Nannotax3 - ntax_mesozoic

Distinguishing features:
Parent taxon (Owenia): Holococcoliths with a narrow rim and a central structure comprising two or four blocks which typically incorporate a distal bridge-shaped structure which may extend into a spine; the blocks may be perforate.
This taxon: Base formed of two blocks each with a pore; process well-developed often with terminal plug

Citation: Owenia hillii Crux, 1991

Taxonomic discussion: Lucianorhabdus compactus is a very similar species and was regarded by Bown et al. (1998) and Bown & Cooper (1998) as a senior synonym of O. hillii. Lees (2007) however regards them as a separate species.

Holococcolith with narrow birefringent rim with transverse protrusions into the central area. The central plate consists of two perforate blocks joined along a transverse suture. The single perforation in each block may be closed due to overgrowth. In side view the narrow rim continues proximally; the central structure comprises two lateral blocks but occasionally a smaller two-part internal block may be visible. A variably developed spine extends distally and may be closed by a distal plug. All these structures observed in side view, generally appear as crystallographically distinct blocks.

Owenia partitum is distinguished by the birefringent four-part bridge structure, observed when the coccolith axes are parallel with the polarising directions of the microscope; however, these blocks are not visible on rotation of the coccolith. In side view, the two species may be indistinguishable.

Geological Range:
Last occurrence (top): within Turonian Stage (89.39-93.90Ma, top in Turonian stage). Data source: Lees 2007
First occurrence (base): near base of BC25a subzone (10% up, 108.1Ma, in Albian stage). Data source: Bown et al. 1998 (fig 5.2)

References:

Bown, P. R. & Cooper, M. K. E. (1998). Jurassic. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series . 34-85. 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

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

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

Kennedy, W. J. et al. (2000). Integrated stratigraphy across the Aptian-Albian boundary in the Marnes Bleues, at the Col de Pre _-Guittard, Arnayon (Drome), and at Tartonne (Alpes-de-Haute-Provence), France: a candidate Global Boundary Stratotype Section and Boundary Point for the base of the Albian Stage. Cretaceous Research. 21: 591-720. gs

Lees, J. A. (2007). New and rarely reported calcareous nannofossils from the Late Cretaceous of coastal Tanzania: outcrop samples and Tanzania Drilling Project Sites 5, 9 and 15. Journal of Nannoplankton Research. 29(1): 39-65. gs O

Owenia hillii

References:

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