Redcliff Point Fossil Hunting

1923–1925 – Upper Oxford Clay subdivision recognised
S.S. Buckman separated the Weymouth-area Upper Oxford Clay into three main parts. At Redcliff Point this framework helped place the fossiliferous Furzedown, Jordan Cliff and Bowleaze clays, including beds with pyritised Cardioceras scarburgense, Quenstedtoceras ammonites and common Gryphaea dilatata.

1933 – Callovian–Oxfordian boundary noted
W.J. Arkell drew early attention to the Callovian–Oxfordian boundary at Ham Cliff, on the east side of Redcliff Point. This was an important step towards recognising the locality as more than a normal fossil cliff, because the boundary later became the focus of international Oxfordian Stage work.

1937 – systematic microfossil sampling
C.D. Ovey collected 25 samples at two-foot intervals from the Upper Oxford Clay at Redcliff. The samples provided a rare bed-by-bed microfossil collection from the Dorset Oxford Clay and became the basis for the locality’s later foraminiferal study.

1947 – Ham Cliff section fixed beside Redcliff Point
Arkell referred to the boundary exposure about 200 m east of Redcliff Point as Ham Cliff. That name and position gave later workers a precise reference section for the clay succession and the Callovian–Oxfordian transition.

by 1948 – Redcliff ammonites established in the Corallian record
Redcliff Point material from the Nothe Grit and Preston Grit had been worked into the classic record of English Corallian ammonites. Important Redcliff fossils include the holotype of Cardioceras persecans from the Nothe Grit, the holotype of Cardioceras cautisrufae from the Preston Grit, and recorded ammonites such as Cardioceras zenaidae, Aspidoceras paucituberculatum and Aspidoceras catena.

1953 – Redcliff foraminifera described
Tom Barnard described foraminifera from the Upper Oxford Clay of Redcliff Point, recognising 23 species, including four new forms. The work made the locality important for micropalaeontology and showed that the clays could be used for detailed fossil correlation as well as for larger ammonites and bivalves.

1956 – holothurian sclerites added to the fossil record
Holothurian sclerites from the Oxford Clay at Redcliff were described, including new taxa such as Rhabdolites dorsetensis. These tiny fossils are exceptionally abundant in the clay and add another useful microfossil group to the Redcliff boundary section.

1985 – Redcliff became a key Jordan Cliff Clay exposure
Sea defences at Furzy Cliff made much of the Jordan Cliff Clay type locality inaccessible. The northern side of Redcliff Point therefore became especially useful for seeing the unit, where well-preserved Gryphaea dilatata, Modiolus bipartitus and other bivalves are common.

1986 – Redcliff Formation and Corallian beds revised
J.K. Wright’s revision clarified the Redcliff Formation around Redcliff Point and Ham Cliff. It recorded the sharp erosive base of the Nothe Grit above the Oxford Clay, the lower Nothe Clay at Redcliff with bivalve-rich sandy limestones, ammonite-bearing Nothe Grit concretions, and Preston Grit blocks with trace fossils and frequent ammonites.

1995–1999 – expanded stage-boundary section clarified
Fresh exposure during the 1990s allowed the Ham Cliff section at Redcliff Point to be logged and interpreted in detail. The work showed an expanded ammonite-bearing succession across the Callovian–Oxfordian boundary, with the transition from Quenstedtoceras to early Cardioceras faunas visible in a way rarely seen elsewhere in Britain.

2001–2002 – conservation and reference-site status recognised
Redcliff Point lies within the South Dorset Coast SSSI, became part of the Dorset and East Devon World Heritage coast in 2001, and the Ham Cliff boundary section was recorded as a Geological Conservation Review site in 2002. This placed the locality in a protected setting and raised its profile as a reference section for Oxford Clay fossils, Corallian rocks and Jurassic stage-boundary research.

2003–2006 – candidate Oxfordian GSSP sampled
An international team began a detailed assessment of the Redcliff/Ham Cliff section as a candidate global reference point for the base of the Oxfordian Stage. More than 30 ammonite faunas were recorded through the boundary interval, alongside sampling for foraminifera, nannofossils, ostracods, holothurian sclerites, belemnite isotope work and magnetic data; the section was re-checked in 2006.

2008 – mollusc isotope work tested the boundary record
Carbon and oxygen isotope work on Redcliff Point macrofossils tested whether the fossils retained useful environmental signals. Belemnites including Hibolithes hastata, Gryphaea and Cardioceras ammonites were shown to be well enough preserved to help interpret water conditions and support a relatively continuous boundary record.

2009–2010 – Cardioceras redcliffense used to mark the Oxfordian base
Integrated work on the Redcliff Point candidate section placed the base of the Oxfordian at the first occurrence of Cardioceras redcliffense in the Ham Cliff beds. The case was supported by ammonites, belemnites, foraminifera, calcareous nannofossils, ostracods, holothurian sclerites, isotope results and magnetostratigraphy, making Redcliff one of Europe’s most complete Callovian–Oxfordian boundary sections.

2014–2015 – Oxfordian boundary task group reviewed the site
A specialist Oxfordian boundary meeting at Weymouth reviewed the Ham Cliff section, carried out new geochemical, nannofossil, microfossil and ammonite sampling, and continued collecting through the summer. Around 3,000 ammonite specimens were added for study, strengthening Redcliff Point’s role in testing a practical ammonite biohorizon framework for the stage boundary.

by 2024 – Redcliff Point remained a leading Oxfordian candidate
International stratigraphic work had narrowed the search for a formal Oxfordian boundary reference section to two main candidate sites, one of them Redcliff Point. The locality therefore remains important not only for collectors of ammonites, bivalves, trace fossils and microfossils, but also for deciding how the base of the Oxfordian Stage should be defined worldwide.

Section Architecture

Redcliff Point is not a single simple cliff log. The point itself is formed mainly by Oxford Clay of the Weymouth Member, but only a short distance away the Corallian is downfaulted and then exposed west of the point in low cliffs, undercliff slips and foreshore ledges. In addition, the classic Callovian–Oxfordian boundary sequence lies in a near-horizontal Oxford Clay block at Ham Cliff about 200 m east of the point, and the lower Osmington Oolite is best known from a rotated slipped block at Red Cliff rather than from an intact upright face. The whole locality therefore has to be treated honestly as a composite of faulted, repeated and landslipped exposures.

Oxfordian Boundary Status

The Ham Cliff boundary section near Redcliff Point remains one of the current candidate localities for the base of the Oxfordian, and the working definition is tied to the base of the Cardioceras redcliffense Horizon. That means Redcliff Point is scientifically exceptional, but it should still be described as a candidate and working-definition section rather than as a formally ratified Oxfordian GSSP.

ANCHOLME GROUP

Oxford Clay Formation (Callovian To Oxfordian)

Stewartby Member

Bed RC1 – Ham Cliff Bed 1 / Tidmoor Point Clay Beds (c. 2 m Exposed)

Medium-pale grey marl, relatively hard when dry, with the top c. 15 cm crowded by fine shell debris, some recognisable as fragments of Oxytoma. Meleagrinella cf. braamburiensis, Dicroloma and Mecochirus occur, and the bed yields a remarkably detailed terminal Callovian ammonite succession. The top of Bed 1 provides the most persistent datum in the Ham Cliff boundary section and has been used as the measurement reference for the higher beds. Ammonites: the fauna ranges upward through Quenstedtoceras praelamberti, typical Q. lamberti, and then the Q. paucicostatum transient α–γ assemblages, with Euaspidoceras hirsutum, Hecticoceras, Alligaticeras, Kosmoceras and juvenile Peltoceras. Biochronology: terminal Callovian, Lamberti Chronozone, Lamberti Subchronozone. Depositional Environment: quiet open-marine mud sedimentation with exceptionally high biostratigraphic resolution.

Bed RC2 – Ham Cliff Bed 2, Trans-Boundary Mudstone Package (c. 4.3 m)

Dark grey clays with paler marl “Bristol bands” and frequent thin pyritic burrow fills. Crushed aragonitic ammonites occur in bands, pyritic nuclei are locally preserved, and partial phosphatic infills of body chambers occur at certain levels. Benthos is sparse but includes oxytomid bivalves, a band of Gryphaea ex gr. dilatata, frequent Hibolithes and, in the lower part, abundant Mecochirus. Several sub-continuous marker horizons occur within the bed, notably a shell-rich seam with small ferruginous nodules at c. 1.2 m above the base, a Gryphaea band at c. 2.15 m, and ferruginous lenticles around c. 2.5 m. This is the critical Redcliff trans-boundary bed: the working base of the Oxfordian is placed 2.4 m above the top of Bed 1, at the base of the Cardioceras (Pavloviceras) redcliffense Biohorizon within Bed 2. Higher in the same bed follow the woodhamense and scarburgense biohorizons. Ammonites: Cardioceras (Pavloviceras) redcliffense, C. woodhamense, C. ex gr. scarburgense, with persistent but diminishing Quenstedtoceras paucicostatum transients low in the bed. Marker-Bed Significance: this bed is one of the most important Oxfordian boundary intervals in Europe and has yielded ammonites, foraminifera, calcareous nannofossils, ostracods, holothurian spicules and stable-isotope data across the stage boundary.

Weymouth Member

Bed RC3 – Ham Cliff Bed 3 / Basal Furzedown Clay Beds (2 m+ Exposed)

Dark grey, plastic clays with abundant mainly juvenile oxytomid bivalves and Dicroloma; Hibolithes is uncommon. Pyritic ammonite nuclei with crushed middle and outer whorls are common at certain levels, and the top passes transitionally into the silty Jordan Cliff Clay above. Ammonites: Cardioceras ex gr. scarburgense, including common morph mariae, with occasional juvenile Peltoceras. Biochronology: basal Oxfordian, Mariae Chronozone, Scarburgense Subchronozone. Interpretation: continuation of offshore mud deposition above the boundary, but now within fully Oxfordian cardioceratid-bearing clays of the lower Weymouth Member.

Bed RC4 – Jordan Cliff Clay On The North Side Of Redcliff Point (c. 9 m)

This unit comprises about 1 m of fissile clay overlain by about 8 m of tough, silty, blocky mudstone. At Redcliff Point it is notably better exposed than at its old type locality at Furzy Cliff and yields abundant, well-preserved Gryphaea dilatata; Modiolus bipartitus is also recorded. Compared with the finer clays below, the member is distinctly siltier and records a shallowing phase within the Oxford Clay. Depositional Environment: offshore marine mud sedimentation still below fair-weather wave base, but with increased quartz-sand input, a more substantial epifauna and a firmer sea floor than in the underlying boundary clays.

Bed RC5 – Small Repeated Bowleaze Clay Exposure At The South-Eastern End Of Redcliff Point

A small low-cliff exposure at the south-eastern end of the point yields Cardioceras spp. from soft, plastic calcareous clays referable to the Bowleaze Clay subdivision of the Weymouth Member. This is not the full Bowleaze Cove section repeated in miniature, but a local structural reappearance showing that higher Weymouth Member beds are faulted or slipped into the point area. It is important because it proves that Redcliff Point itself contains more than one Oxford Clay level and should not be simplified into a single undivided mudstone outcrop.

CORALLIAN GROUP

Redcliff Formation (Oxfordian)

Nothe Grit Member

Bed RC6 – Main Nothe Grit West Of Redcliff Point (full member thought to be c. 9 m; upper two-thirds best exposed here)

Fine-grained, argillaceous sandstone in medium to thick beds, grey to yellow-brown, intensely bioturbated and locally packed with calcareous concretions. No single complete section through the member is visible at Redcliff, but the upper two-thirds are well represented in the low cliff west of the point. The basal junction with the Oxford Clay is a sharp erosive non-sequence, best seen nearby at Ham Cliff, demonstrating a major facies break from offshore mud to sandy shelf sediment. Scattered concretions yield ammonites preserved in honey-coloured calcite. Ammonites: Cardioceras (Cardioceras) cordatum, C. persecans and related cardioceratids. Depositional Environment: shallow offshore to subtidal sand deposition with intense seabed burrowing and repeated early cementation.

Bed RC7 – Preston Grit (highest c. 1.5 m of the low cliff)

The Preston Grit forms the highest part of the low cliff from the Bowleaze side eastwards to Redcliff Point and is one of the best fossil-yielding beds in the immediate tract. It consists mainly of medium-grained, shelly, calcareous sandstone, weathering into blocks on the upper shore that reveal abundant bivalves, superb trace fossils and frequent ammonites. The bed records a more energetic sand phase than the Nothe Grit below and is among the most collector-useful horizons at the site. Typical Fossils: abundant bivalves including Myophorella hudlestoni in fallen blocks, plus well-developed burrow systems. Ammonites: Cardioceras (Cardioceras) cautisrufae and C. (Subvertebriceras) zenaidae. Interpretation: shell-rich, current-worked marine sandstone laid down under shallower and more turbulent conditions than the Nothe Grit below.

Nothe Clay Member

Bed RC8 – Nothe Clay Member At Redcliff (lower c. 8 m visible of a c. 12 m member)

A fine-grained, plastic grey clay succession in which muddy intervals alternate with sandy limestones rich in bivalves. At Redcliff the lower c. 8 m can be examined, though the member is commonly affected by slumping. Upward through the visible sequence the clastic content gradually increases, presaging the transition into the Bencliff Grit above. Typical Fossils: abundant bivalve faunas in the sandy limestones; ammonites are much less conspicuous than in the Preston Grit below. Depositional Environment: renewed quiet-water shelf-mud deposition, interrupted by shell-rich and locally sandier event beds, before a new progradation of sand into the area.

Bencliff Grit Member

Bed RC9 – Bencliff Grit Beneath Redcliff (mainly foreshore blocks and low platform outcrop)

At Redcliff the Bencliff Grit is represented mainly by blocks and low foreshore ledges beneath the cliff rather than by one clean upright section. It consists of argillaceous fine-grained sandstone and siltstone, commonly enclosed in or associated with conspicuous calcareous “dogger” concretions. These concretions preserve excellent trace fossils and locally occasional bivalves and ammonites. In the broader Osmington area the member is celebrated for spectacular swaley cross-stratification, but at Redcliff the fossil and ichnological content of the concretionary blocks becomes the main practical field feature. Typical Fossils: excellent trace fossils, occasional bivalves and rare ammonites. Depositional Environment: storm-influenced shallow-marine sand and silt deposition, transitional upward from the Nothe Clay and recording renewed progradation of clastics across the shelf.

Published Thickness Of The Redcliff Formation In The Wider Redcliff–Osmington Composite Section: About 29.2 Metres, Though No Single Clean Exposure At Redcliff Point Shows The Formation In Full

Osmington Oolite Formation (Middle Oxfordian)

Red Cliff Section Note

Hundreds of blocks derived from the large landslip west of Redcliff Point litter the undercliff and beach. The most useful section is a rotated slipped block at Red Cliff that preserves a published 12-bed section through the upper part of the Upton Member and the overlying Shortlake Member. Those bed numbers are retained below exactly, although the section is landslipped and therefore must not be mistaken for an undisturbed vertical cliff face.

Upton Member

Bed RC10 – Red Cliff Bed 1 (?A5b) – Nodular Micritic Limestone (seen to 0.45 m)

Nodular micritic limestone with very scattered 0.5 mm ooids, many more immature 0.1–0.2 mm ooids and thin curving burrows. This is the basal bed of the rotated Red Cliff block and represents the upper part of the Upton Member only, not the whole member. The mixture of micrite, scattered ooids and burrows indicates a quiet marine shelf floor receiving intermittent ooid influx but not dominated by high-energy shoal conditions.

Bed RC11 – Red Cliff Bed 2 (?A5c) – Medium Grey Silty Mudstone With Scattered Small Ooids (0.50 m)

A thin but distinctive ooid-bearing silty mudstone. The bed continues the more argillaceous character of the Upton Member at Redcliff and shows that the return to carbonate-rich sedimentation above the Bencliff Grit began in relatively deeper, more mud-dominated water than the later Shortlake shoal facies above.

Bed RC12 – Red Cliff Bed 3 (?A5d) – Nodular Calcareous Mudstone With Six Nodule Bands (1.30 m)

Nodular calcareous mudstone with six bands of micritic nodules containing scattered ooids and, in places, ooid-filled burrows. This is one of the most diagnostic Upton beds in the Red Cliff block. It combines offshore muddy deposition with repeated early lithification into nodule bands, and its abundant immature ooids are one of the practical ways in which Upton concretions can be recognised in loose material.

Bed RC13 – Red Cliff Bed 4 (?A5f) – Sandy Marl With Ooidal And Shelly Grains (1.15 m)

Sandy marl with ooidal and shelly grains and two 0.15 m bands of nodular argillaceous micrite containing many immature ooids. This bed closes the Red Cliff Upton section and shows a clear upward increase in sand and ooids before the strongly ooidal Shortlake facies begins. Interpretation: progressive shallowing from muddy offshore carbonate deposition into a more agitated ooid-bearing shelf setting.

Upton Member Ammonites

All ammonites securely sourced from the Red Cliff landslip block come from the Upton Member. The fauna includes Perisphinctes (Kranaosphinctes) maximus, P. (K.) aff. ariprepes, P. oxoniensis, P. (Otosphinctes) ouatius, P. (O.) arkelli, P. (Dichotomosphinctes) antecedens, Goliathiceras aff. elegans and Cardioceras (Maltoniceras) vagum. Taken together, these indicate the lower Antecedens Subzone and show that the Upton Member at Redcliff belongs to the lower part of the middle Oxfordian ammonite succession rather than to the younger Shortlake fauna above.

Shortlake Member

Bed RC14 – Red Cliff Beds 5–6 (?A6b, part) – Lower White Oolite (1.05 m)

Bed 5 is a thick coarsely shelly oomicrite, overlain by Bed 6, a rubbly-weathering densely ooidal micrite described by Arkell as “weathering pellety”. Together they form the Lower White Oolite of the Red Cliff sequence. These beds are much more strongly ooidal than the Upton Member below and mark the clear establishment of the Shortlake ooid-facies system, although they still lack the major cross-bedding of the higher Shortlake units.

Bed RC15 – Red Cliff Bed 7 – Mudstone With Nanogyra nana (0.15 m)

A very thin but important shelly mudstone carrying Nanogyra nana. This bed interrupts the ooid-rich Lower White Oolite and demonstrates that muddy, shell-bearing pauses punctuated the Shortlake shoal succession. It is also a useful marker because it separates the lower ooidal micrites from the thicker cross-bedded Middle White Oolite above.

Bed RC16 – Red Cliff Beds 8–10 (A6c, part) – Middle White Oolite With Mudstone Interbed (3.90 m)

This is the most spectacular Shortlake interval at Redcliff. Bed 8 is a thin-bedded to massive, cross-bedded, very poorly sorted oosparite; Bed 9 is a mudstone with bands of very fissile fine-grained sandy sparry limestone; Bed 10 is another thick cross-bedded, very poorly sorted oosparite. Profuse shale pellets indicate considerable scouring, and the whole package has long been noted as westwardly transitional toward the Forest Marble style of mixed ooid and mud deposition. Ammonites: occasional cardioceratids and perisphinctids include Cardioceras (Maltoniceras) maltonense, Perisphinctes (Kranaosphinctes) aff. decurrens and P. (Dichotomosphinctes) aff. dobrogensis. Interpretation: cross-bedded ooid bars and sand bodies alternating with quieter muddy interludes in a shallow marine but westwardly more mud-influenced setting than farther east at Shortlake Steps and Bran Point.

Bed RC17 – Red Cliff Bed 11 (?A7) – Upper Ooidal Mudstone And Coarsely Ooidal Micrite Bands (0.70 m)

Shelly, ooidal mudstone with bands and nodules of coarsely ooidal shelly micrite. This bed records waning energy above the major cross-bedded oosparites but remains distinctly more ooidal than any part of the Upton Member. It is a transitional upper Shortlake bed in which ooid-rich sediment was still common, but the sea floor was quieter and more muddy than during deposition of Beds 8–10.

Bed RC18 – Red Cliff Bed 12 (?A8) – Nodular Shelly Limestone With Irregular Clay Partings (seen to 1.4 m)

The highest bed seen in the Red Cliff block is a nodular limestone with irregular clay partings. Its base is more massive, coarsely ooidal and shelly, with well-preserved bivalves including pectinids, but upward it passes into more nodular shelly micrite with scattered coarse ooids. The top is only seen to 1.4 m, so the complete thickness is uncertain. This bed closes the local Red Cliff Shortlake section and represents the quieter upper part of the member before the higher Nodular Rubble facies enters farther east.

Shortlake Member Ammonites And Age

The Shortlake Member at Redcliff has yielded only a small ammonite fauna, but it is stratigraphically important. Liosphinctes, Perisphinctes sensu stricto, Dichotomosphinctes and forms close to dobrogensis show that the member belongs to the upper Antecedens Subzone. In other words, Redcliff records a clear faunal shift upward from the lower Antecedens Upton fauna into a sparser but slightly younger Shortlake assemblage.

Higher Osmington Oolite Note

The Nodular Rubble Member is not securely or fully represented in the Red Cliff landslip block used here, and it is better logged farther east toward Bran Point and Black Head. It is therefore not forced into this Redcliff Point page.

Depositional Environment

The Redcliff Point locality records a long environmental progression across the Callovian–Oxfordian transition and into the Corallian shallow-shelf system. The Ham Cliff boundary beds of the Oxford Clay were deposited as open-marine mudrocks rich in ammonites, with the stage boundary lying within an expanded trans-boundary mudstone sequence that remained suitable for high-resolution biostratigraphy, microfossils and chemostratigraphy. Higher in the Weymouth Member, the Jordan Cliff and Bowleaze clays show shallowing and renewed slight deepening within offshore mud deposition, including storm-borne carbonaceous incursions in the broader Bowleaze interval. The Redcliff Formation marks abrupt sandy shallowing: Nothe Grit and Preston Grit represent burrowed shallow-shelf and shell-rich storm-worked sandstones; Nothe Clay records a temporary muddy deepening; and the Bencliff Grit records renewed sand-body progradation and storm reworking. The lower Osmington Oolite at Redcliff records the return of ooid-rich carbonate sedimentation, beginning in argillaceous ooid-bearing Upton offshore facies and passing upward into the cross-bedded ooid shoals, intershoal muds and upper ooidal micrites of the Shortlake Member. At Redcliff these ooid facies are already more clay-rich and westwardly transitional than the cleaner eastern sections around Bran Point.

Total Thickness Note

No honest single total thickness can be given for an undisturbed Redcliff Point cliff because the locality is structurally composite and partly repeated. What can be stated securely is that the Ham Cliff boundary section preserves more than 8 m of terminal Callovian to basal Oxfordian beds across the Bed 1–3 boundary interval, the Jordan Cliff Clay is about 9 m thick where exposed at the point, the Redcliff Formation is about 29.2 m thick in the wider Redcliff–Osmington composite section, and the published rotated Red Cliff block preserves 10.55 m of upper Upton and Shortlake strata with Bed 12 still only seen in part.

References

Page, K.N., Meléndez, G., Hart, M.B., Price, G.D., Wright, J.K., Bown, P. and Bello, J. (2009). Integrated stratigraphical study of the candidate Oxfordian GSSP at Redcliff Point, Weymouth, Dorset.
Wright, J.K. (1986a). A new look at the stratigraphy, sedimentology and ammonite fauna of the Corallian Group (Oxfordian) of south Dorset.
Wright, J.K. (1986b). The Upper Oxford Clay at Furzy Cliff, Dorset: stratigraphy, palaeoenvironment and ammonite fauna.
Wright, J.K. (1997). Oxfordian ammonite faunas of south Dorset.
Wright, J.K. (2011). The ammonite faunas of the Osmington Oolite Formation (Jurassic, Middle Oxfordian) of the Dorset coast.
Wright, J.K. & Cox, B.M. (2001). Osmington, in British Upper Jurassic Stratigraphy (Oxfordian to Kimmeridgian), Geological Conservation Review Series 21.
Arkell, W.J. (1947). Geology of the Country around Weymouth, Swanage, Corfe and Lulworth.
Cope, J.C.W. (2007). Fieldtrip to the Corallian rocks of the Dorset coast.
International Subcommission on Jurassic Stratigraphy: Oxfordian working-group summary and current boundary status.
British Geological Survey Lexicon of Named Rock Units: Oxford Clay Formation, Weymouth Member, Redcliff Formation, Nothe Grit Member, Preston Grit Member, Nothe Clay Member, Bencliff Grit Member and Osmington Oolite Formation.