Catalog - Globigerina rotundaenana

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Globigerina rotundaenana

Citation: Globigerina rotundaenana Shutskaya 1970

Type sample (& lithostrat): lower part of the Middle Danat Subsuite

Type age (chronostrat): Lower Eocene, Bakchisarayan Stage, Globorotalia aequa Zone

Type locality: Malyy Balkhan Mts., westem Turkmenia, USSR

Type repository: Moscow; All-Union Scientific-Research Geological-Prospecting Petroleum Institute (VNIGNI), Moscow (probably)

Translation from the Russian. - Test small (about 0.3 mm.) high, subquadrate, coefficient of elongation 1-1.1, coefficient of broadening 1-1.1. Structure of initial part of test rotaloid, low-trochoid. Number of chambers of initial part of test 7-8. In the last whorl there are 3 chambers, but on the ventral side at the outer margin between the fust and last chambers the last chamber of the preceding whorl shows. Chambers increase in size rapidly. Ratio of dimensions of individual elements of the last whorl: a) ratio of width of penultimate chamber to width of last chamber 1-1.2; b) ratio of length of base of last chamber to its width 1.2-1.4, last chamber narrow, strongly elongated. Height of last chamber exceeds height of preceding part of test. Chambers of last whorl: first chamber round in outline, second and last ones subquadrate, with rounded inner margins and broadly rounded outer margin. Lateral surface of last chamber oval in outline. Surface of chambers flattened-inflated. Arrangement of chambers in last whorl entirely compact. Intercameral sutures thin, not too deep. Outer margin rough, weakly undulate. Umbilical depression narrow or absent. Aperture is a slightly opened, curved slit extending from the center of the test to the beginning of the outer margin. Test wall covered with frequent large pores.

Variation. - In test shape this species stands at the boundary of the transition from subquadrate (tf. 3, figs. 11, 13) to rounded (tf. 3, figs. 12, 14, 15, 16).

Comparison. - This species differs from Globigerina nana Khalilov by: 1) the broad initial part of the spiral in the last whorl, making the last chamber narrower than the preceding one - ratio of widths of penultimate to last chambers 1.0-1.2; 2) the subquadrate shape of the test, which is close to rounded.

The compact chamber arrangement and coarse perforation of the test wall characteristic of this species, together with the size relation between chambers typical for the species, are observed in specimens referred by Loeblich and Tappan (1957, loc. cit.) to Globigerina triloculinoides.

References:

Shutskaya, E. K. (1970a). Morphologic groups and descriptions of species of Globigerina and Acarinina in the lower Paleogene of the Crimea, the Caucasus Foreland, and western Central Asia. Trudy Vsesoyuznego Neftyanogo Nauchno-Issledovatel'skogo Geologo-Razvedochnogo Instituta (VNIGRI). 69: 79-113. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Globigerina rotundaenana Shutskaya 1970

Globigerina rotundaenana

References:

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