Catalog - Pseudoclavihedbergella chevaliensis

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Pseudoclavihedbergella chevaliensis

Citation: Pseudoclavihedbergella chevaliensis Falzoni et al. 2016

Type specimens: Holotype (Micro-Unimi n. 1988; Fig. 12, 3AeC), paratype A (Micro-Unimi n. 1989; Fig. 12, 4AeC), paratype B (Micro-Unimi n. 1990; Fig. 12, 5A-D)

Type sample (& lithostrat): holotype from sample SLT 3480, paratype A from sample SLT 3480, paratype B from sample SLT 2670.

Type age (chronostrat): Lower Turonian (W. archaeocretacea Zone).

Type locality: Clot Chevalier (Vocontian Basin, France),

Type repository: Milan; Micropalaeontological Collection, Universita degli Studi di Milano, Dipartimento di Scienze della Terra ÒA. DesioÓ, Italy.

Small to medium-sized very low trochospiral test, can be nearly planispiral; perforate wall with pores of 3-4 µm in diameter, chamber surface smooth, without muricae, with high-density pores equally distributed throughout the last whorl; oval outline, symmetrical profile, perforate equatorial periphery; inner whorls slightly raised to depressed on the spiral side; five, more commonly six to seven chambers in the last whorl, slowly to moderately increasing in size as added, slightly elongated in the direction of coiling at the beginning of the last whorl in some specimens. Spiral and umbilical sides with globular and inflated chambers and radial and depressed sutures; ultimate chambers very large in lateral view, commonly tilted toward the umbilical side. Primary aperture extraumbilical, opening at the base of the final chamber with a low arch and bordered by a thin lip; umbilical area relatively wide, about 1/3 of the maximum diameter.

Named for the type locality (Clot Chevalier) where it is found.

Distinguishing features. Morphologically resembles M. planispira Tappan (Fig. 5, 6A-C; holotype in Fig. 12, 6A-C), but it differs by possessing a smooth wall texture with larger pores and without muricae, a wider umbilical area, chambers that are slightly elongated in the direction of coiling at the beginning of the last whorl and that grow more slowly in size as added, a more lobate equatorial periphery and a thinner test in later view. It morphologically resembles Liuella praefalklandica Korchagin, 2011, but differs by having a different wall texture with larger pores (4-5 µm in diameter rather than 1-2 µm) and a higher pore density.

Remarks. The wall texture is considered a primary taxonomic character for the classification of planktonic foraminifera at genus level and several Cretaceous genera have been distinguished based on the presence, absence or degree of development of a certain type of wall ornamentation and texture and on the pore density and dimensions (e.g., Brönnimann, 1952; Brönnimann and Brown, 1956; Pessagno, 1967; Robaszynski et al., 1979, 1984; Longoria and Gamper, 1984; Loeblich and Tappan, 1987; Nederbragt, 1990; Georgescu and Huber, 2006, 2007; Georgescu, 2009; Premoli Silva et al., 2009; Huber and Leckie, 2011; Falzoni et al., 2014, among many others). Consequently, despite the strong morphological affinities, the species chevaliensis, planispira and praefalklandica do not belong to the same genus, and thus cannot be lumped in the same species. Regarding chevaliensis, it shows a wall texture that suggests a phyletic relationship with the simplicissima/amabilis morphogroup, recently included in the genus Pseudoclavihedbergella (Georgescu, 2009). Because this genus has been erected to exclusively accommodate morphotypes with clavate chambers (Georgescu, 2009), the accommodation of chevaliensis in Pseudoclavihedbergella requires further investigation. In any event, we believe that features of the wall texture should have taxonomic priority with respect to chambers morphology, particularly for Cretaceous hedbergellids. In fact, specimens with clavate chambers are particularly abundant across the OAE intervals and their elongated chambers have been interpreted as a strategy to favour oxygen exchange in dysoxic to anoxic seawater (e.g., BouDagher-Fadel et al., 1997; Magniez-Jannin, 1998; Aguado et al., 1999; Premoli Silva et al., 1999; Luciani et al., 2001; Coccioni et al., 2006; Coxall et al., 2007), suggesting that chamber morphology could have been somehow controlled by ecologic parameters.

Stratigraphic distribution. Specimens resembling “P.” chevaliensis have never been described and/or illustrated in the literature. They first appear in the middle W. archaeocretacea Zone at Clot Chevalier (Fig. 2). The disappearance level is presently unknown (Fig. 8).

Relative abundance. “P”. chevaliensis represents up to the 7% of the planktonic foraminiferal assemblage >125 µm and its abundance increases throughout the section (Fig. 13).

References:

Falzoni, F., Petrizzo, M. R., Jenkyns, H. C., Gale, A. S. & Tsikos, H. (2016). Planktonic foraminiferal biostratigraphy and assemblage composition across the Cenomanian–Turonian boundary interval at Clot Chevalier (Vocontian Basin, SE France). Cretaceous Research. 59: 69-97. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Pseudoclavihedbergella chevaliensis Falzoni et al. 2016

Pseudoclavihedbergella chevaliensis

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