Osmington Mills

osmington-looking-west

This is another Jurassic location where ammonites can be found. The ammonites from Osmington Mills can be quite worn and hard work is required to get them out of the rocks. However, sometimes if you are lucky, you can find one lying on the foreshore.

osmington-looking-east-to-ringstead
Osmington looking east to Ringstead.
DIRECTIONS

♦ Osmington Mills can be accessed by parking at the bottom of the road there, which is off the A353.
♦ Once on the beach, walk east towards Ringstead. Both Black Head and Bran Point will be seen along this stretch of coastline.
♦ Alternatively, you can park at Ringstead and walk west.
♦ There is a steep path down from the Smugglers Inn car park and an easier (and safer) route to the shore passes around the back of the Smugglers Inn. This is recommended.
♦ Ref: 50.63391°N, 2.37571°W

PROFILE INFO

FIND FREQUENCY: ♦♦♦ – Fossils at Osmington Mills can often be found, but you will need to work to find them. A heavy lump hammer may come in handy. Occasionally, you can find ammonites washed out along the foreshore.
CHILDREN: ♦♦ – Osmington Mills is very rocky and with rocks strewn with seaweed, therefore we do not recommend it for children.
ACCESS: ♦♦♦ – It is an easy location to access, although it can be hard going over the rocky foreshore.
TYPE: – Most fossils are found in the large boulders along the foreshore, but fossils can also be found washed out on the foreshore or within the fallen blocks from the cliff face.

FOSSIL HUNTING

This entire site is part of the Jurassic World Heritage Coastline, is a SSSI and private land. No hammering on the cliff is allowed and digging is strictly forbidden. Damage has already been caused to the heritage site by people using power tools. This is strictly against SSSI rules and any attempt to ignore them may result in prosecution.

There are two areas to search:

Eastwards to Bran Point

bran-point
Bran Point, Osmington Mills, Dorset

At Osmington Mills, walk eastwards on the beach to the slipway at the Smuggler’s Inn car park. The lower cliffs are formed from the fossiliferous Nothe Grit Member of the Redcliffe Formation.

Although exposures are often poor, the grey sandy clay contains many fossil bivalves, particularly the large round oyster, Gryphaea dilatata and are worth exploring before the walk back.

At the lowest point of cliffs, near to the access point to the Smuggler’s Inn, there is a waterfall over the Preston Grit Member (formerly the Trigonia hudlestoni Beds) Here, you can find fossil bivalves (Pleuromya, Gryphaea and Myophorella hudlestoni). Occasionally, the trace fossil Diplocraterion parallelum can be seen.

diplocraterion-parallelum
Diplocraterion parallelum

Generally, the best fossils are found in the boulders along the foreshore. These can be split using a large lump hammer and a chisel. The material is very hard, so you will have to work for your finds. Occasionally, fresh cliff falls yield the ammonites Pictonia and Perisphinctes, which can be extracted from the fallen blocks. At low tide, check the foreshore exposures, as these can also contain good fossils, which the sea has washed out of the rocks for you.

The tall cliffs to the east give an unsurpassed sequence of the Corallian Group of rocks, which are Upper Jurassic rocks of Oxfordian age (163.5 to 157.3 million years ago) and form a very complex succession of limestones, marls, sandstones, silts and mudstones. The Middle White Oolite is crowded with the trace fossil Arenicolites variabilis, which leads onto the Trigonia Beds. Many fallen blocks contain the bivalve, Myophorella clavellata.

A fault then brings the Middle White Oolite Bed of the Osmington Oolite Formation, down to beach level. Search the fallen blocks for fossils of bivalves, echinoids and the ‘U-shaped’ burrows of the invertebrate, Diplocraterion parallelum, seen as trace fossils in the level-bedded oolite that forms the distinct ledge at the base of the cliff. The Middle White Oolite is also crowded with the trace fossil Arenicolites variabilis

 At Bran Point, the landscape marks a distinct junction between the Kimmeridge Clay, so dominant in the cliffs at Ringstead Bay and the hard Corallian rocks of the Osmington Oolite Formation, displayed in the low cliff. The reef here, known as Bran Ledge and the foreshore is littered with the fossil clam, Myophorella clavellata from the Trigonia Beds.

Westwards to Black Head

From Osmington Mills, head west, where concretion blocks, which are derived from the Upper Greensand and slipped Gault Clay. These may contain oysters, serpulids, echinoids, the ammonite Hoplites, and other derived fossils. These can mainly be found along the beach below Black Head, where they have fallen from the rock strata high above or near to the large slumped and slipped mix of Kimmeridge Clay and Upper Greensand that has reached beach level.  Again,  the reef here, known as Black Ledge and the foreshore is littered with the fossil clam, Myophorella clavellata from the Trigonia Beds of the Corallian.

GEOLOGY

At the foot of the small cliff at Osmington Mills, the fossiliferous Nothe Grit and Preston Grit can be seen, the latter forming the small waterfall.

Westwards from the car park, a flat shingle beach, with septaria, is visible under the mudslide of Kimmeridge Clay. Here, the overlying Upper Greensand has also slumped onto the beach. At Black Head, the reefs are the Corallian harder beds of the Nothe Grit, with Bencliff Grit and Osmington Oolite forming much of the rock platform. Black Head takes its name from the black or really, dark grey, Kimmeridge Clay which forms the upper, rather slumped, parts of the cliff. Kimmeridgian ammonites and the gastropod Bathrotomaria reticulate can be found here. Fossils from the Gault can also be brought down to beach level from the rock strata high above.

Eastwards from the car park, the cliff steepens and the sandstone of the Bencliff Grit is obvious in the basal part of the cliff. The Bencliff Grit is a cross-bedded, sandstone of marine origin, displaying ovoid, nearly spherical and very large carbonate cemented nodules, both in the cliff and as ‘doggers’ on the beach. The Bencliff Grit is mostly composed of fine-grained and well-sorted sands with finely broken plant debris. It is not very fossiliferous.

osmington-oolite-formation
Osmington Oolite Formation

Further east, at the large cliffs, the highly complex sequence of the Osmington Oolite is apparent. It is divided into the Upton, Shortlake and Nodular Rubble Members. Above the Bencliff Grit layer, the Osmington Oolite sequence is as follows:

  • A1a.  First Limestone- a bioturbated rock with Rhizocorallium burrows on its top surface. The limestone is a sandy, argillaceous limestone with Nanogyra nana and is of variable in thickness. Thalassinoides burrows are common. This rock helps to form Bran Ledge and causes the third and largest ledge on shore west of Bran Point.
  • A1b. Marl (Oolitic and sandy) with the small oyster Nanogyra nana
  • A2. Chlamys qualicosta Bed – a hard, gritty dark grey to brown limestone, which also forms Bran Ledge at Bran Point, to the east. It is crowded with fossil bivalves including Chlamys qualicosta, Chlamys fibrosa, and Nanogyra nana
  • A3. Black Clay full of crushed shells
  • A4. The Pisolite, a coarse-grained rock of shelly fragments and the bivalves: Chlamys qualicosta, Chamys fibrosa, and Myophorella hudlestoni
  • A5. Clays and white mudstone, in which the ammonite Perisphinctes can be found.
  • A6. The Middle White Oolite
  • A7. Marl and rubbly marlstone with Thalassinoides burrows. The oyster Nanogyra nana is common
  •  A8. Clay with three bands of nolular white mudstone
  • A9. Upper White Oolite (lower half)
  • A10. Clay, grey, the lower part with oolitic while nodules
  • A11. Upper White Oolite (upper half) full of Ostrea dubiensis
  • A12. Nodular Rubble Member, a nodular limestone with fossils, including the echinoid Nucleolites scutatus, the oyster Nanogyra nana, moulds of the bivalve Pholadomya and the gastropods Pseudomelania and Natica.
chlamys-qualicosta-bed
Chlamys qualicosta Bed

The remaining rocks of the Corallian sequence (the Clavellata Beds, Sandsfoot Grit and Clay, Ringstead Clay) and the overlying Kimmeridge Clay are high at the top of the cliff and best studied in exposed sections at Ringstead Bay, where they come down to beach level beyond Bran Point.

Osmington.jpg

SAFETY

Common sense when collecting at all locations should always be used and prior knowledge of tide times is essential. Care should be especially taken at Osmington Mills of tide times, as the sea can cut you off. Access down to the beach at Osmington Mills can also be dangerous after heavy rain, as mud slippages can make the path very slippery.

EQUIPMENT

The material at Osmington is very hard and therefore heavy-duty hammers and chisels should be taken. Ideally, safety goggles should be worn when hitting rock and suitable walking shoes should be worn.

ACCESS RIGHTS

This site is an SSSI and forms part of the UNESCO World Heritage Jurassic Coast. This means you can visit the site, but hammering the bedrock is not permitted. For full information about the reasons for the status of the site and restrictions please download the PDF from Natural England – SSSI Information – South Dorset

It is important to follow our ‘Code of Conduct’ when collecting fossils or visiting any site. Please also read our ‘Terms and Conditions

LINKS

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