BGS Zone 21 (=UKB17 and lower UKB 18 of Hart et al., 1989)

Base: Inception of Gavelinella monterelensis.

Top: Inception of Reussella szajnochae szajnochae.

Biomarkers:

• Gavelinella voltzianus and Globotruncana rugosa as well as Gavelinella monterelensis have their inception at the Farlington Marls (at the G. quadrata / B. mucronata macrofaunal zonal boundary).

• Gavelinella trochus becomes extinct in the early B. mucronata macrofaunal zone (at the top of the Pre-Weybourne Chalk of the East Anglian succession).

Subzones:

21i: The concurrent range of Gavelinella monterelensis and Gavelinella usakensis in the lower part of the B. mucronata macrofaunal zone (between the Farlington Marls in southern England and the top of the Pre-Weybourne Chalk in East Anglia).

21ii: Between the extinction of Gavelinella usakensis and inception of Coryphostoma pliata through to the extinction of Gavelinella lorneiana and Gavelinella thalmanni and inception of Globotruncana bulloides austinensis and Globotruncana plummerae (= lower part of the Weybourne Chalk in East Anglia).

21iii: From the extinction of Gavelinella lorneiana and Gavelinella thalmanni and inception of Globotruncana bulloides austinensis and Globotruncana plummerae through to the extinction of consistent Globorotalites michelinianus and Rosita fornicata and inception of Reussella szajnochae szajnochae (= upper part of the Weybourne Chalk to the base of the Catton Sponge Bed in East Anglia).

Macrofaunal correlation: lower B. mucronata Zone

Age: Campanian