The BGS Lexicon of Named Rock Units — Result Details

Perna Member

Computer Code: PRNA Preferred Map Code: notEntered
Status Code: Full
Age range: Aptian Age (KP) — Aptian Age (KP)
Lithological Description: Grey brown to dark blue, sandy, mudstone with bivalves, overlain by greenish, calcareous, coarse-grained sandstone. The beds are fossiliferous throughout and the lower Bed 1 of Simpson (1985) includes basal coarse-grained quartz 'grit' with bone fragments, fish teeth, phosphatic nodules and rolled ammonites (the Atherfield Bone-Bed of Simpson).
Definition of Lower Boundary: Disconformable contact between the grey rhythmically-bedded sandstones and mudstones of the underlying Shepherd's Chine Member (Vectis Formation) and the fossiliferous coarse-grained quartz grit of the Atherfield Bone-Bed (Simpson, 1985, Bed 1) at the base of the Perna Member.
Definition of Upper Boundary: Boundary at the upward change from coarse-grained greenish sandstone (Simpson, 1985, Bed 2) into chocolate brown to pale bluish grey mudstone (Simpson, 1985, Bed 3) of the Chale Clay Member.
Thickness: 1.8m at the type site.
Geographical Limits: The member is only clearly distinguished on the Isle of Wight. Elsewhere equivalents of the Atherfield Bone-Bed or Perna Member are known from Dorset (Punfield Cove) and around the Weald in Sussex, Surrey and Kent.
Parent Unit: Atherfield Clay Formation (AC)
Previous Name(s): The Perna Bed (-2380)
The Perna Mulleti Bed (-468)
Perna Beds Member (-1773)
Alternative Name(s): none recorded or not applicable
Type Section  Defined as the coastal cliff section of Chale Bay, Isle of Wight, between Shepherd's Chine [SZ 4466 7982] and Whale Chine [SZ 4684 7825]. 
Reference Section  The coastal cliff section at Red Cliff, Sandown [SZ 626 855]. Full succession but generally obscurred by landslide debris. 
Reference Section  The coastal cliff section at Compton Bay [SZ 372 848], Isle of Wight. Full succession generally visible. 
Simpson, M I. 1985. The stratigraphy of the Atherfield Clay Formation (Lower Aptian, Lower Cretaceous) at the type and other localities in southern England. Proceedings of the Geologists' Association, Vol.96(1), 23-45. 
Osborne White, H J. 1921 [1994 reprint]. A short account of the geology of the Isle of Wight. Memoirs of the Geological Survey of Great Britain. 235pp. [HMSO.] 
Fitton, W H. 1847. A stratigraphical account of the section from Atherfield to Rocken-end on the south-west coast of the Isle of Wight. Quarterly Journal of the Geological Society of London, Vol.3, 289-327. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable