Catalog - Globigerinita africana

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Globigerinita africana

Citation: Globigerinita africana Blow & Banner 1962

Type specimens: Plate XV A-C ; Fig . 11 i-iv

Type sample (& lithostrat): sample FCRM 1645

Type locality: Lindi area, Tanzania

The moderately large test consists of about three whorls of fairly rapidly and regularly enlarging, inflated, slightly embracing chambers, arranged in an increasingly high trochospire with about four chambers in each whorl. The equatorial profile of the test is subcircular to subquadrate, and the equatorial periphery is broadly and distinctly lobulate. In axial profile, the dorsal surface of the early whorls is slightly convex and the initial trochospire is fairly low; however, the later chambers are added in an increasingly high trochospire and the dorsal surface becomes increasingly more convex. In axial view, the periphery of the last whorl is broadly and smoothly rounded; the deeply depressed spiral suture between the last two whorls gives a distinctly lobulate axial profile. The primary chambers are initially subglobular, but become subvoid in the last whorl, where they are distinctly more inflated ventrally than dorsally. A broadly rounded dorso-peripheral shoulder may develop in the later chambers. In dorsal view, the chambers are semicircular to reniform; they may become slightly depressed and longer than broad in the later stages of ontogeny. The dorsal sutures are initially obscure but they later become distinctly and often sharply depressed, often narrowly so. The dorsal intercameral sutures are slightly curved or subradial, meeting the lobulate spiral suture at broad angles. The ventral sutures are equally distinctly depressed, and are subradial or slightly curved. The ventral umbilicus (beneath the bulla) is narrow and almost closed, and is not clearly delimited because of the uniform convexity of the umbilical margins of the ventral sides of the chambers. The umbilicus and the primary aperture are completely covered by a broad inflated bulla, which protrudes beyond the ventral surfaces of the primary chambers. The bulla typically extends beyond the limits of the umbilicus, especially interiorly and posteriorly; its outline follows that of the umbilicus, but is modified by extensions along the areas marked by the intercameral sutures of the primary chambers, and by the fact that the bulla usually encroaches more upon the posterior part of the ventral face of the last chamberthan upon the anterior part. At least three accessory apertures are present; two are present on the posterior side of the bulla, one over the suture between the last-formed and the penultimate chambers and one over the suture between the penultimate and antepenultimate chambers. On the anterior side of the bulla, a single broad accessory aperture is usually present, extending the full breadth of the ventral face of the first chamber of the last whorl, but in some exceptionally loosely coiled specimens, where more of the ventral surface of that chamber is exposed, this accesory aperture may be divided and replaced by an accessory aperture over each of the intercameral sutures limiting the first-formed chamber of the last whorl; this produces a maximum of four accessory apertures to the bulla. The accessory apertures are typically furnished with distinct thin lips and are fairly high arches. The sutures between the primary aperture of the final chamber is a high symmetrical arch, sometimes furnished with an indistinct rim-like thickening. The wall of the primary chambers is fairly thick and is uniformly and moderately coarsely perforate; its surface is punctate and distinctly, densely and finely hispid. The wall of the bulla is much thinner than that of the primary chambers; it is more finely perforate and is very finely hispid.

Maximum diameter of holotype 0.38 mm

Remarks: It appears that the increased height of the troche- spire in the later ontogeny of this species is associated with relatively tighter coiling in the last whorl and a narrowing of the umbilicus and the bulla. Occasional specimens which do not show such a marked change in the tightness of coiling and height of the trochospire possess bullae which are broader than the typical; it is these forms which may possess four accessory apertures (Fig. II, iv). This species should be compared to Globigerinita howei sp.nov. (p. 109).

Stratigraphical range: In East Africa, this species is known to range from the base of the Globigerapsis semi-involuta Zone to about the middle part of the overlying Cribrohantkenina danvillensis Zone, Upper Eocene. It may also occur in the upper part of the Middle Eocene, Truncorotaloides rohri Zone.

References:

Blow, W. H. & Banner, F. T. (1962). 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. 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

Olsson, R. K., Pearson, P. N. & Huber, B. T. (2006c). Olsson, R. K., Pearson, P. N. & Huber, B. T. (2006). Taxonomy, biostratigraphy, and phylogeny of Eocene Catapsydrax, Globorotaloides, Guembelitrioides, Paragloborotalia, Parasubbotina, and Pseudoglobigerinella n. gen. In, Pearson, P. N. , Olsson, R. K. , Hemleben, C. , Huber, B. T. & Berggren, W. A. (eds) Atlas of Eocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication. 41(Chap 5): 67-110. In, Pearson, P. N., Olsson, R. K., Hemleben, C., Huber, B. T. & Berggren, W. A. (eds) Atlas of Eocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication . 41(Chap 5): 67-110. gs O

CATALOG OF ORIGINAL DESCRIPTIONS: Globigerinita africana Blow & Banner 1962

Globigerinita africana

References:

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