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 BGS has an important, impartial role to play in terms of better understanding the environmental risks and impacts that might arise from shale gas industry operations. 

Shale gas is extracted from the impermeable shale rock through a process called hydraulic fracturing (also known as hydrofracking or fracking).

What are the risks associated with extracting shale gas?

Groundwater contamination

On average, around 20 million litres of water are needed during the life cycle of a well. The waste water (‘flow back’) needs to be treated properly and kept isolated from the surrounding aquifers. Other potential pathways for contamination of groundwater include poor well design or construction and the migration of contaminants along natural pathways into overlying aquifers.

Climate

Concerns include the emissions of carbon dioxide (CO₂), methane (CH₄) and other greenhouse gasses when the shale gas play is exploited. This also includes ‘fugitive’ emissions, which are composed of CH₄ that flows to the surface after fracking and can affect the atmosphere.

Air quality

There can be a negative effect on local air quality and noise pollution caused by the many truck movements during the life cycle of a shale gas well.

Induced tremors

Induced, low-magnitude tremors, such as those experienced in Lancashire in 2011, can be a consequence of the process of hydraulic fracturing.

How does BGS research help?

The BGS is the coordinator for the pan-European Horizon2020 (SECURe) project, which gathers scientific evidence relating to monitoring the environment and mitigating risk in order to guide subsurface geoenergy development.

We are also a major contributor of the NERC-funded Unconventional Hydrocarbons in the UK Energy System project. This aims to improve the understanding of unconventional hydrocarbon development in the UK, taking a holistic, interdisciplinary approach to identifying the potential environmental, social and economic impacts.

Our research is currently focused in the following main areas.

Environmental impacts and monitoring

Basin analysis

Further reading

Shale gas deposits are regarded as commercially exploitable when the organic matter contained within the shale is of the right type — of marine origin — the net shale thickness exceeds 25 m and when it is found at a depth of more than 1500 m.

Where is shale gas found in the UK?

In the UK, four areas have been identified as potentially viable for the commercial extraction of shale gas:

• the Carboniferous Bowland–Hodder area in north-west England (Lancashire and the Midlands)
• the Carboniferous Midland Valley in Scotland
• the Jurassic Weald Basin in south England
• the Wessex area in south England

Between 2013 and 2016, the BGS was commissioned by the Department of Energy and Climate Change (DECC; now the Department for Business, Energy and Industrial Strategy (BEIS)) to provide for these areas.

How much shale gas do we have in the UK?

Because there is no established shale gas industry in the UK, there is no production data available, which makes estimating the size of the resource extremely difficult. Therefore, in the DECC-commissioned reports, we took a bottom-up estimation approach whereby we used available rock materials from drill cores stored in the National Geological Repository.

Many of the drill cores used for the estimates we developed were not drilled for the purpose of a shale gas resource estimate, resulting in a wide total range of volume estimates.

Shale gas exploration in the UK

The main rock formation of interest for shale gas exploration in the UK is called the , which occurs across a large area of central Britain. These shales were deposited in marine basins during the Visean and Namurian stages of the Carboniferous period (between 347 and 318 million years ago) when the UK was located around the equator. Carboniferous marine shales can reach thicknesses of up to 5000 m and contain enough organic matter (1–3 per cent, but locally over 10 per cent) to generate hydrocarbons.

The Bowland Shale Formation is not restricted to the onshore environment; the basins extend offshore beneath the Southern North Sea and the East Irish Sea.

Andrews (2013) estimated a total gas-in-place estimate for the Bowland Shale Formation and Hodder Mudstone Formation between 822 and 2281 trillion cubic feet (tcf). As a comparison, the total gas consumption in 2018 in the UK was 2.98 tcf. Since then, other estimates have suggested the total gas-in-place volume could be considerably less (around 140 tcf; Whitelaw et al., 2019).

Scotland

Middle Carboniferous, organic-rich shales are also found in the subsurface Midland Valley of Scotland (Girvan to Greenock in the west; Dunbar to Stonehaven in the east) as part of the and the . There, the shales reach a thickness of about 3000 m, contain 2–6 percent organic carbon and are considered as a potential target for shale gas exploration. Monaghan (2014) suggested a total of 49.4–134.6 tcf gas-in-place for the Midland Valley of Scotland.

Wales

In Wales, a paucity of publicly available data currently prevents the calculation of reliable resource estimates. Potential unconventional gas resources in Wales are most likely to be found in association with coal seams or shales. In North Wales, middle Carboniferous shales include the Bowland Shale Formation, thought to be contiguous with strata in north England. Early Carboniferous shales are found in South Wales as part of the Avon Group. However, more research is needed to establish this group’s prospectivity for shale gas.

Much of Wales and central England are underlain by older Palaeozoic rocks, which may be prospective for shale gas. These successions have not been investigated extensively and no evaluation has been conducted by either the BGS or exploration companies.

References

How is shale gas extracted?

Hydraulic fracturing

Shale gas or unconventional gas is extracted from the impermeable shale through a process called hydraulic fracturing (also known as hydrofracking or fracking). A crude form of this technique, involving nitroglycerine, was used for the first time around the 1860s to explore for oil and gas.

During hydraulic fracturing, a mixture of water, chemicals and sand is pumped down a borehole at high pressure. The water pressure opens up cracks in the rock and the sand grains lodge into the spaces to keep them open, allowing the released gas to flow out of the rocks and travel back up the borehole.

The hydraulic fracturing technique is not new; it has been used for over 50 years to improve recovery of conventional oil and gas. 

The moratorium on hydraulic fracturing in the UK (2019)

Shale gas extraction is not presently allowed to proceed in the UK.

In November 2019, the UK Government announced a moratorium on hydraulic fracturing in shale in England. This decision was taken on the basis of a by the Oil & Gas Authority.

In January 2015, the Scottish Government put a moratorium on unconventional oil and gas development in Scotland in place, following the publication of a of an independent, expert, scientific panel.

Since 1 October 2018, licensing powers in Wales have been , which has taken the decision not to support applications for hydraulic fracturing in Wales or fracking consents.

Shale is a fine-grained, sedimentary rock formed as a result of the compaction of clay, silt, mud and organic matter over time and is usually considered equivalent to mudstone. Shales were deposited in ancient seas, river deltas, lakes and lagoons and are one of the most abundant sedimentary rock types, found at both the Earth’s surface and deep underground.

Shale gas is natural gas found in shale deposits, where it is trapped in microscopic or submicroscopic pores. This natural gas is a mixture of naturally occurring hydrocarbon gases produced from the decomposition of organic matter (plant and animal remains). Typically, shale gas consists of 70 to 90 per cent methane (CH₄), the main hydrocarbon target for exploration companies. This is the gas used for generating electricity and for domestic heating and cooking.

How is shale gas different from conventional gas?

Hydrocarbons, such as oil and gas, are produced by the transformation of organic matter (plants; animals; algae, etc.) as a result of increased temperature and pressure. This occurs when a potential source rock, rich in organic matter, is buried and heated at considerable depth (usually thousands of metres below the surface).

The hydrocarbons migrate upwards where they may find their way into porous reservoir rocks, typically a sandstone or a porous limestone. If the reservoir rock is overlain by an impermeable cap or seal rock, such as one rich in clay, the hydrocarbons become trapped in the reservoir rock. Conventional hydrocarbons can be extracted by drilling directly into the reservoir rock.

Shale gas is a form of unconventional hydrocarbons because the rock it is extracted from acts as the source, reservoir and cap rock. The gas is produced, stored and sealed within impermeable shale and can be released only after the shale is drilled and artificially fractured during an extraction process.  

Our role and research

The BGS’s role is to provide independent, expert and impartial geological and environmental advice to industry, government and the public, regarding shale gas in the UK.

We research all aspects relevant to shale gas in the UK and internationally. Our research spans from resource estimation to the environmental impacts associated with shale gas extraction, such as investigating groundwater contamination and microseismicity.

Whilst shale gas extraction is not presently permitted in the UK, we continue to conduct research related to shale gas. We actively publish reports and academic papers on a variety of topics related to shale gas.

Total organic carbon (TOC) is a measure of the dry weight per cent of organic carbon within hydrocarbon source rocks. Hydrocarbons, including natural gas (principally methane, ethane and propane), may be generated by the heating of organic carbon through burial over geological time.

A shale with low concentrations of organic carbon (typically below about two per cent) probably won’t have the capacity to produce oil or gas in useful quantities. It should also be noted that a high TOC value is not necessarily an indicator of shale gas potential. The gas prospectivity of a rock is heavily influenced by the kerogen types within the organic matter, including that derived from plankton, algae, spores, pollen or plant fragments. These can affect gas production, rock porosity and the rates at which gas may be released.