Catalog - Subbotina vialovi

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Subbotina vialovi

Citation: Subbotina vialovi Myatliuk 1970

Type sample (& lithostrat): lower part of Nizhnemenilitovaya (Lower Menilite) Formation, 2797.5-2800.6 m in borehole 482

Type age (chronostrat): lower Oligocene (Rupelian)

Type locality: village of Bitkov, eastern Carpathians, Ukraine

Translation from the Russian. - Test small, with a low, trochoid spire, strongly convex dorsally and less so on the ventral side, where a weak depression is observed in the central region. Spire composed of two whorls. ln the first whorl are five or six very small, rounded-triangular chambers, in the last whorl there are four chambers, three of which are very little different in size, the fourth chamber lies on top of the other three and is as wide as all of them put together, while the total volumes reach up to half of the total test volume. All the chambers closely adjoin one another. Umbilicus absent, and on the ventral side the chambers fit together tightly. Sutures depressed, radial. Peripheral margin broadly rounded, weakly lobate. Aperture marginal, a low arc with a narrow lip, not reaching the peripheral margin. Wall moderately reticulate, finely perforate.

Dimensions of figured specimens, mm.: Fig. 1, diameter 0.15, thickness 0.1; fig. 2, diameter 0.21, thickness 0.16.

Globigerina sp. , Batjes, 1958 , Belgium , Inst. Roy . Sci. Nat. , Mem., no. 143, p. 161, pl. 11, fig. 7.

General remarks and comparison. - Besides the four-chambered tests of this species forms with 3.5 chambers in the last whorl are rarely encountered. They are very similar to S. vialovi but differ by being a little larger (diameter 0.25 mm.). It is entirely possible that at a later stage the number of chambers per whorl in the S. vialovi test decreases with growth from 4 to 3.5. The Subbotina described is somewhat similar to the reticulate "Globigerina" sp. of Batjes (see synonymy) from the Oligocene of Belgium. This form is also very small - diameter 0.25 mm., and similar to ours in the construction of the spire and the number of chambers in the whorls. The two forms differ in the shape of the last chamber's outline. In our tests the last chamber is large and hemispherical, in the Belgian test this chamber is smaller and approaches a rounded triangular outline. D. Batjes mentions in the description that his test has 3.5-4 chambers in the last whorl.

S. vialovii is also similar to S. eocaenica and probably is derived from it. It differs from it only by its smaller dimensions, more compactly coiled spire, and less produced final chamber.

Minute in size (figured specimens 0.15-0.21 mm in diameter), 4 chambers, terminal chamber occupies entire width of test above 3 essentially equal-sized chambers in last whorl, cancellate, primary aperture a low, lipped slit along the base of the terminal chamber. Uncertain affinity, probably benthic; requires further study (holotype not found). [Berggren & Wade 2018]

References:

Berggren, W. A. & Wade, B. S. (2018). Problematica. In, Wade, B. S., Olsson, R. K., Pearson, P. N., Huber, B. T. & Berggren, W. A. (eds) Atlas of Oligocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication . 46(Chap 20): 511-524. gs

Myatliuk, L. V. (1970). Foraminifera from the flysch deposits of the Eastern Carpathians (Cretaceous-Palaeogene). Trudy Vsesoyuznego Neftyanogo Nauchno-Issledovatel'skogo Geologo-Razvedochnogo Instituta (VNIGRI). 282: 1-225. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Subbotina vialovi Myatliuk 1970

Subbotina vialovi

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