Catalog - Globigerina pseudoampliapertura

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Globigerina pseudoampliapertura

Citation: Globigerina pseudoampliapertura Blow & Banner 1962

Type specimens: Plate XII A-C; XVII A, E; Fig. 12c

Type sample (& lithostrat): sample FCRM 1923

Type age (chronostrat): Upper Eocene

Type locality: Lindi area. Tanzania

The fairly large test consists of about 3 whorls of slowly enlarging, moderately inflated, partially embracing chambers coiled in a low trochospire. The adult test possesses about 4 chambers in the last whorl, the number ofchambers per whorl often reducing slightly during ontogeny. The chambers are only slightly convex dorsally but are relatively very convex ventrally, being strongly ovoid to rounded-triangular in axial view. The equatorial profile is subcircular and the equatorial periphery is weakly lobulate. In axial profile the test shows a marked dorsal flattening and a stongly convex ventral side; the axial periphery is broadly and smoothly rounded, but a distinct dorso-peripheral shoulder is present. The ventral intercameral sutures are distinctly but not strongly depressed, and are subradial. Dorsally, the sutures are initially indistinct but become increasingly depressed durng ontogeny. The dorsal intercameral sutures are initially curved, meeting the spiral suture at acute angles, but the rather dorsal intercameral sutures become straighter although remaining oblique. In dorsal aspect, the chambers are initially semicircular in outline, but during ontogeny they become increasingly longer than broad; often the anterior part of the chamber is narrower than the posterior part. The dorsal sides of the chambers tend to become more inflated and less depressed during ontogeny. The ventral umbilicus is small but deep, and is not covered by the umbilical margin of the last chamber. The aperture is interiomarginal, intraumbilical, a fairly high somewhat asymmetrical arch sometimes bordered by a weak and narrow lip or rim. The apertural face is narrow, somewhat falttened and often hispid. The relict aperture of the penultimate chamber may typically be observed within the umbilicus. The wall is fairly thin relative to the size of the test and is uniformly and finely perforate. The surface of the test is smooth except for weakly hispid areas around the umbilicus and aperture and sometimes on the earlier whorls seen dorsally.

Maximum diameter of holotype: 0.60 mm.

? Acarinina centralis (Cushman & Bermudez) Subbotina 1953 (part), pp. 237- 239, pl. 25, figs. 0a- 11c only.
Specimens transitional between Globorotalia centralis and Globigerina ampliapertura, Bolli, 1957, Bull. U.S. Nat. Mus. 215, 164, pl. 36, figs. 9, 10.

Remarks: Globigerina pseudoampliapertura sp.nov. is distinguished from G. ampliapertura by the presence of the smooth 'non-granular', finely perforate wall (see Plate XVIIA-E) in the former species. The chamber shape in Gpseudoampliapertura is typically asymmetncal anteriorly-posteriorly, and resembles that of Globorotalia centralis; this contrasts with Globigerina ampliapertura which has a chamber symmetry resembling that of Globorotalia increbescens. The umbilicus of Globigerina pseudoampliapertura is more open than in G. ampliapertura and the coiling looser. Populations studied suggest that the average size attained by adults of G. pseudoampliapertura is distinctly greater than that attained by adults of G. ampliapertura. Not only does G. pseudoampliapertura differ from Globorotalia centralis in possessing an intraumbilical aperture but also by developing a more open umbilicus (in which relict apertures can be clearly seen) and more mflated dorsal sides of the later chambers.

Stratigraphical range: In the Lindi area, the species evolves from and replaces Globorotalia centralis at about the middle part of the Cribrohantkenina danvillensis Zone. It ranges to the top of the Globigerina turritilina turritilina Zone, Upper Eocene, but does not occur in Oligocene or younger beds. Specimens apparently referable to this species occur in the Bolivina Zone, Upper Eocene, of the Caucasus (Subbotina, 1953). Forms recorded by Bolli (1957 c) from the 'San Fernando formation' may be from derived blocks of Upper Eocene age.

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., Premec-Fucek, V. & Premoli Silva, I. (2006b). Taxonomy, biostratigraphy, and phylogeny of Eocene Turborotalia. 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 15): 433-460. gs O

CATALOG OF ORIGINAL DESCRIPTIONS: Globigerina pseudoampliapertura Blow & Banner 1962

Globigerina pseudoampliapertura

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