BGS Zone 24 (=UKB20 of Hart et al., 1989)

Base: Inception of Bolivinoides peterssoni.

Top: Inception of Bolivinoides paleocenicus.

Biomarkers:

• Globotruncanella havanesis and Rugoglobigerina milamensis are consistently present for the first time from the base of the zone (although very rare specimens may occur immediately below it).

• A number of species appear for the first time at or immediately above the base: Bolivinoides decurrens, Bolivinoides australis, Gavelinella bembix, Osangularia navarroana and Neoflabellina reticulata.

• Pyramidina minuta has its inception in the highest B. mucronata macrofuanal zone (although it is very rare) and becomes more numerous in the early Maastrichtian.

• Eponides beisseli and Valvulineria lenticularis become extinct at the top of the zone.

Subzones:

24i: Concurrent range of Bolivinoides peterssoni and B. decoratus (in the Sidestrand Chalk Member). Hedbergella holmdelensis apparently becomes extinct at the top of the subzone.

24ii:. From the extinction of B. decoratus to the top of the zone (in the Sidestrand Chalk Member).

Macrofaunal correlation: Early B. lanceolata Zone s.l.

Age: Early Maastrichtian