Turonian-Coniacian silicified plants from the flints of Claix (Charente, western France)

Abstract : In western France, most of Cretaceous plant megaremains are preserved as impressions (external casts) in clay or compressions with or without cuticle in lignite. Remains are commonly highly flattened and only the gross morphology can be provided. When the cuticle is preserved, it shows casts of the most peripheral epidermal cells, allowing the description of microstructural details such as morphology and size of ordinary cells and stomatal apparatuses. However, compressions with cuticles never preserved histology. Silica-rich nodules have been recently collected in surface alterite and Palaeolithic or Neolithic habitats of Claix (Charente, western France). Some of the flints contain diverse plant megaremains. Specimens were examined under light microscopy (LM) and scanning electron microscopy (SEM). In order to detect fossil inclusions inside flints we made preliminary imaging tests using high resolution and high energy X-ray synchrotron microtomography (PPC-SRμCT). The plant assemblage is late Turonianearlymost Coniacian in age and consists of abundant leafy axes of conifers (Brachyphyllum Brongn., Frenelopsis (Schenk) emend. J. Watson, and Geinitzia Endl.) and rare leaves of angiosperms and pinnae of ferns. Such plant diversity is for the first time observed is post-Cenomanian flints from this part of Europe. By contrast with most of lignitic plant beds of western France, the plants from the flints of Claix are exquisitely preserved in three dimensions, showing details of cuticle and inner tissues. It consists of silicified petrification/permineralization, the origin of the silicification being questionable.