INTRODUCTION:

BR1 - BRIDPORT SAND FORMATION - STRATIGRAPHY -

Jurassic Palaeogeography

A map is provided above showing the position of the shelf seas of Europe in the Jurassic. Because this is a very generalised and not for a specific time in the period it should not be used as a precise marker of palaeolatitudes. It does indicate the area of extensional tectonics and basin development at the northeastern end of the Atlantic at that time. Not only was the formation of rifted basins responsible for much accumulation of clay, limestone and sandstone sequences of the Jurassic. In addition, the breakup of the old supercontinent Pangaea led to an increase in the number of spreading centres in the oceans (Lemon, 1993). This resulted in a consequent displacement of seawater from the oceans producing a rise in sea-level. Both the rifting and this process caused the transgression of Jurassic marine deposits over Permo-Triassic, desert red-beds.

Also above is a simplified palaeogeographic map showing the generalised distribution of sea and land in the British area during Early Jurassic times. The southern part of the Atlantic Ocean was opening to the southwest, but the North Atlantic was not open at this time. Shallow shelf seas with some locally deeper basins occupied much of the British region. This map is to set the scene in broad terms and the details varied at different times within the Early Jurassic.

.

BRIDPORT SAND FORMATION:

Introduction - Stratigraphy

BRIDPORT SAND FORMATION ("BRIDPORT SANDS"):

The Cliff Exposure

For more on the Bridport Sands see the:
East Cliff, Bridport section of Bridport Sands

Burton Cliff shows Bridport Sands with cyclical carbonate-cemented horizons. The sandstone is blue-grey when unweathered but has a thing weathered surface layer of yellow. Here, fine-grained pyrite is oxidised to limonite or goethite. The sands contain belemnites and trace fossils and occasional moulds of ammonites. Aragonite shells have been dissolved away.

After a long phase of slow weathering the harder, calcite-cemented bands project and show honeycombe weathering. When, however, there is a cliff-fall as has happened here, then a flatter and smoother cliff face is produced. It requires a significant but unknown interval of time for the hard bands to project again.

The Inferior Oolite is present at the top of the cliff. There are many fallen blocks of this on the shore at Burton Cliff. The limestone is much more fossilferous than the sandstone but marine fossils can be found in both. In the far distance are the cliffs east of West Bay . These are also of Bridport Sands and further information on this formation is provided in the Bridport, West Bay website .

Here is the western end of Burton Cliff. Here there is no Inferior Oolite as the cliff top descends. The valley in the middle distance is Burton Freshwater where the River Bride reaches the beach. Beyond the river is a caravan park. East Cliff of West Bay , also of Bridport Sands is in the distance.

The Bridport Sands here dip at a very low angle, and are, in fact, almost horizontal. They are prone to occasional topples, perhaps along joints that are parallel to the cliff. Such falls, however, occur only at rare intervals. These used to be very rare but now they are common with several accumulations of debris at the foot of the cliff. After such a fall the particular part of the cliff does not show the projection of the hard beds. Only after an interval of many years does weathering and erosion by wind and rain wear back the softer material and leave the carbonate-cemented beds protruding. The debris here seems to be mainly Bridport Sands without much or any Inferior Oolite. Similar cliff falls occur from time to time at East Cliff, West Bay , although rock piles on the beach are usually smaller at that locality.

.

For more information on sedimentology of the Bridport Sand Formation, please go to the Sedimentology part of the East Cliff, West Bay, Bridport webpage: -

BRIDPORT SANDS - SEDIMENTOLOGY (START).

.

BRIDPORT SANDS:

Sedimentary Structures and Trace Fossils - Burton Cliff

(this section has also been added to the: Bridport Sands East Cliff, West Bay webpage.)

.

.

.

For information on the palaeontology of the Bridport Sand Formation, please go to the Palaeontology part of the East Cliff, West Bay, Bridport webpage: -

.

BRIDPORT PALAEONTOLOGY.

.

B3a BRIDPORT SAND FORMATION

Fossils - Belemnites and Ammonites

The Bridport Sands are very bioturbated. Thus Trace fossils are common, and may be seen weathered out in the honeycombe weathering (particularly Thalassinoides). Body fossils are not easily found, except for belemnite guards. Belemnites are well-preserved because of the calcite mineralogy, which is relatively stable in meteoric water (providing, of course, there is no acidic dissolution). Aragonite is the mineral component of most most bivalve shells, except oysters and some members of the Scallop family. Gastropods have aragonitic shells. Ammonites, which also have aragonitic shells, are present, but usually only as internal moulds without preservation of the aragonite shell (and usually without neomorphic replacement by calcite in these strata). Ammonites are not very easy to find, but the opportunities for discovery are greater at the top of the sequence near to the Inferior Oolite (where there is more calcareous and somewhat condensed sequence).

BR3b - BRIDPORT SANDS

Fossil Collecting

The cliffs of West Dorset, particularly the clay cliffs are famous for their fossils. The section at West Bay described here is not usually a place for large-scale collecting. Those interested in fossil collecting from any part of the coast under National Trust and Charmouth Parish Council Ownership between Lyme Regis and Hythe Beach at Burton Bradstock, should consult the fossil collecting code of conduct for that area.

Introduction

For a listing of the beds and thicknesses see the vertical succession section given below. A general description and specific aspects of interest in the Inferior Oolite will be discussed here.

This limestone is normally seen when material from the top of the cliffs has fallen, as shown here. The Inferior Oolite is not usually safely accessible in situ. This is not a problem, however, because large blocks of limestone fall and most of the units of the Inferior Oolite are recognisable. Some blocks are a little difficult to identify, though. If you encounter a large block, look for a conspicuous feature like the snuff boxes, and then decide which way up the block is. This fall has brought down Inferior Oolite blocks. At the top of the cliff there is Fuller's Earth visible above the limestone.

INFERIOR OOLITE:

Burton Lane Section

In the past there was a good exposure of the Inferior Oolite in Burton Lane. This locality is south of the village and is a lane leading from the garage (SY 487983) southward towards the cliff top. The Bridport Sands can be seen behind the garage and are also exposed at present in places in the lane. Unfortunately, at the time of writing (August 2012) the Inferior Oolite is not exposed in the lane, but is overgrown. The lane is has houses on both sides and is not a place for hammering. It used to be used as a reference section for the stratigrahy of the Inferior Oolite. Richardson (1928) described the section.

INFERIOR OOLITE:

Succession - Introduction

Middle Jurassic Zonal Listing

(Note: This is given mainly for reference for use with following diagrams, photographs and text. This particular version is based on House (1993) and from time to time might need updating. It is an ammonite zonal scheme, and some of the ammonites, like Kosmoceras jason and Parkinsonia parkinsoni are well-known to geologists in general; some uncommon forms are not familiar to other than specialists.)

_____________________________________________

CALLOVIAN (top of MJ, with UJ Oxfordian above)

Quenstedtoceras lamberti
Peltoceras athleta
Erymnoceras coronatum
Kosmoceras jason
Sigaloceras calloviense
Macrocephalites macrocephalus

BATHONIAN

Clydoniceras discus
Oppelia aspidoides
Proceratites hodsoni
Morrisiceras morrisi
Tulites subcontractus
Proceratites progracilis
Asphinctites tenuiplicatus
Zigzagiceras zigzag

BAJOCIAN
[Note, for reference, that in old accounts (eg. Arkell, 1933) the Bajocian zones are from bottom to top: Strenoceras niortensis, Garantiana garantiana, Strigoceras truellei, Parkinsonia schloenbachi.]

Parkinsonia parkinsoni [Parkinsonia schloenbachi]
Strenoceras garantiana [Garantiana garantiana]
Strenoceras subfurcatum [Garantiana subfurcatum]
Stephanoceras humphriesianum
Emileia sauzei [Otoites sauzei]
Witchellia laeviuscula
Hyperlioceras discites

AALENIAN

Graphoceras concavum [Ludwigella concava]
Ludwigia murchisoni
Leioceras opalinum

________________________________________________

[base of Middle Jurassic. Zone of Dumortiera levesquei of the top Toarcian (Lower Jurassic) lies beneath.] [note: that in old accounts there was once a zone of Ancolioceras and a zone of Tmetoceras scissum below the Ludwigia murchisoni zone.]

_________________________________________________

Some brief comments on the succession shown in the diagram above and in the cliffs are given below. They are based on the summary in Davies (1956) , Perkins (1977) and House (1993) and these in turn are modified from the early work of Buckman (1910) and Richardson (1928) . This is a condensed sequence and full of non-sequences or disconformities (Footnote - In plain language this means that the sequence is much thinner than normal - "condensed"; and there were many gaps in deposition - "non-sequences" , often with some erosion on the seafloor ). The thickness here of nearly 4 m. contrasts with the 110m in the Cotswolds. The reason that it is condensed here is that it is on a structural "high" almost on the east-west line of the Wytch Farm oilfield high. Offshore it is much thicker, 19.3m in Lyme Bay ( Penn, Dingwall and Knox, 1980 ). The sequence seen at Burton Bradstock should be recognised as abnormal, and not a typical Inferior Oolite succession. It is so condensed, that it is reminiscent of the Lower Jurassic, Junction Bed at Eypemouth. It is probably the result of an early phase of the Late Kimmerian movements (extensional - pre the development of the North Atlantic Ocean).

INFERIOR OOLITE:

Succession - Listed Sequence (top-down)

Fuller's Earth Clay (at the top)
The lower part of the Fuller's Earth Clay, 0.61m seen, with about 0.09m of ferruginous marl, the Scroff, at the base; both yielding Oppelia fusca and "Perisphinctes".

Upper Bajocian

The First Bed, including the Zigzag Bed
(note the quarrymen's method of numbering down)
Blue-centred nodular limestone. Ammonites - Zigzagiceras zigzag, Oppelia and Parkinsonia. Belemnopsis, bivalves and gastropods. 0.15m.

The Second Bed, including the Sponge Beds
Massive yellowish limestone with much brown earthy matter. Ammonites are often rotten. Stout Parkinsonia, Terebratula, Rhynchonella and sponges. This is divided as follows:
Massive limestone - 0.63m.
Sponge Beds - Marl with two limestone partings, crowded with sponges, Clypeus, brachiopods, bivalves - 0.36m
Rubbly limestone with similar fossils, including large Nautili - 0.40m.

The Third Bed
Limestone divided as follows:
Blue grey limestone, rubbly top, attached serpulids, the brachiopod -Sphaeroidothyris sphaeroidalis, the echinoid - Clypeus, and bivalves - 0.56m.
Astarte 'obliqua' Bed. Crumbly brown ironshot limestone crowded with fossils. - 0.10 m (including the impersistant conglomerate beneath)

Lower Bajocian

The Red Bed, sensu lato

- a little less than one metre and comprising the subdivisions listed below

Red Conglomerate. Conglomerate of ironshot rock, patchily present with poorly preserved ammonites. - Thin and of variable thickness. Remanie bed of the Stephanoceras humphresianum Zone. 0-0.14m.

Red Bed, sensu stricto. Hard massive grey limestone, the top irregular and stained red with iron (including at the base - limestone with brownish limonitic granules. - 0.18m.). Zones of Witchellia laeviuscula and Emileia sauzei (above). Early laeviuscula is represented by a diastem (non-sequence) ( House (1993)). - 0.8m (thickness in Burton Lane)

Snuff Box Bed. Limestone, bluish, limonitic ooids and large limonitic concretions, the snuff boxes, near the base. Hyperlioceras discites Zone. Ammonites - Stephanoceras, Witchellia, Sonninia. - 0.08m.

.

Aalenian

Yellow Conglomerate. Yellow marl with small pebbles and rolled fossils, reworked and eroded from earlier strata. - 0.04m.

Scissum Beds (or Bottom Bed). Grey sandy limestone with the ammonite Tmetoceras scissum. Effectively the top of the Bridport Sands - 0.30m.

Bridport Sands (part). - about 0.2m? (see Richardson, 1928 and House, 1993 re the Burton Lane section inland of the cliff)

Toarcian

Bridport Sands below (thick).

INFERIOR OOLITE:

More Details

This is a fallen block of the Snuff Box horizon of the Red Bed, perhaps the most well-known stratum of the Inferior Oolite here. This bluish, "ironshot oolite", only 8 cm thick, is easily recognised by the large, brown, limonitic concretions, known as "snuff boxes". The limonitic ooids, which it contains, are quite large and conspicuous.

The strata are largely oxidised at the surface and most iron is in the state of limonite. Offshore, to the south in Lyme Bay, the Inferior Oolite is thicker (19.3m) and here much berthierinte ("chamosite") is present in addition to limonite in the succession ( Penn, Dingwall and Knox, 1980 . It should not, therefore, be assumed that the snuff boxes and associated ferruginous strata were always in brown oxidised condition. The recent cliff fall has revealed that green iron minerals still survive, as shown in the photograph above. This green substance has not be investigated yet to determine whether it is the green iron-ore berthierine (as is more probable) or is the iron-bearing clay mineral - glauconite.

The snuff boxes seem to be formed of algal stromatolitic (microbial) laminations of unusual ferruginous type centred around bivalve shells and other nuclei ( Gatrall et al ., 1972 ; Radley, 1986 , Palmer and Wilson, 1990 ) They have been regarded as a type of oncolite (or oncolith). They occur within in the zone of Hyperlioceras discites of the basal Bajocian. Ammonite found in this bed include species of Stephanoceras, Witchellia and Sonninia. (Photograph by Gareth Lloyd, 27.7.96).

This fallen block of Inferior Oolite limestone is probably from the Sponge Bed. The Sponge Bed is a marl with two limestone partings, crowded with sponges, the echinoid Clypeus, brachiopods and bivalves etc. It is 0.36m in thickness. It is from the higher part of the Inferior Oolite, the Upper Bajocian. See the section on succession .

[end of 3.3 Inferior Oolite - Details]

INFERIOR OOLITE:

Ammonites

Ammonites are quite numerous in the condensed sequence of the Inferior Oolite at Burton Bradstock. They are not usually easy to find, though because of limited amounts of the limestone at beach level and because collectors have taken specimens. They are not as well-preserved as the ammonites of the Liassic clays, but have considerable stratigraphical significance. After a rock-fall from the cliff in April 2005 ammonites and fragments of ammonites were common in the debris. However, this rock debris has been searched by many collectors the fall and there is little that remains now.

Ammonites from the Lower and Middle Inferior Oolite. Modified from Arkell (1933) , Plate 33. The first number after the name and location information is the maximum diameter in millimetres (useful here to give the scale), the second the height of the last whorl, the third the thickness of the last whorl, the fourth the width of the umbilicus.

1. Shirbuirnia stephani Buckman, Sandford Lane, Near Sherborne, Dorset. Chorotype J.W.T. collection. 117. 51.31.18.

2. Hyperlioceras discites (Waagen) pars., H. discitiforme Buckman. Bradford Abbas, Dorset. Topotype. J.W.T. collection. 65. 50.20.13.

3. Ludwigella concava (Sowerby), Wyke, near Sherborne, Dorset. J.W.T. collection. 71. 52.21.15.

4. Tmetoceras scissum (Benecke), Burton Bradstock, Dorset. J.W.T. collection. 35. 33.28.45.

5. Brasilia bradfordensis Buckman, Barrofield, Beaminster, Dorset. J.W.T. collection. 123. 48.21.21.

6. Ludwigia murchisonae(Sowerby), Bradford Abbas, Dorset. From Buckman "Monograph Ammonites Inferior Oolite, plate 3, fig. 1. 114. 41.26.32.

Ammonites from the Middle and Upper Inferior Oolite. Modified from Arkell (1933) , Plate 34. The first number after the name and location information is the maximum diameter in millimetres (useful here to give the scale), the second the height of the last whorl, the third the thickness of the last whorl, the fourth the width of the umbilicus.

1. Parkinsonia schloenbachi Schlippe, Burton Bradstock, Dorset. G.A. Kellaway collection. 75. 34.33.44.

2. Garantiana garantiana (d'Orbigny), Near Sherborne, Dorset. J.W.T. (J.W. Tutcher) collection. 76. 38.34.36.

3. Strigoceras truellei(d'Orbigny), Burton Bradstock, Dorset. J.W.T. collection. 79. 56.36.7.

4. Strenoceras niortensis (d'Orbigny), Oborne, Dorset. J.W.T. collection. 40. 35.30.41.

5. Teloceras blagdeni (Sowerby), Near Sherborne, Dorset. J.W.T. collection. 41. 29.71.47.

6. Otoites sauzei (d'Orbigny), Dundry Hill, Somerset. J.W.T. collection. 36. 42.50.23.

[end of 3.4 Inferior Oolite - Ammonites]

3.5 INFERIOR OOLITE - Other Fossils

FROME CLAY OR UPPER FULLERS EARTH ETC

As noted above, west of the car park the Bridport Sands are exposed in vertical cliffs. However, the Bride Fault disturbs the Bridport Sands where the path climbs to the cliff top to the west. Visible here in the past, and associated with the fault, were white limestones which may indicate the presence of a contemporary fissue (neptunian dyke) of Bajocian date within the Bridport Sands ( Richardson, 1928-30 ). The Bride Fault belt downthrows 60m south and introduces the Middle Jurassic to the east. The grey calcareous mudstones of the Frome Clay or Upper Fullers Earth are seen in sloping and rather slumped cliffs. They are not in general very fossiliferous. These mudstones are not laminated and more resemble the Eocene Barton Clay (without the fossils) or the Jurassic Oxford Clay (again with less fossils) than they do the laminated Liassic or Kimmeridge Clays.

About 200m to the east of the car park the Boueti Bed, a thin calcareous and harder band, can be traced in eroded ground between the footpath and the cliff top and it yields the brachiopods Goniorhynchia boueti, Avonothyris, Digonella, with bivalves and other fossils. In the cliffs below the upper part of the Fuller's Earth Clay can be examined and it crops out in the low cliffs at Burton Common and Cliff End (SY 499883) (House, 1993).

The cliffs to the south-east towards the Abbotsbury Fault are much receded, landslipped and overgrown and are not particularly favourable for examination. However, fossiliferous outcrops of the Forest Marble were recorded by Sylvester-Bradley (1957).

BURTON CLIFF AND ROCK FALLS

Introduction

.

YEAR - 1928

Burton Cliff is a coastal feature that is dependent on rock falls and sea erosion to maintain its characteristics. The falls are not frequent but have been taking place almost every year and will continue to do so. The photograph above, courtesy of BGS Geoscenic, shows they were happening in 1928; of course they have been occurring for thousands of years before. They are normal for this stretch of coast, although there is discussion about whether they are increasing in frequency now. A limited area of Bridport Sand cliff has been completely destroyed by the sea on the west side of Bridport Harbour, West Bay. East Cliff, West Bay has rather similar geology to that of Burton Cliff (but without good development of Inferior Oolite) but has less rock falls at present, probably because of a wider beach. At a later stage this may become similar to Burton Cliff.

Some later records of rock falls at Burton Cliff now follow.

BURTON CLIFF AND ROCK FALLS (ALSO WEST BAY ROCKFALLS)

YEAR - 1956 and Earlier

April 1914 - Easter Field Excursion of the Geologists' Association to Bridport etc. ( Richardson, 1915)

"During a walk along the beach to the place where the huge masses of Oolite have fallen bodily down, the precipitous cliffs of Bridport Sands, capped with Oolite and Fullers' Earth, were much admired. The position of the Red Bed could be easily made out by its red stain."

Rock falls at Burton Cliff have long been known to geologists. The old photograph above shows geologists at work on Inferior Oolite blocks at rock falls. I have, of course, used rock falls to examine the Inferior Oolite from 1960s or earlier. It has been the usual custom for studying the otherwise inaccessible strata cliffs in this area, as shown by the extract above from a Geologists' Association field excursion in 1914.

BURTON CLIFF AND ROCK FALLS (ALSO WEST BAY ROCK FALLS)

YEARS - 1996 - "Pillar Rock", near the mouth of the River Bride

This location of this old rock fall, referred to here for convenience as "pillar rock" is a short distance to the southeast of the mouth of the River Bride at Burton Freshwater. The cliff of Bridport Sand Formation here is lower as the top slopes down to the river. There is no Inferior Oolite in the cliff just here. The image above shows the remains of a cliff fall as seen at 27 July 1996 soon after the collapse. There are many angular, joint-bounded blocks of Bridport Sands and much loose sandy debris. Presumably the blocks are from the more cemented horizons, and the poorly cemented sands between have provided the loose debris.

Above is another older photograph (about 1996 or 1998) of the pillar rock fall towards the northwestern end of Burton Cliff. The rock fall is of the usual type, with vertical collapse and a debris cone on the beach. Even though the cliff is lower here the debris cone is quite impressive.

Apart from rock falls, the erosion of the cliffs in this northwestern area is unusual. Some of the harder bands are very well cemented and relatively resistant to marine erosion. This has resulted a residual projecting platform near the top of the beach. This was probably once protected by beach sand. Notice how the sandstone has been weathered along nearly vertical joints. At the western end of Burton Cliff, at the date of photograph, there have probably been few cliff falls but much erosion has been by rain, wind and spray so as to produce this unusually gullied cliff.

In the late 1990s the beach at the northwestern end of Burton Cliff seemed quite wide in the area of the pillar rock fall.

BURTON CLIFF AND ROCK FALLS

YEAR - 1996 - July - Substantial Rock Fall in Central Area

The rock fall shown above was photographed by Gareth Lloyd on the 21st July 1996 and it seems very fresh in the image, without much erosion or weathering. This was a large rock fall in the central part of Burton Cliff and involved not only Bridport Sand Formation but also the Inferior Oolite and the Fullers Earth. There is a gull (joint probably enlarged during the Pleistocene) on the right hand side (southeast side). Some large flat slabs of Inferior Oolite seem to have split in jigsaw manner as in the case of the 24th July 2012 rock fall.

BURTON CLIFF AND ROCK FALLS (ALSO WEST BAY ROCK FALLS)

YEAR - 2002 November Rock Fall

In 2002 an area of prominance in the central to northwestern part of Burton Cliff had a significant rock fall. The site is probably within 50 or 100m of the fatal rock fall site of July 2012. I am grateful to Alan Holiday for the photograph shown above. It is clear that there have been other rock falls in this area. An older rock fall is indicated by blocks of Inferior Oolite (the Red Bed) with weathered, whitened top surfaces. In addition the photograph seems to show, in the distance, some rock fall debris in or almost in the area of the 2012 fall. The photograph is useful in that it now fixes the location of a cliff scar of 2002.

BURTON CLIFF AND ROCK FALLS (ALSO WEST BAY ROCK FALLS)

YEAR - 2005 CONTINUED - 9th April

This fall of Bridport Sands and Inferior Oolite took place in the late afternoon of Saturday 9 April 2005. The weather had not been particular wet or unusual in any respect. It was not a rotational landslide. It seems to have been a collapse of rock due to undercutting of the Bridport Sands at beach level. This is the result of wave action causing abrasion by the beach shingle. Bioerosion is not significantly involved here.

The type of rock fall is rather like that seen on vertical or near-vertical Chalk cliffs. It resembles the Category 1a, Simple vertical collapse, of Chalk cliffs of Mortimore et al (2004). These simplest cliff failures are vertical collapses where there is usually one formation (but slightly more complex here with the Inferior Oolite above a high cliff of Bridport Sands). A predominant set of joints controls the type and scale of failure. Certainly there is joint control here, but it is a set parallel to the cliff and not the major open gulls which are at a steep angle to the cliff.

There are two complications. One is that there is undercutting at the base of the cliff. This sometimes occurs in the case of Chalk. The second is that there has "runout" on a significant scale. The rock debris has run-out to the sea, but has not reached the scale of a small sturzstrom run-outs [mountain rock falls with very long run-outs], as has happened at the Seven Sisters in Sussex ( Williams et al., 2004). Because of this run-out the rock fall approaches Category 1c, Large rock falls involving entire cliff (partial flow slides) of magnitude 5-7 Mortimore et al (2004). No detailed study has been made, but perhaps some-one will follow the matter further and refine the classification and type of rock fall here.

The occurrence of many Inferior Oolite limestone blocks near to the sea with Bridport Sands blocks closer to the cliff suggests that it fell with some seaward toppling mechanism but distingrated violently into individual blocks of about 2 metres or so. The fallen mass was presumably separated from the main cliff by a fissure; fresh modern, vertical, fissures as opposed to older joints are visible in the cliff in places and obviously indicate areas of potential collapse.

Some older worn blocks of Inferior Oolite are present near the toe of the debris pile. Thus this has been the site of a previous rock fall or rock falls.

From a point of view of safety, such falls are obviously sudden and unpredictable and take place only at intervals of several years. They are clearly sudden events that would be disastrous to any people who happened to be at the location at that time. [long since this was written such a sad event has indeed occurred with a fatality at Burton Cliff on the 24th July 2012.]

BURTON CLIFF AND ROCK FALLS (ALSO WEST BAY ROCK FALLS)

YEAR - 2005 - Undercutting and Future Threat of Rock Falls

Shown above are photographs from 2005 that indicate an unstable cliff to the west of Hive Beach, Burton Bradstock. There has been undercutting in this area, and there are major open joints which have long caused the cliff to be weak and ready for failure.

BURTON CLIFF AND ROCK FALLS (ALSO WEST BAY ROCK FALLS)

YEAR - 2007 - Storm

Photographs of the Burton Bradstock area above, taken by Alan Holiday, show a very stormy sea with a wave pattern of long-wavelength. At Burton Cliff the sea is washing right up to the base of the cliff. A debris cone from a rockfall is shown being eroded by the sea. The debris cones are not permanent and are removed almost completely after a while. Sometimes a few residual large rocks remain at the foot of the cliff indicating the position of the former rock fall.

BURTON CLIFF AND ROCK FALLS (ALSO WEST BAY ROCK FALLS)

YEAR - 2008

BURTON CLIFF AND ROCK FALLS (ALSO WEST BAY ROCK FALLS)

YEAR - 2009 - State of Cliff Prior to the 2012 Rock Fall

The year 2009 does not seem to have been notable for rock falls at Burton Cliff, although the remains of some rock falls could be clearly seen. Some photographs from that year show the state of the cliff then. The Burton Hive end (i.e. the southeast end) at about this date is discussed separately below.

(On Monday, 21st September 2009, Rebecca Evans in the Daily Mirror reported that a boy of nine was seriously injured when he was crushed by a ton of rocks which tumbled from a seaside cliff yesterday as he played on a beach. This was the Chalk Cliffs at the back (north side) of the cove, probably near Black Rocks where there has been a major rock fall accident in the 1950s.)

BURTON CLIFF AND ROCK FALLS (ALSO WEST BAY ROCK FALLS)

YEARS - 2008-2012 - Cliff Changes near Hive Beach

BURTON CLIFF AND ROCK FALLS

YEAR - 2012 - February

The photographs directly above were taken by Alan Holiday on the 19th February 2012, and record the debris of a cliff fall that had taken place on the 10th February 2012. This is not a safe place and the Bridport Sands are not very fossiliferous, so there is no particular reason to scramble over this. Further falls might occur. The process of periodic cliff falls here is a natural result of wave action undercutting the base of the cliff of Bridport Sands. Other photographs show that this is a place where there is frequently an overhang at the base. The reason for this is that the beach is fairly narrow here and at high tide and particularly in storm conditions the sea reaches the foot of the cliff. The fine shingle is very abrasive and easily cuts out an overhang; in addition there are major joints in the Bridport Sands.

This photograph shows a joint at a place where the cliff has not yet fallen. It is a weakness, and at the base of the joint there is a tongue of washed-out sand. Thus rainfall is gradually clearing and opening the joint. Alan Holiday, who took the photograph, mentions that this part of the cliff will fall sooner or later. Notice the darker-coloured sandstone at the base of the cliff (bottom of photograph). This is where undercutting is taken place, and this removes the lighter-coloured and more weathered yellow sandstone.

Sadly, a fatal accident occurred at the sandstone cliffs at Burton Bradstock on the 24th July 2012. There was a large rock fall at cliffs, the base of which is attacked by waves during severe storms. This was at least the second time someone has been killed by fall of sandstone cliffs in the Dorset-Devon region. A similar accident occurred at Dawlish in 1885. Of course the Burton fatal rock fall will not be the last to occur on the south coast.

See also the relevant section of webpage Teignmouth to Dawlish, Devon of which the following is an extract. The cliff is of sandstone above breccia, geological older than that at Burton Bradstock, but with a low dip and considerable similarities. As at Burton Bradstock it was undercut at the base by the sea in storms. [The Dawlish cliff is now much safer, with re-sloping and a promenade].

"On Saturday, August 29th 1885 at around noon, six members of the family and household of Dowager Lady Sawle were preparing for a picnic lunch beneath the overhang, when a large mass of rock (estimated 50 - 150 tons) split from the cliff above them. They had a moment's warning from a seventh party member, Ellie Watson, who was standing nearer the sea and saw the start of the collapse. Three ran towards the cliff, and were buried and killed instantly: nine year old Violet Mary Watson; Mary Radford (lady's maid to Lady Sawle) and Elizabeth Keen (nurse to the Watson children). Three who ran towards the sea, a Miss Watts, Miss Matthews, and Johnny Watson, survived, but were seriously injured. Only Ellie Watson was unhurt."

.

There have been at least three recent rock falls at Burton Cliff. The rock scars and the rock debris on the shore from each is shown in the photograph above. Tragically the last and most recent of the three, at about 12.30 BST on the 24th July caused a fatality. The location is the freshest of the three sites shown here, in a photograph from the sea by Martin Cox, and it the one with the conspicous debris cone extending out across the beach.

Very sadly on the 24th July 2012, there was a fatal accident near the middle part of Burton Cliff. Some people were walking on the beach. According to BBC News Dorset (2012), Witnesses at the beach said Ms Blackman, from Heanor, had been seen walking directly under the cliff. At high tide, at the eastern end this is sometimes necessary, but much depends on weather and wave conditions. In storm conditions the beach is often impassable.

BEACH MATERIAL

Progressive Loss at Burton Cliff.

The beach, however, has shown dramatic changes, becoming much narrower that in the past. This has been investigated by (Calloway, 2009). It is particularly narrow now at the eastern end near Hive Beach. This is also shown in some photographs above and the erosion of the cliffs seems to have increased to some extent here. The loss of beach is more significant.

There is a significant contrast at present between Burton Cliff of Bridport Sands and East Cliff, Bridport, also of Bridport Sands. East Cliff, although with a higher Bridport Sands section does not seem to show as many rock falls as does Burton Cliff.

The beach of Burton Cliff is relatively narrower now than in the past. It is fairly low and there is undercutting taking place at the foot of the cliff of Bridport Sands.

The beach at Burton Bradstock, near the western end (the exact end is debatable) of the Chesil Beach, is fine shingle. It mostly consists of Cretaceous flint and chert (from the Upper Greensand) with a variety of unusual pebbles, including quartzites from the Budleigh Salterton pebbles beds of the Triassic of Devon. The small pebbles are generally fairly well-rounded. Notice that although most of the material is well-sorted, there are some larger pebbles scattered on the surface.

When the beach was observed in April 2005 it seemed to have diminished in width. By March 2008, as shown by the comparative photographs above, there had been substantial loss of beach material at Burton Cliff. The fine shingle (granules) move from west to east by longshore drift as a result of prevailing southwesterly winds. Supply of beach sediment from the west is prevented by the harbour piers (now extended) at West Bay, Bridport. Shingle is moved and banked up by machines at Burton Freshwater to reduce the risk of flooding of the caravan site there. Sea level is rising at an increased rate and in general the low water mark is moving landward along the coast of central southern England (beach narrowing, beach steepening or coastal squeeze). Thus, for various reasons, there is no longer the abundance of fine shingle that there used to be in front of Burton Cliff.

In the longer term the beach at Burton Cliff will probably be lost and this will become a rocky coast with the sea breaking onto the Bridport Sands. Fortunately, fallen blocks of limestone from the Inferior Oolite may provide some natural rock armour (armourstone) that may retard the rate of cliff erosion. It may become a headland, resistant in contrast to the relatively rapid retreat of the Fullers Earth clay cliffs to the southeast (from Burton Hive Beach towards Cogden Beach). The soft cliffs will erode easily once the main part of the shingle beach is lost and the area becomes sediment-starved (cf. Naish Farm at Highcliffe, Christchurch Bay).

. BURTON FRESHWATER

Sea Defences at Burton Freshwater

.

The low flood plain of the River Bride comes down to the sea at Burton Freshwater to the west of Burton Bradstock. Here there has been flooding in the past. If there were no defences here major sea-flooding could extend up the valley into the village of Burton Bradstock. Obviously the mouth of the river has to be left open. However, immediately, to the west of it shingle is banked up by a bulldozer to afford some protection the caravan park there and the flood plain in general. Unfortunately though the supply of fine shingle in the area is diminishing as the beaches here progressively become narrower. Rising sea-level is moving the low-water mark landward. Rising high water level, particularly when raised further by storm surges, is a potential threat to river floodplains which reach the coast.

BURTON FRESHWATER

Jointing in the Bridport Sand Formation

Joints in the calcite-cemented beds of the Bridport Sand Formation at the mouth of the River Bride are apparently widened and very conspicuous. This may be the effect of periglacial activity in the Devensian, simply because this would have been near-surface at that time, and periglacial fracturing is very common at other localities. However, the joints may in fact be hidden tectonic joints, present throughout the Bridport Sand Formation, but not open and therefore not generally visible. This may require further study.

Martin Cox very kindly has allowed me to use some of his photographs taken from the sea after the July 2012 rock fall at Burton Cliff. I am much obliged to him. I would like to thank Gareth Lloyd for the opportunity to scan and use photographs taken by him of the Burton Cliff section. I am obliged to David Sole for informing me about the 2005 cliff-fall. Thanks are due to the staff and students of London South Bank University who helped with field work at Burton Bradstock. I am very much obliged to Adrian Bicker for kindly providing storm and other photographs taken from Burton Cliff. As elsewhere on this website Alan Holiday has very kindly provided some many excellent photographs of overhanging cliffs and of various rock-falls on this stretch of coast. In particular he photographed the rock fall at Burton Bradstock in February 2012 and I am very grateful for his permission to use these photographs. I am very much appreciative of the photography of the cliffs by my daughter Tonya Loades in 2017, taken while she was staying at the Burton Freshwater camp site.

REFERENCES AND BIBLIOGRAPHY

(See also References in the East Cliff, West Bay, Bridport webpage.)

.
Allison, R.J. 1992. The Coastal Landforms of West Dorset. Geologists' Association Guide No. 47. 133 pp. Edited by Robert J. Allison, Department of Geological Sciences, University College, London.

.
Arkell , W.J. 1933. The Jurassic System in Great Britain. Clarendon Press, Oxford, 681pp.

.
Barnard , T. and Hay, W.W. 1974. On Jurassic coccoliths: a tentative zonation of the Jurassic of S. England and N. France. Eclogae Geol. Helv., 67, 563-585.
.
Barrett , C. 1878. The Geology of Swyre, Puncknowle, Burton Bradstock, Loders, Shipton Gorge, Litton Cheney, Longbredy, Littlebredy and Abbotsbury, Dorset. Bridport.
.
Barron , A.J.M., Sumbler, M.G. and Morigi, A.N. 1997. A revised lithostratigraphy for the Inferior Oolite Group (Middle Jurassic) of the Cotswolds, England. Proceedings of the Geologists' Association, London. 108: 269-285. Abstract: Geological surveying in part of the Cotswolds has provided a basis for a modem lithostratigraphical classification of the Inferior Oolite Group. The group is divided into three formations, named the Birdlip Limestone Formation, Aston Limestone Formation and Salperton Limestone Formation, in ascending order. These correspond essentially with the traditional units of Lower, Middle and Upper Inferior Oolite which were defined chronostratigraphically. Each of the three formations is subdivided into members which can be related to units well established in the existing literature. Formal definitions of all these units are given. (Not on Burton Bradstock, but relevant for comparison and key to literature).
.
Bird, E.C.F. 1990 (for 1989). The beaches of Lyme Bay. Proceedings of the Dorset Natural History and Archaeological Society for 1989, published June 1990, 111, 91-97. By the late Eric Bird, then at Department of Geography, University of Melbourne, Australia. Abstract: The beaches of Lyme Bay consist largely of flint and chert shingle, with some sand, derived from eroding cliffs and sea floor sources. They include Chesil Beach, which shows lateral grading from small pebbles in the west to large pebbles in the east. Several other beaches on the north coast of Lyme Bay also show lateral grading, low beaches of poorly sorted sand and shingle to the west becoming higher and often wider, coarser and better sorted to the east. Lateral grading is attributed to an alternation of eastward beach drifting by strong south-westerly wave action with westward movement of finer material by gentler southeasterly wave action. Whereas Chesil Beach is a relict shingle formation, the other beaches are still receiving small quantities of sand and shingle. Cliff erosion and slumping are more rapid behind low beach sectors than where a high, wide accumulation of coarse shingle protects the shore. It is suggested that artificial beach nourishment should be used as a method of coastal protection on the shores of Lyme Bay. [end of abstract - Bird, 1990]

.
Bray , M.J. 1986. A Geomorphological Investigation of the South West Dorset coast. Volume 1: Patterns of Sediment Supply. Report to Dorset County Council, 144pp.

Bray, M.J. 1986. A Geomorphological Investigation of the South West Dorset coast. Volume 1: Patterns of Sediment Transport. Report to Dorset County Council, 798pp.

Bray, M.J. 1992. Coastal sediment supply and transport [re West Dorset]. In: Allison, R.J. (Ed.) 1992. The Coastal Landforms of West Dorset. The Geologists' Association, 134 pp., paperback, pp. 94-105.
.
British Geological Survey (BGS). (Compiler Wood, M.A.) 2011. Geology of South Dorset and South-East Devon and its World Heritage Coast.
Special Memoir for 1:50,000 geological sheets 328 Dorchester, 342 West Fleet and Weymouth and 342/343 Swanage and parts of sheets 326/340 Sidmouth, 327 Bridport, 329 Bournemouth and 330 Newton Abbott. Compiled by M.A. Woods. By Barton, C.M., Woods, M.A., Bristow, C.R., Newell, A.J., Westhead, R.K., Evans, D.J., Kirby G.A., and Warrington, G. Contributors: Biostratigraphy - J.B. Riding; Stratigraphy - E.C. Freshney; Economic Geology - D.E. Highley and G.K. Lott; Engineering Geology - A. Forster and A. Gibson. British Geological Survey, Keyworth, Nottingham, 2011. 161 pp. This is the new version of the Geological Survey Memoir for the Dorset Coast etc. and replaces Arkell (1947) and the earlier memoir by Strahan (1898). It covers a wider area than these old memoirs, though, and includes all of "Jurassic Coast", UNESCO World Heritage Coast. It is a key reference work. Available from BGS Online Bookshop at 24 pounds stirling (in Jan. 2012).
.
BGS. British Geological Survey. BGS Landslide Response Team. Report.
The BGS (British Geological Survey) Landslide Response Team investigated the rock fall on the 25th July, the day following the fatal accident. See: Burton Bradstock Rock Fall, Dorset. Re: The Burton Bradstock rock fall of 24 July 2012. The BGS Landslide Response Team carried out a survey of the site, including a LiDAR survey, on 25 July 2012. Data collected from this survey is logged in the BGS National Landslide Database NLD 18684/1.
"It was reported that approximately 400 tons of rock fell in two rock-fall events approximately 20 minutes apart at around 12:30.. .The rock fall deposit was 30 m long, 20 m wide and 10 m high, which ran out over a gravel beach... The failure was controlled and constrained by a combination of factors: Discontinuities: Joints and fractures within cliff run vertically and parallel to the cliff face enabling wedge-shaped sections of cliff to fall. Coastal erosion and weathering: Coastal erosion and weathering of the cliff face are a continual natural process... The sea is eroding the base of the cliff (undercutting), removing support for the rocks above... The processes of weathering weakens the cliff, making it more susceptible to failure. Recent wet weather has added more water into the cliff from above such that grain support is weakened in the Bridport Sand Formation ... thereby increasing the likelihood of a landslide occurring."
.
Bryant , I. A., Kantorowicz, J. D. and Love, C.F. 1988. The origin and recognition of laterally continuous carbonate-cemented horizons in the Upper Lias Sands of southern England. Marine and Petroleum Geology, 5, 108-133. (cementation of bioclast-rich storm sediments on submerged marine shoal. Compared with Mauritanian shelf).
The Upper Lias Sands of southern England contain numerous, laterally extensive, carbonate-cemented horizons. Petrographic analysis of samples from outcrop sections and Marchwood No.1 borehole indicate that these horizons result from preferential cementation of bioclast-rich, clay-poor sediments by comparison with interbedded clay-rich, bioclast poor sediments. The alternation of the two sediment types is attributed to the effects of, respectively, fairweather and storm processes on a submerged marine shoal. Petrographical and ichnological data indicate an early distinction of the strongly and weakly cemented horizons. The widespread extent of the cemented horizons, as indicated by outcrop studies on the Dorset coast, is considered to be a direct consequence of episodic storm activity on the low relief shoal. Sedimentological, palynological and petrophysical criteria are presented to assist in recognition of similar extensive cements in subsurface reservoir horizons.

Bryant, I. A. and Kantorowicz, J. D. (listed as in prep.). Upper Lias Sands of the Marchwood No. 1 Borehole, southern England, In: The Reservoir Geology of the North Sea, B.S.R.G. core workshop. (Eds J. Melvin and G.M. Walkden).
.
Buckman , S.S. 1881. A descriptive catalogue of some of the species of ammonites from the Inferior Oolite of Dorset. Quarterly Journal of the Geological Society, London, 37, 588-608.

Buckman, S.S. 1883. The brachiopoda from the Inferior Oolite of Dorset and a portion of Somerset. Proceedings of Dorset Natural History and Archaeological Field Club, 4, 1-52.

Buckman, S.S. 1891. The ammonite zones of Dorset and Somerset. Geological Magazine, 28, 502-504.

Buckman, S.S. 1910a Certain Jurassic (Lias-Oolite) strata of South Dorset. Quarterly Journal of the Geological Society of London, 66, 52-89..

Buckman, S.S. 1910b. Certain Jurassic (Inferior Oolite) species of ammonites and brachiopoda. Quarterly Journal of the Geological Society of London, 66, 90-108, 109-110.

Buckman, S.S. 1913-1919. Yorkshire Type Ammonites, 2. London.

Buckman, S.S. 1922-3. Type Ammonites, 4. London

Buckman, S.S. and Secretary. 1908. Illustrations of type specimens of Inferior Oolite ammonites in the Sowerby Collection. Monographs of the Palaeontographical Society of London.

.
Coggan, J.S., Pine, R.J. and Stead, D. 2001. A proposed methodology for rockfall risk assessment along coastlines. Geoscience in south-west England, vol. 10, pp. 190-194.
Available online:
A Proposed Methodology for Rockfall Risk Assessment along Coastlines.
Many of the general public use the coastal zone for recreation during the summer. They often spend time in the vicinity of of cliff exposures that may constitute a risk from instabilities. Rockfall hazard appraisal and risk assessment techniques were applied to a length of Cornish coast, predominantly in sandstones and mudstones between Hayle and Portreath, to assess the threat to the public on the adjacent beaches. The methodology used was similar to assessments of rockfall on highways. Even though risk assessments are voluntary, the general public should be informed of the risks of rockfall. The results of this analysis suggest that for the occasional beach user, the risk may be small, when compared to the risk from other voluntary activities such as rock climbing. Increased exposure and the nature of the recreational pursuit may increase risk. [end of abstract]
Introduction:
The detrimental effects of coastal landslide activity have received extensive coverage in the national press in recent months, following one of the wettest winters for more than 100 years. Many of the public visit the coastal zone for recreation. Where beaches are backed by cliffs, the public often spend time in areas that constitute a risk from instabilities. With the predicted increase in wet-winters and storm-related damage as a result of climate change, then increased rates of coastal recession are forecast. Coastal cliff instability must, therefore, be a consideration for users of coastal zone for business, tourism and recreational purposes. Instability can directly affect both coastal paths and beaches. The potential for instability may therefore have a detrimental impact on small business, local maritime authorities, private landowners, highway authorities and the general public. This is important for Cornwall as over 20% of the gross domestic product is generated by tourism (Shail et al., 1998) and the coastline is over 200 miles long.
Assessment of landslide activity, and the instability of the Cornish coastline, has been carried out under the Shoreline Management Plans (SMP), using qualitative evaluation. The data incorporated in the SMP was based on a review of available literature, air photograph surviellance and field visits. The risk or likelyhood of injury to persons from rockfall when using beaches backed by cliffs for recreation has not been quantified. [continues].
.
Callomon , J.H. 1995a. 'Time from fossils: S.S. Buckman and Jurassic high resolution geochronology'. In Le Bas, M.J. (ed.) Milestones in Geology. Geological Society, London, Memoirs, 16, 127-150.

Callomon, J.H. 1995b. The Jurassic Geology of Dorset, Middle Jurassic. In. Taylor, P.D. (ed.), Field Geology of the British Jurassic. Geological Society, London, 60-85.

Callomon, J.H. and Chandler, R.B. 1990. A review of the ammonite horizons of the Aalenian-Lower Bajocian stages in the Middle Jurassic of Southern England. In: Cresta, S. and Pavia, G. (eds.), Atti del meeting sulla stratigrafia del baiociano. Memorie descrittive della carta geologica d'Italia. 40, 85-111.
.
Calloway, T. 2009. The Use of GIS and Historic Maps to Investigate Temporal and Spatial Shoreline Variation at Burton Bradstock and West Bay, Dorset. 115 pp. Dissertation submitted in partial fulfilment of for the degree of B.Sc. Environmental Science; School of Civil Engineering and the Environment, University of Southampton. April 2009. By Thomas Callaway, April 2009. (supervised by Ian West)
Burton Bradstock and West Bay are situated on the Dorset coast, UK. The cliff sections are under threat from sea-level rise and increased storm frequency and intensity. Erosion rates may vary across different sections, due to famed geodiversity of the 'Jurassic Coast'. Anthropogenic developments and activities could also have an adverse effect on erosion rates. Different stakeholders have different opinions on how coast should be managed here. The World Heritage Site designation prevents further development because erosion is the key factor which makes the coast what it is. Residents and businesses may be concerned that land and buildings are being allowed to fall into the sea. Learning more about the causes and rates of erosion can help to understand predicted rates of change set out by Shoreline Management Plans (SMPs).
Historic Ordnance Survey maps have been used in digital format with ArcMap GIS software to determine differences in the coastline between published years. Rates of cliff-top recession and changes in the beach size and tidal range have been calculated at four cliff sections. The data has been used to investigate temporal and spatial variations in coastal processes, combined with knowledge of historical developments on the coast. The interaction between temporal and spatial factors has also been considered.
The results suggest that there are significant differences between the four cliff sections, due to their geology and structure and also because the development of harbour piers at West Bay over past centuries. Extensive beach mining has also played a part in affecting coastal processes. Significant interactions between spatial and temporal factors suggest that there are many more factors that have not been considered, prompting further research into various coast-related processes and phenomena. [end of Abstract].
.
Cope , J.C.W. et al. A Correlation of Jurassic Rocks in the British Isles. 2. Middle and Upper Jurassic. Geological Society of London, Special Reports, 15, 3-21.

Cope, J.C.W. 2012. Geology of the Dorset Coast. Geologists' Association Guide, No. 22. 232pp., with many colour photographs and diagrams. New edition by John C.W. Cope. (See also the earlier editions by House, M.R. 1989 and 1993.)

.
Davies , D.K. 1966. The Sedimentary Petrology of the Upper Lias Sands and Associated Deposits in Southern England. Unpublished Ph.D. Thesis, University of Wales. Supervised by Gilbert Kelling, University College of Swansea.

Davies, D.K. 1967. Origin of friable sandstone-calcareous sandstone rhythms in the Upper Lias of England. Journal of Sedimentary Petrology, 37, 1179-1188. By David K. Davies, then at Department of Geology, Texas A&M University, College Station, Texas. Later at: Geosystems, David K Davies And Associates Inc., 1410 Stonehollow Drive, Humble, TX 77339-2070. This paper represents a portion ot the Ph.D. thesis of D.K. Davies (1966), referred to above.
The diachronous Upper Lias Sands of southern England are comprised of small scale rhythmic alternations of friable, yellow sandstone and firm grey calcareous sandstone. In general, the alternating layers are parallel to bedding and to one another; exceptions occur where the calcareous sandstones mark out the bases of erosional structures. Individual carbonate-rich or deficient horizons cannot be correlated between outcrops 2 - 3 miles [3 - 5km] apart, but within a single outcrop they preserve a remarkable uniformity in vertical sequence. Petrographic studies demonstrate that original textural relationships are retained in the calcareous sandstones, while the friable sandstone interbeds have undergone compaction effects. Field evidence indicates that the calcareous sandstones were lithified before the deposition of more than 6 inches [15cm] of superimposed sediment. Such lithification is estimated to have taken approximately 150 years [i.e. 10cm per 100 years].
The alternations are considered to be the result of fluctuating rates of detrital deposition: the calcareous sandstones representing temporally and spatially restricted locales characterised by little or no detrital deposition, and the sandstone interbeds representing contiguous area of more rapid detrital deposition.
Within the Upper Lias Sands a gradual increase is observed in the relative proportion of calcium carbonate to detritals. This process established conditions suitable for deposition of the succeeding limestone sequences [Inferior Oolite] - an environment foreshadowed by the calcareous sandstones of the Upper Lias Sands.

Introduction:
General Statement.
The Upper Lias Sands of southern England are characterised throughout their outcrop by regular sedimentary layers alternately rich and deficient in calcium carbonate (fig.1). This, the most striking feature of the Sands at outcrop, has received scant attention despite the many geologists who have worked in the Upper Lias (Boswell, 1924; Buckman, 1875; 1879; Buckman, 1889; and Richardson, 1910, 1915, 1928-30). The purpose of this paper is to describe and explain this characteristic rhythmic alternation of friable sandstones and calcareous sandstones, highly unusual alternation in sediments of this lithology, and to interpret its significance in terms of regional sedimentology.
Regional Stratigraphy.
Sediments involved in this discussion crop out along a north-south line from the vicinity of Cheltenham to the south coast of southern England (fig. 2). The Upper Lias Sands represent a diachronous formation (average thickness, 200 feet [61m] which is almost entirely restricted to the Toarcian Stage of the Lower Jurassic. In the north the Sands are well represented in the Lower Toarcian subzone of Zugodactylites braunianus, but become progressively younger in a southerly direction unit, at the southernmost extremity of outcrop, they characterise in part the uppermost Toarcian subzone of Pleydellia aalenensis and also the basal Bajocian subzone of Leioceras opalinum (fig.3). This progressive change in stratigraphic position is representative of southerly facies migration rather than a change in provenance (Boswell, 1924; Davies 1966). As a result, over the total outcrop this formation preserves a remarkable uniformity both in petrology and rhythmic layering.
With a mean grain size of 4.00 phi (0.60 mm), the Upper Lias Sands bridge the sand-silt boundary. ..... [continues]

Davies, D.K. 1969. Shelf sedimentation: an example from the Jurassic of Britain. Journal of Sedimentary Petrology, 39, 1344-1370, December, 1969. By David K. Davies, of the Department of Geology, Texas A & M University, College Station, Texas. Abstract: The refined biostratigraphic framework that has been developed for Jurassic sediment of northwest Europe enables precise environmental distinctions to he made on a time-equivalent basis. Using such control it can be demonstrated that shelf sedimentation in the Lower Jurassic (Toarcian) of southern England was dominated by the gradual migration of a large sand bar. Despite the general homogeneity of its detrital sandstones and siltstones, this bar may be subdivided into four principal environments of deposition which including 1) bar (beach and upper shoreface), 2) fore-bar (middle shoreface, 3) back bar, and 4) tidal channel. These environments are distinguished on the basis of qualitative and quantitative textural and compositional criteria; succession of sedimentary structures, bioturbation, grain size, sorting, skewness, and petrography. The bar complex is 150 ft thick, and is transitional downward and southward into condensed limestones and argillaceous siltstones (40 ft average thickness). The limestones are principally intramicrites, the intraclasts being of the same composition as the host sediment (biomicrite), and often display oxidation rims. Such deposits are considered to be of shallow, marine origin. On the other hand, the argillaceous siltstones, which may contain up to 20 percent micrite, represent deeper marine conditions of deposition. The bar complex is succeeded upward and to the north by condensed limestones of variable composition, principally oomicrite; pisomicrites, and biomicrites. These limestones (12 ft average thickness) represent a platform interior sand blanket which was developed under shallow marine conditions in the lee of the large bar complex. Because 1) new sediment was constantly added to the southward side of the bar, and 2) subsidence did not quite keep pace with sediment supply, the bar was forced to accrete continually in a southward direction, at a rate of 1 mile per 80,000 years. The gradual southward migration of the bar resulted in preservation of vertical sequences which, when completely developed, comprise a basal argillaceous and calcareous facies (the Upper Lias Clay Formation), succeeded by an arenaceous facies (the Upper Lias Sand Formation), and capped by a calcareous facies (the Cephalopod Bed Formation). Sediments comprising these three facies were deposited in two distinct basins of deposition, separated by an east-west trending structural high (the Mendip Axis). Both basins subsided to receive a maximum thickness of some 340 ft of marine sediments. Because of the southward migration of the bar, the southern basin received its major sediment input only after the northern basin had already been filled. The nature and rate of sediment supply remained constant throughout the 6 million years duration of the Toarcian, the principal source being a meta-igneous complex located in the present western approaches to the English Channel.

.
Davies , G.M. 1956. The Dorset Coast: A Geological Guide. Adam and Charles Black, London, 2nd Edition with 14 photographs and 33 figures. 128pp. Hard cover. This is an interestng old field guide mainly of historic interest.

Evans, R. 2009. Boy Buried in Rockfall [at Lulworth Cove]. Daily Mirror, short newspaper article by Rebecca Evans.
A boy of nine was seriously injured when he was crushed by a ton of rocks which tumbled from a seaside cliff yesterday as he played on a beach. He and a younger girl were on the sand when the boulders suddenly came crashing down, hitting them both. The boy was buried up to his neck and suffered bad injuries to his head, neck and spine.
He was airlifted to hospital where his condition was being assessed last night after the horrific accident at the picturesque Lulworth Cove in Dorset. The girl was less seriously hurt.
Two shocked bypassers dialed 999 after seeing the rocks smash into them. A coastguard spokesman said: "The lad was very lucky not to have been killed. "The first report we had was that rocks weighing at least a ton had buried him up to his neck. When the rocks fall from the cliff - and that is always a possibility around the Dorset coast because of the rock structure - they pick up speed as they tumble down.
The boy and girl from Romsey and Ringwood, Hants, were with their respective dad and mum, who were a couple on a day out to the cove. It is a popular tourist destination on the Jurassic Coast World Heritage Site.
There have been rockfalls there before and around 10 people are killed by similar incidents in Britain every year.
[On Sunday, July 7th 1957, there was a similar rock fall at Black Rocks, Lulworth Cove: "9 in Hospital after Cove Rock Fall". "Nine people hurt by rocks that fell 100 feet to a crowded beach at Lulworth Cove, Dorset, were still in hospital today. A spokesman at Dorchester County Hospital said that were "fairly comfortable". [- continues]. Of course, there will be another rock fall here sooner or later and the consequences could be worse. My comments - It is not that the cliff is much more dangerous than elsewhere; cliff commonly have rock falls. The problem here is that people sit on the beach here almost every day there is fine weather. Rock falls occur at many places; fatal rock falls occur where people go.]

.
Gatrall , M., Jenkyns, H.C. and Parsons, C.F. 1972. Limonitic concretions from the European Jurassic with particular reference to the "snuff boxes" of southern England. Sedimentology, 18, 79-103.
.
Gauthier , H, Rioult, M. and Trevisan, M. 1995. Exceptional biostratigraphical record in the Oolithe-Feruugineuse-de-Bayeux, south of Caen (Calvados) - standard section for future reference as complement of the Bajocian historical stratotype. Comptes Rendus de l Academie des Sciences, Serie ii, Fascicule a -Sciences de la Terre et des Planetes, 321: (4) 317-323. Abstract: New stratigraphical data based on centimetre by centimetre collecting of ammonites at Feuguerollessur-Orne South of Caen, has led to detailed biozonation of the ''Oolithe ferrugineuse de Bayeux'' from the base of the Humphriesianum Zone up to the Parkinsoni one. The presence of relatively thick (3 m) deposits provides data giving far more detailed zonation (16 horizons are recognizable) than the ferruginous oolite in the Bayeux area, very condensed and locally reworked (Rioult, 1964; Pavia, 1994). Complemented by study of the inferior Bajocian and of the Aalenian/Bajocian boundary present in the same quarry, this section stands out as a standard for future reference complementary to the historical stratotype at Sainte-Honorine-des-Pertes near Bayeux (d'Orbigny, 1849-1852). (In French, not on Burton Bradstock, but relevant for comparison.).
.
Hesselbo , S. 1992. Excursion A1. Tectonics and Sedimentation in the Lower/Middle Jurassic of the Wessex Basin. Pp 20-30. BSRG 1992, Southampton, Field Excursion Guides. Department of Oceanography, University of Southampton, 65 p.
.
House , M.R. 1993 (and earlier edition in 1989) - Geology of the Dorset Coast. Geologists Association Guide, No. 22. 2nd edition, 164 pages plus plates. ISBN 0 7073 0485 7. [This inexpensive, conveniently small, paper back guide should be carried in the field as a very useful source of information by all seriously studying the geology of the Lulworth area or other parts of Dorset. It is full of detailed information and is concise and accurate. It enables field leaders to obtain essential information quickly and without carrying much weight of publications.]

.
Jones , L.E. and Sellwood, B.W. 1989. Paleogeographic significance of clay mineral distributions in the Inferior Oolite Group (Mid Jurassic) of southern England. Clay Minerals, 24 (1), 91-105.
.
Lang , W.D. 1962. Aalenian, Bridport Sands. Proceedings of Dorset Natural History and Archaeological Society, 83, p. 34.
.
Lee, E.M. 1992. Urban Landslides: Impacts and Management. By E. Mark Lee, pp. 80-93 in: Allison, R.J. 1992. The Coastal Landforms of West Dorset. Geologists' Association Guide No. 47. 133 pp. Edited by Robert J. Allison, Department of Geological Sciences, University College, London.

.
Melville , R.V. and Freshney, E.C. 1982. British Regional Geology: The Hampshire Basin and Adjoining Areas. British Geological Survey (formerly the Institute of Geological Sciences), London, Her Majesty's Stationery Office. 146 pp.

.
Morris, K.A. 1979. An Integrated Facies Analysis of Toarcian Organic-Rich Shales and Contiguous Deposits in Great Britain. Ph.D. Thesis, University of Reading.

Morris , K. A. and Shepperd, C.M. 1982. The role of clay minerals in influencing porosity and permeability characteristics in the Bridport Sands of Wytch Farm, Dorset. Clay Minerals, (The Mineralogical Society) 17, 41-54.
Abstract: The Bridport Sands is a widespread marine sandstone of Lower Jurassic age found in much of southern England. It is very fine fine grained, moderately sorted quartz-arenite and is characterised by alternations of friable and hard calcareous-cemented layers. The sands form the upper reservoir of the Wytch Farm Field, Dorset, which is currently producing at the rate of around 4000 barrels of oil per day. Investigation of core material to assess the suitability of water injection for gas/oil recovery has shown that significant reductions of liquid permeability compared to air permeability occur. These reductions vary from 30% or less in the best quality reservoir to more than 70% in low permeability sandstones. Clay minerals in the Bridport Sands comprise mainly kaolinite and mixed-layer clays of both the illite-chlorite and illite-smectite types. Small amounts of vermiculite and chlorite also occur. The kaolinite is found as loosely attached, discrete particles, whilst the mixed-layer clays form patchy pore linings. The permeability reductions may be explained by: (i) the adsorption of water and expansion of poorly crystalline mixed layer illite smectites causing blockage of pore space (this reduction is largely reversible) and (ii) the physical movement of authigenic kaolinite crystal aggregates blocking pore throats (this reduction is largely non-reversible). The pore size distribution, clay particle sizes, the distribution of the clays within the pore space, and the composition of the clays are all important factors in controlling porosity/permeability relationships and permeability reductions in the friable reservoir intervals of the Bridport Sands.
.
Mortimore , R.N., Lawrence, J., Pope, D., Duperret, A. and Genter, A. 2004. Coastal cliff geohazard in weak rock: the UK Chalk cliffs of Sussex. Pp. 3-31 in: Mortimore R.N. and Duperret, A. 2004. Coastal Chalk Cliff Instability. Geological Society of London, Engineering Geology Special Publications, No. 20, 173 pp. ISBN 1-86239-150-5. [Not on Burton Bradstock but relevant to cliff falls there.]
.
Natural History Museum , London. (originally as British Museum (Natural History) 1962 and various editions onward). British Mesozoic Fossils. 207pp.

.
Palmer , T.J. and Wilson, M.A. 1990. Growth of ferruginous oncoliths in the Bajocian (Middle Jurassic) of Europe. Terra Nova, 2, 142-147.
.
Parsons , C.F. 1970. A new temporary section in the Inferior Oolite of south Dorset. Proceedings of the Dorset Natural History and Archaeological Society, 93, 117-118.

Parsons, C.F. 1974. The sauzei and 'so-called' 'sowerbyi' Zones of the Lower Bajocian. Newsletters in Stratigraphy, 3, 153-180.

Parsons, C.F. 1975. The stratigraphy of the Stony Head cutting. Proceedings of the Dorset Natural History and Archaeological Society, 96, 8-13.

Parsons, C.F. 1980. Aalenian and Bajocian correlation chart. In: Cope, J.C.W. et al. A Correlation of Jurassic Rocks in the British Isles. 2. Middle and Upper Jurassic. Geological Society of London, Special Reports, 15, 3-21.

Parson, C.F. 1980. Ph.D. Thesis, - also other papers by Parsons - for bibliographic details see: Thomas, J. and Ensom, P. 1989. Bibliography and Index of Dorset Geology. Dorset Natural History and Archaeological Society. 102 pages. [This includes details of 11 publications by Parson, many relevant to the succession at Burton Bradstock.]
.
Penn , I.E., Dingwall, R.G. and Knox, O'B. 1980. The Inferior Oolite (Bajocian) sequence from a borehole in Lyme Bay, Dorset. Institute of Geological Sciences, Natural Environment Research Council, London, HMSO. ISBN 0 11 884098 3, 27 pp. Summary: A borehole drilled in Lyme Bay cored 19.30 m of ammonite-bearing Inferior Oolite limestone and proved all the Bajocian zones from Ludwigia murchisonae to Parkinsonia parkinsoni. Bajocian dinocyst, sporomorph, coccolithophorid, foraminiferal and ostracod assemblages are related to the ammonite zones and subzones for the first time. When the palaeontological and petrographical descriptions are combined with previously published data a reconstruction of the depositional environment and the delineation of the South-Dorset High as one of the several 'swells' controlling Bajocian sedimentation in southern England can be made. (Chamosite present).
.
Perkins , J.W. 1977. Geology Explained in Dorset. David and Charles, Newton Abbot, 224 pp.
.
Radley , J.D. 1986. Notes on a Bajocian stromatolitic limestone from Burton Bradstock, Dorset. Proceedings of the Dorset Natural History and Archaeological Society, 107, 184-186.

.
.
Richardson , L.R. 1915. Report of an excursion to Bridport, Beaminster and Crewkerne. Proceedings of the Geologists' Association, London, 26, 47-78. April 9th to 14th (Easter), 1914. By L.R. Richardson, F.R.S.E., F.G.S., Director of the Excursion.

April 9th. "The official party travelled from Paddington by the 10.30am train and arrived in Bridport at 1.55 pm. Here a number of members from other parts joined those from the town. Headquarters were in the Bull Hotel, Bridport. Mr. Douglas Leighton acted as Secretary of this excursion...."

[p.57. Burton Cliff] "During the walk along the beach to the place where the huge masses of oolite have fallen bodily down, the precipitous cliffs of Bridport Sands, capped with Oolite and Fullers' Earth, were much admired. The position of the Red Bed could easily be made out by its red stain.
Considerable discussion took place as to the origin of the layers of sand-rock and sandburrs; but no satisfactory explanation was forthcoming. The hard beds are highly calcareous and water exuding from their neighbourhood has frequently formed a lace-like travertinous deposit pendent from one hard stratum to another. In places percolating waters, charged with bicarbonate of lime, have originated in the softer intervening deposits a kind of box structure, some said very similar in appearance to that known in the Hastings Sands.
Arrived at the tumbled blocks the Members saw that masses had bodily fallen down, in which it was possible to identify the various beds from the Sands to the Fullers' Earth. Each bed could be conveniently measured and fossils collected. A vertical section of the Inferior Oolite and contiguous deposits to be seen here was given in our Circular and is reproduced (with some slight alteration) on p. 55. [this is the standard Inferior Oolite section for Burton Cliff, shown elsewhere in this webpage]. [continues .]

Richardson, L.R. 1928-30. The Inferior Oolite and contiguous deposits of the Burton Bradstock - Broadwindsor district, Dorset. Proceedings of the Cotteswold Naturalists' Field Club, 23, 35-68; 149-185; 253-264, pl. 2-6, 19-25, 28.

.
Sellwood , B.W. and Jenkyns, H.C. 1975. Basins and swells and the evolution of an epeiric sea (Pliensbachian - Bajocian of Great Britain). Journal of the Geological Society of London, 131, 373-388.
.
Senior , J.R. 1968. Ammonite finds of stratigraphical importance in the Inferior Oolite of Dorset. Proceedings of the Dorset Natural History and Archaeological Society, 89, p.45.

Senior, J.R., Parsons, C.F. and Torrens, H.S. 1970. New sections in the Inferior Oolite of south Dorset. Proceedings of the Dorset Natural History and Archaeological Society, 91, 114-119.
.
Sylvester-Bradley , P.C. 1957. The Forest Marble of Dorset. Proceedings of the Geologists Association , 1556, 26-28.

.
Thomas , J. and Ensom, P. 1989. Bibliography and Index of Dorset Geology. Dorset Natural History and Archaeological Society. 102 pages. See also the internet version - Bibliography and Index of Dorset Geology.