Bouldnor Cliff Fossil Hunting

1856 – Edward Forbes described the Bembridge Oyster Bed and the fossil-rich Bouldnor–Hamstead succession
Edward Forbes was one of the earliest workers to document the fossil-bearing beds at Bouldnor and Hamstead. His work helped establish the importance of the succession, including the oyster-rich horizons and the fossiliferous marls and clays that later became famous for mammals, reptiles and plants.

1925 – Cooper’s classic work on anthracotheres confirmed Bouldnor as a major site for large Oligocene mammals
By the early twentieth century, Bouldnor Cliff had already become known as a classic British site for larger Paleogene mammals, especially anthracotheres. Cooper’s 1925 work is one of the key landmarks in that history and helped establish the site’s reputation for important mammal remains.

1927 – Dyspterna woodi named from Bouldnor Cliff
Bouldnor Cliff provided the type specimen of Dyspterna woodi, named by Hopwood in 1927. This makes the site the type locality for one of its characteristic fossil mammals and adds to its importance in British Palaeogene mammal studies.

1963–1978 – Chandler described the important Hamstead Member plant flora from Bouldnor material collected by G.W. Colenutt and R.L.E. Ford
The fossil flora of Bouldnor Cliff was described in a series of works by Marjorie Chandler, based largely on material collected by G.W. Colenutt and R.L.E. Ford. These studies helped show that Bouldnor preserves the youngest known Palaeogene plant macrofossils in southern Britain, including important conifers, aquatic plants and pyritised plant remains.

1972 – Butselia biveri recorded from the site
The presence of the insectivore Butselia biveri at Bouldnor/Hamstead was noted by Butler in 1972. This was one of the important smaller mammal records from the site and later became significant in discussion of faunal change across the Eocene–Oligocene transition.

1974 – Bosma described the rodent fauna from the Hamstead Member
Bosma’s work on the rodent fauna showed how important Bouldnor and Hamstead are for small mammal assemblages as well as large mammals. These faunas became central to later biostratigraphic work on the late Eocene to early Oligocene of the Isle of Wight.

1979 – Glamys fordi named from a Bouldnor Cliff type specimen
Bouldnor Cliff also provided the type specimen of Glamys fordi, described by Bosma and de Bruijn in 1979. This is one of the locality’s key named mammal species and confirms the site’s importance for Oligocene rodent evolution and biostratigraphy.

1979 – fossil birds from the vicinity of Bouldnor Cliff were described by Harrison and Walker
Bird fossils from the Bouldnor area were described by Harrison and Walker in 1979, adding avian remains to the already important record of mammals, reptiles and plants. This helped underline how diverse the Bouldnor/Hamstead fauna really is.

1980 – Hooker and Ward summarised the reptile fauna, and Moody detailed the turtles
By 1980 the reptile fauna of Bouldnor and Hamstead had been recognised as the best British Oligocene reptile assemblage, including turtles, snakes and crocodilians. Hooker and Ward summarised the fauna, while Moody provided further detail on the turtles, helping establish the site as internationally important for Oligocene reptiles.

1980s–1990s – plant macrofossil work showed Bouldnor to be the youngest Palaeogene flora in Britain
Further work by Collinson and others on the plant-bearing horizons demonstrated that Bouldnor Cliff preserves the youngest known Palaeogene plant macroflora in Britain. The site is also the type locality for Sequoia couttsiae and is especially important for aquatic plants, conifers, seeds, leaves and pyritised logs from the Hamstead Member.

2004 – Hooker and colleagues showed the Bouldnor succession documents the ‘Grande Coupure’ within the Hamstead Member
Intensive collecting and screenwashing demonstrated that the famous mammalian turnover known as the ‘Grande Coupure’ occurs within the Hamstead Member rather than at its base. This made Bouldnor Cliff uniquely important in Europe for showing a superposed succession of mammal faunas across that major faunal change.

SOLENT GROUP

Bembridge Limestone Formation (Upper Eocene To Earliest Oligocene)

Hamstead Ledge Freshwater Limestones

Bed BC1 — Freshwater Limestones Of Hamstead Ledge

Three freshwater limestone beds are developed at the eastern end of the Bouldnor–Hamstead coastal section, where the Bembridge Limestone crops out at Hamstead Ledge. These limestones are hard, pale, pond-limestone facies deposited in shallow freshwater to slightly brackish lakes and marshes. They commonly contain freshwater gastropods and associated lime-mudstone partings, and they form the resistant ledge that makes Hamstead Ledge such a prominent foreshore feature beneath the younger Bouldnor beds.

Bouldnor Formation (Upper Eocene To Lower Oligocene)

Bembridge Marls Member

Bed BC2 — HAM I–IV / Bembridge Oyster Bed (c. 0.9 m)

Grey and black clays with shelly partings and a thin oyster shell bed at the base. This is the classic Bembridge Oyster Bed, resting on the Bembridge Limestone and marking the main transgressive phase at the base of the Bembridge Marls Member. The bed contains abundant shell debris and a restricted brackish-water fauna, and is interpreted as an estuarine or strongly lagoonal deposit with appreciable water movement.

Bed BC3 — HAM V (c. 0.3 m)

Greenish-grey clay with fossil bands containing Melanoides acuta, Serpula sp. and Viviparus lentus. This thin but distinctive bed records fluctuating salinity and a mixed brackish to freshwater fauna, with quieter lagoonal conditions than the oyster bed below.

Bed BC4 — HAM VI–X (c. 2.7 m)

Grey and blue-green laminated clays with brackish-water bivalves and gastropods. Fine lamination and locally varve-like bedding indicate low-energy deposition in a quiet lagoon or estuarine backwater. This is one of the best examples at Bouldnor Cliff of the laminated clay facies that dominate much of the lower Bouldnor Formation.

Bed BC5 — HAM XI–XIV (c. 3.3 m)

Mudstones and siltstones with a bivalve band. These beds continue the generally low-energy lagoonal succession but show slightly more silt input than the lower laminated clays. Molluscs are more conspicuous at particular levels, and the unit represents fluctuating salinity in shallow standing water.

Bed BC6 — HAM XV–XIX (c. 2.6 m combined)

This interval includes black clay with gastropods, green mudstone with a lignite band, and green clays and white marls with bivalves. It marks a transition from darker organic-rich lagoon-floor muds upward into somewhat fresher-water marls and clays. These beds show repeated alternation between organic accumulation, quiet standing-water sedimentation and more oxygenated shallow-water deposition.

Bed BC7 — HAM XX–XXII (c. 1.6 m)

Freshwater clays and silts, indicating that salinity had dropped markedly relative to the lower Bembridge Marls. These beds represent quieter lacustrine or upper-lagoon conditions and contain a less marine and more freshwater molluscan assemblage.

Bed BC8 — HAM XXIII–XXV (c. 2.0 m)

Lignite and clay rich in water-plant seeds, leaf fragments and gastropods. This is one of the most distinctive plant-bearing intervals in the Bouldnor Cliff succession. Seeds of aquatic plants such as Brasenia and Stratiotes occur with Viviparus and other freshwater molluscs, indicating very shallow, plant-rich water on a lagoon margin or floodplain lake.

Bed BC9 — HAM XXVI–XXIX (c. 5.0 m)

Clays with seeds and molluscs, continuing the upper freshwater trend of the Bembridge Marls Member. These beds are less lignitic than the plant-rich interval below, but still yield abundant seeds, freshwater molluscs and comminuted plant matter. They represent quiet lacustrine to floodplain-waterbody deposition.

Bed BC10 — HAM XXX (c. 0.6 m)

A thin lignite with seeds and molluscs. This bed forms a compact organic-rich marker in the upper Bembridge Marls and records a short interval of peat or highly plant-rich mud accumulation in standing freshwater.

Bed BC11 — HAM XXXI–XXXIV (c. 10.2 m)

Green, red and mottled clays forming the highest Bembridge Marls beds at Bouldnor. These beds reflect increasingly terrestrial, floodplain and upper-lagoon conditions with fluctuating water tables and periodic oxidation. Vertebrate remains become more important near the top of the member, and large mammal remains from this level include Anoplotherium, Palaeotherium medium suevicum and Plagiolophus major, characteristic of the MP20 fauna below the main faunal turnover.

Total Thickness Of Bembridge Marls Member At Bouldnor Cliff: Approximately 21.5–34 Metres

Hamstead Member

Bed BC12 — Black Band (c. 0.5 m)

A carbonaceous mud or lignitic horizon full of freshwater gastropods such as Viviparus and the bivalve Unio. Autochthonous root systems penetrate the bed below at its base. This distinctive horizon marks the base of the Hamstead Member and records a widespread pause and organic accumulation on a low-energy lagoon or floodplain surface.

Bed BC13 — Lower Hamstead Green And Black Clays (c. 8.1 m)

Green and black clays with bivalves and gastropods forming the lower Hamstead Member beneath the Nematura Bed. These beds represent quiet lagoonal to low-salinity estuarine deposition and yield the lower Hamstead mammal fauna, including Anoplotherium commune, Xiphodon gracilis, Palaeotherium, Plagiolophus and the theridomyid rodent Theridomys bonduelli. They are important because they still preserve the pre-Grande Coupure endemic European mammal assemblage.

Bed BC14 — Log Bed (Within The Lower Hamstead Member)

A blue-grey clay and sand bed with pronounced ball-and-pillow, convolute and contorted bedding, preserving large tree trunks up to several metres long. Seeds of Potamogeton, monocot and dicot leaves and other plant remains also occur. This is a distinctive unstable horizon recording water-saturated sediment deformation and deposition of large woody debris on a low-energy floodplain or delta-margin surface.

Bed BC15 — Nematura Bed (c. 0.9 m)

Black lignitic clay full of gastropods, especially the mollusc for which the bed is named. Dinoflagellates, ostracods, rootlets and reworked wood fragments indicate brackish-water conditions. This bed is the classic divider between the lower and upper Hamstead Member successions and is a key marker in the Bouldnor Cliff section.

Bed BC16 — Lower Upper-Hamstead Green Clays And Ironstone Nodule Band (c. 10.8 m)

Green clay with an ironstone nodule band and associated silts and clays above the Nematura Bed. The basal few metres of the upper Hamstead include alternating greenish to greyish clays and silts with decalcified Polymesoda shells. These beds mark the beginning of the post-Grande Coupure part of the section, with a distinctly changed mammal fauna and continued fluctuating salinity.

Bed BC17 — Eomys Bed

A fossil horizon within the upper Hamstead Member, roughly 10 metres above its base, named for the eomyid rodent Eomys. This bed is an important mammal marker and helps identify the early Oligocene upper Hamstead fauna that includes new immigrant rodent lineages and other post-Grande Coupure mammals.

Bed BC18 — White Band (c. 1.8 m)

Green clays with pale white shell marls, a conspicuous light-coloured horizon within the upper Hamstead Member. Decalcified Polymesoda and other shell material occur here, and the bed marks one of the clearest internal lithological changes in the upper part of the cliff.

Bed BC19 — Crocodile Bed

A fossiliferous interval above the White Band containing abundant crocodilian remains, especially Diplocynodon hantoniensis. This is one of the best reptile horizons in the Bouldnor Cliff section and demonstrates the richness of the upper Hamstead Member for vertebrates beyond mammals alone.

Bed BC20 — Water-Lily Bed (c. 0.6 m)

Laminated lignite with seeds, palm leaves, water-lily leaves and molluscs. This is one of the most distinctive plant-rich beds in the upper Hamstead Member and records a low-energy waterbody with abundant floating and emergent vegetation. It is particularly important for palaeobotanical work on the subtropical Oligocene flora of the Isle of Wight.

Bed BC21 — Upper Green And Mottled Clays With Lignite Beds And Shell Beds (up to c. 25 m)

The highest part of the Hamstead Member consists of green and mottled clays with lignite beds, shell beds and locally red or brown laminated clays. These beds yield the upper Hamstead mammal fauna, including anthracotheres such as Bothriodon, Elomeryx and Anthracotherium, the beaver Asteneofiber, the hamster Atavocricetodon, the rodent Eomys, the hedgehog Tetracus, the last adapid primate Leptadapis and the first British true rhinoceros Ronzotherium. These beds record the post-Grande Coupure mammal turnover and are of exceptional European importance.

Total Thickness Of Hamstead Member At Bouldnor Cliff: Approximately 20–70 Metres, With Around 25–35 Metres Commonly Recognised In The Main Exposed Coastal Section

Cranmore Member

Bed BC22 — Cerithium Beds (c. 3.4 m)

The lower part of the Cranmore Member, comprising fossiliferous grey, blue and black clays of mainly non-marine to brackish aspect. These beds preserve the remains of the mollusc traditionally referred to as Cerithium and indicate renewed marginal, shallow-water conditions after the more varied lagoonal-floodplain deposition of the Hamstead Member below.

Bed BC23 — Corbula Beds (c. 5.8 m)

The upper and more marine part of the Cranmore Member, consisting of fossiliferous clays with Corbula and other brackish to marine molluscs. These beds show that salinity increased upward again near the end of Bouldnor Formation deposition. Shark remains have been reported from the Cerithium and Corbula beds, although mammal remains are not known from this uppermost member.

Total Thickness Of Cranmore Member At Bouldnor Cliff: Approximately 5–9 Metres, Commonly About 9.2 Metres In The Coastal Section

Depositional Environment

The Bouldnor Cliff succession records a complex low-energy lagoonal, lacustrine, estuarine and marginal-marine system. The Bembridge Limestone formed in shallow freshwater lakes and marshes; the Bembridge Marls record estuarine to lagoonal conditions passing upward into more freshwater lake and floodplain settings; the Hamstead Member records alternating brackish, freshwater and floodplain conditions with major organic beds, log-bearing horizons and the famous faunal turnover across the Grande Coupure; and the Cranmore Member marks a return to more brackish and marine conditions at the top of the succession. The whole section is heavily slipped, so fresh exposures are intermittent but often very productive.

Total Thickness Covered Here: Approximately 90–100 Metres Of Late Eocene To Early Oligocene Stratigraphy Across The Main Bouldnor Cliff–Hamstead Cliff Coastal Section

References

Insole, A. & Daley, B. (1985). Revision of the late Eocene and early Oligocene lithostratigraphy of the Hampshire Basin.
Daley, B. (1972, 1973) on the Bembridge Marls and Bouldnor succession of the Isle of Wight.
Hooker, J.J. and co-authors on the Bouldnor Cliff mammal faunas and the Grande Coupure.
British Geological Survey Lexicon: Bembridge Marls Member, Hamstead Member, Bembridge Limestone Formation.
Geological Conservation Review accounts for Bouldnor Cliff and Bouldnor–Hamstead Cliffs.