Catalog - Globotruncana youssefi

This page provides data from the catalog of type descriptions. The catalog is sorted alphabetically. Use the current identification link to go back to the main database.

Globotruncana youssefi

Citation: Globotruncana youssefi El-Naggar 1966

Type specimens: holotype (fig. 4a-d) P.45564, and unfigured paratypes, P.45565.

Type sample (& lithostrat): upper Sharawna Shale.

Type age (chronostrat): Upper Cretaceous, Maestrichtian. Rare to very abundant in the upper part of the Globotruncana gansseri Zone (Middle Maestrichtian) and dies out in the overlying G. esnehensis Zone (Upper Maestrichtian).

Type locality: Holotype (fig. 4 a-d) and unfigured paratypes from approximately 51 meters above the base of the Gebel Owaina section (27°45'N 32°45.75'E), about 12 km. north of the Nile at El Mahamid, Esna-ldfu region, Upper Egypt.

Test large, planoconvex, umbilico-convex, coiled in a low trochospire; dorsal side almost fiat and weakly imbricate, with the last chambers slightly lower than the early ones; ventral side strongly inflated and very distinctly protruding; equatorial periphery subcircular, distinctly lobate with a single, well developed, much thickened and beaded marginal keel; axial periphery subangular; chambers on the dorsal side 19, arranged in 3 dextrally coiled whorls; the initial chambers are very small, globular and inflated; they increase slowly in size, and are followed by relatively larger, globular, weakly inflated chambers which tend to be slightly elongated in the direction of coiling; the last whorl is composed of 5.5 large, crescentic chambers which increase slowly in size, except for the last which has a peculiar angular shape that makes it appear slightly smaller than the penultimate; on the ventral side the chambers are 5.5, large, angular conical, strongly inflated and distinctly protruding; sutures on the dorsal side short, radial, depressed in the early part, distinctly curved, raised and beaded in the later part, although the beading fades towards the inner whorl; on the ventral side the sutures are straight, radial and strongly depressed; umbilicus pentagonal in outline, wide, deep and covered by complex tegilla of which remnants are still preserved; primary apertures interiomarginal, umbilical; tegilla with accessory apertures, only poorly preserved; wall calcareous, perforate except for the imperforate keel and tegilla; surface rough in the early part, heavily papillose or even nodose with the papillae decreasing gradually towards the last chamber.

Maximum diameter 0.54 mm.; minimum diameter 0.43 mm.; thickness of last chamber 0.31 mm

Main variation. - Chambers 11-21, arranged in 2-3 whorls which are generally dextrally coiled. Chambers in the last whorl 4-6, most commonly 5.

Remarks. - Globotruncana youssefi El-Naggar is morphologically similar to both G. lugeoni var. angulata Tilev and G. arabica. It is distinguished from the former by its ty pically crescentic chambers throughout, peculiarly shaped last chamber, strongly curved, raised, beaded dorsal sutures and more strongly developed marginal keel. It differs from G. arabica by its almost flat to slightly raised dorsal side, its longer, more curved, raised and beaded dorsal sutures and its perfectly marginal keel.

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: Globotruncana youssefi El-Naggar 1966

Globotruncana youssefi

References:

Add Comment

Comments