There are NO formal formation names for the shallow marine sequence of the Central Massif of southern France.
The Lafarge quarry, near the villages of Saint-Jeandes-Vignes, Belmont and Charnay (Beaujolais, RhÃne, SE France), exposes a succession of fully marine strata of Toarcian to Bajocian age that were deposited at relatively shallow depths near the easternmost reach of the Massif Central. The lithostratigraphy and ammonite biostratigraphy of the section were described by Elmi & Rulleau (1991, 1993). Excavations undertaken in 2009 and 2010 in the southern part of the quarry allowed new detailed observations and sampling of the Toarcian to lowermost Aalenian sequence, including the lower Toarcian interval, which is otherwise poorly represented in the quarry (Rulleau, 1997).
(âCalcaires Ã Ammonitellaâ; Elmi & Rulleau, 1991) The lower Toarcian is mainly represented by partly dolomitized, massive and yellowish argillaceous limestone beds interbedded with weathered yellow plastic clays.
The first beds yielded specimens of Dactylioceras (Orthodactylites) diagnostic of the tenuicostatum zone, while overlying beds yielded abundant belemnite rostra and several ammonites diagnostic of the serpentinum ammonite zone.
(âMarnes infÃrieuresâ; Elmi & Rulleau, 1991) This carbonate-rich interval is overlain by an interval â2.5 m thick (from 2.7 to 5.3 m); of dark grey, finely laminated calcareous marl (yellow and structureless when deeply weathered) presenting several millimetre-thick pyritic beds rich in vertebrate debris and belemnite rostra towards its base and equivalent to the classical âSchistes Cartonsâ of the Paris Basin.
(âMarnes mÃdianesâ; Elmi & Rulleau, 1991) The middle Toarcian sequence (bifrons zone to variabilis zone) is represented by an â2.5 m interval of ammonite- and belemnite-rich purplish bioturbated marls with a few dispersed phosphatic ooliths and interrupted by thin and discontinuous oolithic limestone beds.
(âMarnes supÃrieuresâ; Elmi & Rulleau, 1991) The upper Toarcian sequence, from 8 to 12.4 m, consists of purplish to greenish grey bioturbated marls (deep red when weathered) that yielded abundant belemnites, bivalves and ammonites. Several massive, orange to reddish oolithic limestone beds occur towards the base, the lowermost of which being more prominentand especially rich in ammonites and belemnites
(âBanc Ã Haugia et Ã Grammocerasâ; Elmi & Rulleau, 1991). An intensively bioturbated, massive and sandy yellowish bioclastic limestone bed at 12.4 m
(âDalle Ã Leiocerasâ; Elmi & Rulleau, 1991) marks the base of the more calcareous and coarser sequence of the lower Aalenian (opalinum ammonite zone), which consists mainly of yellowish to pinkish sandy calcarenite and calcareous sandstone beds.
ELMI, S. & RULLEAU, L. 1991. Le Toarcien des carriÃres Lafarge (Bas-Beaujolais, France): cadre biostratigraphique de rÃfÃrence pour la rÃgion lyonnaise. Geobios 24, 315â31.
ELMI, S. & RULLEAU, L. 1993. Le Jurassique du Beaujolais mÃridional. Geobios 15, 139â55.
RULLEAU, L. 1997. Nouvelles observations sur le Toarcien infÃrieur de la RÃgion lyonnaise. GÃologie de la France, 2, 13â22.
RULLEAU, L. 2006. Biostratigraphie et palÃontologie du Lias supÃrieur et du Dogger de la rÃgion Lyonnaise (eds L. Rulleau & la Section GÃologie et PalÃontologie du ComitÃ dâEntreprise LafargeCiments). Dedale Editions, 381 pp.