The BGS Lexicon of Named Rock Units — Result Details

Langness Conglomerate Formation

Computer Code: LNCO Preferred Map Code: notEntered
Status Code: Full
Age range: Early Devonian Epoch (DL) — Courceyan Substage (CF)
Lithological Description: Conglomerate with subordinate interbedded sandstone. The conglomerate is reddish brown, generally poorly sorted, occasionally moderately sorted with angular to subrounded clasts typically 0.1m in size, varying up to 0.3m. Clasts are predominantly quartzites, with some slate, vein quartz and mudstone. The conglomerate is typically clast-supported, with matrix comprising fine sand, silt or less commonly clay. In the upper part of the formation the clast size is reduced and sorting and clast sphericity increases. In places bedding can be detected; this is typically erosive into underlying conglomerate beds. Sedimentary structures include crude stratification and rare cross-bedding. This formation represents an alluvial fan deposit, transported by debris flow and streamflow processes.
Definition of Lower Boundary: The formation is unconformable onto the underlying Ordovician aged Lonan Formation. This unconformity is clearly demonstrated at outcrop on the foreshore at Langness Peninsula and illustrated in Chadwick et al. (2001, Plate 10). Contact can be clearly seen to be unconformable on these steeper dipping Palaeozoic mudstone strata.
Definition of Upper Boundary: The Langness Conglomerate Formation is overlain by the Turkeyland Member of the Derbyhaven Formation. The contact is present on the foreshore of the Langness Peninsula [SC 2820 6607], although exposures are discontinuous and poorly exposed. Here it would appear that the Turkeyland Member rests directly on the conglomerate. The contact was also formerly exposed at the now infilled Turkeyland Quarry [SC 2950 6940], where the Turkeyland Member was recorded by Dickson et al. (1987) as resting directly on conglomerates of the Langness Conglomerate Formation. There would appear to be some reworking of the top of the Langness Conglomerate Formation at the Langness Peninsula section because the upper part of the formation comprises clean, cross-bedded sandstones formed by reworking of the underlying terrestrial clastic deposits.
Thickness: 30m.
Geographical Limits: Southern part of the Isle of Man in the Castletown area, from the south-west corner of Langness Peninsula [SC 2819 6604] to Derbyhaven [SC 2918 6810] and north-west to east of Ballasalla, from [SC 2751 7160] to [SC 2960 6936].
Parent Unit: Ravenstonedale Group (RVS)
Previous Name(s): Basement Conglomerate (-3187)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Foreshore exposures along the Langness Peninsula Dickson et al.(1987) estimated 30m of coarse clastic sedimentary rocks are present. 
Reference(s):
Chadwick, R A, Jackson, D I, Barnes, R P, Kimbell, G S, Johnson, H, Chiverell, R C, Thomas, G S P, Jones, N S, Riley, N J, Pickett, E A, Young, B, Holliday, D W, Ball, D F, Molyneux, S G, Long, D, Power, G M and Roberts, D H. 2001. Geology of the Isle of Man and its offshore area. British Geological Survey Research Report, RR/01/06. 
Lamplugh G W. 1903. The geology of the Isle of Man. Memoir Geological Survey of Great Britain 
Dickson, J A D, Ford, T D and Swift, A. 1987. The stratigraphy of the Carboniferous rocks around Castletown, Isle of Man. Proceedings of the Yorkshire Geological Society, Vol.46, 203-229. 
Lewis, H P. 1930. The Avonian succession in the south of the Isle of Man. Quarterly Journal of the Geological Society of London, 86, 234-290. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E400