Mantelliceras saxbii Subzone
Base: The base of the M. saxbii Subzone is recognised by the appearance of common compressed ammonites of the M. saxbii group.
Top: The top of the subzone is immediately below the first appearance of M. dixoni.
Range of index species: Inflated forms of the index species first occur in the S. schlueteri Subzone. The index is abundant in the nominate subzone where inflated forms are scarce, and it occurs rarely in the overlying M. dixoni Zone (Wright & Kennedy, 1984).
|Mantelliceras saxbii (common)|
Heteromorph ammonites like Anisoceras and Idiohamites are absent (Kennedy, 1969).
Faunal abundance and preservation: The fauna is sometimes phosphatised, due to an erosion event at the junction of the M. mantelli and M. dixoni zones (Gale, 1995).
Age: Early Cenomanian