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RESEARCH PRODUCT

First Kimmeridgian/Tithonian flora from thelithographic limestone of the Causse Méjean(Lozère, southern France)

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National audience; Fossiliferous lithographic limestone yielding Kimmeridgian/Tithonian floras has been reported from few localities, mainlylocated in western Europe (e.g., Plattenkalk of Bavaria in Germany,or Canjuers and Cerin in France). They were studied intensivelyduring the twentieth century, when the fossil plants weremainly ascribed to bennettitaleans, conifers, cycads, ginkgophytesand pteridosperms. Here, we report the first flora from the Kimmeridgian/Tithonian lithographic limestone in the northern partof the Causses Basin. These fossils were discovered in the depositsof a small quarry in the Causse Méjean, which is no longeraccessible, as it has been completely filled in. The section of thequarry was composed of homogeneous, micritic, thinly laminatedlimestone, with fine-grained texture (mudstone), conchoidal fractures,and sharp edges. Fossil plants are represented by megaremainspreserved as impressions (external casts). This flora showsa co-occurrence of terrestrial plants and marine algae. The landplants include vegetative remains ascribed to bennettitaleans (ZamitesBRONGNIART, 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 preservationin a flat, homogeneous, protected environment, perhaps abrackish or marine lagoon, influenced by both continental and marineinputs. This discovery complements the few existing reportsof European Late Jurassic floras, and indicates that coastal habitatswere dominated by sub-arborescent vegetation, consisting ofbennettitaleans and pteridosperms, but also arborescent plants,such as conifers. Both the palaeoenvironmental context and certainxerophytic features suggest that these terrestrial plants fromthe Causse Méjean were well adapted to the hot, dry conditionsof coastal areas