Turrilites acutus Subzone

From Earthwise
Jump to navigation Jump to search

Base: The base of the subzone is immediately below the first appearance of the ammonite Turrilites acutus (Robaszynski et al., 1998), although previously it has been placed somewhat lower, at the top of the highest of three widely developed Cenomanian acmes of the brachiopod Orbirhynchia mantelliana (Bristow et al., 1995).

Top: The top of the subzone is immediately below the first appearance of the ammonite Acanthoceras jukesbrownei (Robaszynski et al., 1998)

Range of index species: The index species occurs in the lower half of the subzone only (Robaszynski et al., 1998).

Key fauna:

Brachiopoda: Concinnithyris subundata
Bivalvia: Inoceramus atlanticus
Ammonoidea: Acanthoceras rhotomagense
Turrilites acutus

Faunal abundance & preservation: The subzone is rather sparsely fossiliferous, except for locally common terebratulid brachiopods.Ammonites are rather poorly preserved as iron-stained chalky moulds.

Bio-markers: Inoceramus atlanticus is common in the higher part of the subzone.

Age: Mid Cenomanian