Pemma triquetra
Classification: ntax_cenozoic -> Braarudosphaerales -> Braarudosphaeraceae -> Pemma -> Pemma triquetra
Sister taxa: P. basquense, P. bybelliae, P. papillatum, P. rotundum, P. stradneri, P. triquetra, P. uncinata, P. sp.
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Taxonomy:
Citation: Pemma? triquetra Bown & Dunkley Jones, 2006Rank: SpeciesSynonyms:
- Hexadelus triquetra (Bown and Dunkley Jones 2006) Shamrock & Watkins 2012 - this alternative combination was proposed based on the fact that the angle of the longer edges was near 60° as in Hexadelus archus. However, whilst P. triquetra undoubtedly has the laminar substructure and tangential c-axis orientation typical of pentaliths this has not been demonstrated for H. archus.
Taxonomic discussion: Similar to disaggregated Micrantholithus segments in LM but with a more acute angle between the longer edges (~50°-60°, compared to 72° for typical pentaliths). The c-axis orientation is similar to other pentaliths, i.e., tangential. The liths consist of a series of fine calcite laminae similar to other members of the Braarudosphaeraceae. May be disaggregated liths of Micrantholithus-type pentalith with a concave base.
Distinguishing features: Relatively large (typically >5 µm), triangular-shaped nannoliths that thicken along the longer sides and exhibit low birefringence in XPL.
Farinacci & Howe catalog pages: P. triquetra *
Search data:
| Tags | LITHS: nannolith-radiate, pentagonal, triangular, CA: pores, CROSS-POLARS: T-prominent, |
| Metrics | Lith size: 5->8µm; Segments: 5->5;
Data source notes: lith size (diameter) from OD & illustrated specimens |
The morphological data given here can be used on the advanced search page. See also these notes
Geological Range:
Last occurrence (top): within NP21 zone (32.92-34.44Ma, top in Rupelian stage). Data source: Dunkley Jones et al., 2009
First occurrence (base): within NP19-20 zone (34.44-36.97Ma, base in Priabonian stage). Data source: Dunkley Jones et al., 2009
Plot of occurrence data:
- Range-bar - range as quoted above, pink interval top occurs in, green interval base occurs in.
- Triangles indicate an event for which a precise placement has been suggested
- (NB There is no histogram as there are no occurrence records for the taxon in the Neptune database) Parent: Pemma
References:
Bown, P. R. & Dunkley Jones, T. (2006). New Paleogene calcareous nannofossil taxa from coastal Tanzania: Tanzania Drilling Project Sites 11 to 14. Journal of Nannoplankton Research. 28(1): 17-34. gs V O
Dunkley Jones, T., Bown, P. R. & Pearson, P. (2009). Exceptionally well preserved upper Eocene to lower Oligocene calcareous nannofossils (Prymnesiophycidae) from the Pande Formation (Kilwa Group), Tanzania. Journal of Systematic Palaeontology. 7(4): 359-411. gs
Jones, A. P. & Dunkley Jones, T. (2020). Middle Eocene to Early Oligocene calcareous nannofossils from the Nanggulan Formation, Java, Indonesia. Journal of Nannoplankton Research. 30(1): 57-79. gs V O
Shamrock, J. L. & Watkins, D. K. (2012). Eocene calcareous nannofossil biostratigraphy and community structure from Exmouth Plateau, Eastern Indian Ocean (ODP Site 762). Stratigraphy. 9(1): 1-11. gs
