The BGS Lexicon of Named Rock Units — Result Details

Breakish Formation

Computer Code: BRKH Preferred Map Code: BkL
Status Code: Full
Age range: Hettangian Age (JH) — Sinemurian Age (JS)
Lithological Description: The Breakish Formation comprises blue-grey micritic limestone and dark calcareous mudstones within the lower half of the unit. The upper half of the unit consists of bioclastic limestones, ooidal limestone and nodular limestones. Ammonites are rare within the succession, but bivalve and gastropod fragments are common. Bioturbation of the sediments is locally intense. Coral beds exist near Broadford.
Definition of Lower Boundary: Unconformity - diachronous transgression at start of Jurassic.
Definition of Upper Boundary: Abrupt lithology change to sandstone and siltstone.
Thickness: 0 to 65 m.
Geographical Limits: Sea of the Hebrides Basin.
Parent Unit: Lias Group (LI)
Previous Name(s): Lower Broadford Beds [Obsolete Name and Code: Use BFB, BRKH] (-1345)
Alternative Name(s): Broadford Beds Formation [Obsolete: use ADS, BRKH]
Stratotypes:
Reference Section  Hallaig, Isle of Raasay. Morton, 1999. 
Type Section  Ob Lusa to Lower Breakish Village, Broadford, Isle of Skye. Morton, 1999. 
Reference(s):
Morton, N. 1999. Discussion of the Lower Lias Group of the Hebrides Basin; reply by Hesselbo, S P, Oates, M J and Jenkyns, H C. Scottish Journal of Geology, Vol.35 Part 1, 85-88. 
Waters, C N, Gillespie, M R, Smith, K, Auton, C A, Floyd, J D, Leslie, A G, Millward, D, Mitchell, W I, McMillan, A A, Stone, P, Barron, A J M, Dean, M T, Hopson, P M, Krabbendam, M, Browne, M A E, Stephenson, D, Akhurst, M C, and Barnes, R P. 2007. Stratigraphical Chart of the United Kingdom: Northern Britain. (British Geological Survey.) 
Hesselbo, S P, Oates, M J and Jenkyns, H C. 19998. The Lower Lias Group of the Bebrides Basin. Scottish Journal of Geology, Vol.34, Part 1, 23-60. 
Hesselbo, S P and Coe, A L. 2000. Jurassic sequences of the Hebrides Basin, Isle of Skye, Scotland. In: Graham, J R and Ryan, A, (editors). Field trip guidebook, International Association of Sediementologists Meeting, Dublin, 2000, (University of Dublin, Ireland), p41-58. 
Morton, N. 1999b. Middle Hettangian (Lower Jurassic) ammonites from the Isle of Raasay, Inner Hebrides, and correlation of the Hettangian - lowermost Sinemurian Breakish Formation in the Skye area, north-western Scotland. Scottish Journal of Geology, Vol.35, Part 2, 119-130. 
Morton, N and Hudson, J D, 1995. Field Guide to the Jurassic of the Isles of Raasay and Skye, Inner Hebrides, north-west Scotland. In: Taylor, P D (editor), Field Geology of the British Jurassic. Geological Society of London, 209-280. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S071 S081