Hagenowia (blackmorei) Horizon (Subzone)

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This interval of the G. quadrata Zone has only been formally recognised in southern England.

Base: In southern England, the base of the horizon is placed at Telscombe Marl 4 (Mortimore, 1986; Young & Lake, 1988).

Top: In southern England, the top of the horizon is placed at the Lancing Flint (Mortimore, 1986).

Range of index species: The index, Hagenowia blackmorei ranges from the top of the O. pilula Zone to within the middle of the nominate Horizon / Subzone (Mortimore, 1986).

Key fauna:

Porifera: Retispinopora lancingensis
Anthozoa: Coelosmilia regularis
Brachiopoda: Cretirhynchia intermedia
Isocrania egnabergensis (large)
Kingena blackmoorei
Orbirhynchia bella
Bivalvia: Inoceramus sarumensis
I. subsarumensis
Belemnoidea: Belemnitella mucronata
Gonioteuthis quadrata
Echinoidea: E. sp. (large form of Gaster, 1924)
E. sp. (small form of Gaster, 1924)
Hagenowia blackmorei

Faunal abundance & preservation: This interval is quite poorly fossiliferous, the index species and some of the allied fauna are also quite small and inconspicuous.

Bio-horizons: The index is quite inconspicuous, comprising fragments of the distinctively elongated rostrum. Retispinopora lancingensis and Isocrania egnabergensis are also small fossils. In southern England, there are two successive acmes of Echinocorys, the first, comprising the 'large forms' of Gaster (1924), are large, evenly rounded, hemispherical morphotypes with a sharply defined, flat base. These are overlain by an acme of the 'small forms' of Gaster (1924), comprising morphotypes that resemble Echinocorys cincta and E. depressula from the underlying O. pilula Zone (Young & Lake, 1988). There is a local acme of Belemnitella at this horizon in the Salisbury area, which seems to be more widely developed at a comparable level in the G. quadrata Zone in Northern Ireland (Bailey et al., 1983; Wilson & Manning, 1978).

Age: Campanian