Charton Bay Fossil Hunting

19th century onwards – the Humble Rocks to Charton Bay coast became recognised as part of the classic Axmouth–Lyme Regis undercliff succession
The coast west of Pinhay Bay through Humble Rocks and Charton Bay became important as part of the great Axmouth–Lyme Regis undercliff belt, where Cretaceous Upper Greensand and Chalk rest unconformably on Lower Jurassic clays. This relationship helped make the stretch geologically important even where fossil collecting was less famous than at Lyme Regis itself. [oai_citation:1‡wessexcoastgeology.soton.ac.uk](https://wessexcoastgeology.soton.ac.uk/Lyme-Regis-Westward.htm?utm_source=chatgpt.com)

22 June 1969 – major landslide destroyed the old cart road down to Charton Bay
One of the best-documented events in the history of Charton Bay was the landslide of 22 June 1969, which broke the old cart road to the shore with a sheer drop of about 14 metres. Ian West notes that this transformed access to the bay, while later GCR work treated it as an important example of planar sliding within the undercliff system. [oai_citation:2‡wessexcoastgeology.soton.ac.uk](https://wessexcoastgeology.soton.ac.uk/Lyme-Regis-Westward.htm?utm_source=chatgpt.com)

1986 – Pitts showed that Charton Bay has an unusual two-tiered undercliff
Pitts’ work demonstrated that Charton Bay is unusual because it has two separate landslips, one above the other, within cliffs about 127 metres high. The lower undercliff was interpreted as the recent 1969 feature, while the upper undercliff was considered much older. This is one of the key scientific milestones for understanding the bay. [oai_citation:3‡geoguide.scottishgeologytrust.org](https://geoguide.scottishgeologytrust.org/p/gcr33/gcr33_axmouth?utm_source=chatgpt.com)

1986 – a partial ichthyosaur from Charton Bay was recorded from the pre-planorbis Beds
The Lyme Regis GCR account notes that a partial ichthyosaur in the Philpot Museum from Charton Bay apparently came from the pre-planorbis Beds, well below the usual reptile-bearing beds. That makes it one of the clearest fossil records tied specifically to Charton Bay and an especially interesting one stratigraphically. [oai_citation:4‡geoguide.scottishgeologytrust.org](https://geoguide.scottishgeologytrust.org/p/gcr10/gcr10_lymeregis?utm_source=chatgpt.com)

Late 20th century to modern work – Charton Bay remained important mainly as a specialist stratigraphic and slope-failure site
Modern geological accounts emphasise that Charton Bay is more important for specialists than for general collecting, especially because the Penarth Group and White Lias exposures there are often degraded by landsliding and vegetation. The site is still useful for comparison with Pinhay Bay and for understanding the landslide and undercliff history of the Devon–Dorset coast. [oai_citation:5‡wessexcoastgeology.soton.ac.uk](https://wessexcoastgeology.soton.ac.uk/Lyme-Regis-Westward.htm?utm_source=chatgpt.com)

Modern understanding – the Humble Rocks to Charton Bay stretch is better known for geology than for a long list of named fossil discoveries
Unlike Lyme Regis or Charmouth, this stretch does not seem to have a rich published list of dated named specimen discoveries from the exact locality. Its importance lies more in the combination of Lower Jurassic and Penarth Group exposures, unusual undercliff morphology, and the rare record of reptile material from unexpectedly low in the succession. [oai_citation:6‡geoguide.scottishgeologytrust.org](https://geoguide.scottishgeologytrust.org/p/gcr10/gcr10_lymeregis?utm_source=chatgpt.com)

Section Architecture

This is not a single simple cliff log. The useful geology is distributed across three linked but different exposure styles: the Blue Anchor cliff and degraded undercliff exposures in Charton Bay itself; large slipped blocks at beach level west of the Blue Anchor cliff that contain the Lilstock Formation–Blue Lias junction and the Triassic–Jurassic boundary interval; and the eastern end of the bay at Humble Rocks, where detached lower Jurassic blocks are caught up among landslipped Cretaceous Chalk and Upper Greensand. The coast is therefore a genuinely composite locality and should not be forced into a false continuous face.

Numbering Note

The CB numbers below are site-use numbers. Formal published bed numbers are retained exactly where they can be tied securely to the Charton Bay and east Devon lower Jurassic succession, especially the H-bed numbering of Lang and later workers. In the Langport Member and in the detached Humble Rocks blocks, the subdivisions used here are practical lithological units based directly on published composite logs and recent re-interpretation of the section, not invented formal bed names.

MERCIA MUDSTONE GROUP

Blue Anchor Formation (Upper Triassic: latest Norian–Rhaetian)

Bed CB1 – Highest Blue Anchor Formation Beneath The Penarth Erosion Surface

The highest exposed Blue Anchor beds in Charton Bay are pale green-grey to grey dolomitic silty mudstones, muddy siltstones and thin splintery porcellanous or dolomitic limestone beds. In the wider Charton–Pinhay tract the formation is fully developed, but within the present locality the uppermost part is the critical interval because it is cut by the basal Penarth erosion surface and much repeated by faulting and landslip. The top is irregular, strongly burrowed and locally penetrated by shallow scours and burrow systems later filled by basal Westbury bone-bed sediment. No Williton Member is recognized on the Devon coast, and it is generally taken to have been removed by erosion before Westbury deposition. Depositional Environment: restricted marginal-marine to supratidal mudflat and sabkha conditions with increasing marine influence upward, followed by firmground development and erosion at the onset of the Rhaetian transgression.

PENARTH GROUP

Westbury Formation (Rhaetian)

Bed CB2 – Basal Burrow-Fill Bone-Bed And Pebbly Grit Complex

The basal Westbury Formation at Charton Bay is regularly exposed as a pebbly calcareous grit and bone-bed resting on an irregular, intensely burrowed erosion surface cut into the top of the Blue Anchor Formation. This is not just a thin lag seam: bone-bed sediment occurs in Thalassinoides burrow systems, burrow fills, desiccation cracks and shallow scour hollows that penetrate the top c. 0.3 m of the Blue Anchor. Lithologically it is a pebbly grey mudstone to gritty calcareous bed with angular green mudstone clasts, quartz grains of which many are rounded and frosted, and abundant phosphatic vertebrate debris. The fauna is unusually rich for a basal Rhaetian bone bed and includes sharks and bony fishes in a taphonomically mixed assemblage. Marker-Bed Significance: this is the classic Charton Bay Rhaetian bone bed and one of the most important transgressive horizons on the east Devon coast. Depositional Environment: storm-reworked transgressive lag laid down during abrupt marine flooding of the former Blue Anchor mudflat surface.

Bed CB3 – Main Westbury Black Shales And Thin Limestone Interbeds

Above the basal bone-bed complex, the Westbury Formation continues in dark grey to black shales and mudstones with subordinate thin limestones and fossiliferous layers. At Charton Bay the lower c. 3 m has been the best described in detail, but the unit as a whole is commonly degraded and obscured in the modern cliff and undercliff. The macrofauna is dominated by thin-shelled bivalves characteristic of quiet-water brackish to marine conditions; ammonites and brachiopods are absent. Compared with the basal lag below, these beds record much lower energy and more sustained muddy deposition, though still within a restricted shallow shelf or embayment. Depositional Environment: quiet-water brackish to shallow-marine mud accumulation after the initial Rhaetian transgression.

Lilstock Formation (Rhaetian)

Cotham Member

Bed CB4 – Degraded Cotham Member Lagoonal Mudstones And Thin Limestones

The Cotham Member is present at Charton Bay, but in the modern locality it is seen mainly in degraded undercliff exposures to the east and is too disturbed for a reliable detailed local bed-by-bed log. It consists of grey and grey-green shales, silty mudstones and thin limestones passing upward toward the better-exposed Langport Member above. In regional terms these beds represent the shallow lagoonal and intermittently emergent phase between the dark marine Westbury shales and the pale micritic “White Lias” facies above. At Charton Bay the member is important as part of the transition, but the literature does not support a finer modern foreshore subdivision here without over-interpreting poor exposure.

Langport Member

Langport Member Note

The Charton Bay Langport Member is the classical east Devon “White Lias” facies. Current cliffs expose about the upper 7.2 m, and the whole member at this locality is generally taken to have been about 7.6 m thick when fully visible. The units below are practical site-use subdivisions based on the published composite Charton Bay section and recent work on soft-sediment deformation; they are not formal bed names.

Bed CB5 – Lower Porcellanous And Slumped Limestones With Hardground Surfaces

The lower exposed Langport succession consists of off-white fine-grained limestones, commonly porcellanous and hard, separated by thin marl partings and broken by repeated hardground surfaces. Parallel-bedded limestone alternates with slumped or remobilised units, and some bed tops are stained, corrugated, solution-marked or irregularly channelled. These beds show that the lower Langport sea floor was repeatedly lithified, exposed, bored or burrowed, and then partially reworked. Typical Fossils: fossils are generally sparse, but shell concentrations at some levels include bivalves, brachiopods, gastropods, serpulids and rare corals. Depositional Environment: very shallow warm-water marine lagoon or carbonate-flat sedimentation with repeated pauses, firmground development and local gravitational remobilisation.

Bed CB6 – Middle Nodular And Wavy-Laminated Limestones With Marl Partings

Nodular limestones with thin marl partings pass upward into wavy laminated micritic limestones. These beds show load structures, local ripple-like lamination, small slump folds and, in places, fluid-escape structures. Recent work has shown that one of the important Charton Bay liquefaction and slump levels lies within this middle part of the member, where originally bedded micrite has been partially disorganised but not wholly destroyed. Interpretation: shallow subaqueous carbonate deposition repeatedly destabilised by soft-sediment deformation, probably during rapid remobilisation of semi-lithified lagoonal carbonate sheets.

Bed CB7 – Upper Remobilised Clast-Rich Limestones And Main Slump Bed

Higher in the Langport Member, remobilised limestones with abundant intraclasts, shell debris and bored pebbles rest on a hardground and pass upward into slumped limestones with abundant angular clasts, some very large, concentrated especially toward the base of the unit. This is the main clast-rich slump interval in the modern Charton Bay section and one of the most distinctive deformation levels in the locality. The limestone sheets had clearly already lithified enough to fracture into slabs, pebbles and larger blocks before being redeposited. Depositional Environment: shallow marine carbonate flat or lagoon margin subject to repeated erosion, collapse and redeposition of semi-consolidated carbonate sediment.

Bed CB8 – Upper Finely Laminated Limestones And Sun Bed

The uppermost Langport Member consists of finer, pale wavy laminated limestones culminating in the Sun Bed, the uppermost persistent pale micritic limestone beneath the Blue Lias. The Sun Bed forms the key local datum at the top of the Penarth Group and is overlain by the basal Blue Lias mudstones on an irregular and locally burrowed surface. The uppermost Langport limestones at Charton Bay are the clearest expression of the east Devon White Lias facies: pale, dense, micritic and strongly laterally variable, yet repeatedly marked by emergence, shallow-water reworking and minor soft-sediment collapse. Depositional Environment: very shallow marine lagoon or carbonate flat with repeated emersion, intermittent drainage and rapid return to shallow subaqueous carbonate precipitation.

Total Thickness Of The Langport Member At Charton Bay: About 7.2 Metres Currently Exposed, With The Original Full Local Thickness Estimated At Around 7.6 Metres

LIAS GROUP

Blue Lias Formation (Hettangian)

Blue Lias Numbering Note

The basal Blue Lias at Charton Bay is best seen in large slipped blocks west of the Blue Anchor cliff, not as a simple upright cliff section. Formal H-bed numbers are retained where the literature supports them, but the units below are grouped into practical packages because the locality is landslipped and discontinuous.

Bed CB9 – Basal Blue Lias Paper Shale And Lower Pre-planorbis Beds (Beds H1–H24, grouped)

The Blue Lias begins sharply above the Sun Bed with the dark laminated Paper Shale, the equivalent of Bed H1, draping the irregular top of the White Lias and in places associated with intraformational conglomeratic material. The Paper Shale is organic-rich, finely laminated and records a rapid environmental change from shallow carbonate-flat conditions below to deeper, muddier marine conditions above. The overlying lower limestones and calcareous mudstones continue the pre-planorbis basal Blue Lias succession and are also well displayed in the large slipped boundary blocks. In the east Devon coast sections these lowest beds show syndepositional folding and small growth faults, especially in and just above the Paper Shale. Interpretation: rapid transgression and establishment of laminated offshore mud deposition under a stable, oxygen-poor lower water column, followed by the beginning of the classic limestone–mudstone Blue Lias rhythm.

Bed CB10 – Earliest Ammonite Boundary Interval, Beds H25–H29

This is the critical Triassic–Jurassic boundary interval at Charton Bay. In the east Devon succession the base of the Jurassic is still placed with some uncertainty within Bed H25, and there may be a small non-sequence below the first ammonites. Small crushed psiloceratids and likely Neophyllites occur in Beds H25–H26, and the classic large slipped block at Charton Bay shows the first ammonites immediately below the 11th limestone of the succeeding Blue Lias. Slightly higher, about 0.18 m above the base of Bed H29, the plicatulum Biohorizon is represented by forms such as Psiloceras cf. plicatulum and P. ex grp. sampsoni. Stratigraphic Significance: this is one of the best exposed British examples of the practical Triassic–Jurassic boundary interval in large slipped blocks.

Bed CB11 – Higher Hettangian Blue Lias Blocks To The Lower Liasicus Chronozone

Above the earliest psiloceratid boundary beds, the Charton Bay slipped blocks continue upward through more Blue Lias limestone–mudstone couplets to at least the lower Liasicus Chronozone. These higher Hettangian beds are not exposed as a single measurable cliff log, but they show that the Charton Bay boundary block is not restricted to the very lowest Jurassic. The lithology remains typical Blue Lias: thin limestones alternating with calcareous mudstone and shale in a fully marine shelf setting.

Bed CB12 – Detached Higher Blue Lias Blocks In The Humble Point Landslip Complex

Elsewhere in the wider Charton–Humble Point landslip ground, detached Blue Lias blocks and old collections indicate higher Hettangian levels above the main boundary section. These include evidence of the Portlocki Subchronozone, notably Psilophyllites hagenowi from the north side of the road descending from Rousdon to the shore at Humble Point, and rare loose blocks as high as the early Bucklandi Chronozone, including ?Metophioceras. These finds are real but ex situ within the landslip complex and should not be turned into a spurious continuous local cliff log.

Charmouth Mudstone Formation (Lower Sinemurian)

Shales-with-Beef Member

Bed CB13 – Western Humble Rocks Detached Outcrop, Sauzeanum Subchronozone (Level Of Bed 70)

East of the in-situ Bucklandi-zone Dowlands foreshore and toward Humble Rocks, the western detached lower Jurassic outcrop caught up in the landslip complex yields a fauna indicating the Sauzeanum Subchronozone and is correlated with the level of Bed 70. By correlation with the better-known east Devon succession, this level corresponds to the Pararnioceras alcinoeforme bed and adjacent Arnioceras–Euagassiceras-bearing horizons of the Shales-with-Beef Member. Lithologically these detached beds are represented by shale with limestone nodules and septarian concretionary material rather than by the thin limestone–mudstone couplets of the Blue Lias below. Interpretation: a detached lower Sinemurian marine mudstone block preserved within the Cretaceous landslip complex at the eastern end of Charton Bay.

Bed CB14 – Central Humble Rocks Detached Outcrop, ?Brooki Subchronozone

The central detached outcrop at Humble Rocks is less securely placed, but the fauna indicates ?Brooki Subchronozone age. Caenisites has been recorded from the comparable central detached Shales-with-Beef outcrop, while the absence of Microderoceras and Promicroceras means that higher placement is not demonstrated. This is therefore best treated conservatively as a probable brooki-level lower Sinemurian block within the landslip complex, not as an in-situ member base or top.

Bed CB15 – Eastern Humble Rocks Detached Outcrop, Birchi Subchronozone (Level Of Bed 76)

The eastern detached outcrop corresponds to the level of Bed 76 and indicates the Birchi Subchronozone. Loose concretions and nodules from this area have yielded Promicroceras capricornoides and Caenisites subturneri from just above the Birchi Tabular Bed level, showing that the eastern Humble Rocks blocks represent the higher part of the lower Sinemurian Shales-with-Beef succession. In the full east Devon–West Dorset sequence this is the interval of the Birchi Nodular and Birchi Tabular beds, but at Humble Rocks it is present only as detached blocks and loose nodular debris among landslipped Cretaceous masses.

Bed CB16 – Loose Early Obtusum-Subchronozone Material

Very fragmentary loose material from the Humble Rocks–Charton Bay tract indicates that the lowest part of the Obtusum Chronozone may also be present beneath the local Cretaceous unconformity, but only as beach blocks and not as any continuous exposure. This material probably represents the highest preserved lower Jurassic levels in the immediate tract covered here.

Depositional Environment

The Humble Rocks–Charton Bay succession records a major environmental shift across the latest Triassic and earliest Jurassic, later complicated by landslip transport. The highest Blue Anchor Formation represents restricted marginal-marine mudflat and sabkha conditions. The basal Westbury bone-bed records storm-reworked marine flooding across that surface, followed by quiet muddy brackish to shallow-marine Westbury deposition. The Cotham Member marks a shallower lagoonal phase, and the Langport Member records very shallow warm-water carbonate lagoons and flats subject to repeated lithification, hardground development, soft-sediment collapse and short-lived emergence. The basal Blue Lias records abrupt deepening and establishment of organic-rich offshore mud deposition, followed by more normal marine limestone–mudstone couplets through the Hettangian. The detached Humble Rocks blocks belong to the lower Sinemurian Shales-with-Beef facies of the Charmouth Mudstone Formation and represent deeper, more continuously muddy marine shelf conditions preserved only as landslip-derived outliers beneath the Cretaceous undercliff.

Total Thickness Note

No honest single total thickness can be given for this locality because it is a structurally disturbed composite section. What can be stated securely is that the locality includes the highest Blue Anchor beds, the full Penarth transition into the upper c. 7.2–7.6 m of the Langport Member at Charton Bay, large slipped basal Blue Lias blocks ranging from the Paper Shale through at least the lower Liasicus Chronozone, and detached Shales-with-Beef blocks at Humble Rocks representing the Sauzeanum, ?Brooki and Birchi subchronozones, with loose material reaching into the lowest Obtusum Subchronozone.

References

Hallam, A. (1960). The White Lias of the Devon coast.
Lang, W.D. and co-authors (1923, 1924) and Lang, W.D. & Spath, L.F. (1926) on the Blue Lias bed numbering and lower Jurassic ammonite succession of the east Devon coast.
Page, K.N. (2002). The succession of ammonite faunas in the Jurassic of the east Devon coast.
Wignall, P.B. (2001). Sedimentology of the Triassic–Jurassic boundary beds in Pinhay Bay (Devon, SW England).
Gallois, R.W. (2009). Lithostratigraphy of the Penarth Group of the Severn Estuary region and Somerset coast, including east Devon coastal sections.
Gallois, R.W. & Paul, C.R.C. on the highest Blue Lias and basal Charmouth Mudstone of the east Devon coast.
Korneisel, D., Gallois, R.W., Duffin, C.J. & Benton, M.J. (2015). Latest Triassic marine sharks and bony fishes from a bone bed preserved in a burrow system, from Devon, UK.
Laborde-Casadaban, J. and co-authors (2021). Do soft sediment deformations in the Late Triassic and Early Jurassic of SW Britain result from seismic activity? Evidence from the Langport Member at Charton Bay and Pinhay Bay.
Edwards, R.A. & Gallois, R.W. and later British Geological Survey memoir summaries for the Sidmouth district and the south Dorset–south-east Devon World Heritage Coast.
British Geological Survey Lexicon of Named Rock Units: Blue Anchor Formation, Westbury Formation, Lilstock Formation, Cotham Member, Langport Member, Blue Lias Formation, Charmouth Mudstone Formation and Shales-with-Beef Member.
Geological Conservation Review accounts for the Blue Anchor–Lyme Regis coast, Pinhay Bay and adjacent east Devon Lower Jurassic sections.