Merlingina cretacea Hamaoui 1965

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 : 66-68

Merlingina cretacea Hamaoui 1965 emended Hamaoui & Saint-Marc, 1970

Reference Illustration & Description

Hamaoui & Saint-Marc (1970), Pls. 22-27, Fig. 4 , p. 306- 320.

This description and associated illustrations are excellent and comprehensive. See also Saint-Marc (1974a: plate 6) and Hamaoui in Schroeder & Neumann (1985: plate 15).

The introduction of Merlingina and its type species M. cretacea has a somewhat complex history. Hamaoui (1961) first recognised the taxon as “Gen? (aff. Nezzazata sp. )” from Cenomanian limestones from the Israeli subsurface. The genus and species were first formally described by Hamaoui (1965) with inadequate illustration and limited and inaccurate description. This was acknowledged by Hamaoui & Saint-Marc (1970) who regarded the 1965 description as nomen nudum and therefore provided much more comprehensive and accurate diagnoses and descriptions for the genus and species. Nonetheless, Loeblich & Tappan (1988) regarded the 1965 description as “available” (i.e., valid), thus the most suitable way to describe the authorship of the genus and species is as “ Hamaoui 1965 emended Hamaoui & Saint-Marc 1970 ”.

Essentially, Merlingina is irregularly planispiral throughout; asymmetrical (planoconvex) in the early stage but later becoming more bilaterally symmetrical. In the late stage it tends to uncoil, and the chambers rapidly increase in width so that the apertural face is broad, subcircular, and flattened. The aperture is a U or V-shaped slit (see Hamaoui & Saint-Marc, 1970: fig. 4). Slightly sinuous ribs are prominent in external view. A noticeable characteristic in oblique thin-section views is the combination of widening of later chambers and relatively deep sutures that lead to a (sometimes distinctly pronounced) “saw-tooth” periphery. See the Species Key Chart (Appendix) for diagnostic and other characteristics.

In thin-section (equatorial view) it is similar to Biplanata peneropliformis which is regularly planispiral throughout and lacks the increased width of the later chambers in Merlingina and therefore the ‘saw-tooth’ periphery. It differs from Biconcava bentori by being asymmetrical in the early stage and plano-convex, not bilaterally biconcave. Trochospira avnimelechi is distinctly trochospiral and with a single angular periphery compared with a tendency to form two, subangular peripheries in later chambers of M. cretacea which is best visible in axial view (see Fig. 17b ).

Demirina and Merlingina can appear similar especially in equatorial view where Demirina has a circular and relatively smooth periphery and Merlingina’s periphery attains the least “saw- tooth” appearance. The internal partitions of Demirina are also more numerous (and exoskeletal) but may appear similar to the (fewer) toothplates of Merlingina and its widest chamber width is across the centre rather than nearer the periphery.

Stratigraphic Distribution

(Early?) middle – late Cenomanian.

Most records of M. cretacea are from the middle, late, or undifferentiated middle – late Cenomanian. This follows Saint-Marc (1974a, 1978) who stated the range was middle – late Cenomanian in Lebanon, a range with which Saint-Marc (1981), Arnaud et al. (1981), and Hamaoui in Schroeder & Neumann (1985) concurred but extending the range into the basal Turonian (sometimes questionably). This has led to a certain degree of circular reasoning in subsequent age assignments of the occurrence of the species, in that its presence has been used to argue for an age no older than middle Cenomanian (e.g., Smith et al., 1990; Palci et al., 2008). In fact, it is possible that in the original records of the species from Israel ( Hamaoui, 1961, 1965, 1966), it occurs in the early Cenomanian. This was noted by Lipson-Benitah (2009) who gave the taxon an intra-early Cenomanian inception in Israel. The records of Hamaoui (1961, 1965, 1966) do not subdivide the Cenomanian, but long ranges are indicated, and the co-occurrence with such taxa named as “ Trocholina arabica ”, “ Orbitolina concava ”, “ Praealveolina iberica ”, is suggestive of an early Cenomanian age, although the identity of these taxa needs to be confirmed. A further caveat is that the 1961, 1965, and 1966 records by Hamaoui may use a concept of the taxon different from that established by Hamaoui & Saint-Marc (1970).

It is curious that Hamaoui himself gave no indication of an early Cenomanian age in his 1985 review of this species (Hamaoui in Schroeder & Neumann, 1985), but his statement on the age range of the species contains little supporting data.

Records whose ranges include an attributed early Cenomanian age are infrequent and provide no illustrative material confirming identification. They include Schulze (2003) and Schulze et al. (2004) ( Jordan); Ghanem et al. (2012, Syria) and Solak et al. (2020, Turkey; undifferentiated early – middle Cenomanian). Amongst these, of note is that Schulze (2003) and Schulze et al. (2004) who recorded M. cretacea from the Naur Formation unit b at one locality (RM2) in Jordan. Using ammonites and calcareous nannofossils they attributed the Naur b to the early Cenomanian M. mantelli ammonite zone equivalent. Ghanem et al. (2012) recorded M. cretacea in strata containing the planktonic foraminifera Rotalipora globotruncanoides and Rotalipora balernaensis , which would strongly suggest an early Cenomanian age, but neither have they illustrated any of these forms for confirmation.

Caus et al. (2009) recorded M. cretacea from the Santa Fe, Villa de Ves (see also Consorti et al., 2016b) and Moraillas Formations of Spain, which together they assigned an age range of early – late Cenomanian, but only indicated a late Cenomanian age for this species on their accompanying range chart (and with no verification by illustration).

Berthou & Lauverjat (1979) recorded a taxon referred to as Merlingina cf. cretacea from the latest Albian to earliest Cenomanian from Portugal, but this taxon was unillustrated and undescribed, and its identity cannot be verified.

Shahin & Elbaz (2013, 2014, 2021) illustrate plausible disaggregated specimens of M. cretacea from Sinai. These records are said to be early Cenomanian, but the logic of this age assignment is suspect. The presence of M. cretacea is one of the reasons for the age assignment, but misreporting information from publications in which the age is actually given as middle to late Cenomanian (e.g., Schroeder & Neumann, 1985).

Plausible illustrations in the relatively recent literature are all middle – late Cenomanian and include Aguilera-Franco (2000) ( Mexico); Ghanem & Kuss (2013) ( Syria); Rahimpour-Bonab et al. (2012, 2013) and Mohajer et al. (2021a) (Iranian Zagros); Sari et al. (2009) and Solak (2021) ( Turkey); Chiocchini et al. (2012) (central Italy). That of Chiocchini et al. (2012) straddles their early – late Cenomanian boundary and is thus broadly equivalent to middle Cenomanian.

Uncertain illustrated occurrences are reported by Smith et al. (1990) ( Oman, see also Simmons & Hart (1987); Kennedy & Simmons (1991), and Philip et al. (1995) for unillustrated records); Bomou et al., 2019; Omaña et al. (2012, 2019), and Rosales-Dominguez et al. (1997) ( Mexico, see also (e.g.) Michaud et al. (1984) Aguilera-Franco et al. (2001) and Aguilera-Franco (2003) for unillustrated records); Navarro-Ramirez et al. (2017) ( Peru, see also Jaillard (1986), Jaillard & Arnaud-Vanneau (1993) and Consorti et al. (2018) for unillustrated records); Hamaoui & Brun (1974) (southern Iraq); Menegatti (2004) (Dubai). Almost all these records are middle – late Cenomanian, albeit with a certain degree of circular reasoning, excluding Navarro-Ramirez et al. (2017) who used carbon and oxygen isotope age proxies (as subsequently followed by Consorti et al. (2018)). The exception to the middle – late Cenomanian range is Michaud et al. (1984) who cite their occurrence of M. cretacea within undifferentiated early – middle Cenomanian strata.

Occurrences illustrated as M. cretacea , but which are not that species include Mohseni and Javanmard (2020) (= simple biserial foraminifera); Kiarostami et al. (2019) (indeterminate, but incompatible with M. cretacea ) and Rikhtegarzadeh et al. (2016) (simple biserial to uniserial foraminifera) (all Iranian Zagros – note there are also many unillustrated records from this region e.g., Fourcade et al., 1997). A form illustrated as “ Merlingina cf. cretacea ?” from the undifferentiated Upper Cretaceous of Central Iran ( Rahiminejad & Hassani, 2016) is not related to true M. cretacea . It appears to be a simple trochospiral foraminifera. Fragmentary specimens from “Senonian” strata from southern Italy ( Luperto-Sinni, 1976; see also Luperto-Sinni & Ricchetti, 1978) described as M. cretacea , cannot be confirmed as this species, and can be discounted, as can an unillustrated record from the Turonian of the Iranian Zagros ( Shapourikia et al., 2021).

In previous reviews, extension of the range of M. cretacea into (basal) Turonian strata is based on information from Lebanon (e.g., Saint-Marc, 1981), and as with a number of other taxa, this age assignment needs review. The species occurs in beds that from associated ammonite data appear to straddle the Cenomanian – Turonian boundary, but the precise stratigraphic position of M. cretacea occurrences relative to these ammonite occurrences is uncertain. Given this, and the lack of any other substantiated Turonian records, M. cretacea is excluded from the Turonian.

Cenomanian Paleogeographic Distribution

Neotethys and Caribbean,?S. America.

In addition to those previously mentioned above, other locations where M. cretacea has been recorded (unillustrated) include Algeria ( Benyoucef et al., 2012; Slami et al., 2022); Tunisia ( Touir et al., 2017); France (Aquitaine) ( Deloffre & Hamaoui, 1979); Portugal ( Lauverjat, 1976); Croatia ( Velić & Vlahović, 1994; Husinec et al., 2000; Velić, 2007; Husinec et al., 2009); Greece (Decrouez, 1978; Fleury, 1980; Pomoni-Papaioannou & Zambetakis-Lekkas, 2009); and Slovenia ( Palci et al., 2008).

From the preceding discussion of stratigraphic distribution, it is possible that this species may have originated in the Levant region in the?early Cenomanian but was very widespread throughout Neotethys by middle – late Cenomanian times.

Figures

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

Fig. 17 Representative illustrations of Merlingina cretacea: a Equatorial section, Saint Marc (1974, pl. VI, fig. 1, Lebanon); b Subaxial section, Hamaoui & Saint Marc (1970, pl. 23, fig.3, Lebanon).