Diloma


Classification: Mesozoic -> Eiffellithales -> Eiffellithaceae -> Diloma
Sister taxa: Diloma, Eiffellithus, Helicolithus, Tegumentum,

Distinguishing features: Elliptical loxoliths with a rim that appears tricyclic, composed of inner and outer rim cycles and a proximal plate. The outer rim cycle and proximal plate are only weakly birefringent, while the blocky inner rim cycle is brightly birefringent. Central structures are variable but include cross bars, lateral bars and curving concentric bars.


Daughter taxa: (blue => in age window 0-800Ma)
Central area filled by plate
A species of Diloma with a wide central area filled with numerous fine bars arranged about the long ellipse axis. No axial cross is visible.
Large (7-9┬Ám), distinctive murolith with tricyclic rim appearance (weakly birefringent outer cycle, strongly birefringent inner cycle, and weakly birefringent proximal plate) and cross bars rotated from axial. The spine-bearing central cross is oriented in a position intermediate between diagonal and axial.
Large coccolith with wide central area spanned by narrow axial cross bars, multiple lateral bars (around 44), and a concentric bar running near the edge of the central area.
Medium-sized elliptical form with a relatively delicate rim that in LM appears to consist of three narrow cycles: the inner and outer cycles are weakly birefringent (grey) while the middle cycle is brightly birefringent (white). The complex central structure comprises axial cross bars, concentric bars and numerous lath-like radial bars.
Specimens not identified to species level

Taxonomy:

Citation: Diloma Wind & Cepek, 1979
Rank: Genus
Type species: Arkhangelskiella primitiva Worsley, 1971 designated by Wind and Cepek, 1979.

Farinacci & Howe catalog pages: Diloma *

Distinguishing features: Elliptical loxoliths with a rim that appears tricyclic, composed of inner and outer rim cycles and a proximal plate. The outer rim cycle and proximal plate are only weakly birefringent, while the blocky inner rim cycle is brightly birefringent. Central structures are variable but include cross bars, lateral bars and curving concentric bars.

Geological Range:
Last occurrence (top): in upper part of Cenomanian Stage (65% up, 96.2Ma, in Cenomanian stage). Data source: Total of range of species in this database
First occurrence (base): at base of Valanginian Stage (0% up, 139.4Ma, in Valanginian stage). Data source: Total of range of species in this database

Plot of occurrence data:

References:

Bown, P. R., Rutledge, D. C., Crux, J. A. & Gallagher, L. T. (1998). Early Cretaceous. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series. 86-131. gs

Wind, F. H. & Cepek, P. (1979). Lower Cretaceous calcareous nannoplankton from DSDP Hole 397A (northwest African Margin). Initial Reports of the Deep Sea Drilling Project. 47A: 221-235. gs

Worsley, T. R. (1971). Calcareous nannofossil zonation of Upper Jurassic and Lower Cretaceous sediments from the Western Atlantic. In, Farinacci, A. (ed.) Proceedings of the Second Planktonic Conference Roma 1971. Edizioni Tecnoscienza, Rome 2: 1301-1321. gs


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Diloma compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 19-9-2019

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Short stable page link: http://mikrotax.org/Nannotax3/index.php?id=10378 Go to Archive.is to create a permanent copy of this page - citation notes



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