Beacon Limestone Formation

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 ~185–175 Ma PreꞒ Ꞓ O S D C P T J K Pg N
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	50.9°N 2.8°W / 50.9; -2.8
Approximate paleocoordinates	38.4°N 7.4°E / 38.4; 7.4
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

Among others, the following fossils have been reported from the formation:

Vertebrates

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
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

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