Aspects of the stratigraphy and ammonite faunas of the Aalenian-Bajocian stages in Great Britain

Abstract

A detailed stratigraphic revision of parts of the Aalenian-Bajocian Stages is undertaken. The status of the Sowerbyi zone is discussed and reasons given for its rejection and replacement by the Discites and Laeviuscula
Zones. The Sauzei Zone is redefined. The detailed stratigraphy of the Humphriesianum/Subfurcatum Zone rocks of Southern England is described, its correlation discussed and a detailed analysis of their ammonite faunas given. The litho- and bio- stratigraphy of the Garantiana/Parkinsoni Zone rocks of the Sherborne area are revised. Formations and Members of the Cotswold Inferior Oolite Group are re-defined, and their Bajocian Ammonite faunas listed. The litho- and biostratigraphy of the Aalenian-Bajocian rocks of Dundry Hill, Bristol, are revised and the type horizons of Buckman's and Sowerbys' ammonite species located. The ammonite faunas of the Scarborough Formation of N.E. Yorkshire are revised and its lithostratigr- aphy described.
Two new Bajocian, microconch Otoitid species are described and their phylogenetic and stratigraphic significance discussed. A detailed systematic revision of the Sphaeroceratinae is given. Its constituent genera are re-defined and six species and subspecies of Sphaeroceras (S.), eight of Chondroceras (C.) including one new; and two subspecies of Labyrinthoceraa are described. The evolution of the subfamily is discussed, its problems of sexual dimorphism summarised,and the stratigraphic distribution and significance of its members detailed.
Finally a summary of the stratigraphic part of this work is given in a discussion of the Bajocian standard zonal
scheme.