Catalog - Globigerina praebulloides pseudociperoensis

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Globigerina praebulloides pseudociperoensis

Citation: Globigerina praebulloides pseudociperoensis Blow 1969

Type sample (& lithostrat): lower Palembang Formation. Occurs in a stratigraphic interval between Zone N. 7 and N. 12, lower and middle Miocene, respectively.

Type age (chronostrat): Middle Miocene, Langhian, zone N. 11 Globorotalia (G.) praefohsi Consecutive-range zone)

Type locality: Holotype (figs. 8, 9), from sample C.321, Central Sumatra.

The moderate size test consists of about 12-13 chambers arranged in a distinct trochospire with five chambers present in the last whorl but only 4 chambers are present in the penultimate whorl. The chambers are inflated, subglobular and not much embracing. The dorsal and ventral intercameral sutures are sharply incised and radial in direction. The umbilicus is wide, open and deep. The aperture is a low intraumbilical arch without a distinct rim or lip. The trochospire opens rapidly but the coiling mode is uniform throughout ontogeny without any noticeable change in the laxity or tightness of the coiling. The dorsal spire is high and protrudes significantly above the dorsal surfaces of the chambers of the last whorl. From the dorsal side, the chambers are seen to increase in size quite rapidly and the spiral suture is seen to be distinctly depressed. Wall, calcareous, radial hyaline, finely perforate with the pores opening into small pits. The ridges between the 'honey-comb' network of pits are not greatly thickened and the pits are of much the same diameter as the exterior parts of the pores

Maximum diameter of holotype 0.33 mm.

As viewed from the ventral side Globigerina praebulloides pseudociperoensis is morphologically very close to G. ouachitaensis ciperoensis. Purely from the ventral side intraspecific variation amongst specimens referable to pseudociperoensis appears to be greater than the inter-specific variation seen in comparing populations of pseudociperoensis with populations of ciperoensis. However, the chambers of pseudociperoensis are less closely appressed than in ciperoensis and this is reflected in the ventral aspect of the two taxa. In general, the umbilicus is relatively wider in specimens of pseudociperoensis than it is in specimens of ciperoensis. However, the dorsal view of G. praebulloides pseudociperoensis is quite distinctive and the more rapidly opening and higher spire permits differentiation of the two forms. Further, the wall of G. praebulloides pseudociperoensis possesses smaller surface pits than those of G. ouachitaensis ciperoensis and the ridges between adjacent pits are more thickened and pronounced in the latter form. Usually G. ouachitaensis ciperoensis has five chambers in both the penultimate and ultimate whorls but G. praebulloides pseudociperoensis has 4 chambers in the penultimate whorl and 5 chambers in the final convolution. In G. ouachitaensis ciperoensis the spire opens slowly with the chambers only increasing slowly in size as added. The spire of G. ouachitaensis ciperoensis is depressed and the chambers are usually quite strongly embracing especially in the penultimate whorl.

References:

Blow, W. H. (1969). Late middle Eocene to Recent planktonic foraminiferal biostratigraphy. In, Bronnimann, P. & Renz, H. H. (eds) Proceedings of the First International Conference on Planktonic Microfossils, Geneva, 1967. E J Brill, Leiden 380-381. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Globigerina praebulloides pseudociperoensis Blow 1969

Globigerina praebulloides pseudociperoensis

References:

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