Stratum.black
Oxford Clay Formation — Oxford Clay Formation
Oxford Clay Formation — Wilson44691, Wikimedia Commons, Public domain (US)

Formation · Jurassic

Oxford Clay Formation

Middle Jurassic unit, Cambridgeshire · Bedfordshire · Oxfordshire · Wiltshire

The Oxford Clay of the English Midlands and Dorset is the Middle–Late Jurassic marine clay of the Peterborough brick pits, source of the marine reptiles Liopleurodon, Cryptoclidus and Ophthalmosaurus, the giant fish Leedsichthys, and the ubiquitous crushed ammonite Kosmoceras. Collectors hold pyritised Kosmoceras, belemnites and reptile teeth; new material is scarce since the pits closed. Kosmoceras with its shell preserved as pyrite is prone to decay, so keep it dry.

CountryUnited Kingdom
RegionCambridgeshire, Bedfordshire, Oxfordshire, Wiltshire, Dorset
AgeCallovian, Middle Jurassic
Age range~165–157 Ma
GroupAncholme Group
Macrostrat rankFm· Macrostrat
Macrostrat age165–155 Ma· Macrostrat
PBDB collections94 collections, 370 occurrences· Paleobiology Database

Collecting and legality

The classic Peterborough brick pits are largely closed or restored; the few working pits require company permission and insurance. Beach exposures at Weymouth follow the Jurassic Coast code. Old brick-pit collections (the Leeds Collection era) are the source of most reptile material in trade.

Lithology and setting

Grey-brown fissile mudstone with pyritised and crushed ammonites, laid down in a moderately deep Callovian–Oxfordian sea.

Commonly recorded taxa (PBDB)

Genera most often recorded from this unit in the Paleobiology Database (first 200 occurrences): Mollusca (13), Procerithium (13), Meleagrinella (12), Palaeonucula (11), Mesosaccella (10), Bositra (9), Corbulomima (8), Thracia (6), Anomalodesmatan (5), Dicroloma (5), Gryphaea (5), Grammatodon (4), Pinna (4), Cryptoclidus (3), Nicaniella (3).

Source: Paleobiology Database

Age

Typical taxa

Referenced by

Elsewhere

Cite this article

Stratum Study. "Oxford Clay Formation" (Formation). Stratum Study pack 2026.09, as of 2026-09-19. https://stratum.black/study/formations/oxford-clay-formation. Accessed 2026-09-20.

BibTeX · CSL-JSON

@misc{stratum-oxford-clay-formation,
  title        = {Oxford Clay Formation},
  author       = {{Stratum Study}},
  howpublished = {\url{https://stratum.black/study/formations/oxford-clay-formation}},
  year         = {2026},
  note         = {Formation article, Stratum Study pack 2026.09, as of 2026-09-19; sources: stratum, macrostrat, pbdb, wikidata, commons. Accessed 2026-09-20.}
}

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