Catalog - Helvetoglobotruncana

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Helvetoglobotruncana

Citation: Helvetoglobotruncana Reiss 1957

Type species: Globotruncana helvetica Bolli, 1945

Test flatly trochospiral; chambers globular, slightly to strongly flattened on the dorsal side; keel dorsal, not necessarily peripheral (sub-peripheral keel) at the margin of the flattened part of the chamber-wall with r dorso-septal branches and never dichotomic; keels granular to subspinose; cameral aperture umbilical, extending slightly into a partly interiomarginal position; labial apertures interiomarginal-umbilical-sutural (latter part often reduced through partial fusion of the lips); lips very slightly, if at all arched lengthwise, covering partly the umbilical cavity.

Remarks. The systematic position of Helvetoglobotruncana helvetica has been regarded by various authors as uncertain (see also Bolli, 1945) and it has been repeatedly emphasized by many of them (Bolli, 1945, Schijfsma, 1955, Sigal, 1955b, etc.) that transitions between a Globigerina and this form can be observed. Schijfsma and Sigal (op. cit.) stated that Globotruncana helvetica is derived from a Globigerina. This writer's observations fully support the above-mentioned authors' conclusions. Helvetoglobotruncana helvetica evolves gradually from a certain, apparently as yet undescribed Globigerina (s.l.) ("grandes Globigerines" of Sigal, 1955b, figured by Schijfsma, 1955), which appears in the Cenomanian and is most abundant in later Cenomanian and Turonian strata (praecursors already occur in the Vraconian). It exists together with H. helvetica up to the early Coniacian. The presence of a keel in the latter form is the only difference between it and the mentioned Globigerina (s. l.). The resemblance of H. helvetica to Globotruncana gansseri Bolli (= G. lugeoni Tilev) is only slight: the latter has a dichotomic peripheral keel, as well as lips and labial apertures characteristic of Globotruncanita. The chamber-form is also quite different.

As already pointed out above, the relationship between the Globigerinidae and the Globotruncaninae needs further study, the results of which will show whether or not Helvetoglobotruncana should be placed in the Globotruncaninae.

Upper Cenomanian to lower Coniacian

References:

Bolli, H. M. (1945). Zur Stratigraphie der oberen Kreide in den höheren helvetischen Decken. Eclogae Geologicae Helvetiae. 37: 217-328. gs O

Reiss, Z. (1957b). The Bilamellidea, nov. superfam., and remarks on Cretaceous globorotaliids. Contributions from the Cushman Foundation for Foraminiferal Research. 8(4): 127-145. gs O

Sigal, J. (1955). Notes micropaleontologiques nord-africaines. Du Cenomanien au Santonien. Zones et limites en facies pelagique. Compte Rendu Sommaire des Séances de la Société Géologique de France. 7-8: 157-160. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Helvetoglobotruncana Reiss 1957

Helvetoglobotruncana

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