Catalog - Globorotalia (Turborotalia) tosaensis tenuitheca

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Globorotalia (Turborotalia) tosaensis tenuitheca

Citation: Globorotalia (Turborotalia) tosaensis tenuitheca Blow 1969

Type age (chronostrat): Upper Pliocene, Zanclian, lower part of Zone N. 21 (= Globorotalia (T.) tosaensis tenuitheca Consecutive-range zone). Ranges from the base of Zone N. 21 (Pliocene) to N.22 (Pleistocene).

Type locality: Holotype (figs. 13-15) from sample PEK/F.9 collected near Mbua Mbua, possible equivalents of the " Pteropod Sandstone" of the Suva beds, Island of Vanua Levu, Thakaundrove Peninsula, Fijian Islands; and figured paratypes (figs. 16, 17, 1-3) from the Sarmi Formation (sample BA.40), in the Otim River Section, Island of New Guinea, West Irian.

Test, moderately large, coiled in a low trochospire with about 13 chambers comprising the complete spire and with five chambers in the last whorl. Test plano-convex with a vaulted and conical ventral side. The dorsal-peripheral margin of the test is sub-acute, fairly sharply delimited but narrowly rounded and fully perforate without any carinal structure. The spire opens regularly but slowly so that the chambers do not increase rapidly in size as added. In dorsal aspect the earlier chambers are eq ually clilnensional but the later challibers are distinctly longer tangentially (anterior-posterior) than broad radially. Dorsal intercameral and spiral sutures depressed, slightly incised, not limn bate although a step-like effect gives this impression for the last two dorsa] intercameraJ sutures; this is due to the transparency of [he wall and the probable pinching together of the septal and dorsal walls of the chambers. This 'pinching together' of adjacent chamberae walls is seen over part of the peripheral margin and this area shows a reduction in the density of the pores. However, normal pores are present over all of the dorsal-peripher margin of the test and the more translucent area should not be confused with a true 'imperforate' carina. The ventral intercameral sutures are sub-radial to slightly sinuous. Umbilicus, very small but open and deep with a sharply delimited boundary and with sharply pointed umbilical margins to the ventral walls of the chambers. Aperture, in terio-marginal, a low slit-like opening with a narrow lip. Wall, calcareous, radial hyaline, thin and delicate, very finely perforate with the pores opening to the exterior without pore-pits. Wall pustulose over the dorsal surfaces of the first few chambers and in the vicinity of the aperiure but the pustules are discrete and separated, not fused together.

Maximum diameter of the holotype 0.39 mm.

The holotype of Globorotalia (T.) tosaensis tenuitheca is a phylogenetically primitive form of the taxon and comes from a horizon early in Zone N. 21 . The holotype retains, in part, the tangentially longer than radially broad chambers typically seen in the ancestral G. (T.) crassaformis oceanica. However, the holotype shows a greater degree of plano-convexity of the test and the pointed umbilical margins of the ventral chamber surfaces as compared to G. (T.) crassula oceanica. The holotype of G. (T.) tosaensis tenuitheca has much less inflated chambers than in G. (T.) crassaformis oceanica and the chambers are slightly more embracing in the former taxon as compared to the latter.
The paratype (figs. I , 2) of G.(T.) tosaensis tenuitheca illustrates the slightly later development of the taxon. The stereoscan illustration of a paratype from sample Ba.40 (fig. 3) shows the more nearly equally dimensional aspect of the chambers in dorsal view as well as the development of more collipletely radial dorsal intercameral sutures except for some retortion at their distal ends in phylogenetically advanced forms. These paratypes also illustrate the gradual increase of the average number of the chambers in the final whorl which proceeds concomittantly with the development of more dorsally equally dimensional chambers.
The paratype, drawn by Banner (figs. 16, 17), from sample Ba.40 is a phylogenetically advanced specimen of the taxon. The specimen shows the development of a clear area over the dorsal-peripheral margin but this clear area still contains normal wall-pores and does not possess an 'imperforate' carina. The dorsal and peripheral surfaces of the test are strongly pinched together giving an acute peripheral margin. The degree of plano-convexity of the test is very great and similar to that seen in phylogenetically primitive G. (G.) truncatulinoides truncatulinoides. This paratype is representative of the specimens still referable to G. (T.) tosaensis tenuitheca which occur in the latest part of Zone N. 21 [= Globorotalia (T.) tosaensis tenuitheca Consecutive-range zone I and immediately prior to the development of the carinate G. (G.) truncatulinoicles truncatulinoides at the base of Zone N. 22 [ = Globorotalia (G.) truncatulinoicles truncatulinoides Partial-range zone ] ; the latter taxon is recognised at the first appearance of an 'imperforate' carina regardless of the extent or position of the true carina.
In G. (T.) tosaensis tenuitheca Blow, the wall structure and texture appear to be essentially similar to that seen in most taxa of the Globorotaliidae. The wall is comparatively thin, delicate, moderately densely but very finely perforate. There are no pore-pits and the pores do not seem to greatly change their diameters during ontogeny Of though the thickness of the wall. The test bears pustules mainly in the apertural and umbilical regions but these pustules are discrete, well separated and are similar to those found in other turborotaliid and globorotatiid taxa.

References:

Blow, W. H. (1969). 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. 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 (Turborotalia) tosaensis tenuitheca Blow 1969

Globorotalia (Turborotalia) tosaensis tenuitheca

References:

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