The ammonite succession in the Lower Oxford Clay and Kellaways beds at Kidlington, Oxfordshire, and the zones of the Callovian stage

Abstract

The paper describes temporary sections through the Lower Oxford Clay, Kellaways Rock and Kellaways Clay down to the Cornbrash in a part of England in which these beds were previously little known. All the beds were fossiliferous, and more than 200 ammonites ascribed to twentyfive species were collected in situ , bed by bed throughout the succession. The ammonites of the genus Kosmoceras in the Lower Oxford Clay were sufficiently numerous to allow them to be studied statistically by the methods employed by Brinkmann in 1929 on similar ammonites of the same age from the Lower Oxford Clay at Peterborough. His results for the lower part of the sequence comprising the jason Zone were fully reproduced. In addition, ammonites of other genera were found, including several specimens of Reineckeia, among the first to be recorded from beds of this age in this country. The Kellaways Rock, consisting mainly of sands, was extremely fossiliferous and yielded, besides many lamellibranchs and gastropods, numerous, although poorly preserved, ammonites. These were the same as those of the Kellaways Rock of Wiltshire, with the addition of a specimen of Macrocephalites sensu stricto . The Kellaways Clay was poorly fossiliferous, but it produced six specimens of Macrocephalites (subgenera Kamptokephalites and Dolikephats ), an assemblage similar to that of the Upper Cornbrash of Yorkshire and quite different from that of the Kellaways Clay of Wiltshire. The position of this clay above typical Upper Cornbrash as developed in south-west England, and belonging to the siddingtonensis and in part lagenalis brachiopod Subzones, confirms previous suspicions that the Cornbrash of Yorkshire is later than that of the south-west. In the light of these results, the older evidence relating to the beds of this age in this country and abroad, including some of the old collections, is re-examined. Additional information from new or undescribed exposures at Calvert, Frome, Sutton Bingham near Yeovil, Weymouth, and Herznach in Switzerland, is included. In consequence, a much closer correlation of the beds of the Middle and Lower Callovian than was previously possible is now made between outcrops in Scotland, Yorkshire, north-west Germany, central and south-west England and the Argovian Jura. A revised zonal table of the Callovian has been constructed, designed to be generally applicable to the area outlined above and including as subzones finer divisions which are in practice recognizable more locally. The relation between these west European zones and some of those used in the Mediterranean province is briefly indicated.