Nannotax3 - ntax_mesozoic - Eiffellithus keio

Distinguishing features:
Parent taxon (Eiffellithus): Loxolith coccoliths with a prominent inner rim cycle that is birefringent and conspicuous in cross-polarised light; this cycle is broader than the outer rim cycle. The central area is spanned by variably-orientated cross-bars.
This taxon: Like E. turriseiffellii but with bifurcate tips to the cross-bars.

Citation: Eiffellithus keio Shamrock & Watkins 2009

Taxonomic discussion: This form has a restricted range in the Late Albian and Cenomanian and so is clearly worth distinguishing.

E. parallelus also has diagonal cross-bards and with bifurcet tips but in E. keio the bifurcations are larger, the cross is less regular, and the median extinction line less clear. They also have non-overlapping ranges.

Most likely ancestor: Eiffellithus turriseiffelii - at confidence level 3 (out of 5). Data source: Shamrock & Watkins 2009.

Geological Range:
Notes: Recorded by Shamrock and Watkins (2009) from Late Cenomanian only, but similar forms are docuemnted inthe ltierature from the Late Albian and Early Cenomanian - see images reassigned here to E. keio
Last occurrence (top): within Late Cenomanian Substage (93.90-95.50Ma, top in Cenomanian stage). Data source: Shamrock & Watkins 2009
First occurrence (base): within NC10a subzone (100.45-103.13Ma, base in Albian stage). Data source: images from Bown in Gale (2001) and Applegate & Bergen (1988)

References:

Applegate, J. L. & Bergen, J. A. (1988). Cretaceous calcareous nannofossil biostratigraphy of sediments recovered from the Galicia Margin, ODP Leg 103. Proceedings of the Ocean Drilling Program, Scientific Results. 103: 293-348. gs O

Bown, P. R. (2001). Calcareous nannofossils of the Gault, Upper Greensand and Glauconitic Marl (Middle Albian-Lower Cenomanian) from the BGS Selborne boreholes, Hampshire. Proceedings of the Geologists' Association. 112: 223-236. gs

Gale, A. S. et al. (2011). The uppermost Middle and Upper Albian succession at the Col de Palluel, Hautes-Alpes, France: An integrated study (ammonites, inoceramid bivalves, planktonic foraminifera, nannofossils, geochemistry, stable oxygen and carbon isotopes, cyclostratigraphy). Cretaceous Research. 32: 59-130. gs

Shamrock, J. L. & Watkins, D. K. (2009). Evolution of the Cretaceous calcareous nannofossil genus Eiffellithus and its biostratigraphic significance. Cretaceous Research. 30(5): 1083-1102. gs

Eiffellithus keio

References:

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