Catalog - Globigerina (Globigerina) microcellulosa

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Other pages this level: G. (Globigerina) microcellulosa, G. (Globigerina) pseudobulloides subquadrata

Globigerina (Globigerina) microcellulosa

Citation: Globigerina (Globigerina) microcellulosa Morozova 1961

Type sample (& lithostrat): in a gray clayey marl.

Type age (chronostrat): Lower Danian (Uylin substage), corresponding to the lower part of the Globigerina stage of Western European authors, Dn 1 II Zone (Globigerina microcellulosa Zone); About 500 specimens in good condition and many fragments.

Type locality: Tarkhankhut Peninsula, eastern Crimea, southern Russia. Also found in the Caucasus and on the Russian Platform.

Type repository: Moscow, Inst. of Geol. Sci. of the Academy of Sciences

Translation from the Russian. - Test with a low spire, consisting of two whorls. Early whorl lies in the same plane as the last whorl or very slightly rises above its surface. In each whorl are three and one half to four low broad, gradually inflated chambers, the dimensions of which slowly increase. Chamber arrangement close. Sutures weakly incised. Umbilicus narrow. Aperture small, umbilical, without a lip or with a very weakly expressed tabular outgrowth. Sometimes a short slit-like prolongation of the aperture, taking up 1/3 of the distance from the umbilicus to the periphery, is observed. Wall finely perforate. Surface finely celled.

holotype (fig. ll a-c) : Greatest diameter 0.33, least diameter 0.27, height 0.20 mm.

Variability. - The number of chambers in the whorls (3-3.5), the degree of their inflation, and the rate of growth vary over small limits. In some forms the chambers are arranged somewhat more freely and increase more quickly than in typical specimens, which dominate the population.
Comparison. - In the shape of the test this species is reminiscent of Globigerina (Globigerina) linaperta Finlay, but differs by its rounder, less peripherally compressed chambers, very thin, finely celled wall surface, shorter aperture, taking up about 1/3 of the distance from the umbilicus to the periphery, a very narrow, often absent lip, and small dimensions. In the near Paleocene species G. triloculinoides Plummer the growth of the chambers is more rapid, their arrangement is much more free, the wall is moderately celled, and the aperture is large and covered by a broad flap. The species described is the oldest of the three species being compared, comprising, evidently, a phylogenetic series G. (G.) microcellulosa -> G. (G.) triloculinoides --> G. (G.) linaperta. Change in the features of the representatives of this series favored an increase in the dimensions of the test and its aperture, the rate of increase of the diameter of the chambers, and the number of cells covering their surface. This variation in features indicates the progressive heightening of the flotation qualities of the tests of the series of species considered, likely occurring under the influence of a diminution in the density of the surface waters in the Danian-Montian basin connected to arise in their temperature (Morozova, 1960).]

References:

Morozova, V. G. (1961). Datsko-Montskie planktonnye foraminifery yuga SSSR [Danian-Montian Planktonic Foraminifera of the Southern USSR]. Paleontologicheskiy Zhurnal. (2): 8-19. gs O

Olsson, R. K., Hemleben, C., Berggren, W. A. & Huber, B. T. (1999). Atlas of Paleocene Planktonic Foraminifera. Smithsonian Institution Press, Washington, DC. (85): 1-252. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Globigerina (Globigerina) microcellulosa Morozova 1961

Globigerina (Globigerina) microcellulosa

References:

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