Blue Lias

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Blue Lias Formation
Stratigraphic range: Rhaetian-Lower Sinemurian Planorbis-Semicostatum ~201–198  Ma
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Lower Lias Nash Point Glamorgan.JPG
Lower Lias sequence exposed at Nash Point, Glamorgan, Wales
Type Geological formation
Unit of Lias Group
Sub-unitsWilmcote Limestone Member, Saltford Shale Member, Rugby Limestone Member
Underlies Charmouth Mudstone Formation
Overlies Lilstock Formation
Thicknessup to 120 metres (390 ft)
Lithology
Primary Limestone
Other Mudstone
Location
Region Europe
Country United Kingdom
Extent South West England,
Wales
Type section
LocationSaltford railway cutting

The Blue Lias is a geological formation in southern, eastern and western England and parts of South Wales, part of the Lias Group. The Blue Lias consists of a sequence of limestone and shale layers, laid down in latest Triassic and early Jurassic times, between 195 and 200 million years ago. The Blue Lias is famous for its fossils, especially ammonites.

Contents

Its age corresponds to the Rhaetian to lower Sinemurian stages of the geological timescale, thus fully including the Hettangian stage. It is the lowest of the three divisions of the Lower Jurassic period and, as such, is also given the name Lower Lias . Stratigraphically it can be subdivided into three members: the Wilmcote Limestone, Saltford Shale and Rugby Limestone. [1]

Lithology and facies

The Blue Lias comprises decimetre scale alternations of argillaceous limestone and mudstone. These alternations are caused by short-term climatic variations during the Early Jurassic attributed to orbital forcing (Milankovitch cycles). These limestone-mudstone alternations pass up into a clay member formerly known as the Lower Lias Clay now the Charmouth Mudstone. This lithology consists of monotonous mudstones weathering to clay at the surface. Sparse thin limestone and nodule bands are seen where the rocks are exposed. The deposition of a clay-rich mudstone member normally indicates deposition in a deeper marine environment. The lowest beds of the formation are referred to as the "Pre-planorbis beds" in reference them being deposited before the first appearance of the ammonite Psiloceras planorbis.

Wilmcote Limestone

In certain restricted parts of Britain, the lowermost member of the Blue Lias is the Wilmcote Limestone. It lies above the Cotham Member of the Lilstock Formation and beneath the Saltford Shale Member. [2] The Wilmcote Limestone of central England was formerly quarried close to Stratford-upon-Avon, for example at Wilmcote, Temple Grafton and Binton. It is roughly 200 million years old, dating back to the dawn of the Jurassic Period.

Much of the Wilmcote Limestone is very fine-grained, blue-grey when fresh, and very finely layered. Fossils are quite rare, except in the lowest beds. It was formerly used for a variety of purposes, including walling, building, paving, gravestones, cement-making and as a source of agricultural lime. It is no longer quarried, and most of the old quarries are either infilled or overgrown.

Geologists think that the Wilmcote Limestone originated as layers of fine-grained mud on the floor of a sheltered, shallow muddy sea or lagoon that covered parts of central England at the dawn of the Jurassic Period. Very little life could tolerate the stagnant conditions on the seabed. As a consequence the mud was seldom disturbed, which is why the fine, paper-like layering is preserved.

Above the sea bed, the shallower waters supported ammonites, fish, and marine reptiles (ichthyosaurs and plesiosaurs). Their remains were discovered in the Wilmcote Limestone quarries during the nineteenth century. The Warwickshire Museum [3] houses a collection of these fossils and some are on display at the Market Hall Museum in Warwick. [4] [5]

Occurrence

Blue Lias formation at Lyme Regis, Dorset Blue lias cliffs at Lyme Regis.jpg
Blue Lias formation at Lyme Regis, Dorset

The Blue Lias is a prevalent feature of the cliffs around Lyme Regis and Charmouth, on the Jurassic Coast in Dorset, where it exists in layers of limestone interspersed with softer clay. It is also notable for its presence in Somerset, particularly around the Polden Hills, Keinton Mandeville and Glastonbury area, and it forms a broad plain across the East Midlands. It also appears near Whitby in Yorkshire and Southam in Warwickshire where a pub is named after it. There are outcrops along the coast of South Wales, notably that of the Vale of Glamorgan. [6] The type section of the Blue Lias is at Saltford near Bath.

Use in construction

Lytes Cary, Somerset, built of Blue Lias with Ham stone dressings around the windows Lytes Cary 2009 South front, bay window.JPG
Lytes Cary, Somerset, built of Blue Lias with Ham stone dressings around the windows

Blue Lias is useful as a building stone, and as a source of lime for making lime mortar. Because it is argillaceous, the lime is hydraulic. Since the mid-nineteenth century, it has been used as a raw material for cement, in South Wales, Somerset, Warwickshire, and Leicestershire. The cement plant quarry at Rugby, Warwickshire is probably the best exposure of the formation: more than 100 layers can be seen.

In areas where Blue Lias is quarried it has been used in buildings and churches as well as tombstones in cemeteries. An example of a Blue Lias town is Street, near Glastonbury. Other examples of Blue Lias buildings can be found in the nearby towns of Somerton and Ilchester.

It remains popular in more modern-day surroundings where it is used in the construction of new housing developments and extensions for existing buildings in conservation areas. Blue Lias is mainly used in flooring, walling and paving slabs – both coursed and layered. It is also used in the making of flagstones and cobbles.

There are only four quarries in Somerset quarrying Blue Lias at present. AR Purnell at Ashen Cross Quarry in Somerton have been mining blue lias stone since 1996. Hadspen Quarry Ltd. Hadspen Quarry operate one in Keinton Mandeville. Ham & Doulting Stone Co Ltd. operate one of these, Tout Quarry near Somerton. [7]

Paleofauna

The rock is rich in fossil remains from the Jurassic period. The blue-grey colour is provided by its iron content, enclosed to a large extent in pyrites. [8]

Dinosaurs

Theropods

Theropods of the Blue Lias
GenusSpeciesLocationStratigraphic positionMaterialNotesImages
Dracoraptor D. hanigani Lavernock Point Pre- planorbis Beds, lowermost HettangianNMW 2015.5G.1–2015.5G.11 "a disarticulated, but associated partial skeleton"A coelophysoid theropod
Dracoraptor.PNG

Dornraptor [9]

D. normani

Lower cliff face, Charmouth

Black Ven Marl Member?

  • GSM 109560, Left femur
  • NHMUK OR 39496, Partial hind limb

An Averostran theropod, possible Ceratosaur. In 2024 was formally described, but referred to the Blue Lias. [10] A paper non quoted on the description relocated it on the Charmouth Mudstone Formation. [11]

Merosaurus.jpg
Sarcosaurus S. woodi Wilmcote angulata zone, late Hettangian (NHMUK PV R3542) Rugby Limestone Member liasicus to semicosatum zones, lowermost Sinemurian (WARMS G667–690)Paratype specimens: NHMUK PV R3542, complete right tibia WARMS G667–690, partial skeletonBasal neotheropod, holotype specimen is known from the Scunthorpe Mudstone
Sarcosaurus life restoration.jpg

Pterosaurs

Pterosaurs of the Blue Lias
GenusSpeciesLocationStratigraphic positionMaterialNotesImages
Dimorphodon D. macronyxAust Cliff, Lyme RegisNHMUK PV R 1034, NHMUK PV OR 41212, NHMUK PV R 1035A basal pterosaur
Dimorphodon macronyx.jpg

Fish

Numerous fish species are known from the Blue Lias and overlying Charmouth Mudstone.

Fish of the Charmouth Mudstone Formation
GenusSpeciesLocationStratigraphic positionMaterialNotesImages
Acrodus A hybodont shark
Hybodus A hybodont shark
Palidiplospinax A synechodontiform shark
Squaloraja S. tenuispina,S. polyspondylaClosely related to modern chimaeras
Myriacanthus M. paradoxus, M. granulatusA myriacanthid closely related to modern chimaeras
Dorsetichthys D. becheiA stem-group teleost
Pholidophorus bechei Lyme Regis Teylers.JPG
"Coccolepis""C." liassicusA coccolepidid fish, probably does not belong to the genus
Cosmolepis C. ornatusAn enigmatic basal actinopterygian
FOS275.jpg
Holophagus H. guloA coelacanth
Chondrosteus C. acipenseroidesA chondrosteid acipenseriform fish, related to sturgeon and paddlefish
FMIB 51725 Chondrosteus acipeenseroides Egerton Family Chondrosteidae.jpeg
Oxygnathus O. ornatusA palaeonisciform fish
Saurorhynchus S. brevirostris,S. anningaeA member of Saurichthyiformes
Ptycholepis P. gracilis, P. curtusA palaeonisciform fish
Dapedium Spp.A dapediiform fish
Caturus Spp.An amiiform fish related to bowfins
Platysiagum P. sclerocephalumA platysiagid fish
Furo F. orthostomusA member of Ionoscopiformes within Halecomorphi

Ichthyosaurs

Ichthyosaurs of the Blue Lias
GenusSpeciesLocationStratigraphic positionMaterialNotesImages
Ichthyosaurus I. larkini [12] Lyme Regis & Charmouth in Dorset, Street and the north coast of Somerset, and other inland sites across EnglandUnknown, possibly Pre-planorbis bedsHolotype: BRSUG 25300, referred: AGC 11, CAMSM J5957, NHMUK PV OR5595
Ichthyosaurus communis in London.jpg
I. somersetensis [12] Holotype: ANSP 15766 referred: BRSMG Cb4997, NHMUK PV OR2013AGC 16, ROM 26029
I. communis [13] UnknownBMNH R1162
Protoichthyosaurus P. prostaxalis [14] SomersetUnknown, probably Pre-planorbis bedsHolotype: BRLSI M3553, "a partial skull, pectoral girdle and both forefins, preserved in ventral view"
Wahlisaurus W. massarae [15] Sutton Hill (Stowey) Quarry, Bishop SuttonPre-planorbis bedsBRSMG Cg240, "a practically complete right coracoid"
?Shastasauridae IndeterminatePenarthPsiloceras planorbis BiozoneNMW95.61G.1, radius [16] Estimated length of 12–15 metres
Temnodontosaurus [17] T. platyodonPV R 1158, consisting of a Skull, Lower Jaw and Cervical Vertebrae
Excalibosaurus E. costini [18] [19] North Somerset coastlineArietites (Coroniceras) bucklandi BiozoneHolotype: BRSMG Cc881, "...a complete skull, with associated forefin, pectoral girdle, vertebrae and ribs..."

referred: ROM 47697

ROM 47697, a nearly complete skeleton of Excalibosaurus on display at the Royal Ontario Museum. ROM 47697, Excalibosaurus, Royal Ontario Museum.png
ROM 47697, a nearly complete skeleton of Excalibosaurus on display at the Royal Ontario Museum.

Plesiosaurs

Plesiosaurs of the Blue Lias
GenusSpeciesLocationStratigraphic positionMaterialNotesImages
Atychodracon A. megacephalus [20] Street-on-the-Fosse Lowermost Blue LiasHolotype:BRSMG Cb 2335 Rhomaleosaurid
Plesiosaur skeleton, New Walk Museum.JPG
Avalonnectes A. arturi [10] Street, Somerset (referred specimen)NHMUK 14550, "the posterior portion of the skull, and a partial postcranial skeleton" uncatalogued partial specimenRhomaleosaurid
Holotype of Avalonnectes arturi NHMUK 14550.png
Eurycleidus E. arcuatusStreetNHMUK 2030 (lectotype), 2027-2029, 2047, 2061, R1317-1319 (paralectotypes, probably belonging to the same individual)Rhomaleosaurid
Macroplata M. tenuceps Harbury, WarwickshireNHMUK PV R5488, nearly complete skeletonRhomaleosaurid
Eoplesiosaurus E. antiquior [10] Watchet, SomersetTTNCM 8348, postcranial skeletonBasal Plesiosauroid
Holotype of Eoplesiosaurus antiquior.png
Plesiosaurus P. dolichodeirus [21] Lyme Regis and Charmouth, DorsetSinemurian stage (upper Blue Lias, Shales-with-Beef member or lower Black Ven MarlNHMUK PV OR 22656, complete skeletonPlesiosaurid
The holotype of Plesiosaurus dolichodeirus, on display at the Natural History Museum in London Plesiosaurus dolichodeirus NHM.jpg
The holotype of Plesiosaurus dolichodeirus, on display at the Natural History Museum in London
Stratesaurus S. taylori [10] Street, Somersetlowermost HettangianOUMNH J.10337, "a skull and partial postcranial skeleton including anterior cervical and pectoral vertebrae, a partial hindlimb and ilium"Rhomaleosaurid
Holotype of Stratesaurus taylori OUMNH J.10337.png
Thalassiodracon T. hawkinsiiStreetPre-planorbis BedsNHMUK 2018 "almost complete skeleton missing distal parts of limbs" CAMSM J.35181, partial skeleton Pliosaurid affinities [22]
Thalassiodracon NHM.jpg

Insects

Insect compression fossils are known from the localities of Binton in Warwickshire and Copt Heath near Birmingham. [23] [24] [25]

Insects of the Blue Lias
GenusSpeciesLocationStratigraphic positionMaterialNotesImages
Omma O. liassicaBintonPlanorbisAn ommatid beetle, genus extant
Holcoptera Ho. schlotheimiAn aquatic beetle belong to the extinct family Coptoclavidae
Liassophila L. hydromanicoidesA member of Mecoptera
Orthophlebia O. pictipennisAn orthophlebiid mecopteran related to living scorpionflies
Hagla H. gracilisAn orthopteran belonging to the family Haglidae, related to living grigs
Elcana IndeterminateAn orthopteran belonging to the extinct family Elcanidae
Protocoris P. indistinctusA true bug belonging to the family Protocoridae, related to living stink bugs
Archithemis [26] A. liassinaA damsel-dragonfly belonging to the extinct family Campterophlebiidae
Liassophlebia L. magnificaA damsel-dragonfly belonging to the extinct family Liassophlebiidae
Necrotaulius Copt HeathA caddisfly belonging to the extinct family Necrotauliidae
Locustopsis L. spectabilisA grasshopper belonging to the extinct family Locustopsidae
Phanerogramma P. heeriA primitive earwig belonging to the extinct family Dermapteridae

See also

References

  1. Ambrose, K.; 2001: The lithostratigraphy of the Blue Lias Formation (Late Rhaetian–Early Sinemurian) in the southern part of the English Midlands Archived 7 March 2006 at the Wayback Machine , Proceedings of the Geologists' Association 112(2), pp. 97-110.
  2. "Wilmcote Limestone Member". The BGS Lexicon of Named Rock Units. British Geological Survey. Retrieved 20 April 2014.
  3. "Museum Service – Warwickshire Heritage and Culture". Archived from the original on 21 April 2014. Retrieved 20 April 2014.
  4. Ambrose, K., 2001. The lithostratigraphy of the Blue Lias Formation (Late Rhaetian - Early Sinemurian) in the southern part of the English Midlands. Proceedings of the Geologists' Association vol. 112, 97-110.
  5. Williams, B.J. & Whittaker, A., 1974. Geology of the Country around Stratford-upon-Avon and Evesham. Memoirs of the Geological Survey of Great Britain. HMSO, London.
  6. Wilson et al., 1990 Geology of the South Wales Coalfield, Part VI, the country around Bridgend Mem Br Geol Surv sheet 261 & 262 (England and Wales)
  7. "Strategic Stone Study: A Building Stone Atlas of Somerset and Exmoor" (PDF). English Heritage. p. 11. Retrieved 11 October 2011.
  8. Weishampel, David B; et al. (2004). "Dinosaur distribution (Early Jurassic, Europe)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. Pp. 532–534. ISBN   0-520-24209-2.
  9. Baron, Matthew G. (29 April 2024). "A new name for old bones: A reassessment of Early Jurassic theropod remains from Dorset, England". Palaeontologia Electronica. 27 (1): 1–12. doi: 10.26879/1346 . ISSN   1094-8074.
  10. 1 2 3 4 Benson, Roger B. J.; Evans, Mark; Druckenmiller, Patrick S. (16 March 2012). Lalueza-Fox, Carles (ed.). "High Diversity, Low Disparity and Small Body Size in Plesiosaurs (Reptilia, Sauropterygia) from the Triassic–Jurassic Boundary". PLOS ONE. 7 (3): e31838. Bibcode:2012PLoSO...731838B. doi: 10.1371/journal.pone.0031838 . ISSN   1932-6203. PMC   3306369 . PMID   22438869.
  11. Choiniere, Jonah N.; Wills, Simon; Bennett, S. Christopher; Barrett, Paul M. (2020). "A small theropod dinosaur from the Lower Jurassic Lias Group of Charmouth, Dorset" . Proceedings of the Geologists' Association. 131 (6): 751–757. Bibcode:2020PrGA..131..751C. doi:10.1016/j.pgeola.2020.08.003. ISSN   0016-7878.
  12. 1 2 Lomax, Dean R.; Massare, Judy A. (February 2017). Benson, Roger (ed.). "Two new species of Ichthyosaurus from the lowermost Jurassic (Hettangian) of Somerset, England" . Papers in Palaeontology. 3 (1): 1–20. Bibcode:2017PPal....3....1L. doi:10.1002/spp2.1065. S2CID   89567182.
  13. Mcgowan, Christopher (1989). "Computed Tomography Reveals Further Details of Excalibosaurus, a Putative Ancestor for the Swordfish-Like Ichthyosaur Eurhinosaurus" . Journal of Vertebrate Paleontology. 9 (3): 269–281. Bibcode:1989JVPal...9..269M. doi:10.1080/02724634.1989.10011762. JSTOR   4523265.
  14. Lomax, Dean R.; Massare, Judy A.; Mistry, Rashmiben T. (3 September 2017). "The taxonomic utility of forefin morphology in Lower Jurassic ichthyosaurs: Protoichthyosaurus and Ichthyosaurus" . Journal of Vertebrate Paleontology. 37 (5): e1361433. Bibcode:2017JVPal..37E1433L. doi:10.1080/02724634.2017.1361433. ISSN   0272-4634. S2CID   90238537.
  15. Lomax, Dean R.; Evans, Mark; Carpenter, Simon (January 2019). Somerville, Id (ed.). "An ichthyosaur from the UK Triassic-Jurassic boundary: A second specimen of the leptonectid ichthyosaur Wahlisaurus massarae Lomax 2016". Geological Journal. 54 (1): 83–90. Bibcode:2019GeolJ..54...83L. doi: 10.1002/gj.3155 . S2CID   134448865.
  16. Martin, Jeremy; Vincent, Peggy; Suan, Guillaume; Sharpe, Tom; Hodges, Peter; Williams, Matt; Howells, Cindy; Fischer, Valentin (2014). "A mysterious giant ichthyosaur from the lowermost Jurassic of Wales". Acta Palaeontologica Polonica. doi: 10.4202/app.00062.2014 .
  17. "PV R 1158". NHM Data Portal. NHM. Retrieved 10 August 2022.
  18. McGowan, Chris (2003). "A new specimen of Excalibosaurus from the English Lower Jurassic" . Journal of Vertebrate Paleontology . 23 (4): 950–956. Bibcode:2003JVPal..23..950M. doi:10.1671/1860-20. ISSN   0272-4634.
  19. McGowan, Chris (1986). "A putative ancestor for the swordfish-like ichthyosaur Eurhinosaurus" . Nature. 322 (6078): 454–456. Bibcode:1986Natur.322..454M. doi:10.1038/322454a0.
  20. Smith, As (2015). "Reassessment of 'Plesiosaurus' megacephalus (Sauropterygia: Plesiosauria) from the Triassic-Jurassic boundary, UK". Palaeontologia Electronica. 18 (1): 1–20. doi: 10.26879/504 . ISSN   1094-8074.
  21. Storrs, Glenn W. (1997). Ancient Marine Reptiles. Academic Press. pp. 145–190. ISBN   9780121552107.
  22. Benson, Roger B. J.; Bates, Karl T.; Johnson, Mark R.; Withers, Philip J. (May 2011). "Cranial anatomy of Thalassiodracon hawkinsii (Reptilia, Plesiosauria) from the Early Jurassic of Somerset, United Kingdom". Journal of Vertebrate Paleontology. 31 (3): 562–574. Bibcode:2011JVPal..31..562B. doi:10.1080/02724634.2011.572937. ISSN   0272-4634. S2CID   39844147.
  23. Kelly, Richard S.; Ross, Andrew J.; Coram, Robert A. (2018). "A Review of Necrotauliids from the Triassic/Jurassic of England (Trichoptera: Necrotauliidae)". Psyche: A Journal of Entomology. 2018: 1–12. doi: 10.1155/2018/6706120 . hdl: 1983/06ae01fb-06bc-41d0-bcbd-f7519cb07df6 . ISSN   0033-2615.
  24. "Binton, Warwickshire (Tomes collection): Planorbis, United Kingdom". Paleobiology Database . Retrieved 26 May 2025.
  25. "Copt Heath, near Knowle: Planorbis, United Kingdom". Paleobiology Database . Retrieved 26 May 2025.
  26. Kelly, Richard S.; Nel, André (2 January 2018). "Revision of the damsel-dragonfly family Campterophlebiidae (Odonata) from the Early Jurassic of England reveals a new genus and species". Alcheringa: An Australasian Journal of Palaeontology. 42 (1): 87–93. doi:10.1080/03115518.2017.1377767. hdl: 1983/e56e40ba-31c6-4498-b309-d1d517727b9d . ISSN   0311-5518.