Cayton Bay

The traditional Millepore Bed is a calcareous marine sandstone/limestone interval within this member, not a separate formation. Bryozoan-rich rock is recorded at Osgodby Nab. The much fuller Yons Nab log should not be transferred here.

Sandstone and finer non-marine beds overlie the marine Lebberston interval at the nab. The classic Gristhorpe Plant Bed farther east is not established as a collectable plant bed at this exact exposure by these sources.

At High Red Cliff, more than 1 m of grey silty sandstone is exposed immediately beneath the Cornbrash. Burrows descending from the marine contact include Rhizocorallium. This partial exposure does not represent the full Scalby succession.

The local Cornbrash is Lower Callovian, rather than the Bathonian Lower Cornbrash of southern England. The historical Fleet Member name is superseded by Upper Cornbrash. Published alpha subdivisions vary laterally.

Osgodby Nab south side: alpha 1, alpha 3 and the upper transition

Alpha 1 is 0.79 m of red-weathering berthierine-ooid-bearing limestone with bivalves and rare Macrocephalites. Alpha 2 is absent. Alpha 3 is only 0.08 m of sandy bioclastic limestone with reworked ooidal pebbles, Lopha marshii and the ammonite Macrocephalites kamptus. Alpha 4 is the shelly silty transition assigned in this account to basal Cayton Clay; Meleagrinella, Lopha and Nanogyra occur.

High Red Cliff: a different alpha succession

At High Red Cliff alpha 3 is absent. The comparative coastal log describes alpha 1 as 0.14–0.37 m of iron-rich limestone, alpha 2 as about 0.15 m of pale, shelly limestone with variable ooids, and alpha 4 as a thin silty or sandy shale transition. These ranges belong to the published coastal comparison, not a newly measured constant section. The historical scheme included alpha 4 in Cornbrash; the modern limestone-to-shelly-mudstone boundary places the transition with basal Cayton Clay.

Younger Callovian formations without an invented group

Cayton Clay and Osgodby are formations; the BGS Lexicon does not assign either to a parent group. The Great Oolite bar above applies to Cornbrash only.

At the south side of Osgodby Nab the GCR describes about 9.6 m in beta 1–3; berthierine-ooidal beta 2 includes Kepplerites and Proplanulites. BGS gives 3.5 m of Redcliff Rock in its Osgodby Nab type-section account. The discrepancy remains unresolved: the BGS text does not explicitly identify a north-side measurement, so the values cannot simply be reconciled by assuming opposite sides of the nab.

High Red Cliff beta 4 and possible beta 5

Impersistent pale-weathering berthierine-ooidal sandstone, beta 4, reaches 0.55 m and contains shelly concretions with small bivalves and rare possible Proplanulites. A possible beta 5 soft sandstone, up to 0.65 m, remains uncertain. Neither unit should be drawn as continuously present across the bay.

On the south side of Osgodby Nab the 3.8 m member includes gamma 1 fine- to medium-grained sandstone with clay wisps and bivalves including Chlamys and Modiolus, followed by gamma 2 flaggy-weathering siltstone with rare bivalves, belemnites and Erymnoceras. The member is absent at High Red Cliff.

Condensed iron-ooid-bearing marine beds occur at several separate exposures. The 0.75 m north-side Osgodby log is not a measured thickness for the south side. High Red Cliff has a hard greenish iron-ooid-bearing unit above its truncated older Osgodby succession.

Waterworks foreshore: lower and upper Hackness Rock

At the waterworks exposure, the lower approximately 0.6 m is hard berthierine-ooidal sandstone with Kosmoceras and Binatisphinctes. The upper approximately 0.6 m is ooidal sandstone/oolite yielding Quenstedtoceras, Peltoceras (Peltomorphites) and Hecticoceras. These are local observations, not thicknesses for every Hackness Rock outcrop.

Upper Oxford Clay in the Cleveland Basin straddles the latest Callovian–earliest Oxfordian interval. Its presence does not mean every fossil found loose in Cayton Bay came from Oxford Clay. The sandy Osgodby beds lie beneath it in normal stratigraphic order.

Waterworks basal Oxford Clay: published Bed 5

A 0.45 m black iron-rich siltstone with calcareous nodules yields Quenstedtoceras paucicostatum and possible Longaeviceras. This is terminal Callovian evidence, not proof of the Oxfordian boundary at that bed. The basal Oxfordian Scarburgense interval is expected in the succession but was not specifically fossil-confirmed in this account.

Transition to the Lower Calcareous Grit

The change from muddy Oxford Clay to sandy, sponge-spicule-rich sediment is gradual. At Tenants’ Cliff the lowest numbered bed is still strongly muddy; the lithological formation boundary is not a sharp, universally recognisable surface.

These are the older fossiliferous concretion beds, distinct from the younger Saintoft Ball Beds. Many historical museum specimens labelled simply “Scarborough Ball Beds” were later traced or inferred to originate here; label uncertainty must not be erased.

The younger Saintoft beds cap the measured Tenants’ Cliff succession. The famous large Ball Beds concretions seen at Filey are not exposed in this Cayton section.

Quaternary cover and active landslides

Till and landslide debris obscure and mix the Jurassic outcrops. The Knipe Point and Cayton Cliff instability demonstrates why an old description of a particular bedrock exposure as stable cannot be turned into a modern assurance about the cliff or access route.