Catalog - Globigerina euapertura

This page provides data from the catalog of type descriptions. The catalog is sorted alphabetically. Use the current identification link to go back to the main database.

Globigerina euapertura

Citation: Globigerina euapertura (Jenkins 1960)

Type age (chronostrat): Globigerina euapertura zone to the Pre-Globoquadrina Dehiscens Dehiscens zone.

Type locality: Lakes Entrance Oil Shaft, Victoria, Australia. Holotype: from 1188 feet.

Type repository: Canberra, Australia; Bureau of Mineral Resources

Test trochospiral, compact, spiral side slightly convex,umbilical side convex, equatorial periphery quadrilobate, axial periphery rounded. Wall calcareous, perforate,surface coarsely pitted. Chambers of the final whorl slightly compressed, about 11-13 arranged in 2½ whorls,usually 3½ in the last whorl, increasing fairly rapidly in size. Sutures on the spiral side slightly recurved, depressed; on the umbilical side radial, deepened. Umbilicus fairly small, deep. Aperture distinct, fairly low arch with a rim, interiomarginal, umbilical.

Largest diameter of holotype 0.30 mm.

Globigerina euapertura, has a limited stratigraphic range and occurs in 23 samples out of the 27 within its range.
The height of the aperture is found to vary in most of the populations. In the young forms the aperture is usually a high arch resembling that of Globigerina ampliapertura Bolli, but it becomes a much lower arch as the chambers increase in size. In the more loosely coiled forms the last chamber becomes further removed from the umbilicus and the aperture becomes larger.
The last chamber varies in size from larger to smaller than the penultimate chambers, the smallest being in the form of a bulla over the umbilicus. When this is so, the forms are referred to Catapsydrax unicavus Bolli,Loeblich, and Tappan, whose range in the shaft is the same as Globigerina euapertura, new species.There is a gradual increase in the size of the tests from 0.32 mm. at 1196 feet to 0.4 mm. at 1120 feet, this being due to a slight increase in the number of chambers. In the adult test the chamber number is decided by the size
of the proloculus. The commonest forms are those with a proloculus diameter of 0.02 mm., with 12-13 chambers; the next most common have a 0.01 mm. proloculus, and 14-16 chambers, and the rarest forms have a 0.035 mm. proloculus and 10-11 chambers.

Globigerina euapertura, new species, seems to be intermediate in morphology between Globigerina venezuelana Hedberg and Globigerina ampliapertura Bolli.

It differs from Globigerina venezuelana in having a smaller test, being more loosely coiled, having a larger aperture and in not having a rounded subquadrate appearance peculiar to some of the Globigerina venezuelana specimens examined from the Cipero formation of Trinidad. Globigerina euapertura, new species, differs from Globigerina ampliapertura in having a lower arched aperture in the adult test.

It is possible that Globigerina euapertura, new species, is related to Globigerina venezuelana recorded by Bolli (1957a, p. 110) from the Globigerina ampliapertura zone of the Cipero formation of Trinidad (Dr. W. H. Blow, in a private communication).

References:

Jenkins, D. G. (1960). Planktonic foraminifera from the Lakes Entrance oil shaft, Victoria, Australia. Micropaleontology. 6: 345-371. gs

Spezzaferri, S., Olsson, R. K., Hemleben, C., Wade, B. S. & Coxall, H. K. (2018d). Taxonomy, biostratigraphy, and phylogeny of Oligocene and Lower Miocene Globoturborotalita. 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 8): 231-268. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Globigerina euapertura (Jenkins 1960)

Globigerina euapertura

References:

Add Comment

Comments