Catalog - Globotruncana fornicata globulocamerata

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Globotruncana fornicata globulocamerata

Citation: Globotruncana fornicata globulocamerata El-Naggar 1966

Type specimens: holotype (fig. 2a-c) P.45532; figured paratype (fig. 1 a-c) P.45533; unfigured paratype, P.45534.

Type age (chronostrat): Holotype (fig. 2a-c) from approximately 58.5 meters above the base of the Abou Saboun section; and figured paratype (fig. la-c) from 42 to 55 meters above the base of the same section (sample no. 3) (25° 11.3'N 32°46.3'E), about 5.6 km. north of the Nile at El Mahamid and about 24 km. southeast of the Nile at Esna, Esna-Idfu region, Upper Egypt.

Type locality: Upper Cretaceous, Lower Maestrichtian, Globotruncana fornicata Zone, lower Sharawna Shale. Common to abundant.

Test medium sized, biconvex, coiled in a low trochospire; dorsal side gently arched and moderately inflated, ventral side slightly inflated and weakly protruding ; equatorial periphery roughly ovoid, weakly lobate, with two well-developed, much thickened and delicately beaded marginal keels enclosing a relatively wide, slightly inclined peripheral band, which widens out gradually towards the last chamber; axial periphery distinctly truncate; chambers on the dorsal side 17, arranged in 3 dextrally coiled whorls; the initial chambers are exceedingly small, almost indistinct, slightly depressed, globular, weakly inflated, and increase very slowly in size; they are followed by relatively larger, globular, inflated chambers which increase moderately in size; the last whorl is composed of 5 large, inflated chambers which are subglobular and increase slowly in size except for the last which is crescentic, strongly elongated in the direction of coiling, and constitutes about one-third of the test; on the ventral side the chambers are 5, large, inflated, subglobular, moderately overlapping and increase slowly is size except the last one which is ovoid, elongated, strongly inflated and constitutes about one-third of the test; sutures on the dorsal side slightly curved, raised and delicately beaded, although the inflation of the chambers on both sides makes them appear to run in very shallow sutural depressions; on the ventral side the sutures are curved, slightly raised and delicately beaded; umbilicus irregular in outline, relatively wide, shallow, bordered by slightly raised, delicately beaded ridges 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 keels, peripheral band and tegilla; surface slightly rough, delicately papillose especially on the ventral side with the roughness decreasing gradually towards the last chamber.

Maximum diameter 0.43 mm.; minimum diameter 0.32 mm.; thickness 0.22 mm.

Variation. - The main variation observed in specimens of Globotruncana fomicata globulocall/erara is in the degree of globularity of the last chambers and the degree of surface roughness.

Remarks. - All members of the C. fornicata group are generally characterized by an early globigerine part, and later crescentic chambers which are strongly curved and distinctly elongated in the direction of coiling. The present form, however, re presents a distinct type of this group in which the early globigerine character extends to most of the final whorl, while the last one or two chambers still keep the characteristic chamber form which is strongly elongated in the direction of coiling. As all the other characters of the C. fornicata group are retained in the present form, and as it has a slightly different stratigraphical range from C. fornicata fornicata Plummer, it is here considered as a distinct subspecies. The name G. fornicata globulocamerata describes the globular character of most of its chambers.
G. fornicata globulocamerata is believed to have evolved from G. fornicata fornicata Plummer, and into G. contusa sensu Troelsen, as suggested by the morphology and stratigraphical distribution of these forms.

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 fornicata globulocamerata El-Naggar 1966

Globotruncana fornicata globulocamerata

References:

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