Swanage Bay Fossil Hunting

1816 – Webster published the first description of the Wealden strata of north Swanage Bay
Thomas Webster was the first to describe the Wealden Group at Swanage Bay. His account marked the start of the scientific literature on the bay’s Lower Cretaceous succession and established Swanage as an important Purbeck Wealden locality.

1835 – Buckland recorded fossil bones of Iguanodon from the Wealden of the Isle of Purbeck
William Buckland recorded fossil bones of Iguanodon from the Wealden of Purbeck, and later summaries treat Swanage Bay as part of the earliest record of dinosaur bones from the bay’s Wealden succession. This is one of the key early dinosaur milestones for Swanage.

1859 – Phillips recorded an unusual fossil fruit from the northern Swanage Bay succession
John Phillips reported a small pyritised fossil fruit from beds above the Wealden in northern Swanage Bay. Although not one of the bay’s best-known fossils today, it remains one of the more distinctive early plant-related records from the Cretaceous succession here.

1862 – Samuel Beckles published dinosaur footprints from the Wealden of Swanage
Samuel Husbands Beckles published on natural casts of reptilian footprints from the Wealden of the Isle of Wight and Swanage. These are among the earliest published dinosaur footprints from Swanage Bay and helped establish the locality as a genuine dinosaur site rather than just a Cretaceous coastal section.

1871 – John W. Judd described the Punfield Formation at Punfield Cove
Judd’s work on the Punfield Beds at the north end of Swanage Bay became one of the classic studies of the Lower Cretaceous of Dorset. He recognised the importance of the transitional beds at Punfield Cove, where non-marine Wealden strata pass up towards more marine conditions, making the site historically important in debates about the Cretaceous succession of southern England.

1876 – Barrois gave the first account of the Ballard Point chalk cliffs and recognised the great Ballard Fault
Charles Barrois was the first to provide a published account of the Ballard Point and Handfast Point chalk cliffs. He identified the major Ballard Fault and recognised the importance of the chalk succession there, beginning the long scientific history of the Swanage Bay chalk as a reference section.

1888 – Mansel-Pleydell added further records of Wealden dinosaur bones from Swanage Bay
J. C. Mansel-Pleydell provided later nineteenth-century records of dinosaur bones from the Wealden of Swanage Bay. Together with Buckland and Beckles, his work forms the core of the earliest documented dinosaur record from the bay.

1901 – A. W. Rowe produced the first fully detailed zonal account of the Ballard chalk
Arthur Wade Rowe provided the first detailed and comprehensive zonal stratigraphy of the chalk between Ballard Point and Handfast Point. His work made the Swanage chalk one of the classic Upper Cretaceous reference sections in southern England and documented important fossil horizons including echinoids, brachiopods and characteristic marker beds.

1967 – Drummond described the Upper Greensand–Lower Chalk section at Punfield Cove in detail
R. V. Drummond’s study of Punfield Cove clarified the Albian–Cenomanian succession beneath the Chalk at the north end of Swanage Bay. This was important because it tied the lower part of the Chalk succession to the older Cretaceous beds below and helped refine the geological framework of the bay.

1996 – Gale introduced the Ballard Cliff Member for the basal Holywell Nodular Chalk
Andy Gale introduced the term Ballard Cliff Member for the basal beds of the Holywell Nodular Chalk Formation at Ballard Cliff. This formalised the importance of Swanage Bay’s chalk section in modern Upper Cretaceous stratigraphy and linked the locality directly to a named chalk unit.

2020 – a modern revised framework was published for the Swanage Bay Wealden
A modern reappraisal of the Wessex Formation at Swanage Bay established a new detailed stratigraphic framework with marker beds for the exposed Wealden succession. This was especially important because it allowed older and new fossil finds, including plant debris beds, microvertebrates and the historic dinosaur material, to be placed much more accurately within the Swanage section.

Modern understanding – Swanage Bay remains important for both Wealden dinosaurs and Chalk fossils
Today Swanage Bay is recognised as a rare Dorset locality where dinosaur-bearing Wealden beds and a major Chalk reference section can both be studied in one coastal sweep. The Wealden has yielded dinosaur bones and footprints, while the Chalk at Ballard Point and Ballard Cliff remains important for ammonites, echinoids, brachiopods, inoceramids and marker horizons used in Upper Cretaceous stratigraphy.

WEALDEN GROUP

This Swanage Bay page covers the northern bay from the town and Sheps Hollow through Punfield Cove to Ballard Point, and excludes Peveril Point and the south-side Purbeck and Portland coast. Because Swanage Bay is a composite, partly landslipped and historically variable section, the SB bed numbers used below are site-use labels based on named marker horizons and real lithological packages rather than formal published bed numbers.

About 700 m of Wealden Group strata are present beneath Swanage Bay, but only part of the Wessex Formation is normally exposed today. The uppermost Wealden and the overlying Lower Greensand are known mainly from temporary foreshore exposures, old descriptions and obscured cliff sections rather than from a single clean continuous cliff log.

Wessex Formation (Lower Cretaceous)

Bed SB1 — Lower Exposed Wessex Sandstones Below The Grand Hotel

Inaccessible bedded sandstones beneath the Grand Hotel form the oldest Wessex strata presently visible in Swanage Bay. They are exposed mainly in low clifflets and by occasional scour on the foreshore and probably represent fluvial channel sand bodies passing into adjacent floodplain mudstone. The basal Wealden contact with the Purbeck Group is not visible in the bay today; older records placed it below present ground level beneath Swanage, so the southernmost visible Wessex here is already well above the true base of the formation.

Bed SB2 — Ravine Sandstone (4–5 m)

The Ravine Sandstone is the lowest major named marker horizon of the accessible Swanage Bay Wessex section and forms a laterally extensive yellow-grey very fine- to fine-grained sandstone at and south of Sheps Hollow. It is about 4 m thick at beach level and thickens southward to about 5 m. Rounded quartz grains dominate, with minor feldspar and tourmaline, and angular pale blue-grey mudstone clasts up to about 80 mm across record active bank erosion during floods. Low-angle cross-bedding, ripples, large sand-filled channels, lenticular calcitic concretions and simple burrows are typical, and rare overturned blocks show tridactyl dinosaur footprints in hyporelief. This is a substantial fluvial channel sandstone deposited under energetic river flow with periodic flood reworking and short episodes of subaerial exposure.

Internal Ravine Sandstone mudstone horizons south of Sheps Hollow

Poorly accessible mudstone intervals around a metre thick occur within the sandstone. They contain pale-grey, rounded pedogenic nodules approximately 50 mm across. Penn and colleagues could not determine whether the nodules formed there or had been eroded and redeposited.

Bed SB3 — Heterolithic Siltstone And Clay (c. 3 m)

About 50 m north of Sheps Hollow, a prominent 3 m thick interval of alternating grey silty sandstones and pale blue mudstones forms a spur at the cliff base. The silty beds are thin and laterally variable, show low-angle cross- and trough-lamination, and carry a low-diversity Scoyenia ichnofacies with vertical and horizontal burrows together with isolated tridactyl Iguanodontipus hyporeliefs. The intervening pale blue mudstones are calcrete-rich palaeosols, interpreted as pedogenic vertisols formed under strongly seasonal semi-arid conditions. The unit represents repeated overbank and levee sedimentation across a floodplain that was periodically exposed, trampled and soil-formed.

Thin silty sandstone horizons within the Heterolithic Siltstone and Clay

Penn’s local description identifies at least three fine-grained silty sandstone layers, averaging about 0.15 m individually but varying laterally. They retain small cross- and trough-lamination and are interbedded with the calcrete-rich mudstones described above; the individual layers are not given new invented bed numbers.

Bed SB4 — Middle Wessex Overbank Mudstones And Palaeosols

Overbank mudstones dominate the Swanage Bay Wessex section, locally in packages more than 40 m thick. These beds are red, variegated, grey or pale blue according to oxidation state and pedogenic overprint, and they include small erosive channels, root traces, prominent calcrete horizons and numerous plant-debris concentrations. The main depositional setting was a broad floodplain with seasonally wet standing water, ephemeral crevasse or sheet-flood channels, and repeated soil development. These mudstone intervals are essential for understanding the locality because they contain many of the plant debris beds and much of the palaeoecological information even where body fossils are sparse.

Ms1 mudstone package

Penn’s Figure 6 labels the main mudstone-dominated interval between the Heterolithic Siltstone and Clay and the Middle Sandstone as Ms1. Thin local sand bodies, palaeosol features and overbank deposits interrupt this package. Ms1 is an informal log label, and no numerical total is inferred from the figure scale.

Bed SB5 — Middle Sandstone (3.2 m)

The Middle Sandstone is a 3.2 m thick fine-grained, homogeneous yellow quartz-rich sandstone with well-developed low-angle cross-bedding and an erosive base cut into pale blue mudstones. Mudstone clasts again show local bank erosion during flood events. Trough cross-bedding and trace fossils are rarer here than in the Ravine Sandstone, but the unit is another major fluvial sand body within the otherwise mudstone-dominated succession and records renewed channel migration across the Wessex floodplain.

Bed SB6 — Upper Wessex Mudstones And Plant Debris Beds

The upper mudstone-dominated part of the exposed Wessex contains much of the plant-debris-bed assemblage for which Swanage Bay is important. Plant debris beds make up about 9% of the exposed Wessex here and are the principal source of fossils. Three main plant-rich lithologies occur: finely laminated plant material in mudstone; twig- and log-rich thick mudstones, commonly associated with ironstones; and high-energy gritty clays with logs, twigs and reworked pedogenic nodules. Lignitic conifer wood is common, together with coprolites, termite frass, burrows such as Planolites and Beaconites, and freshwater unionid bivalves including small Subnippononaia fordi and larger Unio-like shells. These beds record a mix of quiet floodplain pools, shallow freshwater bodies and debris-flow or sheet-flood events that swept floral and faunal remains together from fluvial, terrestrial and lacustrine settings.

Ms2 mudstone package

Penn’s Figure 6 separately labels the thick mudstone package above the Middle Sandstone as Ms2, below the higher ironstone-bearing part of the logged succession. This informal package is retained independently from Ms1; a precise thickness is not reconstructed from the drawing.

Bed SB7 — Ironstones 1–6 (individual beds 0.3–1.1 m)

Near the north-eastern end of the present Wessex exposure, plant-rich pale blue-grey mudstones are interbedded with at least six distinct ironstone horizons. Their grain size and quartz content increase upward to the sub-conglomeratic Ironstone 6, and many have erosive bases. Lignitic logs and twigs are common, weathered specimens may show casts of branches and rare conifer cones, large unionid bivalves are frequent, and abraded reptile bones are present. Penn and colleagues specifically recovered microvertebrates from Ironstone 2, including bony fishes, hybodont sharks and small crocodyliforms; these are not verified assemblages for every ironstone. These ironstones are channelized or flood-reworked ferruginous concentrations within the floodplain succession and form some of the most fossiliferous and collector-relevant horizons in the Swanage Bay Wealden.

Ironstone 1

The lowest named ferruginous marker is relatively fine-grained. A landslip above it obscures the interval towards Ironstone 2; Penn and colleagues considered that an additional unconfirmed ironstone might be hidden there. That possible bed is not numbered as a seventh established horizon.

Ironstone 2 and adjacent plant-rich mudstones

This is the sampled microvertebrate horizon. Reported remains include Lonchidion striatum and L. breve, lepisosteiform scales, amiiform and pycnodont remains, and atoposaurid and goniopholidid teeth. The adjacent mudstones carry conifers including Pseudofrenelopsis and Sphenolepis; small indeterminate bivalve impressions occur above the ironstone.

Ironstone 3

A distinct higher ironstone is separated from Ironstone 2 by mudstone. It forms part of the upward-coarsening ferruginous succession. The available publication does not provide a unique measured thickness or independently sampled vertebrate list for this bed.

Ironstone 4

This separate ferruginous marker lies above Ironstone 3 and below Ironstone 5, with intervening mudstones and a sandy interval shown in the published log. No individual thickness is inferred from the drawing’s line width.

Ironstone 5 and overlying laminated plant bed

The fifth ironstone is capped by a laminated plant-debris bed rich in Watsoniocladus. Its flora differs from the plant-rich mudstones associated with Ironstone 2, making the plant horizon a useful local discriminator.

Ironstone 6

The highest named ironstone is sub-conglomeratic and forms the beach-level base of the White Quartz Grit. It thickens towards the north-east. The six ironstones collectively span a published individual-bed thickness range of about 0.3–1.1 m; that range is not a separate measurement for each bed.

Bed SB8 — White Quartz Grit (6–7 m)

The White Quartz Grit is the highest major named Wessex marker horizon exposed in Swanage Bay. It is a 6–7 m thick fining-upward sheet sandstone with prominent basal grit horizons and a sharp, locally erosive base above the ironstones. Inclined fusain-rich surfaces show active accretion on a prograding point bar, and the gritty lower part is a coarse subarkose with quartz, feldspar, tourmaline and mixed lithic grains in a white kaolinitic matrix. The coarse, kaolinized character of the detritus suggests derivation from Cornubian granitic terrain. This bed records a major pulse of coarse fluvial sediment input near the top of the exposed Wessex section and lies close below the concealed passage into the uppermost Wealden and Lower Greensand.

Wessex Formation Logged In 2018–2019: About 110 Metres Vertically, Within About 700 Metres Of Wealden Group Beneath Swanage Bay

Vectis Formation (Lower Cretaceous)

Bed SB9 — Concealed Vectis Formation And Uppermost Wealden Mudstones

The uppermost Wealden at Swanage Bay is mostly concealed by landslip around Punfield Cove and north Swanage, but temporary exposures and older descriptions show that Vectis-like beds are present. Ruffell recorded about 10 m of well-laminated dark grey to black mudstones with white silt partings roughly 25 m below the Punfield Marine Band, with a 1–2 cm shell bed of Unio at the top; older records also mention viviparid gastropods, ostracods and oysters from obscured upper Wealden beds. These quiet-water mudstones represent brackish to freshwater lagoonal or marginal-estuarine conditions that succeeded the largely fluvial Wessex floodplain. Because the beds are rarely exposed continuously, no secure member-level breakdown is attempted here.

LOWER GREENSAND GROUP

The Swanage Lower Greensand is one of the historically most discussed Lower Cretaceous sections in southern England, but it is not a simple, permanently open cliff log. Most exposures around Punfield Cove are temporary, slumped, overgrown or seen only after storm erosion, so the sequence below follows repeatedly recognized horizons and formal formations only where correlation is defensible.

Atherfield Clay Formation (Lower Aptian)

Bed SB10 — Basal Atherfield Clay Micaceous Silty Clays

Above the concealed interval over the upper Wealden, historical local exposures showed unfossiliferous, massive, micaceous grey silty clay and sandy muds that are strongly bioturbated by Thalassinoides and Macronichnus. Ruffell’s 1988 observations record about 10 m of shingle-covered strata between the Vectis-like exposure and these clays; that covered interval is not a measured thickness of exposed Atherfield Clay. The beds are interpreted as Atherfield Clay Formation on stratigraphical and lithological grounds, but it is difficult to assign them securely to the detailed Isle of Wight member scheme. They record the first substantial marine flooding above the Vectis muds and the establishment of a shallow muddy shelf or estuarine embayment at the base of the Lower Greensand.

Historical basal Atherfield pebble bed (0.9 m)

The BGS account records a phosphatic pebble-rich basal bed with fish teeth. Ruffell did not see this bed during the 1988 exposures. It is therefore a historical local record, not an additional part of his exposed clay thickness.

Punfield Marine Band Horizon

Bed SB11 — Punfield Marine Band (c. 1.5 m)

The Punfield Marine Band is the classic named marine-incursion horizon of Swanage Bay. Its lower contact is commonly hidden, but the bed itself includes bioclastic limestones enriched in wood fragments, followed above by about 10 cm of light grey clay and then an uncemented shell bed rich in Filosina gregaria, a brackish-marine bivalve that is also characteristic of nearby Wealden facies. The mixed character of the fauna is one reason the Punfield section became so historically important in debates over the relationship between Wealden and Lower Greensand strata. The bed records a distinct marine transgression into an estuarine or marginal-marine setting, with storm or current concentration of shell material and drift wood.

The BGS historical account gives 0.5–1.5 m for the Marine Band; Ruffell’s observed bed was 1.5 m. The overlying clay and Filosina shell bed are separately identified below.

Lower Punfield Marine Band limestone

The historical three-part description begins with hard iron-stained shelly limestone containing pebbles and muddy-limestone concretions.

Middle oyster-rich division

An oyster-dominated shell concentration forms the middle part of the historical Marine Band description. No independent division thickness is assigned here.

Upper carbonaceous calcareous sandstone

Hard laminated micaceous calcareous sandstone with abundant carbonaceous matter forms the upper historical division; Ruffell described wood-rich bioclastic limestone in the temporarily exposed upper beds. These are source descriptions of a variable horizon, not additional beds to be summed.

Clay above the Marine Band (0.10 m)

Ruffell measured this light-grey clay between the Marine Band and the overlying uncemented shell concentration.

Filosina shell bed above the clay

The shells lie chiefly convex-side upward on one bedding surface. This brackish-marine assemblage is above the Marine Band limestone, and should not be treated as the whole Marine Band fauna.

Bed SB12 — White Cross-Bedded Sandstone And Brown Silty Clays Above The Marine Band

Above the shell bed, the clay coarsens upward into white medium-grained cross-bedded sandstone with rare oysters, including Aeteostreon, and patchy calcite cement. This sand body has long been compared with the Crackers or Upper Lobster interval of the Isle of Wight succession. In the possibly slipped brown silty clays above, Ruffell reported a fragment identified as Deshayesites punfieldiensis by Owen and Rawson. Casey had questioned an older report of that species from Punfield. This is Ruffell’s particular 1988 exposure record and interpretation, not an unqualified diagnostic claim for every occurrence of the bed. The whole package represents a shallower, sandier phase immediately following the main marine-incursion limestone.

Shingle-covered interval above Exposure 3 (about 20 m in Ruffell’s reconstruction)

Ruffell recorded the succeeding approximately 20 m as concealed beneath shingle before reaching the 9 m green argillaceous sand of Exposure 4. This is an observed exposure gap within his historical reconstruction, not a depositional hiatus or an extra thickness added to that reconstruction.

Ferruginous Sands Formation (Aptian)

Bed SB13 — Lower Ferruginous Sands Green Argillaceous Sands With Iron-Pan Horizons (c. 9 m exposed)

A grey-green bioturbated and argillaceous sand body about 9 m thick forms the lower clearly exposed Ferruginous Sands interval. Two iron-cemented silty sand beds 30–60 cm thick occur in its upper part and are separated by a bright green siltstone. Moulds of bivalves and the ammonite Tropaeum bowerbanki have been found near the base of the upper iron-cemented bed. These strata represent a coarsening-up shallow-marine sandy succession with intermittent firmground or cemented horizons and continued marine influence.

Lower iron-cemented silty sand (0.30–0.60 m)

One of two iron-pan horizons in the upper part of Ruffell’s 9 m exposed green argillaceous sand.

Bright-green intervening siltstone

This finer layer separates the two iron-cemented horizons; no thickness is invented.

Upper iron-cemented silty sand (0.30–0.60 m)

Bivalve moulds and Tropaeum bowerbanki were recorded near its base. The ammonite provenance belongs specifically to this upper iron-pan horizon.

Bed SB14 — Upper Ferruginous Sands Coarsening-Up Sands

Above the better defined lower sands, about 12–15 m of soft brown coarse sands are usually only poorly exposed. They carry clay-lined burrows such as Thalassinoides and Diplocraterion and closely resemble the Ferruginous Sands facies of the Isle of Wight. The succession records repeated shallowing and sandier conditions, probably on an inner-shelf to shoreface sand-wave system that remained under marine influence but was much more energetic than the mud-dominated Atherfield Clay below.

Sandrock Formation (Aptian To Earliest Albian)

Bed SB15 — Lower Sandrock-Type White Sands

Higher in the Lower Greensand, slipped micaceous grey mudstones are abruptly overlain by white sands of clear Sandrock type. These sands show tabular cross-stratification and are on strike with the better known Punfield Cove cliff exposures. Rotated palaeocurrent evidence indicates transport broadly towards the south-east. They represent cleaner, higher-energy sand accumulation than the Ferruginous Sands below, probably in migrating coastal bars or sand waves in a very shallow marine to marginal-marine setting.

Bed SB16 — Pebble Bed With Reworked Aptian Nodules And Jurassic Debris

Resting on an undulatory erosion surface cut into the white sands is an iron-cemented pebble bed containing well-rounded quartzite clasts, phosphatic nodules and derived Upper Jurassic debris, including Portland Sandstone, silicified wood and reworked pavloviid ammonites. Red iron-oxide nodules crowded with shell debris contain immature Parahoplites, and although the fauna within the nodules is Aptian, the nodules themselves appear reworked. This is a strongly condensed transgressive lag horizon and one of the clearest signs of erosion and reworking in the Swanage Lower Greensand.

Bed SB17 — Upper Sandrock-Type Sands And Pebbly Silts

For roughly 15 m above the main pebble bed, dark bioturbated silts pass upward into more white Sandrock-type sands, and pebbly silts occur beneath a second sand unit higher in the cliff. These beds show that the top of the Swanage Lower Greensand was built by repeated cycles of silting, renewed sand input and local pebble concentration rather than by one uninterrupted sand body. In older literature the ferruginous top of this interval was sometimes linked with “Carstone”, but at Swanage the outcrop is too poor and too reworked to force a more detailed formal subdivision than the Sandrock-type upper Lower Greensand.

Lower Greensand Thickness: About 90 Metres In Ruffell’s 1992 Composite; Other Published Reconstructions Differ

Ruffell’s 1992 paper used a 90 m composite. The BGS later contrasted Arkell and Casey’s approximately 59 m interpretation with Ruffell and Batten’s 1994 expanded estimate of as much as 170 m, including thicker concealed intervals. These figures reflect differing reconstruction and exposure; they are not a measured range through a single continuously visible section, and the chart therefore uses no single definitive Lower Greensand total.

SELBORNE GROUP

Gault Formation (Albian)

Bed SB18 — Basal Pebbly Gault And Main Gault Mudstones (historically c. 27.8 m at Punfield)

At Punfield Cove the Gault was historically measured at about 27.8 m, but it is now mostly concealed by landslides. Its basal bed is a thin, patchy sandy clay with small pebbles and clasts derived from the underlying Lower Greensand, and the main formation consists of sandy clay to mudstone that is generally only sparsely fossiliferous except at certain levels. As regional context, Gallois and Owen’s account of the Gault across the Dorset and East Devon World Heritage Site lists echinoderms, bivalves, gastropods, scaphopods, arthropods, fish remains and inoceramids such as Actinoceramus concentricus. That regional list is not an independently verified assemblage from a particular Punfield bed. The basal Gault at Punfield is of Hoplites spathi Subzone age and records renewed open-marine transgression across the eroded top of the Lower Greensand.

Upper Greensand Formation (Albian)

Foxmould Member

Bed SB19 — Foxmould Glauconitic Sandstones (historically c. 16.8 m at Punfield)

The Foxmould at Punfield Cove was historically measured at about 16.8 m. For formation-wide context, the following lithological, sedimentological and faunal summary describes the Foxmould across the regional study area; individual Punfield observations are listed separately below. Regionally it consists of fine- to medium-grained, weakly cemented glauconitic sandstones with strong bioturbation and locally calcareous or siliceous cemented beds that weather out as doggers and tabular “cowstones”. Most sedimentary structures indicate quiet subtidal deposition above storm-wave base, but pebble channel-lags, winnowed shell concentrations and hummocky cross-bedding show that strong bottom currents swept the sea floor during storms. Broken oysters, pectinids, serpulids including Rotularia concava, and scattered ammonites are characteristic. The bulk of the member belongs to the Hysteroceras binum interval, with younger ammonites higher up.

The following historical bed measurements are the exact Punfield log recompiled by BGS from Arkell and Tresise. They describe a different published section/definition from Strahan’s 16.8 m Foxmould estimate above; the two are alternative records, not superposed packages.

Historical FOX-PUN1 lower nodule bed (0.30 m)

Fossiliferous calcareous nodules immediately above the Gault were recorded as Arkell’s Bed 2.

Historical FOX-PUN1 upper sandy silt (4.12 m)

Dark argillaceous sandy silt, historically termed loam, forms Arkell’s Bed 3. The two FOX-PUN1 divisions total 4.42 m.

Historical FOX-PUN2(i) doggers (0.46 m)

Calcareous doggers contain bivalves at the base of the next historical package.

Historical FOX-PUN2(ii) fossiliferous green sand (1.10 m)

This sand overlies the dogger horizon in the published Punfield log.

Historical FOX-PUN2(iii) nodular green sand (0.73 m)

Green sand contains calcareous nodules.

Historical FOX-PUN2(iv) upper fossiliferous green sand (3.66 m)

The upper sand completes a combined FOX-PUN2 thickness of 5.95 m.

Bed SB20 — Upper Foxmould And Exogyra Rock Hardground

The top of the Foxmould is marked by the hardground at the top of the Exogyra Rock, a very important field datum immediately below the condensed White Nothe Member. This surface marks a sudden change from weakly cemented glauconitic sandstones below to more calcareous sandstones and calcarenites above. At Punfield the boundary interval is steeply dipping and locally sheared, but it clearly records interruption of sedimentation, marine cementation and renewed current activity before the next highly condensed phase of deposition.

White Nothe Member

Bed SB21 — Condensed White Nothe Member (0.4–0.5 m)

At Punfield Cove the White Nothe Member is reduced to only about 0.4–0.5 m of nodular sandy glauconitic sandstone between the erosion surface at the top of the Exogyra Rock and the base of the Chalk Basement Bed. The member is pervasively penetrated by pebbly glauconitic sands from above and contains indigenous Stoliczkaia-zone ammonites together with Cenomanian Mantelliceras and Schloenbachia introduced from the overlying bed. Here, as elsewhere in the steep Purbeck Monocline limb, beds may dip at 45° or more and some lithological boundaries are tectonically sheared. This is therefore a very condensed, omission-rich marine shelf interval rather than a thick, complete upper Upper Greensand succession.

Historical upper nodular sand, BSM-PUN1 (1.83 m)

The older log calls this fossiliferous dark-green sand with calcareous nodules the Bindon Sandstone Member and notes an oyster-rich basal bed. Modern research describes the much-condensed White Nothe interval at this locality. The 1.83 m historical package is retained as source-specific evidence, without assuming its boundaries coincide exactly with the modern 0.4–0.5 m interval.

Total Thickness Of The Selborne Group At Punfield Cove: Historically About 44–45 Metres, Comprising Roughly 27.8 Metres Of Gault, 16.8 Metres Of Foxmould And Only 0.4–0.5 Metre Of White Nothe Member

CHALK GROUP

Approaching Ballard Point the beds steepen dramatically and the cliffs become loose and hazardous. The chalk breakdown below follows the section from the Cenomanian Basement Bed at Punfield Cove to the top of the lower Lewes Nodular Chalk Formation at Ballard Point only; younger chalk north of Ballard Point belongs in a separate section.

GREY CHALK SUBGROUP

Zig Zag Chalk Formation (Cenomanian)

Bed SB22 — Chalk Basement Bed And Basal Glauconitic Marl (c. 1.5–1.6 m combined)

At Punfield the Chalk begins abruptly on an erosional surface above bored Upper Greensand doggers. The basal 0.3–0.4 m Basement Bed is a condensed nodular glauconitic sandstone of greensand pebbles in a Glauconitic Marl matrix; above it lie about 0.6 m of calcareous sandstone with both phosphatized and unphosphatized fossils and a further 0.6 m of Glauconitic Marl. Phosphatized middle Cenomanian ammonites occur in the Basement Bed, while the overlying marls yield indigenous brachiopods such as Orbirhynchia mantelliana, Grasirhynchia grasiana and Concinnithyris subundata. The West Melbury Marly Chalk is absent here, showing strong condensation over the Mid-Dorset structural high.

Basement Bed (0.30–0.40 m)

Greensand pebbles and glauconitic matrix form a condensed basal bed above an erosional contact. Phosphatised middle Cenomanian ammonites mark reworking within this deposit.

Calcareous sandstone above the Basement Bed (0.60 m)

The GCR records phosphatised Turrilites costatus and Schloenbachia together with unphosphatised fossils, including Dereta pectita.

Upper Glauconitic Marl (0.60 m)

Unphosphatised brachiopods in this marl belong to the local middle Cenomanian assemblage described above. The three divisions total about 1.5–1.6 m.

Bed SB23 — Lower Zig Zag Marly Chalks (about 10 m)

Above the basal Glauconitic Marl, about 10 m of marly chalk are developed below a higher erosion surface. Fossils include Holaster subglobosus, Camerogalerus cylindricus and Concinnithyris subundata, indicative of the Turrilites acutus Subzone. These beds represent open-marine chalk sedimentation with a higher marl content than the overlying Zig Zag and preserve one of Dorset’s key condensed middle Cenomanian successions.

Bed SB24 — Upper Zig Zag Chalk (c. 30 m combined)

Above the erosion surface lies a further 3 m of glauconitic marly chalk followed by about 27 m of more massively bedded Zig Zag Chalk with thin marl seams. The formation yields the characteristic middle Cenomanian chalk fauna, and Acanthoceras jukesbrownei is recorded from Jukes-Browne Bed 7; Calycoceras has also been noted from the Punfield area. Bands of Holaster are a feature of the formation here. The succession records fully marine offshore chalk deposition, but still under the influence of periodic marl input and condensation on the Dorset swell.

Glauconitic marly chalk above the erosion surface (3 m)

This interval overlies the approximately 10 m lower marly chalk and records a further condensed phase.

Main massively bedded Zig Zag Chalk (27 m)

More massive chalk with thin marl seams overlies the glauconitic interval. Jukes-Browne Bed 7 is a named ammonite-bearing marker within the formation; no unverified distance from its base is assigned.

WHITE CHALK SUBGROUP

Holywell Nodular Chalk Formation (Upper Cenomanian To Lower Turonian)

Plenus Marls Member

Bed SB25 — Plenus Marls Member

The Plenus Marls are well developed at Punfield and all of Jefferies’ numbered beds can be identified. The belemnite Praeactinocamax plenus is present, bands of Inoceramus pictus occur in the marls and basal Holywell, and at least one specimen of the zonal ammonite Metoicoceras geslinianum has been recorded from the basal beds. This is the upper Cenomanian marl interval associated with the wider Cenomanian–Turonian boundary succession at Ballard Cliff and one of the most important biostratigraphic levels in the whole Swanage Bay to Ballard Point succession.

Plenus Marls beds 1–8 (combined local thickness about 4.5 m)

The GCR confirms that all eight of Jefferies’ numbered subdivisions are identifiable at Punfield. The BGS quotes approximately 4.5 m for the local member. Gale’s original 1995 Figure 14 supplies a local Swanage graphic log of these divisions and the overlying chalk. The individual descriptions below are a qualitative reading of that local column; it gives no numerical table of eight separate thicknesses. The 4.5 m BGS estimate remains separately attributed, and no thickness is calculated from the scan or transferred from a neighbouring column.

Plenus Bed 1

The basal division is a relatively expanded marly interval with internal lighter and darker bands in Gale’s Swanage column. It rests above the sub-Plenus erosional boundary.

Plenus Bed 2

A thinner, more marly band caps Bed 1 and separates it from the more chalk-rich Bed 3.

Plenus Bed 3

A comparatively chalk-rich bed forms a distinct division above Bed 2; its upper contact is a prominent boundary in the local graphic log.

Plenus Bed 4

A thin marly division overlies Bed 3, beneath the next chalk-rich interval.

Plenus Bed 5

The chalk-rich interval between Beds 4 and 6 is retained as the fifth division, consistent with the GCR recognition of all eight beds. Its numeral is not clearly printed in the retrieved Swanage column, so no finer subdivision or measurement is inferred.

Plenus Bed 6

A thin, distinctly marly band separates the intervening chalk-rich division from Bed 7.

Plenus Bed 7

A comparatively thicker chalk-rich division occurs above Bed 6 and below the thin uppermost division.

Plenus Bed 8

The uppermost thin division completes the Plenus package below the overlying Melbourn Rock succession. No bed-specific fossil assemblage is inferred from the graphic alone.

Holywell Nodular Chalk Formation (above the Plenus Marls)

Bed SB26 — Lower Holywell Nodular Chalk / Basal Ballard Cliff Interval

Above the Plenus Marls, the lower part of the Holywell Nodular Chalk is washed clean on the last part of the accessible beach and then rises into steep, loose cliff faces. The base shows a weakly developed Melbourn Rock, and fallen blocks yield abundant shell-debris layers, flaser marl seams and intraclast beds. A standard succession of lower Turonian Mytiloides shell-beds can be reconstructed from these blocks, and a flint band around the level of the Glyndebourne Flints and Gun Gardens Main Marl has been recognized in the higher part of the accessible interval. The beds record more nodular, omission-prone chalk deposition than the Zig Zag below.

Melbourn Rock Member

The local GCR account describes a weakly developed Melbourn Rock above the Plenus Marls. It is a formal member of the Holywell Nodular Chalk Formation. Gale’s broader historical “Ballard Cliff Member” extends through the Meads Marls and must not be equated automatically with the narrower BGS Melbourn Rock Member; the published member boundary is difficult to place and is commonly related to Meads Marl 1 in the Southern Province.

Holywell Nodular Chalk Formation (higher marker horizons)

Gale’s 1995 Swanage column identifies the following local marl and fossil marker horizons above the basal nodular chalk. The descriptions retain his labels without transferring measurements or fossil lists from the neighbouring Compton Bay, Culver or Eastbourne columns. Meads Marls 1 and 2 are grouped together in that drawing, rather than given individually measured separations.

Meads Marl 1

The lower named marl of the pair labelled 1,2 in the local graphic log.

Meads Marl 2

The second named marl in the same locally grouped pair; no distinct thickness or spacing is assigned.

Meads Marl 3

A separate higher marl marker is shown above the 1,2 pair in the Swanage column.

Meads Marl 4

The next explicitly labelled marker lies above Meads Marl 3.

Meads Marl 6

A prominent higher marl is labelled 6. The figure does not individually label a local Meads Marl 5, so a separate unverified division is not inserted.

Holywell Marl 1

The first numbered Holywell marl lies above the Meads sequence.

Holywell Marl 1a

A separately labelled subsidiary marl occurs above Holywell Marl 1.

Roveacrinus Bed and Fagesia catinus level

The Swanage column marks this fossil horizon between the lower Holywell marls and Holywell Marl 4. The names here reflect the published marker attribution, not a claim that every loose fossil can be assigned to it.

Holywell Marl 4

The higher numbered Holywell marl is explicitly shown above the Roveacrinus/Fagesia level.

Compton Pebble Marl

Despite its geographic name, this marker is also explicitly correlated in Gale’s Swanage column above Holywell Marl 4. No Compton Bay bed thickness is transferred to Swanage.

New Pit Chalk Formation (Middle Turonian)

Bed SB27 — New Pit Chalk Formation

The New Pit Chalk at Ballard Cliff consists of massive white chalk with regularly spaced marl seams and relatively little flint. Historical collecting from air-weathered exposures produced a diverse fauna of echinoids and brachiopods. Much of the formation is now seen in loose bluffs and fallen blocks rather than in a continuously safe cliff face, but it represents the classic open-marine middle Turonian chalk facies between the more nodular Holywell and Lewes formations.

Lewes Nodular Chalk Formation (Middle To Upper Turonian, Lower Part Only Included Here)

Bed SB28 — Basal Lewes Nodular Chalk And Spurious Chalk Rock

Near Ballard Point the onset of the Lewes Nodular Chalk is marked by the yellow-green nodule beds of the Spurious Chalk Rock within the Terebratulina lata interval. Hardground surfaces of this horizon occur in many fallen blocks, and the bed marks a return to harder, more nodular chalk with repeated breaks in sedimentation. The lower Lewes was logged in the high, dangerous bluffs above the beach, where it forms a key part of the Ballard Point section even though access is difficult.

Bed SB29 — Lower Lewes Marker Marls And Lewes Tubular Flints At Ballard Point

The lower Lewes marker marls are well developed at Ballard Point, especially the Southerham, Caburn and Bridgewick marls, and the Lewes Tubular Flints are spectacularly developed in tough red and grey iron-stained nodular chalks. Fallen blocks from this interval are common on the beach. These are the highest beds included in the present Swanage Bay page; farther north, beyond Ballard Point, the chalk succession continues upward into younger units that are best treated separately.

Southerham Marls

The lower Lewes marker marls are identified in the published Ballard cliff log. No regional standard thickness is transferred here.

Caburn Marl

A separately named and locally recognised marl marker higher in the lower Lewes succession.

Bridgewick Marls

These marl markers are also recorded at Ballard Point and retained separately from the Southerham and Caburn levels.

Lewes Tubular Flints

Strong tubular flints occur in tough iron-stained nodular chalk. The GCR records abundant Gauthieria radiata in fallen blocks from this horizon, preserving the fallen-block provenance rather than implying an in-situ collecting bed.

Chalk Range Included Here: From The Basement Bed At Punfield Cove Through The Zig Zag Chalk, Plenus Marls, Holywell Nodular Chalk, New Pit Chalk And Lower Lewes Nodular Chalk To Ballard Point

Depositional Environment

The Swanage Bay to Ballard Point succession records a major long-term environmental transition. The Wessex Formation represents a largely non-marine alluvial plain with fluvial channels, levees, floodplain mudstones, calcrete-bearing palaeosols, plant-debris flows and freshwater to ephemeral standing-water habitats. The Vectis and basal Lower Greensand mark increasingly brackish to marginal-marine conditions, culminating in the mixed estuarine and marine fauna of the Punfield Marine Band. The Ferruginous Sands and Sandrock record shallowing marine sand systems with repeated erosion, pebble lags and strong lateral facies change. The Gault represents renewed open-marine muddy shelf deposition, the Foxmould and White Nothe members record glauconitic to calcareous sandy shelf sedimentation with major omission surfaces, and the Chalk of Ballard Cliff shows condensed but classic Cenomanian–Turonian offshore chalk deposition on the Dorset swell, including the boundary marls and nodular Turonian chalks beneath Ballard Point.

Total Thickness Covered Here

Treated as a composite section, Swanage Bay to Ballard Point includes about 700 m of Wealden Group beneath the bay, of which about 110 m of Wessex Formation was logged in 2018–2019; about 90 m of Lower Greensand in Ruffell’s 1992 reconstruction, distinct from the approximately 59 m older interpretation and the later expanded estimate of up to 170 m discussed above; roughly 44–45 m of Gault plus Upper Greensand at Punfield Cove; and a steeply dipping chalk section from the Basement Bed through the lower Lewes Nodular Chalk Formation at Ballard Point. It is therefore one of the best Dorset localities for following the change from non-marine Wealden facies to Aptian marginal-marine sands and then to fully marine Albian–Turonian shelf sedimentation.

References

Penn, S.J., Sweetman, S.C., Martill, D.M. & Coram, R.A. (2020). The Wessex Formation (Wealden Group, Lower Cretaceous) of Swanage Bay, southern England.
Ruffell, A.H. (1992). The Lower Greensand Group (Aptian–Albian) at Swanage: correlation with the Isle of Wight type section. Proceedings of the Ussher Society, 8, 74–76.
Ruffell, A.H. & Batten, D.J. (1994). Uppermost Wealden facies and Lower Greensand Group (Lower Cretaceous) in Dorset, southern England: correlation and palaeoenvironment.
Cleevely, R.J., Morris, N.J. & Bate, G. (1983). An ecological consideration of the Punfield Marine Band (Lower Aptian) Mollusca.
Gallois, R.W. & Owen, H.G. (2019). The stratigraphy of the Gault and Upper Greensand Formations (Albian Stage, Cretaceous) of the Dorset and East Devon Coast World Heritage Site, U.K.
Arkell, W.J. (1947). Geology of the Country around Weymouth, Swanage, Corfe and Lulworth.
Strahan, A. (1898). The Geology of the Isle of Purbeck and Weymouth.
Gale, A.S. (1995, 1996) on the Cenomanian–Turonian boundary interval, Plenus Marls and Ballard Cliff chalk succession.
Mortimore, R.N. & Pomerol, B. (1987, 1996) on lower Turonian marker marls, Spurious Chalk Rock and Ballard Cliff correlation.
JNCC Geological Conservation Review account: Handfast Point to Ballard Point.
British Geological Survey Lexicon entries: Wessex Formation, Vectis Formation, Atherfield Clay Formation, Ferruginous Sands Formation, Sandrock Formation, Gault Formation, Foxmould Member, White Nothe Member, Zig Zag Chalk Formation, Plenus Marls Member, Holywell Nodular Chalk Formation, New Pit Chalk Formation and Lewes Nodular Chalk Formation.