West, Ian. 2013. Osmington Mills - Ringstead, Upper Jurassic, Corallian strata, Geology of the Wessex Coast (Jurassic Coast). By Dr. Ian West, Romsey, Hampshire and Southampton University, Internet field guide. http://www.southampton.ac.uk/~imw/osring.htm. Version: 18th December 2013.

Geology of the Corallian strata of Osmington Mills - Osmington Mills to Ringstead

Ian West,
Romsey, Hampshire

and Visiting Scientist at: Faculty of Natural and Environmental Sciences,
Southampton University,

Webpage hosted by courtesy of iSolutions, Southampton University
Aerial photographs by courtesy of The Channel Coastal Observatory , National Oceanography Centre, Southampton.
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The main cliff section of the Corallian at Osmington Mills, Dorset, seen from the Chlamys qualicostata ledge

The superb cliff section of the Corallian, Upper Jurassic strata, east of Osmington Mills, Dorset, as seen from the cliff top, 2nd March 2009

Spherical concretions or doggers are being eroded out of the Bencliff Grit, to the east of Osmington Mills, Dorset, 2nd March 2009

Calcite-cemented, non-septarian, nodules in the Bencliff Grit Formation, Corallian Group, seen in the cliff section between Osmington Mills and Ringstead, Dorset, looking west, 2nd March 2009

Bran Point between Osmington Mills and Ringstead, Dorset. Here the Middle White Oolite of the Osmington Oolite descends to the beach

|Home and List of Webpages | Osmington - Introduction |Osmington - Osmington Mills to Ringstead |Osmington - Bencliff Grit |Osmington - Osmington Oolite |Osmington - Black Head | Corallian Fossils |Osmington - Bibliography

The Osmington Mills Geology Field Guides

Osmington Mills Geology - Introduction
Osmington Mills Geology - Osmington Mills to Ringstead (main cliff section)
Osmington Mills Geology - Bencliff Grit
Osmington Geology - Osmington Oolite Formation
Osmington - Black Head Geology
Osmington - Corallian Fossils
Osmington Mills and Corallian - - Bibliography


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Safety during Geological Fieldwork at Osmington Mills

A hazardous area of rock fall from the Red Beds at the cliff east of Osmington Mills, Dorset, 2nd March 2009

The stretch of coast from Osmington Mills to Bran Point must be considered on the day with regard to cliff and weather conditions before proceeding along it. In dry weather in summer there is usually no excessive risk, although, of course, a rock can fall at any cliff anywhere. On certain occasions, particularly during or after heavy rainfall (as in the case shown above), or after frost, the high part of the cliff between Osmington Mills and Bran Point can be hazardous. The foot of the cliffs should not be approached in these conditions, and cliff-fall areas and bombardment zones watched out for. Safety helmets should be worn when adjacent to a cliff as protection against small rocks, but they will, not of course, give protection against falling boulders. There is, as always, more risk of rock-fall injury to a large, spread-out party than to one or two, cautious and observant individual geologists. Keeping well to the seaward side of the beach at low tide may sometimes be necessary. Bouncing boulders from cliffs occasionally reach the sea, but this is less common. The stretch from Bran Point on to Ringstead is much safer at times of cliff-fall risk. Working out on the ledges at low tide can be less risky with regard to cliff falls.

A minor hazard is that of falling on slippery sea-weed covered rocks on the shore. The tidal range is not great but low tide is better because the shore reefs are exposed. Obviously beware of storm wave conditions, although they are not common here.

Note that this website provides only descriptions and photographs of geological, geomorphological, landscape and historical features. The website does not advise or recommend a visit to any particular site, which may be safe on one occasion and very unsafe on another occasion. An individual geologist or walker, or the organiser or field leader of a party should decide whether conditions are suitable and safe on the day for field studies there, with relation to access problems, tide, weather, type, age and ability of participants. They should obtain permission to enter private land, obey any regulations, and always take care not to disturb the public or wildlife. No liability is accepted.

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Osmington Mills to Bran Point - Geology of the Main Cliff Section

Redcliff Point to Bran Point, near Osmington Mills, Dorset - geological map of Arkell

The main cliff exposure of Corallian (Upper Jurassic) strata between Osmington Mills, and Ringstead, Dorset, viewed from Weymouth in evening light, 24th March 2009

View down the cliff from the cliff-top footpath, main Corallian section, east of Osmington Mills, Dorset, 2006

The cliffs of Corallian strata between Osmington Mills and Bran Point, Dorset, 2006

Old, pre-1999, photograph of the cliffs between Osmington Mills and Bran Point, Dorset

The best exposure of the Corallian strata is between Osmington Mills and Ringstead. The geology of this section has been neatly summarised by House (1993), whose handbook to the Dorset is recommended. To see the section descend from the car park at Osmington Mills down the steps alongside the slipway. At the foot of the small cliff the fossiliferous Nothe Grit and Preston Grit can be seen, the latter forming the small waterfall. Then walk eastward crossing by stepping stones the shallow outflowing water at the cascade and continue over the boulders for about 300 metres until the cliff steepens and the sandstone of the Bencliff Grit is obvious in the basal part of the cliff (the place where there are many students grouped in the left photograph below). This is a convenient place to stop, look at maps and sections and review the situation. A decision can now be made as to whether the cliff is in normal relatively safe condition or whether rocks-falls are occurring and no further progress should be made to the east.

Here are three images, each of which is a photomosaic taken in 1991, to give an overview of the cliffs east of Osmington Mills to Bran Point. The panoramic compilation gives an impression of curvature which is false and the cliffs are relatively straight. The photographs were taken at a very low tide and it then possible to walk out some distance seaward from the cliff. Most often it is not possible to go far from the cliffs and the sea is usually fairly close to them. It is rare, however, for the sea to be in contact with the cliffs except during storms coinciding with high tide. Normally a party can walk past, but caution is needed with regard to danger of falling rocks. Further details of these cliffs will be provided in images to follow.

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Succession at Osmington Mills, Bran Point and Ringstead

Succession of the Corallian strata in the Osmington Mills region, Dorset

General succession diagrams are given here, to enable easy identification of the main horizons. More detailed logging is sometimes undertaken here as student exercises and it is not intended that this log replaces or provide an answer to such detailed studies. Carefully measured logs will not give exactly the same results as shown here for several reasons. The original measurements of Arkell were made in feet and inches and may have been estimated to the nearest 3 inches in some cases. Full details are not always shown and some units can be subdivided. Lateral changes occur and the section varies in detail according to where it is measured. Further west at Black Head the main units can be recognised but there some changes in the details of the sequence.

The log here can be used to locate specific lithological and fossil-bearing horizons given by Arkell (1936; 1947) and more details are provided in a list of the individual beds which is given further below.

Sedimentary Logs

These additional logs, modified from part of a diagram by Wright (1986), provide some more information on sedimentary facies. They also indicate the distribution of some trace fossils - burrows, some of which have been made by shrimp-like crustaceans. The logs show, in particular, how parts of the Osmington Oolite Formation expand to Black Head in the west. There are some further interesting lithological changes to Redcliff Point, further west. The original paper, which should be seen, links the sections to Sandsfoot in Portland Harbour and East Fleet in the Fleet Lagoon. It is also useful in providing ammonite zones and subzones, after Sykes and Callomon (1979).

The number on the logs that are preceded by A are once again, the bed numbers of Arkell (1936; 1947).

There has been much discussion (not much of which has yet been reproduced here) about the sedimentary origin of the various subdivisions of the Corallian Group, the palaeoenvironments, the cyclicity and sequence stratigraphy. See particularly Newell (2000), De Wet (1998), Coe (1995) and Sun (1989). The locations of these and other relevant papers will be found in the Osmington Bibliography.

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Corallian Succession - Osmington Mills, Bran Point and Ringstead - Bed Details.

Qualicosta Bed etc.

Junction of Bencliff Grit and Osmington Oolite, Osmington Mills, Dorset

With minor modifications and additions this is based on Arkell (1936; 1947) and uses his well-known bed units with the letter 'A' added. Metric conversions have been added to feet and inches."Fucoidal" structure etc has been changed to refer to Thalassinoides, a trace fossil not recognised in the old literature and some fossil names have been updated. The list is from the Kimmeridge Clay at the top down with the Nothe Clay at the base. The uppermost part is seen in the slumped cliffs near Ringstead and the lower part nearer to Osmington Mills. The stratigraphical terminology is largely based on House (1993), Sellwood et al. (1990) and Sun (1989). It is not claimed that this is the best or the "official" classification, but it can easily be related to any other scheme. Arkell's (1936, 1947) terms are also given to facilitate use of older literature.

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A28. Shaly clay, blue with layers of the flat, triangular oyster,Deltoideum delta, seen to ... 4.6m (15 ft).

A27. Nanogyra nana Bed. A mass of the small, fingernail-sized oysters, locally hardened into a dark limestone like the Forest Marble. Rare specimens of the Lower Kimmeridge ammonite Pictonia sp. in situ. 0.20m to 0.30m (8 inches to 1 foot).

A26. Torquirhynchia inconstans Bed. Purplish-grey clay, locally hardened, with many large Serpulae and some rolled and bored phosphatic pebbles. The ammonite Pictonia densicostata Salfeld, the easily recognised, asymmetical brachiopod Torquirynchia incostans (quite common), the small oyster Nanogyra nana, Exogyra praevirgula and many moulds of other molluscs. 0.61m (2 feet).

(Total thickness on Dorset coast - approximately 60m.)

Ringstead Formation
(Upper Calcareous Grit - used by Arkell, 1936, 1947, to include Ringstead Coral Bed)

A25. Ringstead Coral Bed. Thin and rather irregular, marly limestone, in clay. Not conspicuous or continuous or easily found because of slumping in the low cliffs. Has to be searched for in the small cliff embayments. It is marly limestone, hard and greenish, and a mass of fossils. There are many Serpulae (worm tubes) and these are more conspicuous than the corals. This famous bed has ammonites of the genus Ringsteadia associated with the corals Thecosmilia annularis, Thamnasteria concinna, Th. arachnoides and Protoseris waltoni. There are Cidaris spines and many bivalves including the Pectens - Chlamys nattheimensis, Chlamys splendens, Velata hautcoeuri and the large Ctenostreon proboscideum. This is not a complete list and for more see Arkell (1936). 0.15m to 0.20m (6 inches to 8 inches).

Ringstead Clay Member
(Ringstead Waxy Clays of Arkell, 1936,1947)

A24d. Clay with the flat oyster Deltoideum delta, the bivalve Ctenostreon proboscideum, large Serpulae etc. 0.76m (3 inches).

A24c. Prominant band of reddish-brown, argillaceous siderite nodules (iron carbonate). The ammonite Ringsteadia anglica has been found in situ at this horizon west of Osmington Mills. 0.76m (3 inches).

A24b. Bands of reddish-brown, argillaceous siderite nodules, less prominent. 0.30m (1 foot)

A24a. Clay waxy, mainly unfossiliferous, ferruginous brown and grey; seams of laminated, argillaceous siderite nodules; layers of the oysterDeltoideum delta towards the base; seen to 2.74m (9 feet)

Sandsfoot Formation
Sandsfoot Grit and Clay Members
(here not separable - See Arkell 1947 re Black Head).

A23b. Sandstone, bright red, speckled with white ooids and quartz grains, and much burrowed by Thalassinoides and other trace fossils. Bivalves - Goniomya literata, Chlamys midas, Pleuromya alduini, etc. (Blake and Huddleston, 1877, p. 272, recorded the ammonite Perisphinctes decipiens J. Sowerby). 0.60m (2 feet).

A22-19. Clays, blue and brown, with varying amounts of ferruginous matter (ankerite?), a band of red sandstone, and nodular argillaceous limestone (cementstones) and layers of the oyster Deltoideum delta. Thickness difficult to estimate owing to slipping; according to Blake and Huddleston - 5.49m (18 feet). H.B. Woodward gave 3.05m-3.65m (10-12 feet). Arkell (1947) listed 3.05m-5.49m (10-18 feet).

Trigonia clavellata Formation
These beds contain abundant Myophorella clavellata (J. Sowerby), formerly Trigonia clavellata. These were the "cockles of the Mesozoic", with muscular T-shaped feet so strong that they could jump! They lived nearshore in water only 10 - 15m deep.

These strata are in total about 6.10m (20 feet) in thickness.

The Red Beds Member
(The Red Beds of Damon, 1860;1894)

A18. Limestones, brownish-red, mottled grey, much burrowed by Thalassinoides, the grey parts very oolitic with large ooids. Roughly divided into two beds, with very irregular surfaces. The brownish-red material is ankerite. Fossils, including the conspicuous, triangular, tuberculate bivalve Myophorella clavellata as in the bed below but fewer. Large Perisphinctid ammonites were visible on the surface of the lower course on the shore at low tide according to Arkell (1947). These ammonites include: Perisphinctes uptonensis, Perisphinctes ringsteadensis, Perisphinctes osmingtonensis, and Perisphinctes boweni. Also present is Nautilus hexagonus. 0.76m (2 feet, 6 inches).

A17. Marl parting; casts of Myophorella clavellata. 0.08m - 0.15m (3 inches to 6 inches).

A16. Limestone, tough, sandy, very shelly, greenish brown to reddish, patchily oolitic. Full of Myophorella clavellata etc. Ammonite - Ameoboceras sp. 0.56m (1foot, 10 inches in Arkell, 1936, listed in error as 10 feet in Arkell, 1947)

The Clay Band

A15. Marl, greenish grey, oolitic, with some partly-consolidated masses, passing down into clay. Moulds of the aragonitic bivalves Pholadomya protei, Pleuromya uniformis, etc. Also shells of the bivalves Chlamys superfibrosa, Nanogyra nana, Ostrea delta. 1.22m (4 feet).

The Chief Shell Beds Member

A 14c. Shelly marl, a mass of well-preserved bivalves: Myophorella clavellata, Trigonia (Myophorella?) reticulata, Deltoideum delta, Ostrea solitaria, Nanogyra nana, Plicatula weymouthiana, Gervillia aviculoides, Isognomon subplana, Pteria pteropernoides, Pteroperna polyodon, Mytilus pectinatus, Chlamys superfibrosa, Chlamys qualicosta, Velata anglica, Lima rigida, Entolium demissum, Cucullaea contracta, Isocyprina cyreniformis, Isocyprina glabra, Pleuromya uniformis. Gastropods: Pseudomelania, Ampullina. Worm tubes: Serpulae. The marl passes down into grey shelly limestone with the same fauna. There is a marl parting at the base. 1.06m (3 feet, 6 inches).

The Sandy Block Member

Limestones, grey, rough, lenticular, with hummocky surfaces and marl partings; often sandy and sometimes oolitic, generally fairly bioturbated with Thalassinoides, locally shelly, but with the fossils in most of the bands only present as moulds. Myophorella clavellata, Isognomon subplana, Deltoideum delta, Modiola, Isocyprina, and abundant moulds of Pleuromya uniformis. Gastropods also present. 2.29m (7 feet, 6 inches).

Osmington Oolite Formation
(Osmington Oolite Series of Arkell, 1936, 1947)

A12. Nodular Rubble Member. A bed of bioturbated nodular limestone, composed of minute calcitised kidney-shaped, Rhaxella sponge spicules (visible only microscopically, in thin-section). In the field it appears grey, rough, nodular and is fossiliferous. It is easily recognised in the field because it is not separated into clearly distinct beds but forms a very steep section of the cliff of nodular limestone, reaching the shore at Bran Point. It does show division into two courses, though. There are many fragments of shells and spines of echinoderms. Fossils include the small echinoidNucleolites scutatus, the small oyster Nanogyra nana, moulds of the bivalve Pholadomya and the gastropods Pseudomelania (a large turreted form) and the smaller Natica. The lowest 0.30m (1 foot) is oolitic and clayey. Total thickness 3.35m (11 feet).

A11. Upper White Oolite (upper half). Clay with laminae of fissile white oolite, full of small Ostrea cf. dubiensis. 0.30m (1 foot).

A10. Clay, grey, the lower part oolitic, with oolitic while nodules in the lower 0.3m (1 foot). Thickness: 0.99m (3 feet, 3 inches).

A9. Upper White Oolite (lower half). Cross-bedded oolite with vertical burrows. 0.60m (2 feet).

A.8. Clay with three bands of nolular white mudstone in the highest 1.22m (4 feet). Thickness: 2.51m (8 feet, 3 inches). A.7. Marl and soft rubbly marlstone, in several bands, strongly oolitic, with Thalassinoides burrows. The small oyster Nanogyra nana is common. Chlamys qualicosta is present.

A.6. The Middle White Oolite. At the west end of the cliff towards Osmington Mills, this is 2.29m (7 feet, 6 inches) of solid, cross-bedded while oolite, overlying 1.06m (3 feet, 6 inches) of more thinly-bedded, cross-bedded white oolite. Eastward the whole becomes more marly from the base up, until at Bran Point only the highest 0.60m (2 feet) is solid white oolite. Vertical burrows are a conspicuous feature in the oolite; also cross-lamination, clay partings and some lignite. Thickness: 3.05m (10 feet).

A5. (Littlemore Clay Beds facies of Arkell). Clays and bands of nodular white mudstone. Ammonites of the genus Perisphinctes can be found. Thickness: 3.81m (12 feet, 6 inches).

A4. The Pisolite. An oncolite or oncoid bed (oncolites are pea-sized objects of microbial or algal origin often formed around a piece of shell), coarse-grained, purplish-grey, fairly hard although prone to disintegrate into individual oncolites. It forms a small ledge both west and east of Bran Point (it is repeated by a fault). It is shelly with shell fragments and also specimens of the bivalves: Chlamys qualicosta, Chamys fibrosa, Myophorella hudlestoni (another "Trigonia"). Fragments of the ammonites Perisphinctes sp. and Cardioceras (Cawtoniceras) sp. etc. have been found. 0.46m (1 foot, 6 inches).

A3. Clay, black, full of fragile compressed shells, especially small Trigonia (Myophorella?) bivalves of clavellate form. Also the bivalves Chlamys qualicosta, Cucullaea, Grammatodon, Lucina. Locally this bed is a marl. 0.60m (2 feet).

A2. Chlamys qualicosta Bed. Limestone, hard, oolitic, sparsely pisolitic, gritty, shelly, dark-grey, weathering brown. The highest 0.15m (6 inches) forms a separate course. Crowded with Chlamys qualicosta, Chlamys fibrosa, Nanogyra nana etc. Forms Bran Ledge at Bran Point and the second ledge to the west. 0.76m (2 feet, 6 inches).

A1b. Marl, oolitic, sandy, with Nanogyra nana, passing down into the hard band of the same material beneath (A1a). Thickness: 1.37m (4 feet, 6 inches).

A1a. The First Limestone. Sandy, argillaceous limestone with Nanogyra nana variable in thickness but thickening westward. Bioturbated with Thalassinoides burrows. This helps to form Bran Ledge and also causes the third and largest ledge on shore west of Bran Point. Thickness: variable upto 0.60m (2 feet) (Note - Arkell originally put these two beds together as A1 with a total thickness of 1.98m (6 feet, 6 inches) but it is sensible to label them separately.)

Top of the Bencliff Grit at Osmington Mills, Dorset

Bencliff Grit Formation
(c. 3.96m or 13 feet in total)

BG c. Almost continous band of indurated, calcite-cemented, sandstone nodules (doggers). 0.41m (1 foot, 4 inches).

BG b. Yellow, brown and white sands, locally cross-bedded, with thin sandy clay beds (heterolithic units) and a few calcite-cemented concretions (nodules or doggers). The upper part is strongly impregnated with oil. 3.05m (10 feet).

BG a. Huge calcite-cemented concretions (nodules or doggers) with cross-bedding. Some are more than 1.83m (6 feet) in diameter. In some cases they pass into a more or less continuous band of thin-bedded (flaggy) calcite-cemented sandstone with the large, dark-coloured, round oyster Gryphaea dilatata and worm tubes (Serpula). The nodules weather out as prominant features on the beach.

Nothe Clay Formation
(Classified in the Berkshire Oolite Series by Arkell, 1936, 1947)

NC. Dark blue-grey clay. Only the uppermost part is visible at the western end of the main cliff section. Between that point and the cascade it is obscured by landslides or faulting or both. The lowest 0.91m (3 feet) of this, with the round oyster Gryphaea dilatata can be seen in the small headland between the cascade and the slipway at Osmington Mills (near the Smugglers Inn), map reference SY 734816, so the section can be continued down from there. Total thickness here is uncertain but perhaps about 12m.

Nothe Grit Formation
(This is extended up here for convenience to include the thin Preston Grit Member. The Nothe Grit was classified in the Lower Calcareous Grit by Arkell, 1936, 1947)

Preston Grit Member
(formerly Trigonia hudlestoni Beds) - c. 1.68m (5 feet, 6 inches).

PG 3. Shelly, thin-bedded (flaggy), calcite-cemented sandstone, with some of the fossils in the next hard sandstone below, but not so abundant. 0.46m (1 foot, 6 inches).

PG 2. Sand. 0.41m (1 foot, 4 inches).

PG 1. Shelly calcite-cemented sandstone. Full of the bivalves Pleuromya uniformis, Isognomon subplana and Gryphaea dilatata, with Chlamys fibrosa, Chlamys splendens, Myophorella ("Trigonia") hudlestoni, Nanogyra nana, Lopha gregariea, Gervillia aviculoides, Thracia depressa, Goniomya literata, Pholadomya aequalis, Plicatula weymouthiana, Lucina lyrata and with worm-tubes (Serpula). Ammonites occur in the Preston Grit at Redcliff Point. Thickness of this bed at Osmington Mills: 0.71m (2 feet, 4 inches).

Nothe Grit Member

NG1 - NG5. Grey sandy clay with bands of irregular calcite-cemented sandstone, some containing cannon-ball concretions and the large round oyster - Gryphaea dilatata. This is easily recognised by the large size, the curvature of one valve and the dark blue-grey colour of the calcitic shell. Thickness of Nothe Grit seen at Osmington Mills: 5.18m (17 feet), but the full thickness is 8.08m (26 feet, 6 inches) Redcliff Point, further west.

(Base of the Corallian Group)

(c. 140m thick)

(Dark blue-grey clay with the large round oyster - Gryphaea dilatata and the ammonite Cardioceras. Not exposed at Osmington Mills. See this at Jordan or Furzey Cliff, east of Weymouth, map reference SY 697816-703819, where 45m is exposed.)

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Ammonite Zones of the Corallian Group - Old Scheme
(As in Arkell, 1947, Sellwood et al., 1990, etc)

Ringsteadia pseudocordata (Sandsfoot Grit to Ringstead Coral Bed)
Perisphinctes cautisnigrae (Trigonia clavellata Formation to Sandsfoot Clay)
Perisphinctes plicatilis (Preston Grit, Nothe Clay, Bencliff Grit, Osmington Oolite Formation)
Cardioceras cordatum (pars) (Nothe Grit)

Ammonite Zones of the Corallian Group - New Scheme
(as in House, 1993)

Amoeboceras rosenkrantzi
Amoeboceras regulare
Amoeboceras serratum
Amoeboceras glosense
Cardioceras tenuiserratum
Cardioceras densiplicatum
Cardioceras cordatum

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Bencliff Grit, with Oil Sand and Oil Seep

Ian West examines oil sand and oil seep in the Bencliff Grit, east of Osmington Mills, Dorset, 2006

Oil seep on the ledges above the Bencliff Grit, near Bran Point, Osmington Mills, Dorset, 2006

The Bencliff Grit is a very interesting cross-bedded, sandstone of marine origin. It is notable for containing residual oil sands and an oil seep. These features started the search for oil in the region which eventually culminated in the discovery of the great Wytch Farm Oilfield, near Poole Harbour.

For more information please go to the oil section of the Bencliff Grit Webpage of the Osmington Field Guide

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Osmington Oolite

Undercutting of the sea ledge of the Chlamys qualicostata Bed, Osmington Oolite, near Bran Point, Osmington Mills, Dorset; compare with erosion of Kimmeridge Ledges

This ledge is formed by the Chlamys qualicostata Bed (A2) of the Osmington Oolite Formation of the Corallian Group. Notice that it has been undercut by wave action and blocks have collapsed on the updip side. A similar feature is seen in the Kimmeridge Clay dolomite ledges at Kimmeridge Bay. They are also eroded by wave-undercutting and subsequent collapse. This is also seen at Portland Bill , where the Portland Stone is undercut.

For more on the Osmington Oolite Formation :
Please go to Osmington Oolite Field Guide ; click here!

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Common fossils of the Corallian Group at Osmington Mills, Dorset, and elsewhere

Common trace fossils of the Corallian Group strata at Osmington Mills, Dorset, and elsewhere

Some common fossils and trace fossils of the Corallian are shown above. For more on Corallian fossils see:

Corallian Fossil Webpage.

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Coast Erosion

Disintegration of nodules

As far as I know the rate of coast erosion has not been calculated for the cliffs east of Osmington Mills. The alternations of sandstone, clays, thin limestones etc here seems to be unergoing fairly rapidly erosion and the ledges are evidence of this. The photographs here show just how a nodule is breaking up in a few years. This one is easily identifiable due to boring activities of geophysicists. Palaeomagnetists have been trying to date the strata by remanent magnetism indicating the original positions of the poles. Presumably the drilling was done when the block was in place in the cliffs (and someone, somewhere knows exactly when this was).

This particular stretch of cliff is retreating but east and west of it the erosion seems limited. Study of the topographic map and the geological map, reproduced here may help explain this. Judging from the coastal slopes, there seems to have once been a small headland here, southwest of the fort and it has been truncated by recent erosion to form the present steep cliff. It probably extended to the Poole Ledge area where the wreck is visible. Perhaps the Nothe Grit once formed something of a barrier and now only Frenchman's Ledge and Poole Ledge are the relics.

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A graphic log sheet prepared for student exercises in sedimentary logging at Osmington Mills, Dorset

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Students walk easst beyond Bran Point, near Osmington Mills, Dorset, towards Ringstead, with White Nothe in the distance

Continue eastward to Ringstead and White Nothe?

Continue west to Black Head and Redcliff Point?

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I am very grateful to Ivailo Grigorov for permission to reproduce his SEM photographs. I particularly thank Professor Dorrik Stow and his many sedimentology students who have appeared in field photographs during their field trips. The support of Southampton University in running this website is particularly appreciated.

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Go to Osmington, Corallian, Bibliography

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To continue the Osmington Corallian Field Guide go to the section of interest:

- Osmington - Pt. 1 - Osmington Mills Introduction

- Osmington - Pt. 2 - Osmington Mills to Ringstead.

- Osmington - Pt. 3 - Bencliff Grit

- Osmington - Pt. 4 - Osmington Oolite

- Osmington - Pt. 5 - Black Head

- Osmington - Pt. 6 - Corallian Fossils

- Osmington - Pt. 7 - Bibliography

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Copyright, 2013, Ian West, Catherine West, Tonya Loades and Joanna Bentley. All rights reserved. This is a purely academic website and images and text may not be copied for publication or for use on other webpages or for any commercial activity or for any financial gain. A reasonable number of images and some text may be used for unpaid, non-commercial academic purposes, including field trip handouts, lectures, student projects, dissertations etc, providing source is acknowledged.

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

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Dr Ian West, author of these webpages

Webpage - written and produced by:

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


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