Taphonomie et minéralisation de bois carbonatisés du Purbeckien de l'Usine, à Cherves-Richemont (Charente)

Taphonomy and mineralization of carbonated wood from the Purbeckian facies l'Usine, Cherves-Richemont (Charente). Lower Cretaceous deposits Charentes region, in southwestern France, correspond to continental brackish environments, locally rich evaporitic formations (Manès 1850; Pouech et al. 2006, 2014, 2015; Schnyder 2012; Vullo 2014; Moreau 2017b). Three fossiliferous localities have been previously identified: Berriasian gypsum Champblanc, near Cherves, with both teeth accumulations bone beds fishes, crocodiles dinosaurs, but relatively poor fossil (Buffetaut 1989; Le Loeuff 1996; 2003; Colin 2004; El Albani Mazin 2006; Rees 2013); marls calcareous conglomerate Angeac-Charente, particularly dinosaur megaremains lignitic (Néraudeau Allain Benoît 2017; Polette 2018; 2019); Wealden clay Rochefort area, providing large bones dinosaurs surface blocks, never observed stratigraphical position (Vullo 2012). Another locality Chassiron coast Oleron Island, is vertebrate plant remains, mainly Tithonian age This paper presents a fourth Charentese first case calcite mineralized known Mesozoic France. The located at Cherves-Richemont, Charente (SW France), 3 km east Champblanc quarry, L'Usine (Figs 1; 2). mid-distance lower mid-Berriasian series east, unconformity Cenomanian sands that erode series, west (Fig. 3) (Coquand 1858, 1862; Platel 1980; Bourgueil 1986). Consequently, probable lateral equivalent uppermost about 25 only (Gônet Rozada 2019). There no real outcrop L'Usine, limestones can be on blocks fields vineyards. Two outstanding facies, wood, observed. First, shows abundant relic conglomerate, tubular, fibrous incrusting axes, associated fragments fusain. contains reptile pebbles Lepidotes Agassiz, 1832 fish scales too. At depth 40 cm, an excavation has shown containing pieces (about 1 m), incrusted by spherules 2; 4). geochemical analyses X-ray diffraction, realized according method Moore & Reynolds (1997), confirm carbonate only. Dolomite silica are very scarce lacking 5). Polished sections 2) thin 6; 7) show processes centripetal (Higgins 1960; Buurman 1972; Marynowski 2007; Mustoe Beard 2021). microscopic observations reveal fine cell scale, hyperblastic or polyblastic (sometimes oligoblastic, likely microbial origin. Cell lights filled sparry calcite. Some “tuff structures” characteristic certain tuff filamentous cyanobacteries (e.g. Rivularia C.Agardh ex Bornet Flahault, 1886, ou Shizothrix Kützing Gomont, 1892) common geological record (Freytet Plaziat 1965; Freytet Plet 1991; Caudwell 1997; Verrecchia 1998; 2000; Pentecost Hägele Sanders Arenas Jones 2007). A zonation often corresponds more successive steps cyanobacterial mats than growth. Scanning Electron Microscopy allow identify tracheidoxyl (Creber 1972) araucarioid structures genus Agathoxylon Hartig, 1848, gymnosperm region SW France 8) 2002, Philippe 2008, 2010, 2011; 2014). pitting uniseriate, when punctuation biseriate for gardoniense Crié, typical mid-Cretaceous Charentes. could belong another palaeoecological morph A. gardoniense, possibly species. deposit environment gathered trunks branches, eroded sauropods) freshwater remains Lepidotes) interpreted as coastal, conditions.