The small rotaliids (Foraminiferida) found in Cenomanian rock thin sections of Oman and Morocco are diversified. A continuum of morphotypes is divided within 3 taxa described as subspecies of Rotorbinella mesogeensis Tronchetti 1981 from which they share many morphological characteristics. According to features, including shell shape and size, and spiral thickening of the wall, they are named R. m. microformis ssp. nov., R. m. medioformis ssp. nov. and R. m. mesogeensis ssp. nov., the latter being the typical form of Tronchetti 1981. The subspecies mesogeensis is a biostratigraphical marker of the Cenomanian while microformis is known since the Late Albian up to the Late Cenomanian (possibly Early Turonian). Pararotalia boixae sp. nov. comprises specimens previously attributed to P. tuberculifera Reuss 1862 pro parte. This Cenomanian new species (with Campanian affinis forms) is characterized by morphological features that clearly distinct it from the type of Reuss. We found it in the Cenomanian of Oman, but not in contemporaneous Moroccan sediments.
As part of a micropalaeontological study of Cenomanian—earliest Turonian sediments from the South and Southwest Tethys in Morocco and Oman (Cavin et al. 2010 and other papers in prep.), numerous very small rotaliids were evidenced in rock thin sections. Rotorbinella mesogeensis (Tronchetti 1981) and Pararotalia cf. tuberculifera (Reuss 1862) closely resembling those of Boix et al. (2009) were first recognized. Within the abundant population, various specimens, very different from the typical forms, remained, however, unattributed.
Variants of R. mesogeensis with distinctive morphological features and decreasing size display a morphological gradational series evidenced on the base of four hundred fifty photographs from thin sections. Three different morphological groups are clearly differentiable (taxon) and form a remarkable continuum with outstanding morphological difference between both end members of the series.
On the other hand, sections resembling to P. tuberculifera sensu Boix et al. (2009) are homogenous in our Omani samples (not recognized in Morocco). There is considerable confusion with this species which is, according to the literature, morphologically highly variable (especially since the Maastrichtian) and ranges from the Late Santonian (Boix et al. 2009) up to the Montian (Szczechura and Pozaryska 1972). Our Cenomanian specimens are older, smaller, and significantly differ from the type species description of P. tuberculifera. The aim of this paper is then to describe, illustrate and determine the most common rotaliids found in Cenomanian Moroccan and Omani sediments. Our specimens are actually among the oldest known foraminifera with rotaliid structures. Their occurrence in the Cenomanian makes them possible rootstock for the further diversification of the rotaliines that will expand during the Late Cretaceous and Paleogene (see Boix et al. 2009 cum biblio). Revets (2001), however, state that it is unlikely that Rotorbinella (massive plug) has any direct or indirect relation with the immediate ancestor of Rotalia (multiple pillars) or any of the other rotaliacean genera with strongly sculptured umbilical sides. This can only be clarified by an extensive study of Cretaceous rotaliid genera and species, what is not the aim of this work. The main characteristics of the family and genus we will get onto are summarized as follows:
The family Rotaliidae Ehrenberg 1839 is characterized by a hyaline lamellar-perforated wall, trochospiral chamber arrangement, single foramen to multiple foramina, septa with open interlocular space or canal, folia present with additional structures (plates) delimiting and restricting an umbilical space (Boix et al. 2009 cum biblio). The genus Rotorbinella Bandy 1944, emended by Revets (2001), is characterized by a smooth convex spiral side and a smooth convex to flat umbilical side with a single central massive plug; an interiomarginal aperture, a well-developed free folia separated by an open fissure (intraseptal interlocular space) and marked by a faint notch; an umbilical plate, and an umbilical intraseptal interlocular space remaining open as a long sutural slit. Umbilical interlocular space is transformed into simple spiral canal in earlier whorls. The subfamily Pararotaliinae Reiss 1963 emended by Hottinger et al. (1991) includes trochospiral test with single interiomarginal main aperture into which a toothplate protrudes with a free edge; irregular supplementary apertures may be present; canal system composed of intraseptal interlocular spaces, of a spiral umbilical canal formed by interconnected toothplates, and in some genera of enveloping canals produced by secondary lamination. The genus Pararotalia LeCalvez 1949, following Loeblich and Tappan (1988) and Hottinger et al. (1991), is defined by a low trochospire with a smooth to pustulose surface, umbilicus with prominent umbilical shoulder surrounding a solid umbilical plug, open undivided umbilical sutural interlocular spaces, a spiral canal system, an areal foramen with a lower lip that is the edge of an element called toothplate by Hottinger et al. (1991) and Loeblich and Tappan (1988) but not by Revets (1993) (see below). Folia are inexistent following Hottinger et al. 1991 (see also Revets 1993).
Locality, stratigraphy and associated microfauna
Figure 1 gives the geographic location and three synthetic field sections representative of the studied areas with a provisional stratigraphic repartition of the taxa considered in this paper (other sections are actually under study). The samples involved in this study have been collected in eighteen field sections and the stratigraphic location of every important (holotypes and paratypes) samples is reported in the field sections of Fig. 1. Together with the GPS coordinates given in the type locality below, sample position can be easily located.
The main part of the Moroccan and Omani series is dated Cenomanian by ammonites. The Albian—Cenomanian boundary was not sampled as it was not outcropping in the studied localities. The Cenomanian—Turonian boundary is situated between two ammonite levels, one dated as Late Cenomanian (Neolobites beds, which can be used for correlation from Moroccan to Omani sections), and the uppermost one as upper Early Turonian (Vascoceratidae beds in the eastern Adam foothills synthetic section). As no sharp lithological change was noticed within this interval, this stage boundary cannot be located more precisely.
Southeast Moroccan field sections (published in Cavin et al. 2010) give precise sample location as well as lithology, stratigraphy, ammonites and other macrofossils. Figure 1 gives a synthetic section of the Tazougart Belkassem—Tizi Momrad area. Samples concerned in this study were collected in the Cenomanian/Turonian Akrabou formation which is precisely dated by two ammonite bioevents. The first one with the Neolobites vibrayeanus bioevent (Fig. 1) characterizes the lower part of the Calycoceras guerangeri Zone (lower Late Cenomanian) and the second (see Cavin et al. 2010) with the Mammites nodosoides bioevent correspond to the Mammites nodosoides Zone (upper Early Turonian).
Associated microfauna: The Upper Cenomanian transgression is characterized, during the Neolobites bioevent, by very scarce benthos, but common calcispheres and abundant, simple, little evolved (no keel) and very small morphotypes (70–100 μm, max 150 μm) planktonic foraminifers most of which are attributed to Hedbergella (Asterohedbergella) asterospinosa Hamaoui 1964 together with various primitive type adults, known to be opportunistic species that rapidly colonize shallow, newly opened areas during transgressive periods (Hart and Bailey 1979; Caron 1983; Caron and Homewood 1983; Hart 1999). Above the Neolobites bioevent, various benthic (and rare planktic) foraminiferas as well as stromatoporoids, solenoporaceae, corals, algae, bryozoans, bivalves, ostracods, serpulids, calcispheres, gastropods and echinoderms gradually colonize the shelf. Amongst the sections of benthic foraminifers associated with our rotaliids, we recognized alveolinids (Cisalveolina?, Prealveolina sp.,), Biconcava bentori, Ammobaculites sp., Biplanata peneropliformis, bolivinids, buliminids, Chrysalidina gradata, Cuneolina sp., Dicyclina schlumbergeri, discorbids, epistominids, Haplophragmoides sp., various miliolids (Quinqueloculina spp.), Montcharmontia appeninica, Nezzazata spp., Nezzazatinella picardi, Nummofallotia apula, Peneroplis sp., Pseudolituonella reicheli, Pseudorhapydionina dubia, Pseudorhipidionina casertana, Pseudotextulariella sp., Spiroloculina? sp., Spiroplectammina sp., Textularia spp., Trochammina sp., and Trochospira avnimelechi. The stromatoporoid are attributed to Actinostomaria stellata and the solenoporaceae to Parachaetetes asvapatii. See Cavin et al. (2010) for associated algae.
The material used in this study was collected in 8 field sections along the Adam foothills (south of the Oman mountain), named from east to west, Jabal Madar, Jabal Madmar, Jabal Khaydalah, Jabal Salakh, Jabal Nadah and Jabal Fitri. Two synthetic field sections are given in Fig. 1 illustrating the two main series encountered in the Cenomanian of the area. Western Adam foothills field sections are encountered west of Jabal Salakh, and Eastern Adam foothill field sections east of Jabal Salakh. Detailed field sections will be presented in a paper in preparation, giving precise stratigraphic location of all samples, ammonites, and detailed repartition of associated microfauna. Cenomanian/Turonian Natih formation is subdivided into 7 members locally dated by ammonite bearing levels. Ammonites (under study) give an age (Fig. 1) from Late Albian (for the Knemiceras species found in the Nahr Umr formation) to the upper Early Cenomanian/lower Middle Cenomanian, and Early Turonian (Watinoceras coloradoense Zone) for the Natih formation.
Associated microfauna: The ramp limestone facies (see Philip et al. 1995, van Buchem et al. 1996, 2002; Homewood et al. 2008, for sedimentology, stratigraphy, stratonomy, paleoenvironments) reveals, together with our rotaliids, an association mainly made up of Biconcava bentori, Biplanata peneropliformis, Cisalveolina sp, Praealveolina gr cretacea, Dukhania conica, Chrysalidina gradata, Cuneolina gr pavonia, Dicyclina schlumbergeri, Epistomina sp, Glomospira sp, Haplophragmoides sp, Montcharmontia compressa, Nezzazata spp (N. gr simplex, N. gr gyra, N. gr isabellae), Nezzazatinella cf. picardi, various Orbitolinids (Orbitolina conica, Orbitolina sp A, Heterocoskinolina ruskei), Praebulimina sp, Pseudonummoloculina sp, Pseudorhapidionina cf. laurinensis, diverse and abundant miliolids (Quinqueloculina spp.), Pseudolituonella reicheli, Spiroloculina spp, Spiroplectammina sp, Trochospira avnimelechi, Trocholina spp (T. altispira, T. arabica, T. lenticularis), textularidae, various algae, ostracods, microbivalvs shells. The intrashelf basin facies has a typical association composed of various small hedbergellids (Asterohedbergella asterospinosa, Muricohedbergella?), Macroglobigerinelloides ultramicrus, Heterohelix moremani, Epistomina sp., Praebulimina sp., oligosteginids (mostly Pithonella spaerica with possible Calcisphaerula innominata), Saccocoma, microbivalv shells and ostracods.
Materials and methods
The material of this study results from two fields trip, the first in 2008 in Morocco (Cavin et al. 2010), and the second in 2010 in Oman (papers in prep.). Hard limestone samples imply working with thin section. All characteristics are then deducted from sections as no extracted specimens were available. Optical microscopy (magnification up to 1,000×) is the main tool. About seven hundred sections of rotaliids have been photographed and compared (size, morphology). From the 450 shell sections, photographs attributed below to subspecies of R. mesogeensis, morphological variation (Fig. 2a) and measurement (width, thickness, Fig. 2b) of the 130 better centered axial and sub-axial sections from populations of Morocco, Oman, as well as Spain (Boix 2007), and France (Tronchetti 1981) were considered. The largest diameter versus largest thickness was measured on these (sub) axial sections (i.e. centered enough to pass through the umbilical plug, the latter being about 25 % of the width of the test of the holotype of Tronchetti 1981, Pl. 26 Fig. 6). Spread within every shell sizes, these 130 centered sections are representative of the population. Graphics of Fig. 2 show the remarkable morphological and size continuum between the different taxa. Three morphological groups can be distinctly evidenced and clearly differentiated based on morphological features and size. The continuum implies the boundaries between taxa are obviously faint and subjective (unless there is no continuum), and intermediate forms exist. In our opinion, the paleontological exploration pursued in this work involve splitting as first essential stage of the taxonomic process to maximize information about taxa variability, a precious tool for further studies about stratigraphy, phylogeny, paleoecology, paleobiogeography. At this first stage, lumping (i.e. these three obviously different taxa in R. mesogeensis) can just be an unfortunate loss of information adding nomenclatural confusion and blocking further potential findings like distinct stratigraphic range and/or paleoecological and/or paleogeographical significance as well as phylogeny of the different taxa.
Superfamily Rotaliacea Ehrenberg 1839.
Family Rotaliidae Ehrenberg 1839
Genus Rotorbinella Bandy 1944
Type species: Rotorbinella colliculus Bandy 1944
The history of this genus is proposed in Levy et al. (1979) and Revets (2001). Following Boix et al. (2009), the shell is small to medium size, lamellar perforate trochospiral shell, no evident generational dimorphism, spiral side convex, smooth, without ornamentation, umbilical side convex to flat, smooth, with a single massive umbilical plug, aperture in interiomarginal position, pores of small to medium size on spiral side, slightly larger on umbilical side, folium is small, imperforate, slightly oblique and free and with a suture marked by a faint notch. Umbilical plate (or coverplate, see Revets 2001) clearly present and intraseptal interlocular space open (uncovered) with no feathering (ornamentation by series of grooves perpendicular to the slit produced by the sunken chamber suture), umbilical interlocular space open in last whorl, but possibly covered in earlier whorls and thus be transformed into a simple spiral canal.
Following Revets (2001), the presence of coverplate confirms the rotaliacean nature of the taxon and the presence of a well-developed primary umbilical plug (very different from the multiple lamellar pillars characteristic of Rotalia) differentiates the taxon from most of the other rotaline or discorbine. The aperture, folia, and nature of the plate are the main differences between Rotorbinella and Pararotalia, and the presence in Neorotalia of an enveloping canal system (cover of interlocular space with canal openings) and a compound plug with canals is discriminant.
Remarks about Rotorbinella mesogeensis (Tronchetti 1981)
Numerous and diverse sections with close morphological characteristics are put together with R. mesogeensis in a morphological (Fig. 2a) and size (diameter/thickness ratio, Fig. 2b) continuum of showing very different end members. Generational dimorphism cannot be excluded, but is currently impossible to demonstrate as no evidence of various sizes of proloculus and/or juvenile stage has been noticed. The continuum illustrated in Fig. 2 implies the boundaries between taxa are faint and subjective and suggests considering the morphotyps as subspecies. Sharp boundaries would have clearly indicated different species, and morphological deviation is much higher than what is generally considered as intra-specific variation (e.g. in Haynes and Whittaker 1990 about Rotalia trochidiformis) or as forma (e.g. in Miller et al. 1982; Haynes 1992). Based on more than 450 photographs of shells in thin sections, and considering the evident morphological differences, we separate the specie mesogeensis in the subspecies mesogeensis nov.ssp., medioformis nov.ssp. and microformis nov.ssp. Note that intermediate forms exist between these subspecies (Figs. 2a, 3). The major differences concern the size (the biggest specimen can be up to 5–10 times the smallest), shape (i.e. rugged—slim with various height of spire and thickness of the wall), ornamentation (i.e. size of the umbilical plug, presence/absence of a keel), and number of chambers in the last whorl. As noted Tronchetti (1993) the last chamber are fragile and possess a very thin wall, only visible on some rare sections (e.g. Fig. 3a–b, e, g, j–k, o–p, t–u, z–aa), implying the diameter is not the most decisive criterion for attribution of the section.
1981 Rotalia mesogeensis nsp. Tronchetti, Pl. 26 Figs. 6–12, Pl. 27, Figs. 1–8, Pl. 28, Figs. 1–7
1993 Rotalia mesogeensis Tronchetti, p. 46 Pl. 1, Figs. 1–10 (1–4, 6 from Tronchetti 1981)
2007 Rotorbinella mesogeensis Boix, Pl. XVI, Figs. 2–5, 7a,d,e (7 from Tronchetti 1981); Pl. XVII Figs. 4–7; Pl. XVIII Figs. 1–8.
2008 Rotalia mesogeensis Ettachfini Pl. 20, Figs. 12–15
2009 Rotorbinella mesogeensis Boix et al. Fig. 3. 1–9 (from Boix 2007)
Holotype: One specimen n. HFC 2 (Tronchetti 1981, Pl. 26 Fig. 6, Tronchetti 1993, Pl. 1 Fig. 1) deposited in the laboratoire de Géologie Historique et de Paléontologie de l’Université de Provence, Centre Saint-Charles, Marseille, France (Tronchetti 1981, 1993).
Description: Dissymmetric lenticular test with a clearly convex spiral side and convex to flat umbilical face, smooth on both sides, periphery subacute to rounded always marked by an imperforated keel, massive free plug in the center of the umbilicus, bordered by a furrow (umbilical interlocular space) with diverticulum between chambers, these intercameral furrows (interlocular intraseptal space) do not reach the periphery, thin umbilico spiral canal, spiral chamber walls finely perforated, wider pores on umbilical face, lacking in the foliar walls, three whorls in the adult test, 6–8 (up to 10 following Boix et al. 2009, 6 in Tronchetti 1993) chambers in the last whorl, double septa with intraseptal canals straight to slightly arched, chamber lumen with foliar chamberlet separated from the main chamber lumen by an umbilical plate.
Differences: These are the typical tall forms of R. mesogeensis as described by Tronchetti (1981) (some of his confer specimens correspond then to the medioformis subspecies, see below). This subspecies regroups here the tallest specimens, morphologically well corresponding to the original description, with a diameter higher than 200 μm and thickness higher than 100 μm. Note that Tronchetti (1993) proposed a diameter of 200 μm and thickness of 150 μm as lower limit of R. mesogeensis.
Geographic and stratigraphic distribution: Since its description in 1981, R. mesogeensis is progressively better and more often recognized. Now often cited it is found in numerous localities summarized below, completing the data of Tronchetti (1993). In France, it is known in (Tronchetti 1993 cum biblio) : south-west France in Charente-Maritime in Early Cenomanian sediments; south-east France in the Gard department in the Early Cenomanian; in Provence in middle to Late Cenomanian; in the Pyrenees in the Cenomanian. Bilotte et al. (2008) cite possible R. mesogeensis or R. algeriana in Languedoc. Chiocchini (2008) and Chiocchini et al. (1994) found it in the Late Cenomanian of central Italy. In Spain it is known along of the Pyrenean chain, Boix (2007) and Boix et al. (2009) detail the distribution of various rotaliids, including R. mesogeensis they find from middle to Late Cenomanian in shallow-water facies. In Morocco, Ettachfini (1993); Ettachfini and Andreu (2004); Ettachfini (2008); Cavin et al. (2010) found R. mesogeensis in the Late Cenomanian of the “Haut Atlas occidental” (Essaouira basin), “High Atlas”, and the “Sillon Préafricain” (Goulmima—Erfoud area). In the Karst dinarides, Velic (2007) mention the presence of R. mesogeensis in Cenomanian sediments. In Croatia, Crumiere-Airaud (unpublished phd, 1991, see Tronchetti 1993) found it in southern Istria (Premantura field section) Late Cenomanian sediments dated by ammonites and benthic foraminifers (Tronchetti 1993). In southern Serbia-Montenegro, Golubic et al. (2006) mention R. mesogeensis in Early Cenomanian. In Greece, Mermighis (unpublished phd 1989, see Tronchetti 1993) found R. mesogeensis in the Trapezona area in middle and Late Cenomanian sediments dated by rudists and benthic foraminifers (Tronchetti 1993). In Turkey, Masse et al. (2010) found R. mesogeensis in association with Favusella washitaensis, indicating a Early Cenomanian (or earlier) age. In Tunisia, Bessaïs (unpublished phd 1989, see Tronchetti 1993) in the S-E of Kasserine city (Jabal Selloum) in Early to middle Cenomanian sediments dated by ammonites, rudists, benthic foraminifers and ostracodes (Tronchetti 1993).
Paleoenvironment: Following our observations, R. m. mesogeensis is present in the shallow shelf/ramp environments, but absent from the deeper Omani intrashelf basins. This is in accordance with Tronchetti (1993), for whom R. mesogeensis is known from inner/median shelf environments with some tolerance to the nature of the substrate.
1981 cf. Rotalia mesogeensis nsp Tronchetti, Pl. 27 Fig. 9, Pl. 28 Fig. 8
2007 Rotorbinella mesogeensis Boix, Pl. XVI Fig. 1 (same figure as Boix et al. 2009 Fig. 3.2, intermediate form between R.m. mesogeensis and R.m. medioformis), Pl. XVII Figs. 1, 2
Holotype: Specimen figured in Fig. 3p, sample ap375 deposited in the micropaleontological collection of the Natural history Museum of Geneva, n°MHNG2013-1.
Type locality: Jabal Nadah, Adam Foothills, Oman, coordinates N22°29.409 E057°09.893
Type horizon: Natih C formation, Cenomanian.
Etymology: From medium, for its middle position in the series of subspecies.
Type description: Dissymmetric lenticular test with a clearly convex spiral side and convex to flat umbilical face, smooth on both sides, periphery subacute to rounded sometimes marked by an imperforated keel, massive free plug in the center of the umbilicus, bordered by a furrow (umbilical interlocular space), spiral chamber walls finely perforated, 6–7 chambers in the last whorl, double septa with interlocular intraseptal space, straight to slightly arched, foliar chamberlet (not clearly evidenced in our sections), separated by main chamber lumen by an umbilical plate. This subspecies can be considered as a “small R.mesogeensis mesogeensis” progressively losing its morphological characters (see Fig. 2). Many characteristics of R. m. mesogeensis are although still recognizable in this subspecies, and intermediate forms can be difficult to attribute.
Differences: The main differences with other subspecies are the more robust shape of the test, the scarcity of the keel, and the smaller size with a diameter between 120 and 220 μm and thickness between 50 and 120 μm. R. m. mesogeensis is bigger (200 μm and more diameter, 100 μm and more thickness) with an often thicker spiral wall, and R.m. microformis (see below) is always smaller (50 to 140 μm diameter, 30 to 70 μm thickness) with a thinner wall of the same thickness on both faces of the test (no spiral thickening) and never keeled.
Paleoenvironment: It is not possible at the moment to propose a definite paleoecological significance for this subspecies, although it seem (as for R. m. mesogeensis) restricted to shallow shelf environment (absent of the intrashelf basins of Oman), it may have a slightly higher tolerance to environmental changes than R. m. mesogeensis.
cf. : 2008 Microfacies à discorbidae Ettachfini Pl. 21 Fig. 13.
Holotype: Specimen figured in Fig. 3t, sample ap289 deposited in the micropaleontological collection of the Natural history Museum of Geneva, n°MHNG2013-4.
Paratypes: Specimens figured in Fig. 3u, sample ap289, Fig. 3s, w sample ap327, and Fig. 3x, y sample ap325 (Jabal Madar, Adam Foothhills, Oman, Natih E formation, Cenomanian), deposited in the micropaleontological collection of the Natural history Museum of Geneva, n°MHNG2013-5 and MHNG2013-6.
Type locality: Tazougart Belkassem field section of Cavin et al. (2010) coordinates N32°05.231—W003°46.198
Type horizon: Upper part of Akrabou formation, Late Cenomanian—possibly Early Turonian.
Etymology: From micro, for the very small size of this subspecies.
Type description: The shell shows a smooth convex spiral side with no ornamentation, pores are discernible. The chambers are arranged in a low trochospire, the chambers are ovate in axial section and keel is absent. The shape of the umbilical side varies from slightly convex to plane or even concave if section passes through the last chamber. A single massive plug occupies the center of the unornamented umbilical face. The plug is surrounded by a narrow spiral fissure (umbilical interlocular space) possibly giving rise to a spiral umbilical canal (not evidenced in our pictures). The very small size of the specimen make tough the recognition of internal shell structure and the possible presence of a small folia and notch are suspected, but not clearly identified. The slightly arched septum is bilamellar with interlocular intraseptal space. The trochospire show two spiral whorls with 6–7 chambers in the last one. The size is small to very small with a diameter between 50 and 140 μm and a thickness between 30 and 70 μm. Note that the very small size of the shell means it could easily be omitted by micropaleontologists working with unconsolidated sediments, and possibly also by the ones working in thin sections.
Differences: As internal shell structures cannot be currently certified, attribution of microformis to Rotorbinella and mesogeensis is proposed here based on morphological affinities and continuum with R. m. medioformis and R. m. mesogeensis. This subspecies is characterized by its very small size, axial sections reveal ovate chambers, absence of keel, absence of spiral thickening of the test (contrarily to medioformis and mesogeensis), and possible concave umbilical face. R.m. mesogeensis and R. m. medioformis have always bigger size with a different shape (see Fig. 2).
Geographic and stratigraphic distribution: In Oman is observed the oldest occurrence of R. m. microformis with a Late Albian (Diploceras cristatum ammonite Zone, Nahr Umr Formation) age, up to the Late Cenomanian (Natih A formation). In Morocco, it is observed in the Middle to Late Cenomanian, possibly Early Turonian (high Moulouya, Ettachfini 2008, and Kem–Kem area, south-eastern mountains). The older age of this subspecies makes it the possible ancestor of medioformis and mesogeensis.
Paleoenvironment: R. m. microformis is actually only known from shallow marine environment of Morocco and Oman (not found in the intrashelf basins of Oman). R. m. microformis worth interest as it surely has a paleoecological signification with a wide tolerance to various shallow environment including peculiar (restricted) ones. It can be the only foraminifer found in some sample (e.g. in ap289 where found together with abundant dasyclads and various echinoderm and other shell fragments). The cited above “discorbid microfacies” of Ettachfini 2008 (sample Mib75, p. 62) is most probably another typical example of these peculiar environment.
Differences with discorbids and other nearby taxa: In the micropaleontological works dealing with thin section (note that the taxa cited below are almost only known as extracted specimens), the small low trochospiral shells with hyaline optically radiate wall are often named “discorbids” or “rotalines” (i.e. by Sartoni and Crescenti 1960). The (Albian/Cenomanian up to the Paleocene) “Rotaline” of the latter authors correspond in part to the Rotalina cayeuxi of Agip (1959) which do not correspond to the original illustrations of Lapparent (as noted by Sartoni and Crescenti 1960). Anyway, the fact that all these shells do not have the single central massive umbilical plug and are much bigger (>220 μm) than R. m. microformis (<140 μm) is here sufficient for differentiation. The well-developed massive primary umbilical plug (not the coalescence of the umbilical-most parts of the successive folia) encountered in Rotorbinella is never encountered in D. vesicularis (type species of Discorbis), D. turbo (type species of Discorbina), L. dimidiatus (type species of Lamellodiscorbis), R. auberii (type species of Rotorbis) (Revets 2001). As well the compound plug of N. mexicana (type species of Neorotalia) (Hottinger et al. 1991), multiple pillars of R. trochidiformis (type species of Rotalia) (Haynes and Whittaker 1990; Levy et al. 1982) are not homologous with the umbilical plug found in Rotorbinella (Revets 2001). Also Rosalina globularis (type species of Rosalina) do not show any umbilical plug (see Levy et al. 1979, Hansen and Revets 1992). Note that well-developed umbilical plugs are only found in few taxa among which A. norrisi (Albian type species of Albertinopsis), B. monterelensis (Campanian type species of Brotzenella), R. colliculus (Eocene type species of Rotorbinella), P. inermis (Eocene type species of Pararotalia) (Hottinger et al. 1991), G. praegeri (Recent type species of Gavelinopsis), A. beccarii (Recent type species of Ammonia) (Levy et al. 1986; Revets 1996, 2001, 2002a, b).
Regarding internal chamber structures (difficult to evidence with certainty in R. m. microformis), the presence of umbilical plate (Boix et al. 2009) or coverplates (Revets 2001) in R. colliculus confirms the rotaliacean nature of Rotorbinella. Also, following Hansen and Revets (1992), D. vesicularis (type species of Discorbis) has coverplates and is structurally a rotaliid; it is then proposed to be reclassified (together with Ammonia, Discorbina, Lamellodiscorbis, Rotorbis, Rotorboides, Strebloides, Gavelinopsis) in the Ammoniinae, Rotaliidae, Rotaliacea. The original concept of Discorbis is then well represented by Rosalina (no umbilical plug), which has chambers with no internal structures (Hansen and Revets 1992 but see discussion in Revets 2002a).
Morphological forms close to R.m.mesogeensis
Consulting literature for the above study, we looked for cretaceous rotaliids morphologically resembling our rotorbinellas, i.e. with open intraseptal and umbilical interlocular space and free massive umbilical plug, as well as umbilical plate and folia when visible. Old rarely cited species and more recent ones but just as much cited are most often only seldom (and sometimes partially) illustrated. A lengthy future objective would then be the revision of the type species of Rotalia algeriana Magniez and Sigal (1953), Rotalia saxorum D’Orbigny (1850), Rotalia sigali Drooger (1952), Rotalia minuta Martin (1964), Rotalia hemisphaerica (Reuss 1862), Rotalia pisana Michelotti (1841), Rotalia reticulata Reuss (1863), Rotalia perovalis Terquem (1882), Rotalia germanica Kiesel (1970), Rotalia corbarica Massieux (1973), Rotalia lecalvezae Guillevin (1977), Rotorbinella hensoni (Smout 1954), Rotalia cushmani Applin and Jordan (1945), Rotorbinella skourensis (Pfender 1938), Rotalia bandyi Martin (1964), Rotalia marginata D’Orbigny (1850) to compare them with the well-defined R. mesogeensis mesogeensis and R. campaniola Boix et al. (2009), different species being probably conspecific, while others may have been lumped in one.
Genus Pararotalia LeCalvez 1949
Type species: Rotalina inermis Terquem 1882
The genus Pararotalia is defined by a planoconvex to biconvex test in a low trochospiral coil with an imperforated keel, umbilicus with a single massive plug, areal aperture with a lower lip representing the serrated edge of the spiral umbilical element separating the chamber lumen from the umbilical interlocular space. This element is called toothplate by Hottinger et al. (1991) and Loeblich and Tappan (1988) while Revets (1993) has a more restrictive view of the term toothplate and rather refer to foraminal plate coverplate concept for the internal structures in rotaliids. For Hottinger et al. (1991), the presence of this thoothplate with a free edge in Pararotalia, and the absence of such features as umbilical plate, foramenal plate connected to a cover plate or a folia, set the Pararotaliinae Reiss 1963 well apart from the Rotaliinae Ehrenberg 1839, Cuvillierininae Loeblich and Tappan 1964, and Ammoniinae Saidova 1981, and the open and undivided ventral sutural interlocular spaces separates it from Neorotalia.
The Early to Late Cenomanian (possibly Earliest Turonian) of Oman contains a homogenous population of small rotaliid specimen which is (although a bit smaller) very similar to the Late Santonian—Early Campanian P. tuberculifera illustrated by Boix (2007); Boix et al. (2009). Comparison with the original description and drawings of Reuss (1862), however, generated the research and discussion below.
History and remarks on Pararotalia tuberculifera (Reuss 1862)
Literature: In 1862, Rotalia tuberculifera Reuss is described in isolated form in Cretaceous sediments from Maastricht, The Netherlands. Following the German text (here translated), it is characterized by its diameter (around 875 μm for tall specimens), its rounded flattened shell with a keel interrupted by the suture reaching the periphery, the spiral side with only half of the last whorl recognizable (the rest of the surface being hidden/covered by rather bigger rounded beaded grains); umbilical face with 10 chambers in the last whorl, narrow center of umbilicus hidden by some bigger grains, shallow and narrow umbilical sutures getting deeper near the umbilicus; whole surface of umbilical and spiral faces covered by small grains with discernible pores in-between; spiral face more bulged than umbilical face, opening as a slit on the umbilical face below dorsal margin. In 1949, Hofker (1949) illustrate Nonion tuberculifera (Reuss) from the Late Senonian of south Limburg (Maastrichtian) with irregularly placed large knobs on the surface centre (and often near the periphery too) of both faces the test. The drawings of Hofker are different from those of Reuss by the much larger tubercles and the evidence of a “canal system” on both sides of the shell. These observations make Hofker state that the figures of Reuss are incorrect, but that his specimens correspond to Reuss’s description. In 1950, Visser (1950) states that Rotalia tuberculifera is one of the most common foraminifer in the type maastrichtian (following Reuss 1862 it is rare). His text state the presence of an umbilical plug, but it is neither visible on his drawings nor evidenced on his pictures. In 1951, Hofker (1951) attribute R. tuberculifera to the genus Parella. He discusses this attribution with different morphological arguments including a canal system between the knobs on both faces, the presence of a typical spine at each of the chambers, and the somewhat areal aperture. In 1957, Hofker (1957) attribute P. tuberculifera to the genus Pararotalia in a consequent study with abundant illustration. According to Hofker (ibid), P. tuberculifera is the oldest (Maastrichtian—Montian) species of the genus and a highly variable species with trimorphism (A1, A2 and B forms), the forms at the beginning of the evolution (Maastrichtian b) being very different (size is particularly increasing with time) from those at the end of the series (Montian). In 1957 Brown and Broennimann (1957) propose that P. tuberculifera probably includes Siderolites skourensis. In 1958, Reiss and Merling (1958) detail internal structures (e.g. toothplates, septal flaps) of various rotaliids (characterized by their double septa) among which feature Pararotalia, with illustrations of P. tuberculifera. Hofker (1959) study the evolution of the species with time and include a large list of synonyms. In 1960, Hofker (1960) cite the presence of P. tuberculifera in the Late Santonian of the Aquitaine basin (France), detail the areal loop-shaped aperture with a typical lamella over it and a thin toothplate (lip sensu Hottinger 2006) protruding from the apertural face, and resume the characters of Pararotalia. In 1963 Hofker (1963) detail again P. tuberculifera with a simple septa (contrarily to the observations of Reiss and Merling 1958), and with at the areal aperture a curled part forming the border of the aperture with the toothplate (apertural lip sensu Hottinger 2006), and at the axial wall of the foramen, a short dent protruding at the distal side of the foramen (most probably toothplate sensu Hottinger 2006). Hofker (1966), in his extensive work on Maastrichtian, Danian and Palaeocene foraminifera, illustrates numerous drawings of P. tuberculifera with an important morphological diversity. Pozaryska and Szczechura (1968) illustrate (drawings) this common form of the Palaeocene of Poland for which they note the considerable variation of shape, size and ornamentation; wall surface seems smooth, central plug can be single or divided into several small knob-like plugs, protuberances around central plug, if present, are formed by older raised parts of chambers (tena). Szczechura and Pozaryska (1972) illustrate their work with SEM images pointing out again the variability of the Montian P.tuberculifera of Crimea. Villain (1977) gives SEM views of one Maastrichtian P. tuberculifera shell from south Limburg, Netherland. Luperto Sinni (1978) illustrates thin sections of tall Senonian P. tuberculifera with detailed description and synonymy list attesting to the variable morphology. The remarkable works of Boix (2007) and Boix et al. (2009) on several Late Cretaceous rotaliids give very good description and abundant illustrations of sections of P. tuberculifera from the Late Santonian—Early Campanian, specimens that resemble very much our Cenomanian forms (see below).
Discussion about P. tuberculifera: Comparing the illustrations (drawings and pictures) attributed to P. tuberculifera by Reuss (1862); Egger (1899); Hofker (1949, 1951, 1957, 1959, 1960, 1963, 1966); Visser (1950); Reiss and Merling (1958); Hottinger (1966); Pozaryska and Szczechura (1968), Sprechmann (1981), Szczechura and Pozaryska (1972); Villain (1977); Petters (1978, 1979); Luperto Sinni (1978); Salaj and Nairn (1987); Doppert and Neele (1983); Witte and Schuurman (1996); Boix (2007); Boix et al. (2009), a very high morphological variability is evidenced. Main differences are noticed in terms of shape and size (diameter from 280 to 1460 μm) of the test, presence/absence of a single salient massive umbilical plug, surrounded or not by spiral fissure, with or without bigger tubercles at the umbilical end of the chambers, with varying ornamentation (e.g. size and disposition of tubercles, beaded/smooth sutures, striated/pustuled/smooth chamber walls, presence/absence of peripheral keel and/or spines), number of chambers in the last whorl, and age (Santonian to Montian).
Hofker (1957) explains the large morphological differences within R. tuberculifera with test trimorphism, based on various arguments including test and proloculum size, more or less distinct umbilical plug, shape and ornamentation of the test. But although characteristics are discussed in the text and 3 drawings are respectively attributed to A1, A2 and B, this trimorphism is arduous to acknowledge regarding the accessible drawings and pictures. His figure referred as a B form (Hofker 1957 Fig. 17 firstly described as Rotalia choctawensis by Van Bellen 1946, non Cushman and McGlamery 1938), is almost planispiral with an aperture in a different location, and cannot be conspecific with R. tuberculifera (Szczechura and Pozaryska 1972). Hofker (1963) also refers to micro and macrospheres, but the two sections he uses for demonstration have almost the same shell diameter and thickness (although one is a bit flatter), and the different sizes of the proloculus can then easily result of different centering of the sections; and if the two other specimens he refers to (isolated forms in Hofker 1957) are more different, their proloculus are not visible. Then, if cases of dimorphism are known within rotaliids (see Boix et al. 2009; Billman et al. 1980) it however, has to be revised for P. tuberculifera sensu Hofker (ibid), while it seem to lack for P. tuberculifera sensu Boix et al. (2009) as well as for our specimens from Oman.
Concerning revision of the holotype, Reuss’s complete collection of foraminifera (collection that disappeared for a long period of time and was rediscovered in the 1970s, see Papp et al. 1977), made up of 1839 slides, is now deposited in the Naturhistorisches Museum in Vienna. The related catalogue is however, still missing, and as Reuss did not have any direct link between his publications and his specimens/samples, any work with this collection is now very difficult. During their revision of the work of Reuss (1863); Meyn and Vespermann (1989, 1994), made an unpublished temporary catalogue of the complete collection they left with the collection. Some specimens from the Maastrichtian work of Reuss (1862) had also been identified, but there is no mention of R. tuberculifera (F. Rögl pers. comm.). Although about 65 original glass vials of Reuss were empty (Meyn and Vesperman, ibid.), there is chances that the type species of R. tuberculifera is still somewhere within the 1839 slides. A review of all the samples of the Reuss collection may then be necessary to find the type, or confirm it is definitely lost, but is not conceivable in this study. Meyn and Vespermann (1989) noted that “some of the drawings of Reuss are highly accurate and some are shematic or somewhat idealized but showing all important features of the species”. But Reuss’s original description cite the presence of some bigger grains hiding the umbilicus, and of bigger rounded beaded grains hiding the first whorls of the spiral side, characters that do not appear on his drawings which may then be inaccurate as noted Hofker (1949). The drawings of Hofker (1949) are then probably more realistic, but show a spinose periphery which is not reported neither in the text nor in the drawing of Reuss, and do not show the “deepening of the umbilical sutures approaching the umbilicus” stated by Reuss. Moreover, the presence of a single central massive umbilical plug is at first not mentioned, neither in the text nor on the drawings of Reuss (1862), or in the centered (visible proloculum) sections of Hofker (1949) (Fig. H, 1951 Figs. 16–18). This feature appears with the text of Visser (1950) but is not visible on his drawings although it can possibly be conceived in his (then highly oblique) section of Fig. 10; and then with Hofker (1957). Since then, this “highly variable species” most probably regroup different species with the various morphological characteristics cited above.
In their recent and abundantly illustrated work, Boix (2007); Boix et al. (2009) show morphologically homogenous and rather small specimens they attribute to P. tuberculifera. The centered axial sections of Boix et al. 2009 (Fig. 12.1, 2, 7, 12, 15, 18–20), very close to our sections of Oman (Fig. 4a–j, l–m, o), always display an umbilical face with a large single central massive and prominent umbilical plug surrounded by a spiral fissure and a heavy pustule at the umbilical shoulder of every chamber; a spiral face with raised (possibly beaded) sutures, and smooth wall with possible rare pustules in the center of the spire. Considering these morphological characteristics, and their age (Early to Late Cenomanian of Oman, Late Santonian to Early Campanian of Spain), older than most R. tuberculifera cited above, and as neither the Campanian (Hofker 1959 Figs. 132–134) and Santonian (Hottinger 1966 Fig. 9b) drawings attributed to R. tuberculifera, nor Reuss’s specimens or text, do clearly describe/show the characteristics cited above, the specimens found in Oman and Spain (Boix 2007; Boix et al. 2009) are considered as species different from R. tuberculifera and described as follows:
Pararotalia boixae sp. nov., Fig. 4a–u
aff. : 2007 Pararotalia tuberculifera (Reuss), Boix, Pl. 23 Figs. 1–7, Pl. 24 Figs. 1–8
aff. : 2009 Pararotalia tuberculifera (Reuss), Boix et al. p. 221 Figs. 12.1–21 (without synonyms)
Holotype: Specimen figured in Fig. 4f, sample ap400 deposited in the micropaleontological collection of the Natural history Museum of Geneva, n°MHNG2013-7
Paratypes: Specimens figured in Fig. 4a–e, samples ap367, ap347, ap391, Fig. 4g, sample ap400, deposited in the micropaleontological collection of the Natural history Museum of Geneva, n° MHNG2013-8 to MHNG2013-11.
Type locality: North-West end of Jabal Salakh, Adam foothills, coordinates: N22°24.251 E057°12.027
Type horizon: Natih C formation, Cenomanian.
Etymology: Dedicated to C. Boix for her work on cretaceous rotaliids.
Type description: This species is characterized by a trochospiral plano-convex to biconvex shell with an acute periphery marked by an imperforated keel. The spiral side is flat to slightly convex with a smooth wall and raised (possibly beaded) suture giving in thin sections the aspect of pustules, which, in some sections (e.g. Fig. 4a, d, m), show a dark median line absent from the specimens of Boix et al. (2009) that resemble a pore, but that has not been studied in detail. These raised/beaded sutures concentrate around the apex (as a result of the suture of the first whorls) where additional tubercles (present on the spiral side only) can also be present. Umbilical side is more convex and wall is smooth with umbilical shoulders of spiral chambers bearing each a heavy knob that forms a circle around the single free-standing massive umbilical plug. About 10 chambers are present in the last of 2–3 whorls. The massive umbilical plug stands free in the center of the umbilicus, separated from the adaxial chamber walls by a deep open furrow (umbilical interlocular space). The septa are straight and radial. The intraseptal interlocular space is restricted to the umbilical part of the septum (in the specimens of Boix et al. 2009) and is undivided (no feathering). The opening is present on the umbilical face as a radial sutural slit that reaches the periphery (Boix et al. 2009). The areal foramen is bordered by an upper lip and a lower protruding element forming the serrated edge of the toothplate (not clearly recognizable in our sections but see Boix et al. 2009, Fig. 12.17). Proloculus is less than 15 microns in diameter (Boix et al. 2009). The lack of suitable transverse sections do not allow to precise the presence (or not) of a folia. No evident dimorphism of generation is evidenced, and Cenomanian specimens are smaller (maximum diameter of 300 μm) than the Late Santonian- Early Campanian affinis specimens of Boix et al. (2009) which reach 500 μm in equatorial diameter.
Remarks and differences: P. boixae show a low intraspecific morphological variability. The raised (possibly beaded) sutures of P. boixae, giving the characteristic tuberculate aspect in thin sections, plus its somewhat planoconvex shell (rather plane spiral face and convex umbilical face), distinctly separate this species from the smooth faced R. mesogeensis mesogeensis, R. mesogeensi medioformis, R. saxorum, R. corbarica, R. hensoni, R. algeriana, R. skourensis. The presence of a single large massive prominent umbilical plug surrounded by a deep furrow, the presence of a knob on the umbilical shoulder of the chambers, the raised/beaded sutures and the smooth chamber walls separates it from P. tuberculifera sensu Reuss (1862). Reliable attribution of most drawings of the P. tuberculifera sensu Hofker (op.cit.) to P. boixae cannot be done without looking back to the original specimens. The figures from Villain 1977 (Pl. 6 Figs. 7–9), Hofker 1959 (Figs. 132–133, 1960 Fig. 7, 1966 Pl. 24 Fig. 137, Pl. 28 Figs. 40–41, Pl. 33 Fig. 73), Hottinger 1966 (Fig. 9b), Visser 1950 (Pl. 5 Fig. 14) are probably to be referred to P. tuberculifera sensu Reuss (1862).
Geographic and stratigraphic distribution: Middle to Late Cenomanian (Natih E to Natih A formation) in Oman (not found in contemporaneous sediments of Morocco), Late Santonian to Early Campanian in the south Central Pyrenees for the affinis forms of Boix et al. (2009).
As a part of an analysis of Cenomanian sediments of Morocco and Oman, this study details an abundant microfauna of small rotaliids. Some of these, still unknown, are described as subspecies of Rotorbinella mesogeensis (Tronchetti 1981). A gradational series (continuum) of three morphological groups with clearly differentiated morphology and (obviously) faint boundaries are split within R. mesogeensis mesogeensis ssp. nov., R. m. medioformis ssp. nov. and R. m. microformis ssp. nov. Although it is at the moment not possible to propose a definite palaeoecological significance for each taxon, shallow shelf/ramp environments show the most significant abundance of these taxa, while some of the shallowest (restricted?) environments reveal R. m. microfomis as the only foraminifer. All these taxa are absent from deeper (intrashelf basins) environments. R. mesogeensis and subspecies are the earliest representative of the genus Rotorbinella that persists at least throughout the Palaeogene (Boix et al. 2009). The occurrence of R. mesogeensis microformis in the Late Albian (Diploceras cristatum ammonite Zone) of Oman makes it a probable ancestor of R. m. medioformis and R. m. mesogeensis and lets it possibly (internal structure can still be debated) be one of the oldest known rotaliid foraminifers. The medioformis and mesogeensis subspecies are abundant since the Early Cenomanian (ante Mantelliceras dixoni ammonite Zone) and last up to the Late Cenomanian (possibly basal Early Turonian, ante Mammites nodosoides ammonite Zone). The Cenomanian—Turonian boundary cannot be located very precisely and the disappearance of the rotaliids around the boundary in Morocco and Oman is most probably due to facies change (deepening environment). R. m. microformis may be present in the Early Turonian. The Moroccan and Omani data confirm that, as noted by Tronchetti (1981, 1993) and Boix et al. (2009), R. mesogeensis mesogeensis is restricted to the Cenomanian and can be considered as a marker. The latter is considered by Boix et al. (2009) as the progenitor of all rotorbinellas, which will diversify into Rotorbinella campaniola Boix et al. 2009, Pyrenerotalia longifolia Boix et al. 2009, and Iberorotalia reicheli Hottinger 1966, since Early Santonian by modifications of the umbilical structure and size increase.
Pararotalia boixae sp. nov. regroups specimens that were previously included in the variability of P. tuberculifera (Reuss 1862). Bibliographic research revealed much confusion within this presumed highly variable species (probably containing different morphotyps/species), whose original description was complicated by probable inaccuracies of the original drawings. Seeking the (possibly lost) holotype within the huge Reuss’s collection was not feasible as part of this work. P. boixae has shallow water environment affinities and a clearly distinct morphology and different age (Cenomanian with affinis forms in the Early Campanian) when compared with what we report to P. tuberculifera sensu Reuss (1862). R. m. microformis, R. m. medioformis, R. m. mesogeensis and P. boixae are the oldest reported occurrences of rotaliid foraminifers. These taxa are the rootstock of this family that will start its extensive diversification since the Late Coniacian—Early Santonian (see Boix et al. 2009).
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Best thanks to F. Rögl for his kind answers about the search of R. tuberculifera in the Reuss’s collection of the Naturhistorisches Museum of Vienna; P.A. Proz (Museum, Geneva) for the confection of the numerous thin sections; R. Wernli (University of Geneva) for his numerous advices, our discussions and his comments that greatly improved this paper; and two anonymous reviewers for their stimulating comments, remarks and questions. Salim Omar Al-Ibrahim, Director General of Minerals (Ministry of Commerce and Industry of Oman) and Ali Al Rajhi, Director of Survey and Research are thanked for their logistic support.
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Piuz, A., Meister, C. Cenomanian rotaliids (Foraminiferida) from Oman and Morocco. Swiss J Palaeontol 132, 81–97 (2013). https://doi.org/10.1007/s13358-013-0054-2
- R. mesogeensis
- P. boixae
- P. tuberculifera