Distinguishing features: Holococcoliths with narrow rim surrounding a central-area formed of 1-4 blocks. Typically non-cavate with no spine. Rim bright and central plate dark
| Daughter taxa: (blue => in age window 0-800Ma) | |||||
| 4 central blocks | |||||
| | | | Central plate of 4, high birefringence blocks - obliquely oriented; central pore. Medium sized (ca. 4-6 µm) | |
| | | | Central plate of 4, low birefringence, blocks - one per quadrant. Large (ca 8-11 mm) | |
| | | | Central plate of 4, low birefringence, blocks - one per quadrant, pores along the sutures. Medium sized
(ca 4-8 µm) | |
| 1 central block | |||||
| | | | Single, low birefringence, central plate with 1 or 2 perforations. Small (ca 3-5 µm) | |
| | | | Single, low birefringence, central plate with indistinct cross-like central structure surrounded by multiple perforations. Medium sized (5-6 µm) | |
| anomalous species | |||||
| | | | Holococcolith formed of four large, high birefringence, interlocking blocks forming both a rim and central cross. Medium sized (5-6 µm) | |
| | | | Specimens not identified to species level | |
Taxonomy:
Farinacci & Howe catalog pages: Orastrum *
Distinguishing features: Holococcoliths with narrow rim surrounding a central-area formed of 1-4 blocks. Typically non-cavate with no spine. Rim bright and central plate dark
Search data:| Tags | LITHS: holococcolith, elliptical, CA: pores, bar, V-UNITS: V-prominent, R-UNITS: R-prominent, DETAILS: ca_disjunct, rim-unicyclic, |
| Metrics | Lith size: 3->11µm; Sources: size range of included species |
Geological Range:
Last occurrence (top): at top of Maastrichtian Stage (100% up, 66Ma, in Maastrichtian stage). Data source: Total of range of species in this database
First occurrence (base): in lower part of Aptian Stage (30% up, 122.3Ma, in Aptian stage). Data source: Total of range of species in this database
Plot of occurrence data:
Burnett, J. A. (1998). Upper Cretaceous. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series. 132-199. gs Wise, S. W. & Wind, F. H. (1977). Mesozoic and Cenozoic calcareous nannofossils recovered by DSDP Leg 36 drilling on the Falkland Plateau, south-west Atlantic sector of the Southern Ocean. Initial Reports of the Deep Sea Drilling Project. 36(269-491): -. gsReferences:
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Orastrum compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 22-2-2020
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