First Kimmeridgian/Tithonian flora from the lithographic limestone of the Causse Méjean (Lozère, southern France)
Résumé
Fossiliferous lithographic limestone yielding Kimmeridgian/
Tithonian floras has been reported from few localities, mainly
located in western Europe (e.g., Plattenkalk of Bavaria in Germany,
or Canjuers and Cerin in France). They were studied intensively
during the twentieth century, when the fossil plants were
mainly ascribed to bennettitaleans, conifers, cycads, ginkgophytes
and pteridosperms. Here, we report the first flora from the Kimmeridgian/
Tithonian lithographic limestone in the northern part
of the Causses Basin. These fossils were discovered in the deposits
of a small quarry in the Causse Méjean, which is no longer
accessible, as it has been completely filled in. The section of the
quarry was composed of homogeneous, micritic, thinly laminated
limestone, with fine-grained texture (mudstone), conchoidal fractures,
and sharp edges. Fossil plants are represented by megaremains
preserved as impressions (external casts). This flora shows
a co-occurrence of terrestrial plants and marine algae. The land
plants include vegetative remains ascribed to bennettitaleans (Zamites
BRONGNIART, 1828), conifers (Brachyphyllum BRONGNIART,
1828), and pteridosperms (Cycadopteris ZIGNO, 1853).
Marine algae were ascribed to dasyclads (Goniolina D’ORBIGNY,
1850). Lithological and palaeontological features suggest preservation
in a flat, homogeneous, protected environment, perhaps a
brackish or marine lagoon, influenced by both continental and marine
inputs. This discovery complements the few existing reports
of European Late Jurassic floras, and indicates that coastal habitats
were dominated by sub-arborescent vegetation, consisting of
bennettitaleans and pteridosperms, but also arborescent plants,
such as conifers. Both the palaeoenvironmental context and certain
xerophytic features suggest that these terrestrial plants from
the Causse Méjean were well adapted to the hot, dry conditions
of coastal areas