Microbially induced wrinkle structures in Middle Devonian siliciclastics from the Prague Basin, Czech Republic

The occurrence of wrinkle structures in Middle Devonian deep-water siliciclastic sequences of the Prague Basin (Roblín Member, Srbsko Formation, Givetian) is reported and interpreted to be microbially induced. Current and/or gravitational forces are considered the simplest explanation of the origin of these structures. Taking into account the tectonic activity linked with ongoing Variscan orogeny, the wrinkle structures could also be interpreted as soft sediment deformation structures originating due to exposure of mat-bearing sediment to seismic shocks. The distribution of n-alkanes and isoprenoids suggests two types of prevailing biological sources, namely phytoplankton, representing organic material from the water column, and benthic bacteria. Judging from the sedimentary facies and lack of petrographic characteristics suggestive of light competition, the microbial mats are interpreted to be formed by non-autotrophic bacteria.