Helsby Sandstone Formation
| Helsby Sandstone Formation | |
|---|---|
| Stratigraphic range: Middle Triassic | |
 Exposures of Otter Sandstone at Ladram Bay, Devon, England | |
| Type | Formation |
| Unit of | Sherwood Sandstone Group (SSG) |
| Overlies | Wilmslow Sandstone Formation (disconformity) or Chester Formation (unconformity) |
| Thickness | Up to 500 m |
| Lithology | |
| Primary | sandstone |
| Other | siltstone, mudstone, conglomerate |
| Location | |
| Region | England |
| Country | United Kingdom |
The Helsby Sandstone Formation, formerly known as the Otter Sandstone (in Devon and Somerset), is a geological formation in England. It was deposited during the Anisian stage of the Middle Triassic epoch. It primarily consists of medium to fine grained sandstone, both cross bedded and flat bedded, with minor lenticular beds of siltstone and mudstone and thin beds of conglomerate in some areas. It is found across England, from Devon on the southern coast to Cumbria in the north, with some exposures in Worcestershire and in Staffordshire in the Midlands.[1] It was deposited in a hot, arid climate, when Britain formed part of the Pangean interior[2][3] with the cross-bedded sandstones of the formation representing remnants of wind-blown sand dunes,[4] while the majority of the formation was produced by the action of braided rivers, specifically the ‘Budleighensis’ river system, which flowed northwards from what is now northern France through southern and central England, before draining into what is now the Irish Sea. The environment of the formation likely also included ponds and small lakes, with surrounding vegetation including conifers (whose roots are preserved as concretions) and horsetails. Towards the top of the formation, the conditions become more arid, with the overlying formations showing the disappearance of rivers and the existence of playa-like conditions.[3]
The formation in its southern coastal exposure in Devon in the vicinity of Sidmouth has provided important fossils of contemporary vertebrates, including temnospondyl amphibians, procolophonid, rhynchosaurian, sphenodontian and archosaurian reptiles, as well as fish.[3]
Paleobiota
[edit]Taken from[3] unless otherwise noted:
Fish
[edit]| Fish of the Helsby Sandstone | |||||
|---|---|---|---|---|---|
| Genus | Species | Locality | Materials | Notes | Image |
| Dipteronotus | D. cyphus | A small 10–12 centimetres (3.9–4.7 in) long perleidiform fish, known from complete specimens, most common fish in the formation.[5] |  | ||
| Actinopterygii | Indeterminate | Includes a fish known from a single mostly complete 10–12 centimetres (3.9–4.7 in) long undescribed specimen distinct from Dipteronotus, as well as the jaw of a pike-like fish, as well as other indeterminate microvertebrate remains.[5] | |||
| Elasmobranchii | Indeterminate | Freshwater shark known from a fin spine | |||
Amphibians
[edit]| Amphibians of the Helsby Sandstone | |||||
|---|---|---|---|---|---|
| Genus | Species | Locality | Materials | Notes | Image |
| Eocyclotosaurus | A capitosaurian temnospondyl |  | |||
| Mastodonsaurus? | A capitosaurian temnospondyl, some authors have consider the remains indeterminate and not belonging to the genus[3] |  | |||
| Temnospondyli | Indeterminate | Includes a third taxon apparently distinct from Eocyclotosaurus and Mastodonsaurus, as well as indeterminate fragmentary material | |||
Reptiles
[edit]| Reptiles of the Helsby Sandstone | |||||
|---|---|---|---|---|---|
| Genus | Species | Locality | Materials | Notes | Image |
| Agriodontosaurus [6] | A. helsbypetrae | A sphenodontian reptile known from a partial skeleton | .png) | ||
| Bentonyx | B. sidensis | A rhynchosaurian reptile, known from a skull |  | ||
| Coartaredens | C. isaaci | A reptile of uncertain classifcation, possibly a lepidosauromorph, but this is uncertain as it is only known from fragmentary remains | |||
| Chirotherium | Ichnogenus of fossil trackways thought to be produced by "rauisuchians" | ||||
| Feralisaurus[7] | F. corami | A small lepidosauromorph known from specimen BRSUG 29950-12, an articulated skeleton | |||
| Fodonyx | F. spenceri | A rhynchosaurian reptile, known from postcranial and skull material |  | ||
| Kapes | K. bentoni | A small lizard-like procolophonid reptile, known from a partial skeleton |  | ||
| Archosauria | Indeterminate | Remains include vertebrae, teeth and a jaw fragment, which may represent poposauroids, with the jaw fragment suggested to possibly represent Bromsgroveia. | |||
| Rhynchosauria | Most common vertebrates in the formation, remains include a headless skeleton | ||||
| Procolophonidae | Several indeterminate procolophonids distinct from Kapes, one of which has similarities to Sclerosaurus | ||||
References
[edit]- ^ "Helsby Sandstone Formation- BGS Lexicon of Named Rock Units". webapps.bgs.ac.uk. Retrieved 2025-09-10.
- ^ Bloomfield, J. P.; Moreau, M. F.; Newell, A. J. (January 2006). "Characterization of permeability distributions in six lithofacies from the Helsby and Wilmslow sandstone formations of the Cheshire Basin, UK". Geological Society, London, Special Publications. 263 (1): 83–101. Bibcode:2006GSLSP.263...83B. doi:10.1144/GSL.SP.2006.263.01.04. ISSN 0305-8719.
- ^ a b c d e Coram, Robert A.; Radley, Jonathan D.; Benton, Michael J. (June 2019). "The Middle Triassic (Anisian) Otter Sandstone biota (Devon, UK): review, recent discoveries and ways ahead". Proceedings of the Geologists' Association. 130 (3–4): 294–306. Bibcode:2019PrGA..130..294C. doi:10.1016/j.pgeola.2017.06.007.
- ^ Mountney, Nigel P.; Thompson, David B. (August 2002). "Stratigraphic evolution and preservation of aeolian dune and damp/wet interdune strata: an example from the Triassic Helsby Sandstone Formation, Cheshire Basin, UK". Sedimentology. 49 (4): 805–833. Bibcode:2002Sedim..49..805M. doi:10.1046/j.1365-3091.2002.00472.x. ISSN 0037-0746.
- ^ a b Coram, Robert A.; Radley, Jonathan D.; Benton, Michael J. (September 2021). "Triassic tragedy—a bone bed in the Otter Sandstone of East Devon, south-west England". Geology Today. 37 (5): 176–183. Bibcode:2021GeolT..37..176C. doi:10.1111/gto.12367. ISSN 0266-6979.
- ^ Marke, Daniel; Whiteside, David I.; Sethapanichsakul, Thitiwoot; Coram, Robert A.; Fernandez, Vincent; Liptak, Alexander; Newham, Elis; Benton, Michael J. (2025-09-10). "The oldest known lepidosaur and origins of lepidosaur feeding adaptations". Nature: 1–10. doi:10.1038/s41586-025-09496-9. ISSN 0028-0836.
- ^ Cavicchini, Iacopo; Zaher, Marta; Benton, Michael J. (2020-05-03). "An Enigmatic Neodiapsid Reptile from the Middle Triassic of England". Journal of Vertebrate Paleontology. 40 (3) e1781143. Bibcode:2020JVPal..40E1143C. doi:10.1080/02724634.2020.1781143. ISSN 0272-4634.