Catalog - Globigerina tripartita tapuriensis

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Globigerina tripartita tapuriensis

Citation: Globigerina tripartita tapuriensis Blow & Banner 1962

Type sample (& lithostrat): sample FCRM 1964

Type locality: Lindi area, Tanzania

The moderately large test consists of about three whorls of rapidly enlarging, inflated, little embracing chambers coiled in a low trochospire. Four chambers are present in the early whorls, typically reducing to three in the last whorl. The equatorial profile of the test is subcircular to subquadrate and the equatorial periphery is broadly and smoothly lobulate. In axial profile, the test is subovoid; the dorsal surface is moderately convex whereas the ventral side is strongly convex. The axial periphery is smoothly and broadly rounded with no distinct dorsa-peripheral shoulder. Dorsally, the sutures are initially obscure, but they become distinctly depressed during ontogeny; the dorsal intercameral sutures are initially curved, meeting the lobulate spiral suture at broad angles, but they later become subradial. The ventral intercameral sutures are mod era tely deeply dep ressed. In qo rsal view the chambers are semicircular to reniform throughout ontogeny, but become rather longer than broad. In ventral view the chambers are subcircular to subreniform. The umbilicus is indis- tinctly delimited but appears to be moderately broad and of triangular shape; it is open and deep. The apertural face of the last chamber is convex and not clearly delimited from the rest of the chamber

surface; however, in umbilical view the apertural face may be seen to occupy an ill-defined, roughly reniform re-entrant. The aperture is a fairly low but long arch extending symmetrically across the full

width of the umbilicus, and along the full length of the apertural face. The aperture is furnished throughout its length with a distinct narrow rim- like lip broadest at its mid-point. The relict aperture of the penultimate chamber can be seen within the umbilicus. The wall of the test is fairly thick, moderately coarsely perforate and uniformly hispid.

The hispidity is usually strongest around the umbilical margins.

Maximum diameter of holotype 0·73 mm

Remarks: This subspecies is distinguished from Globigerina tripartita tripartita by its much less depressed chambers, more convex dorsal surface, much more open umbilicus, higher, more convex apertural face, and larger, more open aperture with a reduced apertural lip.

Stratigraphical range: This subspecies occurs only in the Globigerina oligocaenica Zone, Oligocene, Lindi area. Like G. tripartita tripartita, it may be restricted to tropical areas. It has not been recorded from either the 'San Fernando formation' or the Cipero formation of southern Trinidad; we have examined much material from all the zones of the Cipero formation, and have failed to find it. An intermediate form between this subspecies and G. oligocaenica has been observed in a Lower Oligocene sample from Sarawak (see p. 89).

References:

Blow, W. H. & Banner, F. T. (1962). The mid-Tertiary (Upper Eocene to Aquitanian) Globigerinaceae. In, Eames, F. E., Banner, F. T., Blow, W. H. & Clarke, W. J. (eds) Fundamentals of mid-Tertiary Stratigraphical Correlation. Cambridge University Press, Cambridge 61-151. gs

Pearson, P. N. & Wade, B. S. (2015). Systematic taxonomy of exceptionally well-preserved planktonic foraminifera from the Eocene/Oligocene boundary of Tanzania. Cushman Foundation for Foraminiferal Research, Special Publication. 45: 1-85. gs

Wade, B. S., Pearson, P. N., Olsson, R. K., Fraass, A. J., Leckie, R. M. & Hemleben, C. (2018c). Taxonomy, biostratigraphy, and phylogeny of Oligocene and Lower Miocene Dentoglobigerina and Globoquadrina. 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 11): 331-384. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Globigerina tripartita tapuriensis Blow & Banner 1962

Globigerina tripartita tapuriensis

References:

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