Lulworth Cove, on the south coast of England, world-famous for its geology and geomorphology, is the most-visited geological locality in Britain. It is probably the best training location in the world for geology students. There are excellent exposures of folded Jurassic and Cretaceous strata and on the cliffs to the east is the Fossil Forest with an ancient soil and tree remains. There are glauconitic sandstones, sponge chert, cyclical Chalk, oil sands, lignite, ostracods, stromatolites, crocodile and fish teeth, an oyster bed, a transgressive marine pebble bed, a fluvial channel conglomerate, phosphatic strata, carbonate breccias, charophyte limestones etc. etc. The Lower Cretaceous, Purbeck Formation is contorted into the Lulworth Crumples at Stair Hole and the spectacular coast around here has caves, natural arches, sea-stacks and high cliffs of nearly-vertical Chalk. It can be studied at all levels from beginner level with basic geomorphology, to inversion tectonics and isotope geochemistry and spectral gamma ray logging. It is compact, very easy to get to, and has all necessary facilities including an interpretation centre. It is used by numerous universities, colleges, schools and societies and there are geological parties there almost every day of the year.

1. Introduction
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Introduction
The Village
Safety
Strata and Outcrops at Lulworth Cove
Geomorphology - General
--- Geomorphology - More Advanced Problems
Geomorphology - Lulworth Cove Beach
--- Geomorphology - Wave Action
6. North Side of Lulworth Cove
East Side of Lulworth Cove
West Side of Lulworth Cove
Miscellaneous - Lulworth Cove

Acknowledgements

Related Topics
Lulworth Cove Select Bibliography
Strata at Lulworth - Further Information

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. 1.1 Lulworth Cove - Introduction - General

Lulworth Cove is a beautiful small embayment providing a fine example of marine erosion in steeply dipping to vertical strata of very unequal resistance. (On the left, it is shown in aerial view with Durdle Door in the distance to the west. On the right we view it, looking south-eastward, from the top of the white chalk path which goes over Hambury Tout and continues westwards to Durdle Door ). The cove is important as an unusual geomorphological feature and also presents excellent exposures of Cretaceous strata with a wide variety of sedimentological, palaeontological and structural features of great interest. The region is one of petroleum exploration, including the sea-floor south of the cove and oil-sands occur nearby. To the east of the cove is the famous Fossil Forest with remain of trees from the Jurassic-Cretaceous boundary and a fossil soil.

. 1.2 Introduction - History

The cove attracts visitors of all types, more than a million visitors a year at present (House, 1996). In the past, King George III visited it by boat and was received on the shore with welcoming speeches (Mitchell, 1989). Napoleon, with sinister intention, may, perhaps, have visited (Loader and Loader, 1932), and the poet Keats sailed into the cove on his way to Italy and death (Ashley, 1992).

Smugglers were frequent visitors to the coast here. More recently, two Russian spies landed on the beach in the cove one night during the Cold War, perhaps about 1960. This was the second Russian landing to spy on the Underwater Detection Establishment on the Isle of Portland, Dorset. There is an account of this by Houghton (1972) which is rather amusing.

Geologists have been visiting since the early part of the 19th Century. Serious studies started here in about the 1830s. Geological publications on the area appear regularly and from time to time reinterpretations are made of the origins of the geological structures and other features.

2.

. 2.1 The Village of West Lulworth or Lulworth Cove

As a result of the superb geological and geomorphological features and because the locality is of easy access and can take coach parties, Lulworth Cove is visited by large numbers of geologists and geology and geography students. It is one of the most geologically visited places in the UK. It has good facilities for visiting geologists, including a heritage centre (next to the car and coach park as seen in the first image) and shops with books, maps and guides. It is a very popular tourist area and pubs and cafes are situated in the village near to the cove. In the height of summer the area around the cove and Stair Hole has numerous visitors but a short energetic walk over the hills and cliffs will soon take you away from the crowds. (This view is from Pepler's Point, east of the cove. From here you can see the well-worn path up Hambury Tout to the magnificent views of Durdle Door and the coast beyond. Behind you and eastwards is a gate to the Army Range and steps down to the Fossil Forest and the route to Mupe Bay.)

2.2 Down to the Cove

The end of the little road down to the beach is between a small cafe and an old boathouse. This is often a convenient place to meet students after they have used the facilities of the village. For field leaders, it is a good place to give out handout sheets and explain the general aspects of the geology, the basic structure and the mode of formation of the cove.

3.

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3.1 Safety - General

Rock and debris falls are a serious risk. In particular, the southeastern part of Lulworth Cove where the crumbly Pubeck limestones and shales outcrop should be treated with great caution and the foot of the cliff and overhangs avoided, especially in wet weather. See the safety bibliography for details of the danger. The high vertical cliff at the eastern end of Stair Hole presents a risk of falling blocks, and the foot of this should be avoided. Occasional falls occur at Black Rocks. Obviously cliffs everywhere owe their existence to undercutting and cliff-falls and cannot be totally safe. Geologists and geological parties should avoid wet weather, wear safety helmets where necessary and actively look for impact marks, debris piles, overhangs and other such hazardous places so as to strictly avoid them. Do not loiter in a area of potential rock fall. Under no circumstances shelter under or near rock ledges during wet weather. Rain is liable to dislodge debris from above.

Do not try to climb the cliffs, particularly those of Chalk. Routes which might seem feasible in fact lead to steep crumbly chalk which comes away in the hand. There have been many fatalities to climbers on the Chalk cliffs of the Lulworth are in the past.

Adders are occasionally seen in warm weather on rough cliff-top ground and should be watched for when walking on quiet, small footpaths in long grass. They usually present little risk unless an attempt is made to handle them.

Do not hammer flint or chert as these produce high velocity splinter which can damage eyes. Do not try to lift large rocks for study or collection.

Some cliff edges of Chalk and other rock are hazardous. Children, parties and dogs need to be controlled. There can be risk from the sea in the area in exceptional storm conditions. Do not take risks from waves by scrambling onto low ledges near the sea. On rare occasions severe weather conditions have produced risk of hypothermia. Appropriate warm and waterproof clothing may be needed and leaders should be prepared to cancell trips if necessary.

Some reference is made, as a warning, to records of some accidents, only one of which directly involved geological studies, which have occurred over the years in the Lulworth Cove area. Lulworth Cove is not more dangerous than other part of the coast but more people visit it, and therefore statistically the chance of an accident is increased. Probably cliff-climbing and other non-geological activities have led to many more accidents than have geological studies. See the following:

Chalk rock-fall at Black Rocks
Debris-fall accident at southwestern part of the Cove
Sea accident near West Point

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3.2 Conservation

Education parties here will have plenty to see and plenty to do without really needing to use hammers. Conservation needs particular emphasis here because of large numbers visiting. Instead of hammers have hand lenses, compass clinometers, hydrochloric acid, notebooks, maps and planned project work . Occasionally something of importance may need to be collected for laboratory investigation or a rare fossil may be destroyed by erosion if left in the cliffs. Such special cases can usually be dealt with if only a leader or a research worker has a hammer and uses it discretely and only when necessary. It is undesirable for large parties to use hammers and there is little to hammer here because the cliffs are sea-eroded and good collectable fossils are not abundant. In general hammers should not be used. In any case, hammers must not be taken by geologists intending to enter the Army Ranges to see the Fossil Forest or Mupe Bay.

4.

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. 4.1 Stratal Succession - General

This diagram the simplified succession of strata in the Lulworth Cove region. The thicknesses given are only approximate and most units thicken in an eastward direction. FF - Fossil Forest horizon, LGS - Lower Greensand (very thin or absent here), PL - plenus marl, a grey marl marking the boundary between Lower and Middle Chalk. More detail is given in sections on specific formations.

4.2 Cliff Section - General

This diagram shows the strata in the cliffs of the region as seen from the sea. The Chalk zonal scheme shown is that of Rowe and Sherborn (1901) .

The upper map is a simplified geological map of the Lulworth Cove area is based on Townson ( 1975b) with some modifications based on the old edition of the British Geological Survey map of Swanage (sheet 343 and part of 342). The middle map provides the simplified geology further east so as to include Worbarrow Bay. For details consult the current Ordnance Survey Map - Outdoor Leisure 15, 1:25 000 scale and the British Geological Survey map - Swanage, Sheet 342 and part of Sheet 343. This differs in detail from the old edition of the British Geological Survey, Weymouth Sheet 342 which covers the Lulworth - Worbarrow coast. Research workers should consult both editions and recent literature on structure and mapping of the area. The simple maps shown here are intended for initial introduction and to provide an overview of the area; they are mainly illustrative and do not show geological boundary positions with great accuracy. Part of an old geological map (bottom) is also provided for comparison.

The dip in the Portland, Purbeck and Wealden strata is steep and to the north. The synclinal axis can be recognised by the long narrow Tertiary outcrop north of the cove. This axis runs east-west. The main axis of the very asymmetrical anticline is under the sea, at the Lulworth Banks, south of the map. The steeply dipping strata is part of the north limb which runs along the coast. The locations of some of the many notable geological features here are shown. Localities east of those described in this particular guide (the Fossil Forest and Mupe Bay etc.) are in the military firing ranges, which are open most but not all weekends (for enquiries please telephone the Army Range Control - 01929-462721, ext. 819). Those discussed below, including Lulworth Cove, Stair Hole, Dungy Head and Durdle Door, are accessible at all times. A more detailed geological map is provided below.

Of the strata shown in the section above the Kimmeridge Clay lies offshore to the south of Lulworth Cove and is not seen in the cliffs here (go east to Kimmeridge Bay to see this).

Exposures of the strata indicated in the map above can be seen in aerial photographs. The cove has been described in the past as " an almost circular bay or basin, about five hundred yards [metres] in diameter; formed by the action of the sea on the receding Chalk [but in fact the Chalk has not receded much; more Wealden has been lost]. The rocks at the entrance on both sides of the cove being composed of the Portland and Purbeck strata, have been less affected. These last are highly inclined and contorted, while the Chalk and Wealden Beds are nearly vertical. " (Damon, 1884).

The entrance is a breach in the very resistant Portland Stone about 120 metres wide. The overlying Purbeck Formation has been cut back at an angle until sheltered by the Portland Stone. The incoherent sands and clays of the Wealden have been more extensively eroded to produce the circular shape of the cove. The Chalk at the back (north side) is only being eroded slowly.

As shown on this topographic map, the village, slipway and jetty are at the low northwestern part of the cove. The stream and valley might follows the northern course of a fault, although this is not shown on a detailed geological map below of Nowell (1997). The cove is a feature that has developed at a site of river-breach (Poole, 1987). The stream which now flows into the cove would at least at this point have followed the line of a known fault under the water of the cove and cut a valley into the outer ridge of Portland and Purbeck strata. There is no other direction in which it could have flowed and the size of its valley is too great for it to have been a very recent feature.

4.3 Geological Maps - More Details

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This detailed geological map of the area around Lulworth Cove is based on Nowell (1997). This is a good map for showing proven and hypothetical faults not indicated on other, simpler, maps. Notable is fault N trending northwest-southeast through the mouth of Lulworth Cove. Such a fault is clearly the structural feature responsible for locating an original stream valley through the Portland Stone here. Sea erosion subsequently broke through at this weak point. It might be argued that this fault extends northwest up the present stream valley of Lulworth Cove; Nowell, however, shows the fault as terminating against major east-west faults. This is an interesting point for discussion on a field trip and evidence could be sought for and against this argument in the northwestern part of the cove.

Related to this is record on the map of the north-south Hambury Farm Fault (marked with an L), north of Stair Hole. It is very clear when walking up the path from Lulworth Cove onto Hambury Tout in the direction of Durdle Door that the Chalk downs do not line up in an east-west direction. Hambury Tout is displaced northward in relation to Bindon Hill. Nowell does not relate this displacement to a strike-slip fault on the line of the stream but to this north-south dextral fault with a lateral displacement of about 100m. Look at fault N on the map. Could you extend it to get the same effect? Can you see a problem with such an attempted explanation? Yes, it is shown as sinistral, not dextral, in the Purbecks within the cove. But now look carefully at fault I, on the western part of the map, from Hambury Tout to Dungy Beach. Make a comparison.

A controversial aspect of the paper by Nowell is the correlation of quartz grits within the Wealden Group and whether the Coarse Quartz Grit is one bed throughout eastern Dorset as most authors have considered. Nowell correlates the prominent quartz grit (the "Coarse Quartz Grit") of Lulworth Cove with the lower of two quartz grits at Mupe Bay. Radley (1998) takes issue with this new scheme. See the paper of Nowell and the discussion of Radley and reply by Nowell to find out more about this argument. See also the Mupe Bay Field Guide for more information.

( The meaning of most of the symbols on this map is clear and I have added some text; D refers to the "Durlston Formation", the Purbeck Formation from the Cinder Bed upwards, and L the "Lulworth Formation", the strata below the Cinder Bed. S refers to the Portland Sands. The original paper should be consulted for more information. It refers to an unpublished map of the area around Lulworth Cove by Dr C.R. Bristow and acknowledges Dr E.C. Freshney for finding faults at Dungy Head and the back of Lulworth Cove. Fig. 6 in this paper provides another version of Bevan's (1985) cross section ,located just west of the cove. For discussion of some aspects of geomorphology of Hambury Bottom and the Lulworth Cove valley see also Burton, 1937).

Go to More Information on the Succession of Strata and Contained Fossils?

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4.4 Stuctural Geology - Introduction

Above are given a diagrammatic geological cross-section through strata and faults of Lulworth Cove. The simplified version incorporates aspects of cross-sections of West (1964), Bevan (1985) and House (1989) but with modifications. This is intended to be merely illustrative of the general structure, rather than being the best calculated cross-section. It can be considered in different ways, either as a simple hypothetical explanation of the structures or a simple basic model for modification.

A modified version of a very good cross-section by House follows. This is more accurate in that it shows more faults, but it does not deal with the Lulworth Crumples.

To introduce the cross-sections, it is initially quite clear from geological maps and the cliff exposures that that the Chalk is folded so as to produce the Purbeck Monocline. This is a very asymmetrical anticline with a steep north limb and a very gentle south limb bringing the Chalk down to the sea-floor nearly 30 kilometres to the south (a long way south of the Isle of Portland). Note that the fold in the Chalk has a very acute foresyncline (the sharp bend at the base). Note also that there is an unconformity under the Chalk, Upper Greensand and Gault. That is to say, the Jurassic strata underneath are not parallel but were folded before the Chalk was deposited. Note also that the fold is situated over a fault, and this is believed to have originated as a thrust fault in Upper Palaeozoic strata at depth during the Hercynian Orogeny (Carbo-Permian - round about 300 million years ago).

Of major importance both academically and economically (because it is the reason for the existence of the Wytch Farm oilfield) was the Late Kimmerian phase of extension. This (named after the Crimea where is it well shown) was connected with the break-up of the supercontinent Pangaea and the development of the North Atlantic. Although there was some similar early movement, the Late Kimmerian was the Late Jurassic to Early Cretaceous phase of this. In Dorset there was a stretching effect as the ocean started opening to the west. Dorset, including Lulworth Cove, was still an outlying eastern area off Newfoundland at the time (only about 1000 km from the present North America), but beginning to pull away to the east. The English Channel Basin or Channel Inversion, and the strata of the southern part of Lulworth Cove, was thus formed off the western coast of America and has now drifted a long way eastward.

4.5 Structural Geology - Fault Systems

The Lulworth area is an excellent area for the study of faults. It is assumed that the reader is familiar with normal and reversed faults in horizontal or nearly horizontal strata and with simple thrust faults. A basic understanding of extensional and compressional faulting is needed. If not already familiar with these basic concepts then all that is necessary is to refer to an elementary textbooks and in addition study, for example, the normal faulting at Kimmeridge Bay ).

Readers familiar with simple faults can now consider the fascinating complications that can be seen in the Lulworth area:

1. The strata is generally steep dipping and in some cases overturned.
2. A fold is faulted and therefore faulting can bring strata of different dip into contact.
3. Growth faulting [faulting in which movement has take place during sedimentation, and thus having thickness differences across the faults].
4. Two ages of faults. Later faulting, the most obvious, is usually compressional Tertiary (Alpine) but there has been earlier Late Kimmerian movement [Late Kimmerian or Cimmerian - a phase of faulting of Late Jurassic - Early Cretaceous age, named because of its occurrence in the Crimea. In this area it is extensional - i.e. normal].
5. Other problems involve three-dimensional variation, the intersection of faults, the plunge of the folding, the relationship of folding dates to faulting dates etc.

The interpretation of the faults in the field is going to be very imperfect but some progress can be made. Full study needs much supplementary data. Advances have been made because of petroleum geology boreholes and seismic data. Offshore work and comparison with other areas has helped.

To simplify the matter of faulting I have provided below the standard classification of faults in the Lulworth area. Try to recognise these these groups of faults. You can see that interpretations vary but the paper of Bevan (1985) is recommended; although you may not necessarily agree with all aspects, it provides a good interpretation. (A problem of non-compatibility with Phillips (1964) means that there should be some caution exercised in interpreting the Lulworth Crumples of Stair Hole entirely in Phillips terms, although these two authors have concentrated their work on different units.)

I have emphasised the most important faults. At Lulworth Cove it is best to concentrate on the macrofaults, the big faults, so it is only necessary to remember two! Understanding the F4 is most important. The antithetic ("opposite") F5 faults are interesting but may sometimes break the rules and not be normal; the classification is not perfect, of course. For mesofaults (shears etc) examine the Chalk particularly at St. Oswald's Bay and to the Durdle Door area. Man O'War Head is excellent for fault enthusiast who likes a challenge!

We will now discuss the broad theme of faulting in the Lulworth Cove area. As noted above, the Late Kimmerian faulting within the Jurassic and Cretaceous was extensional with the development of normal faults. The major ones were re-activations of old Hercynian thrust planes, originally compressional, of course, and at some depth under the area. The thrust planes were effectively pulled apart as normal faults, probably often listric [curved].

Particularly important from an economic point of view is that the faults were not just normal, but were also growth faults. Growth faults develop during sedimentation with a long phase of small earthquakes and depression of the downthrow side. This allows increased sediment accumulation on the downthrow, and therefore greater thicknesses of Jurassic and Lower Cretaceous deposits. This is needed to obtain the necessary burial depths for oil generation from the source rocks (about 3 km giving a temperature of about 100 degrees C). So the growth faults tied in with subsidence of the basin, later to become the inversion (in petroleum geology terminology).

Much later in the Oligocene to Miocene, Europe was affected by a new phase of stress, the Alpine Orogeny. This was the (second) northward impact of the African Plate. Dorset was by now well-separated from America by the growing North Atlantic. Although quite a long way north of the orogenic belt (the Alps and Pyrenees etc) it was subject to compressive stresses from the south. These stresses were conveyed through the deep basement and had the drastic effect of reversing the sense of movement on the faults. The normal faults now became reversed faults. The basin was now "inverted" (i.e. the direction of vertical movement was reversed). The former basin now became the English Channel Inversion, a raised structure, a high.

For simplicity, the major fault on the cross-section of Lulworth Cove is referred to as the "main inversion fault". This is because it is the northern boundary fault of the English Channel Inversion. The direction of movement on the fault has reversed from Jurassic-Cretaceous downthrow on the south side to Tertiary downthrown north. This is shown on the diagrams.

Before the recent petroleum geological studies of the area and particularly before the accumulation of seismic data, the structures at Lulworth Cove were misunderstood. Emphasis used to be on the Purbeck Monocline. There is, of course, a fold as shown on the sections and it is quite important. The fold, however, is not the primary structure. To some extent, it is a drape structure over a fault. It is not merely a drape though; the steep limb has been subjected to intense compression from the south with consequent thinning of the near-vertical strata.

In addition there are various complications. One of these is the easterly plunge of the monocline. Its importance is that the deep area of the steep limb, near the foresyncline, is brought up to a higher level at Durdle Door. Thus we go there to see the most intense compressional structure.

To follow these topics further see the papers of Underhill and other petroleum geology and structural studies.

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4. Lulworth Geological Cross-Section - Problems and Arguments

Reading of the older publications of Arkell (1938; 1947), West (1964), Phillips (1964), Bevan (1985), Selley and Stonely (1987), Penn et al. (1987) and House (1989) is recommended to consider some of the various views on this much visited structure. Many theories have been put forward and various ones have involved substantial thrusting, gravity folding, drag folding, collapse, rollover anticlines, and inversion. Recent petroleum exploration will have advanced knowledge of the structures in this area appreciably.

Attention is drawn to some of the many disputable points. This is only a limited discussion and the matters can be followed much further in the literature. There is the problems of compression, " gaping " and the Lulworth Crumples and the other crumples. Sir Aubrey Strahan, about 100 years ago was perceptive on this. He said in 1898, referring to the lower part of the fold at Lulworth Cove that " Here, therefore is indicated a region of compression. Upwards .. the rapid divergence of the two groups (Wealden and Lower Purbeck) points to a region in the monocline where there was a tendency to gape. " Strahan then suggested that you take a paper-book - a thin journal or a thick reprint will do nicely - and fold it into an S. Observe the gape at the top. This seems very unscientific now but it should be noted that Bevan (1985) found Sigma One to be nearly horizontal in the Chalk of the steep zone of the Purbeck Monocline (Bevan, 1985, fig. 3, p. 340). He argued, though, for a different explanation. He suggested layer parallel extension during draping over reactivated Jurassic growth faults during N-S shortening.

The Lulworth Crumples, one of which is shown here, are small folds always in the Middle and Upper Purbeck strata and within the north limb of the major monocline. They are usually asymmetrical folds or overfolds of some type and plunge down to the east at a small angle. Similar crumples occur at Blashenwell near Kingston, at Herston near Swanageand are well-exposed at Peveril Point in Durlston Bay. They are shown diagrammatically in the diagram and attributed here to (disharmonic) movement of incompetent Wealden strata at the contact with the more competent Purbeck Formation. If the Wealden sediments moved to some extent towards the inclined axial plane (the area of " gaping "), the directions of vergence of the small folds is explained. Bed-over-bed drag effects would add to the effects at the base of the Wealden and compensate at the top. Thus, there are no crumples in the Gault and Greensand (West, 1964). Other interpretation of the crumples have involved collapse (Phillips, 1964) or gravity movement (Lees in Phillips, 1964)(if there was space at this low level for the material to slump into!)

Another disputable point is how many faults are there in the fold. I simplified the diagram and have shown one. Bevan (1985) has shown two and a possible minor branch. House (1989) has shown three. Some early interpretations (Strahan, 1898) showed one and those of intermediate date none. There does not seem to be much disagreement at present that at least one major south-dipping fault lies beneath the monocline. The major fault in the Chalk at the back of Lulworth Cove is believed to be the continuation of it (as shown in the diagram here). The regional plunge of structures down to the east results in a low-level view of related structures further west where faults are clearly seen (Abbotsbury-Ridgeway Fault system - see House, 1989, fig 22 and references to earlier work).

Another problem is that of whether or not there is a rollover anticline in the pre-Gault strata. Selley and Stoneley (1987) have argued for one; Penn et al. have argued against. I have simplified the section here and (unlike House, 1969) have omitted a rollover from this diagram. Without it the diagram not only explains Lulworth Cove but also the sections further east. Plunge of the fold down to the east means that Worbarrow Bay represents part of the " gaping " region with thick Wealden. Other factors, however, are involved in Wealden thickness changes that I will not discuss fully here. One of these is that the present coast is oblique to the north limit of the inversion in basin sedimentation terms and thus localities from Worbarrow to Durlston are actually in the inversion and, therefore, units there have greater thicknesses.

Yet another complication is that the diagram generally does not show thickness changes within the formations. This is a further simplification here . The only one shown is the thinning of the Purbeck Formation in the compression zone, as seen in the Durdle Door area (the upper part of the Purbeck is lost by strike faulting).

Also see House (1969) for consideration of borehole data from the area to the north of Lulworth Cove.

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Geomorphology - General

For a discussion of the geomorphology of the Lulworth Cove area see Goudie and Brunsden (1997).

This simplified geological map of the Isle of Purbeck shows Lulworth Cove, just beyond the limits of the " island " (limit is Luckford Lake and Arish Mell in Worbarrow Bay). Before considering the details of the Lulworth area it is intended to place the geological outcrop in broad perspective. The relatively harder, less easily eroded rocks are shown cross-hatched. Note the narrow steep-dipping Chalk outcrop forming the ridge of Purbeck Hills and also note the upland of Portland and Purbeck stone in the south. Between these two sets of hills is a valley of Wealden sand and clays. This Wealden valley is very wide at Swanage in the east and extremely narrow in the Lulworth area. A steep dip, a thinner Wealden succession and some strike faulting are the major reasons for the narrow outcrop in the west.

This simplified map does not show the full details or the cross-sections. The reader needing further information should see the British Geological Survey 1:50,000 geological map - Swanage, Sheet 343 and 342. This map covers much the same area as the diagrammatic map given here and includes Lulworth Cove and Durdle Door. Some more specialist readers may wish to see the area in terms of both onshore and offshore geology (not shown on the map here). For this consult British Geological Survey 1:250,000 Series, Portland Map, Sheet 50 degrees N. -0.4 degrees W. This includes Lulworth Cove but is on a smaller scale and more complex. It does, however, include an enlargement of the area south of the cove which is based on the work of Donovan and Stride (1961).

The theory that the coast west of Lulworth Cove was developed as a series of coves similar to Lulworth Cove. The southern barrier was the Portland and Purbeck stone. Breaches in these steeply dipping rocks led to the erosion of the Wealden behind in several cases. The Chalk at the back was eroded at a much slower rate and thus became effectively another barrier. The coves, so formed linked up, leaving as a relic - the Durdle Door promontory, each side of which resembles the horns of Lulworth Cove, and finally outlying rocks like the Cow, the Blind Cow, the Bull and Man O' War Rock. This diagram is based on one of Calkin (1968), with minor modifications.

Details in the western part - Durdle Door to Bats Head and the Cow rock.

This is a simple theoretical model of the manner in which cove size is controlled by the dip, and therefore outcrop width, of the Portland-Purbeck barrier limestone and the outcrop width of the Wealden which is controlled by thickness in addition to dip angle. Early views on these controlling factors were given by Arkell (1938). Since then there has been much more discussion about the Wealden Group.

Consider whether this simple theory is correct? If you study the topographic map you will begin to see some complications. One point which has been the subject of some dispute is that Lulworth Cove is clearly connected with a former stream valley running out to sea through the Portland and Purbeck barrier. Water flows down the valley near the cove but much of the valley system is dry now. The upper valleys are typical dry chalk valleys that have been cut in the Pleistocene at times of periglacial conditions when water flowed on the surface of frozen soil. We can see typical solifluction deposits of this type in a similar valley at Scratchy Bottom, west of Durdle Door.

When you examine the topographic map note whether all these postulated former coves at the sites of former stream valleys? Is the multiple cove theory really the correct explanation for the evolution of the coast here? Does Bacon Hole (SY 840797) and Chapmans Pool (SY 955770) and Pondfield Cove (SY 871796) fit into this theory?

Another "Lulworth Cove"

The general geomorphological features of Lulworth Cove are not unique. Near Coos on the Oregon coast is Sunset Bay, another "Lulworth Cove", with several similarities and some differences. It is a small circular bay with landward-dipping Eocene clays and weak sandstones (like the Wealden) eroded out. The horns are, like Lulworth Cove, of landward-dipping harder and more resistant rock, but in this case are of sandstone of the Eocene Coaledo Formation. Like the true Lulworth Cove a small stream enters the cove, partly to one side. Waves are refracted on entering the bay, and there is a quiet low energy beach at the back of the cove. Whereas Lulworth Cove faces the open sea to the south, Sunset Bay faces the Pacific Ocean to the west.

(For more information on this and for an aerial photograph (on p. 199) see: Lund, E. H., 2001 (originally 1973). Landforms along the coast of southern Coos County, Oregon. The Ore Bin (a monthly journal), vol. 35, No.12, December 1973. Originally published by the State of Oregon, Department of Geology and Mineral Industries, 1069 State Office Bldg, Portland, Oregon, 97201. Historical publication reprinted in June 2001 by Friends of Shores Acres, Inc., Coos Bay, Oregon, and on sale for 2 dollars, 50 cents at the gift shop at the Shore Acres Park, a coastal site worth visiting, near Coos, Oregon. See also: Moore, E. J. 2000. Fossil Shells from Western Oregon: A Guide to Identification. Chintimini Press, Corvallis, Oregon, 131 pp. Sunset Bay is discussed on p. 113 et seq. )

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Geomorphology - Additional Problems

This section is a type of open-ended exercise. Some questions are put. Answers are not given, even if they are available. It is intentionally not referenced so that it can be used for projects or dissertations without being too easy!

Perhaps, you would like to try an interesting puzzle so as to answer some of the questions. Consider the various clues given here and using your general knowledge of the area and the relevant literature try to visualise the changes in the geomorphology of the area in the last part of the Quaternary.

1. First we should note that a higher raised beach of Hoxnian or of earlier Boxgrove raised beach is missing in East Dorset, although it ought to be found at round about 30 metres above sea-level (I could suggest some places to look and some possibilities have been mentioned in the literature). Therefore, an earlier phase of marine erosion is not understood.

Let us start instead with the last Interglacial coast. At this time, the Ipswichian about 120 thousand years ago, the ice had melted and sea level was a few metres higher than at present. The Raised Beaches at the end of Portland have been dated as 125,000 and 210,00 BP. If these dates are correct the younger of these would be about Ipswichian. The trend of these raised beaches is northeast - directly in the direction of the Fossil Forest. This would not be very significant, as it would be unlikely, of course, that the beach was straight but for the fact that the Budleigh Salterton quartzites (conspicuous liver-coloured pebbles derived from the Triassic Budleigh Salterton pebble bed in Devon) occur on the shore in Lulworth Cove. Did the Portland Raised Beach end near Lulworth Cove? The Fossil Forest Ledge is at about the height of the Portland Raised Beach but I know of no evidence that it was the cliff of raised beach. I believe it to be due to recent storm erosion, although this is a disputable point. Cans we eliminate the possibility that the Budleigh Salterton pebbles have reached Lulworth Cove by some other means such as ship ballast, or is this very unlikely? Could they have got here by some other geological means (such as debris in a solution pipe. But I do not think so - see Solution Pipes below)?

Look at the geological maps. Note the position of the Portland raised beach. Study the sea-floor geology. Try to make some correction for erosion, especially over the Lulworth Banks and the offshore Portland outcrop (you could draw a north-south structural cross-section and raise the topography - but a rough estimate made in your head would do!). Consider the prevailing wind direction. Think particularly about that offshore Portland Stone outcrop. Compare the situation with the modern coasts and think about the possible palaeodrainage and the Chesil Beach. From all this what deduce the approximate outline of the coast.

One problem is whether there was a predecessor of the Chesil Beach. We need to consider this because Portland Harbour was a possible route of Ipswichian sea entry into the area (personally, I rather doubt it!). Another problem, mentioned above, is to where did the Portland raised beach extend. It is probably too simplistic to take it directly to Lulworth. The Isle of Portland provides evidence in its periglacial debris for an appreciably greater height at that time and the present "island" is only a relic of a larger southern Portland outcrop now under the sea. That should have caused a swing of the beach in more easterly direction. You can clearly see where it might have gone at one stage (clue - a monk at 693). However, did it at some later stage go back and if so - to where?

2. Following this what was the situation in the Devensian (last glacial)? The English Channel was dry but where did the local streams extend to? What sort of erosion occurred? Was there a river channel through the Portland outcrop (now under the sea) to the south or was the main channel under the Chesil Beach (you can get specific information on this because the Chesil Beach has been much studied and there have been boreholes through it).

3. Having now some theories about the former geomorphology now consider the Flandrian Transgression. This was the rise in sea-level from about 140 metres down up to the present level in the last 10,000 years. It was initially fast and later slower. Consider the flooding and erosion of the Ipswichian coastline, which would not have been far away. From this we reach the stage of development of coves discussed above. A specific question here is how old is Lulworth Cove? You could make a reasonable estimate if you consult a Holocene sea-level curve and have some idea of the depth of the cove. If you then calculate an approximate erosion rate I think that you will find it to be quite slow. You might make further progress on its history if you knew the depth of the entrance in Portland Stone.

Another curious feature of the cove requires attention. The stream valley meets the cove at almost the same level (it is slightly above the beach). It is not drowned as an estuary (but was it once?) and it is not truncated as at Scratchy Bottom. It shows a little rejuvenation by cliff retreat but not on the scale of the streams at Chapmans Pool or Kimmeridge. Why is this?

4. Think about future coastal erosion here. As we know from pollution and radioisotope markers in the sediments of Southampton Water and studies in the Severn Estuary it has accelerated again since about 1940 and in this region the sea is rising at about half a centimetre per annum, about 3 times the normal rate. Are we seeing the consequences of this in the loss of the Coastguard Hut and surrounds on the West Horn and the recent incipient collapse of the Hard Cockle Member on the East Horn? Are these random events or part of a pattern? What is going to happen next?

A guide to the geomorphology of the area by Goudie and Brunsden (1997) contains some interesting comments relevant to this topic. They comment as follows: ": It is not known how the development of the coast was affected by the high sea-levels of the last interglacial which formed the Portland raised beaches between 9-15m OD. There are beaches at the mouth of Lulworth and Stair Hole at this height and so the sea may have flooded the area. There is a notch above the Lulworth ice cream cafe at the same height but it is not known if this is of marine origin. "

Is there some clue here to a local source of the Budleigh Salterton pebbles?

.

Lulworth Cove Beach - Project Work

The beach is well suited to project work on the pebble composition. This might be good for school, college or University parties in the field after they have made an initial study of the area or, in more detail, for individual school, college or University projects (with laboratory studies - including microscopic study of smear slides, X-ray Diffraction if available or chemical determination of carbonate content etc.). If a larger project is required set a comparison with Durdle Cove, Worbarrow Bay or elsewhere in the area.

Pebbles can be classified in terms of: Angular, Subangular, Subrounded or Rounded (see Tucker, 1982 or later edition). The sediment can also be classified in terms of Very Well Sorted, Well Sorted, Moderately Sorted or Poorly Sorted. The composition can be determined using quadrats and counting the pebbles within or by counting a specific number (200?) pebbles at random. Look at the sand with a hand-lens or portable microscope. Can you see glauconite grains (dark green - almost black) derived from the Upper Greensand? How is this mineral distributed around the beach? Look for shell material and for shell sand. Try to determine the exact source of any such carbonate sand.

Find out the dominant components in various parts of the cove. Is the distribution around the cove symmetrical? How far do chalk pebbles travel from the Chalk outcrop? Do they change shape? Contrast with flint pebbles. What are the characteristics of Purbeck and Portland limestone pebbles. Can you find any Budleigh Salterton Quartzites referred to above. Are there any very unusual pebbles for this area? Are there any igneous rocks? How does the beach vary from low-water to the top? How is wave action affecting the beach?

At low tide further project work can be done on the freshwater springs emerging at the foot of the Chalk cliff. Record their exact location and relative rate of flow. Test the pH with pH paper of a pH meter and take the temperature. Compare with the sea. Find out from the literature how the pH of water in contact with carbonate is affected by carbon dioxide content. Think about the flints in the Chalk. Their precipitation probably required a fall in pH from a high figure (over 9.4) at which silica is readily soluble. Could the present water easily dissolve silica? Find out, also, whether these springs occur up to the limits of the Chalk outcrop and if not, why not? How do they relate to the main spring (resurgence) and stream at the seaward end of the valley. Do they occur in the Durdle Door area, and if not, why not? Incidentally, the hydrogeology of this area has been investigated professionally with a series of boreholes. See also the hydrogeological map given in the reference list below.

If you have a pH meter compare the Chalk water with water seeping from the Wealden strata. Explain the difference. Which would you prefer to drink and why (remember that some people like chalybeate (iron-rich) water - but I do not advise you to drink any you find here)?

Wave Action

(text to be added)

6.

6.1.1. Upper Greensand - Introduction

To start on a tour of the geology of Lulworth Cove, one can first look at the general features from the shore near the beach cafe. Then a short distance eastward along the beach, and just after the huts the Upper Greensand is seen, as in the photograph above. This unit is mostly of Albian age (Cretaceous) and is about 40 metres thick in this area. For details of stratigraphic classification see the diagrams above and refer to the paper of Drummond (1970) which contains much of interest to anyone studying the Lulworth area.

The Upper Greensand is a greenish, glauconitic, calcite-cemented sandstone, argillaceous in the lower part, and entirely of marine origin. Notice in the photograph above how the softer, lower part (in the left and centre of the picture) gives way stratigraphically upwards (to the right) into harder more carbonate-rich sandstone. There is much bioturbation and burrows are obvious.

The green mineral glauconite occurs as rounded grains, appearing almost black under a hand lens, and this is a soft silicate mineral, a type of clay, but green and in granular form. The glauconite grains are sand-sized, ovoid or spherical aggregates of dark green, iron-bearing clay minerals. There are separate smectite, illite and mixed-layer varieties so the broad term "glaucony" is sometimes used to refer to a green glauconite-type mineral of unspecified clay mineral composition. The mineral contains both ferrous and ferric iron and the implication of this is that it has been formed at the oxic/anoxic boundary (i.e. with normal oxygenated water above reduced sediments). The rounding of the grains is a result of current or wave activity, also shown by the presence of quartz sand. Sea-floor conditions were probably rather like those of the current swept English Channel at the present day, but appreciably warmer.

It is not certain as to why glauconite was so abundant in southern England at this time, but the shallow current-swept sea-floor and the relatively ambient temperatures weres probably important factor. The same facies reappears in the Middle Eocene Bracklesham Group of Hampshire and Isle of Wight, where there are greensands with similar scallop shells Amusium corneum. At this time, too, the temperature was relatively high for the palaeolatitude. It also occurs in the Portland Sand, and there is an anomalous freshwater variety present in the Upper Purbeck strata of Lulworth Cove, and elsewhere.

In the upper part of the Upper Greensand (that is further east) there is much chert; the silica for this has come from opaline sponge spicules. These are sometimes visible if the rock is examined carefully with a good hand lens, although they are now probably chalcedony.

The top of the Upper Greensand is remarkable here in containing a thick boulder bed. The boulders are of calcite-cemented, glauconitic sandstone that have been rolled around by storm waves on the sea-floor. They have been coated with a thin outer layer of glauconite. The reason that the Upper Greensand, with its boulder bed, is of rather unusual facies here is probably because it was deposited on a residual Late Kimmerian swell or high, even though it is, of course, above the basal Gault (main Late Kimmerian) unconformity. It is an interesting condensed sequence and this ties in with the penecontemporaneous erosion (Drummond, 1970 ). For more recent information on the ending of the Cretaceous extensional phase see the petroleum geology literature.

Robust marine fossils, like those shown above are common in the Upper Greensand. It has undergone some diagenesis and calcitic shells are preferentially preserved. Fossils such as Exogyra obliquata bivalves and serpulid worm tubes are common, although often at beach level good fossils have often been removed by collectors.

Ammonites had aragonitic shells and thus they can be present as either internal moulds of sandstone or more frequently as phosphate moulds in certain phosphatic, and usually more argillaceous, horizons.

Calcite-cemented glauconitic sandstone of the Exogyra Rock which occurs in the middle of the succession. This bed is conspicuous because it projects in the cliffs and is full of fossils, particularly Exogyra obliquata (Pulteney). In older literature this is referred to as Exogyra conica (J. Sowerby). Although elsewhere in Dorset it is almost 3 metres thick, in the Lulworth area it only about a metre It contains Pecten (scallop) bivalves of which a part is visible in the photograph. Small echinoids ( Caratomus, Salenia, Hyposalenia, Discoidea ) are fairly common in certain other exposures where there has not been too heavy collecting. This bed occurs near the entrance to Lulworth Cove but the easily accessible fossils have gone. You can look up, though, and see the Exogyra shells. There are three argillaceous beds above each of about a metre thickness, of which the top one is the Ammonite Bed (see Arkell, 1947, p. 190 for summary faunal list). Large nautili occur in the bed beneath it at some localities.

The bivalve Aequipecten aspera (Lamarck) (Pecten asper in older books) is a very common scallop (like the modern "sea-butterfly") of the Upper Greensand with Exogyra obliquata (Pulteney) and some other shell material including serpulid worm tubes Rotularia concava (J. Sowerby).

Entolium orbiculare (J. Sowerby), another common member of the Pecten family in the Upper Greensand. This small specimen (about 5 cm) is not perfect because the " ears " are not visible. Perhaps, this small scallop and Aequipecten asper were able to swim as many modern scallops do by flapping their valves and thus avoiding being buried in the sand. Relatives of this mollusc at the present day have a number of small eyes in the edge of the mantle, useful for these more active members of the Bivalvia.

6.1.2 Upper Greensand continued - Bioturbation

Bioturbation or burrows by organisms is best developed in sediments of shallow or fairly shallow, marine origin. The Upper Greensand is usually well-bioturbated. Burrows, probably made by crustaceans and worms, are common. At some localities particular types of burrow systems that form trace fossils can be identified. In the photograph here we see a vertical cross-section through various unidentified burrows, some of which are partially compacted. They are very clearly visible because dark glauconitic sand has filled the burrows which have been excavated in buff sand, now carbonate-cemented, which was relatively deficient in glauconite (I am using "glauconite" in a general sense here for simplicity - i.e. like "glaucony"). The exposure is a small one of about half a metre at the back of the beach next to the shingle, a short distance east of the beach cafe. It varies in quality from time to time depending on movement of the shingle by storms.

Upper Greensand - Eastern Exposure

Here is an interesting fault system at the contact between Upper Greensand and Lower Chalk at the eastern end of the Chalk section at the back of Lulworth Cove. To understand this fault see the table above of the classification of Lulworth area faults according to various authors.

Look at the rough Upper Greensand fault breccia towards the right. This passes down into in situ Upper Greensand. It very heterogeneous and shows little sign of brittle fracture. It is obviously earlier than the narrow and well-defined Chalk fault breccia on the left. It is too late, however, for typical Late Kimmerian (the mid-Cretaceous movements); it is post-Albian (after the Late Cretaceous Albian Age). Furthermore if the bedding is returned to a low angle, as it would be before the Tertiary (Alpine) movements, then the fault is too low-angle for extension (Late Kimmerian movements were mainly of extension). Thus, it seems likely that both fault breccias are Tertiary but perhaps formed under different compression regimes at different stages in the development of the Inversion.

With regard to the orientation of the fault plane and type of displacement, it seems to be an F5 on Arkell's classification. It hades northwards and the fault plane is at a steep angle. Bevan (1985) reclassified Arkell's F5 faults as antithetic [i.e. a minor, secondary fault, usually one of a set, whose sense of displacement is opposite to its associated major and synthetic faults]. Certainly the later chalk fault breccia shows brittle-fracture, it is sheared and almost monomict [of one rock type, as opposed to oligomict and polymict]. These features are compatible with a Tertiary antithetic origin, probably at a time of low-angle, maximum compressive stress.

A further problem in addition to those discussed above is that there is the reduction of dip northward, onto the hanging wall [the side of the fault to which the fault plane hades, or inclines from the vertical - thus this wall appears to hang. Opposite of footwall.] Why is this? The continuation of this fault also deserves thought. Where is it on the western side of the cove?

Gault Clay - Introduction

The name "Gault Clay" is a tautology - "Gault" is an old English word for clay, as in "Gaulters Gap", Kimmeridge where there is no geological Gault. In southeastern England the Gault is a purer black clay, but here at Lulworth Cove is very sandy and largely a black or dark grey loam. It passes up transitionally into the Upper Greensand, gradually becoming more sandy and greener and more glauconitic. The Gault, known in the Isle of Wight as the "Blue Slipper" is a common cause of landslides. The result of this is that it is not well-exposed on the Dorset coast, and is often concealed by debris. Further east in the Weald area, the Gault Clay is a black clay about 30 to 80 m in thickness. The boundary between the Gault and the Upper Greensand is diachronous [from the Greek - "across time" - diachronous refers to the crossing of time planes], and is usually quoted as the best example of diachronism in Britain.

The Gault is well-known for its good aragonitic fossils, such as ammonites of the genus Hoplites and its relatives (usually small compressed subinvolute shells with strong ribs). These are not normally found at Lulworth because the exposure is poor. Only some bivalves have been found, and these in boulders in the talus.

If the Gault is regarded as the black, more argillaceous beds of the Albian sequence, then the thickness at Lulworth Cove of these is only 11.3 m according to Arkell (1947). Contrast this with the 34 m of black beds, clay and loam of the "Gault" at Worbarrow. No less than 23 m have been lost in that short distance. This type of change is like that seen in the Jurassic strata affected by Late Kimmerian extension regime. So, although the Albian was deposited round about the end of this phase, the switch to the compressional phase may not have been completed at that time. In other words Lulworth Cove was still, even at this late stage, showing more "high" characteristics than Worbarrow, which is transitional to "basinal" in term of facies and thicknesses (there is even some Albian - Purbeck analogies in local variations West (1975) ).

This diagram is useful to explain some characteristics of the Dorset Gault. Notice that the clay mineral composition contains the expandible clay mineral smectite, whereas this is generally absent in the continental Wealden. The properties of the "Blue Slipper" are affected by the presence of the expandible and greasy smectite. In the Wealden, in contrast the acid soil conditions of the early Cretaceous would have been adverse to the preservation of smectite and more favourable for kaolinite.

Notice that the Wealden palynomorphs shown are Hauterivian. Is there any Barremian here? Of course, there is a hiatus anyway; there is no Aptian so the Barremian could be missing too. The dinocysts are interesting; these are late Albian. This ties in with the reduction in thickness of the Gault in the Lulworth Area; presumably the lower beds are missing. You are probably wondering about the age of the pebble bed. Perhaps this is diachronous and also rather young.

6.2.1 Gault Clay continued - The Overstep

The base of the Gault is probably the most well-known horizon in Britain for overstep. This is the "stepping over" of a stratum above the angular unconformity from younger strata to older in a particular direction. If the angle is great the overstep may be actually visible in the field but this is rarely the case. More often the angle of the unconformity is very small and the overstep is recognised from stratal relationships over a significant distance.

As shown above, the Gault commences with a pebble bed that marks the major unconformity at the base of the Albian. On a broad scale there is pronounced overstep westward, as shown in the diagram above. This new and drastic phase of the tilting of England and Wales towards the east commenced at this time. It still continues: London and the East Coast is still going down (note Thames Barrier).

Now, to consider further the problem of overstep of Albian we should examine again a N-S cross sections through Lulworth Cove. The Gault oversteps quite abruptly onto the Corallian and other Jurassic strata. At White Nothe, east of Weymouth, you can observe the Gault and Upper Greensand on the Kimmeridge Clay. This northern overstep is shown on the diagram as mainly due to inversion [reversal of direction of throw over time] on the fault. You can see though that pre-Albian folding is also involved, and this is visible at White Nothe. Observe also that directly north of the Inversion boundary fault the direction of overstep is locally opposite and is actually from north to south.

Thus, the east-west diagram is a simplification, but important in showing the broad features. Go west to Lyme Regis or Charmouth, look at Black Ven, the Gault and Upper Greensand are on Lower Lias clays - and the westward overstep becomes very clear. Local overstep in the Lulworth area is complicated because here we are at the northern margin of the English Channel Inversion.

In broad structural term, the Basal Gault Pebble Bed marks a drastic change in tectonic regime here. In the Jurassic to the early Cretaceous the Wessex region was off the east coast of America, there was N-S extension of the developing English Channel Basin. Later the Wessex region was separated from America by the North Atlantic Ocean. Then came the gradually developing N-S compression from the African Plate, and in due course, the Alpine folding. The Basal Gault Pebble was formed at the very end of the extension phase and is associated with the Late Kimmerian movements and unconformity.

6.2.1 Gault Clay continued - The Basal Pebble Bed

The Basal Gault Pebble Bed on the NE side of Lulworth Cove is shown again above, together with a photograph of the same pebble at St. Oswald's Bay, where it is sometimes better exposed. This is a good example of the classic relationship of a basal pebble bed to an unconformity. Because the strata are steeply folded the stratum is almost vertical and is overturned in some places. Younging is to the north.

Description of the stratum

Very useful information on the Basal Gault Pebble Bed has been provided by Garden (1988) who studied the sections at Durdle Door promontory (SY 806803) and St. Oswald's Bay east (SY 816800). The pebble beds are O.5-0.7m thick, and contain cobbles and pebbles set in a muddy, ferruginous sandstone and fine rapidly upward into micaceous mudstones. Garden (1988) found that where the exposure is good intensive bioturbation can be seen in the basal sandstones. Burrows also extend down into the underlying Wessex Formation (Wealden) siltstones and sandstones to depths of O.l5m. You may or may not see this at Lulworth Cove.

The pebble suites

The bed is an example of a fairly mature pebble bed and the components are mostly composed of silica, notable for its resistance. The phosphorite, mentioned below, has a hardness of only 4.5 to 5 on Moh's Scale and although, less resistant, it has probably not been transported very far. Garden (1988) reported (p. 45 and p. 211) that the the pebble suites of the basal Gault Pebble Bed of east Dorset (i.e. Lulworth area) are trimodal. The three main groups are as follows:

1. Large pebbles - coarse-pebble to cobble-grade clasts of pale, weathered cherts and dark phosphorites. He found at Durdle Door and St. Oswald's Bay cobbles of up to 450 mm, almost half a metre, of pale-coloured weathered chert. The weathered chert is very interesting with regard to Lulworth Cove and region. Garden (1988) pointed out that they are typical Portland Group cherts, including the Rhaxella cherts (the dominant sponge cherts of the Portland Cherty Series), oolitic and coarse-grained bioclastic chert. There is some Purbeck chert of silicified evaporite type from the basal Purbecks and also silicified freshwater limestone of Cherty Freshwater Member type.
2. Small pebbles - small rounded pebbles of vein quartz, tourmalinite (mostly microcrystalline quartz and tourmaline - tourmalinised mudstones or cherts, but tourmalinised breccias and coarse quartz with acicular tourmaline is also present) and sandstone (quartzites).
3. Small phoshorite pebbles - a minor group - subangular to subrounded clasts of brownish black phosphorite up to 35 mm in length. Phosphorite clasts in the Basal Gault Pebble Bed include bivalve (Protocardia) and ammonite casts from the Kimmeridge Clay.

A notable aspect of Garden's (1988) research is that Carboniferous chert is rare in the Basal Gault Pebble Bed in the Lulworth region but that Jurassic Portland chert is abundant, particularly at Durdle Door. This, of course, all accords with the overstep northward of the Basal Gault Pebble Bed onto the Portland Group, a feature which is seen in the field at White Nothe. For further details see Ross Garden's (1988) thesis.

Origin of the pebble bed

This pebble bed represents shoreline retreat Garden (1988); it is a relic of a shingle beach of the mid Albian marine transgression migrating across this tilted land (Owen 1971). Because of the local overstep northward onto Lower Cretaceous Jurassic strata, the pebble bed includes clasts of material from the Wealden Coarse Quartz Grit, particularly vein quartz pebbles. The chert derived from the Portland Group has come from a cliffed coastline, not very different from that of the Isle of Portland at the present time. Back in geological time the Albian coast was very similar in many respects to the present Dorset coast. At most other times there were no significant cliffs and a quite different geomorphology. Both the Albian pebble bed and the modern pebble deposits of Dorset like the Chesil Beach are transgressive deposits above a plane of unconformity (both with westward overstep).

Garden (1988) considered that the poor sorting of the bed and the presence of clay-filled burrows extending down below the unconformity indicate that the deposits are unlikely to be high-energy, upper shore face deposits. The mixing of gravel, sand and mud is more consistent with deposition in the nearshore zone on the lower shoreface

Chalk - Introduction

The Chalk at the back of Lulworth Cove is now considered. The strata are dealt with in the order in which they are encountered walking round the cove and not in stratigraphical order. Because the strata are steeply dipping northward, they young in a northward direction, and therefore the Chalk outcrop is at the northernmost of Lulworth Cove. The chart above gives the terminology of the Chalk in both old traditional terms and in new lithostratigraphic nomenclature of of Mortimore and of the British Geological Survey.

The Upper Cretaceous Chalk is very well-known as a fine grained coccolith limestone that is usually relatively soft. At Lulworth Cove only the Lower and parts of the Middle Chalk are seen. The Lower Chalk is greyer and harder than the typical white chalk and has a significant clay content. It is cyclical and does not contain flints. The Middle Chalk is rather harder and more nodular than elsewhere. All the Chalk in the Lulworth has been sheared to some extent by tectonic action and in the Durdle Door area the flint is fragmented into small pieces. The main Upper Chalk the White Chalk is not properly exposed in the cove but lies under Bindon Hill to the north. You can see it at other places such as Studland and the Isle of Wight.

The general stratigraphy, sedimentology and origin of the Chalk is not discussed here in detail. See the diagram above and also Gale and Kennedy (2002) in Smith and Batten's (2002) guide to Fossils of the Chalk. As they point out that the Chalk is distinctive and very widespread. Virtually identical Cretaceous deposits, with the same fossils, extend across northern Europe and into central Asia, and are found as distant as Texas and Western Australia. A type of unconsolidated chalk forms in the modern oceans from the rain of of calcareous plankton debris. In the Late Cretaceous, pelagic chalks spread from the more usual ocean environment onto the continental shelf and epicontinental seas of northern Europe as a result of a major rise in sea-level. Hundreds of metres of chalk formed a blanket-like cover over vast areas. Salinities were normal, and the sea floor was generally well-oxygenated. The sea floor was also below the limit of light penetration, and there is an absence of organisms that characterise shallow-water limestones that formed in the photic zone. At its maximum extent, the Chalk Sea probably covered all of the British Isles except the Scottish highlands (see Gale and Kennedy, 2002) for more information).

Some Chalk fossils are mentioned briefly in the following sections on the Chalk. For more information on Chalk fossils the reader should again refer to Smith and Batten (2002).

6.3.2 Lower Chalk

These images give an overview of the Chalk exposures at the back (north side) of Lulworth Cove. In the middle of the Chalk cliff, high above the beach, is the major east-west strike fault. It is shown in the geological map above and on the general cross-section.

Here is the junction, between the rather weathered (and therefore rather brownish in the photograph) Upper Greensand and the Chalk. The Chalk here has a Basement Bed with small phosphate nodules. They are mostly only one or two centimetres in length and of a light brown colour. Some of these have replaced fossils and occasionally a phosphatised ammonite may be visible.

Phosphate-rich beds usually form when there is very slow deposition and gradual accumulation of phosphate from organic remains such as debris of plankton. In fact, the base of the Chalk here does represent a hiatus (a pause in sedimentation - a gap in the time sequence), and this can be shown by the fossil content.

Above the Basement Bed the Lower Chalk, of Cenomanian Age, is cyclical with alternating beds of fairly pure chalk, without flints, and thinner, compacted beds of argillaceous (marly) chalk. They are better seen where they are washed by the sea, as at Man O' War Head between Dungy Head and Durdle Door.

At beach level Lower and Middle Chalk are seen separated by the Plenus Marl and dip steeply northward. The Lower Chalk is cyclical, rather argillaceous and without flints. The Middle Chalk is nodular, without flints and forms the lower part of the cliffs at the back of the cove. The Upper Chalk is white chalk, rather harder than is usually case in England, and contains flints. It is only present in the upper part of the cliff north of the fault and is overturned to some extent.

The Lulworth Cove Chalk has been briefly described by C.W. Wright in Arkell (1947). The Basement Bed (see below for more details) is preserved immediately above the Albian as 0.91m (3 feet) of buff sandy chalk with a few phosphatic nodules and fossils.

Ater that distinctive and peculiar bed we encounter the main cyclical sequence of the Cenomanian or Lower Chalk. Wright ( in Arkell, 1947) commented that it is so faulted that only about 9.14m (30 feet) remain. In comparision it is about 27.43m (100 feet) at Worbarrow Bay and thicker still at Ballard Down, Swanage.

Is the reduction in thickness in the Lulworth area the result of strike faulting or of condensation or of both condensation and strike faulting? Bear in mind the proximity of the section to the main Inversion Fault (of F4 type) and the possibility that the exposure here is of Cenomanian Chalk between two strike faults at the margin of the Inversion (examine the House cross-section shown above). It is likely that both are involved.

6.3.3 Chalk continued - The Plenus Marl

These pictures above are given as illustrations of the Plenus Marl at the eastern exposure. Notice that, in addition, comparison between the photographs reveals that the action of the 3 November 2005 storm seems to remove the chalk talus, leaving mostly the flint pebbles. It has also resulted in a small fresh cliff at the base of the main and old cliff. This particular storm sadly caused the deaths of two boys who were washed away by the large waves actually entering the cove. Perhaps this storm has initiated a new phase of erosion and undercutting within Lulworth Cove.

The upper limit of the Lower Chalk is marked by the Plenus Marl, a grey marl, much softer than the adjacent chalk and breaking into small angular fragments. It is very easy to recognise. At the present time there is a well-developed beach at the back of Lulworth Cove. A result of this and of the protection afforded by the narrowness of the inlet to the cove is that the erosion of the Chalk is limited and slow. Thus the Plenus Marl is not normally seen at Lulworth Cove in a fresh and clean exposure. I have added a photograph of the same bed on the west side of Durdle Door where it is eroded clean by the sea, but is highly sheared.

The Plenus Marl at Lulworth Cove is about 1.83m (6 feet) thick. The characteristic belemnite is Actinocamax plenus, although this fossil is not easy to find. The Plenus Marl is a well-known and widespread marker horizon and is the subject of many papers. It is important because it is linked to evidence of a palaoeoceanograph perturbation. In Gubbio in northern Italy its equivalent is a one-metre thick dark bank of organic-rich shale and radiolarian sands known as the 'livello Bonarelli'. It is interesting that the Bonarelli horizon has a pronounced positive shift in delta 13C (the isotope of carbon). This peak can be identified in Plenus Marls of East Kent. See

In terms of zones and stages there has been some argument about the position of the Plenus Marl. Kennedy (1970) classified as Cenomanian-Turonian and assigned the lower part to the zone of Metoicoceras geslinianum and the upper to the zone of Metoicoceras gourdoni. Skelton (2003) for more information on this.

Some useful details, with a faunal list, have been given by Jefferies (1963) of the plenus Marl at Durdle Door: "North-east corner of Durdle Cove at foot of cliff. Fig. 10. 30/805803. Despite great regional tectonic disturbance the plenus Subzone seems complete. Base Bed 1 abrupt. No 2b or 3a. Bed 8 consists of 8a, band c. Aragonitic fauna abundant in Bed 1 (highly exceptional) as well as in Beds 2-3 and 4-8. Characteristic fossils: Bed 1, large Ostrea vesicularis, Neithea quinquecostata; 2, Entolium membranaceum (c), Calliderma smithiae; 3, Metoicoceras geslinianum; 4, Actinocamax plenus, Oxytoma seminudum; 5, Sciponoceras sp., Metoicoceras gourdoni." It is very interesting that an aragonitic fauna has been preserved in Bed 1. In most of the Chalk the aragonitic fossils have been dissolved so that only the calcitic fauna is visible. I do not know whether the aragonitic bed is preserved at Lulworth Cove.

For information on the palaeoecology of the Plenus Marl, with emphasis on a section at Merstham in Surrey see also Jefferies (1961).

For more on the Chalk and Chalk fossils see: British Chalk Fossils - by Robert Randall.

6.3.4 Middle Chalk

The Turonian (Middle Chalk, excluding the Holaster planus Zone at the top) is seen at the base of the cliff at the back of the cove where the chalk is in the Inoceramus labiatus Zone. Characteristic fossils have been obtained. They include a single specimen of Cardiaster pygmaeus Forbes. Rowe (1902) recorded "Ammonites cunningtoni (?= Prionotropis woollgari Mantell sp.) and sometimes worn ammonites are visible in situ. The present author has seen a large specimen collected from the central part of the back of the cove. Wright mentioned that it is sometimes possible to reach a face of the Terebratulina lata Zone by climbing up the talus. This is not recommended.

At the back of the cove look for a Middle Chalk zone fossil, the bivalve - Mytiloides labiatus Schlotheim. This was formerly known as Inoceramus labiatus von Schlotheim, 1813 and the name Inoceramus labiatus has been widely used in the older literature; from this species the I. labiatus Zone takes its name. In the USA the similar Inoceramid known as Mytiloides mytiloides is common in the Upper Cretaceous (see Cobban, 1983). See Cleevely and Morris (2002) for more information on Inoceramid taxonomy.

The Inoceramids are very interesting because they had a prismatic calcite layer of the shell which is preserved in the British Chalk. Aragonitic shells have been lost in most of the Chalk so quite a distorted impression of the original benthic fauna is given by the cliff exposures. There would have been many aragonitic bivalves and other organisms of which there is no record. Gale and Kennedy, 2002) commented that the aragonitic shells probably dissolved on the sea floor or just below it and that typical White Chalk faunas, dominated by originally calcitic organisms are 'preservation faunas' in which the aragonite component has been lost. Of course, it should be noted that aragonite is usually lost in permeable limestones through which meteoric water can percolate, and thus some later loss is possible (c.f. Portland Stone). Aragonitic layers of the Inoceramids have been lost but the prismatic calcite is more resistant to dissolution. Inoceramid prism are common throughout the Chalk even where near-complete fossils are not preserved. They are quite conspicuous in thin-section.

Although they are not usually preserved in the Middle Chalk, a mould of a large ammonite has been found near this part of the cliff some years ago (by Dr Page).

Because of sea erosion and extensive collection this is not a locality at which to find echinoids easily. Eroded specimens might just be found, so some examples of Chalk and other Cretaceous echinoids are shown here. Echinoids in the Chalk are important in showing that the sea was not very deep, certainly not too deep for this benthic and burrowing fauna. This distinguishes the coccolith ooze of the Chalk from the coccolith oozes which form in deep oceans.

For more on the Chalk and Chalk fossils see the webpage: British Chalk Fossils - by Robert Randall.

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6.3.5 Chalk contin. - The Black Rocks

At the back of Lulworth Cove, towards the western side and not far from the access to the beach and the cafe are the Black Rocks. As you can see they are actually not black but green with algae, although appearing dark from a boat. These rocks only occur at this one place and yet the Chalk cliff has much the same strata and structure along its east-west length. Why are there "black rocks" here and not elsewhere? When did they fall here?

Although little seems to have come down recently, at distant intervals of time it seems that some debris falls from the scar providing new boulders for the Black Rocks. The accident in 1957 happened when a heavy boulder fell almost vertically from about 30 m (about 100 feet) up and then impacting on the lower part of the cliff with high velocity, disintegrated explosively in part with a loud bang, the "shrapnel" causing injuries to sunbathers ( Anonymous, 1957 ). The remaining lump bounced into the sea but, fortunately, no-one was killed. Fortunately, such falls are very rare so the risk of walking past the site is usually very small.

The lower photograph has the suggested location of the source of the Black Rock boulders, but even if this is correct there are many interesting problems. Wright (in Arkell, 1947) referred to boulders from the Holaster planus zone, that is of the lowest part of the Upper Chalk, being present on the beach. He was probably referring to the Black Rocks. These boulders seen at low tide are of fairly hard chalk containing flints. They contrast with the Lower and Middle Chalk in the cliff without flints. They seem to have fallen from the higher part of obvious scar seen in the photograph above Arkell's F4 (steep south dipping) fault, the great inversion fault, and has some relationship to it. This is Upper Chalk with flints. The exact position of the faults is not placed with certainty in the image, but is approximately in this position. Examination with binoculars may fix it more precisely. As can be seen on a geological map above, at this point the fault shows some curvature and trends into the cliff at the west side of the scar.

In the photograph above we see the overturned Upper Chalk, probably from the Holaster planus Zone north of the F4 fault high in the cliffs above Black Rocks.

Some questions arise.

1. Was there at one stage a large fan of fallen talus with the boulders on the outer, seaward side? No fan of talus remains. Alternatively, have the boulders fallen individually and bounced out from the cliff, as in the 1957 incident?

2. Why was a fall of Upper Chalk only here? It occurs most of the way along the middle to upper part of the Chalk cliff.

3. Did the original fall, have any connection with neotectonics [recent movement on faults]? It seems unlikely but some small movement on this fault could have destabilised the adjacent cliff. The fault is one of the largest in southern England, it marks the boundary of the English Channel Inversion and is connected to a deep basement structure. (Incidently, in the Purbeck Unio Bed of Stair Hole you can see the evidence of earthquake liquifaction associated with a Late Kimmerian precursor of this fault. There have been earthquakes here but it was a very long time ago.)

4. If you can look with binoculars can you see whether the cliff seems stable now?

5. Look at extent of vegetation on the cliff, the extent of scars from falls, the extent of undercutting by the sea. Think about "global warming", sea-level changes. Is the present time a phase one of rapid erosion or is it perhaps a phase of slow erosion, with more rapid erosion to come in the future?

7.

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7.1 Wealden Group (East Side)

See also: Wealden at the west side of Lulworth Cove.

The Wealden fluvial and mudflat strata are only 166m in thickness just here (Arkell, 1947). They are abnormally thin because the Wealden Group reaches about 750m in thickness at Swanage, further east. It is necessary, of course, to consider whether the various parts of the thick sequence are uniformly thinned (the Purbeck Formation tends to do this but not perfectly so) or whether a large part of the sequence is missing. On the east side of the cove the Wealden is steep dipping and almost vertical in parts, but rarely overturned as they are on the west side.

Firstly I will list the main characteristics of Wealden strata in the Wessex region:

1. Clays and silts with sandstones, of the Lower Cretaceous System; deposited from about 146-125 million years ago.
2. No limestones are present, and there are no typical shales of marine type (i.e. like Kimmeridgian) in Dorset.
3. Marine fossils are generally absent, but freshwater and brackish water fossil occur.
4. Clays often show palaeosol weathering and oxidation - reddish or purple colours.
5. Some sandstones are coarse and show channel features and cross-bedding.
6. Lignite (black, carbonised fossil wood) is common throughout.
7. The Wealden is the source of most of the British dinosaur bones, particularly in the Isle of Wight; the name 'dinosaur' was first applied to the remains of an animal found in the Wealden.
8. Very shallow water facies are dominant, with dinosaur footprints on the Isle of Wight and elsewhere.
9. Oil sands occur.

There is an extensive literature on the Wealden of southern England. The Wealden of the Weald (southeastern England) has been much studied by Professor P. Allen. He originally put forward a deltaic model but later realised that everything was of very shallow water origin. What he had once regarded as pro-delta clays proved to contain dinosaur footprints! In his later interpretation - Allen (1976) "Wealden of the Weald: a new model" he explained the evidence for palaeoenvironments of coastal mudplains with lagoons and sandy water-courses. This paper makes interesting reading, summarises earlier evidence and provides references to most of the earlier publications. The work on the Wealden of the Weald does not explain in any detail the western areas like Lulworth Cove. Understanding the southeastern mudplains and rivers helps interpret the Wealden of the west. The general view is that to the west, as here in Dorset, the Wealden is more fluvial. (discussion - to be continued)

(for comparison here is the Coarse Quartz Grit at Worbarrow Bay, where the exposure of the Wealden is much better and the dip is less. See the Worbarrow Bay website - Wealden section.)

We will have a look at the prominent exposure of the Coarse Quartz Grit at the east side of Lulworth Cove. As you can see it is not as well exposed as at Worbarrow Bay, but the cliff is still informative. The bed show a channel features produced by the Wealden river. It is multistorey, that is there are fine pebble beds one on top of another. At times the channel was abandonned and logs were washed into into it. These are preserved as lignite, somewhat squashed by the weight of overburden. Bones of dinosaurs are sometimes found in channel deposits like this. I have found an Iguanodon tooth in the equivalent bed at Swanage.

It is easy to see that many of the small pebbles here consist of vein quartz. The nature of the black ones cannot satisfactorily be determined in the field. Some are of black chert, usually known as "lydite", others are of tourmalinised quartzite. All are hard and resistant. Garder (1957) has provided more details and discussion. He gave the composition of the Coarse Quartz Grit at Lulworth Cove (for the -3.5 phi particle size) as - opaque quartz - 28, radiolarian chert - 25, quartz plus tourmaline - 24, translucent quartz - 13, fibrous quartz - 10. Allen has found a clast at Durdle Door in the same bed to be of Precambrian age (Allen, 1972). This has brought up interesting problems about a source of old tourmalinised detritus in the west. Armorica (Brittany) is a large area of very old rocks and could have provided debris for the Wealden river (there is, after all, Wealden in the English Channel north of Brittany). Allen points out, though, that there is a problem of finding tourmalinisation of Precambrian date there. He also discussed the possibility of some derivation from a former extension of a Newfoundland Grand Banks area, since fragmented by sea-floor spreading. There is little doubt that the Wealden river came from the west but its details are still sketchy!

Much of the remainder of the Wealden consists of finer, overbank rather than channel, sediments. There are clays and silts from the floodplains, oxidised in a patchy manner and forming gley soils. These are now the variegated marls. Some sandstones might be crevasse splay sands (sand deposited on the flood plain when floods splay out from breached levees or banks of a channel). A better place to study the sandstones, though, is Worbarrow Bay. Ironstones are usually siderite, although some pyrite occurs. The iron comes from chemical weathering beneath the forest soils and then transport into the rivers. In fluvial environments it is often concentrated as the iron carbonate siderite, rather than pyrite, the iron sulphide, because of relative deficiency of sulphate ions that are available in abundance in seawater (sulphate-reducing bacteria convert the sulphate to sulphide and then iron is trapped by the sulphide ions as pyrite).

The succession (Arkell, 1947) is as follows (from top down to bottom):

(probable thin Lower Greensand above)
Variegated marls and sands - 26 m.
Four or five bands of soft ironstone - 1.5 m.
Variegated marls and ferruginous sands - 30 m.
Coarse Quartz Grit (which we have just seen)
Variegated marls and sandstones (lower beds are partly obscured; they were formerly worked for bricks and you can see remains of the brick kilns in the photograph, shown here). Arkell (1947) comments on black oil sand here. I think that the black bed visible now is carbonaceous (with plant debris) and if you would like to see a good oil sand in the Wealden go to Mupe Bay. Thickness of the variegated marls and sandstones - 70 m.
Variegated marls and sandstones, exposed intermittently - 34 m.
(Purbeck Formation below)

Total Wealden Thickness - 166m. (544 feet). Strahan, 1898, recorded the beds above the Coarse Quartz Grit as 40 feet (12m.) thicker, perhaps because of measuring at the foot of the cliff, unlike Arkell who measured in the upper part. Thus it is possible that the Wealden reaches 178 m. here, but this is not certain )

After a quick look at the finer Wealden sediments and lignite, with an eye open for dinosaur remains, we go down, stratigraphically to the Purbeck Formation at East Over (where the limestones project forward). There is a path up the cliff here, if you want to go to Pepler's Point with a high viewpoint over the cove and, perhaps, on to the Fossil Forest. Otherwise we continue to the Purbeck Formation at the foot of the cliffs as shown below.

The photograph above shows a possible effect of the Lulworth Crumples on the Wealden strata. It is very obvious at Lulworth Cove and Stair Hole that the the Purbeck Formation is folded with minor folds within the major structure. The Wealden is also distorted and a careful examination of Stair Hole will reveal overturning in relation to the Crumples in the main Purbeck cliff section. Here, on the east side of Lulworth Cove we seem to observe minor effects of the Crumple folding. There is an altenative explanation, though. These structure could be the result of minor thrust faults northward (of S3a type). The lower one does sheem to show a fault plane. Of course, they could be both fault structures and consequences of Crumple development to the south. If you have the opportunity, examine the structures further in the field and look for evidence in relation to origin.

East Over and Pepler's Point

East Over is where the soft Wealden strata end and the harder, thin-bedded Purbeck limestones project out westward into the cove. The name presumably refers to the fact that the walker will usually go up over the top here, and there is a steep, but not difficult, upward path. This leads to Pepler's Point, a promontory within the cove and overlooking the Purbeck outcrop.

At Pepler's Point you will notice that the ground level is about the same as that on the Purbeck ridge extending eastward to Bacon Hole (near Mupe Bay ). This has significant geomorphological implications. It implies that there was no large Pleistocene valley at the mouth of Lulworth Cove before sea level rose to its present position. Most streams of any size in the region have some form of river terraces. That is to say, they have been progressively cut down and there is often a younger steeper and narrower valley within a broad one. Thus the old stream valley out through the cove entrance was almost gorge-like and relatively young, Devensian or later.

Notice also that from the Purbeck outcrop there is a gentle slope seaward towards the former Portland Stone outcrop. This is the opposite of the situation at Gad Cliff where the ground rises southward from Purbeck to Portland. This may be related to the former presence of the Ipswichian raised beach just south of Lulworth Cove. There is no firm evidence and it is good subject for discussion at Pepler's Point, if you have time.

From Pepler's Point it a very short walk to a rather hazardous footpath extending in the direction of East Point. This is not safe for student parties because on slipping it is possible to fall south to the sea or north to the cove. This path shows exposures of ripple-bedded Cypris Freestone Member of the Purbeck Formation. It would be dangerous to climb to East Point and this not recommended.

PURBECK FORMATION

Introduction - Isopach Map

7.2.1 East Side of Lulworth Cove - Purbeck Formation - Introduction

(To understand the Purbeck Formation more fully please see the guides to the type section at Durlston Bay, Swanage. These contains more detail on the Purbeck facies, fauna, sedimentology and palaeoenvironments.

Durlston Bay - Peveril Point
Durlston Bay - Middle Purbecks and Building Stones
Durlston Bay - Lower Purbecks
Durlston Bay - Central Zizag Path area
Durlston Bay - Bibliography )

A simplified cross-section through the Purbeck Formation is shown here for the east side of Lulworth Cove. This is based with modifications on a section in Damon (1884) and shows some of the major features of the Purbeck succession.

The area south of the fault, shown on the above diagram, and just north of the East Over promontory needs modification now there is a good exposure of a small monocline, one of the Lulworth Crumples, in the back of the cliff. The correct interpretation of this is an interesting problem (and it would make a good small project for a visiting student party).

At the end of the promontory of East Over there is a small syncline and anticline in the Middle Purbeck Formation. These are part of the "Lulworth Crumples". You can examine this fold well on the shore at low tide (take care with slippery algal-covered rocks). It is interesting that a very similar syncline, shown above, and associated anticline occur at Peveril Point, at the northern end of Durlston Bay, Swanage. The folds at Swanage are in the Upper Purbeck whilst those at East Over, Lulworth Cove are in the Middle Purbecks. The similarity is important in relation to Phillips (1964) gravity-slip theory. Contemplate the implications of similar structures having developed in the Swanage area with a dip of only 3 degrees, and in a thicker sequences of Purbeck and Wealden strata. Incidently the Lulworth Crumple type structures are not present at Mupe Bay and Bacon Hole or Worbarrow Bay but are present in the Isle of Purbeck further east from Herston to Peveril Point (and perhaps in other parts of the Isle of Purbeck). Contemplate the implications of this too!

[Student Project: Make large scale tape and compass maps of the fold structures at East Over and at Peveril Point, Swanage. Record structural features such as dips and strikes of bedding and of joints and shears. Plot the data on stereonets and interpretation the data in terms of tectonic history and make comparisons between the structures at the two localities. (This would involve at least a few days fieldwork, probably 4 days or a week or more, and subsequent desk study and write-up. It would be suitable for second year or third geology or geophysics students. Note that low tide would be needed for most of the work. I would appreciate some feedback if this project takes place.)]

Purbeck Limestone Petrography - Introduction

Purbeck limestones can be identified in general descriptive terms in the field with the aid of a hand lens and dilute hydrochloric acid. There are obviously bivalve shelly limestones in the Middle Purbeck for example. There are glauconitic, bivalve shelly limestones in the Upper Purbeck. The Cinder Bed is an oyster shelly limestone. With a hand lens it is easy to recognise ostracodal limestones in the Cypris Freestone Member. The stromatolites of the Caps are very conspicuous in the field. Some limestones are more difficult to identify and all the limestones provide much more information in thin-section. Because of the presence of dolomite, siderite, aragonite, quartz, gypsum, celestite, pyrite etc in various Purbeck strata it is recommended for the researcher to have X-ray diffraction data at hand if that is possible (the content of Sr etc is most useful if trace element data is also available). Some introductory information on petrography is now given.

Thin-section petrography of the Purbeck carbonates is not dealt with in detail here. It is convenient, though, to refer to a few limestone types. Most geologists probably use the well-known Folk's Classification, although some, particularly in the oil industry, prefer Dunham's Classification.

For reference, a simple, student-level version of Robert Folk's (1962) scheme is given here. It is only satisfactorily used with good thin-sections, but with experience you can often make an intelligent guess at the Folk's name using a hand-lens. A trap for the novice is that many limestones which might appear to be micrites are are in fact pelsparites or pelmicrites. Another trap is that some apparent micrites are in in fact dolomicrites, not limestone micrites. However these are mainly in the Soft Cockle Member. The Cinder Bed has unusual petrography: it is biomicrosparite (or biomicrosparrudite).

A minor modification to the scheme has been made so as to include Carozzi's grumeleuse micrite. Carozzi's classic work was on the Purbecks of the Jura Mountains, so it not surprising that grumeleuse micrites are important in the equivalent strata of Dorset. Some of these are compacted pelmicrites or pelsparites; do not confuse grumeleuse micrites with thrombolites, which show poorer sorting and are normally found within stromatolites. Both grumeleuse micrites and thrombolites, together with pelsparites, pelmicrites, quiet-water oosparites, and ostracodal biosparites and biomicrites (especially in Cypris Freestones Member) are very common in the basal Purbecks. With them are typical evaporite replacement features, such as lutecite, length-slow chalcedony, euhedral quartz, nodular structure, celestite and pseudomorphs after lenticular gypsum and anhydrite. Secondary limestone replacement of evaporites are present. The lower part of the Broken Beds is really an unusual type of cargneule, not reddish and polymict as in the Pyrenees and Alps but oligomict and grey.

Higher in the Purbecks (Middle Pb upwards) biosparudites and biomicrudites are very common. Quartz sand increases in quantity and glaucony is common in the Upper Purbeck. The well-known Purbeck Marble is a "biomicrite", in more precise terms a biomicrudite.

Purbeck Formation - Clay Mineralogy

The clay mineralogy of the Purbeck of Lulworth Cove has been discussed in a recent paper by Schnyder, J., Ruffell, Deconinck, J-F and Baudin, F. 2006 on the conjunctive use of spectral gamma-ray logs and clay mineralogy in defining late Jurassic–early Cretaceous palaeoclimate change (Dorset, U.K.). The SGC log will be of particular significance to specialists concerned with boreholes. The clay mineral log is more direct interest to field studies of the Purbeck Formation.

To understand the clay mineralogy, it is necessary to note the general pattern of Purbeck palaeoclimatology (already well-established at Durlston Bay). The Lulworth Cove section shows clearly the Lower Purbeck the semi-arid phase, and then a transitional phase until the Cinder Bed, after which subhumid conditions existed. The clay mineral assemble for the Lower Purbeck is illite/smectite mixed layer with illite, but, interestingly, no kaolinite (except for some in the Caps). As at Durlston Bay there is episodic palygorskite [the Mg clay mineral] in the Lower Purbeck. Supplementary information is provided on TOC [total organic carbon]. This is generally low in the Lower Purbeck but in the Middle Purbeck Mammal Bed it rises to almost 7%. If you look at this bed in the field you can see the organic matter and it seems to be carbonaceous rather than bituminous (i.e. this is not a potential oil source rock). The paper contains other informaton on K, U, Th and ratios of these, but the values are not remarkable. The Purbeck above the Cinder Bed is not studied in detail.

Purbeck Formation - Upper (East side)

Upper Purbeck

UPPER OSTRACOD SHALES MEMBER

(formerly " Upper Cypris Clays and Shales ")

See also:

Upper Purbeck strata at Peveril Point, Durlston Bay, Dorset.

Shales, often pyritic and with some siderite and with glauconitic Viviparus limestone - Purbeck marble, as shown here (but from Peveril Point). This gastropod limestone (a biomicrite with glauconite) was quarried further east and extensively used for carvings in churches before alabaster was used as a replacement. Look for it as narrow projecting beds of rock on the foreshore at the top of the Purbeck succession.

It is a little confusing that a Unio Bed occurs within the Upper Cypris Clays and Shales and that Unio is also abundant in shales and limestones of the Unio Member beneath, and discussed below. The Unio Bed of the Upper Cypris Clays and Shales is a conspicuous greenish bed with " Unio " occurs in association with pyritic shales. It contains remarkable liquefaction structures in limestone. Reworked Portland and Kimmeridge detritus occurs in the region at this level and earthquake activity associated with the Late Kimmerian movements were probably responsible for the liquefaction (this is very well seen in Stair Hole but it extends to Mupe Bay).The pond-snail Viviparus , the freshwater bivalve Unio ,fish remains( Pycnodus, Lepidotus ) and ostracods such as the beaked freshwater form Cypridea are common in these beds. These strata are of freshwater lacustrine (lake) origin.

4.8 m.

UNIO MEMBER (as used by Damon, 1884)

(Unio Beds) Soft green, glauconitic shale full of Unio porrectus . Viviparus .Bands of hard limestone. " Beef " , shelly limestone and dark grey shales. Damon (based on Bristow) gives too great a thickness for this unit at Lulworth Cove (east side). It is less than 1 metre in thickness and lies directly on top of the Broken Shell Limestone. These strata originated in low salinity, lacustrine conditions. The bones of turtles and teeth, scutes and bones of crocodiles from this lake or lagoon can be found in this unit at various places. Examples are shown above with a modern "Unio" and Viviparus - type of pondsnail.

1.14 m.

Here, for examples, are some cross-sections of turtle bones (carapace or plastron?). Notice the dense external part and the honeycombed lower part, which reduced the weight. The original bony material white or buff in colour like modern bones but the phoshorite becomes darker with burial and time and the cavities have become filled with calcite. Thus these turtle remains like all the other fossil bones in the Purbeck Formation are brown. These are not good specimens because they are broken across and seen in cross section and would be too difficult to extract. Occasionally better specimens may be seen with the shiny top surface preserved and with the characteristic grooves of turtle carapaces. Excellent complete carapaces have been found in the Purbeck Stone quarries of the Isle of Purbeck (near Swanage). At Lulworth Cove, look amongst the common fish teeth of these beds for striated crocodile teeth. These have been found at Stair Hole, Durlston Bay and other places in the Unio Member and other parts of the Purbeck Formation.

The presence of crocodiles and turtles is not suprising in the warm lagoons and lakes of the Purbeck. They are fairly common from the Cherty Freshwater Member (Middle Purbeck) to the top of Purbecks, but are rare in the Lower Purbecks. This is because the salinities in the lagoon were often too high for the comfort of reptiles during earlier Purbeck time.

7.2.3 East Side of Lulworth Cove - Purbeck Formation - Middle Purbeck Strata

(Safety Check - If you examine this cliff section in the field inspect the cliff for safety and do not approach if there are any signs of very recent rock fall.)

See also:

Middle Purbeck strata of Durlston Bay, Purbeck Type Section, Dorset.

The Middle Purbeck Building Stones of the Intermarine Member are very well-developed in the Swanage and adjacent area of the Isle of Purbeck. They are much reduced in thickness and poorly developed at Lulworth Cove and Stair Hole. This is because of the transition from "Basin" facies at Durlston to "Shelf" facies at Lulworth. The basin was downwarping at about twice the rate of the shelf but in both areas water depths in the lagoon were shallow. As you can see, there is some offlap from basin to shelf.

The form of fibrous calcite known as beef or cone-in-cone is most thickly developed for the Dorset region at East Over, Lulworth Cove. It is in the Chief Beef Member of the Middle Purbeck Formation. The usual source of carbonate for this is the aragonite of the Neomiodon shells ( El-Shahat and West (1983).

The Purbeck Cinder Bed is quite conspicuous at East Over and because of the folding it crops out three times (look for the three outcrops!). It is blue grey in colour with small, bluish-black oysters of lagoonal type - Praeexogyra distorta. These superficially resemble the small oyster of the Texas coastal lagoons - Crassostrea virginica and it is likely that they lived in a similar but much broader environment. The lower photograph shows details in a cross-section, but this was taken on the other side of the cove, at West Over.

Under the Cinder Bed, and separated by an ostracod-rich shale with Cypridea is the white Cherty Freshwater Limestone. This is grumeleuse micrite (clotted micrite) or pelmicrite. It is important for containing pulmoniferous gastropods such as Physa, Ptychostylus and Planorbis. Viviparus is also usually present. The gastropods are often silicified but not conspicuous on a broken surface because they break through. A weathered surface is needed. The best place to find these, in fact, is not here but in this bed where soil-weathered on the coast between Durlston Head and St Albans Head. Silificied examples can be extracted from blocks by use of appropriate acid. Charopytes also occur and these too can be silicified, in which case they also can be extracted with acid. If you look carefully at loose blocks of the Flint Bed on the shore you may be able to see charophyte stems in cross-section with the standard 12 cells arranged in a circle.

Small calcite pseudomorphs after halite occur in the Cherty Freshwater Limestone, and these also may be seen in loose blocks (although probably more easily at the Fossil Forest exposure). They reveal that in spite of the very low salinity fauna there was a small of sodium chloride in the interstitial water from which halite could be precipitated on occasions when the bed dried out in the hot summer.

We will examine the cliff in photographs (of various dates). The first one which follows show the Cinder Bed as the upper and grey limestone of the pair at the top of the cliff section. The Flint Bed of the Cherty Freshwater Limestone Member is whiter, harder and more splintery. The underlying beds are more argillaceous. Find the Cinder Bed and the Flint Bed in the first photograph before continuing to ones below with more detail.

Also provided is a false colour image with micrite shown pale blue and surface ferric iron staining shown as the larger brown patches.

Partial Log of the Middle Purbeck Formation

Wealden Group (Wessex Formation) - West Side

See also: Wealden at east side of Lulworth Cove.

The Wealden is exposed in a patchy and irregular manner in low, slumped cliffs on the west side of the cove (the flowers are there to commemorate the boys lost in the sad accident here in the storm of Nov 3 2005).

Nowell (1998) noted that the units within the Wealden succession are thinner here than on the east side of the cove. He considered that this supports the view that the mouth of the cove was cut by a fault that was active during deposition of the Wealden strata. The evidence of growth faulting in the area is also known in the Purbecks ( West, 1975) but mainly in relation to a fault in Worbarrow Bay.

The top of the Wealden sequence on the west side of the cove is cut out by an east-west fault, according to Nowell (1998).

We will now look at a few details of the Wealden here.

Here are some interesting, thin and lenticular sandstone bodies in the Wessex Formation. They seem to be of fine or medium-grained sand, quite unlike the Coarse Quartz Grit. Note that the direction of younging in these slightly overturned strata is towards the north (to the right of the photograph). If you look carefully at the small channel-like feature in one of these you will some ichnofossils or trace fossils (please leave them there or demonstration purposes).

The worm burrows shown here seem to be of Planolites. This occurs in the Vectis Formation, which represent the upper and brackish to marine part of the Wealden Group in the Isle of Wight ( Stewart, et al., 1991). It is not usually present in the fluvial facies of the Wessex Formation that is present here at Lulworth Cove. Probably this occurrence needs further investigation.

We will now examine a small sequence of weakly cemented sandstone with lignite. This is partly overturned. The origin of it is of interest. A general photograph is reproduced here again for location purposes.

We can examine this sandstone with lignite and try to determine its origin. The sandstone is fine to medium grained; it does not show obvious coarsening-up or fining-up. It is appreciably cross-bedded and the lignite drapes on foresets and in small channels. I have not studied this in detail and have definate information on the conditions in which it was deposited.

Consider the possibilities. Was it the deposit of a rather low-energy river channel. Are we seeing evidence of lateral accretion from the growth of small point bars? Is the lignite the plant debris that accumulated as a flood subsided? Is there some other explanation such as crevasse-splay? Is is unlikely, though, that there were so many crevasse splays at the same place? Could these sands have accumulated at the mouth of the river at the lagoon or lake margin? Could they be a type of very shallow water, delta-front sands? What are your views?

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8.1.1 West Side of the Cove - Purbeck - Introduction

The Unio Member of the Purbecks is well-exposed in a conspicuous wall on the west side of the cove, just north of West Over. Here there is steeply north-dipping, glauconitic, shelly limestone with Unio and with fish teeth. This is a good location for teaching the use of the compass-clinometer to beginner students (another good place is at East Over).

The Purbeck succession is similar to that at the eastern side of the cove and at Stair Hole.

8. West Side of Lulworth Cove - West Over

West Over is less pronounced as a promontory than is East Over. This is because the prevailing wind direction is from the southwest. Naturally most erosion takes place towards the northeast. As you might expect, on the east side of the cove the Wealden deposits (Wessex Formation) have been eroded back further in relation to the Purbecks than on the west side. Because the erosion is generally more rapid there the Purbeck strata have been cut by almost vertical cliffs just to the south of West Over.

Landslides of mud and limestone in the 1970s led to the destruction of the coastguard huts on the cliffs here. These old slips are not very active now but are still wired off. A new phase of erosion has commenced at the foot of the cliff though. Thus the toe of the landslide is being removed and eventually a new phase of slipping will take place. While slipping of mud and rock could present a hazard to a person it is usually just a risk to property. A more serious hazard to persons occurs where vertical cliffs are undercut, as south of West Over, and where rock falls are common. Sadly, though part of the cliffs from West Over to West Point have been the site of a tragic accident when two boys watching a storm were washed away by the waves.

At low tide and in normal weather conditions it is possible to walk over the shore rocks to the Purbeck outcrop, although this is not necessarily recommended and it may not be possible at high tide. It is probably unnecessary for general parties concerned with geomorphology and the major geological features. Many of the basal Purbeck features are better seen at the Fossil Forest exposure. The Hard and Soft Cockle, the Marly Freshwater and the Cherty Freshwater can be seen quite well and in safer conditions than at the base of Stair Hole. Take care with algal-covered, slippery rocks. The cliffs are mostly fairly low but be careful to avoid getting beneath any loose debris and do not go into the cave in the Broken Beds. Attempting to climb to West Point is not advised.

We will now consider some of the interesting features of the Purbeck Formation here.

The Cinder Bed at West Over

The Middle Purbeck Cinder Bed is easily recognised at West Over. It has the usual dark bluish grey shells of the small lagoonal oysterPraeexogyra distorta (pronounced "Pre - Exogyra). It is a wackestone according to Dunham's classification but it is only just matrix-supported, so I am suspect that in places it can become a packstone. In Folk's it is really a biomicrosparrudite but for simplicity might be called a biomicrite. Thin-sections show that the matrix is usually microspar not micrite and the allochems are of rudite size. I have not examined it petrographically though at this locality.

In the field at West Over an interesting aspect is that a broken section through an echinoderm is visible. Echinoderms occur in the Cinder Bed but are difficult to find. This may well be an example of the famous Hemicidaris purbeckensis , which at one pushed the whole Purbeck into the Jurassic, but is not now regarded as evidence for this! (Most of the Purbeck is now regarded as Cretaceous).

We skip some units now, although it is hoped to add information on them later. Do note, though, the probable equivalent of the Mammal Bed of Durlston Bay. This is dark carbonaceous marl with freshwater gastropods. It represents the marshy margins of a freshwater lake. At Durlston Bay is the source of the famous fossil mammal discoveries of Victorian times. We move on downwards to the Lower Purbeck, and in particular the Soft Cockle Member.

8. The Pellety Bed - the intraclast bed of the uppermost Soft Cockle dolomites and limestones

The uppermost part of the Soft Cockle Member consists of dolomites with pseudomorphs after halite and probably some limestones. These carbonates alternate with softer marls. They are seasonal salt-lake deposits, resulting from the late restriction of the hypersaline Purbeck lagoon. The lakes dried completely at times and thus the halite crystals were produced as the white dolomitic sediment (with palygorskite in places). This was the last phase of dry conditions and the Marly Freshwater Member which follows has a good freshwater fauna.

The most conspicuous bed of this sequence is the Pellety Bed. This is browner than the other beds and composed of flat clasts of argillaceous limestone or marlstone with some rounded ends and some angular fractures. The Pellety Bed is a good marker horizon in the Lulworth area. I have not studied it in detail.

The Pellety Bed of Lulworth Cove is probably the equivalent of bed 77 of Worbarrow Tout in Ensom's (1985) Worbarrow Purbeck log? Note that intraclasts are also present at the top of 69b. Look for the algal stromatolite and serpulid limestone - 76b of Worbarrow, which may be present in the Lulworth Section. It is very interesting to observe that this flat-pebble conglomerate is not present at Durlston Bay. See the extract from the classic log of Roy Clements (1969; 1992) also provided above. The absence at Durlston Bay is because this locality has a thicker Purbeck sequence which represents that of the "basin" as opposed to the shelf facies of Lulworth. The salt lake at Durlston was not subjected to storm erosion by the lake margin waves; it was probably still under water. If the correlation suggested above for Worbarrow Bay is correct then it is appropriate to consider DB 59 and its vicinity for comparison at Durlston. It ties in very well with serpulid beds just below (and these in turn probably relate to the stromatolite bed of Perryfield Quarry, Portland - see House, 1968 ). Thus the lateral equivalents are well-known but more research is needed on the details. A further point of interest is that the high Soft Cockle dolomites, of which the Pellety Bed is the base are important fossil insect horizons at Durlston Bay and elsewhere (look for insects at Lulworth Cove). See Coram (2002) and other publications by Coram and by Jarzembowski.

The flat pebble clasts in flat pebble conglomerates are one of several type of intraclasts. It should be noted that Folk's (1962) defination of intraclasts is very broad, including almost everything of intrabasinal carbonate detrital origin from many peloids to bahamites, grapestones to plasticasts and tidal flat clasts (i.e. flat pebble conglomerates). This approach may seem rather confusing but the original definition made it clear that Folk intended the term to be generic: "Intraclast should be used as broad class term without specifying the precise origin" Folk (1962), p. 64.

To summarise, the intraclast bed or flat pebble conglomerate of the upper Soft Cockle Member of the Lulworth area is almost certainly a storm accumulation on the supratidal flats of dried lime mud ripped up from the desiccated playa lake to the southeast. This debris was built up quite rapidly on the Lulworth Shelf which formed a sabkha-like margin to the terra firma of the South Dorset High, just to the north of Lulworth Cove. Worbarrow Bay was at the very gentle break of slope between the shelf and the "basin" (just slightly lower) and there the storm channeled the underlying carbonate. On the Dorset mainland the distribution of the flat pebble conglomerate approximately mirrors that of the Great Dirt Bed with pebbles, lower down, and of course the GDB fossil forest (Worbarrow Bay is the southeastern limit of this). These are all shelf features, not present in the "basinal" facies of the Durlston Bay type section of the Purbecks. In contrast the Soft Cockle gypsum beds of Durlston Bay just reach Worbarrow Tout, where they show abundant supratidal enterolithic features (as you would expect), but they do not extend into the Lulworth area (the dry margin of the lagoon).

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West Side of Lulworth Cove - Lulworth Crumple

The diagram above is modified, with additions, from one of Phillips (1964). The photographs shows detail within this section and include the "southward overthrust" of Arkell (1938) (fig.5). Another, taken in 2002, reveals the details of a "knee-bend" of a Lulworth Crumple.

Phillips commented that on the west side of Lulworth Cove there are several shallow asymmetric folds with steeper lower limbs in the Cypris Freestones. These folds plunge at 10° in a direction N.285°E. approximately parallel to the strike, though this varies slightly because of undulations which plunge at 30° in a direction N.338°E. A number of tighter minor folds which have been overturned down-dip are present in some of the limestone bands in the lower part of the Hard Cockle Member. There is a broad fold in the main Hard Cockle limestones which are almost vertical just above beach-level. Shear fractures dipping at 56° S. curve into the vertical bedding planes and show marked displacements downward on the south side.

Several small faults, steeply dipping to the south, occur in some of the limestones of the Soft Cockle Member, and a displacement of 3.7m has occurred on the largest fault. The beds on the north side of the large fault dip at 65°N. at beach-level but become vertical in the cliff face, a change which indicates tilting of the beds to the north. Arkell regarded this fault as a southward overthrust formed by the dragging of the overlying beds up the steep limb of the anticline (Arkell, 1938). Phillips (1964) considered that the northward tilting of the beds could not be explained by this interpretation and he thought it more likely that these faults are steep thrust faults formed as a result of the downward sliding of the beds.

He thought that the curved southward dipping shear planes in the vertical part of the main Hard Cockle Limestone may have been formed as steep northward dipping thrust faults that were subsequently rotated and modified during the formation of the fold.

West Side of Lulworth Cove - Purbeck Formation - Broken Beds

The Broken Beds near the base of the Purbeck Formation are shown here as seen in the cliff near West Point, Lulworth Cove. To explain the sequence a diagram that related to the similar section at the Fossil Forest (further east) is also provided.

The Broken Beds have originated as a sequence of calcium sulphate (initially primary lenticular gypsum) overlain by thin-bedded ostracodal and peloidal limestones of the Cypris Freestones Member. This evaporite-limestone was tectonically brecciated by movement northward of the overlying Cypris Freestones. Small drag folds show the direction of movement

The Great Dirt Bed near West Point

The Great Dirt Bed is a well-known palaeosol (ancient soil) of rendzina (carbonate-rich) type. It is well seen at the Fossil Forest section and on the Isle of Portland, as in one of the photographs above. It occurs in the higher part of the Caps, the basal limestone of the Purbeck Formation that are characterised by stromatolites, pelletoidal and fine-grained oolitic limestones of lagoonal origin. The trees of the Fossil Forest and the Portland exposures were rooted in this soil.

This dark carbonaceous bed with black and cream-coloured pebbles and some irregular clasts is visible on the dipping limestones near West Point. It is not easily accessible and it is much more easily studied at the Fossil Forest exposure. It is dangerous to climb up on the projecting rocks of West Point.

We will consider briefly the palaeopedology. This ancient soil (palaeosol or paleosol) was once thicker and is now compacted. It is a rendzina, a calcareous soil of a type that develops on limestones. See the paper of Dr. Jane Francis (1986) - The calcareous paleosols of the Basal Purbeck Formation (Upper Jurassic), southern England for more information. It has a simple A/C rendzina profile, consisting of a dark organic rich horizon, with both lignite and charcoal overlying limestone bedrock that was already lithified by early cementation. It is interesting that the upper O-horizon of undecomposed plant litter is lost, but some organic matter has been reworked in places into the overlying limestone.

Francis (1986) was able to classify the the Great Dirt Bed into particular catergories of rendzinas. Because it has formed on lithified parent rock it can be described as a lithomorphic rendzina. Because of the presence of secondary carbonate (i.e. caliche), resulting from seasonally arid conditions, it can also be termed a xero-rendzina.

At this particular site near West Point of Lulworth Cove it is not sufficiently accessible for detailed study. Furthermore there do not seem to be any well-developed stromatolites with tree moulds just here. To understand this bed more fully it is best to visit the Fossil Forest exposure, and read the key publications by Jane Francis.

8.2.1 West Point

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12. Stair Hole

Go to Stair Hole Field Guide?

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13. Dungy Head

Go to Dungy Head and St. Oswald's Bay Field Guide?

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14. Durdle Door

Go to Durdle Door Field Guide?

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15. The Fossil Forest with Trees and Stromatolites

Go to the Fossil Forest Field Guide?

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16. Mupe Bay and Bacon Hole

Go to Mupe Bay Field Guide?

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18. BIBLIOGRAPHY AND REFERENCES

Go to Lulworth Cove Bibliography?