Catalog - Globigerinoides pseudosellii

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Globigerinoides pseudosellii

Citation: Globigerinoides pseudosellii Brönnimann & Resig 1971

Type age (chronostrat): Lower Miocene

Type locality: South West Pacific, Ontong Java Plateau or Soloman Rise New Guinea: DSDP Leg 7, Hole 64.1

Type repository: Washington; USNM

The medium-sized axially compressed, tightly coiled trochospire consists of at least 8 chambers with 3 chambers in the final whorl. The ultimate chamber is slightly larger than the entire preceding test. The outline of the test in umbilical and spiral view is broadly oval: 350 microns maximum length against 300 microns maximum breadth. In side view, the test is axially flattened, with about 250 microns axial height, and umbilically concave. The intercameral sutures of the final whorl are well incised. The sutures of the early trochospire are indistinct. The chamber arrangement and the form of the test are closely homeomorphic to those of Globigerina sellii Borsetti, 1959 (Plate 8, Figure 9), which however is stratigraphically much older than Globigerinoides pseudosellii (Blow,1969, pi. 19, fig. 4-6). The primary aperture of the
holotype of Globigerinoides pseudosellii is a short,rather low-arched opening in umbilical position. It is situated at the intersection of the umbilical inter-cameral sutures. The primary aperture is about 100 microns long, and about 48 microns high. The arch is slightly lower in its central position than laterally. The border is fully pustulate and an imperforate band or lip is not detectable. There is only a single supplementary aperture in the form of a very small slit-like opening of about 20 microns in length at the intersection of the suture between the ultimate chamber and that separating the ultimate and the penultimate chamber of the penultimate whorl.
The calcareous walls are coarsely pustulate and perforate. The large, composite pustules coalesce laterally and form polygonal compartments, each with a wall pore in its funnel-like depression. The walls of the polygons consist, like the pustules, of smaller units or "crystallites". On the early chambers of the tight trochospire the pustules seem to be enlarged and almost close the openings to the wall pores.

The maximum diameter of the holotype is about 350 microns. It coils to the left. The specimen is from Hole 64.1, Core 3, Section 6, 33-35 centimeters; Zone N6.

As already mentioned, Globigerinoides pseudosellii,n. sp., closely is homeomorphic in its gross morphology to Globigerina sellii Borsetti. It also resembles in umbilical view Globigerinoides sicanus praesicanus Brönnimann and Resig, n. subsp., which however differs clearly from Globigerinoides pseudosellii by the larger almost globular ultimate chamber, the elongate slit-like primary and the large equally slit-like secondary apertures, by the absence of an umbilical depression, and by the absence of axial compression of the chambers of the final whorl. The maximum diameter of paratypes from Hole 64.1 ranges from about 320 to 370 microns.

In comparison with Globigerinoides sicanus praesicanus, Globigerinoides pseudosellii generally has somewhat smaller tests. The outer wall formations of Globigerinoides pseudosellii as illustrated by the scanning micrographs of the umbilical and spiral sides of paratypes, Plate 9, Figures 7 and 9, are characterized by a very strong pustulation. The pustules are composite structures and normally interconnected by equally composite polygonal walls. On the apertural face of the specimen illustrated by Plate 9, Figure 7, the basic polygonal meshwork is modified by the formation of short irregular ridges. On the early trochospiral chambers, the pustules are laterally enlarged and considerably reduce the openings of the polygonal compartments, which have in their centers the wall pores. The rounded wall pores of the ultimate
chamber of the specimen illustrated on Plate 9, Figure 9 reach diameters of about 4 to 5 microns.

References:

Brönnimann, P. & Resig, J. (1971). Brönnimann, P. & Resig, J. (1971). A Neogene globigerinacean biochronologic time-scale of the southwestern Pacific. Initial Reports of the Deep Sea Drilling Project. 7(2): 1235-1469. Initial Reports of the Deep Sea Drilling Project. 7(2): 1235-1469. gs O

CATALOG OF ORIGINAL DESCRIPTIONS: Globigerinoides pseudosellii Brönnimann & Resig 1971

Globigerinoides pseudosellii

References:

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