Subzone of abundant Offaster pilula
The subzone is only developed in southern England. In Northern Ireland, a non-sequence is thought to omit this horizon (Wilson & Manning, 1978).
Base: In southern England, the base of the subzone is placed at a thin marl c. 1 m beneath the Old Nore Marl (Young & Lake, 1988).
Top: In southern England, the top of the subzone is placed at Telscombe Marl 4.
Range of index species: The index is the same as for the parent zone, except that it is characteristically much more common, being concentrated into two acmes, one at the base of the subzone and another at the top. The index ranges above the nominate subzone, but is much rarer.
|O. pilula planata|
Bio-markers: An acme of Offaster pilula at the base of the subzone coincides with an acme of Terebratulina rowei and Echinocorys truncata (Mortimore, 1986; Young & Lake, 1988). In the centre of the subzone Echinocorys cincta is predominant and Offaster pilula scarce or absent, followed by a return to abundant O. pilula in the top of the subzone, accompanied by the giant subspecies O. pilula planata (Mortimore, 1986; Young & Lake, 1988). Brydone (1939) named the acme of giant O. pilula at the top of the subzone the 'Planoconvexus Bed'.