Quelques aspects des conditions de depot du flysch

Abstract

Analysis of the Niesen flysch between Le Sepey and Mosses lake does not confirm the deep-water bathymetry commonly attributed to flysch deposits. The juxtaposition of organic material over continental alluvium--a typical flysch characteristic--was observed only at shallow depths. The muddy sands, source of the flysch deposits, are actually formed at shallow depths. Bird tracks reported from certain flysch beds also suggest shallow-water origin for the deposits. Cross currents produced after periodic disruption of tectonic and climatic equilibria in parts of a marine basin corresponding to the continental platforms explain the mechanical sorting of the organisms and detrital material as well as the granoclastic structure of the flysch. After deposition of the flysch and before its compaction orogenic mobility at the bottom of the basin affected the petrography of the flysch causing corrosion of the quartz and feldspars at the moment of consolidation. Evidence presented by proponents of a deep-water origin for the flysch deposits--based on foraminifera and the petrographic and paleo-oceanographic characters of the deep-water sands--is reviewed.