Catalog - Globorotalia (Globorotalia) paralenguaensis

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Globorotalia (Globorotalia) paralenguaensis

Citation: Globorotalia (Globorotalia) paralenguaensis Blow 1969

Type sample (& lithostrat): lower part of the Muruan Formation. Ranges from the upper part of Zone N. 15 to the lower part of Zone N. 16, both in the Upper Miocene.

Type age (chronostrat): Upper Miocene, Tortonian, basal part of Zone N.16 (= Globorotalia (Turborotalia) acostaensis acostaensis - Globorotalia (G.) merotumida Partial-range zone)

Type locality: Holotype (figs. 3-6) and figured paratype (figs. l , 2) from the Dariava-Hadina Creek Traverse (sample CS.222), Papua, New Guinea.

Test small, coiled in a low trochospire with about 15-16 chambers comprising the spire and with 6 chambers in the final whorl. The spire opens slowly at first then shows a more rapidly opening coiling mode with a distinct flare for the later parts of the last convolution at least; the chambers are tightly coiled in the early part of the test but become much less tightly coiled later. The equatorial profile is non-lobulate becoming very slightly lobulate over the periphery of the last two or three chambers. The ax'ial profile shows an unequally biconvex test with the dorsal surface slightly vaulted and the ventral surface rather more distinctly vaulted. The peripheral margin bears a distinct 'imperforate' carina but the dorsal Intercameral sutures are not limbate. Dorsal intercameral sutures only very slightly incised and show step-like features for the last two or three chambers. The earlier dorsal intercameral sutures are strongly recurved but time later dorsal intercameral sutures become more nearly radially disposed with some peripheral retortion. In dorsal aspect the earlier chambers are almost hemi-circular in shape but the final two or three chambers are more quadrate or rectangular in overall shape. The ventral intercameral sutures are radial to slightly sinuous, moderately incised between the somewhat inflated ventral surfaces of the chambers. The umbilicus is completely closed. The aperture is interiomarginal, umbilical-extraumbilical but IS laterally restricted and is bordered by a distinct rim-like lip; the aperture is a moderately arched opening. The wall is calcareous, radial hyaline, translucent with only very small scattered pustules confined to the area in the vicinity of the aperture. The wall is very finely perforate but the pores are comparatively widely spaced and do not open into distinct pore-pits.

Maximum diameter of holotype 0.25 mm.

Globorotalia (G.) paralenguaensis combines many of the morphological features seen in G (T.) lenguaensis and G. (G.) merotumida and the taxon appears to be a morphogenetic link between the two forms. Thus G. (G.) paralenguaensis displays, in the earlier stages of ontogeny, the chamber shape, arrangement and coiling mode seen in G. (T.) lenguaensis. On the other hand, the later stages in the ontogeny of G (G.) paralenguaensis display the morphological features of chamber shape, presence of a carina, apertural characteristics and later coiling mode similar to those of G. (G.) merotumida. Thus, the earlier stages of G. (G.) paralenguaensis show the similar strongly recurved dorsal intercameral sutures as seen throughout the whole of the test of G. (T.) lenguaensis. The spire in G. (T) lenguaensis opens slowly and regularly and the chambers are similar in shape for all stages of ontogeny but in paralenguaensis the early 'lenguaensis-like' morphology is followed by the spire suddenly opening more rapidly and the chambers adopting the dorsal shape as seen in G. (G.) merotumida.
G. (G.) paralenguaensis retains the ventral characteristics of G. (T.) lenguaensis in possessing a completely closed umbilicus but possesses a true 'imperforate' carina which is characteristic of the descendant from G. (G.) merotumida. Both the holotype and the figured paratype are completely carinate but the paratype also possesses limbate dorsal intercameral sutures (fig. 2) which are not seen in the holotype. It is likely that the paratype should be considered as a little more phylogenetically advanced than the holotype.

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: Globorotalia (Globorotalia) paralenguaensis Blow 1969

Globorotalia (Globorotalia) paralenguaensis

References:

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