Nouvelles données géologiques et biostratigraphiques du gisement paléontologique à vertébrés de Mauvières, à Marcilly-sur-Maulne (Miocène inférieur et moyen; Indre-et-Loire, France)

Abstract

The paleontological site of Mauvières is located in the South-West part of the Paris Basin, on the northern border of the Ligerian Basin, 55 kilometers to the North-West of the city of Tours (Fig. 1). It is a small quarry, occasionally exploited by the Poirier family (the owner of the site and of the farm of La Brosse). In 2000, a first paleontological study reported the presence of a rich fauna of continental vertebrates from the Early Miocene (Orleanian European Land Mammal [ELMA], biozone MN3) (Ginsburg et al. 2000). Between 2020 and 2022, new excavations have been performed in these fossiliferous strata. Our study complements previous works (Ginsburg et al. 2000) by adding detail concerning the geological and taphonomic contexts, as well by actualizing the faunal content. The sedimentary succession is divided into six formations: Eocene-Oligocene lacustrine marl, lower Miocene continental sand, upper Burdigalian-lower Langhian marine limestone, Langhian marine conglomerate, upper Miocene-Pliocene fluvial sand, and Quaternary superficial formations. The faciological analyses show a relation between Cenozoic tectonics (Pyreneo-Alpine orogenic phases) and the development of sedimentary architectural elements. During the Paleogene, the activation of normal faults - with a South Armorican Hercynian heritage direction – generated many small lacustrine basins. A shortening begins during the Early Miocene with a significant folding of the area and subsequent erosion of the “Château-la-Vallière anticline” (Fig. 2) as well as the channeling of a fluvial system in the “Esvres syncline” valley (Gagnaison et al. 2020). At the end of the Burdigalian, the farfield westward progradation of alpine deformation is responsible for tectonic subsidence and the first transgressive pulse to the East of the Ligerian Basin. The marine sediments are channeled into pre-existing structures (Bouchet 2009). This tectonic activity occurres throughout the Middle Miocene (Temey 1996) forming submarine reliefs. At that time, the “Château-la-Vallière anticline” is still a structural high and blocks the marine transgression to the North-East (Fig. 2). This tectonic influence slows down at the end of the Neogene (Bouchet 2009). The new paleontological and taphonomic data bring out two coherent Miocene vertebrate assemblages. The assemblage 1 consists of 53 taxa, including the 32 taxa of Ginsburg et al. (2000; Tableau 1) found in situ in the Lower Miocene fluvial deposits (*synonymy, **new attribution, ***new for the locality): Tinca sp., ***?Lates sp., ***Amphibia indet., Chelydropsis sp., Ptychogaster sp., Testudo promarginata Reinach, 1900, Trionyx sp., ***Ligerosaurus pouiti (Augé, Bailon & Malfay, 2003), ***Lacertidae indet., Diplocynodon styriacus (Hofmann, 1885), Diplocynodon sp., Tomistoma cf. lusitanica (Vianna & Morales, 1945), ***Aquilavus sp., Rallidae indet., ***Talpidae indet., ***Erinadeidae indet., ***Soricidae indet., Lagopsis cadeoti (Viret, 1930), Prolagus vascociensis (Viret, 1930), Amphilagus ulmensis (Tobien, 1963), ***Ochotonidae indet., Eucricetodon infralactorensis (Viret, 1930), Steneofiber depereti Mayet, 1908, *Megamphicyon carnutense (Antunes & Ginsburg, 1977) (synonym of Amphicyon lathanicus (Ginsburg, Cheneval, Janvier, Pouit & Sen, 2000) in Ginsburg et al. (2000), ***Amphicyon sp., Cynelos helbingi (Dehm, 1950), ***Ballusia hareni (Ginsburg, 1989), ***Phoberocyon aurelianensis (Mayet, 1908), ***Phoberocyon dehmi (Ginsburg, 1955), ***Plithocyon bruneti Ginsburg, 1980, ***Hemicyon gargan Ginsburg & Morales, 1998, ***Ursavus isori Ginsburg & Morales, 1998, ***Plesiogale angustifrons Pomel, 1854, Martes laevidens Dehm, 1950, ***Viverridae indet., ***Broiliana nobilis Dehm, 1950, ***Semigenetta elegans Dehm, 1950, ***Stromeriella franconica Dehm, 1950, *Styriofelis turnauensis Hoernes, 1882 (synonym of Pseudaelurus turnauensis in Ginsburg et al. 2000), ***Paratapirus intermedius (Filhol, 1885), ***Protaceratherium minutum (Cuvier, 1822), Diaceratherium aurelianense (Nouel, 1866), ***Plesiaceratherium sp., Aureliachoerus aurelianensis (Stehlin, 1899), ***Xenohyus venitor Ginsburg, 1980, Brachyodus intermedius Mayet, 1908, Cainotherium lintillae Baudelot & Grouzel, 1974, **Palaeomeryx kaupi Meyer, 1834 (synonym of Oriomeryx willii Ginsburg, 1985 in Ginsburg et al. 2000), **?Heterocemas sp. (synonym of Procervulus praelucidus (Obergfell, 1957) in Ginsburg et al. 2000), Ligeromeryx praestans (Stehlin, 1937), Andegameryx andegaviensis Ginsburg, 1971, ***Andegameryx serum (Ginsburg, 1999), ***Amphimoschus cf. ponteleviensis Bourgeois, 1873. Similar assemblages are already known in other paleontological localities of the region: Chitenay (Ginsburg et al. 2000), Les Beilleaux (Ginsburg 1989b), La Guimardière (Gagnaison 2013), and Pont-Boutard (Gagnaison 2017). It is a typical fauna of the MN3 biozone (early Orleanian = early-middle Burdigalian). The confirmation of the presence of five taxa (Ligerosaurus pouiti, Ballusia hareni, Hemicyon gargan, Ursavus isori and Paratapirus intermedius) in the Ligerian Basin during the biozone MN3 is to be noted. The assemblage 2 includes three terrestrial mammal taxa (Prodeinotherium bavaricum Meyer, 1831, Plesiaceratherium sp., and Palaeomeryx kaupi) whose fossils have been found reworked at the base of the Langhian marine conglomerate. This fauna may come from an indeterminate continental interval of the Middle-Late Orleanian (biozone MN4-5; Steininger 1999) or has been transported from a nearby shore. This assemblage is already known in Anjou-Touraine (Ginsburg 2001) but is described here for the first time. The Mauvières quarry presents a remarkable natural heritage combining geological, paleontological and taphonomic data that are key for the period and regional context. In our opinion, it deserves to be included in the French national inventory of the important geological sites to be preserved (project launched by the Paris Museum).