Biostratigraphical criteria for the recognition of the Coniacian to Maastrichtian stage boundaries in the Chalk of north-west Europe, with particular reference to southern England.

Abstract

The biostratigraphical criteria for the recognition of Coniacian to Maastrichtian stage boundaries in the English Chalk, published in the Abstracts to the Copenhagen Symposium on Cretaceous Stage Boundari­es 1983, are reviewed in the light of the discussion at the Symposium and the final recommendations. Particular attention is given to problems relating to the base of the Coniacian and Santonian Stages. A critical assessment is made of criteria used by French workers for recognising the base of the Senonian Stage in the Anglo-Paris Basin. Benthonic Foraminifera used to identify the base of the Senonian are shown to have discrepant ranges in Kent compared with Sussex and Senonian stratotype. The nannofossil Marthasterites furcatus first appears below the level of acme-occurrence of ammonites of the Late Turonian Subprionocyclus neptuni Zone in southern England, and cannot therefore be used as a marker to identify the base of the Coniacian in the Anglo-Paris Basin. Extended comment is made on the bio­stratigraphy of the successions in southern England and northern Germany across the Coniacian - Santonian boundary, and it is suggested that the Upper Coniacian Micraster bucaillei/Gonioteuthis praewestfalica Zone of the German Lligerdorf standard section should be re-assigned to the basal part of the Santonian. The base of the Campanian Stage in southern England is arbitrarily taken at the evolution­ary first appearance of Bolivinoides culverensis, a level coincident with the top of the local Uintacrinus anglicus Zone, rather than at the extinction-level of Marsupites and/or entry of Gonioteuthis granulata­quadrata lower in the succession. The entry of the nannofossil Broinsonia parca, widely taken as a criterion for recognising the base of the Campanian Stage, is shown to occur at an horizon well above the entry-level of B. culverensis.