- Research Article
- Open Access
New biostratigraphical data (calcareous nannofossils, ammonites) and Early to Late Barremian transition in the Urgonien Jaune facies and Marnes de la Russille complex of the Swiss Jura Mountains
Swiss Journal of Palaeontology volume 139, Article number: 6 (2020)
In the central Jura Mountains (Western Switzerland), the Urgonien Jaune (UJ) facies with the Marnes de la Russille beds (MRu) have provided very rich nannofloras associated with very rare Tethyan ammonites. A late Early Barremian nannoflora of the Mid-Barremian Event (MBE, following a regional tectonic event of an earliest Barremian synsedimentary tectonic crisis) was found in MRu of the lower UJ and includes 42 genera with 90 species. Among them, Biscutum jurensis De Kaenel, n. sp., Flabellites eclepensensis De Kaenel, n. sp., Palaeopontosphaera giraudii De Kaenel, n. sp., Rhagodiscus buisensis De Kaenel, n. sp., and Vagalapilla rutledgei De Kaenel, n. sp., are recognized as five new species. This nannoflora is a mixture of Boreal and Tethyan taxa with 20 nannofossil markers (Assipetra terebrodentarius, Broinsonia galloisii, Calcicalathina oblongata, Cyclagelosphaera rotaclypeata, Diloma placinum, Ethmorhabdus hauterivianus, Flabellites eclepensensis, Gorkaea pseudoanthophorus, Nannoconus abundans, Nannoconus pseudoseptentrionalis, Palaeopontosphaera giraudii, Palaeopontosphaera pinnata, Placozygus howei, Placozygus reticulatus, Reinhardtites scutula, Rhagodiscus buisensis, Rhagodiscus eboracensis, Tegulalithus septentrionalis, Tubodiscus jurapelagicus, Zeugrhabdotus moulladei) indicating very precisely the nannofossil Zones LK19 (Boreal)–NC5D (Tethyan) as well as the Elegans (Boreal) and Moutonianum (Tethyan) ammonite Zones of the latest Early Barremian. The ammonites in the basal UJ facies of Early Barremian age are reworked Lyticoceras claveli (Nodosoplicatum Zone, Early Hauterivian) and reworked Cruasiceras cf. cruasense (Sayni Zone, early Late Hauterivian), and Pseudometahoplites sp. juv. (Compressissima to Vandenheckii Zones, Early to Late Barremian transition) from the basal MRu. The new palaeontological and sequential results of this study allow a revision of previous data from Godet et al. (2010) precisely assigning a Barremian age to the MRu of the central Jura Mountains (Tethyan Compressissima to lower Sartousiana and Boreal uppermost Fissicostatum to middle Denckmanii ammonite Zones, Boreal LK20B-LK19-LK18 and Tethyan NC5D nannofossil Zones), within the Early to Late Barremian UJ (Tethyan Hugii to lower Sartousiana and Boreal Rarocinctum to middle Denckmanii ammonite Zones, Boreal LK20C to LK18 and Tethyan NC5C-NC5D nannofossil Zones) and below the Late Barremian Urgonien Blanc facies (Tethyan Sartousiana ammonite Zone).
The shallow marine deposits of the Urgonian facies of this study (Figs. 1, 2, 3) are historically well known since the middle 19th century in the Swiss Jura Mountains. Marcou (1859, p. 127) evoked the Roches du Mauremont for the Urgonien Jaune facies and Marnes de la Russille complex of the Mormont Hill (cf. Eclépens quarry section). Jaccard (1969, p. 141) gave the first description of the Marne(s) de la Russille [with marl(s) indicated in the singular or plural] within Couches de Bôle (= calcaires intermédiaires de Bôle, De Tribolet 1856, p. 70), also named Urgonien inférieur (Desor and Gressly 1859) or Russillien (Schardt and Dubois 1902). More recently, Strasser et al. (2016) have placed the Urgonien Jaune sensu Remane et al. (1989) in their Gorges de l’Orbe Formation and the topmost Marnes de la Russille intercalation with Urgonien Blanc (UB) carbonates in their Vallorbe Formation.
However, these two formations remained poorly defined and poorly dated and are in need to be revised in detail. Furthermore, the new nomenclature of Strasser et al. (2016) is hardly applicable to the peculiar section of Eclépens. For these reasons, a more sedimentological, facies-based approach was chosen, using as terminology the Urgonien Jaune (UJ) facies for shallow marine and tidal yellowish bioclastic limestones, and the Marne(s) de la Russille (MRu) facies for the marly intercalations. We consider the Couches de Bôle (Merdasson section in Cotteau 1862–1867, p. 107–108) as Barremian strata between "Neocomian" and Aptian, as they were already well known to be particularly fossiliferous with, among many other marine invertebrates, common stromatopororoids and Alcyonarian corals (Fig. 1j, Octocorallia mainly characterized by a profusion of typical calcitic sclerites in the sediments), some colonial corals (Hexacorallia), rudists forming local reefs (Pachytraga tubiconcha Astre 1961, Remane et al. 1989, Blanc-Alétru 1995), echinoids [Goniopygus peltatus (L. Agassiz 1838), Pseudocidaris clunifera (L. Agassiz 1840), Cidaris lardyi Desor 1855, Astrolampas productus (L. Agassiz 1836), Heteraster couloni (L. Agassiz 1839)] and brachiopods [Glosseudesia ebrodunensis (de Loriol 1864), including Rhynchonella lata d’Orbigny 1847, Sulcirynchia gillieroni (Pictet 1872), Sulcirynchia picteti (Burri 1956), Sulcirynchia renauxiana (d’Orbigny 1847), Lepidorynchia dichotoma Burri 1956, Loriolithyris and Sellithyris spp.]. The Urgonien Blanc (UB) facies is used for the topmost, rudist-rich, whitish limestones characterized by rudists such as Requienia ammonia (Goldfuss 1838) and Agriopleura spp. and interpreted as lagoonal deposits.
Detailed studies and descriptions of the Urgonian platform series in the Swiss Jura Mountains are given by Remane et al. (1989) and Blanc-Alétru (1995), but their Hauterivian or Barremian age has remained uncertain and controversial until now. A Late Hauterivian age was assigned to the Gorges de l’Orbe Formation and a Late Hauterivian to Early Barremian age to the Vallorbe Formation with the topmost MRu layers, based on orbitolinid biostratigraphy and sequence stratigraphy (Clavel et al. 2007, 2013, 2014; Charollais et al. 2008, 2013; Conrad et al. 2012; Granier et al. 2014; Strasser et al. 2016). But, for other authors with a quite different interpretation of the orbitolinid biostratigraphy and sequence stratigraphy, both formations are mainly considered as Late Barremian according to sequence stratigraphy, biostratigraphy of orbitolinids, nannofossils and K–Ar isotopes (Arnaud-Vanneau and Arnaud 1990; Blanc-Alétru 1995; Arnaud et al. 1998; Adatte et al. 2005; Godet et al. 2010, 2011, 2012, 2013). Our new biostratigraphical data mainly based on nannofossils and ammonites allow to solve this age discrepancy. The aim of this study is to close more than 30 years of controversy about the age of the Urgonian facies in the Swiss Jura Mountains.
The Eclépens quarry section across the Mormont Hill (coord. 2531.250/1167.180, map 1:25′000 of Switzerland) is well known since the studies of Blanc-Alétru (1995) and Godet et al. (2010) with an unusually thick Urgonien Jaune–Marne de la Russille complex of 47 m (Figs. 2, 3). The section is dated with the standard Tethyan ammonite biozonation of Reboulet et al. (2018) and begins with dark grey Early Hauterivian marls corresponding to the top of the Marnes bleues d’Hauterive (Radiatus Zone) overlain by marly and calcareous beds (Mergelkalk Zone in Godet et al. 2010, p. 1091, fig. 2) attributed to the Loryi Zone in the Neuchâtel area (Remane et al. 1989; Mojon et al. 2013). These layers constitute a transitional facies preceding the oolithic yellowish Pierre jaune de Neuchâtel (PJN) well developed above, with in its middle part (between lower and upper PJN) the thin marly and glauconite-rich layer of the Marnes d’Uttins having provided in Eclépens and in the Swiss Jura Mountains some ammonites of the Nodosoplicatum Zone (Remane et al. 1989; Godet et al. 2010; Mojon et al. 2013) such as Lyticoceras claveli Busnardo and Thieuloy 1989, Lyticoceras subhystricoides (Kilian and Reboul 1915) and Saynella clypeiformis (d’Orbigny 1841). These Hauterivian deposits were recently formalized within the Grand-Essert Formation (Strasser et al. 2016), subdivided into Hauterive Member for the basal marly complex and Neuchâtel Member for the PJN complex (Strasser et al. 2018). The basal part of the UJ facies with very rare reworked Hauterivian ammonites (L. claveli and Cruasiceras cf. cruasense (Torcapel 1884) of the late Early Hauterivian Nododosoplicatum ammonite Zone and early Late Hauterivian Sayni ammonite Zone, respectively, cf. Reboulet et al. 2018; this study, Fig. 4.1–5) is constituted by a very thin yellow marly layer overlaid by two massive beds of yellowish bioclastic glauconite-bearing limestones. Small basal, erosive channels with glauconitic and phosphatized/silicified quartz-sand-rich infillings are also well visible locally (Godet et al. 2010, p. 1095–1097, fig. 7D, E, F). More abundant greyish and yellowish/reddish Marnes de la Russille (MRu) intercalations are usually recognized on top of the UJ–MRu complex in the Eclépens section, but the UJ limestones alternate also with several other dark grey marly layers (yellow by alteration) containing early Late Barremian nannofloras attributed to the Sartousiana ammonite Zone incl. the Feraudianus Subzone on its top (De Kaenel in Godet 2006 and Godet et al. 2010). Frequent stromatoporoids characterize a large part of the UJ limestones and the dark marls of the Eclépens section which commonly correspond to the classical feature and definition of the MRu with well-developed stromatoporoid bioconstructions in the Swiss Jura Mountains (Remane et al. 1989; Blanc-Alétru 1995). The benthic foraminifera from the UJ and UB facies of the Eclépens quarry section notably include Neotrocholina friburgensis Guillaume and Reichel 1957, Choffatella decipiens Schlumberger 1905 and orbitolinids (Praedictyorbitolina, Paracoskinolina, Valserina and Paleodictyoconus spp.) associated with some Dasycladalean algae (cf. Montcherand section below), all attributed to the Late Hauterivian–Early/Late Barremian by Blanc-Alétru (1995) or to the Late Hauterivian only by Clavel et al. (2007, 2014). Godet et al. (2010) identified in the Urgonian facies of Eclépens two sequence boundaries (SbE2, SbE3) and two maximum flooding surfaces (mfsE2, mfsE3), whereas SbE3 and mfsE3 are correlated with the late Barremian sequence Ba3 defined by Arnaud (2005) in his reference sections of SE-France.
The section of the La Sarraz–Les Buis quarry (Fig. 1 b–d, f–i; coord. 2528.240/1168.170, map 1:25′000 of Switzerland) is thinner than in the Eclépens quarry, both sections being separated by the Mormont–La Sarraz fault system in the extension of the Pontarlier fault system (Fig. 1a; Sommaruga et al. 2012, p. 54; Schmitt et al. 2016). The La Sarraz–Les Buis quarry section starts with 8 m of yellowish massive PJN facies which end with a major discontinuity forming a well-developed hardground bioperforated and incrusted by very large, flat oysters. The overlying UJ–MRu complex has a thickness of only 12 m and is subdivided in three main parts separated by sedimentary discontinuities or sequence boundaries (Fig. 1b, h). The lower part of the UJ limestones with two massive beds overlay the PJN facies. These lower UJ beds are mainly yellowish, roughly bioclastic and oolithic limestones. Some thinner layers are whitish and around 1 m of reddish tabular cross-bedding can be observed in the middle part of the first basal massive UJ bed above the PJN carbonates (Fig. 1f, g). The glauconite-rich layers observed in the basal UJ of the Eclépens quarry are absent. The upper yellowish UJ limestones (5–7 m) include two marly bioclastic and quartz-rich levels MRu1 and MRu2. Locally, very fine-grained siliciclastic marls from the layers MRu1 and MRu2 constitute marly infillings in metric to decametric erosive channels analysed in this study (Fig. 1c-d, h-i and Fig. 3). Other overlapping channel structures with truncated oblique strata can be observed in the upper bioclastic UJ and basal UB limestones. The upper part of the section, represented by 15 m of massive whitish UB facies, provided orbitolinids (Praedictyobitolina, Valserina and Paleodictyoconus spp.) and Dasycladalean algae (Salpingoporella genevensis Conrad 1969 ex Conrad, Praturlon and Radoičić 1973), which would indicate a Late Hauterivian age according to Clavel et al. (2007, 2014).
The Montcherand section (Gorges de l’Orbe, 7 km north of La Sarraz) described by Blanc-Alétru (1995) is characterized by a thick marly MRu series (20 m) and UB carbonates (50 m) with Late Hauterivian–Early/Late Barremian microfossils like benthic foraminifera (Choffatella decipiens Schlumberger 1905, orbitolinids: Praedictyorbitolina, Paracoskinolina and Valserina spp.) and Dasycladalean algae [Dissocladella hauteriviana Masse 1999, Actinoporella fragilis (Conrad 1970) Granier 1994, Angioporella neocomiensis Conrad and Masse 1989]. The particular interest of this section is the channelized base of the MRu (Fig. 1e) characterized by a tiny Mid-Barremian ammonite Pseudometahoplites sp. juv. found in 2014 and presented in this study for the first time (cf. Results, Fig. 4.6–18).
Materials and methods
During this study lasting from 2014 to 2019, three very rare ammonites were collected, 2 fragments from the basal marly layer and surrounding glauconitic limestone of the Urgonien Jaune (UJ) in the Eclépens quarry, and a juvenile specimen collected with microfossils from the basal Marnes de la Russille (MRu, sample OM4) in the Montcherand section. Micropalaeontological material was isolated in the laboratory from marls (MRu) of the Eclépens quarry (3 samples EC72b, EC79, ECMRu10), La Sarraz–Les Buis quarry (10 samples LSBMRu 0 to 9) and Montcherand section (1 sample OM4). These samples each of about 1–5 kg dry weight were wet-sieved with mesh width ranging from 250 µm to 2 mm and picked using a binocular loupe. 16 samples with nannofossils from the sections of Eclépens (6 samples EC51, EC55, EC57, EC72b, EC79, ECMRu10) and La Sarraz–Les Buis (10 samples LSBMRu 0 to 9) were prepared on glass slides (Figs. 5, 6) according to the improved method described by De Kaenel and Villa (1996) and studied using a Leica DM2500P light microscope. Photographs and micrographs of the palaeontological material were obtained using natural light, CLSM “confocal laser scanning microscopy” and optical microscopy with artificial light (cross-polarized/XP light and phase-contrast light for nannofossils using an Olympus DP71 digital camera) or scanning electron microscopy (SEM). Light micrographs (LM) are included in Figs. 7, 8, 9, 10, 11. The reference material for the nannofossils is conserved in the collection of E. De Kaenel, reference samples of sediments for the nannofossils (Figs. 12, 13) as well as the ammonites are deposited in the collection of the Musée géologique de Lausanne (abbr. MGL, UNIL-Dorigny, Lausanne).
The UJ facies of the studied sections have provided ammonites and nannofossils presented in detail hereafter and in Fig. 3, with other miscellaneous micro- and macro-fossils, and particular sedimentological features.
Ostracods, benthic foraminifera, other micro- & macro-fossils and minerals of varying significance
In the sections of La Sarraz–Les Buis quarry and Montcherand (Gorges de l’Orbe), typical Barremian ostracods (according to Babinot and Colin 2011) were collected in the MRu: Rehacythereis gr. geometrica Damotte and Grosdidier 1963, Neocythere (Centrocythere) gottisi Damotte and Grosdidier 1963, Cytherelloidea ghabounensis Bischoff 1964, Trochinius consuetus Kuznetsova 1961 (rare taxon from La Sarraz–Les Buis and Eclépens sections), Paracypris levis Kuznetsova 1961, and Schuleridea, Bairdoppilata (very large and smaller specimens), Asciocythere, Cytherella spp. In these two sections, benthic foraminifera such as Neotrocholina friburgensis Guillaume and Reichel 1957, Choffatella decipiens Schlumberger 1905, big Reophax sp. and Nodosariids are also present as well as very frequent sclerites of Alcyonarian corals. The very fine-grained siliciclastic and nannofossil-rich marls constituting the Marnes de la Russille (MRu) at La Sarraz–Les Buis quarry also have provided heavy minerals: grains of red garnet reworked/transported from distant northern crystalline massives and abundant pyrite with frequent large diagenetic framboids (about 200–250 µm) indicating organic-rich sediments (Wilkin et al. 1996; Gallego-Torres et al. 2015), well-preserved in the lower dark grey part of the channelized marly infilling.
From the Eclépens quarry section, EC72b-79 samples have yielded a rare and poorly preserved microfauna with ostracods [Protocythere triplicata (Roemer 1841), Strigosocythere strigosa Grosdidier 1964, R. gr. geometrica, N. (C.) gottisi, C. ghabounensis, T. consuetus, P. levis, and Schuleridea, Bairdoppilata, Asciocythere, Cytherella spp.] and benthic foraminifera (C. decipiens, N. friburgensis, big Reophax sp.). Grey marly layers and yellowish limestones below EC72b are further characterized by large brachiopods as Glosseudesia ebrodunensis (de Loriol 1864) of biostratigraphical interest (Gaspard 1989, Lobacheva 1990, Middlemiss 1981, 1983, Middlemiss in Remane et al. 1989), big rounded stromatoporoids and nautilids as Cymatoceras pseudoelegans (d’Orbigny 1840). ECMRu10 sample with siliciclastic rubefied marls (Fig. 14c, d) provided microfossils such as mainly very recrystallized marine benthic foraminifera (orbitolinids, C. decipiens, N. friburgensis, Cuneolina hensoni Dalbiez 1958, big Reophax sp.), rare ostracods (Strigosocythere cf. chalilovi Kuznetsova 1961, N. (C.) gottisi, large Bairdoppilata sp.) and sclerites of Alcyonarian corals. Rubefied marls indicate a subsequent emersion trend with terrestrial input/alteration before the deposits of the prograding lagoonal UB facies upon a horizontal bedding-surface and almost isochronous surface like in La Sarraz–Les Buis only 2 km to the Northwest.
The few ammonites collected during this study in the Urgonien Jaune (UJ) facies of the Swiss Jura Mountains (Fig. 4) are of Tethyan affinity according to the biostratigraphical references for the ammonite biozonation (Vermeulen and Thieuloy 1999; Vermeulen 2007; Reboulet et al. 2009, 2014, 2018). Two ammonites (Fig. 4.1–5) were collected in 2014–2015 by workmen of the Eclépens quarry at the base of the UJ, a little above the upper Pierre jaune de Neuchâtel (UPJN). A fragment of Lyticoceras claveli Busnardo and Thieuloy 1989 (in Remane et al. 1989) from the Early Hauterivian Nodosoplicatum Zone was firstly collected in a thin marly layer just below the bioclastic UJ limestones and is clearly reworked from the underlying UPJN according to the oolithic grainstone infilling of the shell. Later, a negative imprint of Cruasiceras cf. cruasense (Torcapel 1884) from the early Late Hauterivian Sayni Zone was found in the basal yellow massive and glauconite-rich UJ limestones. These two Hauterivian ammonite species have a very close morphology (Thieuloy et al. 1983). Lyticoceras claveli exhibits large-sized evolute shells, a subrectangular section a little higher than wide with a wide slightly rounded and relatively smooth venter, broad radial and rounded ribs firstly alternating with short intermediate ribs then regularly bifurcated from mid-flanks. Cruasiceras cruasense is characterized by generally larger-sized specimens with distinctly evolute shells, a subrectangular section clearly higher than wide and with a narrow well-rounded venter area crossed by ribs. The ornamentation is typical with slightly prorsiradiate and flexuous ribs bifurcated in the upper third of the flanks. In November 2014, a very small specimen (nucleus) assigned to Pseudometahoplites sp. juv. (Compressissima to Vandenheckii Zones, Early to Late Barremian transition, Vermeulen 2007) was collected in the first lowermost layer of the Marnes de la Russille in the Montcherand section within the Gorges de l’Orbe (Figs. 1e, 4.1–18). This tiny ammonite was found fortuitously by searching for ostracod microfossils in a marly sample from the layer OM4 of the section described by Blanc-Alétru (1995, fig. 67, p. 159), in an outcrop along the Orbe river (coordinates 2528.790/1175.510, map 1:25′000 of Switzerland). It is a juvenile specimen with a very small (< 1 mm) embryonic conch and the first stages of ornamentation typical of the Holcodiscidae (D. Bert, pers. comm. 2015). The genus Pseudometahoplites is characterized by specimens of small size. The shell is evolute with thick whorls characterized by a sub-trapezoidal section as high than wide, and with a flat venter. The ornamentation is strong with radial to prorsiradiate ribs bearing pinched umbilical bullae and massive rounded latero-ventral tubercles linked on the venter by a rib (Vermeulen 2007).
The results below concentrate on sample LSBMRu1, which was the key sample to date the Marnes de la Russille. After dating this sample (Figs. 5, 6), additional samples were collected in the La Sarraz–Les Buis quarry and the detailed list of species observed in these samples is presented in Fig. 12. Moreover, previous samples EC72b and EC79 from Godet et al. (2010) were re-analysed with unpublished samples EC51, EC55 and EC57 from the base of the Urgonien Jaune (UJ) facies collected by E. De Kaenel with A. Godet and K. Föllmi at Eclépens in 2005. These new results are presented in Fig. 13.
Calcareous nannofossil abundance and preservation
The nannoflora of the sample La Sarraz–Les Buis quarry/Marnes de la Russille (abbr. LSBMRu1) is common (4 specimens per field of view, cf. In situ Assemblage, Fig. 12). The preservation of nannofossils is variable, generally moderate but some specimens are well preserved. Nannofossils show some minor etching and minor overgrowth.
Calcareous nannofossil assemblage and biostratigraphy
The assemblage of sample LSBMRu1 is characterized by a high diverse nannoflora with 42 genera and 90 species observed despite the fact that some subspecies are not considered in this study (e.g. A. infracretacea larsonii and A. terebrodentarius youngii). This high diversity of species may reflect the surface-water fertility. Previous studies, however, have not reported such a high diversity. Aguado et al. (2014a) reported 37 species from samples of the same age in the Tethyan Realm. Crux (1989) and Jeremiah (2001) reported about 45 species from samples of the same age in the Boreal Realm. The novelty of sample LSBMRu1 is the presence of both Boreal and Tethyan species resulting in this exceptionally high diversity. This sample represents a unique nannoflora assemblage of endemic Boreal and Tethyan species. In addition, this sample shows that during the Barremian, selected endemic taxa (both in the Boreal and Tethyan realms), along with select cosmopolite taxa, are more widely distributed than previously reported. The assemblage in sample LSBMRu1 comprises a mixture of cosmopolitan, endemic, Tethyan and Boreal taxa. The detailed systematic taxonomy chapter discusses the origin of the taxa.
The nannoflora is dominated by abundant Watznaueria barnesiae, Watznaueria fossacincta and Watznaueria ovata with a few Glaukolithus choffatii, Lithraphidites carniolensis, Palaeopontosphaera elliptica, Retecapsa octofenestra, Rhagodiscus asper, Reinhardtites scutula and Tegulalithus septentrionalis. The abundance of Gorkaea pseudoanthophorus is between few and rare. Other species are rare to very rare. LSBMRu1 is also characterized by very rare species of Nannoconus abundans, Nannoconus pseudoseptentrionalis, Micrantholithus hoschulzii and Micrantholithus obtusus. Broinsonia galloisii, Calcicalathina oblongata, Ethmorhabdus hauterivianus, Flabellites eclepensensis, Cyclagelosphaera sulcata, Rhagodiscus buisensis and Tubodiscus jurapelagicus, which is explained by the fact that these species have their lowest or highest occurrences at this time.
The following terms are used to indicate the individual species abundance: HO = highest occurrence, HRO = highest regular occurrence, HFO = highest few occurrence, HIO = highest increase occurrence, LIO = lowest increase occurrence, LFO = lowest few occurrence, LRO = lowest regular occurrence, LO = lowest occurrence. The stratigraphical distribution of the nannofossils in this sample is presented in Fig. 6.
An integrated approach utilizing both Tethyan and Boreal schemes, calibrated to GTS2012, was taken to determine the age of this sample:
- Tethyan zonal scheme (NC zones) of Roth (1978, 1983) with subdivisions of Bralower (1987): LSBMRu1 belongs to the lower part of Zone NC5D. This subzone is defined at the base by the HRO of Calcicalathina oblongata and at the top by the LRO of Flabellites oblongus. One Tethyan event described by Aguado et al. (2014a) is of primary importance to date this sample: LO of Flabellites eclepensensis De Kaenel, n. sp. (his small Flabellites oblongus). Other important Tethyan events are the LO of Placozygus howei and HO of Calcicalathina oblongata.
- Boreal zonal scheme (LK zones) of Jeremiah (2001): this scheme uses single, multiple and quantitative events to define zonal and subzonal boundaries. LSBMRu1 belongs to Zone LK19 defined at the base by the HIO of Cyclagelosphaera margerelii and at the top by the HRO of Diazomatolithus lehmanii. C. margerelii is rare and D. lehmanii is present in LSBMRu1. Because of the number of Boreal nannofossil species, the LK scheme is more accurate to date LSBMRu1. Four Boreal events observed by Crux (1989) are of primary importance to date this sample: the re-entry (term used by Crux 1989) of Tegulalithus septentrionalis, the increase of Reinhardtites scutula, the presence of Ethmorhabdus hauterivianus and Broinsonia galloisii.
The present study provides an excellent opportunity to correlate the Boreal and Tethyan nannofossil markers and to improve the biostratigraphy of the Early–Late Barremian. During this period, the nannofloras show some strong provincialism. Most of the events observed belong to the Boreal zonal scheme (LK) of Jeremiah (2001), but Tethyan (NC) markers are also present. The outcrop of the Marnes de la Russille with sample LSBMRu1 is intermediate between these two realms and other studies on nannofossils do not exist for this intermediate palaeolatitude corresponding to the location of the central Jura Mountains. The stratigraphic distribution of calcareous nannofossils from LSBMRu1 is shown in Fig. 6 with the standard marker species of the NC and LK zonal scheme. With all Tethyan and Boreal markers, the age of LSBMRu1 is very precisely determined by the ammonite zonation: upper Moutonianum Zone (Tethyan) or middle-upper Elegans Zone (Boreal). A very precise correlation of the Moutonianum and Elegans Zones (Fig. 5) is from Mutterlose et al. (2014), who correlated the base of Elegans Zone with the uppermost Compressissima Zone and its top with the lowermost Vandenheckii Zone. These biostratigraphic correlations indicate that the LO of B. galloisii (Boreal) and F. eclepensensis (Tethyan) are in the same horizon. Calcicalathina oblongata (Tethyan) recorded in the same horizon indicates an age not younger than the Moutonianum Zone. The HO of C. oblongata (Tethyan) in sample LSBMRu4 is correlated with the the top of the Moutanianum Zone (Figs. 5, 12). Aguado et al. (2014a) moved the NC5D/NC5E subzonal boundary to LO of F. eclepensensis in the uppermost Early Barremian Moutonianum Zone. We are not following this new position and this boundary is still better placed at LRO of F. oblongus in the Late Barremian Giraudi Zone. In the same way, the NC5C/NC5D subzonal boundary is not moved to HO of C. oblongata, but still placed in the upper Nicklesi Zone with a position corresponding to HRO of C. oblongata.
Additional results and data
Data of samples LSBMRu1 and EC72b-79 are completed with analyses of 9 other samples LSBMRu0/2–9 and ECMRu10 (Figs. 12, 13, 14a, b) collected in the Marnes de la Russille (MRu) of La Sarraz–Les Buis quarry and Eclépens quarry. LSBMRu1 in the middle part of the channelized dark grey marls (MRu) was by far the richest and most interesting sample for nannofossils. The nannoflora observed in LSBMRu can be placed mostly in the Moutonianum ammonite Zone of the late Early Barremian. Rare typical specimens of the Late Barremian marker Flabellites oblongus were observed in EC79 and ECMRu10 only, but not in the highest LSBMRu7-9 samples of yellowish more calcareous marls with decreasing nannofossil diversity. Rhagodiscus gallagheri Rutledge and Bown 1996 was found in EC72b/EC79 and in LSBMRu5/LSBMRu7/LSBMRu9 with a first occurrence above the Early/Late Barremian boundary marked by a sudden change of colour from dark grey to yellow (Fig. 14b), thus with a first occurrence in the lower Vandenheckii ammonite Zone and not higher in the Late Barremian (De Kaenel in Godet et al. 2010) or in the basal Aptian (Rutledge and Bown 1996). The top of Ethmorhabdus hauterivianus in the highest LSBMRu7-9 samples and in EC72b is placed in the Vandenheckii Zone and Tubodiscus jurapelagicus in LSBMRu9 indicates an age not older than the Late Barremian Vandenheckii ammonite Zone. LSBMRu9 and EC72b contain specimens of large Nannoconus indicating influxes of warm Tethyan water. Nannoconus abundans is a typical Boreal endemic species found in EC72b and LSBMRu1, this taxon restricted to the Barremian is very rare (or absent) in upper LK19 and lower LK18 nannofossil Zones.
The Late Barremian marker Lucianorhabdus salomonii Bergen 1994 is absent in LSBMRu5-9 and EC72b-79/ECMRu10 samples, and after revision of the material observed and figured by Godet et al. (2010, Table 2, fig. 14B.10) must be referred to the genera Owenia or Orastrum, and the age of EC72b-79/ECMRu10 is thus a little older than the upper Sartousiana Zone as previously reported by De Kaenel in Godet (2006) and Godet et al. (2010). According to these new data and considering the HO of Tegulalithus septentrionalis (NG) still present in LSBMRu9 and ECMRu10, the biostratigraphical range of the samples LSBMRu5-9 and EC72b-79/ECMRu10 extends from the Vandenheckii to the lower Sartousiana ammonite Zones. Incidentally, Aptian-Albian nannofossils reworked from huge palaeokarstic Late Eocene Siderolithic deposits (Fig. 14e, f, Hooker and Weidmann 2000) were also reported in some samples of the Marnes de la Russille at Eclépens (De Kaenel in Godet 2006, p. 373/380; Early Albian Flabellites oblongus of nearly 10 μm in Clavel et al. 2007, Pl. 8, fig. H).
Samples EC51 and EC55-57 are very similar to the other samples of Eclépens and La Sarraz–Les Buis, they contain also the markers Assipetra terebrodentarius, Cyclagelosphaera margerelii, Nannoconus abundans and Zeugrhabdotus moulladei. EC55 is placed in the LK20B nannofossil Zone (Hauptblätterton facies of the North Sea Basin, Jeremiah 2001; within the Mid-Barremian Event/MBE of the Boreal Realm, Møller et al. 2019) and the lower Compressissima Zone with the acme of C. margerelii (LIO), which is particularly abundant. EC51 was sampled in the marly discontinuity between the limestones of the upper Pierre jaune de Neuchâtel and the basal Urgonien Jaune, it belongs to the lower LK20C nannofossil Zone and the upper Hugii Zone, with LO of Nannoconus abundans, HO of Palaeopontosphaera salebrosa, HO of Haqius ellipticus (Fig. 5), and large typical Barremian A. terebrodentarius (8 μm) much younger than the first occurrence of this species in the Late Hauterivian.
This section includes all species observed in LSBMRu1, taxonomic discussion of key taxa, the description of five new species (Biscutum jurensis, Flabellites eclepensensis, Palaeopontosphaera giraudii, Rhagodiscus buisensis and Vagalapilla rutledgei) and eight new combinations (Cyclagelosphaera sulcata, Glaukolithus choffatii, Palaeopontosphaera pinnata, Placozygus howei, Placozygus reticulatus, Placozygus trivectis, Placozygus xenotus, and Vagalapilla recta). Taxa considered in this section are listed by generic epithet. Only references not cited in Perch-Nielsen (1985) and Bown et al. (1998) are included in the reference list. All pictures are in cross-polarized light or in phase-contrast. Most of the taxa observed are illustrated in Figs. 7, 8, 9, 10, 11 with 71 species. The magnification for all pictures is × 2500. Dimensions of some taxa are indicated on bottom of the pictures.
Genus Assipetra Roth 1973
Discussion: Both small A. infracretacea infracretacea (< 7.5 μm) and large A. infracretacea larsonii (> 7.5 μm) (Fig. 7.22) were observed in sample LSBMRu1. Tremolada and Erba (2002) indicated that LO of A. infracretacea larsonii is of Aptian age, but these large forms are present in the late Early Barremian.
Discussion: Few specimens of A. terebrodentarius were observed. Some specimens observed have petaloid to globular structures. A part of a specimen may have globular elements and the other part petaloid elements (Fig. 7.18). Large (> 8 μm) A. terebrodentarius specimens are present in sample LSBMRu1 (Fig. 7.20). Forms of A. terebrodentarius (> 7.5 μm) have been included in the subspecies A. terebrodentarius youngii by Tremolada and Erba (2002). They indicated that LO of this subspecies is Aptian, but these large forms are present in the late Early Barremian. LO of A. terebrodentarius is in the Late Hauterivian Balearis Zone (Fig. 5) and its HO is in Early Campanian.
Genus Axopodorhabdus Wind and Wise in Wise and Wind 1977
Axopodorhabdus dietzmannii (Reinhardt 1965) Wind and Wise 1983
Genus Biscutum Black 1959 emend. De Kaenel and Bergen 1993
Biscutum constans (Górka 1957) Black in Black and Barnes 1959
Discussion: Only small forms less than 4.5 μm were observed and are included in B. constans. The large forms (between 4.5–6.6 μm) of Biscutum constans assigned to the subspecies Biscutum constans cavum described by Jeremiah (2001) from the North Sea Basin were not observed in samples from the Eclépens or La Sarraz–Les Buis quarries. Specimens of large Biscutum observed (Fig. 8.9–12) in LSBMRu1 have a size of 6.7 and 7.0 μm but with a central area closed by a plate and they belong to the new species B. jurensis.
Biscutum jurensis De Kaenel, n. sp.
Derivation of name: Named after the Jura Mountains.
Diagnosis: A medium-sized, broadly elliptical species of Biscutum with a thick rim, and a medium-sized central area closed by several elements forming a plate.
Differentiation: B. jurensis is differentiated from all other Biscutum species by its larger size and closed central area.
Dimensions: Length (L) = 5.0–8.0 μm, Width (W) = 4–6.5 μm.
Holotype: Fig. 8.9–10, L = 6.7 μm, W = 5.4 μm.
Paratype: Fig. 8.11–12, L = 7.0 μm, W = 5.8 μm.
Type locality: Les Buis quarry near La Sarraz, western Swiss Jura Mountains (coord. 2528.240/1168.170, map 1:25′000 of Switzerland).
Type level: Marnes de la Russille (sample LSBMRu1).
Discussion: Specimens observed of B. jurensis are between 5.7 μm (sample EC51) and 7.0 μm (sample LSBMRu1). P. elliptica is smaller and with an open central area and B. constans has a small central area and a spine base. Similar forms are observed by Burnett (1998, Pl. 6.5, figs. 22–23) in the Albian-Maastrichtian.
Range: B. jurensis is observed from the bottom sample EC51 (Early Barremian Hugii ammonite Zone) to sample EC72 (Late Barremian Vandenheckii ammonite Zone).
Discussion: Most researchers still call this form Discorhabus ignotus (e.g. Bown et al. 1998). The holotype of the species B. ignotus from Górka (1957) is a placolith with a distal shield composed of 14 elements joined along oblique sutures lines. The forms observed in LSBMRu1 have radial suture lines and correspond to the species B. rotatorium described by Bukry (1969). B. rotatorium is a small circular species with a distal shield composed of 16–23 elements, and an imperforate centre. The shields exhibit faint birefringence and the central area is slightly birefringent.
Genus Bownia Varol and Girgis 1994
Discussion: B. mutterlosei is the type species of the genus Bownia described by Varol and Girgis (1994). This genus includes murolith species with a biclyclic rim structure showing a spiraled (zeugoid) rim extinction pattern and a central cross structure. In B. mutterlosei the central cross is slightly off-axis. B. mutterlosei is differentiated from Vagalapilla by its rim extinction pattern with two equally birefringent cycles. Very rare specimens of B. mutterlosei are recorded in LSBMRu1. Crux (1989) observed the HO of B. mutterlosei in North Germany sections in the middle Elegans ammonite Zone. Bown et al. (1998) placed the HO of B. mutterlosei in the lower Cenomanian.
Genus Broinsonia Bukry 1969
Discussion: Very rare specimens of B. galloisii are recorded in LSBMRu1. B. galloisii is differentiated from B. matalosa by its smaller size (< 5.5 μm). In the sample from the Eclépens quarry, specimens are larger (> 6.5 μm). Specimen from LSBMRu1 (Fig. 9.11) and from the Eclépens quarry (Fig. 9.12) have the same structure with the same thin axial cross bar. Both specimens, small and medium-sized, are named B. galloisii in this study. Other names have been used in the literature for these forms. Thierstein (1973) and Crux (1989) used Vagalapilla matalosa. Bown (in Kennedy et al. 2000) tentatively classified the small form (< 5.5 μm) as Broinsonia galloisii and the medium-sized specimens as Broinsonia cf. galloisii. Jeremiah (2001) used Acaenolithus galloisii for small and medium-sized specimens. LO of B. galloisii is recorded by Jeremiah (2001) in middle LK19 Zone of the North Sea Basin. This is one of the key taxa to date the oldest age of LSBMRu1 together with the Tethyan species Flabellites eclepensensis (Fig. 5). B. galloisii occurs first in Boreal area and is reported later (base of the Aptian) in Tethyan area. Bown (1992) and Mutterlose (1992a) reported Broinsonia matalosa in the Indian Ocean down to the Valanginian of the Argo Abyssal Plain. This occurrence is unique to this region and B. galloisii/B. matalosa have not been observed in sediments older than late Early Barremian in North Sea Basin and in North Germany sections.
Genus Bukrylithus Black 1971
Bukrylithus ambiguus Black 1971
Genus Calcicalathina Thierstein 1971
Discussion: C. oblongata is very rare but present in LSBMRu1. Specimens observed have the typical high, narrow rim and a wide central granular area. C. erbae, the other Calcicalathina species present in Barremian strata, was not observed. LSBMRu1 belongs to the NC5 nannofossil Zone. The NC5 zone of Roth (1978, 1983) has been subdivided in 5 subzones (NC5A to NC5E) by Bralower (1987). HRO of C. oblongata is the subzonal marker of the NC5C/NC5D boundary in the Tethyan nannofossil zonation. Based on Gradstein et al. (2012), HO of C. oblongata is at 130.08 Ma and is correlated with the upper Nicklesi Zone. Above this level C. oblongata is scarce but present. In many sections these scarce occurrences of C. oblongata are always taken of evidence of reworking (e.g. Bralower 1987). Von Salis (1998) correlated HO of C. oblongata in Italy with the upper Hugii Zone and in France with the base of Moutonianum Zone. Thierstein (1973) and Bergen (1994) correlated in SW-France the HO of C. oblongata with the middle of Compressissima Zone. HO of scarce occurrence of C. oblongata is at the top of the Mountonianum Zone and specimens recorded in LSBMRu1 represent the uppermost range of C. oblongata (Fig. 5). The calibration of Gradstein et al. (2012) corresponds to HRO of C. oblongata. The NC5C/NC5D subzonal boundary is not moved to HO of C. oblongata recorded at the top of Moutonianum Zone. To keep some consistency in zonal scheme, HRO of C. oblongata used widely in many sections is retained as marker event for the NC5C/NC5D boundary. New HO of C. oblongata position also allows to correlate better the low latitude (Tethyan) and high latitude (Boreal) nannofossil zonal schemes. Both HO and HRO of C. oblongata events could be used to better improve the Barremian biostratigraphy.
Genus Conusphaera Trejo 1969
Conusphaera mexicana Trejo 1969 ssp. mexicana (cf. Bralower et al. 1989)
Conusphaera rothii (Thierstein 1971) Jakubowski 1986
Discussion: Bralower et al. (1994) noted that C. mexicana and C. rothii may represent preservational morphotypes. These two species are differentiated by the extinction lines of the core segments. In C. mexicana the segments have axial extinction lines and in C. rothii the extinction lines are curving. Both taxa are observed in LSBMRu1. C. rothii is frequent in the Valanginian—Early Barremian of the North Sea area, whereas C. mexicana is extremely rare or absent. As noted by Jeremiah (2001) in Zone LK19, only rare C. rothii are observed. Both species range in the Aptian: Early Aptian by Varol and Bowman (2019) and Late Aptian by De Kaenel and Bergen (1996, Tables 3, 4).
Genus Cretarhabdus Bramlette and Martini 1964
Cretarhabdus conicus Bramlette and Martini 1964
Cretarhabdus inaequalis Crux 1987
Discussion: Very rare specimens of Cretarhabdus with an irregular central grill are observed in samples EC55 and LSBMRu1 and are assigned to the species inaequalis. Crux (1987) described C. inaequalis from the Otto Gott section in North Germany and recorded it from the Late Hauterivian Gottschei ammonite Zone to the Late Barremian. Jeremiah (2001) recorded it up the Early Albian in North Sea Basin.
Genus Cyclagelosphaera Noël 1965
Cyclagelosphaera margerelii Noël 1965
Discussion: Rare specimens of C. margerelii are observed in LSBMRu1. According to Jeremiah (2001), the top of the interval with common/abundant C. margerelii is correlated with the end of Zone LK20 in the lower Elegans Zone and the uppermost Hauptblätterton facies (organic-rich laminated clays) recorded in North Sea Basin and Lower Saxony basin. Rare C. margerelii indicate therefore that LSBMRu1 is slightly younger than LK20 (upper Elegans Zone) and belongs to the Zone LK19. Sample EC55 from the Eclépens quarry contains common/abundant C. margerelii and no Reinhardtites scutula. This sample belongs to the subzone LK20B of Jeremiah (2001) (Figs. 5, 13), which is defined at the base by the LIO of C. margerelii and at the top by the LFO of Reinhardtites scutula.
Cyclagelosphaera puncta Black 1973
Discussion: Specimens of C. puncta observed in LSBMRu1 are small, less than 5 μm, with a distinct small opening in the central area. The holotype of Black (1973) from the Middle Albian is 7.2 μm. Cyclagelosphaera species with small central opening ranges from the Bajocian to the Hauterivian (C. lacuna, C. argoensis) and then from the Albian with C. puncta. HO of C. puncta is not yet constrained. Specimens observed in the Barremian are assigned to C. puncta based on the thin structure of the distal shield cycle.
Cyclagelosphaera rotaclypeata Bukry 1969
Discussion: Specimens of C. rotaclypeata recorded in sample LSBMRu1 are small (between 3.0 and 4.9 μm), but they have the typical large central area filled by radial elements forming a plate. Bukry (1969) described C. rotaclypeata in Tethyan areas for forms between 5–8 μm. LO of these larger forms of C. rotaclypeata is placed in the Albian by Burnett in Gale et al. (1996). Crux (1989) recorded C. rotaclypeata from the Late Hauterivian to the upper Elegans Zone in NW-European basins. The Boreal upper Elegans Zone is correlated with the top of the Tethyan Moutonianum Zone (Mutterlose et al. 2014). Jeremiah (2001) reported some rare occurrence of C. rotaclypeata in Late Barremian and Aptian sediments from the North Sea Basin.
Cyclagelosphaera sulcata (Forchheimer 1972) De Kaenel, n. comb.
Discussion: Cyclagelosphaera species differ from Markalius species by the bright birefringence of the distal shield. In Markalius the distal shield is non-birefringent. C. sulcata differs from other Cyclagelosphaera species by its elevated large central plug with angular sutures forming the inner tube cycle which exhibits a yellow birefringence. The species Cyclagelospheara shenleyensis described by Black (1973) from the Early Albian is similar to C. sulcata. C. sulcata is a Boreal species described by Forchheimer (1972) from Barremian sediments in the North Sea Basin. C. shenleyensis is also a Boreal species (Black 1973). LO of C. sulcata is placed in the Late Hauterivian and its HO at the base of the Late Barremian (Fig. 5) in the Elegans ammonite Zone (Fig. 5).
Genus Diazomatolithus Noël 1965
Diazomatolithus lehmanii Noël 1965
Discussion: Only rare specimens of D. lehmanii are observed in sample LSBMRu1. Jeremiah (2001) indicated that this species is abundant from the Early Valanginian to the Early Barremian Fissicostatum Zone and rare to the top of Elegans Zone. In the Late Barremian, D. lehmanii occurs very sporadicaly in North Sea Basin. In NW-European basins, Crux (1989) recorded the HO of D. lehmanii at the top of Elegans Zone. So, rare specimens of D. lehmanii indicate that LSBMRu1 can be correlated with the upper Elegans Zone, but the abundance of this species is quite variable in core/outcrop samples. Thus, the low abundance of this species may have no age significance.
Genus Diloma Wind and Čepek 1979
Diloma placinum Wind and Čepek 1979
Genus Ethmorhabdus Noël 1965
Discussion: Specimens observed of E. hauterivianus are the typical large forms, between 8 and 12 μm, with a finely perforated net and no central spine base. HO of E. hauterivianus was observed at the top of Hugii Zone in SE-France (Bergen 1994) and in the lower Denckmanii Zone of NW-European basins (Crux 1989). E. gallicus, the other similar species of Ethmorhabdus has a perforated net with only 4–5 cycles of perforations, but has also a central spine base. HO of E. gallicus is observed in the Late Tithonian (De Kaenel and Bergen 1996). According to recent and important calibrations of Boreal and Tethyan ammonites (Mutterlose et al. 2014), HO of E. hauterivianus in the Boreal lower Denckmanii Zone can thus be correlated with the Tethyan lower Vandenheckii Zone in the Jura Mountains (Fig. 5). E. hauterivianus is one of the key markers to date the top of the Marnes de la Russille in the La Sarraz–les Buis quarry. E. hauterivianus is present (rare to very rare) in almost all LSBM samples and is recorded to the top sample LSBMRu9 (Figs. 12, 14a). This indicates that the top of the MRu in the La Sarraz–les Buis quarry is in the lower Vandenheckii Zone. In the Eclépens samples, E. hauterivianus is present in sample EC72b, but not in sample EC79, which contains the LO of F. oblongus (Fig. 13).
Genus Flabellites Thierstein 1973
Flabellites eclepensensis De Kaenel, n. sp.
Flabellites oblongus in Aguado et al. 2014a, fig. 4.25–29.
Derivation of name: Named after the Eclépens quarry (Eclépens, VD), W-Switzerland.
Diagnosis: A small (3 to < 5.0 μm), normally elliptical species of Flabellites with a narrow central area spanned by a blocky, low angle diagonal cross. The two bars of the cross may fuse together and forms a single bridge with a middle suture line
Differentiation: F. eclepensensis is differentiated from the only other species of Flabellites, F. oblongus, by its smaller size and its blocky diagonal cross, which appears in cross-polarized light in early form as a bridge with a median suture.
Dimensions: Length (L) = 3 < 5.0 μm, Width (W) = 2.5 to 3.8 μm.
Holotype: Fig. 8.20–21, L = 4.0 μm, W = 3.2 μm.
Paratype: Fig. 8.22–23, L = 4.4 μm, W = 3.3 μm.
Type locality: Eclépens quarry nearby Eclépens, western Swiss Jura Mountains (Godet et al. 2010, coordinates 2531.256/1167.183, map 1:25′000 of Switzerland).
Type level: Marnes de la Russille (sample EC79).
Discussion: The three specimens of Flabellites oblongus illustrated by Aguado et al. (2014a) are small (between 4.3 and 5 μm) with a blocky bridge and correspond to Flabellites eclepensensis. Aguado et al. (2014a) correlated LO of these forms with the middle part of the uppermost Early Barremian Moutonianum Zone in the section of Arroyo Gilico (Southern Spain). This basic correlation is one of the primary data defining very precisely the age of LSBMRu1, which is not older than the middle Moutonianum Zone.
Range: According to the Tethyan nannofossil biozonation, F. eclepensensis ranges from late Early Barremian (Zone NC5D of Roth, 1978, 1983) to Late Aptian (Zone NC8). Because most of the bioevents belong to the Boreal Realm, LO of F. eclepensensis is better defined by using the North Sea Basin zonation (Boreal) of Jeremiah (2001) and can be placed within the upper Zone LK19. This zone is defined by HIO of Cyclagelosphaera margerelii (base) and HRO of Diazomatolithus lehmanii (top). Presently F. eclepensensis is recorded up to the Late Aptian in samples from the Angles outcrop in SE-France (E. De Kaenel, unpubl. pers. obs.).
Discussion: F. oblongus was not recorded in LSBMRu1, but observed in samples from the Eclépens quarry. F. oblongus has a central area spanned by a thin low angle diagonal cross aligned with the short axis. The distal shield is asymmetric with one shield broader than the other. Typical forms measure between 5–10 μm. The two specimens illustrated in Fig. 8.16–19 are from Late Aptian samples of the Angles outcrop and measure 5.6 and 5.9 μm. F. eclepensensis is smaller (3 < 5 μm) μm) with a narrow central area and a very blocky diagonal cross. In the early forms, the two bars of the diagonal cross are touching and appear in cross-polarized light as a bridge with a middle suture line. Bergen (1994) indicated with his text-fig. 2 the presence of early morphotypes of F. oblongus in the Late Hauterivian. These early specimens have almost no flange and a higher angle diagonal cross (De Kaenel and Bergen 1996), they correspond to the species Crucibiscutum trilensis described by Bown and Concheyro 2004 from the same Late Hauterivian interval.
Genus Glaukolithus Reinhardt 1964
Glaukolithus choffatii (Rood, Hay and Barnard 1973) De Kaenel, n. comb.
Basionym: Zeugrhabdotus choffati Rood, Hay and Barnard 1973, p. 369–370, Pl. 1, fig. 7.
Discussion: The genus Glaukolithus [type species: Glaukolithus diplogrammus (Deflandre 1954) Reinhardt 1964] includes species with faint birefringent rim and transerve bar. G. choffatii is a small species of Glaukolithus with a faint birefringent rim and faint transverse bar. The genus Zeugrhabdotus (type specimen: Z. erectus) includes species with bicyclic rim with a bright inner cycle and a bright bridge.
Glaukolithus diplogrammus (Deflandre in Deflandre and Fert 1954) Reinhardt 1964
Genus Gorkaea Varol and Girgis 1994
Gorkaea pseudoanthophorus (Bramlette and Martini 1964) Varol and Girgis 1994
Discussion: Gorkaea pseudoanthophorus is the type species for the genus Gorkaea (Varol and Girgis 1994). The genus Gorkaea includes murolith species with a sigmoid outer distal cycle, a thick inner distal cycle, and a bridge spanning the central area. Many authors incorrectly placed G. pseudoanthophorus within Zeugrhabdotus embergeri. The holotype of Zeugrhabdotus embergeri in Noël (1958) has a unicyclic sigmoid rim. Jeremiah (2001) recorded a short increase of G. pseudoanthophorus (his Parhabdolithus embergeri) in Zone LK19 (middle-upper Elegans Zone). Few G. pseudoanthophorus recorded also place LSBMRu1 in the same part of Zone LK19. This increase is indicated in Figs. 5, 6 as LIO and HIO of G. pseudoanthophorus (NS).
Genus Grantarhabdus Black 1971
Grantarhabdus meddii Black 1971
Genus Haqius Roth 1978
Haqius peltatus Bown 2005
Discussion: Bown (2005) described H. peltatus for small (< 6.5 μm), elliptical species of Haqius. The specimen illustrated (Fig. 11.23) has a length of 5.4 μm. Bown (2005) reported for H. peltatus a range from Berriasian to Albian. Larger forms are Haqius ellipticus (Grün in Grün and Allemann 1975) Bown 1992 emend. Bown 2005. In sample EC51, specimens of H. ellipticus are 9 μm. Bergen (1994) reported the HO of H. ellipticus in the bed ANG090 of the Barremian stratotype of Angles. This bed is located in the Colombiana Subzone at the upper part of the Hugii Zone (Reboulet et al. 2018, = Kiliani Zone in Vermeulen 2005). The HO of large forms, H. ellipticus, is placed at the top of the Early Barremian Hugii Zone. Also recorded in sample EC51 are specimens of Nannoconus abundans, which is used as subzonal marker by Jeremiah (2001) to define the base of subzone LK20C (Fig. 5).
Helenea chiastia Worsley 1971
Helenea staurolithina Worsley 1971
Genus Kokia Perch-Nielsen 1988
Kokia curvata Perch-Nielsen 1988
Discussion: The specimen of Kokia observed in LSBMRu1 (Fig. 7.26) has a rosette-shaped structure with 10 elements joined along curving suture. The terminations of the rays are rounded. The diameter is 10.2 μm. In XP (cross-polarized) light, this specimen displays a grey-yellowish birefringence. Kokia curvata described by Perch-Nielsen (1988) from Early Valanginian North Sea sediments has 8–10 rays with grey to yellowish birefringence and a diameter between 10–13.3 μm. Perch-Nielsen (1988) also illustrated a form, Kokia sp. 1, from the Late Hauterivian with 10 rays. Kokia cf. K. stellata observed by Bown (2005) in Late Hauterivian in the northwest Pacific Ocean has 12 rays but is smaller (7.0–8.5 μm) and has a low birefringence in XP light. The observed specimen is better described as K. curvata. Kokia curvata is abundant in Berriasian sediments from the North Sea Basin (Jeremiah 2001) and rare to the Late Valanginian. K. curvata is a typical Boreal taxon as T. septentrionalis. Some Boreal species are absent from the Early Barremian, but return in the uppermost Early Barremian Elegans Zone. The Early Barremian re-entry of the Boreal species T. septentrionalis was observed by Crux (1989) in North Sea and NW-European basins. The return of Boreal species is due to a transgressive interval establishing marine connections to the North (Crux 1989). The presence of Kokia species in the uppermost Early Barremian LSBMRu1 sediments follows the same pattern and also indicates establishments of marine connections to the North.
Genus Lithraphidites Deflandre 1963
Lithraphidites carniolensis Deflandre 1963
Genus Loxolithus Noël 1965
Loxolithus armilla (Black in Black and Barnes 1959) Noël 1965
Genus Manivitella Thierstein 1971
Manivitella pemmatoidea (Deflandre ex Manivit 1965) Thierstein 1971
Genus Micrantholithus Deflandre in Deflandre and Fert 1954
Micrantholithus hoschulzii (Reinhardt 1966) Thierstein 1971
Micrantholithus imbricatus (Manivit 1966) Varol and Bowman 2019
Discussion: Small forms of Micrantholitus, less than 7 μm, are present in sample LSBMRu1. Typical M. hoschulzii specimens are larger, between 7 and 12 μm. On the smaller specimens the outline of the segments varies from straight to rounded and the position of the sutures between the segments is not always in the angles. Varol and Bowman (2019) illustrated similar small forms of Micrantholithus (between 4.8–5.2 μm) from the Late Valanginian in northwestern Atlantic Ocean on DSDP Leg 76, Site 534A.
Micrantholithus obtusus Stradner 1963
Discussion: M. hoschulzii and M. obtusus are considered as Tethyan taxa (Bown 2005). Both species are observed in LSBMRu1, but they are rare and most of them show overgrowth, especially the large specimens.
Genus Nannoconus Kamptner 1931
Nannoconus abundans Stradner and Grün 1963
Figure 7.16, 21
Discussion: Rare specimens of N. abundans are observed in sample LSBMRu1 and in samples from the Eclépens quarry (EC51, EC57, EC72b). Specimens illustrated in Fig. 7.16 (side view) and in Fig. 7.21 (proximal view) are from sample EC51. On the side view, N. abundans has a clear upper flange and a medium-sized central canal. Similar forms in cross-polarized light have been illustrated by Bown et al. (1998) and Rückheim et al. (2006). SEM pictures of N. abundans (holotype of Stradner and Grün 1963) shows that the central canal is wider on the distal end and very narrow on the proximal end. LM picture of the proximal view of N. abundans (Fig. 7.21) also shows the very narrow end of the proximal canal. N. abundans is an endemic species only observed in NW-European basins (Bown et al. 1998). Very rare specimens observed in LSBMRu1 indicate the presence of a connection with the North Sea area. The presence of this connection is additionally supported by the presence of few T. septentrionalis, a typical Boreal–Arctic taxon (Crux 1989). The LO of N. abundans is a well-calibrated event and has been used in different zonal schemes. Crux (1989) placed this event at the base of the Rarocinctum ammonite Zone in North Sea Basin and North Germany sections. Jeremiah (2001) also placed this event at the base of the Rarocinctum Zone and used it to define the base of its subzone LK20C. The occurrences in sample EC51 of N. abundans together with P. salebrosa and H. ellipticus are the key taxa to place the base of the Urgonien Jaune in the lower part of subzone LK20C and in the Tethyan Early Barremian Hugii ammonite Zone (Figs. 3, 5, 13).
Nannoconus bucheri Brönnimann 1955
Nannoconus kamptneri kamptneri Brönnimann 1955
Nannoconus ligius Applegate and Bergen 1988
Discussion: N. ligius is a small, delicate species with 8 petaloid elements with a small central canal. Applegate and Bergen (1988) reported a Late Hauterivian–Early Barremian range. Bergen (1994) indicated that HO of N. ligius is Late Aptian in the section Angles of SE-France.
Nannoconus pseudoseptentrionalis Rutledge and Bown 1996
Discussion: N. pseudoseptentrionalis was described by Rutledge and Bown (1996) from the Early Barremian Elegans Zone in North Sea Basin. This species is differentiated from T. septentrionalis by its margin without regular-spaced elements and by the absence of the weakly birefringent flange observed in some T. septentrionalis specimens. LO of N. pseudoseptentrionalis occurs at the base of the Elegans Zone and its HO in the lower Denckmanii Zone. Specimens of N. pseudoseptentrionalis observed and illustrated by Jeremiah (2001) from the Early Aptian LK14 Zone have a wide central diaphragm and correspond to Farhania varolii (Jakubowski 1986) Varol 1992. N. pseudoseptentrionalis has not been reported outside of the North Sea Basin.
Nannoconus steinmannii steinmannii Kamptner 1931
Genus Orastrum Wind and Wise in Wise and Wind 1977
Orastrum perspicuum Varol in Al-Rifaiy et al. 1990
Genus Palaeopontosphaera Noël 1965 emend. De Kaenel and Bergen 1993
Discussion: The emendation of the genus Palaeopontosphaera by De Kaenel and Bergen (1993) is based on the type species of the genus, Palaeopontosphaera dubia Noël 1965. Biscutaceae species possessing an inner wall of non-imbricate elements with an imperforate, vacant, or spanned by a simple structure (cross or bar) are included in the genus Palaeopontosphaera. P. elliptica differs from other Palaeopontosphaera species by its distinct very thin inner wall and by the non-birefringent central plate. This plate can be observed in some specimens (Fig. 8.2). Biscutum constans is separated from P. elliptica based on the larger thickness of the rim and the smaller dark central area with a spine base.
Palaeopontosphaera giraudii De Kaenel, n. sp.
Derivation of name: Named after Dr Fabienne Giraud (Université Grenoble-Alpes, France), a nannopalaeontologist.
Diagnosis: A medium-sized, broadly elliptical species of Palaeopontoshaera with a thick rim and a medium-sized central area spanned by a thick birefringent axial cross structure.
Differentiation: P. giraudii is differentiated from P. salebrosa by its larger size and prominent central cross. Crucibiscutum hayi is also a medium-sized species that may belong to the genus Palaeopontosphaera. C. hayi is very similar to P. giraudii but the central axial cross is thin and there is a large stratigraphical displacement between these two species. The LO of C. hayi is placed at the base of the Albian by Bown et al. (1998).
Dimensions: Length (L) = 4.5–8.0 μm, Width (W) = 3.5–6.5 μm.
Holotype: Fig. 8.29, L = 6.6 μm, W = 5.3 μm.
Paratype: Fig. 8.30, L = 7.6 μm, W = 5.5 μm.
Type locality: Les Buis quarry near La Sarraz, western Swiss Jura Mountains (coordinates 2528.240/1168.170, map 1:25′000 of Switzerland).
Type level: Marnes de la Russille (sample LSBMRu1).
Discussion: Specimens observed are between 4.5 μm and 8.0 μm (Fig. 8.29–30). The presence of these medium-sized specimens of Palaeopontosphaera was also observed by Crux (1989) and Jeremiah (2001) in Early Hauterivian-early Late Barremian from the North Sea Basin. Jeremiah (2001) also recorded P. giraudii in the upper LK19 Zone and the lower LK18 Zone. The larger specimens recorded from LSBMRu1 correspond to the specimens recorded by Jeremiah (2001) in the interval including upper LK19-lower LK18 Zones. The HO of P. giraudii is observed in sample EC79. Jeremiah (2001) recorded the HO of P. giraudii in the lower LK18 Zone (Fig. 5).
Range: LO in Early Hauterivian Boreal Amblygonium ammonite Zone. HO in early Late Barremian Tethyan Vandenheckii ammonite Zone (Boreal early LK18 nannofossil Zone).
Palaeopontosphaera pinnata (Black 1971) De Kaenel, n. comb.
Discussion: The species pinnatus was recombined with the genus Sollasites by Perch-Nielsen (1984) and with the genus Crucibiscutum by Rutledge and Bown in Bown et al. (1998). Because of the structure of the rim with a thin bright inner distal cycle, this species is transferred to the genus Palaeopontosphaera following the emendation of the genus by De Kaenel and Bergen (1993). Two species of Palaeopontosphaera with central cross structure are present in LSBMRu1: P. pinnata and P. giraudii. P. pinnata is small, between 3 and 5 μm with a thin central cross weakly birefringent which does not fill the central area. Specimens observed are between 4.5 and 4.9 μm. P. salebrosa and P. giraudii are differentiated from P. pinnata by its larger central cross that practically fills the central area. P. pinnata was described by Black (1971) for large forms of Cruciplacolithus. The holotype, from the Hauterivian, is 12.6 μm. Crux (1989) illustrated a form (Pl. 8.2, fig. 9) from the Late Hauterivian of the North Sea Basin with a thin central cross and a length of 3.25 μm. Rutledge and Bown in Bown et al. (1998) used the specimen illustrated by Crux (1989) for their new combination Crucibiscutum pinnatus. The size of the holotype of Black (1971) is problematic and we are using the size, 3 to 5 μm, indicated by Young et al. (2019). Crux (1989) recorded P. salebrosa up to the Boreal upper Denckmanii ammonite Zone in NW-European basins, but he did not separate P. salebrosa from P. pinnata. HO of P. pinnata is placed in the Late Barremian Tethyan Sartousiana ammonite Zone (Fig. 5).
Discussion: Typical P. salebrosa specimens are small, between 3 and 5.5 μm with a birefringent central cross filling the central area. The holotype of Black (1971) is 5.4 μm and these forms are not observed above the basal Early Barremian Hugii Zone (Fig. 5). The HO of P. salebrosa is used by Jakubowski (1987) to define the top of the NLK13 Zone in North Sea area and is correlated with the middle Early Barremian Rarocinctum Zone by Crux (1989) and Bown et al. (1998). P. salebrosa is only observed in sample EC51 at the base of the UJ. The specimen illustrated in Fig. 8.28 is 4.4 μm with a narrow central area completely filled by the central cross. The presence of P. salebrosa in sample EC51 is one of the key taxa with N. abundans to place the base of the UJ in the lower part of subzone LK20C and in the Boreal Early Barremian Rarocinctum ammonite Zone, which corresponds to the Tethyan Early Barremian Hugii ammonite Zone. P. salebrosa is considered as a high-latitude bipolar species (Street and Bown 2000) and is typical of Boreal and Austral latitudes. P. salebrosa is very similar to Crucibiscutum hayi, but this latter species is Albian-Cenomanian (Burnett 1998).
Genus Percivalia Bukry 1969
Genus Perissocyclus Black 1971
Perissocyclus tayloriae Crux 1989
Genus Placozygus Hoffman 1970
Discussion: Species of the genus Placozygus are separated from species of the genus Zeugrhabdotus by their bicyclic structure of the rim exhibiting a spiral interference pattern. In Early Cretaceous species, the inner bright cycle is thin. In Late Cretaceous species, the inner and outer distal cycles of the rim have a more distinct spiral extinction pattern.
Placozygus howei (Bown in Kennedy et al. 2000) De Kaenel, n. comb.
Basionym: Zeugrhabdotus howei Bown in Kennedy et al. 2000, p. 643–644, fig. 31 i, j, e’, f’.
Discussion: The species howei is transferred to the genus Placozygus based on the bicyclic extinction pattern of the rim. In early specimens from the Barremian or Aptian the bicyclic pattern of the rim is still diffuse (Fig. 10.23). In Albian specimen (Lordia sp. A in Bergen 1998) the bright inner distal is more characteristic. Rare specimens of P. howei are present in LSBMRu1. LO of P. howei is placed by Bergen (1994) in the uppermost Early Barremian Compressissima and Moutonianum Zones (= Zygodiscus elegans in Bergen 1994).
Placozygus reticulatus (Black 1971) De Kaenel, n. comb.
Basionym: Zygodiscus reticulatus Black 1971, p. 420, Pl. 34, fig. 9.
Discussion: The species reticulatus is transferred to the genus Placozygus based on the bicyclic and sigmoid extinction pattern of the rim. The holotype of Black (1971) is a proximal view of a specimen observed in Early Barremian from the North Sea area with a transverse bridge supporting a finely perforated floor granular. Rare specimens of P. reticulatus are observed in LSBMRu1. In XP light, the floor on each sides of the bridge exhibits a bright extinction pattern, which differentiate this species from all other Placozygus species. Black (1971) indicated a range from Early Barremian to Late Albian in North Sea Basin.
Placozygus trivectis (Bergen 1994) De Kaenel, n. comb.
Basionym: Zeugrhabdotus trivectis Bergen 1994, p. 65, Pl. 1, figs. 26a-b, 27a-c.
Discussion: The species trivectis is transferred to the genus Placozygus based on the bicyclic and sigmoid extinction pattern of the rim. P. trivectis is differentiated from other Placozygus species by the structure of the transverse bridge composed of three fused elements. LO of P. trivectis is placed by Bergen (1994) in the Early Valanginian Campylotoxus Zone (= Neocomiensiformis and Inostranzewi Zones, Reboulet et al. 2014). Rare specimens of P. howei are observed in LSBMRu1. This species is described as being cosmopolite.
Placozygus xenotus (Stover 1966) De Kaenel, n. comb.
Basionym: Zygolithus xenotus Stover 1966, p. 149, Pl. 4, figs. 16–17, Pl. 9, fig. 2.
Discussion: The species xenotus is transferred to the genus Placozygus based on the bicyclic and sigmoid extinction pattern of the rim (Fig. 10.27). P. xenotus has a well-developed inner distal cycle showing a bright sigmoidal birefringence pattern. P. xenotus is differentiated from other Placozygus by the structure of the central bridge composed by two well-separeted elements. Rare specimens of P. xenotus are observed in LSBMRu1. LO of P. xenotus is placed by Bergen (1994) in the Early Valanginian Campylotoxus Zone (= Neocomiensiformis and Inostranzewi Zones, Reboulet et al. 2014).
Genus Reinhardtites Perch-Nielsen 1968
Reinhardtites scutula Bergen 1994
Discussion: R. scutula was identified as Zeugrhabdotus sisyphus by Crux (1989) and Zeugrhabdotus scutula by Jeremiah (2001). This species has a distinct elongated, diamond-shaped transverse bar and is the ancestral species of the genus Reinhardtites (Bergen 1994). A few (10 specimens per traverse) of R. scutula can be observed in LSBMRu1. Rare to few R. scutula are also observed in samples from the Eclépens quarry up to the top of the Marnes de la Russille (MRu), in sample ECMRu10 (Fig. 13). These observations are one of the key observations to date these samples. Both Crux (1989) and Jeremiah (2001) observed in North Sea Basin and NW-European basin an increase in abundance of this taxon from the base of Elegans Zone to the middle Denckmanii Zone. Jeremiah (2001) defined the base of LK20A Subzone and top of LK18 Zone by, respectively, LFO and HFO of R. scutula (Fig. 5). The increase in abundance of R. scutula in LSBMRu1 corresponds to the same increase event and therefore the Eclépens (EC) samples belong to the nannofossil LK18 Zone of Jeremiah (2001). The increase of R. scutula in the Boreal basins and MRu of the Jura Mountains is associated with influx of northern cold/more saline waters due to improvement of connections to the north (Crux 1989). HO of R. scutula is in the Early Santonian (Burnett 1998).
Genus Retecapsa Black 1971
Retecapsa angustiforata Black 1971
Retecapsa crenulata (Bramlette and Martini 1964) Grün in Grün and Allemann 1975
Discussion: The genus Retecapsa includes Cretarhabdids species with an axial cross and accessory lateral bars. Based on the original definition of the genus Retecapsa by Black (1971), only forms with eight openings are included in this genus. Grün in Grün and Allemann (1975) emended the genus to include forms with more than eight openings as R. crenulata (12 pores) or R. surirella (12–16 pores). R. surirella has a distinct central platform surrounded by 12–16 pores and has been included in the genus Cretarhabdus by Reinhardt (1970) or Thierstein (1971). The emendation of the genus Retecapsa by Grün in Grün and Allemann (1975) is followed in this study.
Retecapsa octofenestrata (Bralower in Bralower et al. 1989) Bown in Bown and Cooper 1998 or Bergen 1998 (N.B. Bown’s publication at 31/8/1998 is a little earlier to Bergen’s paper in the last volume of Géologie Méditerranéenne for 1998).
Genus Rhagodiscus Reinhardt, 1967
Rhagodiscus achlyostaurion (Hill 1976) Doeven 1983
Discussion: R. achlyostaurion was neither observed in LSBMRu1 nor in the Eclépens quarry samples. The rim of R. achlyostaurion is weakly bicyclic with a thin inner bright distal cycle. A bright circular spine is present in the centre of the central area. R. buisensis is differentiated from R. achlyostaurion by the presence of a spine base and the absence of the bright spine. Specimens larger than 6.5 μm are R. hamptonii and have a distinct bicyclic rim with an outer grey cycle and a thin inner bright cycle. The central area is larger with a small spine base and no spine. LO of R. achlyostaurion (Fig. 5) is younger than samples from the Eclépens quarry and is correlated with the middle of Feraudianus Zone (= upper Sartousiana Zone). An Aptian specimen from the Angles outcrop is illustrated in Fig. 10.7 to show the different spine structure compared to R. buisensis.
Rhagodiscus asper (Stradner 1963) Reinhardt 1967
Rhagodiscus buisensis De Kaenel, n. sp.
Derivation of name: Named after Les Buis quarry (La Sarraz, VD), W-Switzerland.
Diagnosis: A medium-sized species of Rhagodiscus with a weakly birefringent rim. The central area is narrow with a weakly birefringent small circular spine base and no developed spine.
Differentiation: R. buisensis is differentiated from R. achlyostaurion by the absence of a bright circular spine. Bown (in Kennedy et al. 2000) recorded specimens of R. buisensis as morphotypes of typical R. achlyostaurion. R. buisensis is also described to better detected/placed the LO of R. achlyostaurion.
Dimensions: Length = 5–6.5 μm, Width = 3.5–5 μm.
Holotype: Fig. 10.5, L = 5.1 μm, W = 3.6 μm.
Paratype: Fig. 10.6, L = 5.3 μm, W = 3.8 μm.
Type locality: Les Buis quarry near La Sarraz, western Swiss Jura Mountains (coordinates 2528.240/1168.170, map 1:25′000 of Switzerland).
Type level: Marnes de la Russille (sample LSBMRu1).
Discussion: Early morphotype of R. achlyostaurion (R. buisensis) were also recorded in the Eclépens quarry samples and these occurrences are important for biostratigraphy. LO of R. achlyostaurion occurs in the upper Sartousiana Zone (Fig. 5) and the presence only of specimens of R. buisensis indicates older samples. R. buisensis is an intermediate form between R. asper (granular plate) and R. achlyostaurion (granular plate with a thick, bright circular spine base).
Range: R. buisensis is not observed below the uppermost Early Barremian. Bown (in Kennedy et al. 2000), Herrle and Mutterlose (2003) and Giraud et al. (2018) reported R. buisensis (R. achlyostaurion no spine) in the Late Aptian and Early Albian.
Rhagodiscus eboracensis Black 1971
Rhagodiscus gallagheri Rutledge and Bown 1996
Discussion: R. gallagheri is a small species of Rhagodiscus (< 5 μm) with slightly convex or straight longer sides. R. gallagheri is neither observed in sample LSBMRu1 or in samples from the Moutonianum Zone. Its LO is recorded in sample LSBMRu5 or one sample as EC72b above the HO of C. oblongata and is present to the top of the LSBMRu samples and in the Eclépens samples EC72b/EC79 (Figs. 12, 13), which are in the early Late Barremian LK18 Zone. Rutledge and Bown (1996) placed the LO of R. gallagheri at the base of the Aptian. Aguado et al. (2014b) recorded R. gallagheri in the upper Barremian Sarasini Zone (Zone NC5E). De Kaenel in Godet et al. (2010) illustrated R. gallagheri from sample EC79 of the Eclépens quarry.
Rhagodiscus pseudoangustus Crux 1987
Rhagodiscus robustus Bown 2005
Rhagodiscus sageri Bown 2005
Genus Rotelapillus Noël 1973
Genus Sollasites Black 1967
Sollasites horticus (Stradner, Adamiker and Maresch in Stradner and Adamiker 1966) Čepek and Hay 1969
Discussion: The two species of Sollasites present in Barremian can be identified by their size when the central area structures are not preserved. S. lowei is a very small to medium-sized species with a medium-sized central-area (Fig. 8.13). S. horticus is a medium-sized species with a narrow rim and a large central-area (Fig. 8.15). S. horticus is a Boreal taxon. A short increase of S. horticus is observed by Jeremiah (2001) in the upper Zone LK19 associated with LO of B. galloisii. Crux (1989) observed in North Sea Basin the re-entry of S. horticus and T. septentrionalis. Both species range from the Jurassic to the Late Cretaceous.
Genus Tegulalithus Crux 1986
Tegulalithus septentrionalis (Stradner 1963) Crux 1986
Discussion: The re-entry of T. septentrionalis at the base of Elegans Zone was well observed and illustrated by Crux (1989) in North Sea Basin and NW-European basin. The same specimens are observed in sample from LSBMRu1 and are typical forms, similar to the holotype. The holotype of Stradner (1963) has a size of 7 μm with 18 elements. Many variations are observed. Smaller forms have a wider central tube and less elements (Fig. 7.6–8), but are still included in the same species. The smaller form has a size of 3.6 μm with 14 elements and a wide central tube (Fig. 7.8). These smaller specimens have been sometimes identified as Diazomatolithus lehmanii. Crux (1989, Pl. 8.2, fig. 7) illustrated a nice specimen of small T. septentrionalis (identified as D. lehmanii) from the middle Elegans Zone. On this SEM picture, the upper cycle (4 μm) and lower cycles (2.7 μm) are quite visible. The abundance of T. septentrionalis is relatively high (10 specimens per traverse) in LSBMRu1. Crux (1989) explained the re-entry of the Boreal species T. septentrionalis by the improvement of marine connections to the north during a transgressive period. He also associated this return with the increase of R. scutula. HO of T. septentrionalis in the Swiss Jura Mountains follows the calibration from Crux (1989) in the northwestern area of Europe (north Germany) and is placed in the middle Denckmanii Zone (Fig. 5) with very rare specimens observed in ECMRu10 sample (Fig. 13). The HFO of R. scutula is recorded by Crux (1989) just above the HO of T. septentrionalis. The total range of T. septentrionalis is recorded by some nannopalaeontologists as intra-Late Hauterivian, as per Bown et al. (1998) and Jeremiah (2001). And this is one of the best markers, with a very short range, used to zone the Late Hauterivian in many North Sea wells. For these nannopalaeontologists, the presence of T. septentrionalis in mid-Barremian is either due to reworking or attributable to the superficially similar Nannoconus pseudoseptentrionalis. Both species are present in sample LSBMRu1 (see also the last chapter "Discussion" below).
Genus Tegumentum Thierstein in Roth and Thierstein 1972
Tegumentum octiformis (Köthe 1981) Crux 1989
Discussion: T. octiformis is a typical endemic Boreal species not recorded in Tethyan areas. HO of T. octiformis is placed in the Late Barremian Bidentatum Zone (upper LK15 Zone) by Jeremiah (2001) in North Sea Basin.
Tegumentum stradneri Thierstein in Roth and Thierstein 1972
Genus Tranolithus Stover 1966
Tranolithus gabalus Stover 1966
Genus Tubodiscus Thierstein 1973
Tubodiscus burnettiae Bown in Kennedy et al. 2000
Discussion: T. burnettiae is a medium-sized species, between 6 and 8 μm. T. burnettiae is distinguished from T. jurapelagicus by the shape of the rim, broadly elliptical, its broader rim, and by its thicker inner distal cycle.
Discussion: Two species of Tubodiscus are present in LSBMRu1, T. burnettiae and T. jurapelagicus. T. burnettiae ranges from the Valanginian to the Albian and T. jurapelagicus from the Berriasian to the early Late Barremian (Fig. 5). Applegate and Bergen (1988) recorded the HO of T. jurapelagicus in the Barremian. T. jurapelagicus was not observed in sample EC79 from the Eclépens quarry from the Vandenheckii Zone. HO of T. jurapelagicus in sample LSMRu9 occurs between the HO of E. hauterivianus and the LO of F. oblongus and is correlated with the early Late Barremian Vandenheckii Zone. These two species of Tubodiscus are considered as cosmopolite species.
Genus Vagalapilla Bukry 1969
Discussion: Several genera (Staurolithites, Vekshinella and Vagalapilla) have been used to combine this group of muroliths with a central cross. De Kaenel and Bergen (1996) used the genus Vagalapilla based on the detailed description of the type species of the genus (V. imbricata of Gartner 1968) by Bukry (1969). The holotypes for the genus Staurolithites (Caratini 1963) and for the genus Vekshinella (Loeblich and Tappan 1963) are dubious. Caratini (1963) includes in this genus all circular and elliptical forms with an open central area spanned by all kind of central structure crosses. The type species for the genus Vekshinella (Ephippium acutiferrus of Vekshina 1959) has a short, slightly convex proximal spine and a long sharp distal spine and represents a very different group of forms.
Discussion: Following the combination from Lyulyeva (1980), the genus Vagalapilla Bukry (1969) is used herein for this species because of the questionable type species and holotype of genus Staurolithites. V. crux is differentiated from other Vagalapilla species by its thin rim and very thin, simple axial cross. The inner distal cycle of the rim is not visible in XP light.
Vagalapilla recta (Black 1971) De Kaenel, n. comb.
Basionym: Staurolithites rectus Black 1971, p. 419, Pl. 34, fig. 6.
Discussion: Genus Vagalapilla Bukry (1969) is used herein for this species because of the questionable type species and holotype of the genus Staurolithites. The rim of V. recta is similar to the rim of V. crux, but the central axial cross is larger with distinct axial suture lines. Black (1971) described V. recta from the Barremian of the North Sea Basin. Young et al. (2019) considered V. recta as a junior synonym of V. crux. But the structure of the axial cross of specimens of V. recta observed in sample LSBMRu1 is different from the axial cross of V. crux. The structure of the axial cross with the median suture line is also distinct on the holotype of Black (1971) and supports the splitting of these two species.
Vagalapilla rutledgei De Kaenel, n. sp.
Figure 9.8–10, 13
Eiffelithus? sp. 2 Covington and Wise 1987, p. 630, Pl. 2, figs. 7, 8, 9.
Derivation of name: Named after Dr David Rutledge (PetroStrat Ltd, Wales, United Kingdom), a nannopalaeontologist.
Diagnosis: A medium-sized species of Vagalapilla with a birefringent bicyclic rim and a broad inner distal cycle. The central area is almost closed by a broad birefringent axial cross bar with flaring terminations and median suture when observed at 45°.
Differentiation: V. rutledgei is differentiated from other bicyclic species of Vagalapilla by its broad birefringent axial cross. In V. mitcheneri, the other bicyclic Vagalapilla present in Barremian, the axial cross structure is different, distinctly flaring from the centre with a median suture at 0°, that does not fill the central area.
Dimensions: Length = 5–6.5 μm, Width = 3.5–5 μm.
Holotype: Figs. 9.8–10, L = 5.9 μm, W = 4.2 μm.
Paratype: Fig. 9.13, L = 5.1 μm, W = 3.8 μm.
Type locality: Eclépens quarry nearby Eclépens, western Swiss Jura Mountains (Godet et al. 2010, coordinates 2531.256/1167.183, map 1:25′000 of Switzerland).
Type level: Marnes de la Russille (sample EC79).
Discussion: Applegate and Bergen (1988) placed Eiffellithus sp. 2 in synonymy with their new species V. mitcheneri. The holotype of V. mitcheneri has a quite different central cross structure that specimens illustrated as Eiffellithus sp. 2 by Covington and Wise (1987). These specimens correspond to V. rutledgei.
Range: Rare specimens of V. rutledgei are recorded in LSBMRu1 and from EC51 to EC79. V. rutletgei (= Eiffellithus sp. 2) is very rare in uppermost Hauterivian, common in Early Barremian and rare in Late Barremian from the northwestern Atlantic Ocean on DSDP Leg 93 (Covington and Wise, 1987). The HO is near the top of the Barremian (Fig. 5 ).
Discussion: V. stradneri is differentiated from other Barremian Vagalapilla species with unicyclic rim by the shape of the rim, broadly elliptical and the thin axial cross supporting a bright spine base. The attachments of the axial cross to the rim show some enlargements.
Genus Watznaueria Reinhardt 1964
Watznaueria barnesiae (Black in Black and Barnes 1959) Perch-Nielsen 1968
Watznaueria biporta Bukry 1969
Watznaueria manivitiae Bukry 1973
Watznaueria ovata Bukry 1969
Watznaueria rawsonii Crux 1987
Discussion: W. rawsonii is a small (3.5–5 μm) species of Watznaueria with a normal width central area filled by a delicate and irregular grill. When preserved (Fig. 11.1), the grill is weakly birefringent. In sample LSBMRu1, W. rawsonii is relatively common, but much less than W. barnesiae, W. fossacincta and W. ovata. LO of W. rawsonii is placed by Crux (1989) in the Late Hauterivian Variabilis Zone in the Northern Germany basin. HO of W. rawsonii is not yet well constrained, but is present in the Late Barremian Sartousiana Zone (sample ECMRu10 from the Eclépens quarry).
Genus Zeugrhabdotus Reinhardt 1965
Zeugrhabdotus moulladei Bergen 1998
Discussion: LO of Z. moulladei (= Zeugrhabdotus sp. A) is placed by Bergen (1994) in the latest Hauterivian Angulicostata (= Ohmi) Zone (Fig. 5). Z. moulladei is differentiated from Z. erectus by the latitudinal extinction line on each sides of the transverse bar.
Zeugrhabdotus noeliae Rood, Hay and Barnard 1971
The very rich and well-preserved nannoflora presented in this study combined with those published by Godet et al. (2010) confirm the Barremian age of the MRu intercalations and therefore allow to refute the Late Hauterivian age as proposed by Clavel et al (2007) according to a poor number of 8 recognized nannoplankton species and some erroneous determinations or inaccurate time distributions. In Clavel et al. (2007, Pl. 8, fig. H), Crucibiscutum trilensis Bown and Concheyro 2004 is confounded with a typical, very large-sized Early Albian Flabellites oblongus of nearly 10 μm (Bown 2005, p. 30) obviously reworked from a Late Eocene palaeokarst (Siderolithic deposits), whereas early smaller specimens of F. oblongus recognized by Aguado et al. (2014a) correspond to Flabellites eclepensensis De Kaenel, n. sp. Crucibiscutum salebrosum is recombined into the species Palaeopontosphaera giraudii De Kaenel, n. sp. and Palaeopontosphaera pinnata, not at all "extremely rare or absent in deposits younger than Late Hauterivian" (Clavel et al. 2007, p. 1038). Moreover, Tegulalithus septentrionalis is absolutely not "restricted in Sayni-Ligatus Zone" as asserted by Clavel et al. (2007), but likewise a typical Barremian species well represented in the North Sea and NW-European basins (Mutterlose and Harding 1987; Crux 1989).
According to the new biostratigraphical nannofossil data presented in this study, all the orbitolinids from the Urgonian facies at Eclépens and La Sarraz–Les Buis assigned to the Late Hauterivian by Clavel et al. (2007, 2014) are indeed Barremian, notably with Early to early Late Barremian species of biostratigraphic importance such as Praedictyorbitolina busnardoi Schroeder, Clavel, Cherchi and Charollais 1999, Praedictyorbitolina claveli Schroeder 1994, Praedictyorbitolina carthusiana Schoeder, Clavel and Charollais 1990 and Valserina primitiva Schroeder, Charollais and Conrad 1969. An Early to Late Barremian age is therefore mainly applicable to the associated assemblages of other fossils and microfossils from the UJ–MRu complex including echinoids, brachiopods, benthic foraminifera, dasycladacean algae, ostracods, dinokysts (Clavel et al. 2007, p. 1037–1038, Pl. 7; Ghasemi-Nejad in Godet 2006, p. 364–369, Pls. 1–3), and spores and pollens (Ghasemi-Nejad in Godet 2006, p. 370/Pl. 4).
The studied sections of Eclépens and La Sarraz–Les Buis differ strongly regarding thickness and facies distribution, and are separated by faults within the Mormont–La Sarraz fault system in the extension of the Pontarlier fault system (Fig. 1a). Their differences of thickness and facies distribution as well as the hiatus of the Late Hauterivian deposits can be explained by synsedimentary tectonics of tilted blocks with differential subsidence generated by oblique-slip faults of the Pontarlier fault system (synsedimentary faults), a major and presumed very deep Late Palaeozoic Hercynian break until the crystalline basement of the Jura Mountains. This synsedimentary tectonic activity or "Barremian crisis" experienced his maximum activity with a "Hauterivian–Barremian tectonically enhanced unconformity" observed at the Hauterivian–Barremian transition in the Urgonian facies of the Western Alps of SE-France (Arnaud 1981: hauts-fonds du Trièves et du Vercors méridional, in Résumé, p. 2–3; Arnaud 2005, p. 13–15; Arnaud-Vanneau et al. 2005, p. 98, 123). Accordingly, the reddish cross-bedding of the sequence Ha7 at La Sarraz–Les Buis (Fig. 1b, f-g) can be interpreted as eroded and reworked Late Hauterivian ferruginous palaeosols or "terra rossa" developed in a hot and wet climate on emersion surfaces of tilted blocks. Similarly, coeval bauxite deposits with lacustrine sediments of this "Barremian crisis" are also known on the western and eastern Tethyan margins forming an extensive archipelago, in NE-Spain (Mojon 1996, 2002) and in NW-Romania (Dragastan et al. 1988), respectively.
The difference in thickness (35 m) of the UJ–MRu complex between Eclépens (47 m) and La Sarraz–Les Buis (12 m) seems considerable, but is misleading according to differential subsidence in fault-bounded compartments and deposition of very fine-grained and pyrite/organic-rich marls (MRu) with nannoflora at La Sarraz–Les Buis that certainly took place much slower (cf. Gallego-Torres et al. 2015 for comparable paleoenvironment of deposition) when compared to the very thick bioclastic UJ limestones with stromatoporoids well developed at Eclépens. Thus, the 44 m of late Early to early Late Barremian UJ with MRu deposits in the Eclépens quarry (with EC72b-79/ECMRu10 samples) overall correspond to the channel infilling of the La Sarraz–Les Buis quarry with a little more than 1 m thickness deposited in about 1.2 million years (Fig. 5), and characterized by a very slow MRu sedimentation rate as well as rich nannofloras (LSBMRu0-9 samples). The topmost interval EC79-ECMRu10 is not represented in the La Sarraz– La Sarraz–Les Buis quarry section, probably eroded and reworked by the prograding Urgonien Blanc (UB) facies.
Sedimentological and sequential interpretation of the La Sarraz–Les Buis section compared to the Eclépens section
According to the sedimentological and micropalaeontological features, the channel of the La Sarraz–Les Buis quarry with its very fine-grained marly MRu infilling (Fig. 1c) is interpreted as a deep tidal channel in an estuarine palaeoenvironment with turbid waters, well-known to be very rich in clayey sediments (Reynaud and Dalrymple 2011) and nutriments ideal for increased growth of nannoplankton (Cloern et al. 2014). MRu infillings of smaller channels in the NW cliff of the quarry (Fig. 1h-i) are interpreted as proximal linear dendritic ramifications (cf. Hughes 2011) of the distal larger channel analysed in this study (Figs. 1c, d and 3), observed approximately 20 m below and 250 m laterally at the base of the opposite SE cliff (slope around 8% and 3.5°). The depth can be estimated with the photic zone necessary for the nannoplankton photosynthesis, generally optimal down to a depth of 130–150 m in open marine environment (Gundersen et al. 1976; Winter et al. 2002), but only down to 1 to 50 m in estuaries or turbid coastal waters (Harding et al. 1987, p. 404).
The storm wave base indicates a maximum depth for sediment erosion and reworking, in the case of shallow epicontinental seas such as the Urgonian platform of the Jura Mountains, down to 50 ± 20 m according to Immenhauser (2009). As the UJ–MRu complex was deposited in a small coastal area particularly protected by offshore oolithic/bioclastic carbonate sand bars and stromatoporoid bioconstructions/rudist reefs, the MRu infilling of the channel at La Sarraz–Les Buis probably lied at an estimated palaeodepth of 40–50 m, coherent with other field observations reported.
The channel itself was incised on an erosional shallow surface by tidal currents at the beginning of the 3rd order sequence Ba2 in the late Early Barremian Moutonianum Zone (Fig. 3), then rapid subsidence generated a significant deepening with deposition of the very fine-grained MRu infilling corresponding to the Ba2 transgressive interval. This dynamic process of subsidence was still active in the beginning of the 3rd order sequence Ba3 (Vandenheckii Zone) and its boundary with sequence Ba2 is included within the MRu. Finally, the MRu infilling is overlaid by the middle Late Barremian prograding Urgonien Blanc (UB) facies of the Ba3 highstand system track (Godet et al. 2010).
The stratigraphical scheme of the Eclépens quarry section can be transposed to the La Sarraz–Les Buis quarry section (Figs. 1b, 3). Our sequence stratigraphy interpretation includes the sequences E2 and E3 previously defined by Godet et al. (2010) at Eclépens and located between the early Late Hauterivian Ha4 and early Late Barremian Ba3 sequences introduced by Arnaud (2005). The nannofossil datings clearly indicate two sequences Ba1′ and Ba2 within the interval corresponding to the highstand system track (HST) of sequence E2 introduced by Godet et al. (2010), in a series influenced by synsedimentary tectonics. Maximum flooding surface (MFS) E2 of Godet et al. (2010) distinctly denotes a sedimentary change, but we consider the massive bioclastic limestone bed with cross-stratification placed below as a shallow tidal bar preceding marly sediments with Early Barremian nannofloras EC55-57 in the transgressive system track (TST) of sequence Ba1′ (Pulchella and Compressissima Zones). Thus, we rather interpret mfsE2 as a sedimentary discontinuity or sequence boundary (SB) corresponding to SbB1′. Nannofossil dating of the marly sample EC72b also unequivocally shows the beginning of the early Late Barremian (Vandenheckii Zone) corresponding to the TST of Late Barremian sequence Ba3, above more calcareous beds of the presumed HST of late Early Barremian sequence Ba2.
According to the nannofossil data, the sequence boundary SbB3 therefore must be placed a little lower than the equivalent SbE3 positioned by Godet et al. (2010), and the two massive bioclastic limestone beds with cross-stratification below the early Late Barremian sample EC79 can also be interpreted as shallow tidal bars in the TST of sequence Ba3. Without precise nannofossil datings in this Early to early Late Barremian UJ series of Eclépens, there are objectively no absolute sedimentological criteria available to recognize and to interpret sequences with certainty.
At La Sarraz–Les Buis section, two marly superimposed Barremian sequences Ba2 and Ba3 including each an alternation of marls and more calcareous layers can be reported in the channelized MRu infilling. The late Early Barremian sequence Ba2 is well developed with very fine, dark grey and organic-rich marls and the nannofossil-rich key sample LSBMRu1 illustrating perfectly the Mid-Barremian Event (MBE) recognized in SE-Spain and the Tethyan Realm by Aguado et al. (2014a). The lower part of the UJ limestones with two massive beds (sequences Ha7 and Ba1) overlay the PJN facies above a major 3rd order discontinuity marked by a bioperforated hardground incrusted by large oysters. Two thick, whitish, roughly bioclastic/oolithic layers at the top of the sequences Ha7 (latest Hauterivian-earliest Barremian) and Ba1 (earliest Barremian) are interpreted as lagoonal deposits of highstand system tracks (HST) during stable sea level, and reddish cross-bedding in the middle part of Ha7 indicate a transgressive system track (TST) with reworked red palaeosols from emerged areas nearby (Fig. 1f-g, i).
The key marker Tegulalithus septentrionalis and the Barremian age of the Marnes de la Russille
In the Boreal Realm, the key marker Tegulalithus septentrionalis is well represented and abundant in the lower Late Hauterivian Speetonensis–Gottschei ammonite Zones (Crux 1989; Rutledge 1994; Jeremiah 2001) and LK24A-LK23-LK22 nannofossil Zones with an acme in a very small interval between 132.5–133 Ma corresponding to LK22 (upper Speetonensis and Gottschei Zones). In the Early Barremian of the northern Boreal basins (North Sea, Barents Sea), this species is absent (Rutledge 1994), or very rare in the upper-Early Barremian (transition Fissicostatum-Elegans ammonite Zones and LK20A-LK19 nannofossil Zones) and latest Hauterivian (Variabilis ammonite Zone, LK20D nannofossil Zone) and considered as reworked (Jeremiah 2001, p. 52, fig. 7 and p. 67–68, fig. 19). Mutterlose and Harding (1987, p. 199) first observed T. septentrionalis with Nannoconus abundans in the Early Barremian (Hauptblätterton facies, uppermost Fissicostatum and Elegans ammonite Zones, LK20B-LK20A-LK19 nannofossil Zones) from the Lower Saxony Basin of North Germany. Then, Crux (1989) clearly reported the mid-Barremian re-entry or return of T. septentrionalis (excluding reworkings) in the same Early Barremian interval of Boreal basins closer to continental margins (Lower Saxony Basin of North Germany, cf. Mutterlose and Harding 1987 and Mutterlose 1984; North Sea Basin with Speeton section in Eastern England, cf. Rawson and Mutterlose 1983; Norwegian coast).
In the Lower Saxony Basin, T. septentrionalis is present over a thickness of several meters and sometimes common (Moorberg, Gott, Aegi and Letter sections in Mutterlose and Harding 1987; Otto Gott brick pit at Sarstedt, samples in Crux 1989 according to Mutterlose 1984, p. 38, fig. 18), Mutterlose and Harding (1987, p. 188) even asserted that "Lithastrinus septentrionalis, which has been found in most samples, is probably another good marker species, possibly restricted to the Lower Barremian, for it has not been found further down in the uppermost Hauterivian", because the abundance of T. septentrionalis indeed reached 10% to 30% of the nannofossils present in samples from Gott, Aegi and Letter sections studied by these authors. The specimens of T. septentrionalis observed in both Speeton and Lower Saxony sections are typical but often not as well preserved than those from the early Late Hauterivian, thus Rutledge (1994) introduced the name Nannoconus pseudoseptentrionalis to include roughly similar nannoconids possibly confused in the corresponding Speeton section.
In the Tethyan Realm, T. septentrionalis is rare and reported in the early Late Hauterivian (Sayni and Ligatus ammonite Zones, Tethyan NC4B-NC5A nannofossil Zones), but not from the Early Barremian (Silvia Gardin pers. comm., Rutledge 1994, p. 122, 274; Gardin in prep., Mutterlose et al. 1996, p. 22; Gardin et al. 2000, short meeting abstract without pictures or detailed informations, quoted by Clavel et al. 2007 as a proof for the Late Hauterivan age of the Marnes de la Russille in the Jura Mountains; Gardin in Godet 2006, Annexe 5, fig. 1, p. 385), and was not mentioned by Bergen (1994).
In the Urgonien Jaune (UJ) and Marnes de la Russille (MRu) facies of the studied sections at Eclépens (EC) and La Sarraz–Les Buis (LSB) in the central Jura Mountains, T. septentrionalis is absent in the basal UJ and MRu levels (samples EC51, EC55-57) and its re-entry is observed just above in younger MRu intercalations (samples LSBMRu0-9), the specimens observed are well preserved and identical to the early Late Hauterivian Boreal material. Moreover, typical Late Hauterivian nannofossil markers (cf. Bergen 1994) were not observed in the MRu intercalations, but T. septentrionalis can be associated with Early Barremian species as Broinsonia galloisii and Nannoconus abundans in the lower MRu intercalations (LSBMRu0-9). In the early Late Barremian, T. septentrionalis is associated with typical Flabellites oblongus in the upper MRu intercalations (samples EC79-ECMRu10). So, T. septentrionalis from the MRu must be reported to Barremian and not to early Late Hauterivian, as in the Lower Saxony Basin and in the Speeton section.
Considering the palaeontology, an Early Barremian age for the basal MRu is supported by a Tethyan ammonite of the genus Pseudometahoplites firstly occurring in the Compressissima Zone and determined with certainty according to Vermeulen (2007, p. 91–92, Pl. 1). No Late Hauterivian ammonites have such a small size and very particular morphology. According to the regional geology and sedimentology in the Jura Mountains, there is no possibility of reworked Late Hauterivian nannofloras in the MRu intercalations, because the underlying Early–?Late Hauterivian Pierre jaune de Neuchâtel (PJN) is mostly constituted by massive limestones with shallow oolithic and bioclastic facies of high energy. These deposits with glauconite and rare marly layers are not at all favourable to the development and good preservation of nannofloras (cf. Godet et al. 2010 and Mojon et al. 2013 for the sedimentology and stratigraphy at the Hauterivian–Barremian transition between PJN and UJ). The two Hauterivian ammonites Lyticoceras nodosoplicatum Busnardo and Thieuloy 1989 and Cruasiceras cruasense (Torcapel 1884) recorded in this study from the basal UJ facies (marly layer with earliest Barremian nannoflora EC51 and limestones with glauconite directly above) are undoubtedly reworked from the shallow-water Early–Late Hauterivian PJN carbonates due to their identical infill.
A Late Hauterivian age for LSBMRu1 (in deposits locally generated by synsedimentary tectonic shifts) implies that only one metre of MRu with LSBMRu0-9 at La Sarraz–Les Buis would cover a period of more than 4 million years from the early Late Hauterivian to the early Late Barremian, absolutely without any apparent sedimentary discontinuity in a perfectly similar and regular deposit with the early Late Barremian sample LSBMRu5 located only 40 cm above LSBMRu1. Also, very problematic are notably the much greater MRu thickness of 44 meters at Eclépens (Fig. 3, only 2 km nearby) or several tens of metres in other parts of the central Jura Mountains, and the contradiction with the Early Barremian age of the ammonite Pseudometahoplites sp. juv. from the basal MRu intercalation.
The sudden re-entry of the species observed by Crux (1989) in the Early Barremian of the southern Boreal Realm can also perfectly be explained in the MRu of the central Jura Mountains by its absence in the basal Barremian (EC 51, 55–57) followed by a sudden occurrence and frequency higher up in the Early Barremian (LSBMRu0 and LSBMRu1, respectively). Palaeoecological and palaeoenvironmental changes could maybe explain its unexpected re-entry in the Early Barremian of the southern Boreal Realm and its sudden abundance in the MRu of the Jura Mountains, geographically located not far away in the northwestern Tethyan area.
Early Barremian occurrences of T. septentrionalis in Boreal basins far away from each other (Lower Saxony Basin/North Germany, North Sea Basin/Eastern England, Norwegian coast) correspond to a biological event (and not to reworkings), as also observed by this study in the Jura Mountains. According to these data, T. septentrionalis had never completely disappeared from the Boreal Realm after its acme in the early Late Hauterivian and always remained present but very rare with a highly dispersal and a very low frequency, almost undetectable in drill cores of open sea basins. A new proliferation at the end of the Early Barremian indicates palaeoenvironmental changes with a return of better ecological conditions for this species, becoming adapted preferably to higher temperate and shallower waters of more confined basins along the continental margins of the Boreal Realm. The HO of T. septentrionalis according to Crux (1989, fig. 8.7, p. 158–159 and figs. 8.12–8.13, p. 166–167) and Jeremiah (2001, fig. 7, p. 52) is also not exactly the same was recognized at Eclépens the uppermost LK19 nannofossil Zone/Elegans ammonite Zone (North Sea Basin/Speeton section) and the LK18 nannofossil Zone/lower Denckmanii ammonite Zone (Lower Saxony Basin). Our study likewise indicates that the species disappeared a little later (middle Denckmanii Zone or lower Sartousiana Tethyan ammonite Zone) at the NW-Tethyan margin.
These interpretations are highly coherent with the Mid-Barremian Event (MBE) reported herein and following the tectonic synsedimentary activity of a "Barremian crisis" at the Hauterivian–Barremian transition (Adatte et al. 2005, p. 13–15, 98, 123). Therefore, the total biostratigraphical range of Tegulalithus septentrionalis is from the early Late Hauterivian to the early Late Barremian (albeit discontinuous from a practical biostratigraphy perspective) over more than 4 million years, its geographical distribution in Europe covers mainly the Boreal Realm and the NW-Tethyan area (Jura Mountains), it is typically a Boreal and also Austral (Late Hauterivian from Irian Jaya/Indonesia, Varol 1992) species.
The Urgonien Jaune (UJ) and Marnes de la Russille (MRu) facies can be dated locally in the central Swiss Jura Mountains to the earliest to early Late Barremian with abundant nannofloras including a mixture of Tethyan and Boreal taxa, as well as a Tethyan ammonite. The basal marls and limestones of the UJ have provided at Eclépens an Early Barremian nannoflora (Boreal LK20C and Tethyan NC5C nannofossil Zones) with reworked late Early to early Late Hauterivian ammonites as Lyticoceras claveli (Busnardo and Thieuloy 1989) and Cruasiceras cf. cruasense (Torcapel 1884). At Montcherand (Gorges de l'Orbe), the lowermost marly layer of the MRu located 20 m below the UJ facies top have yielded a Mid-Barremian ammonite Pseudometahoplites sp. juv. (Compressissima to Vandenheckii Zones, Early to Late Barremian transition), and several MRu marl layers at Eclépens and La Sarraz–Les Buis are characterized by Early to early Late Barremian nannofloras (Boreal LK20B to LK18 and Tethyan NC5C-NC5D nannofossil Zones).
At La Sarraz–Les Buis section, these nannofloras allow very accurate and reliable correlations with the Tethyan and Boreal biozonations of ammonites and nannofossils from the late Early Barremian to early Late Barremian, and as a consequence, the Tethyan Moutonianum to Sartousiana ammonite Zones within NC5D nannofossil Zone can be very precisely correlated to the Boreal Elegans/Denckmanii ammonite Zones and LK19-LK18 nannofossil Zones. The MRu nannofloras are dominated by Boreal species indicating active water circulation and exchanges between the southern temperate Tethys Ocean and northern colder Boreal basins, through presumed straits crossing a northern "Rheno-Bohemia" landmass outlined by Mutterlose (1992b, fig. 5) and Wulff et al. (2020, fig. 1). The very fine dark grey and organic-rich MRu marly layers with nannofossil-rich key samples EC55 and LSBMRu1 belong to the late Early Barremian sequences Ba1′ and Ba2 (cf. sequence stratigraphy of Arnaud 2005 and Godet et al. 2010) and characterize the Mid-Barremian Event (MBE) identified in Europe and Middle East (Coccioni et al. 2003; Aguado et al. 2014a, b; Mahanipour and Eftekhari 2017; Wulff et al. 2018; Møller et al. 2019). The biostratigraphical and sequential data of the MRu imply that the overlaying Urgonien Blanc (UB) facies of the central Jura Mountains starts in the middle Late Barremian (Sartousiana Zone). In the southern Jura Mountains (SE-France), the deeply karstified UB top is overlied by the Poet Beds of the Perte-du-Rhône, which delivered a Tethyan ammonite Martelites sp. juv. (Sarasini Zone) of the Latest Barremian (Pictet et al. 2019).
The "Hauterivian–Barremian tectonically enhanced unconformity" in the Western Alps of SE-France (Adatte et al. 2005) was recognized at Eclépens/La Sarraz–Les Buis corresponding to a hiatus of Late Hauterivian sediments due to erosion (and formation of red palaeosols with "terra rossa" on emerged tilted blocks), reworked in the basal Early UJ deposits or not having been deposited. This event marked the climax of a "Barremian synsedimentary tectonic crisis" with low sea level, linked to global tectonics marked by active strike-slip and oblique-slip faults inducing block tilting during the Late Hauterivian-Early Barremian. The Marnes de la Russille (MRu) facies document the MBE locally at Eclépens and La Sarraz–Les Buis sections. Finally, the MBE (MRu within UJ) and the early Late Barremian UB facies of the Jura Mountains can now be correlated with the Helvetic shelf (northern Swiss Alps, Eastern Switzerland), where the MBE (Pictet et al. 2018) occurs in the Moutonianum Zone of the Drusberg Member/Tierwis Formation (SbB2, sequence Ba2) and the Schrattenkalk Formation begins in the Vandenheckii Zone with massive UB facies of the Lower Schrattenkalk Member (SbB3, sequence Ba3) according to Bonvallet et al. (2019).
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The authors thank a lot Mr Rui Esteves and Mr Matthieu Honorat (Lafarge-Holcim, Eclépens) for the ammonites collected in the Urgonien Jaune of the Eclépens quarry, Dr Didier Bert (Réserve naturelle nationale géologique de Haute-Provence, Digne-les-Bains) and Dr Jean Vermeulen (Barrême) for the identification of the ammonites from the Urgonien Jaune, Prof. Dr Peter Oliver Baumgartner (UNIL, Lausanne) and Dr André Piuz (Natural History Museum, Geneva) for the optical and SEM microphotography, as well as Prof. Dr David Watkins (University of Nebraska, Lincoln), Dr Jason Crux (San Antonio, Texas) and Dr David Bord (Houston, Texas) for their comments and improvements about the content and the text of the manuscript. Many thanks also to the editor Dr Daniel Marty, the associate editor Dr Susanne Feist-Burkhardt and the journal reviewers Dr David Rutledge (PetroStrat Ltd, Wales, UK), Prof. Dr Thierry Adatte (UNIL, Lausanne), Dr Alain Morard (Swisstopo, Wabern) and Dr Fabienne Giraud (University Grenoble-Alpes), who have kindly revised our manuscript. To all of them, we are very grateful and express our heartfelt thanks.
The authors declare that they have no competing interests.
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De Kaenel, E., Mojon, PO. & Pictet, A. New biostratigraphical data (calcareous nannofossils, ammonites) and Early to Late Barremian transition in the Urgonien Jaune facies and Marnes de la Russille complex of the Swiss Jura Mountains. Swiss J Palaeontol 139, 6 (2020). https://doi.org/10.1186/s13358-020-00209-5
- Urgonian facies
- Jura Mountains