The coastal section at Black Head, near Osmington, displays Jurassic rocks from the Kimmeridge Clay Formation of 152-157 million years ago. Fossils to be found include ammonites, brachiopods, coral, worm tubes and bivalves, as well as marine reptile remains, especially vertebrae and fish bones and teeth.. This site is where the huge skull of the famous Weymouth Bay pliosaur, Pliosaurus kevani was discovered but expect to find a less sensational specimen!
DIRECTIONS
♦ The beach is best accessed by parking at the car park of the Smuggler’s Inn at Osmington Mills. The coastal path is accessed round the back of the pub, walk west (towards Weymouth) along the coastal path and then drop down onto the beach, via a series of metal steps, beneath the PGL Osmington Bay Centre (Adventure Centre) and walk along the beach, west to Black Head.
♦ Alternatively, walk from Bowleaze Cove, heading east along the coastal path and taking in the lovely scenery before reaching PGL Osmington Mills and descending to the beach.
♦ Smuggler’s Inn Pub: Postcode: DT3 6HF: Google maps link
♦ Bowleaze Cove, Parking: Postcode: DT3 6PW: Google maps link
♦ What3Words: location of site: ///arrived.glare.crescendo
PROFILE INFO
FIND FREQUENCY: ♦ ♦ ♦ A good selection of fossils can be collected, from the Kimmeridge Clay Formation.
CHILDREN: ♦ ♦ ♦ Older children will enjoy the location. Younger children might find the walk to the site and the steps to the beach rather challenging.
ACCESS: ♦ ♦ ♦ ♦ Access is easy, with parking at the car park at Osmington Mills, or in the lane leading to the pub. Please be aware the steps down to the beach at the PGL Osmington Mills has subsided, and the steps are sloped at various angles.
TYPE: – Fossils are found in the small section of Kimmeridge Clay. Fossils are found with more frequency in the winter months, when coastal erosion is at its peak.
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FOSSIL HUNTING
Fossil collecting at Black Head, near Osmington Mills, can be highly rewarding, though it often requires patience and careful extraction due to the nature of the material preserved here. The foreshore exposes fossiliferous mudstones that yield a diverse assemblage of Late Jurassic marine life, much of which is not seen at nearby Kimmeridge Bay. Fossils are most commonly collected from fallen blocks and slabs on the foreshore and from material weathered out close to the base of the cliff, where erosion regularly reveals fresh specimens.
By far the most abundant fossils found along the ledges between Black Head and Bran Point are bivalves, particularly Myophorella clavellata. These shells often occur in dense shell beds and are easily recognised by their strong ribbing and robust form. Although Myophorella is notoriously difficult to extract intact due to its firm attachment to the surrounding matrix, the shell banks at Black Head are frequently softer than at other localities, making this one of the better places to recover complete or near-complete specimens. Many examples are preserved as paired valves, though single valves are also common.
Oysters are also widespread and easily found, with Deltoideum delta being especially common. These typically occur as single valves and may be preserved either flattened within the matrix or weathered free on the foreshore. Other bivalves may also be encountered, including Camptonectes, Astarte, Pholadomya and Gervillia, often appearing as moulds or partially preserved shells. In places where material derived from underlying beds is present, bivalves such as Trigonia reticulata and Gervillia aviculoides can also be found, sometimes showing excellent surface detail.
Ammonites are less common than bivalves but remain an important and sought-after component of the fauna. Specimens are usually found flattened within shale slabs or as partial impressions, though occasional more three-dimensional examples occur in harder nodules. Typical ammonites from the area include Rasenia cymodoce, which is one of the more characteristic species, along with occasional finds of Aulacostephanus and Pictonia. Preservation quality varies, but shell ornamentation can be well defined when specimens are carefully prepared.
The mudstones at Black Head also yield occasional remains of marine vertebrates, adding to the scientific and collecting interest of the site. Fish material is encountered sporadically and includes isolated teeth, scales and bone fragments, often requiring close inspection of shale surfaces to spot. More significantly, remains of marine reptiles occur with some regularity, particularly those of ichthyosaurs and pliosaurs. Isolated vertebrae are the most commonly found elements, with the ichthyosaur Brachypterygius extremus being especially well represented. These vertebrae are often found loose on the foreshore or partially embedded within fallen blocks and can usually be identified by their distinctive disc-like shape.
Occasional fragments of ribs, limb bones and jaw elements from marine reptiles may also be encountered, though complete or articulated material is extremely rare and should be left in situ if discovered. Other fossils found less frequently include belemnite guards, trace fossils and indeterminate shell fragments, all contributing to a picture of a rich Late Jurassic marine ecosystem.
As with all Kimmeridge Clay sites, specimens can be fragile and are best collected from loose blocks rather than from in situ exposures. Careful splitting of slabs and patient preparation often rewards the collector with well-preserved fossils that capture a snapshot of life in the Jurassic seas that once covered this area.
GEOLOGY
The coastline between Osmington Mills and Black Head displays some of the most structurally complex geology in Dorset and provides clear evidence of the Weymouth Anticline, a large dome-shaped fold formed as a distant consequence of the Alpine Orogeny around 20 million years ago. These earth movements, responsible for building the Alps, sent powerful compressional forces far beyond their point of origin. The outer effects of this “Alpine storm” buckled, folded and faulted the sedimentary rocks of southern Dorset, producing the Weymouth Anticline, a broad upfold that dominates the structure of the region.
Along the northern margin of the Weymouth Anticline, the structure becomes increasingly complex, with the main fold disrupted by smaller subsidiary folds and intersected by a major fault system. To the south, the strata rise out of the sea to form the distinctive wedge-shaped Isle of Portland, while to the north they dip steeply back beneath younger deposits. This structural arrangement gives rise to the characteristic landscape of alternating limestone ridges and clay vales that run broadly east to west, stretching inland from the Fleet Lagoon through to Osmington and beyond.
At beach level beneath Black Head, the Kimmeridge Clay forms imposing dark cliffs that show surprisingly little obvious internal variation at first glance. The cliff face often appears as a near-continuous mass of black mudstone, with few easily recognisable marker horizons. However, closer inspection reveals the presence of two important cementstone beds that stand out from the surrounding softer clay. One of these is the Virgula Limestone, a distinctive pale band composed almost entirely of the small oyster Nanogyra virgula, which can form dense shell concentrations. This bed often weathers proud of the surrounding clay and can be traced intermittently along the cliff and foreshore.
The second notable cementstone is the Nano cardioceras Cementstone, a nodular limestone horizon that is particularly significant due to its fossil content. This bed contains ammonites of the genus Amoeboceras, specifically Amoeboceras (Nanocardioceras), which are preserved in uncrushed calcite rather than being flattened as they usually are in the surrounding mudstones. These nodules provide an important marker within the Kimmeridge Clay succession and are among the few horizons here that resist weathering.
The Kimmeridge Clay at Black Head frequently develops a thick crust of weathered clay during warmer and drier periods. This surface layer can obscure fresh exposures in the lower part of the cliff and along the foreshore, giving the impression that little detail is visible. Beneath this weathered skin, however, the clay is often much fresher and better preserved. While loose material on the foreshore may be examined, the cliff itself must not be disturbed, as this stretch of coastline lies within a Site of Special Scientific Interest. Digging into the cliff face is both unsafe and prohibited.
Running parallel to the shoreline is a series of prominent rock ledges that form a stark contrast to the softer Kimmeridge Clay. These ledges are composed of the Nothe Grit and the Upton Member of the Osmington Oolite Formation, both of which are extremely hard, well-cemented limestones. Their resistance to erosion creates the stepped profile of the foreshore in this area. Although these rocks are largely unfossiliferous and too hard to yield collectible material, they play an important role in shaping the coastal platform and influencing wave action and erosion patterns along this stretch of coast.
Recent coastal change has been highlighted by a significant landslide event at Black Head during 2024, following prolonged periods of heavy rainfall and storm activity. A large volume of Kimmeridge Clay slumped from the lower cliff, adding fresh debris and blocks to the foreshore and further reshaping the undercliff. Such events are typical of this stretch of coast, where weak, water-saturated clays are prone to failure, and they serve as a reminder that the cliffs here are highly unstable. While landslides can expose fresh geological material, visitors should keep well clear of the cliff base and avoid lingering beneath active or recently slipped sections.
SAFETY
The site is generally safe but be aware of incoming or rough tides, particularly during the winter months. Be aware also of any potential slippages on the cliff.
EQUIPMENT
A pick and small trowel is ideal for removing fossils from the matrix of the Kimmeridge Clay. You will need a geological hammer and chisels to extract bivalves and ammonites from fallen blocks of the Cementstone beds or Myophorella clavellata blocks on the foreshore. Leave sufficient matrix around the fossil, to enable finer preparation at home.
CLEANING AND TREATING
Begin by removing any loose sediment very carefully using a soft toothbrush. Take your time, as many fossils are fragile and easily damaged. Do not soak bones as this can make them fragile and crack, if bones are already wet, slowly dry out slightly using a wet cloth on top to keep moisture in and clean carefully using a small brush and needle.
Once fully dry, we recommend sealing fossils with Paraloid B-72, dissolved in acetone. This is a museum-grade consolidant that is widely available in pre-mixed bottles. Paraloid B-72 is stable, long-lasting, and does not yellow or react chemically over time. Importantly, it is also fully reversible, making it suitable for scientifically important or display-quality specimens.
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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