Nannotax3 - ntax_cenozoic - Rhomboasteraceae

Citation: Rhomboasteraceae Bown, 2005

Taxonomic discussion: Rhomboaster and Tribrachiatus nannoliths comprise an evolutionary lineage from the oldest, rhombic nannoliths (cuspis-type), through intermediate forms with two superimposed tri-radiate cycles (bramlettei-type), to the youngest, single-cycle tri-radiate forms (orthostylus-type). Bybell & Self-Trail (1995, 1997) argued for the use of one genus only, whereas others have retained both (e.g. Aubry, 1996), see also von Salis et al. (2000). Both genera are included here: Rhomboaster for nannoliths with three-dimensional, rhombic to bicyclic tri-radiate morphologies, and Tribrachiatus for flatter morphologies with a single tri-radiate cycle.

Distinguishing features: Nannoliths with rhombic and tri-radiate morphologies, and non-birefringent images in XPL. Incorporating the genera Rhomboaster and Tribrachiatus.

Morphology: Crystallography: the c-axis is parallel to rotational axis of the nannolith and so in plan view they show no birefringence, they are, however, often tilted and so show moderate birefringence. IN side view they show high birefringence.

Geological Range:
Last occurrence (top): in upper part of Ypresian Stage (67% up, 50.5Ma, in Ypresian stage). Data source: Total of range of species in this database
First occurrence (base): within Ypresian Stage (47.84-55.96Ma, base in Ypresian stage). Data source: Total of range of species in this database

References:

Aubry, M. -P. (1996). Towards an Upper Paleocene-Lower Eocene high resolution stratigraphy based on calcarous nannofossil stratigraphy. Israel Journal of Earth Sciences. 44(239-253): -. gs

Bown, P. R. (2005d). Palaeogene calcareous nannofossils from the Kilwa and Lindi areas of coastal Tanzania (Tanzania Drilling Project 2003-4). Journal of Nannoplankton Research. 27(1): 21-95. gs V O

Bybell, L. M. & Self-Trail, J. (1995). Evolutionary, biostratigraphic and taxonomic study of calcareous nanofossils from a continuous Palaeocene-Eocene boundary section in New Jersey. U.S. Geological Survey, Professional Paper. 1554: 1-36. gs V O

Bybell, L. & Self-Trail, J. (1997). Late Paleocene and Early Eocene calcareous nannofossils from three boreholes in an onshore-offshore transect from New Jersey to the Atlantic continental rise. Proceedings of the Ocean Drilling Program, Scientific Results. 150: 91-110. gs V O

von Salis, K., Monechi, S., Bybell, L. M., Self-Trail, J. & Young, J. R. (2000). Remarks on the calcareous nannofossil genera Rhomboaster and Tribrachiatus around the Paleocene/Eocene Boundary. GFF. 122(138-140): -. gs

Daughter taxa: (blue => in age window 0-800Ma)		Granddaughter taxa
	Rhomboaster Solid nannoliths that include rhombic, rhombic with spinose extensions and forms composed of two superimposed tri-radiate cycles.	R. bramlettei R. calcitrapa R. cuspis R. sp.
	Tribrachiatus Solid nannoliths with three rays that typically have terminal bifurcations.	T. contortus T. digitalis T. orthostylus T. absidatus T. lunatus T. sp.

Tags	LITHS:
Metrics	Lith size: 5->20µm;

Rhomboasteraceae

References:

Comments (0)

Add Comment