The Cenomanian lignitic clays of Hucheloup (Écouflant, Maine-et-Loire) : palaeobotanical and palaeoenvironmental study
Résumé
The Anjou region is located in the western part of the Paris
Basin at the south-east of the Armorican Massif. The Cenomanian
clays of Le Brouillard quarry (near Ecouflant, Maine-et-
Loire) yielded exceptionally preserved plant macroremains. They
included centimetric compressions of Conifers, Ginkgoales, and
Angiosperms. This quarry was studied during the second half of
the 20th century but was partially filled in 2005, rendering further
studies impossible. However, in 2006, new fossiliferous deposits
were discovered in the Hucheloup quarry, located one kilometer
west of Le Brouillard. The Hucheloup quarry displays a succession
of sand and clay, presumably Cenomanian in age. Clays yield
a diverse fossil assemblage which was already, partly, studied by
Néraudeau et al. (2013) and Durand (2014). It is dominated
by coastal marine and brackish bivalves, mostly of the genera
Brachidontes (fam. Mytilidae) and Protocardia (fam. Cardiidae),
and contains an important diversity of plant impressions
and compressions, mainly preserved as fragmented leaf remains,
with or without cuticle. The plants have been transported, only
the brackish bivalves seem to be autochtonous. Plants were
ascribed to diverse Pinales (29%), Pteridophytes (29%), Ginkgoales
(24%), Angiosperms (17%) and Cycads (1%). The most
abundant species are Frenelopsis alata (Pinales) and Eretmophyllum
andegavense (Ginkgoales). The co-occurence of those two
species is frequently found in Europe in estuarine mid-Cretaceous
deposits. The fauna also includes arthropod remains such as insect
eggs and a fragmented carapace of Meyeria sp. (Crustacean),
as well as bryozoans and brachiopods. The taphonomical, sedimentological,
and palaeoecological data revealed that the fossil
remains were deposited in a brackish lagoon or the lower part
of what was likely an estuary. It allowed the preservation of a
rich biodiversity that developed under a tropical climate, at the
ocean/land transition.