Catalog - Globigerina gradationis

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Globigerina gradationis

Citation: Globigerina gradationis Voloshinova 1960

Type age (chronostrat): Upper Miocene

Type locality: Figured specimens (figs. 1Oa-c, 11 a-c) from Katangli; and also found at Sevemaya Okha and Okha; all along the east coast of Sakhalin Island, U.S.S.R.

Type repository: Leningrad; (VNIGRI), Leningrad, U.S.S.R.; figured "original" (fig. lOa-c), no. 11 7/454.

[Translation from the Russian. - Test very small, inflated, sometimes almost spherical, with a strongly lobate outline; consists of 2 1/2.-3 whorls, positioned stepwise over one another and forming a relatively high conical spire. Chambers inflated, globular, not joined together too closely, slowly and uniformly increase in size as added; in the last whorl are four chambers almost identical in size and shape, sutures between them are short, depressed, almost straight. Umbilical area weakly depressed, the rather sharp umbilical margins of the chambers of the last whorl converge towards the center. Aperture slitlike, very small , intramarginal, close to the umbilicus, usually poorly discernible. Wall coarsely perforate, relatively smooth.

Dimensions, in mm. - Diameter 0.1 0-0. 15 ~ thickness 0.07-0.12.

This is an extraordinarily characteristic species with its strongly convex dorsal side and the uniformly expanding, stepwise-positioned whorls of the spire. Among its peculiarities should be included the frequent formation of a " float" (N. Subbotina, 1953, Leningrad: Vses. Neft. Nauchno-lssled. Geol.-Razvecl. lnst. (VNIGRI), Trudy, n. s., vypusk 76, pp. 74-77), which falls in the most varied positions. Sometimes a kind of fifth chamber is produced in the last whorl. The irregular asymmetrical position of this formation, the more transparent wall, and the absence of any sign of the aperture indicates that here we are dealing with the formation of a bulla, often encountered among the globigerinids.In size, its distinct, convex, globular chambers in the last whorl, and the inflated test Globigerina gradationis Voloshinova is very similar to the late Eocene-early Oligocene species G. off icina/is Subbotina (1953, op. cit .. p. 78, pl. II , figs. 1-7). But this similarity is superficial, since the species described is quite definitely distinguishable by the spire of the initial part of the test, which is larger and more convex relative to the last whorl, and by the intramarginaJ position of the aperture.

References:

Voloshinova, N. A. (1960). Novye neogenovye rotaliidy ostrova Sakhalin. In, Markovsky, B. P. (ed.) Novye vidy drevnihk rasteniy i bespozvonochnyhk SSSR, Chast Pervaya, vypusk 1, chasti 1. Vsesoyuznyy Nauchno-Issledovatel'skiy Geologicheskiy Institut,, Moscow 163-169. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Globigerina gradationis Voloshinova 1960

Globigerina gradationis

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