Mat−forming coccoid cyanobacteria from early Silurian marine deposits of Sudetes, Poland

Mass occurrence of mats comprised of benthic coccoid cyanobacteria is reported from early Silurian black radiolarian cherts exposed at Żdanow village (Bardzkie Mountains, Sudetes, southwestern Poland). The cherts contain laminated organic mat− ter representing degraded benthic coccoid cyanobacterial mats. The remains of cyanobacteria occur as laminated agglomer− ations of variously preserved subglobular colonies composed of spherical cells of variable size and numbers. The morphol− ogy of remnants of cells and their mucilaginous envelopes, structure of colonies, and particularly the presence of small gran− ular structures resembling reproductive cells known in extant coccoid cyanobacteria as baeocytes, permit to compare the Si− lurian microbiota with modern cyanobacteria assigned to the genera Stanieria or Chroococcidiopsis.