An Upper Bajocian ammonite from the Raasay ‘Cornbrash’

Abstract

Until quite recently the ‘Cornbrash’ of Rassay has been an anomaly in the regional setting. The identification of a brachiopod fauna by S. S. Buckman as including Cererithyris intermedia (J. Sowerby) led Lee (1920, pp. 65 & 76) to a correlation with the Lower Cornbrash (Upper Bathonian) of southern and eastern England, but the litho- and biofacies of the Upper Bathonian on the neighbouring Trotternish peninsula of Skye are not at all similar (Hudson, in Torrens 1980; Bradshaw and Fenton 1982). After study of the rich microflora extracted from parts of the ‘Cornbrash’ outcrop, Bradshaw and Fenton (1982) were able to date the rocks as late Bajocian, subfurcatum to parkinsoni Zone. This was based primarily on a marine microplankton assemblage. The subfurcatum Zone is preferred by Bradshaw and Fenton because of lithological correlation with units of probable subfurcatum Zone age of south Trotternish (Morton 1976). During my recent undergraduate mapping project carried out in northern Raasay I examined the ‘Cornbrash’ outcrops in some detail. I was fortunate enough to find an ammonite within brown, gritty, fossiliferous sandstone 1.5 km N.E. of Storav's Grave above the middle branch of Glam Burn \[NG 5701 4290\] (Section 2 in fig. 1 of Bradshaw and Fenton 1982). The specimen comprises one third of a whorl in a good state of preservation with the ribs and ventral surface clearly visible. The specimen has been presented to the Royal Scottish Museum, registration number RSMGY. 1983. 16. 1. Prof. J. H. Callomon and Dr. H. S. Torrens . . .