Taxonomy:
The affinities of this species are unknown, but since it is formed of a single crystallographic unit it may be related to the Triquetrorhabdulaceae. The crystallographic orientation is wrong for it be related to Florisphaera.
Distinguishing features: Smooth apart from marginal ridges
Farinacci & Howe catalog pages: M. convallis + *
Morphology: Plate-like rhomboidal nannoliths, with a raised rim on both sides. Acts as a single crystallographic unit with the optic axis nearly perpendicular to the plate.
Remarks: In plan view M. convallis shows only low birefringence and is easily overlooked. The dog-bone like side view, first described by Theodoridis (1984), is more distinctive and makes identification unambiguous. Can also give a Y-shaped cross-section - see comments below.
Size: : 4-8 microns long, usually 4-6 microns.
Tags | LITHS: nannolith-other, quadrate, CROSS-POLARS: 1ou, V-prominent, |
Metrics | Lith size: 4->8µm; Data source notes: lith size from OD & illustrated specimens |
Geological Range:
Notes: This species is often abundant but distribution is rather sporadic.
Last occurrence (top): in upper part of NN11a subzone (70% up, 7.7Ma, in Tortonian stage). Data source: Young 1998, position in zone estimated from fig 8.1, see also Raffi et al. 2006
First occurrence (base): in upper part of NN9 zone (70% up, 9.8Ma, in Tortonian stage). Data source: Young 1998, position in zone estimated from fig 8.1, see also Raffi et al. 2006
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 Bukry, D. (1973c). Coccolith stratigraphy, eastern equatorial Pacific, Leg 16, Deep Sea Drilling Project. Initial Reports of the Deep Sea Drilling Project. 16: 653-711. gs V O de Kaenel, E. & Villa, G. (1996). Oligocene-Miocene calcareous nannofossil biostratigraphy and paleoeecology from the Iberian Abyssal Plain. Proceedings of the Ocean Drilling Program, Scientific Results. 149: 79-145. gs V O Perch-Nielsen, K. (1977a). Albian to Pleistocene calcareous nannofossils from the Western South Atlantic, DSDP Leg 39. Initial Reports of the Deep Sea Drilling Project. 39: 699-823. 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 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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Minylitha convallis compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 15-4-2021
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