# Helsby Sandstone Formation

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Geological formation in England

Helsby Sandstone Formation Stratigraphic range: Middle Triassic Anisian PreꞒ Ꞓ O S D C P T J K Pg N Exposures of Helsby Sandstone Formation 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](/source/Devon) and [Somerset](/source/Somerset)), is a geological formation in England. It was deposited during the [Anisian](/source/Anisian) stage of the [Middle Triassic](/source/Middle_Triassic) epoch. It primarily consists of [medium to fine grained](/source/Grain_size) [sandstone](/source/Sandstone), both [cross bedded](/source/Cross-bedded) and flat bedded, with minor [lenticular beds](/source/Lenticular_bedding) of [siltstone](/source/Siltstone) and [mudstone](/source/Mudstone) and thin beds of [conglomerate](/source/Conglomerate_(geology)) in some areas. It is found across England, from [Devon](/source/Devon) on the southern coast to [Cumbria](/source/Cumbria) in the north, with some exposures in [Worcestershire](/source/Worcestershire) and in [Staffordshire](/source/Staffordshire) in the Midlands.[1] It was deposited in a hot, [arid climate](/source/Desert_climate), when Britain formed part of the [Pangean](/source/Pangaea) interior[2][3] with the cross-bedded sandstones of the formation representing remnants of [wind-blown](/source/Aeolian_processes) [sand dunes](/source/Sand_dunes),[4] while the majority of the formation was produced by the action of [braided rivers](/source/Braided_river), 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](/source/Irish_Sea). The environment of the formation likely also included [ponds](/source/Pond) and small [lakes](/source/Lake), with surrounding vegetation including [conifers](/source/Conifer) (whose roots are preserved as [concretions](/source/Concretion)) and [horsetails](/source/Equisetaceae). Towards the top of the formation, the rocks indicate that the conditions became more arid, with the overlying formations showing the disappearance of rivers and the existence of [playa](/source/Endorheic_basin)-like conditions.[3]

The formation in its southern coastal exposure in Devon in the vicinity of [Sidmouth](/source/Sidmouth) has provided important fossils of contemporary vertebrates, including [temnospondyl](/source/Temnospondyli) amphibians, [procolophonid](/source/Procolophonidae), [rhynchosaurian](/source/Rhynchosauria), [sphenodontian](/source/Sphenodontian) and [archosaurian](/source/Archosaur) reptiles, as well as fish.[3]

## Paleobiota

Taken from[3] unless otherwise noted:

### Fish

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] Fossil of the closely related species D. aculeatus 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

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

Reptiles of the Helsby Sandstone Genus Species Locality Materials Notes Image Agriodontosaurus [6] A. helsbypetrae A sphenodontian reptile known from a partial skeleton Bentonyx B. sidensis A rhynchosaurian reptile, known from a skull Coartaredens C. isaaci A reptile of uncertain classification, 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

1. **[^](#cite_ref-1)** ["Helsby Sandstone Formation- BGS Lexicon of Named Rock Units"](https://webapps.bgs.ac.uk/lexicon/lexicon.cfm?pub=HEY). *webapps.bgs.ac.uk*. Retrieved 2025-09-10.

1. **[^](#cite_ref-2)** 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"](https://www.lyellcollection.org/doi/10.1144/GSL.SP.2006.263.01.04). *Geological Society, London, Special Publications*. **263** (1): 83–101. [Bibcode](/source/Bibcode_(identifier)):[2006GSLSP.263...83B](https://ui.adsabs.harvard.edu/abs/2006GSLSP.263...83B). [doi](/source/Doi_(identifier)):[10.1144/GSL.SP.2006.263.01.04](https://doi.org/10.1144%2FGSL.SP.2006.263.01.04). [ISSN](/source/ISSN_(identifier)) [0305-8719](https://search.worldcat.org/issn/0305-8719).

1. ^ [***a***](#cite_ref-:0_3-0) [***b***](#cite_ref-:0_3-1) [***c***](#cite_ref-:0_3-2) [***d***](#cite_ref-:0_3-3) [***e***](#cite_ref-:0_3-4) 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"](https://linkinghub.elsevier.com/retrieve/pii/S0016787817300925). *Proceedings of the Geologists' Association*. **130** (3–4): 294–306. [Bibcode](/source/Bibcode_(identifier)):[2019PrGA..130..294C](https://ui.adsabs.harvard.edu/abs/2019PrGA..130..294C). [doi](/source/Doi_(identifier)):[10.1016/j.pgeola.2017.06.007](https://doi.org/10.1016%2Fj.pgeola.2017.06.007). [hdl](/source/Hdl_(identifier)):[1983/e9769a73-9c34-43b5-813c-bdd2b9478d9f](https://hdl.handle.net/1983%2Fe9769a73-9c34-43b5-813c-bdd2b9478d9f).

1. **[^](#cite_ref-4)** 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"](https://onlinelibrary.wiley.com/doi/10.1046/j.1365-3091.2002.00472.x). *Sedimentology*. **49** (4): 805–833. [Bibcode](/source/Bibcode_(identifier)):[2002Sedim..49..805M](https://ui.adsabs.harvard.edu/abs/2002Sedim..49..805M). [doi](/source/Doi_(identifier)):[10.1046/j.1365-3091.2002.00472.x](https://doi.org/10.1046%2Fj.1365-3091.2002.00472.x). [ISSN](/source/ISSN_(identifier)) [0037-0746](https://search.worldcat.org/issn/0037-0746).

1. ^ [***a***](#cite_ref-:1_5-0) [***b***](#cite_ref-:1_5-1) 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"](https://onlinelibrary.wiley.com/doi/10.1111/gto.12367). *Geology Today*. **37** (5): 176–183. [Bibcode](/source/Bibcode_(identifier)):[2021GeolT..37..176C](https://ui.adsabs.harvard.edu/abs/2021GeolT..37..176C). [doi](/source/Doi_(identifier)):[10.1111/gto.12367](https://doi.org/10.1111%2Fgto.12367). [ISSN](/source/ISSN_(identifier)) [0266-6979](https://search.worldcat.org/issn/0266-6979).

1. **[^](#cite_ref-6)** 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"](https://www.nature.com/articles/s41586-025-09496-9). *Nature*: 1–10. [doi](/source/Doi_(identifier)):[10.1038/s41586-025-09496-9](https://doi.org/10.1038%2Fs41586-025-09496-9). [ISSN](/source/ISSN_(identifier)) [0028-0836](https://search.worldcat.org/issn/0028-0836). [PMC](/source/PMC_(identifier)) [12629995](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12629995).

1. **[^](#cite_ref-7)** Cavicchini, Iacopo; Zaher, Marta; Benton, Michael J. (2020-05-03). ["An Enigmatic Neodiapsid Reptile from the Middle Triassic of England"](https://www.tandfonline.com/doi/full/10.1080/02724634.2020.1781143). *Journal of Vertebrate Paleontology*. **40** (3) e1781143. [Bibcode](/source/Bibcode_(identifier)):[2020JVPal..40E1143C](https://ui.adsabs.harvard.edu/abs/2020JVPal..40E1143C). [doi](/source/Doi_(identifier)):[10.1080/02724634.2020.1781143](https://doi.org/10.1080%2F02724634.2020.1781143). [ISSN](/source/ISSN_(identifier)) [0272-4634](https://search.worldcat.org/issn/0272-4634).

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Adapted from the Wikipedia article [Helsby Sandstone Formation](https://en.wikipedia.org/wiki/Helsby_Sandstone_Formation) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Helsby_Sandstone_Formation?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.