The Beacon Limestone Formation, historically known as the Junction Bed, is a formation of the early Jurassic age (Pliensbachian–Toarcian). It lies above the Dyrham Formation and below the Bridport Sand Formation. It forms part of the Lias Group. It is found within the Wessex Basin and parts of Somerset,[1] in England. It is well known for the Strawberry Bank Lagerstätte, which contains the 3-dimensionally preserved remains of vertebrates, including marine crocodyliformes, ichthyosaurs and fish, as well as insect compression fossils.[2]
| Beacon Limestone Formation | |
|---|---|
| Stratigraphic range: Upper Pliensbachian–Toarcian Spinatum-lowermost Thouarsense ~ | |
.jpg){kind=tracking} Cliff exposure at Thorncombe Beacon | |
| Type | Geological formation |
| Unit of | Lias Group |
| Sub-units | Marlstone Rock, Barrington & Eype Mouth Limestone Members |
| Underlies | Bridport Sand Formation |
| Overlies | Dyrham Formation |
| Thickness | Up to 5 metres (16 ft) Averaging <1.5 metres (4.9 ft) |
| Lithology | |
| Primary | Limestone |
| Location | |
| Coordinates | 50°54′N 2°48′W / 50.9°N 2.8°W |
| Approximate paleocoordinates | 38°24′N 7°24′E / 38.4°N 7.4°E |
| Region | Somerset, Dorset |
| Country |  England |
| Extent | Wessex Basin |
| Type section | |
| Named for | Thorncombe Beacon |
| Location | Cliff exposure beneath Thorncombe Beacon |
  Beacon Limestone Formation (England) | |
Fossil content
editAmong others, the following fossils have been reported from the formation:
Vertebrates
edit| Vertebrates of the Beacon Limestone | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Abundance | Notes | Images |
| Hauffiopteryx | H. typicus | Strawberry Bank | Falciferum zone | Lectotype: GPIT 1491/4, referred: BRLSI M1399, BRLSI M1400,
BRLSI M1401, BRLSI M1403, BRLSI M1404 and BRLSI M1406[3] partial skeletons |
Ichthyosaur subsequently suggested to belong to Leptonectes[4] | |
| Stenopterygius | S. triscissus | Holotype: GPIT 12/0224-2 referred: BRLSI M1405, BRLSI M1407, BRLSI M1408 and BRLSI M1409[3] partial skeletons | Ichthyosaur | |||
| Pelagosaurus | P. typus | "four isolated skulls and associated postcranial skeletal elements along with two articulated specimens, one of which is a small juvenile"[5] | Thalattosuchian | |||
| Pachycormus | P. macropterus | BRLSI M1297, BRLSI M1299, BRLSI M1320, BRLSI M1332, BRLSI M1359, BRLSI M1389, BRLSI M1395, BRLSI M1341, BRLSI M1351, BRLSI M1366, BRLSI M1393[6] | Pachycormiform fish | .png) | ||
| Leptolepis | Indeterminate | BRLSI M1259 complete specimen.[2] | 4–8 cm (1.6–3.1 in) in length | GB3D | ||
| Lepidotes | Indeterminate | 40–45 cm (16–18 in) in length | ||||
| Caturus | Indeterminate | "two specimens, including an isolated neurocranium (BRLSI M1288)"[2] | Amiiform fish | BRLSI | ||
Invertebrates
edit| Invertebrates of the Beacon Limestone | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Abundance | Notes | Images |
| Trivenapteron[7] | T. moorei | Strawberry Bank | Falciferum zone | Dermapterid earwig | ||
| Fulgoridulum | Indeterminate | Fulgoridiid planthopper | ||||
| Necrotaulius[8] | N. parvulus | Necrotauliid Trichopteran | ||||
| Liassogomphidae | Indeterminate | Odonata | ||||
| Elcanidae | Orthoptera | |||||
| Archegocimicidae | Hemiptera | |||||
References
edit- ^ "Beacon Limestone Formation". BGS Lexicon of Named Rock Units. Retrieved 8 March 2018.
- ^ a b c Williams, Matt; Benton, Michael J.; Ross, Andrew (November 2015). "The Strawberry Bank Lagerstätte reveals insights into Early Jurassic life". Journal of the Geological Society. 172 (6): 683–692. Bibcode:2015JGSoc.172..683W. doi:10.1144/jgs2014-144. hdl:1983/a7fc8bb4-889c-4fe9-b049-86d284141316. ISSN 0016-7649. S2CID 52971056.
- ^ a b Caine, Hannah; Benton, Michael J. (September 2011). "Ichthyosauria from the Upper Lias of Strawberry Bank, England". Palaeontology. 54 (5): 1069–1093. Bibcode:2011Palgy..54.1069C. doi:10.1111/j.1475-4983.2011.01093.x.
- ^ Marek, Ryan D.; Moon, Benjamin C.; Williams, Matt; Benton, Michael J. (15 June 2015). "The skull and endocranium of a Lower Jurassic ichthyosaur based on digital reconstructions". Palaeontology. 58 (4): 723–742. Bibcode:2015Palgy..58..723M. doi:10.1111/pala.12174. ISSN 0031-0239. S2CID 131581009.
- ^ Pierce, Stephanie E.; Benton, Michael J. (11 September 2006). "Pelagosaurus typus Bronn, 1841 (Mesoeucrocodylia: Thalattosuchia) from the Upper Lias (Toarcian, Lower Jurassic) of Somerset, England" (PDF). Journal of Vertebrate Paleontology. 26 (3): 621–635. doi:10.1671/0272-4634(2006)26[621:PTBMTF]2.0.CO;2. ISSN 0272-4634. S2CID 131524957.
- ^ Cawley, John J.; Kriwet, Jürgen; Klug, Stefanie; Benton, Michael J. (20 September 2018). "The stem group teleost Pachycormus (Pachycormiformes: Pachycormidae) from the Upper Lias (Lower Jurassic) of Strawberry Bank, UK". PalZ. 93 (2): 285–302. doi:10.1007/s12542-018-0431-7. hdl:1983/1a98e5d7-53a8-4f69-b1cd-64c284303128. ISSN 0031-0220.
- ^ Kelly, Richard S.; Ross, Andrew J.; Jarzembowski, Edmund A. (June 2016). "Earwigs (Dermaptera) from the Mesozoic of England and Australia, described from isolated tegmina, including the first species to be named from the Triassic". Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 107 (2–3): 129–143. Bibcode:2016EESTR.107..129K. doi:10.1017/s1755691017000329. hdl:1983/d363e702-e4cb-4285-8ee8-393e808c890e. ISSN 1755-6910.
- ^ 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.