Exceptional preservation of Cretaceous biota (plants and invertebrates) in flint-bearing alterites from Moragne (western France)
|Author(s)||Moreau Jean-David1, Neraudeau Didier2, Benoit Roch-Alexandre2, Depre Eric3, Le Couls Matthieu2, Fernandez Vincent4|
|Affiliation(s)||1 : Univ Bretagne Sud, CNRS, UMR 6538, Ctr Rech Yves Coppens,Lab Geosci Ocean, Campus Tohannic,Rue Andre Lwoff, F-56017 Vannes, France.
2 : Univ Rennes 1, CNRS, UMR 6118, Geosci Rennes, Ave Gen Leclerc, F-35042 Rennes, France.
3 : GIP GEVES Grp Etud & Controle Varietes & Semences, F-17700 Le Magneraud, Surgeres, France.
4 : Nat Hist Museum, Imaging & Anal Ctr, Cromwell Rd, London SW7 5BD, England.
|Source||Palaeontologia Electronica (1935-3952) (Coquina Press), 2019 , Vol. 22 , N. 3 , P. 66 (14p.)|
|WOS© Times Cited||1|
|Keyword(s)||Upper Cretaceous, flints, silicification, time-averaging, fossil plants, X-ray synchrotron microtomography, France|
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 pinnae of ferns as well as diverse structures of conifers including leafy axes (Geinitzia sp.; Glenrosa carentonensis Moreau, Neraudeau, Tafforeau and Depre) and isolated ovulate 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 compaction and selective dissolution of matrix in the context of a late continental weathering.