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

Abstract : 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
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Submitted on : Thursday, October 27, 2016 - 10:32:00 AM
Last modification on : Friday, April 5, 2019 - 8:17:50 PM

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  • HAL Id : insu-01388492, version 1

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Jean-David Moreau, Louis Baret, Gérard Lafaurie, Carmela Chateau-Smith. First Kimmeridgian/Tithonian flora from the lithographic limestone of the Causse Méjean (Lozère, southern France). 25 ème Réunion des sciences de la Terre (RST 2016), Société Géologique de France, Oct 2016, Caen, France. pp.229. ⟨insu-01388492⟩

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