple Ledge Fault in Kimmeridge Bay, Dorset, taking the precaution of wearing hard hats, although the risk is very low except close to the cliff

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Maple Ledge Fault  a normal fault in Kimmeridge Bay, Dorset, downthrowing the Maple Ledge Dolomite Bed

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Above is shown the Maple Ledge Fault. This fault is about 30m west of Maple Ledge and roughly parallel to Maple Ledge. It extends from the car park to the southeastern headland of Kimmeridge Bay. Like Corner Fault it trends south-southwest and downthrows to east-southeast.

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Evidence of pre-faulting compaction at the Maple Ledge Fault, Kimmeridge Bay, Dorset, 16th April 2014

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Alongside the main plane of the Maple Ledge Fault in Kimmeridge Bay is a rotated slice. This has had the formerly horizontal bedding rotated into almost vertical attitude. The very interesting aspect is that ammonites within this rotated slice have been almost fully compression, prior to the rotation, and therefore prior to the faulting. This would not be unusual if the fault was late (e.g. Tertiary). However, the conventional view is that the extensional faulting is Late Cimmerian and originated during the extension phase of the English Channel Inversion (note that this locality is just within the Inversion). Therefore, this evidence suggests that the Kimmeridge Clay was almost fully compacted by about mid-Cretaceous times and probably rather earlier. So, the Maple Ledge fault seems to shed some light on the history of the English Channel Inversion.

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[END OF STRUCTURE SECTION]

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EROSION OF KIMMERIDGE BAY



KB-22e EROSION OF KIMMERIDGE BAY:

(Section to be added)

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[END OF EROSION]

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CYCLOSTRATIGRAPHY



KB-23 CYCLOSTRATIGRAPHY:

Cycles of Sedimentation,

(Milankovitch Cycles).

The rhythmic or cyclical part of the Aulacostephanus autissiodorensis Zone of the Lower Kimmeridge Clay at Kimmeridge Bay, Dorset, high tide, 23rd October, 2009, with graduate students of London South Bank University

London South Bank University Students examine the cycles of KC 34, autissiodorensis Zone, Lower Kimmeridge Clay, Kimmeridge Bay, Dorset, 23rd October 2009

Cycles in the autissiodorensis zone of the Kimmeridge Clay at  Kimmeridge Bay, Dorset

Log of Cycles in Lower Kimmeridge Clay

The cliff at the back of Kimmeridge Bay, just west of the path to the foot of the cliffs, near the cottages is easily accessible at almost tide conditions. Clearly visible are well-defined cycles of sedimentation with hard beds of bituminous shale projecting and relatively crumbly mudstone recessed. There are other cycles like this in the Kimmeridge Clay and they have been considered to have originated as a result of the Milankovitch scheme of climatic cycles produced by astronomical changes (Dunn, 1974; House, 1985; Waterhouse, 1995; Weedon et al. 1999). The cycles are discussed further below.

A log of these cycles at the back of Kimmeridge Bay based on the work of Waterhouse (1995), and showing, according to this author, the apparent sediment thicknesses for the main 38 ka (thousand year) obliquity cycles and the less significant 20 ka precession cycles. (Compare this with the photograph shown in the centre and the image with the Washing Ledge Stone Band shown below.)

Note that this earlier work should be considered in the light of a recent publication by Weedon, Coe and Gallois (2004) to be discussed further below.

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Footnote: Explanation of Milankovitch Cyclicity

For explanation and discussion of Milankovitch Cyclicity (used with reference to the Mediterranean Sea sedimentation) go to: The Dark Secret of the Mediterranean; a case history in past environmental reconstruction, by Dr Eelco J. Rohling. Particularly see the section The Astronomical Pacemaker for explanation of the Precession Cycle and the Obliquity Cycle.


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KB-24 CYCLOSTRATIGRAPHY continued:

Cycles of Sedimentation - Further Discussion

Thus it has long been noticed that in the cliff sections at Kimmeridge that there seems to be a cyclicity or rhythmicity. Cycles, cyclicity and cyclothems were subjects of particular interest in the 1930s (e.g. Anderson,1932), although not with regard to this formation, and have now come back into vogue again, studied now by statistical methods and with better absolute dating information. Although cycles or rhythms are easy to see and easy to measure they are unexpectly difficult to understand. The Kimmeridge Clay Formation here seems a very promising succession for study of cycles, because, as pointed out by House (1985) and Gallois (2000). It contain rhthymic variations in clay mineralogy, faunal and organic content and it consists of an almost unbroken sequence of relatively uniform, highly fossiliferous marine-shelf mudstones that have suffered little deformation. The excellence of the cliff sections is another positive factor for such study here.

It should be noted, though, as everywhere, there are bound to be some negative factors. Here it is mainly the rapid and major thickness variations in the Kimmeridge Clay in this region and the fact that Late Kimmerian tectonism was taking place in the region at the time of deposition. Kimmeridge is situated only just within the basin of the English Channel Inversion (the Jurassic depositional basin to the south). There is drastic thinning west-northwest to the Ringstead area near Weymouth, where the formation is only about half the thickness according to Arkell (1947) and presumably even more drastically northward to the Wytch Farm High. The reworking of sediments from the highs which became common by late Purbeck times (Garden, 1991) was not appreciable, at least in terms of large clasts, during Kimmeridgian times here (but reworked clay would not be easily seen). There is, however, a seismic fluidised bed (Gallois, 2000), as in the Purbecks, and small clasts occur within oil-shale and debris deposits in a coccolith limestone (House, 1985). The major consequences of the basin-margin location are the thickness changes, which occur in the cliffs at Kimmeridge and also between the boreholes used for cyclicity studies, which show a 7% thickness change in 6 km (Gallois, 2000). Fortunately, within a short distance the changes seem to be regular and only one dolomite bed, the Washing Ledge Stone Band, has disappeared at the boreholes of Swanworth Quarry. Elsewhere, where the formation thins drastically, as in the Ringstead area, many stone bands have disappeared or been replaced by nodule horizons (Cox and Gallois, 1981). Thus the sequence at Kimmeridge seems good for cyclicity studies, in spite of its special location.

The attempts to interpret cyclicity have led to important new information emerging on the Kimmerige Clay sedimentation. Although a general pattern of cycles or rhythms has emerged, there are complications and there does not seem to be a simple model available which is applicable to the British Jurassic sequence in general. Recent research shows similarities between the Kimmeridgian and Rhaetican-Sinemurian cyclicity but not that of the Pliensbachian (Weedon et al., 1999), and that is a little surprising. Shifts in time in types of cycles "presumably reflect changing local or global palaeoclimatic and/or palaeoceanographic conditions" (Weedon, et al., 1999).

Some of the first Kimmeridge cyclity work is that of Downie (1995, unpublished thesis referred to in Dunn, 1974) who studied 205m of the Kimmeridge sediments and found 141 cycles with an average thickness of 1.45m. This is close to the 1.43m cycle of Dunn referred to below and to the 1.20m cycles found by Waterhouse (1995).

Dunn (1974) carried out a detailed investigation of cyclicity in the Kimmeridge Clay using geochemical data. He studied the most bituminous part of the Kimmeridge Clay. This, a 20m section of the Upper Kimmeridge Clay, is in the wheatleyensis and hudlestoni Zones which includes the Blackstone (the main oil-shale), the Rope Lake Head Stone Band (dolomite) and the Short Joint Coal. Strangely, since cyclicity appears rather obvious lower in the succession, this particular interval has no lithological variation that indicates a cyclicity, and even the geochemical data does not at first sight indicate a cyclicity.

The Fourier analysis used only brought out regular periodicities and could only be meaningful if it was assumed that there was a fairly constant rate of deposition. The very presence in this sequence, however, of the unusual bed of oil-shale, the Blackstone, may indicate that sedimentation was not constant. Some time estimation is needed. Dunn took the duration of the Kimmerige Clay Formation to be 5 my from published literature. For the 500m thick sequence of sediments at Kimmeridge this gives an average period of about 10,000 years for the deposition of of 1m of sediment. If there has been a reasonable diagenetic reduction in thickness of the fine-grained, organic-rich, clay sediment of about 60% (it could have been 80%) then the original, theoretical, thickness of the Kimmeridgian sequence was about 1250m according to Dunn. This works out to an average deposition rate of 25cm per thousand years, a figure comparable to estimates of deposition in parts of the Black Sea. Note, of course, that the huge compaction would have been progressive (think about the possible effects of this on the deposition of the Purbeck lagoonal strata above). Dunn estimated a duration of 14,000 years for the 1.43m cycles. Later authors have considered that cycles of this size correspond to larger time intervals.

House (1985) made some calculations on a thick Kimmeridge succession and on a Liassic sequence and analysed them, taking into account recent radiometric age dates for the beginning and end of the Jurassic Period and the number of ammonite zones involved. He found that there is good agreement with present day cycles resulting from obliquity of the ecliptic. The ecliptic is the name for the plane of the earth's orbit around the sun. The equator is, of course, at an angle to this, which results in winter and summer seasons. The Obliquity of the Ecliptic , also known as Axial Tilt, is the inclination of the plane of the ecliptic relative to the plane of the earth's equator (see website on Milankovitch Cycles) . The angle at present is 23278.26 and this obliquity of the ecliptic may have varied in extent in a cyclical manner in the past. This change in the tilt of the earth results in the tropical belts expanding and contracting periodically with resulting climatic changes. He compared these supposed obliquity cycles with present ones of 41 kyr (41 thousand years).

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Footnote: Using the "Amazing Double Sunset" to study the obliquity of the ecliptic.
Incidently, the obliquity of the ecliptic has been discussed more than 3 centuries ago by an early geologist, but without reference to sedimentary cycles. Dr Robert Plot was a famous fossil collector, Keeper of the Ashmolean Museum and Professor of Chymistry at Oxford. He proposed in 1686 to use a double sunset at a churchyard at Leek, Staffordshire to measure changes in the angle of the Earth's tilt, the obliquity of the ecliptic. The present figure of about 23.5 degrees varies over many thousands of years and is reducing at a rate of 47 arc-seconds per century. See, too, the Leek website for an imaginitive reproduction of the double sunset, as seen at the summer solstice, from the Gentleman's Magazine of 1738.
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More recent work on the Kimmeridge Clay by Weedon, Jenkyns, Coe and Hesselbo (1999) has included magnetic-susceptibility measurements made on exposures, core material and down boreholes. A large-amplitude sedimentary cycle was detected in the lower part of the formation was considered to to be related to the 38 thousand year obliquity cycle, supporting House (1985) and Waterhouse (1995). Thus at present, there seems to be good evidence that the cycles visible in Kimmeridge Bay are about 38 ka cycles, apparently of obliquity origin. It is interesting that this period of cyclicity is also indicated by the Blue Lias, but it is not, however, by the Belemnite Marls of the Lias which seems to have been dominated the shorter term, 20 ka Precession Cycles, although with 123 ka Eccentricity Cycles (Weedon et al., 1999). It is clearly a complex matter that will be much clarified with better absolute dating of the formations.

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KB-25 CYCLOSTRATIGRAPHY - continued

Cycles of Sedimentation - Update on Cyclicity

Important new work on the whole Kimmeridge Clay succession was published in a special set of thematic papers on organic-carbon burial published in the Quarterly Journal of the Geological Society in 2004. Weedon, Coe and Gallois (2004) have provided a new assessment of cyclicity with efforts to find an overall pattern for the Kimmeridgian (sensu anglico). The matter has not proved simple, however. The overall succession gives obliquity cycles of 1.87 - 4.05 m and precession cycles of about half this. The relatively large range with regard to the supposed obliquity cycles may not be surprising. The Kimmeridge Clay succession at Kimmeridge is very varied in character from bottom to top. In particular, is situated at the very margin of the English Channel Inversion. The succession has long been known to vary in thickness in the cliffs between the Brandy Bay area (closer to the shelf) and the main cliff section to the east of Kimmeridge Bay. There is also variation between the local boreholes and the cliffs, and of course quite a major change to Ringstead Bay further west where the dolomite beds disappear. With regard the matter of lateral thickness changes (and the possibility of missing strata), it has to be noted that the Late Kimmerian movements were taking place during deposition of the Kimmeridge Clay. One consequence of this is that local tectonic affects have probably been superimposed on the effects of eustatic changes of sea-level. Dorset, particularly East Dorset is notable as a place of Jurassic and Cretaceous thickness and facies changes (quite drastic in the Purbeck, e.g. West (1975)); this provides variety and interest in the coast sections, but makes them more complicated as reference sections.

The new studies are of great value in providing a quite remarkable degree of detail on the Kimmeridge Clay. There is a vast amount of information which has been made readily available in papers and on the internet. It has increased the importance of the Kimmeridge cliff sections.

The paper of Weedon, Coe and Gallois (2004) is recommended for giving much insight into the Kimmeridge Clay sequence and has discussion on various matters including absolute dating, the significance of the zones and an interpretation of water depths. It is also a good source for finding other references. Here is the abstract; it is well worth-while reading the paper in full.

"Three independently measured variables (magnetic susceptibility, photoelectric factor and total gamma-ray) obtained from throughout the type Kimmeridge Clay Fm in Dorset (Southern England) were used to identify regular metre-scale, sedimentary cycles. Spectral analysis demonstrates that for long stratigraphical intervals the cycles are expressed as large-amplitude cycles of 1.87-4.05 m wavelength and smaller-amplitude cycles of around half that wavelength. These cycles are interpreted to record orbital obliquity and precession, respectively. The much larger amplitude of the inferred obliquity cycles compared with the precession cycles may indicate a high-latitude climatic forcing transferred to lower latitudes via sea-level variations. Orbital tuning indicates that the Early Kimmeridgian (sensu anglico) lasted at least 3.6 Ma (95 longer-wavelength cycles) and the Late Kimmeridgian at least 3.9 Ma (103 longer-wavelength cycles). The first detailed productivity estimates for the Kimmeridge Clay Fm, on a cycle-by-cycle calculation, indicate that average productivity of the type Kimmeridge Clay (220 g m-2 a-I) was less than the average productivity on modem continental shelves. The high average organic carbon content of the type Kimmeridge Clay (3.8% total organic carbon) cannot be attributed to high average productivity. However, the average organic carbon content is consistent with low siliciclastic mineral dilution of organic matter and/or elevated preservation linked to reduced bottom-water oxygenation."

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[END OF CYCLOSTRATIGRAPHY]

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SEDIMENTOLOGY



KB-26 SEDIMENTOLOGY:

Clay Mineralogy

The clay mineralogy of the Kimmeridge Clay is not particularly remarkably, but does show some vertical variation in composition. The clay mineral data on the Dorset Kimmeridge Clay has been presented by Hesselbo et al. (2009) for a 600m composite core, obtained for the RGGE project (Rapid Global Geological Events research project funded by NERC and several oil companies).

Hesselbo et al. (2009) found that the clay mineral assemblages of the Dorset coast Kimmeridge Clay comprise mainly illite and kaolinite with minor, randomly interstratified illite-smectite, mixed layer clays. The clay minerals are mainly detrital except in silty strata of Late Tithonian age, which contain abundant pore-filling kaolinite aggregates. The illite and kaolinite composition is fairly normal for nearby European localities, except that there are smectite horizons in the both the Kimmeridgian and the Tithonian in the nrthern Paris Basin. Kaolinite deficient horizons indicate an increase in aridity. In NW France there is a major decrease in kaolinite from the albani Zone (i.e. basal Portland Sands of UK) upward towards the end of the Tithonian (where in the UK the Purbeck evaporites appear). The true Kimmeridgian (i.e. Lower Kimmeridge Clay equivalent) may have originated in rather more humid conditions, although the proportion of kaolinite in this is not much higher. There is a hudlestoni Zone decrease in kaolinite, probably as a result of a minor increase in aridity at this time.

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KB-27 SEDIMENTOLOGY continued:

DOLOMITE BEDS: Introduction

Researchers examine beef beneath the Washing Ledge Dolostone Bed, Lower Kimmeridge Clay, Kimmeridge Bay, Dorset, 8th October 2012

Horizon of beef beneath Washing Ledge in the Lower Kimmeridge Clay at  Kimmeridge Bay, Dorset, 8th October 2012

The symmetry of the diagenetic, Washing Ledge Dolostone Bed, Lower Kimmeridge Clay, Kimmeridge Bay, Dorset

The Washing Ledge Stone Band (bed 34/1, autissiodorensis Zone) in the Lower Kimmeridge Clay at the back of Kimmeridge Bay near the old coastguard cottages is one of several ferroan dolomite beds in the Kimmeridge. It is not entirely surprising that it is symmetrical on either side of a dark shale because it is diagenetic in origin (although probably based on a primary sediment difference - higher carbonate as in the Blue Lias cycle) and has been formed under more than a kilometre of burial from some pre-existing source of magnesium, probably high-magnesium calcite (which still survives here) and/or clays. See Bellamy, (1977; 1980), Irwin (1979;1980; 1981), Leddra et al., (1987) and later papers, some of which may present different views (Ramsey, 1992). See Scotchman (1989;1991). The Flats Stone Band, another and more conspicuous burial dolomite, is of great interest in showing small thrusts, the origin of which - due to diagenetic processes or tectonism or both has been disputed.

Interesting new data on iron-isotope fractionation in the dolomites has recently been published by Matthews et al. (2004) (and available online). The compared 57Fe against 54Fe. They found that a isotopic profile across the Yellow Ledge Dolomite Bed in a borehole sample from Swanworth Quarry showed a double peak of del57Fe above and below the centre of the band. It was found to be decoupled from the Fe wt% which is highest (about 5%) at the margins of the bed and lowest (about 3%) in the centre.

The authors reported that the form of isotopic zoning is consistent with a one dimensional model of diffusional-chromatographic Fe-isotope exchange between dolomite and isotopically enriched pore water. An alternative mechanism envisages the infiltration of dissolved ferrous iron from variable (high and low) del57Fe sources during coprecipitation of Fe(II) ion with dolomite.

Matthews et al. (2004) also provided a very good and convenient summary of the research into the origin of the Kimmeridge dolomite beds:

"The carbonate stone bands are viewed as a form of laterally extended or coalesced concretionary carbonate growth (Coleman, 1993) [see also Bellamy (1977; 1980)]. Raiswell and Fisher (2000) distinguished two modes of growth based on cement textures: (i) concentric (or outward) growth where successive carbonate layers are added to the outer surface, increasing the radius (thickness) with time, and (ii) pervasive growth where the carbonate crystals simultaneously grow throughout the concretion volume and with little radius (thickness of the stone band) variation with time. Both growth mechanisms require porosity that can be filled by later cements, with the result that chemical or isotopic gradients across the concretionary bands may reflect changes in the relative proportions of early and later cements (Fisher et al., 1998; Raiswell and Fisher, 2000). Irwin et al. (1977) and Scotchman (1991) favored a concentric model, whereas Feistner (1989) showed that textural features of dolostone bands were consistent with pervasive growth. Our mineralogical observations have indicated that the ferroan dolomites contain negligible amounts of pyrite, as illustrated in Figure 10, where the calculated stability fields of ferroan dolomite and pyrite as a function of pH and total sulfur (log ST) are plotted. Similar to siderite-FeS phase relations, ferroan-dolomite stability over Fe2+ and pyrite is favored by increasing pH and low sulfur activity, respectively. Such conditions are consistent with the inference that the stone bands grew in reduced (methanogenic) conditions below the SR zone. Dolomite growth favored by high alkalinity and low sulfate activities has been suggested in a number of studies."

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KB-28 SEDIMENTOLOGY continued:

DOLOMITE BEDS: The Flats Dolostone Bed

(some subject matter used here is reproduced in the Kimmeridge-Brandy-Bay webpage - Kimmeridge Bay to Gad Cliff.)

Dr Peter Cobbald examines a thrust plane in the Flats Dolostone Bed, Kimmeridge Bay, Dorset, 8th October 2012

Students investigate megapolygons with thrusts at Kimmeridge Bay, Dorset

The Flats Dolomite Bed is an excellent stratum for burial diagenesis studies. Its burial history has been much investigated, yet some questions still remain. Its burial diagenesis was in parallel to that of the Kimmeridge Blackstone or oil shale which lies stratigraphically higher in the Kimmeridge Clays sequence.

The Flats is also useful for student exercises on stress history. The pattern of the megapolygons that are the notable feature of this bed can be examined statistically. Direct orientation of megapolygon thrusts can be measured and plotted as rose diagrams. Orientations of slickensides can be measured on plotted on stereonets. Students can then discuss the significance of the statistical data and consider both tectonic and diagenetic theories. The main site for investigation is within a few minutes walk from the car park and easy to approach.

There are, however, limitations on access to the more southwestern exposures of the Flats, particularly at Broad Bench. The outcrop closer to the centre of Kimmeridge Bay is accessible at all times. Broad Bench is inaccessible at all times and you cannot take a party there. Charnel is at the border of the firing range. It is particularly important that when the range walks are closed and the red flag is flying you must take care not to proceed beyond the danger notice southwest of Charnel. A CCTV camera on the cliff top above Broad Bench is probably in use at times. Abide by the notices, and be aware that there really can be unexploded tank shells west of Kimmeridge.

To complete an exercise successfully an ordinary low tide is needed, although, some features are visible even at mid-tide. The tidal range is small and there is no problem of being cut off in normal weather conditions. Students should wear hard hats and keep away from the foot of the cliff where debris is likely to fall. Use of hammers is not permitted.

Broad Bench, west of Kimmeridge Bay, Dorset

An aerial view of the Flats Dolomite Bed at Broad Bench, Kimmeridge, Dorset, in 2001, courtesy of the Channel Coastal Observatory

Joints in the dolomite of Broad Bench, Kimmeridge, Dorset

The Broad Bench Ledge with expansion megapolygons in the Flats Dolomite Bed, west of  Kimmeridge Bay, Dorset, 3 Jan 2006

This dolomite is characterised by a polygonal pattern of small thrusts, shown in the photographs above. Bellamy, (1977; 1980) has presented the evidence for lateral expansion of the bed during diagenesis. For more information see also Irwin (1979;1980; 1981) , Leddra et al., (1987) and later papers, some of which may present different views (Ramsey, 1992) . See Scotchman (1989;1991).

Expansion megapolygons in the Flats Dolomite Bed, Kimmeridge Bay, Dorset

Expansion megapolygons in the Flats Dolomite Bed, East of Charnel,  Kimmeridge Bay, Dorset, looking eastward

Expansion megapolygons in dolomite of burial diagenesis origin, the Flats Dolomite Bed, Kimmeridge Bay, Dorset, England

The front of a megapolygon thrust with jointing, between Charnel and Broad Bench, Kimmeridge Bay, Dorset

Relationship between expansion megapolygons in the Flats Dolomite Band and a small fault, near Charnel, Kimmeridge Bay, Dorset, Jan 2006

Any relationship between the megapolygons and faults is well-worth exploring. Here is a small fault near Charnel. You will easily find it from the warning sign and it is close to a larger fault. In the field, you should measure its trend, its hade and its throw, which is very small. Compare the trend of this fault to other faults which cut the Kimmeridge Clay in the Kimmeridge cliffs.

The question on the photograph relates to a problem as to whether the little fault, and a nearby larger fault, is Late Kimmerian or Alpine. You will know that one of these phases was an extensional regime and the other compressive. Thus identifying this Charnel fault with a group of local Kimmeridge faults that have resulted from either an extensional or a compressive regime can give you an approximate date. That, in turn, aids the understanding of the megapolygons. However, this might be too simplistic, since there may have been more than one extensional and more than one compressional phase - this point is for your further discussion.

You will also have noticed some parallelism of joints. You may wish to follow this matter further by comparing the trend of these joints with those further away from the small fault. You might also like to examine other joints near faults (try for example the Yellow Ledge at the east end of Hen Cliff).

Conjugate thrusts in a block of the Flats Dolomite Bed, from between Charnel and Broad Bench, Kimmeridge Bay, Dorset; with an exercise on stress history

More conjugate thrusts in a block of the Flats Dolomite Bed, from near Charnel, Kimmeridge Bay, Dorset

Small thrust with thrust breccia beneath a megapolgyon front, near Broad Bench, Kimmeridge Bay, Dorset

The Flats Dolomite Bed is upfaulted in the cliffs on the west side of Kimmeridge Bay, Dorset, between Charnel and Broad Bench

Bellamy (1980) examined the composition of the acid-soluble minerals of the Flats dolomite bed using geochemistry and X-ray diffraction and calculated the proportion of isomorphous substitution. A sample from the Flats was found to have the following composition:

Ca 51.09 Mg 44.37 Fe 4.47 Mn 0.07 CO 3

There is up to 95 wt% dolomite in this bed, compared to only 77wt% in the Maple Ledge. The fact that this rock is a relatively pure carbonate is relevant to the thrusting if that process was due to burial diagenesis. There is no significant clay to buffer expansion growth or retard water flow. Fe 2+ is fairly low at less than 0.5 wt%. It is interesting though that siderite, as such, occurs in sediments 6m above the Flats. Sr 2+ in the Flats is 314 ppm, about the same as Washing Ledge. As noted below, this seems to be a fairly high figure for a local Jurassic dolomite.

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KB-29 SEDIMENTOLOGY continued:

Petrography of the Flats Dolomite Bed

Thin section normal to bedding of the lower part of the Flats Dolomite Bed,  Kimmeridge Bay, Dorset, after Bellamy (1980)

Thin section parallel to bedding from the central part of the Flats Dolomite Bed,  Kimmeridge Bay, Dorset, after Bellamy (1980)

Bellamy (1980) made an excellent petrographic study of the Flats Dolomite Bed, and most of the others. For detailed information please refer to this thesis. A representative thin section normal to bedding is shown above. Distinguishing features are preferential orientation of long axes and c-axes normal to bedding, and the occurrence of reddish kerogen streaks. A section parallel to bedding is, of course, quite different and shows dolomite crystals that are interlocking and equigranular but without the kerogen lamination being obvious (sometimes, though, the cut may be through a kerogen layer and show more kerogen than is seen here). Note that a small proportion of pyrite is present at intercrystalline (re dolomite) sites. Bellamy (1980) found, in places, a distinctive subradial development of dolomite crystals which he termed "sunflower structure" in places.

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SEDIMENTOLOGY continued:

KB-30 DOLOMITE BEDS: Washing Ledge Dolomite Bed

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Out on Washing Ledge of the Aulacostephanus autissiodorensis Zone, Lower Kimmeridge Clay,  Kimmeridge Bay, Dorset, low spring tide, 16th April 2014

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The Washing Ledge Dolomite Bed rises from the beach in Kimmeridge Bay, Dorset, and is seen in an anticline on the west of the bay, with the oil well on the cliffs above, October 2009

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Burial diagenesis dolomite, the Washing Ledge Dolomite Bed, near Gaulter Gap, Kimmeridge Bay, Dorset, on 4 October 2005

The Washing Ledge Dolomite Bed with central parting of bituminous shale, Lower Kimmeridge Clay, Kimmeridge Bay, Dorset

[KB-30 contin]

Washing Ledge stone band is on the shore a short distance to the west of the path to the beach at Gaulter Gap. The ledge is close to the coastguard cottages (Gaulter Cottages) at Gaulter Gap and in the past was presumably a very convenient ledge from which to do the washing. The dolomite bed is within the Aulacostephanus autissiodorensis Zone of the Lower Kimmeridge Clay.

The Washing Ledge dolomite was investigated by Bellamy (1980) using X-ray diffraction and geochemistry to determine the composition of the dolomite and the proportion of isomorphous substitution and a sample was found to have the following composition:

[KB-30 contin]

Ca 50.75 Mg 40.88 Fe 8.29 Mn 0.08 CO 3

(or without using subscripts - Ca 50.75 Mg 40.88 Fe 8.29 Mn 0.08 CO 3)

[KB-30 Washing Ledge Dolostone contin.]

Thus the Washing Ledge dolomite is very ferroan. There is only 81 wt% dolomite in this bed, compared to 95% in the Flats, so like the Maple Ledge dolomite it is somewhat impure (a 'cementstone'). Sr 2+ is 313 ppm, again fairly high.

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KB-31 SEDIMENTOLOGY continued:

DOLOSTONE BEDS: Maple Ledge Dolomite Bed in Kimmeridge Bay
(autissiodorensis Zone, Lower Kimmeridge Clay)

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Maple Ledge and eastern  Kimmeridge Bay, Dorset

[KB-31 Maple-Ledge contin]

Undercutting and erosion of Maple Ledge Dolostone Bed at Maple Ledge, Kimmeridge Bay, Dorset, 3 Jan 2006

[KB-31 Maple-Ledge contin].

The eastern corner of Kimmeridge Bay, Dorset, with Maple Ledge and Corner, at low spring tide, 16th April 2014

[KB-31 Maple-Ledge contin]

Maple Ledge, with some fracture and fall of blocks after winter storms, Kimmeridge Bay, Dorset, 16th April 2014

[KB-31 Maple Ledge contin]

Maple Ledge Stone Band, Kimmeridge Bay, Dorset

[KB-31 Maple Ledge contin]

Boulders from the Maple Ledge Dolomite Bed at Kimmeridge Bay, Dorset

[KB-31 Maple-Ledge contin]

The Maple Ledge is in the eastern part of Kimmeridge Bay. The Maple Ledge Dolomite Bed is also within the Aulacostephanus autissiodorensis Zone of the Lower Kimmeridge Clay but higher than the Washing Ledge Dolomite Bed. Ammonite-bearing mudstone occurs a short distance above (with Nannocardioceras ) and below with crushed Aspidoceras and Aulacostephanus (and also with Nannocardioceras ).

The Maple Ledge dolomite was also examined by Bellamy (1980) and sample was found to have the following composition:

[KB-31 Maple-Ledge - contin]

Ca 51.87 Mg 40.24 Fe 7.84 Mn 0.04 CO 3

[KB-31 Maple Ledge contin]

You will notice from these figures that the Maple Ledge dolomite is, like the Washing Ledge dolomite, very ferroan. This indeed is one of the most ferroan of the dolomites in the Kimmeridge coast section. There is only 77 wt% dolomite in this bed, compared to 95% in the Flats, so this is another impure dolomite or cementstone. The bed is kerogenous, like the Washing Ledge dolomite bed, but almost certainly contains clay in addition. Sr 2+ is 320 ppm. When ratioed to Ca this gives 616 ppm, which is useful for comparison with limestones. Sr 2+ is thus quite high not only for a dolomite but also in comparison with local Jurassic limestones. This is presumably a consequence of an almost closed system during burial diagenesis and the original presence of some shell aragonite (still preserved in the shales).

[KB-31 Maple Ledge - end]

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KB-32 SEDIMENTOLOGY - continued:

Maple Ledge Shales or Maple Ledge Mudstone Member
(Aulacostephanus autissiodorensis Zone)

A lunch break for a field part at the eastern end of Kimmeridge Bay, Dorset, with some members sitting on Corner Rib, in the Maple Ledge Mudstone Member, 16th April 2014

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The Maple Ledge Mudstone Member of the Lower Kimmeridge Clay at the eastern corner of Kimmeridge Bay, Dorset, 16th April 2014

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The Maple Ledge Shales of the Aulacostephanus autissiodorensis Zone of the Lower Kimmeridge Clay, Kimmeridge Bay, Dorset, 4 March 2007

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[KB-32 - Maple Ledge Mudstone Mb. contin]

The Maple Ledge Mudstone Member is the uppermost sequence of bituminous shales and of mudstones in the Lower Kimmeridge Clay. It is well-exposed in the eastern corner of Kimmeridge Bay; this place is just referred to in this website text as "Corner", intentionally avoiding an impolite adjective used locally in the past, and referring to former accumulations of rotting seaweed. Arkell (1947) referred to the shales from and including the Maple Ledge Dolomite Bed up to Blake's Bed 42 as the Maple Ledge Shales (21m or 70 feet thick). Gallois (2012), referred to them as the Maple Ledge Mudstone Member. He described them as "20.6 to 20.4 m of thinly interbedded organic rich, clay mineral rich and calcareous mudstones." He grouped them into 15 units, M1 to M15 and gave some lithological details (his Fig 2.). He also provided a detailed comparison with a slightly thinner sequence of the same beds in Brandy Bay. The lower part of the Maple Ledge Mudstone Member, which is shown in photographs above, was described by Cox and Gallois (1981) as consisting of "Rhymic alternations of grey and brownish grey, bituminous mudstones, sparsely shelly with crushed Aulacostephus, pectinatitids and rare Gravesia. Amongst bivalves Protocardia striatula and the small oyster Exogyra virgula are common ((Blake, 1875).

[KB-32 contin]

For information on the higher parts of the Maple Ledge Shales go to description and photographs of Hen Cliff, just to the east of Kimmeridge Bay (and below Clavell Tower). These are available in the associated : Hen Cliff, Yellow Ledge and Cuddle Webpage. For more technical information see the paper by Gallois (2012) - A Revised Description of the Lithostratigraphy .. etc..

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KB-32c SEDIMENTOLOGY - continued:

Pyrite Diagenesis

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A good place to study Kimmeridge Clay pyrite diagenesis is in the Maple Ledge Shale Member and associated strata in the central to eastern part of Kimmeridge Bay. Visit at low tide and examine the shale ledges, from the Maple Ledge Fault to Washing Ledge.

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Diagenetic history of the Kimmeridge Blackstone or oil shale in comparison to that of the Kimmeridge Basalt Stone, a dolomite microsparite, strata of the Upper Kimmeridge Clay, east of Kimmeridge Bay, Dorset

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Shown above is a simplified diagram based on classic published work, with some modifications in relation to Kimmeridge oil shale. This diagram is also relevant to pyrite development. The reason is that pyrite should develop on the sulphate-reduction diagenetic zone. Now this is not very deep, actually extremely shallow, and has been shown to extend to about 10 metres. Some rather imperfect evidence below suggests that the sulphate reduction extended a substantial way deeper than 10 metres. Compaction at 10 metres would have been very limited and it is unlikely that incipient joints could develop.

Should the diagram above be modified and the the base of the sulphate reduction zone taken down to about 50 metres or even more in these special situations of late pyritisation? This website contains no detailed study, but it does suggest that the base depth might be underestimated if one applies a version of the classic diagram to some of the pyrite features of the Kimmeridge cliffs. Note that the Kimmeridge dolostone beds at Kimmeridge have classic fermentation zone features, a subject which is discussed elsewere in this website. [See: Bellamy and the work of Irwin.

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There might be implication from a late extension of the sulphate-reduction zone to petroleum geology and the matter needs further thought.

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Pyrite - Angel-Wing

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Angel Wing Pyrite in the Maple Ledge Shales, Aulacostephanus autissiodorensis Zone, Kimmeridge Clay, Kimmeridge Bay, Dorset, 4 March 2007

The lower part of the Maple Ledge Shales are very pyritic. Much Angel Wing Pyrite at certain horizons, as shown above. This type of pyrite, with paired horizontal growths, also occurs in the Lias at Lyme Regis and is sold in the fossil shops (it is quite common and no real value but probably of interest to children). The name comes from Lyme Regis where it has been well-known, probably since the days of Mary Anning or before.

Angel Wing Pyrite is a fibroradiating habit of pyrite that only seems to occur in bituminous strata where at one stage of diagenesis there were abundant sulphide ions. It occurs roughly parallel to the bedding of bituminous shales. So the bedding was fairly well defined. However, it is not post-lithification and it penetrates the argillaceous rock as shown in the photograph. It is thus fairly early, and presumably developed in the sulphate reduction diagenetic zone. However, its orientation suggests that it might perhaps be later than some early compaction. Some early compaction before the end of sulphate reduction is also suggested by some features discussed below.

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Pyrite in Early Incipient Joints

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Relatively late pyrite, in early incipient joints, Lower Kimmeridge Clay, Aulacostephanus autissiodorensis Zone, at Gaulter Gap, Kimmeridge Bay, Dorset, 16th April 2014

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Pyrite that appears to relate to early jointing in the Lower Kimmeridge Clay, Kimmeridge Bay, Dorset

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Another example of fairly late pyrite developed along part of the very first phase of jointing in the Lower Kimmeridge Clay, near Washing Ledge, Kimmeridge Bay, Dorset, 16th April 2014

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Yet another example of fairly late pyrite developed in an early joint, Lower Kimmeridge Clay, just east of Washing Ledge, Kimmeridge Bay, Dorset, 16th April 2014

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Shown below for comparison is early joint-controlled pyrite in the Top Copper Bed of the Blue Lias, in the Monmouth Beach to Ware Cliffs area, west of Lyme Regis, Dorset.

The Top Copper Bed in the Blue Lias, west of Lyme Regis, Dorset, 2011

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Examination of the above photographs, both from the Lower Kimmeridge Clay of Kimmeridge Bay, seem to indicate that the Sulphate Reduction Zone persisted deep enough for significant compaction, and apparently even the first phase of development of joints. This is compatible with evidence of compacted pyritised vertebrae of an ichthyosaur from the Upper Kimmeridge Clay at Rope Lake Head. Pyritised oysters in the same general part of the Lower Kimmeridge Clay as that of the pyritised ammonites shown above, indicates the sea-floor was not euxinic. The matters discussed are only in relation to the diagenetic zones of Irwin et al. (1977). She showed diagrammatically the sulphate reduction zone as ending at about 10 metres down. This seems insufficient for the features shown above and a greater thickness, in this particular case, is suggested.

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Kimmeridge Pyritisation that Postdated Early Compaction?

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An ammonite that descended to the sea floor on the venter, and was compacted and pyritised, Maple Ledge Shales, Lower Kimmeridge Clay, Kimmeridge Bay, Dorset, possible evidence for late sulphate reduction, 2014

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The inner whorls of this ammonite (edge-on) seem to have been compacted prior to pyritisation. This is supplementary evidence for the relatively late pyritisation. This is at least in terms of conventional views on the burial stage of sulphate diagenesis zone. No indication has been found here for very late hydrogen sulphide. There is no pyrite in the fault veins (and not usually dolomite, because they are post-fermentation or methanogenesis). At present this is just a possible refinement on the diagenetic history.

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Comparision with Blackstone Pyrite Nodules

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In contrast, the Kimmeridge Blackstone has large pyrite nodules that are completely unrelated to early jointing. In fact an obvious feature is the manner in which later jointing crosses and breaks the nodules. See the photgraph below (not from Kimmeridge Bay but from near Rope Lake Head):

The jointing pattern in the Kimmeridge oil shale, seen from above, and showing joints crossing pyrite nodules, near Clavell's Hard, Kimmeridge, Dorset, 31st March 2014

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[KB-32c end]
[END OF SEDIMENTOLOGY]

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KB-32e PALAEONTOLOGY




KB-32ePALAEONTOLOGY - Fossil Collecting
KB-32e PALAEONTOLOGY:

Fossil Collecting

Go also to separate webpage:

Kimmeridge Clay Fossils.

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Steve Etches, the famous fossil collector, out on the ledges at Brandy Bay, Kimmeridge, Dorset, 2012

Steve Etches the well-known collector and palaeontologist of the Kimmeridge Clay, Dorset, UK

Catalogue of the Steve Etches Kimmeridge Clay collection, Dorset

Generally, as noted elsewhere in these webpages, hammering is not allowed at Kimmeridge Bay. Notices now (2011) state that no fossil collecting is permitted. This applies to the public.

Fossil collecting here is only undertaken by a famous specialist. The fossil and palaeontological expert on the Kimmeridge Clay of Kimmeridge and elsewhere is Steve Etches. He has a remarkable collection of vertebrate remains, including those of pliosaurs, plesiosaurs, ichthyosaurs and pterosaurs. This collection is private, but with some specimens on display in the Heritage Centre at Lulworth Cove. It is hoped that the main collection of Steve Etches will eventually be on public display in the Kimmeridge area. For enquiries about fossil bones or any vertebrate remains it is best to contact Steve Etches.

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KB-33 PALAEONTOLOGY:

Ammonites

Go also to separate webpage:

Kimmeridge Clay Fossils.

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A crushed ammonite, associated with oyster shells, Lower Kimmeridge Clay, Kimmeridge Bay, Dorset, 16th April 2014

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Ammonites of Kimmeridge Clay

More ammonites of the Kimmeridge Clay

Aulacostephanus eudoxus, Kimmeridge Clay, Black Head area

A coarse-ribbed ammonite, still preserved as aragonite, in the Basalt Stone Band, a ferroan dolostone, Hudlestoni Zone, Upper Kimmeridge Clay, Rope Lake Head, east of  Kimmeridge Bay, Dorset, 31st March 2014

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KB-34 PALAEONTOLOGY continued:

Lower Kimmeridge Ammonites - Aulacostephanus

Aulacostephanus pseudomutabilis - an ammonite species from the Lower Kimmeridge Clay

The image above is of the ammonite Aulacostephanus pseudomutabilis , Lower Kimmeridge Clay, autissiodorensis Zone, Weymouth, Dorset. Ammonites of the genus Aulacostephanus can be recognised by the laterally compressed shell, the subinvolute coiling (i.e. partial overlapping) of the whorls, the fasciculate ribbing branching out from bullate tubercles on the umbilical (i.e. inner) shoulder. There is a prominant smooth ventral band, as shown in the image above. The genus is known from Europe and Russia and belongs to the superfamily Perisphinctaceae.

Examples of this genus (although most likely crushed and fragmentary) in the Lower Kimmeridge Clay which is well exposed from about the centre of Kimmeridge Bay to Broad Bench and beyond to the west. The tubercles and the branching ribs aid recognition; if an ammonite which fallen into the sediment on its venter, as occasionally happened, the smooth band on the venter will be easy to observe. This is not present in most other Kimmeridgian ammonite genera.

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KB-35 PETROLEUM GEOLOGY - KIMMERIDGE OIL WELL


KB-35 PETROLEUM GEOLOGY

Kimmeridge Oil Well

Location of oil well at Kimmeridge Bay, Dorset

The Kimmeridge oil well has been operating since 1959 and eventually will become an interesting historic relic - photo with Ian West, 2011

The nodding donkey or beam pump of the Kimmeridge No.1 oil well, producing from the Cornbrash at about half a kilometre down, Kimmeridge Bay, Dorset, 2010

A diagram showing the principles of the nodding donkey or beam pump, as at  Kimmeridge Bay, Dorset

Diagram showing the mechanism of a downhole sucker-rod pump

The Kimmeridge No. 1 Oil Well, of BP, at Kimmeridge Bay, Dorset, seen from the cliffs, 23rd October 2009

The small nodding donkey or beam pump of the Kimmeridge No. 1 oil well, Kimmeridge Bay, Dorset, 2005

Oil well at Kimmeridge Bay, Dorset, as seen outside the fence

Oil well at Kimmeridge Bay, Dorset

Contours on the top of the Cornbrash limestone reservoir, and information on boreholes of the Kimmeridge Bay oilfield, Dorset

Kimmeridge Oilfield - Introduction

Northwest of Kimmeridge Bay is the oil well of British Petroleum Co. Ltd. This well site is small with a single beam pump or "nodding donkey". It has a high wire-mesh fence around it but it can be clearly viewed and there is an explanatory notice provided by BP on the front. This is probably the oldest continuously producing well site in the UK and was drilled in 1959. This was the original successful Dorset oil well before the much large Wytch Farm oil discovery was made. It has produced 350 barrels per day from fissured shelly limestone of the Middle Jurassic Cornbrash at about 320m depth. Production now is only 80 barrels per day (12,720 litres), according to the BP information notice. The oil is collected twice a week by tanker and transported to the main BP Gathering Station at Wytch Farm near Corfe Castle. It is then stabilized and exported by pipeline to a terminal at Hamble on Southampton Water. From there it travels by tanker to oil refineries for production of high quality fuels.

The pump is a conventional beam pump or sucker-rod pump, although this one is very quiet because it is electrically driven rather than having the more common diesel engine for power. At depth in the anticline, at about the level of the Cornbrash, both oil and gas enter the casing which is perforated (this is usually done by firing shots out of the well).The oil is pumped up by a long string of narrow rods within the tubing (the inner piping) of the well on a system operated by valves. There is a significant weight of rods and oil to be lifted at each movement of the beam so there are two heavy, half-moon-shaped, counter-weights which rotate. You can see these in the photograph. The gas rises to the surface between the tubing and casing and is piped away separately at the surface. There is, according to the notice, intention to use the gas for fuel in the future to provide energy to drive the pump mechanism. Some bushes or small trees are being grown in front of the oil well and this single pump causes very little disturbance to the environment and, indeed, is something of a tourist attraction. Had a large quantity of oil been found here then more screening of the pumps by trees, as at Wytch Farm, might have been necessary.

Of course it is obvious that the oil is not coming from the Kimmeridge Clay which is at surface in the cliffs at Kimmeridge. However, such an origin is sometimes a misconception amongst the non-geological public, probably because the Kimmeridge Clay is the major source rock for the oil in the North Sea. There is no liquid oil in the exposed Kimmeridge cliffs, only oil-shale and bituminous shale containing kerogen, a brown waxy substance. The Kimmeridge Clay at Kimmeridge is not thermally mature (it has not been suffficiently heated by sufficiently deep burial at this particular locality). The real source of this oil is probably the deeper-buried, Lower Jurassic (Lias) bituminous shales in the offshore English Channel Basin.

Addendum - Sinking Land at Kimmeridge shown by Satellite

Satellite data on the rising and falling of the ground surface in southeast Dorset, including the Sandbanks Peninsula, and also the Kimmeridge and Durlston Head region etc., Dorset, southern England, date of the measurements unknown, but recent

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The Oil Field - General

The search for oil in Dorset started in 1935. The first prospecting licences under the 1934 Petroleum Production Act were granted to the D'Arcy Exploration Company, who worked with BP. Exploration wells on whaleback anticlines at Poxwell and Portsdown in 1936 were unsucessful. Generally oil was not discovered in quantity in the Tertiary anticlines, which were compared to those in Iran, from whence Britain obtained its oil. It is now known that the oil of the large oilfields like Wytch Farm are in concealed fault traps of Cretaceous age (Late Kimmerian), not generally in the Tertiary anticlines. These can only be detected by seismic methods.

The Kimmeridge field was discovered in 1959, long after the initial search for oil in Dorset. It began producing in 1961 ( (Gluyas et al. 2003). For a short time the production was up to 350 barrels a day, but later declined to about 100 BOPD and is now about 60 BOPD. The Kimmeridge Field was developed under a Mining Licence (ML5) granted in 1964. The field still produces under that licence and it is due to expire in 2014 (Gluyas et al.). Between 1959 and 2000 six wells were drilled in Kimmeridge Bay (these are shown on a map above and listed below).

The reservoir is a fissure system in the Middle Jurassic Cornbrash Limestone. This belongs to the top Bathonian to basal Callovian, and includes the zones of Cydoniceras discus and Macrocephalites macrocephalus. It is about 27 metres thick here. The nearest surface exposures are at the shores of the Fleet Lagoon (Shipmoor Point near Abbotsbury, access difficult; Butterstreet Cove, near East Fleet, access easy).

History of the Oil Well

The search for oil in Dorset started in 1935. The first prospecting licences under the 1934 Petroleum Production Act were granted to the D'Arcy Exploration Company, who worked with BP. Exploration wells on whaleback anticlines at Poxwell and Portsdown in 1936 were unsucessful. Generally oil was not discovered in quantity in the Tertiary anticlines, which were compared to those in Iran, from whence Britain obtained its oil. It is now known that the oil of the large oilfields like Wytch Farm are in concealed fault traps of Cretaceous age (Late Kimmerian), not generally in the Tertiary anticlines. These can only be detected by seismic methods.

Volume of the Oil Reservoir

It is interesting to note that by 1986 the well had produced 2.7 x 10 6 bbl House (1993) . This was thought to be greater than the original volumetric capacity of the reservoir according to ( Stoneley and Selley (1986). They considered that the reservoir was being replenished by migration of oil from lower horizons. However, Evans, Jenkins and Gluyas (1998) in a paper entitled - The Kimmeridge Bay oilfield: an Enigma Demystified - have provided new information. New calculations have made on the reservoir. Further details are given below, in the Structural Closure section. The oil column was known to be 14.3 metres (47 feet) to 17.4 metres (57 feet) thick in about 20 metres of Cornbrash under a seal of Oxford Clay.

Porosity

The porosity of the Cornbrash limestone here is very low (around 1 percent) and permeability is negligible. However fracture porosity is present, and this not well understood. Different estimates were made for the average porosity including that provided by the fractures. It is very difficult to average out the variable volumes of fracture porosity in relation to the volume of almost non-porous limestone. The details of the fractures are not known, and the extent of fracture porosity is one of the uncertain variables.

Structural Closure

The main structure is a tight, structurally complex, monoclinal faulted fold, known as the Purbeck Disturbance Gluyas et al. (1998). The Kimmeridge trap is south of this. The northern limit of the trap, as shown above, is an east-west fault. The other limits are dips, east, west and south off the dome-like structure. A problem lies with the closure, in effect, the size of the trap or structure from which oil cannot escape.

This has been difficult to calculate because of uncertainties regarding fracture porosity. Different closures have been calculated, usually larger, and sometimes much larger, than the originally mapped closure of 120 to 160 acres. Problems of estimating closure is why the hypothesis of resupply or of much extended fractures systems originated.

Evans, Jenkins and Gluyas (1998) having studied the decline behaviour believe that the reservoir contains a finite ultimate recoverable reserve of 3.5 million barrels. They have stated that: "Despite being the most popular myth surrounding the field, the reservoir is neither fed from a deeper accumulation nor is migration into the field still occurring. Neither is oil being produced from a single isolated fractured zone which was only penetrated by the first well."

They point out that if migration was continuing then the production history would not show the conventional decline which it does. The well results are consistent with a fractured reservoir contained within an anticlinal trap. Nevertheless the extent of the reservoir system and effective porosity are still not fully understood. All other similar traps in the Wessex Basin seem to have either been breached or never been charged. Their final remarks are: "Perhaps, like the Wytch Farm field to the north, it is the sole survivor of a much more significant play which was wiped out during inversion" [inversion was the uplift of the basin to the south].

The Low Pressure Problem

A special aspect of the well, and one which has generated some discussion, are the abnormally low reservoir pressures, actually below hydrostatic. The initial pressure in Kimmeridge - 1 well was 400 PSI at 520m SS. This pressure would be expected in a reservoir several hundred metres shallower. Brunstrom (1963) suggested that oil may have been sealed in the fracture prior to Miocene folding and that the fissures were physically enlarged during folding leading to reduced pressures. Evans, Jenkins and Gluyas (1998) comment that some such explanation is necessary because there is no history of recent burial which might otherwise explain the pressures.

The Succession in the Boreholes

Other boreholes have been drilled in the Kimmeridge Bay area and although not useful in terms of production have provided more information. See Evans, Jenkins and Gluyas (1998) for details. The succession in the original borehole was given by Brunstom, 1963 as follows:

Lower Kimmeridge Clay

0-243m

Corallian

243-340

Oxford Clay

340-519

Kellaways Beds

519-537

Cornbrash

537-564

Forest Marble and Fuller's Earth

564-889

Inferior Oolite

889-909

Bridport Sands

909-1042

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KB-36 PETROLEUM GEOLOGY continued:

The Kimmeridge Wells

(Summarised from Evans et al. and Gluyas et al. See these papers for details.)

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Broadbench 1.

1936-1937. Intended to reach Bencliff Grit, Corallian, because of the oil in that at Osmington Mills. Found a joint in Sandsfoot Grit wet with light oil, but did not get to the Bencliff.

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Broadbench 2. (later renamed Kimmeridge No.1)

Oil oozed from partially-leached calcite veins in the Cornbrash at 512m. subsea. (Why were the calcite veins partially leached?). Production tests yielded 30bbl/day. Two acid treatments caused the well to flow briefly at the very high rate of 4300 barrels a day. Completed as a producing well. This is now the producing Kimmeridge No.1, with the nodding donkey and shown in photographs above.

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Kimmeridge No.2.

Drilled 1960, east of Kimmeridge No.1. Top Cornbrash at 583m. Some oil in sands within the Oxford Clay. Very small quantity of oil from Cornbrash. Pressures showed Oxford Clay and Cornbrash in communication.

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Kimmeridge No.3.

Drilled 1959-60, prior to Kim 2. Location 762m. to SW of Kim 1. Small test production from Cornbrash.

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Kimmeridge No.4.

1960. Mechanical breakdown.

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Kimmeridge No.5.

In 1980, post Wytch Farm Sherwood discovery. Weak gas shows throughout Jurassic. Important for going into the Triassic Sherwood Sandstone at 2272. Sherwood has only weak oil shows and reservoir quality was poorer than at Wytch Farm. (Useful information on Sherwood).

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The RGGE (Rapid Global Geological Events) Boreholes.

Three continuously cored boreholes for research were drilled through the Kimmeridge Clay by 2000. Two boreholes were in Swanworth Quarry, near Worth Matravers, and the third, Metherhills No.1 was at Metherhills, adjacent to the road down to Kimmeridge Bay. Metherhills No.1 went into the Sandsfoot Clay of the Corallian. These boreholes were not intended for petroleum exploration. See Gallois (2000) for details.

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[END OF PETROLEUM GEOLOGY]

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KB-36d QUATERNARY - Weathered Brown Clay - Head


The weathered zone of brown clay at the top of the Kimmeridge Clay cliffs,  Kimmeridge Bay, Dorset, 16th April 2014

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At the top of the cliffs in Kimmeridge Bay is two or three metres of a weathered brown clay, quite unlike the hard black shale and mudstone of the Kimmeridge Clay underneath. This is classified on the 2000 Edition of the Swanage Geological Survey Sheet 342 and part of 343 as "Head". It is not shown a separate geological unit on the old editions, which simply map Kimmeridge Clay in the area. Head is a general term for Quarternary deposits of debris on top of the "solid" geological formations. In the general area there is also old landslip debris, usually at the base of and on the slope of the hills that are capped with Portland Stone. At Kimmeridge Bay there is no obvious extraneous debris. There is no abandance of Portland limestone or chert debris is the cliff tops, only the brown clay. This affects the beach. There is a remarkable lack of supply of hard clastics such as chert or flint. It a reason for good exposure of the Kimmeridge Clay in ledges and for the unusual feature of dolostone boulders on the beach. Contrast this situation with other Kimmeridge Clay cliffs, as at Ringstead and at Black Head, near Osmingto Mills. Those cliffs are not vertical, but sloping, and there is much hard clastic material,such as chert derived from the Upper Greensand on the beaches.

The brown clay, a type of Head, is not described in detail here. It is easily seen in general in the cliff tops, as shown in the photograph above, but it is not easily accessible. The exposures are generally at dangerous cliff edges. The details of the brown clay are not known. At its top archaeological remains, relating to former oil shale working, may be present in places.

A question remains, though, as to why no stoney or cherty head or other deposit has not been washed onto the Kimmeridge Clay of Kimmeridge Bay area in Pleistocene or early Holocene times. The purity of the bay, as a place of only Kimmeridge Clay is an unusual feature. There may be some special explanation for this. (Do you know of similar localities elsewhere?)




KB-37 KIMMERIDGE BAY - SPECIFIC LOCATIONS


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KB-37 SPECIFIC LOCATION:

The Oil Shale Port
Southeastern Corner of Kimmeridge Bay

Map showing Relics of oil shale industry at the southeastern corner of Kimmeridge Bay and near Hen Cliff and Clavell Tower

The old shale tips at at the southeast corner of Kimmeridge Bay, with Clavell Tower,  aerial photo 2001 by Channel Coastal Observatory

Former industrial area on the southeast corner of Kimmeridge Bay, Dorset

Most of the Kimmeridge oil shale and probably a large part of the waste shale was transported by tramways to the southeast corner of Kimmeridge Bay. There are shale tips here of various dates. The lower ones have been used to make a type of platform on which is the car park and the huts, including the marine centre. In the past this had been a location of alum works and later a small port for the shipping of oil shale, the Kimmeridge Blackstone.

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KB-38 SPECIFIC LOCATION:

Clavell Tower

(For more on Clavell's Tower and Hen Cliff beneath - go to Hen Cliff, Kimmeridge webpage.

Clavell's Tower at  Kimmeridge Bay, Dorset, 9 Oct 2005

Clavell's Tower at Kimmeridge Bay, Dorset, seen at dusk, 9 Oct 2005

Clavell's Tower at dusk

Clavell's Tower at night, Kimmeridge Bay, Dorset

Kimmeridge Bay, Dorset, seen from the rebuilt Clavell Tower

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Shown for general interest are some photographs of Clavell's Tower (or 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.

A low sun over the Isle of Portland as seen across and beyond Kimmeridge Bay, Dorset, March 2006

Approaching squall in the evening, Kimmeridge Bay, Dorset

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[END OF SPECIFIC LOCATIONS]

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KB-39 GEOARCHAEOLOGY

Re. The Flats Dolostone Bed
(Roman Use of the Kimmeridge Dolostones)

A geoarchaeology student investigates the Flats as a probable source of dolomite tesserae, used by the Romans, Kimmeridge Bay, Dorset

There has been appreciable quarrying of Kimmeridge dolomite by the Romans to provide the tesserae or small blocks for making ornamental mosaic floors (White, 2003; Allen and Fulford, 2004). At best (i.e. the Flats) it is an unusual tough and resistant, grey, carbonate rock; a composite of equal-sized dolomite crystals with evenly-spaced micro-lenses of brown waxy, long-chain hydrocarbons (kerogen). It has been naturally constructed with almost zero porosity under the pressure of a kilometre of overbruden. Lacking any quantity of quartz it can be worked easily by chesil or saw.

Kimmeridge dolomite has been used very extensively over southern England and into Wales. At Insula IX, northwest of the Forum-Basilica of Silchester in Northern Hampshire, about 71% of the flooring is from kerogenous, ferroan dolomite beds of the type which form the Kimmeridge Ledges at Kimmeridge. Although the Kimmeridge Clay is also exposed on the coast at Ringstead, near Weymouth, the dolomite beds are not developed there. At the Isle of Portland the Kimmeridge Clay is not well exposed and the dolomite beds have not been recorded there. Thus a source from Kimmeridge Bay or nearby seems almost certain. Just which dolomite bed or beds was used is less certain, but the Flats Dolomite is being investigated, amongst others, by Pari White of Birkbeck University.

Allen and Fulford (2004) have provided photomicrographs, X-ray diffraction data and descriptions of the Kimmeridge dolomite tesserae. I have compared their compositional data from the various southern England sites with data from Bellamy (1980). The dolomite percentage within individual tesserae samples ranges from 77% - 92%. The highest dolomite percentages, which are particularly noted in the London samples, are compatible with an origin in the Flats Dolomite Bed, which seems to have the highest dolomite percentage at Kimmeridge. Other beds which have to be considered though as a source for some dolomite tesserae include (upwards) the Washing Ledge Dolomite Bed, Maple Ledge Dolomite Bed, Yellow Ledge Dolomite Bed and Cattle Ledge Dolomite Bed (which naturally distintegrates into small blocks). Others that are higher in the sequence cannot all be eliminated, as yet, but are usually argillaceous and with a lower percentage of dolomite. The frequency of occurrence of fish bones in the various beds is not known at present. They occur in the Rope Lake Head Stone Band, but may well be in others. Fish bones have been observed in various Kimmeridge dolomite tesserae, and in one case, at Insula IX, Silchester, there are "especially skull bones" (Todd and Morris in Allen and Fulford, 2004). At the time of writing Pari White is intending to make a more detailed investigation of the source of the Kimmeridge dolomite at Fishbourne and elsewhere.

In Roman times was about 2m lower than at present. Probably the coastline was in general between half and one kilometre further seaward. Thus, because of strike considerations major Roman oil shale workings in the cliff (see Calkin, 1955) would have been southeast of Rope Lake Head. Although the coastal details would have been different, the Flats Dolomite Bed would have been accessible and could have been worked somewhere in the Charnel, Broad Bench to Hobarrow Bay area. As discussed below, Kimmeridge oil-shale was cut on lathes to make armlets nearby at Gaulter on the present cliff top of Kimmeridge Bay Calkin, 1955).

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KB-40 GEOARCHAEOLOGY continued;

Oil Shale Armlet Workshop;
at Gaulter, Kimmeridge Bay

The site of the Roman oil shale workshop just to the west of Gaulter Cottages, Kimmeridge Bay, Dorset

Stages in the manufacture of armlets by the Romano-British at Kimmeridge, Dorset

A Roman mosaic at Kourion, near Akrotiri, Cyprus, showing the young woman KTICIC, the Founding Spirit or Creation,  wearing an armlet and carrying a measure of the Roman foot

On the cliff top at the northern side of Kimmeridge Bay near the Gaulter Cottages is an important archaeological site. This is one of the places where the Romans worked the Kimmeridge Blackstone to produce polished, black armlets or bangles, using a primitive lathe. These armlets, like those of jet, were probably believed by the Romans and the local tribesmen to have had magical properties and were frequently worn. The oil shale or Kimmeridge Blackstone, from which they were made, is not present within Kimmeridge Bay but crops out in the cliffs both east and west of the bay. Calkin, (1955, p.48) has excavated the site and provided a brief account.

"Gaulter, near Kimmeridge (Site 2):

At various times between 1939 and 1947 I have excavated some 80 sq. yards of the shale workshop site, just within the parish boundary of Steeple, at Gaulter near Kimmeridge. This area extends for some 12 yds. along the cliff, and is all within 7 yards of its edge. The site, which is shown on the map in Dr. Davies' paper, is about 25 yards west of the back gardens of Gaulter Cottages. Trial trenches showed that the floor died out within a few yards in three directions, but it must have extended for some distance seawards.
The workshop debris consisted almost entirely of worked shale and worked flint. The turning was done by means of flint tools, to be described later (p. 60). An abundance of waste flint showed that knapping was done on the spot. The commonest shale objects were the waste cores, about 240 all told, of which all but two probably belonged to Class C. Whereas the flint tools were widely dispersed over the whole site, the cores were often concentrated, groups of 90,44. 16, 16, and 12 being found in areas little more than one foot across. The first three of these concentrations also included 58 fragments of armlets. They were all plain and undecorated, and of a light variety generally less than 0.2 inches in thickness. Their jagged internal edges showed that they had been broken in manufacture. In addition there were a few discs prepared ready for turning. Here also were found two pebbles, probably of the local light grey cement-stone, with flat blackened facets, evidently burnishers. From elsewhere on the site came a worn piece of grit-stone about 3 x 0.8 x 0.25 inches, admirably suited for smoothing down the inside of the rings after removal from the lathe (Plate IB).
There was a considerable quantity of waste shale, the largest pieces, some dozen in all, being about one inch thick, and varying in length and breadth from six to twelve inches. Nearly all were badly laminated, and fell to pieces upon drying. Three such slabs, two lying one on the other, and the third standing upright beside them, were closely associated with the group of 44 cores. These slabs recall Hutchins' statement that the coal-money at Kimmeridge was generally found enclosed between two stones set edgeways, and covered with a third. We are here perhaps concerned with some structural arrangement to do with the lathe. The first three groups of cores already mentioned were quite close together, their centres being only 3f, 3f and 4f ft. apart.
Except for occasional irregular small groups of large cobble stones, and a few pieces of burnt daub, no structural remains came to light. In every case any relics of walls in situ appeared to belong to the Iron Age occupationl. The eastern end of the site had been greatly disturbed by rabbits. Pottery was scarce, mostly small fragments of coarse wares of the 2nd and 3rd centuries. The finds included two scraps of Samian, two of New Forest ware, and a small piece of glass. There was one large piece of an olla with obtuse-angled lattice ornament. The only stratification observed was in that of a grave which had been dug through part of the working floor. A coin of Carausius found in the grave-pit shows that this part at least of the working site was abandoned well before the end of the 3rd century. No other coins have been recorded, so it appears that the shale workers lived entirely by barter. Half a mile to the north there survive traces of a Celtic field system."

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[END OF GEOARCHAEOLOGY]

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MISCELLANEOUS




. KB-41 MISCELLANEOUS:

An Odd Fish of Kimmeridge!

Unusual fish at Kimmeridge

The Kimmeridge coast is a marine nature reserve and is of interest and importance because of this. It has a good marine fauna and flora and is used for educational purposes. Thus it is appropriate that I mention a dead modern fish of unusual appearance that I found in 1979 whilst doing geology here. It was washed up on the rocks between Clavell's Hard and Rope Lake. It was low on the shore just here, but to photograph it I put it on this boulder of Kimmerigian dolomite, alongside a large-size geological hammer for scale.

Twenty-two years later it seemed time to ask what it was! I thank Dr Ken Collins of Southampton Oceanography Centre for identifying this as a lumpfish or lumpsucker - Cyclopterus lumpus. He has made a video of a male of this species tending a clutch of eggs glued to a rock ledge in Kimmeridge Bay, nearby. For more information on this unusual fish see: Norge - Seafood from Norway: Lumpfish and Fisheries and Oceans, Canada, - Coastal Zone Species Profile No. 8.

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[END OF MISCELLANEOUS]

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BIBLIOGRAPHY



KB-42 - BIBLIOGRAPHY:

Kimmeridge and Kimmeridge Clay

Please see separate Bibliography and References

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[END OF BIBLIOGRAPHY

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KB-43 ACKNOWLEDGEMENTS

In writing this webpage much reliance has been placed on the excellent work of Dr. Jon Bellamy on the Kimmeridge dolomite beds. I am very grateful to Dr. Jim Andrews for discussion regarding the megapolygons of the Flats Dolomite Bed and for providing information on a long series of field projects for students at Kimmeridge. I much appreciate helpful discussion with various geologists on the coast at Kimmeridge. Field trips with students of London South Bank University have been very helpful. Discussion with participants on field trips to Kimmeridge arranged by various geological organisations and university parties is much appreciated. In particular I acknowledge guidance from the Kimmeridge expert, palaeontologist and fossil collector - Steve Etches. I thank the geoarchaeologist Pari White for help on archaeological matters and for help with field work. Much essential information for this webpage comes from the key work of Dr. Ramues Gallois, the Kimmeridge Clay expert, and much use has been made of the major publication - Cox and Gallois (1981), which every Kimmeridge geological visitor should have at hand. Alan Holiday has very kindly provided me with good photographs of this locality. I am very grateful to Madelaine Simpson for kindly allowing me to use photograph of hers taken from Clavell Tower in 2012. I much appreciate the advice and help of my daughter, Tonya Loades of Bartley West, Chartered Surveyors.

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Copyright © 2016 Ian West, Catherine West, Tonya Loades and Joanna Bentley. All rights reserved. This is a private, academic website intended to be useful for research, reference and educational purposes. Images and text may not be copied for publication or for use on other webpages such as MOOCs or for any commercial activity. A reasonable number of images and some text may be used for non-commercial, non-charged, non-online and non- published academic purposes, including field trip handouts, student projects, dissertations etc, providing the source is acknowledged. All images so used must contain the original caption, including the copyright statement. Some images are not those of the author and the copyright is that of the original photographer and these are not for any use without specific permission from the source photographer. This particularly applies to aerial photographs, but also to some sets of field photographs.

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.

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KB-44 - Author

Dr Ian West, author of these webpages

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.