Catalog - Globigerina pseudoeocaena

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Globigerina pseudoeocaena

Citation: Globigerina pseudoeocaena Subbotina 1953

Type specimens: pl. 4, fig. 9a-c; pl. 5, figs, la-c, 2a-c; 6a-c; all X 72: 9, holotype; 1, 2, 6, "originals.” In all figures, a indicates a dorsal view, b a ventral view, and c a peripheral view. [See also Globigerina pseudoeocaena Subbotina var. compacta Subbotina, 1953; and Globigerina pseudoeocaena Subbotina var. trilobata Subbotina, 1953* ]

Type age (chronostrat): Holotype (fig. 9) from the lower to middle Eocene, zone of conical Globorotalias; in green sandy marls and marly sandstones ("green series"). Occurs also in the middle to upper Eocene, Acarinina zone; the upper Eocene of the Crimea; and the undifferentiated Paleogene, Kutaisskaya (F2) and Kaluzhskaya (F3) horizons. Abundant.

Type locality: Holotype and two figured "originals" from along the Kuban River, Northern Caucasus, U.S.S.R. Other figured "original" (fig. 6a-c) from Nalchik, along the Kheu River, Northern Caucasus. Found also in the northwestern Caucasus (Kutaisskaya and Kaluzhskaya horizons); at Mangyshlak and Ustyurt, Kazakh A.S.S.R.; and in the Crimea; all in the U.S.S.R.

[Translation from the Russian. - Tests of this species have been identified by the author of the present work, as well as by other paleontologists, as Globigerina ex gr. bulloides d'0rbigny or as Globigerina pseudobulloides Plummer. Actually, this species has much in common with Globigerina bulloides, but it has very little similarity to the Rotalia-like and flattened Globigerina compressa pseudobulloides.

[The test of Globigerina pseudoeocaena is intermediate between the structure of Globigerina triloculinoides Plummer and Globigerina bulloides d'0rbigny. It is close to the first in general appearance, test dimensions, and arrangement of chambers; it differs essentially in the number of chambers in the final whorl and their relative dimensions. Moreover, Globigerina pseudoeocaena is primarily found in horizons where Globigerina triloculinoides is found less frequently, as if the former were being replaced by the latter. Not very long ago, in respect to geologic age, both of these species existed together; then Globigerina triloculinoides gradually disappeared and Globigerina pseudoeocaena became the predominant form. It is close to Globigerina bulloides in rapid growth of chambers and their loose attachment to one another. Moreover, if the test is oriented so that its final chamber is rectilinearly upward, then the sutures on the ventral side will be the same as in Globigerina bulloides, and will look like a slated cross.

[However, this species differs basically from Globigerina bulloides in the position of the aperture along the marginal suture. The placement of the aperture brings this species close to Globigerina inflata d’Orbigny, from which, however, it is well distinguished by having much larger dimensions as well as by an aperture that is considerably less open and is not as gaping as in Globigerina inflata. Because of the large dimensions, the regular spherical shape of chambers in the final whorl, and the constant number of chambers, and also because of the short straight sutures, tests of this species are very close to Globigerina eocaena Gumbel, differing in the considerably more rapid growth of chambers in the final whorl. In contrast to Globigerina eocaena, the first and final chambers of the last whorl greatly differ in dimensions, and the test does not have as well defined a square outline.

[Three varieties of Globigerina pseudoeocaena are found in our material. One of these is Globigerina pseudoeocaena Subbotina var. pseudoeocaena Subbotina, usually encountered in great numbers. Another is Globigerina pseudoeocaena Subbotina var. compacta Subbotina, and the third is Globigerina pseudoeocaena Subbotina var. trilobata Subbotina, few specimens of which have been found.

[Globigerina pseudoeocaena var. compacta differs in having chambers very closely attached to one another. Globigerina pseudoeocaena var. trilobata differs in having fewer chambers in the final whorl, sometimes only three, but more often three and one-half chambers. In addition, the last two varieties are slightly smaller in dimensions than Globigerina pseudoeocaena var. pseudoeocaena. Stratigraphically, the compact and three-chambered varieties of this species are mainly found on the uppermost levels through which this species ranges, i.e., in the Acarinina zone.]

References:

Subbotina, N. N. (1953). Foraminiferes fossiles d'URSS Globigerinidae, Globorotaliidae, Hantkeninidae. Bureau de Recherches Geologiques et Minieres. 2239: 1-144. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Globigerina pseudoeocaena Subbotina 1953

Globigerina pseudoeocaena

References:

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