Variants (could also be distinguished informally) (time control age-window is: 0-800Ma)![]() | ||||
![]() | Discoaster bolivariae 4-rayed D. hamatus | |||
![]() | Discoaster triuncinus 3-rayed D. hamatus |
Taxonomy:
Browning et al. (2017) record that the smaller specimens (<15µm) occur above and below NN9 so for stratigraphic rigour the large specimens need to be used.
Distinguishing features: 5-rayed; ray tips with clockwise deflected (in distal view) proximal extensions.
Farinacci & Howe catalog pages: D. hamatus + * , E. hamatus *
Morphology: Symmetric 5-rayed discoaster; rays with clockwise deflected (in distal view) proximal extensions. The central area is small with a featureless distal surface and small proximal knob.
Size: Usually only large specimens, (>10 µm) show the characteritic raytip development
See also: Discoaster calcaris - similar but with 6-rays and longer ranging;
Search data:Tags | LITHS: nannolith-radiate, star-shaped, CA: process, CROSS-POLARS: 1ou, V-prominent, |
Metrics | Lith size: 10->25µm; Segments: 5->5; Data source notes: size from OD & illustrated specs |
Geological Range:
Notes: Defines Zone NN9
Last occurrence (top): at top of NN9 zone (100% up, 9.5Ma, in Tortonian stage). Data source: zonal marker (see e.g. Young 1998)
First occurrence (base): at base of NN9 zone (0% up, 10.6Ma, in Tortonian stage). Data source: zonal marker (see e.g. Young 1998)
Plot of occurrence data:
Browning, E., Bergen, J. A., Blair, S. A., Boesiger, T. M. & de Kaenel, E. (2017). Late Miocene to Late Pliocene taxonomy and stratigraphy of the genus Discoaster in the circum North Atlantic Basin: Gulf of Mexico and ODP Leg 154. Journal of Nannoplankton Research. 37(2-3): 189-214. gs V O Martini, E. & Bramlette, M. N. (1963). Calcareous nannoplankton from the experimental Mohole drilling. Journal of Paleontology. 37(4): 845-855. gs Perch-Nielsen, K. (1972b). Remarks on Late Cretaceous to Pleistocene coccoliths from the North Atlantic. Initial Reports of the Deep Sea Drilling Project. 12: 1003-1069. gs V O Theodoridis, S. (1984). Calcareous nannofossil biostratigraphy of the Miocene and revision of the helicoliths and discoasters. Utrecht Micropaleontological Bulletin. 32: 1-271. gs V O Wei, W. (2003). Upper Miocene nannofossil bistratigraphy and taxonomy of Exxon core CH30-43-2 from the Gulf of Mexico. Journal of Nannoplankton Research. 25(1): 17-23. gs V O Young, J. R. (1998). Neogene. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series. 225-265. gs V OReferences:
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Discoaster hamatus compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 24-1-2021
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