Catalog - Globanomalina rakhiensis

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Globanomalina rakhiensis

Citation: Globanomalina rakhiensis Warraich et al. 2000

Type specimens: Figure 12; Holotype, IGUT coll. no, 50101; Paratype, IGUT coli. cat. no. 50103

Type sample (& lithostrat): Sample R41, Dungan Formation

Type age (chronostrat): P7, Early Eocene

Type locality: Rakhi Nala section, Central Pakistan

Type repository: Tuskuba; Institute of Geosciences, University of Tsukuba

Test very small, spiral side flat to slightly convex, umbilical side low convex: equatorial periphery elongate, distinctly lobulate: peripheral margin acute, strongly to moderately compressed with a keel; 14 or 15 chambers arranged in 3 whorls, all visible from spiral side; commonly five (rarely six) chambers in the last whorl increase very rapidly in size: on umbilical side intercameral sutures depressed and weakly curved whereas strongly recurved and limbate on spiral side; surface finely perforate; umbilicus narrow and shallow; aperture low arch-shaped, interiomarginal, umbilical- extraumbilical with distinct lip.

Holotype: maximum diameter 0.27 mm, width 0.20 mm. The largest specimen is 0.27 mm in diameter, but specimens are usually less than 0.15 mm.

This new species is named after a local river, Rakhi Nala, along which this section is exposed.

Remarks.- The species is common in Sample R41. Globanomalina rakhiensis sp. nov. is a small but very distinctive species and might have been overlooked previously due to its small size. lt can be missed if using the 150 µm size fraction. This species shows variation in size and degree of compression of the peripheral margin. The holotype (Figure 12.1- 12.3) is less compressed than the paratype (Figure 12.6 - 12.8). Planorotalites pseudoscitula (Glaessner, 1937) is very similar to G. rakhiensis sp. nov. but differs in having more chambers in the last whorl (6 or 7) and a circular periphery, and in being more lenticular.

Globanomalina rakhiensis sp. nov. is a homeomorph of the late Paleocene Globanomalina pseudomenardii (Bolli, 1957) as both forms possess a compressed planoconvex lest, 5 chambers in the last whorl, and a low-arched umbilical-extraumbilical aperture that bears a lip. G. rakhiensis sp. nov. is easily distinguished from G. pseudomenardii by its small size and relatively weak keel.

The stratigraphic range of G. pseudomenardii is restricted to Zone P4 (late Paleocene) In many works (Toumarkine and Luterbacher, 1985; Berggren and Miller, 1988, Berggren et al., 1995; Berggren and Norris, 1997; Olsson et al., 1999, etc). However, Blow (1979) extended the age range of this species to his Zone P7 (early Eocene). We suggest that Globorotalia (G.) pseudomenardii identified by Blow (1979) from his Zone P7 (pi. 111, figs. 1- 4; pl. 112, figs. 2, 3; 9-1 0) is quite similar to our new species (G. rakhiensis). Therefore, he might have misidentified G. rakhiensis sp. nov.

Stratigraphic range. - Globanomalina rakhiensis sp. nov. yielded by Sample R41 is assigned to the M. formosa formosa Zone (P7), corresponding to Zone P7 of Berggren and Miller (1988) and Berggren et al. (1995). Therefore, the stratigraphic range of this species is within the middle lower Eocene.

References:

Berggren, W. A. & Miller, K. G. (1988). Paleogene tropical planktonic forminiferal biosttatigraphy and magnetobiochronology. Micropaleontology. 34(4): 362-380. gs

Berggren, W. A. & Norris, R. D. (1997). Biostratigraphy, phylogeny and systematics of Paleocene trochospiral planktonic foraminifera. Micropaleontology. 43(supplement 1): 1-116. gs

Berggren, W. A., Kent, D. V., Swisher, I. , C. C. & Aubry, M. -P. (1995b). A revised Cenozoic geochronology and chronostratigraphy. In, Berggren, W. A., Kent, D. V., Aubry, M. -P. & Hardenbol, J. (eds) Geochronology, Time Scales and Global Stratigraphic Correlations. SEPM (Society for Sedimentary Geology) Special Publication No. 54, 129-212. gs

Blow, W. H. (1979). The Cainozoic Globigerinida: A study of the morphology, taxonomy, evolutionary relationships and stratigraphical distribution of some Globigerinida (mainly Globigerinacea). E. J. Brill, Leiden. 2: 1-1413. gs

Olsson, R. K., Hemleben, C., Berggren, W. A. & Huber, B. T. (1999). Atlas of Paleocene Planktonic Foraminifera. Smithsonian Institution Press, Washington, DC. (85): 1-252. gs

Toumarkine, M. & Luterbacher, H. (1985). Paleocene and Eocene planktic foraminifera. In, Bolli, H. M., Saunders, J. B. & Perch-Neilsen, K. (eds) Plankton Stratigraphy. Cambridge Univ. Press, Cambridge 87-154. gs

Warraich, M. Y., Ogasawara, K. & Nishi, H. (2000). Late Paleocene to early Eocene planktic foraminiferal blostratigraphy of the Dungan Formation, Sulaiman Range, central Pakistan. Paleontological Research, Tokyo. 4(4): 275-301, 218 figures, 273 aendices. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Globanomalina rakhiensis Warraich et al. 2000

Globanomalina rakhiensis

References:

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