Paléoécologie des mollusques du Maastrichtien du Mont Aimé et de Vertus (Marne)
Résumé
New data are provided on the mollusk fauna from the Maastrichtian of Marne (France), which was highlighted in the volume Stratotype Danien (Merle and Pacaud in Montenat and Merle, 2018). This study focuses on the calcareous sandstones from Vertus and Mont Aimé, which were the subject of two fieldtrips in 2014 and 2017. They contain external shell imprints which are very fine, delicate and their silicone elastomer casts allow to faithfully reproduce the original morphology of the shells and thus to identify them. The result is an inventory of 41 taxa. In comparison to the list presented by Montenat et al. (2018), eleven additional taxa are reported. At Vertus and Mont Aimé, assemblages are very similar and share forms with the basal sandy limestone of Vertus (Chama sp., Arca sp., Barbatia sp., Inoceramidae indet. and Vicinocerithium sp. 1) which encourages recognizing a homogeneous association. The taphonomic observations indicate a very low transport of shells, not compatible with the hypothesis of reworked material. The palaeoecological analysis highlights the abundance of herbivores that unequivocally sign environments of the infralittoral zone associated with the development of marine plants. These plants can also explain the dominance of sessile forms and small herbivores living on rock that may have found fixation supports. This gulf bottomed facies thus evokes a coastal environment contrasting with the pelagic facies of the Cotentin (Baculites limestone) located at the northwest margin of the Paris Basin.