Nannotax3 - ntax_mesozoic - Eiffellithus monechiae

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: Medium sized Eiffellithus with cross bars aligned within 20° of the major axes (within 10° according to Watkins & Bergen 2003).

Citation: Eiffellithus monechiae Crux, 1991

Taxonomic discussion: Hill & Bralower (1987) showed that E. eximius as understood at the time (i.e Eiffelithus specimens with sub-axial crossbars) consisted of two separate forms with a gap between their ranges - a late Albian - Early Cenomanian form and a Turonian to Campanian form. These are now known respectively as E. monechiae and E. eximius.

The original diagnosis states that the cross bars should be aligned within 20° of the major axes. Watkins and Bergen (2003) emended this diagnosis stating that the species has an asymmetrical diagonal cross subparallel to the ellipse axes, with rotation of not greater than 10°. They described two additional species, Eiffellithus praestigium, with asymmetric bars rotated by 10-20°, and Eiffellithus vonsalisiae rotated by 20-35°.

Geological Range:
Last occurrence (top): within Early Cenomanian Substage (96.24-100.50Ma, top in Cenomanian stage). Data source: Bown et al. 1998
First occurrence (base): at base of BC26 zone (0% up, 104.1Ma, in Albian stage). Data source: Bown et al. 1998 - zonal marker

References:

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

Bown, P. R. (2005c). Early to Mid-Cretaceous Calcareous Nannoplankton from the Northwest Pacific Ocean, Leg 198, Shatsky Rise. Proceedings of the Ocean Drilling Program, Scientific Results. 198: 1-82. gs O

Bown, P. R., Rutledge, D. C., Crux, J. A. & Gallagher, L. T. (1998). Lower Cretaceous. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series . 86-131. gs O

Crux, J. A. (1991a). Albian calcareous nannofossils from the Gault Clay of Munday’s Hill (Bedfordshire, England). Journal of Micropalaeontology. 10(203-221): -. 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

Hill, M. E. & Bralower, T. J. (1987). Early evolution, stratigraphy and taxonomy of Eiffellithus eximius and closely-related species. In, Stradner, H. , & Perch Nielsen, K, (eds) Proceedings of the INA Meeting, Vienna 1985. Abhandlungen der Geologischen Bundesanstalt . 39: 89-97. gs

Jeremiah, J. (1996). A proposed Albian to Lower Cenomanian nannofossil biozonation for England and the North Sea Basin. Journal of Micropalaeontology. 15(97-129): -. gs

Kanungo, S., Bown, P. R. & Gale, A. S. (2020). Cretaceous (Albian-Turonian) calcareous nannofossil biostratigraphy of the onshore Cauvery Basin, southeastern India. Cretaceous Research. 118 [2021]: 1-22. gs

Lambert, B. (1993). Nannofossiles calcaires de l'Albien supérieur et du Vraconnien du Cameroun méridional (Deuxième Partie). Cahiers de Micropaléontologie. 8(2): 183-225. gs

Watkins, D. K. & Bergen, J. A. (2003). Late Albian adaptive radiation in the calcareous nannofossil genus Eiffelithus. Micropaleontology. 49(3): 231-252. gs

Eiffellithus monechiae

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