Stratigraphy and ammonite faunas of the Cenomanian rocks of Northern Ireland, UK

Abstract

A re-examination of surviving outcrops of the Cenomanian parts of the Hibernian Greensands Formation of south and east Antrim in Northern Ireland, together with a revision of the limited ammonite faunas, provide a basis for dating and interpreting the sequence. The lower part of the Belfast Marls Member yields an early Cenomanian Mantelliceras dixoni Zone assemblage, whilst other faunal elements suggest the upper part extends into the lower part of the middle Cenomanian. The succeeding Islandmagee Siltstones Member yields the index species of the middle Cenomanian Acanthoceras rhotomagense and A. jukesbrownei zones. The Collinwell Sands Member is in part, or whole, of late Cenomanian age on the basis of the occurrence of the benthic foraminiferan Orbitolina. The erosion surface at the base of the Belfast Marls Member corresponds to the Ce3 maximum flooding surface recognised in the Anglo-Paris Basin; the erosion surface at the base of the Islandmagee Siltstones to the Ce4 maximum flooding surface and the erosion surface at the base of the Collinwell Sands Member to the sub-plenus erosion surface at the base of the late Cenomanian Metoicoceras geslinianum Zone.