Kimmeridge Bay can be reached either directly by car via a toll road or alternatively by foot along the South West Coast Path, which passes through Kimmeridge from Worth Matravers and on to Worbarrow Bay. The bay forms part of the Jurassic Coast World Heritage Site.

Geology

The rocks at Kimmeridge Bay are composed of highly organic, black mudstones with a slate-like bedding structure, allowing it to be broken easily along these lamination planes. The rock, known as the , is of Kimmeridgian age (157.3 and 152.1 million years old) from the Jurassic Period. The names of the rock and time period are not a coincidence; the Kimmeridge Clay Formation is one of the most geologically significant formations in the UK. The rock acts as the source rock for much of the UK oil reserves under the North Sea. You can see, or perhaps more easily smell, the oil content in the Kimmeridge Clay Formation on fresh exposures of the rock.

Structure

The rocks across the Isle of Purbeck, to the east of Kimmeridge, are significantly folded and form part of the Purbeck Monocline. This enormous, east–west-trending structure runs under the English Channel but is exposed here where the near-vertical limb of the fold is exposed. It produces the unique structure of the Isle of Purbeck, with two hard rock ridges (the Purbeck Ridge and the coastal cliffs) separated by the soft Wealden clays and muds, which formed 145 and 126.3 million years ago during the Cretaceous Period. Today, these soft clays are responsible for the large number of small bays along the Purbeck coast.

Fossils

When the formation was deposited, Kimmeridge was part of a shallow sea environment where silts and muds settled down upon the sea floor alongside a host of expired organic life. The isolated, low-oxygen environment of this sea floor promoted the rapid preservation of fossils, which can now be found in great abundance at Kimmeridge today. If you would like to see a comprehensive collection of these fossils, the nearby Etches Collection Museum can be found in the village of Kimmeridge itself.

At Kimmeridge Bay, the rock is layered into thin horizons of strata called ‘laminations’. The fossils are preserved between them and the sequential layers of the shale rock allow for a detailed view of the geological time period when you study the fossils from different horizons. Do note that the site is a Site of Special Scientific Interest (SSSI), so hammering the rock wall in search of fossils is forbidden (and dangerous!)

There is great number of shelled creatures, such as ammonites and bivalves, at Kimmeridge because the preservation process preferentially preserves the hard, outer parts of the animals. The soft parts of the dead creatures often decay before being buried under the ocean sediments, which eventually form the encapsulating rock.

As groundwater filters through the rock during the fossilisation process, the corpse of the creature is steadily replaced with minerals present in the water, leaving a replaced stone cast of the original form. Kimmeridge Clay is special in that fossils are preserved in huge abundance, which also allows for larger, more intricate and rarer fossils to be observed: for example, the first instance of ammonite eggs was found at Kimmeridge Bay.

Modern flora and fauna

Kimmeridge contains several secluded rock pools and shallow rocky reefs that can be accessed with relative ease. Kimmeridge Bay is a particularly great place to investigate rockpools, as the bay is a wave-cut platform of rock as opposed to a singular sandy bar. Sea anemones, crabs and other shallow, benthonic life can be found in abundance here. More rarely, barrel jellyfish, seals and dolphins can also be seen in the bay, depending on the time of year and the presence of people. Fantastic underwater flora such as peacocks tail and coralline seaweed can also be found at Kimmeridge, as the area is a Marine Conservation Zone, which prevents trawling and other extractive activities.

Activities

Kimmeridge Bay has facilities for modest outdoor watersports including kayaking and paddleboarding, as a pontoon, nearby car park and toilets can be found at the south-eastern tip of the beach, alongside the Wild Seas Centre, which is a marine life conservation visitor outpost. The bay is a natural shield from the wind, which makes it relatively calm internally for watersports (weather depending!) compared to the open ocean. Adventurous kayakers may consider making the six-mile westward voyage to Worbarrow Beach and back, but do consider that the mobile phone signal is patchy, the area remote and the sea currents considerably stronger outside of the bay.

Warnings

Coastal paths can be treacherous, particularly in wet and windy conditions, so sturdy boots are advisable. The Kimmeridge Clay and other associated rock formations in south Dorset are prone to building high, somewhat unstable cliffs, which pose a significant risk of landslides and rockfalls. Always maintain a safe distance from the cliffs in order to prevent personal injury whilst walking! Tides can also pose a significant risk to certain parts of the shore if you walk outside of the main Kimmeridge Bay. Walking along the South West Coast Path on the cliffs is safer for hikers looking to explore further along the coast.

The western access along the South West Coast Path from Kimmeridge to Tyneham may be blocked by the Ministry of Defence as it passes through military firing ranges: check online for accessibility details. When passing through military ranges, it is imperative you stay within the marked public walkways, avoid touching military debris and observe red flags and red lights, as these are indicative of live firing.

Further information

• Firing range information:
• Etches Collection Museum:
• Wild Seas Centre:
• Ballard Down lies about 10 km east of Kimmeridge Bay, while Lulworth Cove is approximately 5 km to the west

Reference

Etches, S, Clarke, J, and Callomon J. 2009. . Lethaia, Vol. 42, 204–217. DOI: https://doi.org/10.1111/j.1502-3931.2008.00133.x

About the author

Cameron Fletcher is a core scanning technician at BGS.

The Giant’s Causeway and Causeway Coast form Northern Ireland’s only UNESCO World Heritage Site (WHS), one of only two such sites in the UK inscribed because of their geological heritage.

The Giant’s Causeway is made up of over 40 000 columns of basalt and, together with the wider Causeway Coast, tells the story of the sequence of events at the start of the Palaeogene period, some 60 million years ago.

During that time, the ancient continent of Laurasia began to fragment, causing the opening of the North Atlantic Ocean. The resulting cataclysmic volcanic activity along this zone of crustal weakness formed the rocks of the WHS, as well as those on adjacent parts of western Scotland. Lava poured out onto the existing landscape, extending from the volcanoes and fissures that littered the area and covering the entire land surface.

The first lavas to erupt came from at least six eruptions, followed by a long quiescent period during which all volcanic activity ceased. This hiatus led to heavy weathering of the topmost layer of lava, leading to a series of chemical changes producing the thick iron- and aluminium-rich, red layer known as the Interbasaltic Formation. During this long dormant period, the surface of the lava developed into a richly forested landscape of low hills and deep, wide valleys.

Volcanic activity resumed suddenly and dramatically, with lava initially draining into the valleys: at the Causeway, it accumulated as a large lava lake some 90 m deep. This body of lava cooled slowly and evenly, developing regular stress patterns as it solidified, which caused contraction cracks that permeated the entire mass and created thousands of columns.

Following this, there was another long period of dormancy that was succeeded by the final, gigantic series of eruptions (Upper Basalt Formation), with the pipes and fissures supplying these last flows passing through the earlier rocks on their way to the surface.

Whilst most people come to the Giant Causeway to see the impressive columnar basalts, in order to the gain a full appreciation of why the site has been inscribed on the World Heritage List, the full name of ‘The Giant Causeway and Causeway Coast World Heritage Site’ is ultimately more useful. Of course, some say it was built by a giant called Fionn mac Cumhaill, or Finn McCool, but violent volcanic eruptions are much more exciting!

The Giant’s Causeway has attracted visitors for over 300 years, all of whom come to see the enigmatic basalt columns and the surrounding landscape. It is now one of the most popular tourist attractions in Northern Ireland and, prior to the COVID-19 pandemic, attracted over one million visitors from all around the world to see this special place every year.

About the author

Swanage is a coastal resort in the south-east of Dorset, situated at the eastern end of the Isle of Purbeck. The small town primary industry is tourism but it is also a small port and fishing village with many Victorian elements. The town is located at the eastern end of the , a stretch of coastline designated as a World Heritage Site. Swanage Bay faces east and is protected from the south-westerly storms. To the north of the bay is a prominent headland, which is a major Cretaceous exposure called .

Ballard Down can be reached via several footpaths from Swanage. The chalk grassland that covers the headland is at its prime in the summer when calcareous-loving wildflowers are most abundant. The wildflowers include ragwort, hogweed, purple orchids, bird’s-foot trefoil, common vetch, scabious, marjoram, harebell — to name a few!

Ballard Down is owned by the National Trust, which allows grazing on the down to prevent it converting to natural beech woodland. An obelisk on down commemorates the building of a new water supply for the town in 1883. 

Walking along Ballard Down, the most easterly point is called . ‘Old Harry’ is a sea stack comprised of pure white chalk. Old Harry was formerly linked to the Needles Chalk Hills on the Isle of Wight. Old Harry was formed from a headland that formerly jutted out into the water. Over hundreds of thousands of years, the sea eroded the headland and left the sea stack.  

The chalk of Ballard Down and Old Harry Rock is formed from the shells of tiny marine algae known as coccoliths. Chalk is a type of soft limestone, usually white or pale grey and very friable. Swanage town itself sits on soft clays of the , while to the south are hard limestones of the . The Purbeck limestone was extensively quarried in the past and examples can be seen in the town buildings. 

Back in Swanage, the beach is pebbly in parts, with pebbles mainly composed of hard , which occurs in the chalk. Flint is a type of quartz formed from silica sponges through a geological process of melting and condensing. 

Further information

The walk from Swanage over Ballad Down to Old Harry Rocks is strenuous in parts and the weather can be unpredictable on the down. From the down, the views across Dorset coast and countryside are breathtaking. The chalk cliffs at Old Harry Rocks are vertical and potentially dangerous. Stay on the well-worn path and keep a good distance from the cliff edge. 

• Visit Swanage provides tourist information as part of 
• Approximately 10 km to the west of Ballard Down is Kimmeridge Bay and Lulworth Cove lies a further 5 km west

About the author