Perouvianella peruviana ( Steinmann, 1929 )

SIMMONS, MICHAEL & BIDGOOD, MICHAEL, 2023, “ Larger ” Benthic Foraminifera Of The Cenomanian. A Review Of The Identity And The Stratigraphic And Palaeogeographic Distribution Of Non-Fusiform Planispiral (Or Near-Planispiral) Forms, Acta Palaeontologica Romaniae 19 (2), pp. 39-169 : 135-137

Perouvianella peruviana ( Steinmann, 1929)

Reference Illustration & Description

Consorti et al. (2018), Figs. 2-4 , p. 5-6 .

The illustrations in Jaillard & Arnaud-Vanneau (1993) are also useful. Perouvianella peruviana is a highly endemic species seemingly confined to the coastline of the Eastern Pacific, specifically central Peru. It is internally complex with 2-4 sets of pillars (sometimes interlocking) in the chambers. The diagnosis of the genus was recently emended by Consorti et al. (2018) and the species was also comprehensively redescribed and illustrated to which the reader is referred to for details.

P. peruviana is a large species, 2-7 mm in diameter. Its mode of coiling (planispiral at first then uncoiling into a flat, flabelliform shape) and complex internal chamber structures are superficially similar to Pseudorhipidionina and Praetaberina in certain thin section views, but it is not closely related. It has 2-4 whorls disposed in a planispiral involute arrangement with 8-10 chambers in the first whorl and 13-15 in the second whorl. The megalospheric proloculus can be large: 0.2 – 0.33 mm. See the Species Key Chart (Appendix) for diagnostic and other characteristics.

The porcellaneous wall, presence of several rows of both radial and intercameral pillars, as well as alternating septula (although the latter may be hard to confirm, see for example Fig. 82A herein), caused Consorti et al. (2018) to provisionally assign it to the family Soritidae .

The species was introduced by Steinmann (1929) as Orbiculina peruviana with illustration and limited description, then subsequently made type species of the new subgenus Perouvianella (genus Archaias Montfort ) by Bizon et al. (1975). Perouvianella was subsequently raised to generic status (e.g., Loeblich & Tappan, 1988).

Stratigraphic Distribution

Late Cenomanian – early Turonian.

The stratigraphic distribution of P. peruviana is noteworthy because (a) it represents a data point significantly outside the Caribbean-Atlantic-Neotethyan realm to where the vast majority of species in this study are confined and (b) it was seemingly unaffected by events around the Cenomanian-Turonian boundary that led to the general extinction of the vast majority of LBF elsewhere (Consorti et al., 2018; Consorti & Schlagintweit, 2021a; Schlagintweit & Yazdi-Moghadam, 2021). Jaillard & Arnaud-Vanneau (1993) attribute this to less drastic anoxic conditions on the more open Western Platform of Peru compared with those around the Tethys-Atlantic-Caribbean margins.

In Peru, P. peruviana is often present in near rock-forming abundances throughout sediments associated with (and slightly above and below) OAE2 ( Navarro-Ramirez et al., 2017; Consorti et al., 2018). Consorti et al. (2018) consider this to have been related to “ local mesotrophic conditions and salinity changes of shallow-shelf water masses that were severely restricted and separated from oceanic blue water aquafacies ”. Clearly, P. peruviana thrived in the localised environmental conditions (oxic, but with significant environmental perturbations) that existed in the Peru region in the late Cenomanian and early Turonian ( Navarro-Ramirez et al., 2016, 2017).

Using carbon isotope chronostratigraphic calibration and ammonite occurrences, Navarro-Ramirez et al. (2016, 2017) showed that P. peruviana ranges from as old as the regional Neolobites vibrayeanus ammonite zone to as young as the nodosoides Tethyan ammonite zone (upper early Turonian). Neolobites vibrayeanus (d’Orbigny) is said to have its main occurrence in the guerangeri Tethyan ammonite zone (lower late Cenomanian), at least in the Middle East ( Wiese & Schulze, 2005; Meister & Piuz, 2015).

Jaillard & Arnaud-Vanneau (1993) slightly extend the range downwards into the latest middle Cenomanian, and upwards into the earliest middle Turonian, but these are shown as uncertain occurrences. Furthermore, the precise age interpretations of these authors are challenged by the new chronostratigraphic calibration presented by Navarro-Ramirez et al. (2016, 2017).

The species was originally considered to be a Santonian marker (e.g., Bizon et al., 1975; Loeblich & Tappan, 1988), but its correct age calibration was demonstrated by Jaillard & Arnaud-Vanneau (1993). Nonetheless, there are relatively recent literature statements that mistakenly continue to mention it as a Santonian species (e.g., Caus et al., 2013; BouDagher-Fadel et al., 2017).

Cenomanian Paleogeographic Distribution

Eastern Pacific.

Recorded from Peru only - see references in previous discussion.

Figures

Fig. 2 Some morphological descriptions and visualisations of wall and/or chamber components of planispiral or part-planispiral LBF taxa. (a after Hamaoui & Saint-Marc, 1970; b-f after Hottinger, 2006; G: after Vicedo et al., 2013; h after Consorti et al., 2015; j after Consorti et al., 2018). Other abbreviations shown in image j are bl=basal layer; cs=conical spaces; if=intercameral foramina and sc=socculi crest.

Fig. 3 Cenomanian paleogeography with regions indicating the location of most planispiral LBF in this study. There are a few additional records from, for example, Peru, Afghanistan and Tibet. (Base paleogeographic map courtesy of Halliburton).

Fig. 4 Distribution map of type descriptions/specimens in this study.

Fig. 5 Representative illustrations of Biconcava bentori: a Equatorial section, Hamaoui & Saint Marc (1970, pl. 21, fig. 1, Israel); b Axial section, Hamaoui in Schroeder & Neumann (1985, pl. 13, fig. 3, Lebanon).

Fig. 6 Cenomanian paleogeographic distribution of Biconcava bentori

Fig. 82 Representative illustrations of Perouvianella peruviana: a Equatorial section, Consorti et al. (2018, fig. 4b, Peru); b Subaxial section, Consorti et al. (2018, fig. 4j, Peru); c Schematic chamber section with 2 rows of pillars, Consorti et al. (2018, figs. 2a, 2d).