Blue Lias
Blue Lias Formation | |
---|---|
Ma | |
Type | Geological formation |
Unit of | Lias Group |
Sub-units | Wilmcote Limestone Member, Saltford Shale Member, Rugby Limestone Member |
Underlies | Charmouth Mudstone Formation |
Overlies | Lilstock Formation |
Thickness | up to 120 metres (390 ft) |
Lithology | |
Primary | Limestone |
Other | Mudstone |
Location | |
Region | Europe |
Country | United Kingdom |
Extent | South West England, Wales |
Type section | |
Location | Saltford railway cutting |
The Blue Lias is a
Its age corresponds to the
Lithology and facies
The Blue Lias comprises decimetre scale alternations of
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
Occurrence
The Blue Lias is a prevalent feature of the cliffs around
.Use in construction
Blue Lias is useful as a building stone, and as a source of
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
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
Dinosaurs
Dinosaurs of the Blue Lias | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Dracoraptor | D. hanigani | Lavernock Point
|
Pre-planorbis Beds, lowermost Hettangian | NMW 2015.5G.1–2015.5G.11 "a disarticulated, but associated partial skeleton" | A coelophysoid theropod | |
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 skeleton | Basal neotheropod, holotype specimen is known from the Scunthorpe Mudstone |
Pterosaurs
Pterosaurs of the Blue Lias | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Dimorphodon | D. macronyx | Aust Cliff, Lyme Regis | NHMUK PV R 1034, NHMUK PV OR 41212, NHMUK PV R 1035 | A basal pterosaur |
Fish
Numerous fish species are known from the Blue Lias and overlying Charmouth Mudstone.
Fish of the Charmouth Mudstone Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Acrodus | A hybodont shark
|
|||||
Hybodus | A hybodont shark | |||||
Palidiplospinax | A synechodontiform shark | |||||
Squaloraja | S. tenuispina, S. polyspondyla | Closely related to modern chimaeras | ||||
Myriacanthus | M. paradoxus, M. granulatus | A myriacanthid closely related to modern chimaeras | ||||
Dorsetichthys | D. bechei | A stem-group teleost | ||||
"Coccolepis" | "C." liassicus | A coccolepidid fish, probably does not belong to the genus | ||||
Holophagus | H. gulo | A coelacanth | ||||
Chondrosteus | C. acipenseroides | A chondrosteid acipenseriform fish, related to sturgeon and paddlefish | ||||
Oxygnathus | O. ornatus | A palaeonisciform fish | ||||
Saurorhynchus | S. brevirostris, S. anningae | A member of Saurichthyiformes | ||||
Ptycholepis | P. gracilis, P. curtus | A palaeonisciform fish | ||||
Dapedium | Spp. | A dapediiform fish
|
||||
Caturus | Spp. | An amiiform fish related to bowfins
|
||||
Platysiagum | P. sclerocephalum | A platysiagid fish
|
||||
Furo | F. orthostomus | A member of Ionoscopiformes within Halecomorphi |
Ichthyosaurs
Ichthyosaurs of the Blue Lias | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Ichthyosaurus | I. larkini[9] | Somerset | Unknown, possibly Pre-planorbis beds | Holotype: BRSUG 25300, referred: AGC 11, CAMSM J5957, NHMUK PV OR5595 | ||
I. somersetensis[9] | Holotype: ANSP 15766 referred: BRSMG Cb4997, NHMUK PV OR2013AGC 16, ROM 26029 | |||||
I. communis[10] | Somerset | Unknown | BMNH R1162 | |||
Protoichthyosaurus | P. prostaxalis[11] | Somerset | Unknown, probably Pre-planorbis beds | Holotype: BRLSI M3553, "a partial skull, pectoral girdle and both forefins, preserved in ventral view" | ||
Wahlisaurus | W. massarae[12] | Sutton Hill (Stowey) Quarry, Bishop Sutton | Pre-planorbis beds | BRSMG Cg240, "a practically complete right coracoid" | ||
?Shastasauridae | Indeterminate | Penarth | Psiloceras planorbis Biozone | NMW95.61G.1, radius[13] | Estimated length of 12–15 metres | |
Temnodontosaurus[14] | T. platyodon | PV R 1158, consisting of a Skull, Lower Jaw and Cervical Vertebrae |
Plesiosaurs
Plesiosaurs of the Blue Lias | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Atychodracon | A. megacephalus[15] | Street-on-the-Fosse
|
Lowermost Blue Lias | Holotype:BRSMG Cb 2335 | Rhomaleosaurid | |
Avalonnectes | A. arturi[16] | Street, Somerset (referred specimen) | NHMUK 14550, "the posterior portion of the skull, and a partial postcranial skeleton" uncatalogued partial specimen | Rhomaleosaurid | ||
Eurycleidus | E. arcuatus | Street | BMNH 2030 (lectotype), 2027-2029, 2047, 2061, R1317-1319 (paralectotypes, probably belonging to the same individual) | Rhomaleosaurid | ||
Eoplesiosaurus | E. antiquior[16] | Watchet, Somerset | TTNCM 8348, postcranial skeleton | Basal Plesiosauroid | ||
Stratesaurus | S. taylori[16] | Street, Somerset | lowermost Hettangian | OUMNH J.10337, "a skull and partial postcranial skeleton including anterior cervical and pectoral vertebrae, a partial hindlimb and ilium" | Rhomaleosaurid | |
Thalassiodracon | T. hawkinsii | Street | Pre-planorbis Beds | BMNH 2018 "almost complete skeleton missing distal parts of limbs" CAMSM J.35181, partial skeleton | Pliosaurid affinities[17]
|
Insects
Insect compression fossils are known from the localities of Binton in Warwickshire and Copt Heath near Birmingham.[18]
See also
- White Lias
- List of dinosaur-bearing rock formations
References
- ^ 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.
- ^ "Wilmcote Limestone Member". The BGS Lexicon of Named Rock Units. British Geological Survey. Retrieved 20 April 2014.
- ^ "Museum Service – Warwickshire Heritage and Culture". Archived from the original on 21 April 2014. Retrieved 20 April 2014.
- ^ 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.
- ^ 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.
- ^ 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)
- ^ "Strategic Stone Study: A Building Stone Atlas of Somerset and Exmoor" (PDF). English Heritage. p. 11. Retrieved 11 October 2011.
- ISBN 0-520-24209-2.
- ^ S2CID 89567182.
- JSTOR 4523265.
- S2CID 90238537.
- S2CID 134448865.
- .
- ^ "PV R 1158". NHM Data Portal. NHM. Retrieved 10 August 2022.
- ISSN 1094-8074.
- ^ PMID 22438869.
- S2CID 39844147.
- ISSN 0033-2615.
External links
- "Explore the Jurassic Coast" at the National Trust
- The Philpot Museum website
- Geology of Whitby
- Geology of Lyme Regis Area
- Geology of the Wessex Coast
- Ham & Doulting Stone Co Ltd
- Conservation of Blue lias article
- Fossils of the Blue Lias Formation -- A quick guide
- Hadspen Quarry Ltd
- AR Purnell Ltd
- Blue Lias, Stockton