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Exceptional preservation of Cretaceous biota (plants and invertebrates) in flint-bearing alterites from Moragne (western France)

Abstract : Cretaceous fossil inclusions were recently discovered in silica-rich nodules from the diachronic alteritic deposits of the Moragne hill, Charente-Maritime, western France. Nodules contain marine organisms such as sponge spicules, putative algae, echinoids (Periaster undulatus Agassiz and Desor) and rudists (Sphaerulites foliaceus Lamarck; hippuritids and radiolitids). These inclusions co-occur with fragmented pin-nae of ferns as well as diverse structures of conifers including leafy axes (Geinitzia sp.; Glenrosa carentonensis Moreau, Néraudeau, Tafforeau and Dépré) and isolated ovu-late scales or subtending bracts of cones. The palaeontological assemblage shows that the alterites from Moragne are condensed deposits resulting from the alteration of the Cenomanian to Turonian-Senonian regional series. Conifer leafy axes display diverse kinds of preservation: permineralization in silica, empty external casts of the gross morphology, and casts filled by ferruginous siltstone. Propagation phase-contrast X-ray synchrotron microtomography revealed exceptional preservation of some leafy axes up to the cell level. We support a multi-phase silicification including at least: (1) a precocious phase occurring during the sedimentation of the Upper Cretaceous deposits or during the earliest diagenesis, and that could be linked with the abundance of sponge spicules; then (2) a late phase occurring during Eocene-Oligocene period that corresponds to a hard climate event with strong and long paedogenitic alteration associated with an important phase of silicification (nodulation). The alterites from Moragne are an uncommon example of long-term time-averaged deposits caused by compac-tion and selective dissolution of matrix in the context of a late continental weathering.
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Jean-David Moreau, Didier Neraudeau, Roch-Alexandre Benoit, éric Dépré, Matthieu Le Couls, et al.. Exceptional preservation of Cretaceous biota (plants and invertebrates) in flint-bearing alterites from Moragne (western France). Palaeontologia Electronica, Coquina Press, 2019, 2 (3), pp.Art. n°66. ⟨10.26879/925⟩. ⟨insu-02335686⟩

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