Triquetrorhabdulus carinatus
Set number: 784
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10µm
with dentate margin
Set number: 785
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10µm
Set number: 786
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10µm
with rim
Set number: 787
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10µm
with wide blades >4.0µm
Set number: 788
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10µm
with rim
Set number: 789
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10µm
with dentate margin
Set number: 790
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10µm
Set number: 791
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10µm
Set number: 792
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10µm
Triquetrorhabdulus carinatus Martini, 1965
Elongate biconical nannolith with three birefringent blades having an axial c-axis [parallel to the length of the blades]. The identical blades joined each other at the same angle.
This form naturally settles with the median blade's keel facing outward, exposing the two blades' faces. The blades are extinct at 0° (parallel extinction) and displayed strong interference colours at 45°.
Triquetrorhabdulus carinatus differs from Velonalithus rioi by having an axial c-axis, whilst the latter has a tangential c-axis. Moreover, the blades joined each other at a different angle in Velonalithus rioi, whereas the blades' angles are equal in Triquetrorhabdulus carinatus.
Triquetrorhabdulus carinatus is distinguished from Triamutilaferrum martini in its plan view by having a biconical shape with an axial c-axis. The latter has blades truncated at one end with a vertical c-axis in the plan view and a tangential c-axis in the side view. Triquetrorhabdulus carinatus has parallel extinction, whereas Triamutilaferrum martini has oblique inclined extinction.
Orthorhabdus serratus has two blades and a ridge truncated at one end and pointed at the other with a toot-like projection. It is non-birefringent (vertical c-axis) in its plan view but displays high birefringence with a tangential c-axis in the side view. In contrast, Triquetrorhabdulus carinatus is a biconical form with an axial-c axis in every profile. Both species have parallel extinction.
Bramlette, M. N. & Wilcoxon, J. A., (1967): Middle Tertiary calcareous nannoplankton of the Cipero section, Trinidad, W.I. - Tulane Studies in Geology and Paleontology. 5: 93-131.
Martini, E., (1965): Mid-Tertiary calcareous nannoplankton from Pacific deep-sea cores. - Colston Papers. 17: 393-411.
Olafsson, G., (1989): Quantitative calcareous nannofossil biostratigraphy of upper Oligocene to middle Miocene sediment from ODP Hole 667A and middle Miocene sediment from DSDP Site 574. - Proceedings of the Ocean Drilling Program, Scientific Results. 108: 9-22.
Holotype
Triquetrorhabdulus carinatus
Martini, 1965
Oligocene