Orastrum


Classification: Mesozoic -> Holococcoliths -> Common genera -> Orastrum
Sister taxa: Calculites, Lucianorhabdus, Orastrum, Owenia,

Distinguishing features: Holococcoliths with narrow rim surrounding a central-area formed of 2-4 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 blocks - obliquely oriented
Central plate of 4 blocks - one per quadrant
Central plate of 4 blocks - one per quadrant, pores along the sutures
1 central block
Single low birefringence central plate with 1 or 2 perforations. Small (ca 3-4 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 interlocking blocks forming both a rim and central cross.
Specimens not identified to species level

Taxonomy:

Citation: Orastrum Wind & Wise in Wise & Wind, 1977
Rank: Genus
Type species: Orastrum asarotum Wind & Wise in Wise & Wind, 1977

Farinacci & Howe catalog pages: Orastrum *

Distinguishing features: Holococcoliths with narrow rim surrounding a central-area formed of 2-4 blocks. Typically non-cavate with no spine. Rim bright and central plate dark

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:

References:

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): -. gs


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Orastrum compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 13-10-2019

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Short stable page link: http://mikrotax.org/Nannotax3/index.php?id=10821 Go to Archive.is to create a permanent copy of this page - citation notes



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