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East Cliff - Major Beach Loss, - Compare Old and New Photographs

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[this is the BRIDPORT EAST CLIFF WEBPAGE. see also the Bridport West Webpage]

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The rock fall shown above took place on the night of the 28th June 2017. It was not the only fall at about this date, but it was the largest and it was exceptional in cutting the cliff-top footpath and just extending back into the golf course. Two other falls were small but there is threat of at least one more large one in the near future because of an overhanging bulge of sandstone (with a small rock fall in the lower part of the cliff). The situation regarding East Cliff is not stable and not predictable. With luck, no-one may be directly affected, but it is necessary to keep clear of the foot of the cliff and stay out on the beach near the sea.

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Comparison of the two photographs above shown that there has been a substantial loss of beach sand from 2013 to 2018. At some places this would not be a major problem. Here it means that this beach may be less safe from rock falls than previously. Obviously, no-one should sit or delay next to the cliff! People passing should be as low down the beach, near the sea, as far as is reasonable and not linger. For geological study the lower, eastern and western ends of the cliff may present less risk than the high parts. It is just obvious, commonsense measures which are indicated. Rock falls are rare but warning has been given!

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Related Field Guides ---

|Bridport - West or Watton Cliff | Burton Bradstock, Bridport Sands and Inferior Oolite | |Chesil Beach Field Guide |Lyme Regis - west | |Lyme Regis to Charmouth | |Eype Mouth | |Middle Lias, Staithes, Yorkshire |

General [and "Broadchurch"]

West Bay, near Bridport, Dorset is situated somewhat west of the centre of the English Channel coast of southern England. The British National Grid Map Reference is SY 467902. It is easily reached by road from Weymouth or Dorchester. There is no railway station there now. West Bay or Bridport Harbour and adjacent cliffs has been used in a television play under the fictitious name "Broadchurch". So this is a geological description of the now well-known Broadchurch cliffs.

West Bay is small attractive holiday resort with an artificial harbour built in 1722. In 1403 Joan of Navarre arrived here en route to marry King Henry IV. Shipbuilding in the River Brit around here dates from the days of Alfred the Great in the 9th Century. More recently the schooner "Speedy " was built here in 1853 to compete with American clippers. West Bay, at the present time is used for yachts, fishing boats, fishing, beach activities and tourism. The mouth of the artificial harbour has been changed in recent years and a large "Jurassic Pier" has been built on the west side, so as to facilitate the entry of boats. This is a good, initial view point.

The cliffs on both sides of the harbour provide excellent exposures of Jurassic strata. This guide is concerned with the eastern cliffs which expose the Bridport Sands of the Upper Lias, Lower Jurassic. This is also the western end of the Chesil Beach, 27 kilometres in length. The beach material here is very fine shingle, almost grit, of just a few mm. diameter. There are now erosion problems regarding the Chesil Beach which will be mentioned below.

INTRODUCTION:

Access and Parking

West Bay can be reached in about half an hour from Weymouth or Dorchester and in about one and a half hours from Southampton and probably about in an hour from Exeter. On both sides of the harbour there is parking for cars, mostly of short-term type. There is no coach parking just here. There is some long-term parking near East Cliff. There is a large long-term car park next to the old railway station, left of the road when approaching West Bay. There are toilets adjacent to the old Salt House northwest of the harbour also toilets adjacent to the small chapel east of the harbour.

Other localities which could be used in conjunction with West Bay include West or Watton Cliff, just a walk round the harbour, or perhaps the Inferior Oolite of Burton Bradstock. At West Cliff there is middle Jurassic Frome Clay (Fullers Earth) and Forest Marble, and beyond, other parts of the Lias. There is an interesting fault at Fault Corner near Eype Mouth. Charmouth, near Lyme Regis is another good locality.

INTRODUCTION:

Safety - The formerly wide beach is now narrow and with much increased risk in 2018!

Note that unfortunately the cliff is now significantly more dangerous than previously, and do not imitate people who in the past who have gone close to it. Keep seaward as far as possible, limit the time there, and do not linger near the cliff. Do not imitate people seen in old photographs, close to the cliff in the past when the beach was larger and the risk was much less. The beach is becoming narrower and its width and weight are less than in the past. At one time rock falls were rare at East Cliff, but now they are becoming more frequent. Photographs in this website show the changes - do not take risks here! It may be at least ten times more hazardous now than in the past, and unfortunately it is probably too near to car parks and easy access.

Even geologists, who are usually accustomed to cliff risks, should take care, now. Re the public, particularly do not take children anywhere near the foot of East Cliff (or Burton Cliff) - keep away! Common sense!

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At West Bay and the coast in its vicinity there are obvious risks, especially at at East Cliff. Major rock falls take place on rare occasions. At any time small rocks can fall at high velocity, sometimes being dislodged by seagulls. Geological parties should, therefore, wear hard hats and minimise the time spent at the foot of the cliffs.

Care should be taken with regard to sea and tide in stormy conditions. If a cliff top route is used then it is obvious that it can be dangerous to approach the cliff edge. Visitors and party leaders should make their own risk assessment in relation to the conditions at the time.

Note particularly that on the 24th July 2012 a fatal accident took place at Burton Cliff, further southeast, as a result of a rock fall.
See: Burton Cliff - Geology.
The general geology of Burton Cliff and East Cliff is similar, except that at Burton Cliff the succession extends higher, up into Inferior Oolite and Fullers Earth. What has happened at Burton Cliff could happen at East Cliff. At the present (2012) East Cliff still seems to have less cliff falls than Burton Cliff, probably because the shingle beach is better develeoped at East Cliff. However, this situation may change and some rock falls are occurring at the Burton Freshwater (i.e. southeastern) end. Although it is less likely, there is no guarantee that accidents will not happen at East Cliff. Minimise time spent close to the cliff and do not hammer the Bridport Sand Formation of East Cliff. If leading a party discuss the cliff and its geology from lower down on the beach, and then if conditions seem safe, approach the cliff only briefly to see the geological details of the formation.

INTRODUCTION - ROCK FALL:

East Cliff, Major Rock Fall, 2017 (and as seen later)

Rock falls from the high and vertical cliffs of Bridport Sands are on average fairly rare to the east of West Bay or Bridport Harbour and more common at Burton Cliff. However, because the beach is decreasing in width they may be beginning to become more frequent. Hot and dry weather conditions in early July 2017 seems to have been the cause of some major falls. More may occur, so there is a real hazard here. Some photographs of the July 2017 falls are shown below, as seen in 2017 and later (2018).

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A major rock and some lesser ones took place in East Cliff, West Bay near Bridport in early July 2017. There had been a long, hot and dry spell, with then some rain. Subsequently hot conditions continued. Rocks falls can occur at the cliffs just to the east of the harbour but this rarely seems to happen. More rock falls have taken place in the past at Burton cliff, and sadly, there has been a fatal accident there in 2012. The geology of the cliff at Burton Bradstock is similar to that at East Cliff, but usually the beach is narrower there and can be very narrow at high tide. The large rock fall of 2017, shown above, cut the cliff-top footpath and actually just penetrated into the golf course area adjacent. This is abnormal and no previous falls seem to have affected the gold course. Weather conditions were hot and dry and continued hot and dry afterwards. It was said that there had been some rain which might have affected the otherwise dry cliff.

A fundamental problem is that the western part of the Chesil Beach, which originally extended unbroken and evenly to West Bay, is, perhaps, becoming somewhat depleted of fine shingle. It may not be passing Burton Bradstock as readily as in the past. The Chesil Beach as a whole is not receiving new material and is an old beach that is now shut off by sea-walls at both ends and presumably will just progressively but slowly decline. At the same times the coast near West Bay, Bridport is probably becoming even more popular with the public (and it has received further publicity in connection with the Broadchurch television programme).

Considered in relation to the long-term, the beach at East Cliff does not seem to have become significantly broader over the years. The effective cut-off at the southeastern end of Burton Cliff may be a factor.

In addition, the hot weather conditions of 2017 seem to have been a factor in increasing cliff falls. Some geological fieldwork shown here was undertaken when falls were rare at East Cliff, near West Bay.

INTRODUCTION:

General

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The two photographs above, although in very different format show the same piece of cliff and beach. Note that the 2017 photograph seems to show a general scouring of the cliff. In particular there seems to have been a lowering of the beach directly adjacent to the cliff, and this has revealed a lower band of bluish-grey, unoxidised, calcite-cemented sandstone. In other words the beach seems rather starved and the top seems to be lower than it was eight year before. The occurrence of a major (and also a minor) cliff fall, near here, in the summer of 2017 was unusual, and probably an indication of new weaknesses in the East Cliff of West Bay, Bridport. Unfortunately, this may mean that East Cliff is becoming dangerous in part, at least in some weather conditions.

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These beds from the lower part of the Bridport Sand Formation are blue because they have not been oxidised. The natural colour of the formation, as seen in borehole, is a bluish colour that results from the content of pyrite, preserved only in reduced conditions. The colour of oxidised Bridport Sand Formation is, of course, a yellowish brown. If these blue strata are exposed any substantial length of time, then the pyrite would be oxidised and the colour would change to brown. So these strata have only been exposed to the atmosphere for a relatively short time, as a result of loss of beach material (almost certainly drited eastwards because of privailing southwesterly winds. This is proof, of course, of rapid coast erosion and real beach loss at East Cliff, West Bay.

[the matter is hardly disputable, but if separate proof was needed then there is the recent re-exposure of a large drainage pipe just west of the cliff at the harbour end, and the evidence of beach-lowering at the edge of the eastern pier. There is no doubt that there has been recent loss.]

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STRATIGRAPHY:

General

The Bridport Sands Formation are of Upper Lias age and the sedimentary features and fauna of this oil reservoir rock, of much interest in relation to the petroleum geology of southern England and the English Channel.

STRATIGRAPHY:

The Lower Jurassic System of West Dorset.

The simplified outcrop map above shows the distribution of Jurassic strata at the surface on the British land areas. The offshore outcrops, such as in the North Sea and the English Channel are not shown here. Jurassic also underlies extensive areas in southeastern England, as in the Weald of Kent and Sussex. Lyme Regis is shown at the southwestern end of the Yorkshire to Dorset outcrop.

The top table above gives the chronostratigraphy of the Jurassic System in terms of stages with dates mainly from Odin as given in the International Stratigraphic Chart of UNESCO, 2000. It is is recommended that checks be made with regard to correction and updating from time to time. It is likely to be modified but mostly only to a small extent. The Jurassic/Cretaceous boundary presents special problems and there is some uncertainty here.

The section in the bottom left diagram is a simplified and introductory scheme to the lithological sequence of the Lower and Middle Jurassic strata. It consists of marine clays or shales alterning with some limestones and sandstones. The bottom right-hand diagram gives the traditional zonal scheme of the Lower Jurassic with lithological equivalents, based on House (1993) and Cope et al. (1980) .

The section to be discussed is east of Bridport Harbour or West Bay is in the Bridport Sands of the Upper Lias, one of the major sandstones in the Jurassic sequence in Dorset, and of importance as an oil reservoir rock. It is, as shown in the right-hand diagram, of Toarcian and Aalenian age, and represents parts of the ammonite zones - Dumontieria levesquei and Leioceras opalinum.

To gain some understanding of the formation in broad perspective it is worth giving a little thought to sedimentation rates. The Bridport sand are 43m thick here (and 48m at Chideock) so in broad terms (assuming roughly a million years for an ammonite zone) it had an average sedimentation rate of something like 20K years per metre here (and slower elsewhere). This is fairly normal for the Jurassic of Dorset, unlike the condensed Junction Bed (at West Cliff) or the Inferior Oolite (at Burton Bradstock. Being on a structural high, it is, of course, not suprising that the formation is somewhat thinner here than elsewhere, but it does not show great condensation. It did maintain a rather constant facies, always relatively shallow but tending to shallow-up further towards the Inferior Oolite. Increasing proximity upwards of the carbonate bands, as seen in the photographs, suggests progressive reduction of sedimentation rate. It is worth noting that although this is a sand facies (i.e. with short-term rapid sedimentation rates), the average sedimentation rate is not drastically different from clay facies such as the Belemnite Marls.

The vertical East Cliff is impressive with clean exposures at the base that are fossiliferous in places. The view from the top of the cliff shows the excellent exposures of the Lias and overlying Cretaceous strata to the west. From this viewpoint the coast erosional problems at the harbour mouth can be seen. Further west of the harbour is Middle Jurassic Frome Clay or Upper Fullers Earth and some Forest Marble seen at West Cliff or Watton Cliff . For information on the strata in the cliffs beyond those see the Eype Mouth webpage.

GEOLOGICAL MAPS

A prerequisite for a geological visit to Bridport, Eype, Burton Bradstock, Charmouth, Beaminster or adjacent areas is the British Geological Survey map, Sheet 327. So too is the new memoir - British Geological Survey Memoir (2011), Geology of South Dorset. (Note that it includes Charmouth and east of Charmouth, including St. Gabriels Mouth and Golden Cap, but not Lyme Regis).

Above is a simplified map showing the geology of the West Dorset coast including the Bridport and Lyme Regis area. Note that other field guides for localities shown on this map include:
Burton Bradstock, Bridport Sands and Inferior Oolite , Lyme Regis - west , Lyme Regis to Charmouth , Chesil Beach .

A simplified section of the cliffs near West Bay or Bridport Harbour is shown above. The account which follows mostly concerns the Bridport Sands of East Cliff, which is to the right on the section. (Note that " boueti Bed " refers to a bed with the brachiopod - Goniorhynchia boueti. A small oyster common in Watton Cliff is Praeexogyra hebridica. Note also that although the Inferior Oolite occurs in East Cliff, it is not accessible and is best seen by going to Burton Bradstock, to the east, descending to the shore and examining the large fallen blocks of this fossiliferous limestone.)

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.

BR ?? - BRIDPORT SANDS:

Facies and Palaeogeography

(text to be added)

B2a - BRIDPORT SANDS - SEDIMENTOLOGY - (START)

Bridport Sands - East Cliff - General Sedimentary Features

The cliff exposures here shows splendid example of Jurassic marine shoal sands. The Bridport Sand Formation, 43 metres thick here, represents a relatively shallow facies of a major ryhthm of Jurassic sedimentation. This formation is an important oil reservoir rock underground at the Wytch Farm Oilfield and these are the best exposures at the surface.

This sandstone formation is a classic diachronous sequence that youngs southward. The main sequence is Upper Toarcian (Dumortieria levesquei ) zone but in Dorset the top 2 metres are Aalenian (Leioceras opalinum zone). It is interesting in containing heavy minerals of metamorphic type (e.g. garnet), probably ultimately derived, via the Permo-Trias, from Brittany (Davies, 1967).

Carbonate-cemented and well-burrowed sands alternate with poorly cemented and less burrowed sands. Mica flakes are distorted by compaction in the softer units and undistorted in the harder bands, suggesting early cementation (Davies, 1967). The well-cemented layers may be storm deposits, high in bioclasts and low in clay content (Bryant et al. , 1988 ). Look at the cliff and note how the rhythmic units become thinner (closer) at the top as the carbonate facies of the Inferior Oolite above is approached. The sand supply was presumably decreasing.

Notice that in places the lower part of the cliff is blue-grey and so too is the the rock where it is freshly broken away (and it is blue-grey in boreholes, as at Marchwood near Southampton). The natural colour of the Bridport Sands Formation is blue-grey. The yellowish colour seen in the cliffs is a surface effect of oxidation of pyrite (i.e. it is like superficial rusting).

Observe that the foot of the cliff at the top of the fine shingle beach has been undercut by abrasion.

BRIDPORT SANDS SEDIMENTOLOGY continued:

Sediment Composition and Clay Mineralogy

Introduction

The diachronous Upper Lias Sands of southern England, the Bridport Sand Formation is a unit of fine-grained sandstone, a quartz arenite, with hard, calcite-cemented beds at frequent intervals. There ae small scale (of one or two metres) of rhythmic alternations of friable, yellow sandstone and firm grey calcareous sandstone. The hard bands are fairly regular sedimentary layers, although in detail, they arre not simply depostional but also have diagentic nodular features. They do not have perfectly bedding-parallel boundaries, but they do not transgress the stratigraphy greatly and broadly match depositional sedimentary structures.

The Bridport Sand Formation (or "Bridport Sands" in the older literature consist of marine sediment of uppermost part of the Lias, Lower Jurassic, specifically Toarcian (with a very small amount in Aalenian). Because of diagenesis and bioturbation the Bridport Sands have relatively few obvious fossils. Some belemnites and ammonites occur but are not abundant. When fossils are of calcite or are calcite replacements of aragonite, or are moulds. No aragonite is preserved.

At first sight one aspect of the sequence, the colour, is liable to be misunderstood. It appears yellow in the cliff but this is a relatively near surface effect that results from oxidation above the water table. In boreholes it is usually blue-grey, like most of the Lias beneath it. The blue-grey unweathered colour can sometimes be seen at the foot of the cliff, because the yellow colour does not normally extend below sea-level.

Related to the originally reduced condition is the fact that in the Wytch Farm boreholes the Bridport Sand Formation contains "sour gas" or hydrogen sulphide, h2S. A practical application of this at the coast is the Fe had been hydrated from FeS2 to ferric hydroxide. Presumably this change produces a mineral volume increase and therefore either a small porosity decrease or a small physical bulk expansion. It may also weaken cementation.

The sand particle size is so fine that it does not provide good beach sand, and in any case, rock falls although a hazard, do not occur frequently enough to supply a large quantity of sand to the beach (there are other factors involved, though, the beach is sorted and coarser as part of the Chesil Beach system).

The median grain size of the Bridport Sand Formation sediments in the Bridport - Burton Bradstock cliffs is 4 phi or about 63 microns ( Davies, 1967) (bridging the sand - silt boundary but being fine skewed). The sediments were considered by Davies (1967) to be marine sediment deposited in barrier bar, marine lagoon and off-bar subenvironments. The sediments on the coast at East Cliff, West Bay and at Burton Clif are very uniform except of a progressively closer spacing of hard, calcite cemented beds towards the top and towards the very condensed Inferior Oolite. There is no indication of abnormal salinities, either high or low and the fauna indicate marine conditions throughout.

The alternations were considered by Davies (1967) to be the result of fluctuating rates of detrital deposition in Toarcian Jurassic times. The hard-cemented calcareous sandstones represent phases at a particular place of limited detrital deposition, that is little input of fine sand, but where calcium carbonate, probably largely from the shells of organisms, could have accumulated. According to Davies' theory the friable sandstone interbeds representing phases and areas of more rapid detrital deposition.

The thickness of friable sandstones, between the hard beds, decreases upwards so that overall and generalising there is an increase in the calcium carbonate content of the sediments. This was a progressive change leading eventually to the almost entirely limestone facies of the Inferior Oolite above. ------- [in progress] .

[ Notes in progess - 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.
----- 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. ]

BRIDPORT SAND FORMATION - SEDIMENTOLOGY continued:

Sedimentation Rate

Field evidence studied by Davies (1967) indicated to him that the calcareous sandstones were lithified before the deposition of more than 15cm of superimposed sediment. He estimated that such lithification took approximately 150 years. If that is correct that would give a sedimentation rate of about 10cm per 100 years, a very fast rate of deposition. See more recent literature to try to assess this further.

In very simple terms, it is worth noting that almost all of the Bridport Sand Formation, 43m at East Cliff, belongs to one ammonite zone, that of Dumortiera levesquei (and the Down Cliff Clay is also in this zone). Contrast this with the Junction Bed or Beacon Limestone Formation which has five ammonite zones in a thickness of 4 metres.

A very rough assumption is sometimes made that an ammonite zone is deposited in round about 1 million years. Using the 43m thickness the round figure is about 23 thousand years a metre. This is fairly fast sedimentation but not remarkably fast; it about twice as fast as the 40,000 years a metre common in Jurassic Obliquity Cycles. This rough calculation merely suggests that the sedimentation rate for the Bridport Sand Formation was not particularly unusual. What is unusual is the very low sedimentation rate in the condensed sequences of the Junction Bed or Beacon Limestone, below the Bridport Sand Formation and the thin Inferior Oolite above. The Bridport Sand Formation was consequence of fairly normal, shallow-water sedimentation in the subsiding basin.

Following the alternations of hard cemented beds and friable sandstone up the cliff, these division become closer and are very close just beneath the condensed Inferior Oolite. Thus the sedimentation rate and subsidence rates decreased as the Inferior Oolite phase was approached but in a smooth and progressive manner.

BRIDPORT SAND FORMATION:
SEDIMENTOLOGY continued:

Hard Bands - Calcite-cemented Horizons

The carbonate-cemented beds have about 30 to 40% calcium carbonate, in contrast with about 3% in the friable sandstones. An example of compositional changes in a short vertical sequence is shown by (Davies, 1967), fig. 8. The carbonate distribution is very bimodal, but with some transition at the bases and tops of the hard bands.

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 mile (3 to 5 km) apart (Davies, 1967).

Were the sequence not sandy it might be broadly similar to the Blue Lias with its stone bands, resulting from early diagenesis superimposed on a sedimentary difference.

BRIDPORT SAND FORMATION:
SEDIMENTOLOGY continued:

Compaction History and Petrography

Petrographic studies by (Davies, 1967) demonstrate that original textural relationships are retained in the calcareous sandstones, while thd friable sandstone interbeds have undergone compaction effects. There is a dramatic difference in the mica flakes (common in this formation) in the carbonate-cemented sandstones, in comparison with those in the friable sandstones.

An interesting aspect of the carbonate-cemented beds is that individual quartz grains show the effect of dissolution (Davies, 1967, fig. 9). Why should this have occurred? Silica is soluble at very low and very high pH values. Obviously, low pH would seem impossible in a carbonate environment, but very high pH might be feasible in certain circumstances and is a more probable explanation. The mechanism is not understood.

BRIDPORT SAND FORMATION:
SEDIMENTOLOGY continued:

Porosity

The spar-filled pore space of the calcite-cemented sandstone was found by (Davies, 1967) to be between 36 and 48%. The mean is is 43%, an interesting figure. This high figure lies within the range of modern sands as deposited (e.g. Bournemouth beach sands), which is 39 to 49%. Thus there was no significant compaction before the hard carbonate-rich bands were cemented. Thus (Davies, 1967) demonstrated that they were cemented very early before any significant burial. This accords with the undistorted mica. It brings to mind comparison with the Blue Lias cementstones (with uncompacted fossils). Further evidence for lack of any degree of compaction comes from "floating" grains and a minimal number of grain contacts, all in accordance with non-deformation of mica flakes. It is not disputable that there was only a thin veneer of sediment at the time of cementation.

Davies (1967) drew attention to the fact that low-dimension channels or virtually planar erosion surfaces did not cut through the hard beds. Thus they were hardened very rapidly after deposition. Davies (1967) suggested that they were hardened before more than 6 inches or 15cm of sand was deposited above them. Thus they were almost hardgrounds.

Where the original sea-floor bottom was irregular, and shows channel-like features, the cemented beds broadly parallel the irregularities. Cemented bases of channels can be seen in photographs of this webpage. Davies (1967) appropriately used this as evidence against unmixing (unmixing is not in any case compatible with the petrographic evidence for very early cementation).

An interesting question arises as to what happened to aragonitic shells. Presumably the aragonite was lost early in mineralogical terms but may have supplied calcium carbonate for some of the calcite cementation.

In comparison with the cemented beds, the friable sandstones are quite different. As noted above, mica flakes are deformed by compaction. Pore space varies between 15% and 37%, with a mean of 26%. This is still quite a high figure. However, remember the rather fine particle size and note that there are pemeability problems connected with expandible clay minerals.

An BP oil industry report (BP 2009 (re Relinquisment of Licence P1022) contains the following brief comments on porosity and permeability of the Bridport Sand Formation in the Wytch Farm Field.

"Sedimentologicaly, the Bridport Sandstones are very uniform, typical of shallow shelf bioturbated sand bodies. The major control on porosity and permeability is the extent of the hard bands. These have very poor reservoir quality and are non-pay, and form extensive production barriers. Average net porosities in the Bridport Sandstones range from 20-27%, and layer average permeabilities range from 5mD at the base of the sands to 64mD at the top. Bridport oil is produced from the Wytch Farm and Wareham Fields. Conventional sub vertical wells in the Bridport on Wytch farm and Wareham sustained production of 500bopd with pressure support [i.e. water-injection]".

With regard to the origin of the hard cemented beds, it is important to see the paper of Bryan, Kantorowicz and Love (1988). They provided much detailed evidence. In particular they showed evidence from ichnofacies of very shallow deposition and the presence of "firmground" (i.e. like hardground) at times. In particular they attributed the occurrence of the hard bands with the higher carbonate to episodic storm processes on a submerged marine shoal. They made comparison to sediments of the distal shelf (6 to 120m water depth) off Mauretania at present. Trace fossils are similar to those of the Liassic sands.

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BRIDPORT SAND FORMATION:

OIL RESERVOIR PROPERTIES:

Introduction to the Bridport Reservoir

Some brief notes are given here regarding the main properties of the Bridport Sand Formation Reservoir of the Wytch Farm Oilfield at Poole Harbour, Dorset. The Bridport Reservoir is a carbonate-cemented slightly ferruginous sandstone reservoir. The following information is based on the paper by Aplin and Coleman (1995). This paper is recommended for reading and is obtainable from the Geological Society of London in Special Publication, volume 86, The Geochemistry of Reservoirs.

Wytch Farm is located on the southern English coast and is the largest onshore oilfield in western Europe Most of the oil produced in recent years occurs in the Triassic Sherwood Sandstone, much lower in the succession. The Bridport Sand Formation, of Toarcian, Lower Jurassic age is the higher and smaller reservoir. It is only about a tenth the size of the deeper and more extentive Sherwood Sandstone Reservoir. The Bridport Reservoir contain 30 million barrels of undersaturated oil, compared with 300 million barrels or more in the Sherwood Reservoir. The Bridport Reservoir oil has a GOR or Gas/Oil Ratio of 150 scf/bbl (standard cubic feet per barrel of oil). This higher reservoir occurs at a depth of about 900 m, at a temperature of 40°C and a pressure of 1500 psi (pounds per square inch).

The Bridport Sand Formation of the Upper Lias is thought to have been deposited on the mid-continental shelf. It is a very fine sandstone with about 10% clay minerals,including the Fe-bearing minerals chlorite and berthierine. Note that at the surface the greenish mineral berthierine may be oxidised to brown limonite. Authigenic siderite (FeCO3) is common and comprises up to 10% of the rock. This is interesting to note because it is probably the sideritic composition that produces the conspicuous brown colour in the cliffs. Pyrite (FeS2) typically comprises 1 to 2% of the rock, when not oxidised. Laterally extensive (kilometre scale) calcite-cemented horizons, the hard beds in the cliff at East Cliff, West Bay, are up to 1 metre thick. They occur at intervals of 1 to 2 m throughout the reservoir and severely reduce large-scale vertical permeability. Some of these are barriers with compartmentalize the reservoir.

Production from the Bridport Sands started in 1979. This was the first major reservoir for production, and the Sherwood Reservoir was only discovered much later. It was at a level of 6000 bbl/day in 1984. The original brines in the reservoir were at about twice seawater salinity, probably because of dissolution of some evaporites from some horizon (not in the Lias).

Seawater injection, using water from Poole Harbour, was used to increase the pressure and facilitate production. This started in November 1980 at Well D10. The injected seawater had broken through to Well D9 by 1984.

BRIDPORT SAND FORMATION:

WEATHERING

Oxidation in the Cliff

The Bridport Sand Formation in boreholes is blue-grey and the rock is in reduced condition, and as noted above is sideritic. At the Wytch Farm Field it is not only in reduced condition but it contains sour gas or hydrogen sulphide (H2S). Details are given by Aplin and Coleman (1995). The presence of hydrogen sulphide is attributed to reduction of formation-water sulphate possibly by bacteria. Some in the past has reacted with iron-bearing minerals but there is still at Wytch Farm a significant amount of H2S dissolved in the formation water. At the coast in vadose or top (exposed) phreatic conditions the formation water may have lost the hydrogen sulphide.

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BRIDPORT SAND FORMATION:
SEDIMENTOLOGY continued:

Rhythmicity

Davies (1967) considered the problems of apparent rhythmicity of hard bands. He did not find a relationship between the positions of cemented bed and the positions of primary sedimentary structures (e.g. bioturbated versus non-bioturbated horizons). He considered climatic changes were not responsible, but this is probably not conclusively disproved. He thought that the rate of supply of detrital sediment may have varied while the rate of supply of calcium carbonate remained constant. An alternative view is that the hard bands were originally more shell-rich, that is with an initially higher carbonate content.

BRIDPORT SAND FORMATION:
SEDIMENTOLOGY continued:

A Tree with Roots - Very Early Cementation

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A mould of the stump of a small tree was found in a fallen block of carbonate-cemented sandstone, that is apparently derived from the Bridport Sand Formation in the cliff above. The location is East Cliff, West Bay, Bridport, towards the eastern end. It is not a good or impresive specimen and has no value in terms of collecting (the Isle of Portland is the place for finding fossil tree remains). It does reveal an interesting story to the sedimentologist and therefore should be left in place for specialist study.

The mould is about half a metre in length and oval in cross-section. The tree is not quite normal to bedding but projects through the strata, one of the honeycombed-weathered and calcite-cemented beds of the Bridport Sand Formation. There is particularly hard and well-developed cementation around the tree. This cemented area is brownish in colour as a result of iron-staining, probably from oxidised pyrite. It is interesting to note that bivalve and other fossil remains are visible in cross-section in the hard-cemented sandstone around the tree. These are not common in the usual hard sandstone beds of the Bridport Sand Formation. It is reasonable to assume that the cementation around the tree was slightly earlier than then usual (early) cementation of the hard bands. In other words there was a phase of mollusc shell dissolution after the cementation around the tree and before the main banding cementation. This is of interest because the relative lack of resistant calcitic bivalves, such as oysters, within the main part of the Bridport Sand Formation is clearly a puzzling matter. It was not just aragonite which was lost in early diagenesis but also bivalve calcite.

The early cementation around the tree took place before rotting of the tree. Although modified by the particular complications discussed above,the discovery does in general confirm the theory of early cementation put forward by Davies (1967).

A local source for the small tree can he explained by derivation from a nearby island. The location is only two kilometres from the Eype's Mouth Fault, which is well-known for its penecontemporaneous movement during Middle Lias times (as shown by the Beacon Limestone Formation or Junction Bed). Thus the penecontemporaneous fault movement on this bed here or somewhere else nearby was continuing into late Upper Lias times. However, the presence of an unrecognised palaeosol, as a rooting material for the tree, here at East Cliff cannot be completely eliminated. Further study is needed.

BRIDPORT SAND FORMATION:
SEDIMENTOLOGY CONTINUED:

Permeability and Clay Mineralogy

The clay mineralogy of the Bridport Sands differs from that of some other local Jurassic Formations and has some interesting features, including perhaps some capabilities of expansion and contraction.

The clay minerals of the Bridport Sand Formation comprise mainly kaolinite and mixed layer clays of both the illite-chlorite and illite-smectite type ( Morris and Shepperd, 1981). In particular the adsorption of water can cause expansion of poorly crystalline mixed layer illite-smectites causing blockage of pore space. This can be a problem in the subsurface Bridport Sand Formation of the Wytch Farm Oil Field. It is interesting that this reduction is largely reversible on drying out. A possible matter of bulk expansion at the surface in wet weather conditions resulting from clay mineral expansion has not been researched. If the illite-smectite expansion is reversible then, at least in theory, some small contraction might occur during drying out of the Bridport Sand Formation in East Cliff and Burton Cliff. If this happens it would relevant to matter of the triggering cause of rock falls.

B2c BRIDPORT SAND FORMATION:
SEDIMENTOLOGY continues

Tafoni - Honeycombe Weathering

Obvious features of East Cliff are the hard bands. These have appreciable carbonate content which is the result of early cementation due to local migration of calcium carbonate. They show abundant honeycombe weathering or the development of tafoni (the Italian for caverns).

Very similar sandstone facies, with tafoni or honeycombe weathering, occurs in the Eocene of Oregon. It is shown for comparison. The honeycombed surface develops because some of the carbonate is dissolved by rainwater containing carbon dioxide and the combined action of rain and wind erodes out the sand in patches where the carbonate cement has been dissolved. This honeycombe weathering is only present in the cliff above the level at which storm waves can erode the surface fairly smooth. It can be seen in some fallen blocks. The honeycombe weathering in the Bridport Sands often accentuates trace fossils (this is not obviously the case in the Oregon sandstone). Thallassinoides,(large and branching horizontally - common and easily seen) Chondrites (very small branching tubules - not very easy to see here), Siphonites, Rhizocorallium (horizontal U-shaped burrows and Arenicolites are present in the Bridport Sands Bryant et al. , 1988 .

B2d. BRIDPORT SAND FORMATION:
SEDIMENTOLOGY continued

Pyrite Nodules

There are small brown limonitic concretions in the cliff. These are oxidised pyrite nodules. They accord with the fact that the Bridport Sands are blue grey, reduced and pyritic beneath the surface. This is seen in boreholes. In addition the Bridport Sand Formation contains sour gas, i.e. hydrogen sulphide, FeS2 in the Wytch Farm field. The sandstone in the cliff is now, of course, above the water-table and subject to percolation of meteoric water which is oxidising.

BRIDPORT SAND FORMATION:
SEDIMENTOLOGY continued:

Major Scour Structures

From the beach, and from the sea, some broad curved sedimentary structures can be seen in the Bridport Sands near the base of the cliff. There are 11 of these between West Bay and Burton Bradstock, further east. These undulations have a mean wavelength of 37m and amplitude of about 1.4 metres, have near symmetrical cross-section and rounded crests(Pickering, 1995)..They do not seem to be present at higher levels. They could not be sand-waves because cross-stratification is not visible within them. They are probably scours indicating a major storm event (Davies, 1967).

For further discussion see Pickering (1995). Measurements have been made, wavelength and aspect ratio etc. have been determined. There is similarity as bedforms to modern tidal sandwaves in 5 to 10 metres of water but, as mentioned above, they lack the cross-stratification and have only internal lamination. Pickering suggested that they were formed as erosional, wavy sandy bedforms developed below standing waves, probably during a very severe tropical cyclone, consistent with the low latitudes for that time. He thought an origin from the effects of a Tsunami was unlikely. However, it should be remembered that this locality is very close to the Eype Mouth Fault (see Bridport to Eype Mouth Webpage), which has been proved to have been active during deposition of the Middle - Upper Lias, Junction Bed, not long before.

Note, incidently, that if the carbonate-cemented beds are storm lags of shell material, as mentioned above, that they drape the curved bedforms in a nearly continuous manner. According to the theory of Pickering (1995), after the standing waves which made these bedforms ceased to exist then the intervening troughs were filled with subhorizontal sediment.

[
SUPPLEMENT
BRIDPORT SAND FORMATION
SEDIMENTOLOGY continued:

Sedimentary Structures and Trace Fossils - at Burton Cliff, Burton Bradstock.

]

For more information of the Bridport Sand Formation of Burton Cliff go to:
Burton Cliff Geology.]

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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.

Geophysics

Petroleum Reservoir Rock

The Bridport Sands are well known as the Upper Reservoir of the Wytch Farm Oilfield, Dorset. As a marine Jurassic sandstone, with good porosity and permeability, they form a good, conveniently accessible example of a Jurassic reservoir, and are not greatly different from North Sea sandstones, such as the Brent Sandstone. They have been much studied (and further information will be added).

BRIDPORT SAND FORMATION:

P1. PETROLEUM GEOLOGY:

Petroleum Reservoir Rock - Subsurface Brines [to be added]

More Information

For more on the Bridport Sands see:
Burton Bradstock webpage - Bridport Sands

and

Petroleum Geology, South of England.]

INFERIOR OOLITE

Limited Exposure

The Inferior Oolite is present, but only in part (i.e. the lower part) at the top of East Cliff, in some parts, particularly towards Burton Freshwater. The exposures are better at Burton Cliff so please see the: Burton Cliff Webpage for more information on this stratigraphical unit.

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Our daughter, Tonya Loades, is sincerely thanked for early morning, photographs of East Cliff and adjacent area, including details of rock-falls, taken in July 2017. I particularly wish to thank Dawn and Tony Denyer for the opportunity to visit a coastal locality with similar features in Oregon. Doreen Smith has very kindly provided some photographs used in this webpage. I thank Dr. Laurence North and Dr. Tongcheng Han for discussion in the field of geophysical properties of the Bridport Sand. My wife Cathy West has supported in many respects the production of these webpages and this is much appreciated. I am very grateful to Martin Cox for his generosity in allowing me to use photographs of East Cliff, West Bay and of Burton Cliff taken by him from the sea, soon after the accident of the 24th July 2012. The scours of Davies (1967) are very well shown in Martin's photograph.

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Aplin, A.C. and Coleman, M.L. 1995. Sour gas and water chemistry of the Bridport Sands reservoir, Wytch Farm, UK. In: The Geochemistry of Reservoirs, Geological Society Special Publication No. 86, pp. 303-314.
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Bjorkum, P.A., and Walderhaug, O. 1993. Isotopic composition of a calcite-cemented layer in the lower Jurassic Bridport sands, southern England - implications for formation of laterally extensive calcite-cemented layers. Journal of Sedimentary Petrology, 63, pp. 678-682.
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Boswell, P.G.H. 1924. The petrology of the sands of the Upper Lias and Lower Inferior Oolite in the west of England. Geological Magazine, 61, 246-264.
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BP. 2009. See: DECC. Department of Energy and Climate Change (British Government).

BP. 2009. Relinquishment Document by BP - Old Harry - 1 Prospect. To DECC, Department of Energy and Climate Change. Licence determination of surrender document filed to DECC, November, 2009. Re. Old Harry - 1 Prospect. (Details given in the DECC section, and in the Petroleum Geology, South of England, webpage.)

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Bradshaw, M.J., Cope, J.C.W., Cripps, D.W., Donovan, D.T., Howarth, M.K., Rawson, P.F., West, I.M. and Wimbledon, W.A. 1992. Jurassic. Pp. 107-129 in: Cope, J.C.W., Ingham, J.K. and Rawson, P.F. 1992. Atlas of Palaeogeography and Lithofacies. Geological Society of London, Memoir 13,
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British Museum (Natural History). 1962 and various editions onward. British Mesozoic Fossils. 207pp.
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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).
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Buckman, S.S. 1889. On the Cotteswold, Midford and Yeovil Sands, and the division between the Lias and the Oolite. Quarterly Journal of the Geological Society, London, 59, 445-458.

Buckman, S.S. 1889. Certain Jurassic (Lias-Oolite) strata of south Dorset; and their correlation. Quarterly Journal of the Geological Society, London, 66, 80-89.
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Buckland, W. 1837. Geology and Mineralogy Considered with Reference to Natural Theology. The Bridgewater Treastise on the Power, Wisdom and Goodness of God as Manifested in the Creation. Treatise VI. London, William Pickering, Vols 1 and 2.
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Calloway, 2009 [Incomplete reference; more to be added if found.] (re Channel Coastal Observatory and West Bay; perhaps a student project)

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Cope, J.C.W., Getty, T.A., Howarth, M.K., Morton, N. and Torrens, H.S. 1980. A Correlation of Jurassic rocks in the British Isles. Part One: Introduction and Lower Jurassic. Blackwell Scientific Publications, Oxford.

Cope, J.C.W., Ingham, J.K. and Rawson, P.F. (editor). 1991. Atlas of Palaeogeography and Lithofacies. Geological Society of London. Geological Society Memoir No. 13. ISBN 0-903317-65-6. (see Jurassic section - Bradshaw et al., p. 107 - 129.)
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Cox, C.C. (undated - 1950s?). The History of the Church of St. Michael The Archangel, Lyme Regis. By C. Carew Cox, Vicar, 5th Edition, The British Publishing Company Limited, Gloucester, 16 pp.
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Damon, R. 1884. Geology of Weymouth, Portland and Coast of Dorsetshire, from Swanage to Bridport-on-the-Sea: with Natural History and Archaeological Notes. Weymouth. R.F. Damon. London, Edward Stanford, 55, Charing Cross, S.W. 2nd Edition.
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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.

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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 interesting old field guide mainly of historic interest.

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De La Beche, H.T. 1822. Remarks on the geology of south coast of England from Bridport Harbour, Dorset, to Babbacombe Bay, Devon. Transactions of the Geological Society, London, Series 2, vol 1, 40-47, Plates iii-viii.
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Dorset Coast Forum. 1999. Newsletter of the Dorset Coast Forum. 1999. Issue 4: November 1999. Dorset Coast Strategy moves into implementation. Web Site: www.dorset-cc.gov.uk/dcf. Extract regarding West Bay: "West Bay Improvements - Exhibition. An architectural model of the proposed coastal defence and harbour improvements scheme for West Bay will be the centre piece of an exhibition that will go on display at West Bay between 29 and 31 October and at Bridport between 1 and 3 November 1999. The two piers at West Bay have experienced major failures throughout their life; with there being seven extensive repairs in the last 50 years. They are an integral part of West Bay's coastal defences, as well as providing an entrance channel to the harbour. The piers are again in need ofattention in order to ensure they continue to protect West Bay from storm attack. The scheme includes the demolition of the existing West Pier and the construction of a 230 m long replacement pier on a new alignment, with strengthening work being undertaken to East Pier. The scheme will also include the construction of a newgroyne and shingle replenishment of West Beach; this will give protection to the western side of West Bay as well as providing an improved amenity beach. The East Pier will have a small rock extension which, together with a beach management plan, will maintain East Beach at a safe width. The scheme has been jointly developed by West Dorset District Council's engineers and Hydraulics Research Limited. A 1:45 scale physical model of the scheme has been tested at Hydraulics Research, with the proposed scheme significantly increasing the number of days the harbour entrance can be safely navigated. Currently the entrance can only be used on average 50% of the year. The new scheme will allow access to the harbour for all but the worst storm conditions, as well as providing a safe haven for craft using Lyme Bay. [The new harbour piers and entrance was opened in March 2005.]
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Dranfield , P. Langley, G.O., McLean, F. and Scottong, G. 1986. Wytch Farm oilfield development; geological, geophysical and reservoir engineering considerations. BP Petroleum Development Ltd..
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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. (Bridport Sands show changes between Thorncombe Beacon and East Cliff - see Fig 4.).

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Hollingworth, S.E., Taylor, J.M. and Kellaway, G.A. 1944. Large-scale superficial structures in the Northampton Ironstone Field. (By Sydney Ewart Hollingworth, James Haward Taylor and Geoffrey Arthur Kellaway.) Quarterly Journal of the Geological Society, vol. 100, pp. 1-44. January 1944.
Abstract
Detailed mapping reveals many structures, unrelated to the slight regional tilting, folding and faulting, that are determined not by deep-seated movements but by disturbances that are demonstrably of superficial origin. These structures include cambers, gulls, dip-and-fault structure and valley bulges. As a result of these movements dissected Inferior and Great Oolite strata are lowered vertically to the extent of 100 feet or more, so that they swathe the hill tops and valley sides. The causal processes of this camber structure include sub-surface erosion and valleyward outflow of the underlying Lias. Gulls are widened joints in the camber filled with material from above. They usually trend parallel to the strike of the cambered strata and may attain a width of 40 yards. Step-faulting of similar trend is commonly associated with advanced cambering. The throw of each fault in this "dip-and-fault" structure is compensated for by steep downslope dips (up to 40 degrees) in the inter-fault blocks. Valley bulges comprise a variety of upward displacements of the strata that are confined to the valleys and are due to differential loading of the incompetent Lias. Their origin and mode of development are discussed in relation to the physiography of the area and the fundamental part played by the Lias clay. The economic significance of the structures in the exploitation of ironstone and in water supply are briefly considered and reference is made to analogous structures in other areas.
[See also: Discussion of the paper by S. E. Hollingworth, J. H. Taylor, and G. A. Kellaway. Large-scale superficial structures in the Northampton Ironstone Field. In Quarterly Journal of the Geological Society, January 1945, v. 101, p. 135.]
[This paper by Hollingworth, Taylor and Kellaway is relevant to East Cliff, West Bay, Bridport because similar structures occur in the Bridport Sand Formation which exposed in the cliff there. See details in this website above.]

Hollingworth, S.E. and Taylor, J.H. 1951. The Northampton Sand Ironstone; Stratigraphy, Structure and Reserves. Memoirs of the Geological Survey of Great Britain, Department of Scientific and Industrial Research, The Mesozoic Ironstones of England. By S.E. Hollingworth and J.H. Taylor, with contributions by W. D. Evans, G.A. Kellaway, F.B.A. Welch, V. Wilson, and A.W. Woodland. London, Her Majesty's Stationery Office, 1951. 2011 pp. with 1 photograph (Plate 1) and three (or four) foldout maps. See Figure 18 on p. 198, for a good cross-sectional diagram of the structures.
[See also associated: Taylor, J. H. 1949. Petrology of the Northampton Sand Ironstone Formation. Memoir of the Geological Survey of Great Britain.]
Section relevant to the Bridport Sand Formation, East Cliff, Bridport (although not discussed in the book):
Chapter IV. Superficial Disturbances. [pp. 31-34 plus Plate V.]
Extract from p. 31.
Modifications of the lie of the ironstone and of the overlying beds that do not follow any regional pattern are quite inexplicable in terms of deep crustal movements are widespread in the Ironstone Field. The structures falling into this category, which have been described in detail elsewhere (Hollingworth, Taylor and Kellaway, 1944; Hollingworth and Taylor, 1946), and are briefly defined and illustrated in the Appendix (p. 197), represent a comparitively late series of movements closely related to the valley system. They are subsequent to the initiation of the excavation of that system and so are also younger than the uplift of the surface on which the rivers developed. The available evidence indicates that the main operative element was movement in the Lias Clay with subordinate movement in other clay formations. These acted as incompetent bed that yielded by internal distortion or plastic flow under differential pressure. Such pressure was due to unequal unloading as the topographic relief became accentuated with the progressive downcutting of the valleys. The plasticity of the clay was probably at a maximum following a period when deep freezing had broken down its internal structure." ... [continues]

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Hounslow, M.W. 1987. Magnetic fabric characteristics of wave-produced grain orientation in the Bridport-Yeovil Sands (Lower Jurassic) of southern England. Sedimentology, 34, 117-128.
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House, M.R. 1993. Geology of the Dorset Coast. Second Edition. Geologists' Association Guide No. 22. The Geologists' Association, Burlington House, Piccadilly, London, 164 pages & plates. Paperback and not expensive. ISBN 07073 0485 7. This contains much detailed information on localities, excellent reference list and is inexpensive. This and the guide by Allison are parts of a series of field guides published by the Geologists' Association, Burlington House, Piccadilly, London W1V 9AG.
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Kantorowicz, J.D., Bryant, I.D. and Dawans, J.M. 1987. Controls on the geometry and distribution of carbonate cements in Jurassic sandstones: Bridport Sands, southern England and Viking Group, Troll Field, Norway. pp. 103-118 in: Marshall, J.D. (ed), Diagenesis of Sedimentary Sequences. Geological Society, Special Publication, No. 36, 103-118.
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Knox, O'B., R.W., Morton, A.C. and Lott, G.K. 1982. Petrology of the Bridport Sands in the Winterborne Kingston borehole, Dorset. In: Rhys, G.H., Lott, G.K. and Calver, M.A. (eds.) The Winterborne Kingston Borehole, Dorset, England. Institute of Geological Sciences Reports, 81/3, 107-126.
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Lake, S. D. 1985. West Bay, Bridport, In: Continental Extension Tectonics (ed. P.L. Hancock), Preconference excursion guidebook, Geological Society of London.
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Lang, W.D. 1962. Aalenian, Bridport Sands. Proceedings of Dorset Natural History and Archaeological Society, 83, p. 34.
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Lee, E.M. 1992. Urban landslides, impacts and management. Pages 80 - 93 in: Allison, R.J. (Ed. ) 1992. The Coastal Landforms of West Dorset. Geologists' Association Guide No. 47. 134 pp. (Dorset rock fall - accidents - p. 80.)
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Lemon, R.R. 1993. Vanished Worlds: an Introduction to Historical Geology. Wm.C.Brown Publishers, Dubuque. 480pp. [A good informative and interesting textbook with good illustrations, describing historical geology in American and international terms. Chapter 17 is on the Jurassic.]
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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.
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Morris, J.E., Hampson, G.J. and Johnson, H.D. 2006. A sequence stratigraphic model for an intensely bioturbated shallow-marine sandstone: the Bridport Sand Formation, Wessex Basin, UK. Sedimentology, Vol. 53, Issue 6, pp.1229-1263. [Authors: Jenny E. Morris, Gary J. Hampson, and Howard, D. Johnson.].
Abstract: The Bridport Sand Formation is an intensely bioturbated sandstone that represents part of a mixed siliciclastic-carbonate shallow-marine depositional system. At outcrop and in subsurface cores, conventional facies analysis was combined with ichnofabric analysis to identify facies successions bounded by a hierarchy of key stratigraphic surfaces. The geometry of these surfaces and the lateral relationships between the facies successions that they bound have been constrained locally using 3D seismic data. Facies analysis suggests that the Bridport Sand Formation represents progradation of a low-energy, siliciclastic shoreface dominated by storm-event beds reworked by bioturbation. The shoreface sandstones form the upper part of a thick (up to 200m), steep (2 to 3 degrees), mud-dominated slope that extends into the underlying Down Cliff Clay. Clinoform surfaces representing the shoreface-slope system are grouped into progradational sets. Each set contains clinoform surfaces arranged in a downstepping, offlapping manner that indicates forced-regressive progradation, which was punctuated by flooding surfaces that are expressed in core and well-log data. In proximal locations, progradational shoreface sandstones (corresponding to a clinoform set) are truncated by conglomerate lags containing clasts of bored, reworked shoreface sandstones, which are interpreted as marking sequence boundaries. In medial locations, progradational clinoform sets are overlain across an erosion surface by thin (<5 m) bioclastic limestones that record siliciclastic-sediment starvation during transgression. Near the basin margins, these limestones are locally thick (>10 m) and overlie conglomerate lags at sequence boundaries. Sequence boundaries are thus interpreted as being amalgamated with overlying transgressive surfaces, to form composite erosion surfaces. In distal locations, oolitic ironstones that formed under conditions of extended physical reworking overlie composite sequence boundaries and transgressive surfaces. Over most of the Wessex Basin, clinoform sets (corresponding to high-frequency sequences) are laterally offset, thus defining a low-frequency sequence architecture characterized by high net siliciclastic sediment input and low net accommodation. Aggradational stacking of high-frequency sequences occurs in fault-bounded depocentres which had higher rates of localized tectonic subsidence.
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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.

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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.

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Natural History Museum, London. (originally as British Museum (Natural History) 1962 and various editions onward). British Mesozoic Fossils. 207 pp.

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Penn, I.E., Chadwick, R.A., Holloway, S., Roberts, G., Pharaoh, T.C., Allsop, J.M., Hulbert, A.G. & Burns, I.M. 1987. Principal features of the hydrocarbon prospectivity of the Wessex-Channel Basin, UK. Pp. 109-118 in: Brooks, J. and Glennie, K., Petroleum Geology of North West Europe, Graham and Trotman, London. vol. 1, 598p + xxiii, (see page 116, Fig. 6 for Distribution and potential of the main reservoir horizons. A Bridport Sands map shows a region of relatively high porosity where the formation could form an effective reservoir. The cut off is - net thickness greater than 5 metres of sandstone with porosity above 21 per cent. The area extends from near Lyme Regis to about Southampton and northwards to the Cotswolds. The offshore area to the south is not shown on this map as having good porosity.)
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Pickering, K.T., Taira, A. and Soh, W. 1991. Scale of tsunami-generated sedimentary structures in deep water. Journal of the Geological Society, London, 148, 211-214.

Pickering, K.T. 1995. Are the enigmatic erosional sandy wave-like bedforms in Jurassic Bridport Sands, Dorset, due to standing waves? Journal of the Geological Society, London, 152, 481-485.

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Storey, J. 1987. Bridport Sands etc. At BSRG - British Sedimentological Research Group Meeting (low-Mg calcite precipitated in equilibrium with seawater. Na - 200-300, Sr high - ca 600 ppm near margins of beds. Usually about 300 ppm. Fairweather deposits finer. Storm deposits coarser, often with shell lag. Thickness is ca 75 m in west Dorset, 125m at Wytch Farm area - more central)
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Symonds, H. 1912. Bridport Harbour through seven centuries. Proceedings of the Dorset Natural History and Archaeological Society, 33, 161-199.

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Thomas, J. and Ensom, P. 1989. Bibliography and Index of Dorset Geology. Dorset Natural History and Archaeological Society. 102 pages. (with 25 references on the Bridport Sands). See also the internet version - Bibliography and Index of Dorset Geology.

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Underhill, J.R. and Stoneley, R. 1998. Introduction to the development, evolution and petroleum geology of the Wessex Basin. In: Underhill, J.R. (Ed.) Development, Evolution and Petroleum Geology of the Wessex Basin. Geological Society, London, Special Publications, 133, 1-18.

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Wilson, V., Welch, F.B.A., Robbie, J.A. and Green, G.W. 1958. Geology of the Country around Bridport and Yeovil (Explanation of Sheets 327 and 312). With contributions on: The Purbeck Beds by F.W. Anderson, Palaeontology by R.V. Melville, and Groundwater by S. Buchan. London, Her Majesty's Stationery Office, 239 pp. Department of Scientific and Industrial Research. Memoirs of the Geological Survey of Great Britain.
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West, I.M. 2000. Select Bibliography of Petroleum Geology of the Wessex Basin, southern England, UK - www.southampton.ac.uk/~imw/oilsot.htm. - The largest onshore oilfield of northwest Europe is at Wytch Farm, Dorset. Jurassic source rocks - Lias. Jurassic reservoir - Bridport Sands (Upper Lias).
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Woodward, H.B. 1887. Excursion to Bridport, Bothenhampton, Burton Bradstock, Bridport Harbour and Eype. Proceedings of the Geologists' Association, 9, 200-209.

Go west of Bridport Harbour (West Bay)? --
Bridport - West or Watton Cliff Go east of Bridport Harbour (West Bay)? --
Burton Bradstock

See also:
Chesil Beach.
Chesil Beach Storms.