Gonioteuthis quadrata gracilis / Belemnitella mucronata Zone
Base: In both the European standard and English successions, the base of the zone is recognised by the first occurrence of B. mucronata (Christensen, 1991).
Range of index species: In both the European standard and English successions the range of G. quadrata gracilis is from the base of the underlying G. quadrata gracilis Zone to the top of the current zone (Christensen, 1991). B. mucronata ranges upwards from the base of the current zone (the top of the range of B. mucronata was not detailed by Christensen, 1991). The zone is thus characterised by the co-occurrence of G. quadrata gracilis and B. mucronata.
Biostratigraphical correlation: The zone equates with the top of the G. quadrata Zone (top 'post Applinocrinus beds') of the standard macrofossil zonal scheme for the UK Chalk Group (Christensen, 1991).
Lithostratigraphical correlation: The zone can be inferred to equate with the basal part of the Portsdown Chalk Formation of southern England.
Age: Campanian (Christensen, 1991).