Catalog - Globorotalia pusilla mediterranica

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Globorotalia pusilla mediterranica

Citation: Globorotalia pusilla subsp. mediterranica El-Naggar 1966

Type specimens: holotype (fig. 3a-c) P.45624; unfigured paratypes P.45625.

Type sample (& lithostrat): lower Owaina Shale

Type age (chronostrat): Paleocene. Appears in the upper part of the Globorotalia pusilla Subzone (upper Middle Paleocene), rare to common in the Globorotalia pseudomenardii Subzone, and dies out in the basal part of the Globorotalia aequa/Gioborotalia esnaensis Subzone (Upper Paleocene).

Type locality: Holotype ( fig. 3a-c) and unfigured paratypes from approxima tely 115.5 meters abo ve the base of the Gebel Owaina section (27°4 5' N.. 3'2°45.75'E), about 12 km. north of the Nile at El Mahamid, Esna-Idfu region, Upper Egypt.

Diagnosis. - A Globorotalia pusilla with relatively larger, papillose test; more chambers and whorls; more protruding ventral side and moderately convex dorsal one; roughly quadrangular last chambers on dorsal side, very narrow and very strongly elongated in direction of coiling: very high, angular conical chambers on ventral side, strongly protruding from the periphe1y, leaving it as a thick, marginal pseudo-keel.
Description. - Test medium-sized, unequally biconvex, coiled in a low trochospire; dorsal side moderately convex, ventral side strongly and distinctly protruding; equatorial periphery almost circular, moderately lobate; axial periphery acute, without keel, but the chambers on the ventral side are so strongly protruding that the marginal periphery appears as if separated from this protruding mass by a very shallow groove in the form of a thick marginal pseudo-keel; chambers on the dorsal side 18, arranged in 3½ dextrally coiled whorls; the initial ones are small, infl ated, globigerine, almost masked by the surface rugosity and are followed by crescentic, elongated chambers; the last whorl is slightly lower thfan the preceding whorls, and is composed of 4 ih, long, nanow, roughly quadrangular chambers, which are strongly elongated in the direction of coiling and increase slowly in size; on the ventral side the chambers are 4½, large, roughly triangular, conical, moderately inflated and distinctly protruding; sutures on the dorsal side curved, depressed in the early part, very short, slightly curved and depr essed later; on the ventral side the sutures are straight, radial and strongly incised; umbilic us relatively small, deep and open; aperture interiomarginal, extraumbilical-umbilcal. a narrow, long arch, with a delicate, narrow lip; wall calcareous perforate : surface distinctly papillose, especially in the early part. "

Maximum diameter 0.35 mm.; minimum diameter 0.30 mm.: thickness 0.19 mm.

Remarks. - Globorotalia pusilla mediterranica has all the main characteristics of the G. pusilla group: the biconvex, strongly inflated test; the protruding ventral side, with its triangular, conical, high chambers; radial, depressed ventral sutures; small umbilicus; and long, narrow, arched aperture, with an occas ional delicate apertural lip. It is thus included as a subspecies of G. pusilla, although it is quite distinct from theother two subspecies, G. pusilla pusilla and G. pusilla laevigata. It differs from the former in protruding more on the ventral side, in having a higher umbilical shoulder, a thick, marginal pseudo-keel, and quadrangular chambers on the dorsal side. From the latter it is distinguished by its more convex dorsal side, greater protrusion of the ventral surface, its thick marginal pseudo-keel, rough surface, and the shape of the chambers on the dorsal side. "'Globorotalia pusilla m edirerranica is be lieved to have evolved from G. pusilla pusilla but nothing is known as yet about its evolution in younger strata, as no morphologically similar forms have so far been described."""

References:

El-Naggar, Z. R. (1966). Stratigraphy and planktonic foraminifera of the Upper Cretaceous-Lower Tertiary succession in the Esna-Idfu region, Nile Valley, Egypt, U. A. R. Bulletin of the British Museum (Natural History). supplement 2: 1-291. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Globorotalia pusilla subsp. mediterranica El-Naggar 1966

Globorotalia pusilla mediterranica

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