Catalog - Globigerina bathoniana

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Globigerina bathoniana

Citation: Globigerina bathoniana Pazdrowa 1969

Type age (chronostrat): Middle Bathonian

Type locality: Ogrozieniec, Czestochowa region, Poland

Tests white, calcareous, trochospiral, usually with diameter nearly equal to height, consisting of 7-13, most often 9 chambers, spherical, rapidly increasing in size, coiled helicoidally in 2-3 whorls. The first whorl around the proloculus consists of 4 chambers, arranged often planispirally, the next whorls are more trochospiral. The last whorl consists of 3-4 chambers. The last chambers increase their dimension less rapidly. Chambers in the first whorl are less distinctly separated by shallow sutures. During the formation of a younger chamber the wall is formed not only on it, but also on the whole older part of the test. Consequently the external walls of older chambers are thicker and consisting of several layers. Only the last chamber has a single-layer wall. This does not contradict the bilamellar character of the structure of the walls, i.e. the primary layer consists of two lamellae, best visible in septa or in the wall of the last chamber. Pores are small and densely distributed, perpendicular to the surface of the wall. Aperture relatively large semicircular, umbilical, enclosed on the peripheral side by a narrow lip nearly perpendicular to the test wall. There is no lip on the umbilical margin. The apertures of the older chambers maintain their shape, lip and position forming the foramen. The last chamber is often broken, the traces of the break being so small that they are visible only when appropriately illuminated. The ratio of sinistrally coiled to dextrally coiled tests is approximately 1:1. The surface of the test is rough, covered by a dense irregular network of tubercles and ridges between which the pores are situated (fig. 8). The picture of this surface is very similar to that of recent Globigerina (vide F. Brotzen and K. Pozaryska, 1961 pl. 4, figs. 1, 2) and of Oxfordian ones (vide G. Bignot and J. Guyader, 1966, pl. 1, figs. 1, 10). A black cross appearing during observation with crossed nicols indicates a fibrous radial structure of the wall. Details of the ornamentation and structure of the surface are shown on electron micrographs. Attempts to distinguish between megalospheric and microspheric forms were not successful. The diameter of the proloculus is 0.01-0.02 mm. the exceptional limiting values being 0.02 and 0.005 mm. Generally specimens with a large number of chambers have a smaller proloculus, but occasionally a large proloculus is present in specimens consisting even of 12 chambers. The lack of morphological features permitting to distinguish between forms with large and small proloculuses and numerous intermediate forms hamper the separation of the population into two generations.

References:

Bignot, G. & Guyader, J. (1966). De couverte de Foraminifères planctoniques dans L’Oxfordien du Havre (Seine Maritime). Revue de Micropaléontologie. 9: 104-110. gs

Brotzen, F. & Pozaryska, K. (1961). Foraminiferes du Paleocene et de l'Eocene inferieur en Pologne septentrionale; remarques paleogeographiques. Revue de Micropaléontologie. 4: 155-166. gs

Pazdrowa, O. (1969). Bathonian Globigerina of Poland. Rocznik Polskie Towarzystwo Geologiczne = Annales de la Société Géologique de Pologne. 39: 41-56. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Globigerina bathoniana Pazdrowa 1969

Globigerina bathoniana

References:

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