Composition and significance of the Katian (Upper Ordovician) conodont fauna of the Vaux Limestone ('Calcaire des Vaux') in Normandy, France.
The Late Ordovician limestone unit exposed locally in continental Europe has long been known as being the only significant calcareous deposit in Ordovician successions otherwise dominated by siliciclastic sediments. Its thickness varies from a few centimetres (e.g. in Germany: Ferretti & Barnes 1997) to some dozens of metres or more (e.g. in Spain: Del Moral & Sarmiento 2008). Shelly fossils such as trilobites and brachiopods, echinoderms and bryozoans are generally abundant. Conodonts have been reported as well from several localities (e.g. Knupfer 1967; Serpagli 1967, both using form taxonomy). Sweet & Bergstrom (1984) made the first attempt of a global assessment of the conodont fauna from continental Europe identifying a specific Mediterranean Province, distinct from the approximately coeval British and Baltoscandic provinces, and documented there two different biofacies: the dominant Sagittodontina robusta-Scabbardella altipes biofacies (Spain, northwestern France and Thuringia) and the Hamarodus brevirameus-Dapsilodus mutatus-Scabbardella altipes (HDS) biofacies (Carnic Alps). Sardinia was later assigned to the same HDS biofacies (Ferretti & Serpagli 1999), suggesting that this area and the Carnic Alps in Katian time occupied a lower latitude as the same biofacies had been reported in the British and Baltoscandic provinces (Sweet & Bergstrom 1984). More recently, several papers have been published establishing the age of these European faunas in terms of the new global classification of the Ordovician System (e.g. Bergstrom et al. 2009). For a review of these studies, see Ferretti et al. (2014a).
The purpose of this paper is to briefly describe, discuss and establish the age of a new conodont fauna that has recently been recovered from the Vaux Limestone ('Calcaire des Vaux') in southern Normandy, northern France.
Although Ordovician and Silurian rocks are well represented in France, they are predominantly developed in clastic facies with only rare limestone occurrences. Different palaeogeographic regions have been documented. Particularly significant is the Armorican Massif in northwestern France (Fig. 1A), as the Palaeozoic series exposed there played a crucial role in the sedimentary and faunal evolution of the Gondwana margin (Vidal et al. 2011).
As regards the Upper Ordovician exposed in southern Normandy, based on conodonts and other fossils, the Vaux Limestone as well as limestone olistoliths in the overlying 'Tillite de Feugueroles' ('Pelites a fragments') were dated as Ashgillian (Weyant et al. 1977), an age later confirmed by chitinozoans (Babin et al. 1988). Conodonts were reported in form taxonomy, but no description or illustration of the elements was provided. The 'Calcaire de Rosan' (Rosan Formation) in Brittany, which traditionally has been regarded as coeval with the Vaux Limestone (Fig. 2), has also yielded a conodont fauna described by Lindstrom & Pelhate (1971) and Paris et al. (1981). A latest Ordovician Hirnantian brachiopod fauna from Camaret (Crozon Peninsula) has also been reported by Melou (1987).
The limited natural outcrop, located 2 km SW of Saint-Hilaire-la-Gerard in the Sees syncline (Fig. 1B) and described earlier by Weyant et al. (1977), was restudied and sampled for conodonts during fieldwork in 2006 and 2007. A calcareous succession is exposed there in a discarded quarry that is now part of the Normandie-Maine Regional Natural Park. It represents a single 1-m-thick bed that has been faulted and repeated several times in the diverse spots of the little outcrop, with erosion surfaces present both below and above the Vaux Limestone, indicating gaps in the succession (Avoine et al. 2011). The unit consists of hard massive micritic limestone without any distinct macrofossils exposed. The dominant microfacies in the conodont-productive intervals consists of a bryozoan-echinoderm packstone with subordinate trilobites, gastropods and brachiopods. A distinctive iron ooid horizon was also located in a single exposure. This ferruginous level represents a widespread and recurrent time-specific facies known from the Upper Ordovician as well as from other specific intervals in the Palaeozoic (Brett et al. 2012).
A total of 13 levels were sampled and more than 90 kg of limestone was processed in formic acid using standard methods of conodont extraction. All samples were productive and yielded abundant conodonts. Lithological samples, residues and conodont elements are housed in the 'Inventario Paleontologia Universita di Modena e Reggio Emilia-IPUM' at the Dipartimento di Scienze Chimiche e Geologiche, Universita degli Studi di Modena e Reggio Emilia, Modena, Italy.
All samples produced conodonts. Brachiopods, bryozoans, ostracodes, gastropods and silicified echinoderm fragments were found as well. An unexpectedly abundant collection of conodonts of several thousand elements representing 12 multielement taxa was recovered. Preservation of specimens is highly variable, ranging from well-preserved specimens to more or less encrusted elements. The conodont specimens exhibit a CAI (Colour Alteration Index; cf. Epstein et al. 1977) of 4-5, indicating a heating of 300-400[degrees]C. No significant change in the composition of the conodont fauna through the study material was observed. The following taxa were identified:
Amorphognathus duftonus Rhodes, 1955
Amorphognathus ordovicicus Branson & Mehl, 1933
Dapsilodus mutatus (Branson & Mehl, 1933)
Eocarniodus gracilis (Rhodes, 1955)
Hamarodus brevirameus (Walliser, 1964)
Icriodella cf. superba Rhodes, 1953
Istorinus erectus Knupfer, 1967
Panderodus gracilis (Branson & Mehl, 1933)
Sagittodontina robusta Knupfer, 1967
Scabbardella altipes (Henningsmoen, 1948)
Amorphognathus and Scabbardella are dominating the fauna but Hamarodus and Sagittodontina are also common, with the former being abundant in some intervals. Remarkably, the Vaux fauna contains Hamarodus brevirameus, which appears to be absent in the Rosan fauna from Brittany (Lindstrom & Pelhate 1971; Paris et al. 1981). Simple-cone taxa (Dapsilodus, Panderodus) are less frequent. The presence of A. ordovicicus, A. duftonus and Sagittodontina robusta indicates that the fauna represents the A. ordovicicus Zone and is possibly of middle Katian age (Stage Slices 3-4 of Bergstrom et al. 2009). Similar co-occurrences of A. ordovicicus and A. duftonus are also documented in continental Europe from the Carnic Alps (e.g. Serpagli 1967; Bagnoli et al. 1988; Ferretti & Schonlaub 2001), Sardinia (Ferretti & Serpagli 1991, 1999), Poland (Dzik 1999), Spain (Ferretti 1992; Del Moral & Sarmiento 2008) and possibly Bohemia (Ferretti 1998). The Vaux conodont fauna strikingly differs in diversity and composition from coeval middle-upper Katian faunas from the United Kingdom, such as the Sholeshook Limestone from South Wales (Ferretti et al. 2013, 2014a) and the Keisley Limestone of northern England (Rhodes 1955; Bergstrom & Ferretti, in press) and the Portrane Limestone of Ireland (Ferretti et al. 2014b).
The composition of the conodont fauna indicates that it represents the Sagittodontina robusta-Scabbardella altipes biofacies of Sweet & Bergstrom (1984), which is characteristic of this limestone interval in the Upper Ordovician of continental Europe.
Acknowledgements. The authors would like to thank M. Robardet for providing detailed information for locating the outcrop, and C. Corradini, S. Gouwie and P. Serventi for their help in the 2006 conodont sampling. We acknowledge useful comments on the manuscript by Guillermo Albanesi and Peep Mannik. M. Tonelli (Centro Interdipartimentale Grandi Strumenti CIGS, Modena, Italy) and M. Barbieri are recognized for the skilled assistance during SEM investigations and figure preparation, respectively. This paper is a contribution to IGCP Project 591 'The Early to Middle Palaeozoic Revolution--Bridging the Gap between the Great Ordovician Biodiversification Event and the Devonian Terrestrial Revolution'.
Avoine, J., Dugue, O., Dupret, L. & Huteau, M. 2011. Etude geologique de la carriere des Vaux (Saint-Hilaire-la-Gerard, Orne). Association Patrimoine geologique de Normandie, Rap. Et., 47 pp.
Babin, C., Feist, R., Melou, M. & Paris, F. 1988. La limite Ordovicien-Silurien en France. Bulletin of the British Museum of Natural History (Geology), 43, 73-79.
Bagnoli, G., Ferretti, A., Serpagli, E. & Vai, G. B. 1988. Late Ordovician conodonts from the Valbertad Section (Carnic Alps). Giornale di Geologia,
Bergstrom, S. M. & Ferretti, A. Conodonts in the Upper Ordovician Keisley Limestone of northern England: taxonomy, biostratigraphical significance, and biogeographic relationships. Papers in Palaeontology, doi 10.1002/spp2.1003 [in press].
Bergstrom, S. M., Chen, X., Gutierrez-Marco, J.-C. & Dronov, A. 2009. The new chronostratigraphic classification of the Ordovician System and its relations to major regional series and stages and to 513C chemostratigraphy. Lethaia, 42, 97-107.
Branson, E. B. & Mehl, M. G. 1933. Conodonts from the Maquoketa-Thebes (Upper Ordovician) of Missouri. University of Missouri Studies, 8, 121-132.
Brett, C. E., McLaughlin, P. I., Histon, K., Schindler, E. & Ferretti, A. 2012. Time-specific aspects of facies: state of the art, examples, and possible causes. In Time-Specific Facies: the Colour and Texture of Biotic Events (Ferretti, A., Histon, K., McLaughlin, P. I. & Brett, C. E., eds), Palaeogeography, Palaeoclimatology, Palaeoecology, 367-368, 327-339.
Del Moral, B. & Sarmiento, G. N. 2008. Conodontos del Katiense (Ordovicico Superior) del sector meridional de la Zone Centroiberica (Espana). Revista de Micro paleontologia, 40, 169-245.
Dzik, J. 1999. Evolution of Late Ordovician high-latitude conodonts and dating of Gondwana glaciations. Bollettino della Societa Paleontologica Italiana, 37, 237-253.
Epstein, A. G., Epstein, J. B. & Harris, L. D. 1977. Conodont color alteration--an index to organic metamorphism. U.S. Geological Survey Professional Paper, 995, G1-G27.
Ferretti, A. 1992. Biostratigrafia a conodonti del margine settentrionale del Gondwana (Ordoviciano sup.-Ashgill). Unpublished Ph.D. thesis, University of Modena, 281 pp.
Ferretti, A. 1998. Late Ordovician conodonts from the Prague Basin, Bohemia. In Proceedings of the Sixth European Conodont Symposium (ECOS VI) (Szaniawski, H., ed.), Palaeontologia Polonica, 58, 123-139.
Ferretti, A. & Barnes, C. R. 1997. Upper Ordovician conodonts from the Kalkbank limestone of Thuringia, Germany. Palaeontology, 40, 15-42.
Ferretti, A. & Schonlaub, H. P. 2001. New conodont faunas from the Late Ordovician of the Central Carnic Alps, Austria. Bollettino della Societa Paleontologica Italiana, 40, 3-15.
Ferretti, A. & Serpagli, E. 1991. First record of Ordovician conodonts from southwestern Sardinia. Rivista Italiana di Paleontologia e Stratigrafia, 97, 27-34.
Ferretti, A. & Serpagli, E. 1999. Late Ordovician conodont faunas from southern Sardinia, Italy: biostratigraphic and paleogeographic implications. In Studies on Conodonts: Proceedings of the Seventh International Symposium on Conodonts (Serpagli, E., ed.), Bollettino della Societa Paleontologica Italiana, 37, 215-236.
Ferretti, A., Bergstrom, S. M. & Barnes, C. R. 2013. Data from: Katian (Upper Ordovician) conodonts from Wales. Dryad Digital Repository. http://dx.doi.org/10.5061/dryad.j673f.
Ferretti, A., Bergstrom, S. M. & Barnes, C. R. 2014a. Katian (Upper Ordovician) conodonts from Wales. Palaeontology, 57, 801-831.
Ferretti, A., Bergstrom, S. M. & Sevastopulo, G. D. 2014b. Katian conodonts from the Portrane Limestone: the first Ordovician conodont fauna described from Ireland. Bollettino della Societa Paleontologica Italiana, 53, doi:10.4435/BSPI.2014.11.
Henningsmoen, G. 1948. The Tretaspis Series of the Kullatorp Core. In Deep Boring Through Ordovician and Silurian Strata at Kinnekulle, Vestergotland (Waern, B., Thorslund, P. & Henningsmoen, G., eds), Bulletin of the Geological Institution of the University of Uppsala, 32, 374-432.
Knupfer, J. 1967. Zur Fauna und Biostratigraphie des Ordoviziums (Grafenthaler Schichten) in Thuringen. Freiberger Forschungshefte, C220, 1-119.
Lindstrom, M. & Pelhate, A. 1971. Presence de conodontes dans les calcaires de Rosan (Ordovicien moyen a superieur, Massif Armoricain). Colloque Ordovicien-Silurien, Brest 1971. Memoire du Bureau de Recherches Geologiques et Minieres, 73, 89-91.
Melou, M. 1987. Decouverte de Hirnantia sagittifera (M'Coy 1851) (Orthida Brachiopoda) dans l'Ordovicien superieur (Ashgilllien) de l'extremite occidentale du Massif Armoricain. Geobios, 20, 679-686.
Paris, F. & Le Herisse, A. 1992. Palaeozoic in Western Brittany (Outline of the Armorican geological history and geological itinerary in the Crozon Peninsula). 8th International Palynological Congress, Aix-en-Provence, 13-16th Sept. 1992. Cahiers de Micropaleontologie, 7, 5-28.
Paris, F., Pelhate, A. & Weyant, M. 1981. Conodontes ashgilliens dans la Formation de Rosan, coupe de Lostmarc'h (Finistere, Massif armoricain). Consequences paleogeographiques. Bulletin de la Societe Geologique et Mineralogique de Bretagne, 13(2), 15-35.
Rhodes, F. H. T. 1953. Some British Lower Palaeozoic conodont faunas. Philosophical Transactions of the Royal Society of London Series B, 237, 647, 261-334.
Rhodes, F. H. T. 1955. The conodont fauna of the Keisley Limestone. Quarterly Journal of the Geological Society of London, 111, 117-142.
Serpagli, E. 1967. I conodonti dell'Ordoviciano Superiore (Ashgilliano) delle Alpi Carniche. Bollettino della Societa Paleontologica Italiana, 13, 17-98.
Sweet, W. C. & Bergstrom, S. M. 1984. Conodont provinces and biofacies of the Late Ordovician. In Conodont Biofacies and Provincialism (Clark, D. L., ed.), Geological Society of America Special Paper, 196, 69-87.
Vidal, M., Dabard, M.-P., Gourvennec, R., Le Herisse, A., Loi, A., Paris, F., Plusquellec, Y. & Racheboeuf, P. R. 2011. Le Paleozoique de la presqu'ile de Crozon, Massif armoricain (France). Geologie de la France, 1, 3-45.
Walliser, O. H. 1964. Conodonten des Silurs. Abhandlungen des Hessischen Landesamtes fur Bodenforschung, 41, 1-106.
Weyant, M., Dore, F., Le Gall, J. & Poncet, J. 1977. Un episode calcaire ashgillien dans l'est du Massif armoricain; incidence sur l'age des depots glacio-marins fini-ordoviciens. Comptes Rendus de lAcademie des Sciences, Paris, 284, Serie D, 1147-1149.
Annalisa Ferretti (a), Andrea Messori (a) and Stig M. Bergstrom (b)
(a) Dipartimento di Scienze Chimiche e Geologiche, Universita degli Studi di Modena e Reggio Emilia, 1.go S. Eufemia 19, I-41121 Modena, Italy; email@example.com, firstname.lastname@example.org
(b) School of Earth Sciences, Division of Earth History, The Ohio State University, 125 S. Oval Mall, Columbus, Ohio 43210, USA; Bergstrom.email@example.com
Received 30 June 2014, accepted 11 September 2014
|Printer friendly Cite/link Email Feedback|
|Author:||Ferretti, Annalisa; Messori, Andrea; Bergstrom, Stig M.|
|Publication:||Estonian Journal of Earth Sciences|
|Date:||Dec 1, 2014|
|Previous Article:||The stratigraphic imprint of a mid-Telychian (Llandovery, Early Silurian) glaciation on far-field shallow-water carbonates, Anticosti Island, Eastern...|
|Next Article:||Carbon isotope chemostratigraphy of the Llandovery in northern peri-Gondwana: new data from the Barrandian area, Czech Republic.|