King’s Dyke Pit Fossil Hunting

1920s – Clay extraction in the future reserve pit
Clay working began in the old Central No. 1 pit. This is the pit later restored as the nature reserve, rather than a claim that every subsequent King’s Dyke working face opened at the same time.

March 1923 – Fish specimen collected
P. J. Phillips collected the King’s Dyke fish specimen now held as PETMG F34. Although historically labelled Leedsichthys, that identification was rejected in a later scientific revision.

1994 – Detailed Peterborough Member section published
J. D. Hudson and D. M. Martill published the King’s Dyke section measured in 1992–93. Its 55 numbered beds established a detailed reference for the Peterborough Member and for comparisons between Oxford Clay brickpits.

July 1994 – Unusual marine-reptile skeleton found
Alan Dawn found the skeleton subsequently named Pachycostasaurus dawni in the working quarry. The find became the type specimen, PETMG R338, and was important for its unusually thickened skeletal elements.

1995 – Former pit restored as a nature reserve
The worked-out Central No. 1 pit was restored as King’s Dyke Nature Reserve. This changed the use of the old excavation while preserving a setting for wildlife and managed geological education.

1996 – Pachycostasaurus dawni described
A. R. I. Cruickshank, D. M. Martill and L. F. Noè formally described the King’s Dyke holotype. Its dense, thickened ribs and vertebrae distinguished it from more familiar Oxford Clay marine reptiles.

2012 – Managed fossil collecting documented
The reserve’s designated collecting area and supplied fossiliferous clay were documented as a case study in managing geological collecting. The arrangement separated casual visitor collecting from operational quarry workings.

2013 – Historic fish identification revised
Jeff Liston reassessed PETMG F34 and rejected its referral to Leedsichthys. The specimen was treated more cautiously as an indeterminate suspension-feeding bony fish.

2019 – King’s Dyke sauropod material studied
Femke Holwerda, Mark Evans and Jeff Liston described Oxford Clay sauropod material including the King’s Dyke tail vertebra PETMG R272. This is the date of scientific publication; the specimen’s discovery date is not established.

This is the historical King’s Dyke working-quarry section measured in 1992–93 and published by Hudson and Martill in 1994. It is described from youngest to oldest and is not a log of the reserve’s transported fossil stockpile. The record does not establish that these faces remain exposed or accessible.

Bed numbers below follow Hudson and Martill (1994). Older Peterborough descriptions also use Callomon’s 1968 numbers, which are not interchangeable throughout the succession. This account is qualitative and unscaled: measurements are included only where their source association is clear, and omitted thicknesses must not be read as zero. The historical table’s available transcription leaves some thickness values, extra taxa beside Beds 6–8 and the precise within-bed position of the Bed 14 concretions uncertain. These details are omitted rather than inferred; the securely associated lithology, fossils and contacts are retained.

ANCHOLME GROUP

The marine mudstone succession belongs to the Ancholme Group. The Oxford Clay and underlying Kellaways formations are separate units within that group.

Oxford Clay Formation

The described Oxford Clay includes the Stewartby Member above the Peterborough Member. Their contrasting mudstone facies, shell-rich intervals and contacts are retained below rather than reduced to a single undivided clay unit.

Stewartby Member

These six unnumbered intervals lie above Peterborough Member Bed 55. They are listed in the source order from top to bottom; no new bed numbers or complete member thickness are implied.

Highest described calcareous mudstone
The uppermost recorded interval is blocky and calcareous, with 2.00 m seen. It contains Genicularia, Gryphaea and Procerithium, together with part of an articulated ichthyosaur cautiously identified as cf. Ophthalmosaurus. The exposed thickness is not the total member thickness.

White-weathering fissile shale
A fissile shale that weathers white follows below the highest mudstone. Its weathering is a distinguishing feature in the recorded face; no separate formal bed name is established.

Resistant fissile shale
This hard, fissile shale forms a prominent interval in the historical section.

Hard calcareous mudstone
Blocky, hard mudstone contains Procerithium, nuculoid bivalves and Meleagrinella.

Slightly fissile shelly shale
Compressed, pyritic ammonites occur with Meleagrinella, nuculoids, Mesosaccella and Procerithium.

Basal non-fissile mudstone
The lowest described Stewartby interval has a sharp base above Peterborough Member Bed 55. These six Stewartby intervals retain their source order without invented continuation bed numbers.

Peterborough Member

This is the former Lower Oxford Clay. Repeated changes between organic-rich shale, more blocky clay and thin shell concentrations record changing conditions at the seabed. Burrows, shell preservation and internal contacts are as important for recognising the beds as colour. The following 55 numbered descriptions refer only to the original measured section.

Bed 55: Brown shale at the member top
Fissile brown shale contains abundant Meleagrinella, together with nuculoid bivalves, Bositra, Dicroloma, Parainoceramus and a recorded fish scale. It is the highest numbered Peterborough Member bed in this section.

Bed 54: Shell-rich interval
A concentration dominated by Meleagrinella also contains nuculoid bivalves, interrupting the shale succession.

Bed 53: Brown fissile shale
The fauna resembles that of Bed 55. Wood carrying Parainoceramus adds a record of organic debris and attached shells to the marine assemblage.

Bed 52: Green blocky clay
Green clay breaks more blockily than the neighbouring fissile shales. Meleagrinella, nuculoids and shell debris are recorded.

Bed 51: Gradational shell concentration
A shelly interval with gradual boundaries is dominated by Meleagrinella, with nuculoids and the gastropod Procerithium. The transitions should not be drawn as sharp contacts.

Bed 50: Shelly shale
Bositra, Meleagrinella, Procerithium and Dicroloma occur with fish scales and wood in this shale.

Bed 49: Three blocky-clay and shelly-shale pairs
Three repeated pairs of blocky clay and shelly shale make up this interval. Individual sublayers are reported as 5–15 cm thick; that range is not the thickness of the whole bed. Procerithium is recorded in the shelly shale.

Bed 48: Sharp-based nuculoid concentration
A shell-rich layer rests on a sharp base and grades into the bed above. Nuculoid bivalves dominate, with Procerithium, Meleagrinella and Kosmoceras.

Bed 47: Blocky clay
The clay contains Meleagrinella, Procerithium and nuculoid bivalves. Its blocky fracture contrasts with the thin splitting of adjacent shales.

Bed 46: Fissile shale with a blockier middle
Nuculoids and shell fragments occur in fissile shale. Its central 15 cm is less shelly and more blocky than the rest of the bed; this measurement refers only to that internal portion.

Bed 45: Fissile shale passing into hard calcareous clay
Fissile shale at the base grades upwards into hard, blocky, calcareous clay and contains burrows. Recorded fossils include nuculoids, Bositra, Procerithium, Kosmoceras and Belemnotheutis.

Bed 44: Blue-toned calcareous clay
The calcareous clay has gradual contacts. Its lighter, more calcareous character is part of the repeated change between clay and organic-rich shale in the measured succession.

Bed 43: Less-fissile shelly shale
This shelly shale splits less readily than Bed 42 and has a gradational lower contact.

Bed 42: Brown fissile shale with pyritic debris
Shell debris is associated with pyrite. Kosmoceras, Hecticoceras, nuculoid bivalves and fish scales are recorded.

Bed 41: Clay changing from green to blue upwards
The clay becomes more blue-toned upwards from a greenish lower part. Both joined and separated nuculoid valves occur in varied orientations, with Procerithium and Dicroloma.

Bed 40: Shale becoming more fissile upwards
Brown shale becomes more thinly splitting towards its top. The deposit-feeder assemblage includes Procerithium, fragments of Kosmoceras and shell debris. The upper surface is only slightly burrowed.

Bed 39: Green clay above the marker interval
Large perisphinctid ammonites form a shell layer at the base of the green clay. Other recorded material includes Kosmoceras, Genicularia and coprolites.

Bed 38: Acutistriatum interval
Brown shale becomes especially fissile towards its top. Large burrows descend from the upper surface and are filled with greenish clay; the trace fossil Chondrites also occurs. Abundant microconchs of Kosmoceras phaeinum occur with coarsely ribbed Kosmoceras, nuculoid bivalves, Parainoceramus and perisphinctid ammonites. This is the upper part of the formal Acutistriatum-Comptoni Bed.

Bed 37: Comptoni interval
A nuculoid-rich shell concentration has a gradational base and contains Binatisphinctes, Cylindroteuthis and Procerithium. It forms the lower part of the Acutistriatum-Comptoni Bed. BGS defines the combined marker from the base of Bed 37 to the top of Bed 38 and records 0.45 m at the type section; that value must not be assigned to either component alone.

Bed 36: Upward decline in shells
The shell content of this brown shale decreases upwards. It has a deposit-feeder assemblage, with Erymnoceras recorded at the base.

Bed 35: Sharp-based shell concentration
Nuculoids, Meleagrinella and Procerithium occur in a concentration that becomes less shelly upwards.

Bed 34: Thin fissile shale, 0.05 m
Kosmoceras occurs in shale with burrows in its upper part. The quoted thickness belongs to this historical measured section.

Bed 33: Shell concentration, 0.06 m
A Meleagrinella shell concentration with abundant shell debris and nuculoid bivalves grades upwards into Bed 34.

Bed 32: Darker blocky clay, 0.30 m
This comparatively fossil-poor clay breaks blockily and contrasts with the more shell-rich beds above and below.

Bed 31: Pale green-grey clay, 0.20 m
Nuculoids occur in clay that is more fissile than Bed 30.

Bed 30: Burrowed shell concentration
Pale-weathering shelly material contains Meleagrinella, Procerithium and nuculoids. Large Erymnoceras are recorded towards the top.

Bed 29: Green clay with articulated shells
Joined nuculoid valves occur with Thracia, Meleagrinella and Genicularia. Burrows extend from the base of this green clay.

Bed 28: Deposit-feeder shale
Nuculoid bivalves characterise the shale. Green-filled burrows descend into it from the overlying material, providing a visible contact-related feature.

Bed 27: Concentrated bivalve debris
An accumulation of Meleagrinella and abundant shell debris forms a distinct shell-rich interval.

Bed 26: Nuculoid-bearing shale
The shale records a deposit-feeder assemblage containing nuculoid bivalves.

Bed 25: Repeated shell concentration
The original description compares this concentration with Bed 23. That comparison refers to the same measured King’s Dyke section, rather than establishing a separate named bed or a correlation to another pit.

Bed 24: Dark-weathering, burrowed grey-green shale
The grey-green shale weathers dark and has a deposit-feeder assemblage. Burrows, abundant wood, Thracia and coarsely ribbed Kosmoceras are recorded.

Bed 23: Sparse pyritic shell concentration
The pyritic concentration includes winnowed shell debris, belemnites, wood and Kosmoceras, together with a recorded tooth of the fish Hypsocormus. The occurrence is a specific quarry-bed record, not a prediction of visitor-stockpile finds.

Bed 22: Less-fissile shale
The shale is less fissile than Bed 21 and has a gradual lower boundary.

Bed 21: Shelly fissile shale
Abundant nuculoid bivalves occur in readily splitting shale.

Bed 20: Tough green shale
The tough shale represents another interval characterised by deposit-feeding bottom-dwellers.

Bed 19: Shell concentration in clay
The shell-rich layer retains a clay matrix. Pyrite is concentrated through the middle 3 cm; this is an internal feature, not a total bed thickness.

Bed 18: Dark Bed
Weakly fissile shale contains wispy lamination, tentatively interpreted as burrow-related in the original description, and weathers conspicuously dark grey. “Dark Bed” is an informal marker name within the member, not a separate formation.

Bed 17: Pyritic nuculoid concentration
Nuculoid shells and pyrite form a distinct concentration between shale intervals.

Bed 16: Deposit-feeder shale
The shale resembles Bed 14 and records a deposit-feeder assemblage. The similarity does not make the two intervals one bed.

Bed 15: Pale-weathering fissile shale
A nuculoid-rich concentration occupies the upper 2 cm. Retain the distinction between the thin shell-rich top and the shale beneath.

Bed 14: Weakly fissile shale with septarian concretions
Fairly uniform, weakly fissile shale contains rather inconspicuous large burrows and relatively sparse fossils, with a deposit-feeder assemblage. Occasional calcareous and pyritic septarian concretions reach 30 cm in diameter and contain well-preserved juvenile Meleagrinella.

Bed 13: Shell concentration with wood
Rounded wood fragments occur in the shelly interval. This bed marks the top of the Jason Subzone in the source’s correlation scheme.

Bed 12: Organic-rich shale
The shale is more fissile in its lower part and contains ammonites.

Bed 11: Oyster and bivalve concentration
Gryphaea and Grammatodon occur in a concentrated shell layer.

Bed 10: Organic-rich shale and septarian concretions
Fissile shale contains abundant ammonites and large calcareous septarian concretions, with burrows towards the top. The concretions are a distinctive feature of this original quarry horizon.

Bed 9: Pyritic oyster concentration
Gryphaea occurs in a pyritic shell-rich interval.

Bed 8: Dark ammonite-bearing shale
Dark, organic-rich shale is fissile and contains ammonites.

Bed 7: Shell concentration with a pyritic top
Gryphaea and Pinna are securely associated with this concentration. Its upper part is pyritic.

Bed 6: Grey fissile shale
Abundant Kosmoceras occurs in the grey, thinly splitting shale.

Bed 5: Oyster shell concentration
Gryphaea valves occur both in life position and overturned, with belemnites, ammonites and wood.

Bed 4: Brown shaly clay
Overturned Gryphaea valves occur in brown clay with a shaly character.

Bed 3: Pyritic oyster concentration
Overturned Gryphaea valves and belemnites occur in a pyritic concentration.

Bed 2: Olive-brown shaly clay
The lower contact is gradual, contrasting with the sharp base of Bed 1 below.

Bed 1: Basal silty clay
Silty clay has a sharp lower contact above the Kellaways strata. This is the lowest numbered Peterborough Member bed in the historical log.

Beds 1–13 form the informal “Gryphaea and Reptile Beds” in the published scheme. This name is not a guarantee of vertebrate material in every bed or in the visitor stockpile. Particular historic skeletons depend on their recorded original bed and quarry provenance.

Kellaways Formation

Beneath Peterborough Member Bed 1, the historical section records the following six unnumbered intervals, again from top to bottom. They retain the sandy and silty basal context without assigning an unverified member rank or a full formation thickness.

Upper shell-rich fine sand, 0.14 m
Fine sand is locally cemented to calcareous sandstone. It contains Gryphaea, some overturned, together with belemnites, ammonites, coprolites and wood immediately beneath the numbered Oxford Clay succession.

Silty clay, 0.06 m
A thin, finer-grained layer separates the shell-rich sand above from the concentrated cephalopod material below.

Belemnite–ammonite lag, 0.02 m
A very thin concentration contains belemnites and ammonites. It is a fossil-rich lag, not evidence that the entire underlying formation is only this thick.

Upward-fining silt and clay, 0.15 m
The sediment becomes finer upwards within this interval, retaining a grain-size change absent from a simple formation-name list.

Irregular shell pockets, up to 0.10 m
Discontinuous pockets contain abundant belemnites, wood and overturned Gryphaea. The value describes local pocket thickness rather than a uniform continuous bed.

Lowest exposed clayey silt, about 1.5 m seen
Clayey silt extends to the lower limit of the recorded exposure. Its full thickness was not established; the visible interval must not be labelled as the complete Kellaways Formation.

References
Hudson, J. D. and Martill, D. M. (1994), The Peterborough Member (Callovian, Middle Jurassic) of the Oxford Clay Formation at Peterborough, UK. Journal of the Geological Society 151, 113–124, especially Table 1.
BGS Lexicon: Oxford Clay Formation; Peterborough Member; Acutistriatum-Comptoni Bed.
Horton and colleagues (1974), The geology of Peterborough. Report of the Institute of Geological Sciences 73/12.
British Middle Jurassic Stratigraphy, GCR Volume 26: Peterborough Brickpits.