Set number: 786

  • Triquetrorhabdulus carinatus rimosus 27816 1
  • Triquetrorhabdulus carinatus rimosus 27818 2
  • Triquetrorhabdulus carinatus rimosus 27820 3
  • Triquetrorhabdulus carinatus rimosus 27824 4
  • Triquetrorhabdulus carinatus rimosus 27815 5
  • Triquetrorhabdulus carinatus rimosus 27817 6
  • Triquetrorhabdulus carinatus rimosus 27822 7
  • Triquetrorhabdulus carinatus rimosus 27823 8
    10µm
Triquetrorhabdulus carinatus, Early Miocene, DSDP Leg 25, Site 242, Mozambique Channel (Davie Ridge), Indian Ocean

with rim

Set number: 784

  • Triquetrorhabdulus carinatus dentatus 28073 1
  • Triquetrorhabdulus carinatus dentatus 28077 2
  • Triquetrorhabdulus carinatus dentatus 28079 3
  • Triquetrorhabdulus carinatus dentatus 28083 4
  • Triquetrorhabdulus carinatus dentatus 28075 5
  • Triquetrorhabdulus carinatus dentatus 28076 6
  • Triquetrorhabdulus carinatus dentatus 28080 7
  • Triquetrorhabdulus carinatus dentatus 28081 8
    10µm
Triquetrorhabdulus carinatus, Late Oligocene, DSDP Leg 25, Site 242, Mozambique Channel (Davie Ridge), Indian Ocean

with dentate margin

Set number: 792

  • Triquetrorhabdulus carinatus 240 1
  • Triquetrorhabdulus carinatus 239 2
  • Triquetrorhabdulus carinatus 237 3
  • Triquetrorhabdulus carinatus 238 4
    10µm
Triquetrorhabdulus carinatus, Early Miocene, DSDP Leg 25, Site 242, Mozambique Channel (Davie Ridge), Indian Ocean

Set number: 791

  • Triquetrorhabdulus carinatus 241 1
  • Triquetrorhabdulus carinatus 242 2
  • Triquetrorhabdulus carinatus 244 3
  • Triquetrorhabdulus carinatus 243 4
    10µm
Triquetrorhabdulus carinatus, Early Miocene, DSDP Leg 25, Site 242, Mozambique Channel (Davie Ridge), Indian Ocean

Set number: 790

  • Triquetrorhabdulus carinatus 263 1
  • Triquetrorhabdulus carinatus 264 2
    10µm
Triquetrorhabdulus carinatus, Early Miocene, DSDP Leg 25, Site 242, Mozambique Channel (Davie Ridge), Indian Ocean

Set number: 785

  • Triquetrorhabdulus carinatus 27863 1
  • Triquetrorhabdulus carinatus 27862 2
  • Triquetrorhabdulus carinatus 27867 3
  • Triquetrorhabdulus carinatus 27869 4
  • Triquetrorhabdulus carinatus 27865 5
  • Triquetrorhabdulus carinatus 27861 6
  • Triquetrorhabdulus carinatus 27866 7
  • Triquetrorhabdulus carinatus 27868 8
    10µm
Triquetrorhabdulus carinatus, Early Miocene, DSDP Leg 25, Site 242, Mozambique Channel (Davie Ridge), Indian Ocean

Set number: 789

  • Triquetrorhabdulus carinatus dentatus 2312 1
  • Triquetrorhabdulus carinatus dentatus 2314 2
    10µm
Triquetrorhabdulus carinatus, Late Oligocene, Angola, West Africa

with dentate margin

Set number: 788

  • Triquetrorhabdulus carinatus rimosus 2315 1
  • Triquetrorhabdulus carinatus rimosus 2318 2
  • Triquetrorhabdulus carinatus rimosus 2317 3
    10µm
Triquetrorhabdulus carinatus, Late Oligocene, Angola, West Africa

with rim

Set number: 787

  • Triquetrorhabdulus carinatus eurys 2319 1
  • Triquetrorhabdulus carinatus eurys 2320 2
    10µm
Triquetrorhabdulus carinatus, Late Oligocene, Angola, West Africa

with wide blades >4.0µm

Set number: 783

  • Triquetrorhabdulus carinatus 33 1
  • Triquetrorhabdulus carinatus 34 2
    10µm
Triquetrorhabdulus carinatus, Early Miocene, Angola, West Africa
Final Epithet
Triquetrorhabdulus carinatus Martini, 1965
Basionym

Triquetrorhabdulus carinatus Martini, 1965

Description

Elongate biconical nannolith with three birefringent blades having inclined tangential c-axis [perpendicular 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' face. The faces of the blades have an inclined tangential c-axis. The c-axis appear oblique in the keel segments. The yellow appearance of the keel at -45° and +45° confirms the oblique c-axis in this profile for the medial keel.

Remarks

Triquetrorhabdulus carinatus differs from Velonalithus rioi (Olafsson) Varol, n. comb. 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 Orthorhabdus serratus Bramlette & Wilcoxon (1967) in its plan view by having the biconical shape with an axial c-axis. The latter has blades truncated at one end with a vertical c-axis.

Orthorhabdus serratus, in its side view, is a hockey-stick shape nannolith displaying high birefringence with a tangential c-axis. In contrast, Triquetrorhabdulus carinatus is a biconical form in every profile.

References

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.