Nannotax3 - ntax_mesozoic - Broinsonia cenomanica

Distinguishing features:
Parent taxon (Broinsonia): Outer rim of V-units, with slight clockwise obliquity, visible on distal surface and form dark rim in LM; central-area spanned by an axial cross, grill or perforate plate. 3 tiers visible in side view.
This taxon: axial cross with lateral bars, supporting low spine

Citation: Broinsonia cenomanica (Black, 1973) Bown 2001

Basionym: Acaenolithus cenomanicus Black, 1973

Variants:

Acaenolithus undatus Black, 1973 - similar but with "one or two triangular expansions on either side of the long arms of the cross"
Acaenolithus vimineus Black, 1973 - similar but with robust grill in central area
Broinsonia dempta Forchheimer 1972 - similar but with better developed spine, possibly a senior synonym

Taxonomic discussion: Similar to B. dentata but with a low central spine, and a disjunct range.

Geological Range:
Last occurrence (top): in lower part of UC3b subzone (20% up, 95.7Ma, in Cenomanian stage). Data source: Burnett 1998, fig. 6.2
First occurrence (base): within Albian Stage (100.50-112.95Ma, base in Albian stage). Data source: Burnett 1998

References:

Black, M. (1973). British Lower Cretaceous Coccoliths. I-Gault Clay (Part 2). Palaeontographical Society Monograph. 127: 49-112. gs

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

Burnett, J. A. (1998). Upper Cretaceous. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series. 132-199. gs V O

Forchheimer, S. (1972). Scanning electron microscope studies of Cretaceous coccoliths from the Köpingsberg Borehole No. 1, SE Sweden. Sveriges Geologiska Undersökning, Series C. #668, 65: 1-141. 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

Püttmann, T., Mutterlose, J., Kaplan, U. & Scheer, U. (2019). Reworking of Cenomanian ammonites decoded by calcareous nannofossils (southern Münsterland Basin, northwest Germany). Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen. 291(1): 1-17. gs

Tags	LITHS: placolith, elliptical, CA: cross-axial, grill, process, CROSS-POLARS: rim-bicyclic, V-prominent, R-prominent,
Metrics	Lith size: 5->10µm; Data source notes: original descriptions & illustrated specimens

Broinsonia cenomanica

References:

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