Catalog - Globigerina microfoliata

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Globigerina microfoliata

Citation: Globigerina microfoliata Brönnimann & Resig 1971

Type locality: South West Pacific, Eauripik Ridge, Micronesia-New Guinea:Hole 62.1, Core 8, Section 3,15-17 centimeters, Zone N. 20 (including N. 19)

Type repository: Washington; USNM

The very small-sized test is a fairly high, broadly turriline, but not pointed, trochospire consisting of more than 12 chambers. There are four fairly rapidly decreasing in size, subglobular to somewhat axially compressed chambers in the final whorl. The ultimate chamber is tangentially larger (75 microns) than radially (22 microns). The intercameral
and spiral sutures are deeply incised on the dorsal side and the cameral sutures also on the ventral side. The cameral sutures are radial on both sides. The deep incision of the intercameral radial sutures and the well-separated subglobular to axially slightly compressed chambers of the final whorl produce, in dorsal and in ventral view, a distinct lobate outline of the test. This lobation is also seen in side view because the final chamber is slightly displaced toward the umbilical side. The aperture is directed into the umbilical cavity. It is an arched opening of about 35-micron diameter, surrounded
by a lip-less border. In the deep umbilical cavity of about 17- to 20-micron diameter, the opening of the penultimate chamber is discernible. The wall is calcareous,thin, with irregularly distributed, relatively large wall pores. The openings of the wall pores are about 1 to 3 microns in diameter. They lie in smooth-contoured,shallow, funnel-like depressions of maximum 5-micron diameter. In between the pores occur, also irregularly distributed, low-rounded pustules which exhibit minute axially situated openings of from less than 1 micron to about 1 micron diameter. The specimen coils to the left.
It is from Hole 62.1, Core 8, Section 3,15-17 centimeters, Zone N. 20 (including N. 19). It is illustrated on Plate 6, Figure 6.

The maximum diameter of the holotype is about 175 microns; its axial height is about 125 microns.

Under the optical microscope the surface appears glossy, smooth to minutely pustulate. The scanning micrographs on the other hand show a minutely granular surface. The diameters of paratypes from Hole 62.1, Core 8, Section 5, 16-18 centimeters, Zone N. 20 (including N. 19) range from about 100 to 200 microns. The ultimate chamber of paratypes may be considerably longer radially than that of the holotype, thus increasing the lobation of the test in paratypes. Also, the height of the trochospire is very variable, from a distinctly turriline to a flattened cone.
The coiling of the paratypes is random. The paratypes shown of the dorsal side, are both damaged in the early portion of the trochospire leaving only the final whorl intact. The ratio of increase of the tangential diameter of the chambers of the final whorl, which throughout are tangentially larger than radially, are 1:1.33 : 1.54 : 1.83, and 1:1.34 : 1.1 : 1.65. The walls of the early chambers are at least 2 or 3 layered,through the addition of supplementary layers in the course of growth. This very small Globigerina resembles in its general morphology Globigerina falconensis Blow,
1959, and Globigerina multilobata Romeo, 1965. It differs from falconensis by its small size,by the lobate outline, by the frequent umbilical displacement of the final chamber, by its lipand rimless aperture and finally by its different wall and surface development. Globigerina multiloba Romeo, 1965, which according to Romeo's illustration (Romeo, 1965, plate 118) does not possess a discrete lip, is homeomorphic in size and umbilical aperture to Globigerina microfoliata. The outline of the test however is by far less regularly lobate and the surface of the test less smooth than in the new species from the southwestern Pacific.
Furthermore, the number of chambers in the final whorl, normally 6 to 7, exceptionally 5, is greater than that in Globigerina microfoliata where 3 to 4 chambers, maximum 5 chambers, occur in the final whorl. Stratigraphically,Globigerina multiloba has been recorded in the basal Messinian, in the Orbulina suturalis Zone of Selli (1960). It is therefore clearly older than Globigerina microfoliata. An interesting Recent quasi-homeomorph of Globigerina
microfoliata has been described from the North Atlantic by Cifelli and Smith (1970, Plate 3,
Figures 4 and 5) under the name Globigerina quinqueloba egelida Cifelli and Smith, 1970. Though in general morphology this subspecies of quinqueloba is close to Globigerina microfoliata, the minutely and densely pustulate surface and the slightly up-turned liplike apertural margin of quinqueloba egelida dis-tinguish these small globigerines.

References:

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. gs O

CATALOG OF ORIGINAL DESCRIPTIONS: Globigerina microfoliata Brönnimann & Resig 1971

Globigerina microfoliata

References:

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