Kimmeridge Clay

The Kimmeridge Clay is a sedimentary deposit of fossiliferous marine clay which is of Late Jurassic to lowermost Cretaceous age and occurs in southern and eastern England and in the North Sea.^[1] This rock formation is the major source rock for North Sea oil. The fossil fauna of the Kimmeridge Clay includes turtles, crocodiles, sauropods, plesiosaurs, pliosaurs and ichthyosaurs, as well as a number of invertebrate species.

Kimmeridge Clay
Stratigraphic range: Kimmeridgian–Berriasian PreꞒ Ꞓ O S D C P T J K Pg N
Grey cliffs of Upper Kimmeridge Clay above the beach at Egmont Bight
Type	Geological formation
Unit of	Ancholme Group (onshore), Humber Group (offshore)
Sub-units	Birch Sandstone Member Burns Sandstone Member Claymore Sandstone Member Dirk Sandstone Member Magnus Sandstone Member Ptarmigan Sandstone Member Ribble Sandstone Member
Underlies	Portland Sand Formation, Speeton Clay Formation, Spilsby Sandstone
Overlies	Ampthill Clay, Corallian Group
Lithology
Primary	Mudstone
Other	Siltstone, Sandstone, Conglomerate
Location
Region	England (surface) North Sea (subsurface)
Country	United Kingdom
Type section
Named for	Kimmeridge Bay
Location	Type section - North Sea well 47/15- 1 at 885-919 m depth Type area - coastal outcrops from Black Head, Weymouth to Chapman's Pool

Description

Kimmeridge Clay is named after the village of Kimmeridge on the Dorset coast of England, where it is well exposed and forms part of the Jurassic Coast World Heritage Site.^[2] Onshore, it is of Late Jurassic (Kimmeridgian) age and outcrops across England, in a band stretching from Dorset in the south-west, north-east to North Yorkshire. Offshore, it extends into the Lower Cretaceous (Berriasian Stage) and it is found throughout the Southern, Central and Northern North Sea.^[1]

The foundations of the Humber Bridge on the southern (Barton) side of the bridge are on Kimmeridge Clay beneath superficial deposits, under the Humber estuary.^[3]

Economic importance

Kimmeridge Clay is of great economic importance,^[2] being the major source rock for oil fields in the North Sea hydrocarbon province.^[4] It has distinctive physical properties and log responses.^[5]

Vertebrate fauna

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Fauna uncovered from the Kimmeridge Clay include:^[6]

Ray-finned fish

Ray-finned fishes of the Kimmeridge clay Formation
Genus	Species	Location	Stratigraphic Position	Abundance	Notes	Images
Thrissops[7][8]	Indeterminate	Dorset		Most common Kimmeridge clay fish, known from several complete specimens	Housed at the Etches Collection, discovered by Steve Etches	Complete specimen
Pachythrissops	Indeterminate	Dorset			Housed at the Etches Collection, discovered by Steve Etches
Allothrissops	Indeterminate	Dorset			Housed at the Etches Collection, discovered by Steve Etches
Chondrostei	Indeterminate	Dorset		One specimen, a fin	Housed at the Etches Collection, discovered by Steve Etches
Lepidotes	Indeterminate	Dorset			Housed at the Etches Collection, discovered by Steve Etches
Gyrodus	Indeterminate	Dorset			Housed at the Etches Collection, discovered by Steve Etches
Caturus	Indeterminate	Dorset			Housed at the Etches Collection, discovered by Steve Etches	Caturus furcatus
Aspidorhynchus	Indeterminate	Dorset			Housed at the Etches Collection, discovered by Steve Etches
Hypsocormus	H.tenuirostris	Dorset		Rare	Housed at the Etches Collection, discovered by Steve Etches
Pachycormus	Indeterminate	Dorset		Rare	Housed at the Etches Collection, discovered by Steve Etches
Eurycormus	Indeterminate	Dorset		Rare, one complete specimen	Housed at the Etches Collection, discovered by Steve Etches
Leptolepidae	Indeterminate	Dorset		Fairly common, multiple near complete specimens.	Housed at the Etches Collection, discovered by Steve Etches

Lobe-finned fish

Lobe-finned fishes of the Kimmeridge clay Formation
Genus	Species	Location	Stratigraphic Position	Abundance	Notes	Images
Holophagus	Indeterminate	Dorset		One specimen, cranial material	Coelacanth. Housed at the Etches Collection, discovered by Steve Etches. More than 2 metres long

Cartilaginous fish

Cartilaginous fishes of the Kimmeridge clay Formation
Genus	Species	Location	Stratigraphic Position	Abundance	Notes	Images
Asteracanthus	Indeterminate	Dorset		Known from many dorsal spines	Housed at the Etches Collection, discovered by Steve Etches
Chimaera	Indeterminate			Known from many dorsal spines	Housed at the Etches Collection, discovered by Steve Etches
Hybodus	Indeterminate			Known from many dorsal spines, perhaps a complete head	Housed at the Etches Collection, discovered by Steve Etches
Ischyodus	Indeterminate			One specimen	Housed at the Etches Collection, discovered by Steve Etches
Rhinobatidae	Indeterminate			Known from a complete specimen, and other isolated remains	Housed at the Etches Collection, discovered by Steve Etches
Kimmerobatis[9]	K. etchesi		Encombe (holotype) and Rope Lake Head (paratype)	Known from two partial skeletons	A spathobatid ray; housed at the Etches Collection, discovered by Steve Etches
Durnonovariaodus [10]	D. maiseyi		Pectinatites pectinatus ammonite zone	One partial skeleton	A hybodontid

Turtles

Turtles of the Kimmeridge clay Formation
Genus	Species	Location	Stratigraphic Position	Abundance	Notes	Images
Craspedochelys	C. passmorei	Swindon		"NHMUK R5871 (holotype), subcomplete shell with associated postcranial remains, including parts of the girdles, the left humerus, and partial cervical vertebrae"[11]	Thalassochelydian sea turtle
Achelonia	A. formosa	Ely, Cambridgeshire		"CAMSM J29898 to CAMSM J29955 (holotype), a partial, disarticulated skeleton"[11]	Thalassochelydian sea turtle, formerly considered the distinct species "Enaliochelys chelonia"[12]
Pelobatochelys	P. blakii	Weymouth		Carapace fragments	Thalassochelydian sea turtle
Plesiochelys[13]	P. etalloni			"basicranium with partial otic chambers and fragment of the right maxilla"	Thalassochelydian sea turtle
Thalassemys	T. bruntrutana, T. hugii	Isle of Purbeck (bruntrutana), Abingdon, Oxfordshire (hugii)		"A partial carapace and associated limb and girdle elements (NHMUK R8699)" (Purbeck) "A large shell (OUMNH J.66966)" (Oxfordshire)[13]	Thalassochelydian sea turtle
Tropidemys[13]	P. langii	Weymouth		"NHMUK OR44178b, an isolated neural; NHMUK OR45920, right costals 1–3; NHMUK OR45921, a left first costal; NHMUK R2733, a left fourth costal"	Thalassochelydian sea turtle

Archosaurs

Thalattosuchians

Genus	Species	Location	Member	Abundance	Notes	Images
Bathysuchus	B. megarhinus				A pelagic teleosaurid.[14]	Cricosaurus Dakosaurus Plesiosuchus Torvoneustes
Cricosaurus	C. gracilis				A metriorhynchine metriorhynchid
Dakosaurus	D. maximus				A geosaurine metriorhynchid
Metriorhynchus	M. brevirostris				A metriorhynchine metriorhynchid
Plesiosuchus	P. manseli				A geosaurine metriorhynchid
Torvoneustes[15][16]	T. carpenteri[15]				A geosaurine metriorhynchid
	T. coryphaeus[17]				A geosaurine metriorhynchid

Ornithischians

Indeterminate ankylosaur osteoderms have been found in Wiltshire, England.^[18] Indeterminate stegosaurid remains have been found in Dorset and Wiltshire, England.^[6]

Genus	Species	Location	Member	Abundance	Notes	Images
Cumnoria[6]	C. prestwichii[6]	Oxfordshire[6]		"Fragmentary skull and skeleton."[19]	Iguanodontian	Cumnoria Dacentrurus
Dacentrurus[6]	D. armatus[6]	Cambridgeshire[6] Dorset[6] Wiltshire[6]		vertebrae, a massive right femur (thigh bone), ribs and a near complete pelvis.	Stegosaur. Wiltshire remains include specimens previously referred to Omosaurus armatus and O. hastiger.[6]
Ornithopoda	Indeterminate[6]	Dorset?[6]			Kimmeridge clay remains considered to represent a possible close relative of Bugenasaura[20] are now regarded as the remains of an indeterminate euornithopod.[6](The specimen may have had its locality and horizon mislabelled.)
Omosaurus[6]	O.armatus[6]	Wiltshire[6]		Reclassified as Dacentrurus armatus because the generic name Omosaurus was preoccupied.[6]
	O. hastiger[6]	Wiltshire[6]

Saurischians

Indeterminate ornithomimmid remains have been found in Dorset, England.^[6] An undescribed theropod genus was found in Dorset.^[6]

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Bothriospondylus[6]	B. suffosus[6]	Wiltshire[6]		"[Seven] dorsal and sacral centra."[21]	Considered a nomen dubium.	Juratyrant
Cetiosaurus[6]	C. humerocristatus[6]	Dorset[6]			Now Duriatitan.[22]
	Indeterminate[6]	Oxfordshire[6]			Remains previously referred to an indeterminate species of Cetiosaurus are now regarded as indeterminate sauropod material.[6]
Duriatitan	D. humerocristatus	Dorset[6]		Humerus[23]	A titanosauriform[22]
Gigantosaurus[6]	G. megalonyx[6]	Cambridgeshire[6]			Remains previously referred to Gigantosaurus megalonyx are now regarded as indeterminate sauropod material.[6]
"Ischyrosaurus"[6]	I. manseli[6]	Oxfordshire[6]		"Humerus."[24]	Remains previously referred to Ischyrosaurus manseli are now regarded as indeterminate sauropod material.[6]
Juratyrant[25][26]	J. langhami	Dorset		Partial skeleton	A primitive tyrannosaur
Torvosaurus[27]	Indeterminate	Swindon, Dorset		Tibia (OUMNH J.29886) and maxilla fragment, collected separately	A megalosaurid
Theropoda[6]	Indeterminate	Wiltshire[6] Dorset[6]		A tooth from Foxhangers, Wiltshire (NHMUK 46388), phalanges from an unspecified locality in Wiltshire (DZSWS 3009), and a proximal caudal vertebra from Shotover, Oxfordshire (OUMNH J.47134).[27]	Remains previously referred to Megalosaurus are now regarded as indeterminate theropod material.[6]
Sauropoda[6]	Indeterminate[6]	Oxfordshire[6] Cambridgeshire[6] Norfolk[6]			Remains previously attributed to one or more indeterminate species of Ornithopsis (incl. O. leedsii) are now regarded as possible indeterminate sauropod material.[6]

Pterosaurs

Genus	Species	Location	Material	Notes	Images
Cuspicephalus	C. scarfi[28]	Dorset	Partial Skull	Missing Crest, lower jaw and dentition	Cuspicephalus Rhamphorhynchus
Germanodactylus	indeterminate[29]	Charnel, Dorset		May be a non-pterodactyloid monofenestratan instead[28]
Rhamphorhynchus	R. etchesi[30]	Encombe, Dorset[30]
Ctenochasmatoidea	indeterminate[31]	Abingdon, Oxfordshire	Left first wing finger phalanx

Plesiosaurs

Genus	Species	Location	Member	Abundance	Notes	Images
Bathyspondylus	B. swindoniensis				Plesiosaur of unknown affinities	Kimmerosaurus Pliosaurus brachydeirus
Colymbosaurus	C. megadeirus				A cryptoclidid
	C. trochantericus				Nomen dubium
Kimmerosaurus	K. langhami				A cryptoclidid
Plesiosaurus	"P." manseli				Distinct from Colymbosaurus.[32]
Pliosaurus[33][34]	P. brachydeirus				A thalassophonean pliosaurid
	P. brachyspondylus[33]				Nomen dubium
	P. carpenteri				A thalassophonean pliosaurid
	P. kevani				A thalassophonean pliosaurid
	P. portentificus[35]				A nomen dubium
	P. ?rossicus				A thalassophonean pliosaurid; taxonomic identification of specimens tentative[33]
	P. westburyensis				A thalassophonean pliosaurid
	P. sp. 1			Partial skeleton, CAMSM J.35991	A thalassophonean pliosaurid; previously assigned to the nomen dubium P. brachyspondylus[33][34]
	P. sp. 2			Mandible, NHMUK PV OR 39362	A thalassophonean pliosaurid; previously assigned to the nomen dubium P. macromerus[33][34]
Spitrasaurus	Indeterminate

Ichthyosaurs

Genus	Species	Location	Stratigraphic Position	Abundance	Notes	Images
Brachypterygius	B.extremus	Dorset				Brachypterygius Grendelius Nannopterygius Thalassodraco Ophthalmosaurus
Grendelius	G.mordax	Dorset
Ichthyosauridae	Indeterminate	Dorset			Giant, near complete specimen. Proposed to have been 6 metres long when complete. Housed at the Etches Collection in Dorset.
Macropterygius	M.trigonus	Dorset			Nomen dubium - classified by a single vertebra
Nannopterygius	N.enthekiodon	Dorset
Thalassodraco	T. etchesi	Dorset	The Pectinatites pectinatus ammonite zone
Ophthalmosaurus	Indeterminate	Dorset

Invertebrates

An aptychus with the name Trigonellites latus, from the Kimmeridge Clay Formation

The invertebrate fauna of the Kimmeridge Clay includes:^[36][37]

• Mollusca:
  • Cardium striatulum
  • Ostrea deltoidea
  • Gryphaea (Exogyra) virgula
  • Trigonellites
  • Belemnotheutis
  • Etchesia
• Arthropoda:
  • Phlyctosoma sp.
  • Eryma sp.
  • Magila latimana
  • Mecochirus sp.
  • Archaeolepas redtenbacheri

See also

• List of dinosaur-bearing rock formations