Peveril Point Fossil Hunting

1854 – Rev. P. B. Brodie made the first mammal discoveries from Durlston Bay
The first discoveries of fossil mammals from Durlston Bay were made around 1854 by the Reverend P. B. Brodie, who sent his finds to Richard Owen. These early discoveries helped establish the northern half of the bay as one of the classic British localities for Purbeck mammal remains.

1850s – Samuel Beckles opened the famous mammal excavations near the top of the cliffs
Shortly after Brodie’s finds, Samuel Beckles organised excavations in the northern part of Durlston Bay. These workings, later known as Beckles’ Mammal Pit, produced many mammal fossils and became one of the most famous vertebrate localities in the Purbeck Limestone Group.

19th century – the Peveril Point to mid-bay section became recognised as one of the finest Purbeck vertebrate localities in Britain
The northern half of Durlston Bay soon became famous not just for mammals, but also for its rich reptile and fish faunas. The beds in this part of the bay are especially important because they preserve a wide range of small vertebrates in the Middle and Upper Purbeck succession.

1915–1919 – A. Smith Woodward showed that the Middle Purbeck beds of Durlston Bay were exceptionally important for fossil fishes
Woodward’s work demonstrated that some of the best fish specimens from Durlston Bay came from the Intermarine Member and Upper Building Stones in the northern and central part of the bay. This helped establish the locality as one of the most important Late Jurassic to earliest Cretaceous fish sites in Britain.

1969 – Torrens renewed detailed attention on the Durlston Bay bed succession
Twentieth-century work revived close study of the numbered bed succession in Durlston Bay, helping tie older discoveries to a more precise stratigraphic framework. This was an important step towards the detailed DB bed numbering later used through the bay.

1979 – Clemens and colleagues placed the Durlston Bay mammal fauna into a modern scientific framework
Modern work on the Purbeck mammals showed that Durlston Bay contains a diverse early Cretaceous mammal fauna including triconodonts, docodonts, multituberculates, symmetrodonts and eupantotheres. This confirmed the importance of the northern half of the bay as one of Britain’s key early mammal sites.

1980s – the reptile fauna of northern Durlston Bay was recognised as exceptionally important
Later studies showed that the bay is arguably Britain’s most important fossil reptile site for this age, with abundant lizards, turtles, crocodilians, pterosaurs and dinosaurs. Much of the fame of the northern and central bay comes from the small size, diversity and fine preservation of these vertebrates.

1991 – Nunn published a detailed geological map of the northern part of Durlston Bay
Nunn’s mapping of the Peveril Point area and the northern part of Durlston Bay was one of the most important modern milestones for this stretch of coast. It clarified the detailed structure and bed relationships in the part of the bay most associated with the mammal pits and classic Purbeck vertebrate horizons.

1993 – Clements published the bed-by-bed reappraisal of Durlston Bay
Clements’ reappraisal of the Durlston Bay stratigraphy provided the standard modern DB bed framework. This was especially important for the northern half of the bay because it allowed historic mammal, fish and reptile discoveries to be tied more accurately to individual horizons.

Modern understanding – the Peveril Point to mid-bay stretch remains one of the key Purbeck vertebrate sections in Britain
Today the northern half of Durlston Bay is recognised as a classic section for Purbeck mammal, fish and reptile faunas, as well as for the detailed stratigraphy of the Purbeck Limestone Group. Its importance lies not only in the famous historic finds, but in the way those discoveries can be related to one of the best exposed and best studied Purbeck successions in the country.

PURBECK GROUP

Durlston Formation (Berriasian, Lower Cretaceous)

Section Character And Scope

This northern Durlston Bay page covers the coast from Peveril Point south to the middle of the bay and stops at the Cinder Bed ledge and its central faulted repetition. Beds below the Cinder Bed in the lower Purbeck succession are excluded here and belong with the separate middle-bay-to-Durlston-Head section.

Numbering And Stratigraphic Order

The coast is commonly walked southward from Peveril Point down-section, but the breakdown below is arranged in normal stratigraphic order from the basal Cinder Bed upward into the top of the Durlston Formation. The DN bed numbers are site-use interval labels only; formal Clements DB bed numbers are retained wherever they are securely established. In older terminology, the Stair Hole Member corresponds broadly to the upper part of the traditional “Middle Purbeck Beds” above the Cinder Bed, and the Peveril Point Member corresponds to the traditional “Upper Purbeck Beds”.

Stair Hole Member

Bed DN1 — Cinder Bed (formal DB111; c. 2.95 m)

The Cinder Bed forms the basal bed of the Durlston Formation and the lowest horizon included in this northern Durlston Bay section. It is a bluish-grey, massive oyster-rich shelly limestone and calcareous mudstone, packed with Praeexogyra distorta in a matrix of calcareous mudstone and muddy micrite. The bed is divisible into three internal units, DB111a–c, of which the lowest is the more limestone-rich and the upper two are relatively more clayey. Associated fossils include Serpula coacervata, the echinoid Hemicidaris purbeckensis and rarer “Protocardia” major. This is the clearest marine-incursion bed of the northern bay, recording a short-lived transgression into the Purbeck lagoonal system. In the field it forms the main ledge at the middle of the bay and is repeated again on the central faulted promontory.

Bed DN2 — Lower Intermarine Freshwater Return: Soft Cinder To Lias Rag (formal DB112–120 in part; lower part of the 15.5 m Intermarine Member)

Immediately above the Cinder Bed the succession becomes unexpectedly fresh to nearly fresh rather than remaining near-marine. The basal Ptychostylus Bed (DB112) carries abundant Ptychostylus; the Downs Vein (DB113), about 0.86 m thick, is a massive shell limestone crowded with small lamellibranchs and has yielded fish, turtle, pterosaur and crocodilian remains as well as small vertebrate trackways; the Laper and Underpicking (DB114) are argillaceous ostracod biomicrites with desiccation cracks and dinosaur footprints; and the Planorbis–Lias Rag part of the interval (DB115–116 and associated beds) contains Physa bristovii, Planorbis, charophytes, silicified conifer wood and other low-salinity fossils. These beds record a brief post-Cinder return to shallow freshwater or nearly freshwater shelly flats and lake-margin carbonate muds. They are important because they show that the marine Cinder incursion was followed rapidly by renewed lacustrine conditions.

Bed DN3 — Main Intermarine Building-Stone Shell-Beach Interval: Freestone, Sugar, Roach And Thornback (formal DB121–128 in part)

This middle part of the Intermarine Member contains the classic upper building-stone limestones of Durlston Bay, including the Freestone and Sugar beds (DB121–123) and the Roach–Thornback interval (DB125). These are massive shell-debris limestones, mostly early-cemented biosparrudites or coarse biosparites, deposited as low-salinity lagoonal shell-beaches or beachrock-like shoal-margin bodies. The Roach is particularly important because it is the most famous dinosaur footprint bed in the Purbeck building stones; many classic footprint slabs came from quarries on this same horizon, and the Durlston Bay equivalent records the same prolonged exposure of firm carbonate shell sand that favoured trampling and preservation. This interval represents broad shell flats and beach ridges on the margin of the Purbeck lagoon, repeatedly exposed and reworked by waves and storms.

Bed DN4 — Upper Intermarine Shaly And Ferruginous Building-Stone Interval: Shingle, Shed Bed, Under Rag, Red Rag, Royal And Laning Vein (formal DB129–145)

Higher in the Intermarine Member the succession becomes more variable and muddier, but still includes important shell limestones and marker beds. The Shed Bed and Lead Bed (DB129b) are relatively soft laminated grey beds, rich in carbonate sand and mud, with small channels, ripples and storm-cycle lamination; the top surface behaves as a minor hardground with scattered attached Praeexogyra. At the base of the Shed Bed, at the junction with the Shingle, a crocodile skull of Goniopholis simus was found. The Under Rag (DB131) is a rough sandy muddy shell limestone with abundant bivalves and gastropods, especially Viviparus, and carries a leaf bed on its top. The Red Rag (DB133), about 0.74–0.79 m thick, is a conspicuous coarse mottled ferruginous biosparrudite with cross-lamination, discontinuous shaly beds, pockets at its base, and concentrations of bones, coprolites and plant debris on its upper surface; it also preserves a famous elongate groove interpreted as a tool mark or possible carcass-drag structure. Higher up, the Royal Limestone (DB140) and the Laning Vein interval (DB141–144; c. 1.62 m) continue the shell-limestone and muddy-limestone alternation. Collectively these beds record storm-reworked lagoon-margin shell sands, carbonate tempestites, local hardgrounds and increasing terrigenous and kaolinitic input under a wetter climate than that of the lower Purbeck.

Bed DN5 — Scallop Beds (formal DB146–153; c. 1.4 m)

The Scallop Beds are a thin but important near-marine interval above the Intermarine building-stone succession. They consist mainly of hard sandy shell limestones with Chlamys and other more marine molluscs, showing a salinity rise almost comparable with that of the Cinder Bed below. Although the unit is not thick, it is stratigraphically important because it marks a second clear marine pulse into the lagoonal basin before the overlying muddier Corbula-dominated succession developed.

Bed DN6 — Corbula Beds (formal DB154–189; c. 11.4 m)

The Corbula Beds form a thick succession of limestones and shales best exposed on the shore south of Peveril Point. The classic Corbula Beach Bed is easily recognized, and the member as a whole contains abundant Corbula alata, together with Neomiodon, Praeexogyra and “pecten”-type bivalves. The fauna and lithology indicate fluctuating brackish to near-marine lagoonal conditions rather than normal marine shelf sedimentation. This interval is also a major fossil horizon: insects occur within it, including fossil wasps from DB175; fishes and turtles are well known; and dinosaur footprints have also been recorded. The Corbula Beds therefore form one of the most biostratigraphically and collector-significant parts of the northern bay section.

Bed DN7 — Chief Beef Beds (formal DB190–219; c. 8.3 m)

The top of the Stair Hole Member consists of the Chief Beef Beds, a dark, soft, organic-rich shaly interval with bands of shell limestone and numerous fibrous calcite “beef” veins. Neomiodon shells are common and aragonite was locally preserved long enough to contribute carbonate to the later fibrous calcite during burial. These beds are characteristically paper-shaly and weather soft in the cliff, but are one of the most distinctive lithologies in the bay because of the abundance of beef seams. A dinosaur footprint has been recorded from this interval around DB191. The Chief Beef Beds represent quiet brackish lagoonal mud accumulation under low-energy, organic-rich conditions, and they form the transitional upper mud-rich part of the Stair Hole Member immediately beneath the coarse Broken Shell Limestone.

Total Thickness Of Stair Hole Member At Durlston Bay: About 39.5 Metres In Clements’ Measured Type Section

Peveril Point Member

Bed DN8 — Broken Shell Limestone / Soft Burr (formal DB220; c. 2.9 m)

The Broken Shell Limestone forms the conspicuous Peveril Ledges and defines the base of the Peveril Point Member. It is a thick, coarse, shell-fragment bioclastic limestone or biosparrudite, rich in bivalve debris and forming one of the strongest ledges in the whole bay. Fish and turtle remains are characteristic, and fragmented reptile debris is common; dinosaur footprints have also been recorded from this bed. Sedimentologically it is a shallow, energetic shell-bank or shell-beach deposit laid down in a very low-salinity lagoonal to marginal coastal setting rather than in open marine water. At Peveril Point its top surface also shows small circular solution-collapse pits formed long after lithification.

Bed DN9 — Unio Beds Including The Crocodile Bed (formal DB221–223; c. 1.1 m average)

Above the Broken Shell Limestone lie the Unio Beds, a thin but very fossiliferous interval of soft green glauconitic shale, dark grey pyritic shale and irregular limestone bands rich in Unio porrectus and Viviparus. The most important subhorizon is DB221, a complex bed 0.38–0.53 m thick with rough limestones, clays and shales, abundant plant remains, fish teeth and scales, bones, coprolites and shell debris. Its top is the classic Crocodile Bed, a rough light-grey biosparite with strong brown staining, very abundant Viviparus, calcite-lined cavities and hydrocarbons. Turtles and crocodiles, including Goniopholis, have long been recorded from the Unio interval at Peveril Point. The whole package represents shallow freshwater to very low-salinity lacustrine marginal deposits, with vertebrate and plant debris washed into quiet lake-edge settings.

Bed DN10 — Upper Ostracod Shales, Purbeck Marbles And Upper Viviparus-Rich Clays (formal DB224–245; c. 12.9 m, partly obscured)

The highest beds exposed in the northern bay belong to the historical Upper Cypris Clays and Shales, now forming the upper part of the Peveril Point Member. They are mainly grey pyritic and locally sideritic shales crowded with freshwater to oligohaline ostracods, especially Cypridea, and they contain the three principal Purbeck Marble horizons of Peveril Point: the Green Marble (around DB234–237), the Lower Purbeck or Red Marble (DB241) and the Upper Purbeck or Blue Marble (DB244). These are Viviparus-rich gastropod biomicrudites or packstones, darkened by pyrite and commonly coloured green, blue or red by authigenic glauconite and iron oxides. The uppermost part of this interval passes into the historical Viviparus Clays. At Peveril Point these beds are folded and faulted into the Blue Marble Syncline and related minor crumples, so their true thickness is not obvious in the foreshore exposure. The environment was a low-energy freshwater to very slightly brackish lake, rich in pond snails and ostracods, representing the final freshwater-dominated phase of the Durlston succession before the last limestones disappear beneath the overlying Wealden muddy clastics north of the point.

Total Thickness Of Peveril Point Member At Durlston Bay: About 16.9 Metres In Clements’ Measured Section

Structural Style

The northern Durlston Bay section is composite and structurally disturbed rather than a single flawless dip section. At Peveril Point, the upper marbles and associated shales are folded into minor Lulworth-crumple style structures, including the Blue Marble Syncline, and some beds become locally steep or even vertical. In the middle of the bay, southward-downthrow normal faults repeat the Cinder Bed and part of the lower Stair Hole Member on the central promontory. This means that the coastal traverse shows the full Durlston Formation superbly, but not as a perfectly uninterrupted simple cliff log.

Depositional Environment

The northern half of Durlston Bay records repeated oscillation between marine, brackish and freshwater conditions on the Purbeck coastal plain. The Cinder Bed marks a short normal-marine incursion with oysters and echinoids. The lower Intermarine Member above it records renewed freshwater or nearly freshwater lake and shelly-flat conditions, followed by broad low-salinity shell-beaches and storm-reworked lagoonal carbonate sands in the main building-stone interval. The Scallop Beds record another salinity rise; the Corbula and Chief Beef beds show the development of muddier brackish lagoons with rich invertebrate and insect faunas and widespread organic accumulation; and the Broken Shell, Unio and Upper Ostracod–Purbeck Marble beds of the Peveril Point Member record the shift into shallow freshwater to oligohaline lakes with pond snails, freshwater bivalves, ostracods, fish, turtles and crocodiles, immediately below the onset of the overlying Wealden clastic regime.

Total Thickness Covered Here

The northern Durlston Bay subsection from the Cinder Bed upward through the full exposed Durlston Formation covers about 56–57 metres of Berriasian Purbeck strata: roughly 39.5 m for the Stair Hole Member and about 16.9 m for the Peveril Point Member. The topmost transition into the Wessex Formation lies north of the main bay foreshore and is not the focus of this section.

References

Clements, R.G. (1993). Type-section of the Purbeck Limestone Group, Durlston Bay, Swanage, Dorset. Proceedings of the Dorset Natural History and Archaeological Society, 114, 181–206.
Westhead, R.K. & Mather, A.E. (1996). An updated lithostratigraphy of the Purbeck Limestone Group in the Dorset area. Proceedings of the Geologists’ Association, 107, 117–128.
Arkell, W.J. (1947). The Geology of the Country around Weymouth, Swanage, Corfe and Lulworth. Memoir of the Geological Survey of Great Britain.
Barton, C.M., Woods, M.A., Bristow, C.R. & Newell, A.J. (2011). South Dorset and south-east Devon and its World Heritage Coast. British Geological Survey Special Memoir.
British Geological Survey Lexicon entries and A Stratigraphical Framework for the Lower Cretaceous of England, for the Durlston Formation, Stair Hole Member and Peveril Point Member.
Nunn, J.F. (1991). A geological map of Purbeck Beds in the northern part of Durlston Bay. Proceedings of the Dorset Natural History and Archaeological Society, 113, 145–148.
Dineley, D.L. & Metcalf, S.J. (1999). Fossil Fishes of Great Britain, Geological Conservation Review Series, Durlston Bay account.
Benton, M.J. & Spencer, P.S. (1995). Fossil Reptiles of Great Britain, Geological Conservation Review Series, Durlston Bay account.
Benton, M.J., Cook, E., Grigorescu, D., Popa, E. & Tallódi, E. (2005). Mesozoic and Tertiary Mammals and Birds of Great Britain, Geological Conservation Review Series, Durlston Bay account and table of designated stratal units.
Jarzembowski, E.A., Siveter, D.J., Palmer, D. & Selden, P.A. (2010). Fossil Arthropods of Great Britain, Geological Conservation Review Series, Durlston Bay account.
Marshall, J.D. (1982) on Purbeck beef; El-Shahat, A. & West, I.M. (1983) on petrography and geochemistry of the Durlston Purbeck limestones; West, I.M. and related Wessex Coast field guides on Peveril Point and middle Durlston Bay; Ensom, P.C. (1983, 1994) and West & El-Shahat (1985) on dinosaur footprints and Purbeck vertebrate-bearing horizons.