The Cabrières Biota inhabited a polar wave-influenced delta

The recent discovery of the Cabrières Biota provides unique insight into a complex, polar community during the Early Ordovician. This biota was discovered in the southeastern part of the Montagne Noire, within the Pic de Vissou unit (Hérault, France). Although there is general agreement on the marine affiliation of the strata yielding the Cabrières Biota, the detailed processes driving sedimentation during their lifetime, which may have influenced their ecological distribution and preservation, remain unknown. In this study, we examined a stratigraphic succession from the Mont Peyroux unit, which includes the Cluse de l'Orb (Floian; early Fl2), Foulon (Floian; late Fl2), and Landeyran (Floian; early Fl3) formations, and is coeval with the fossil-bearing unit. These sedimentary formations are well exposed along the Rieuberlou and Landeyran rivers, and a 350 m thick composite section was logged and analysed for sedimentary facies. The results indicate that the studied interval records a wave-influenced delta flanked by shoreface environments. While the delta likely shifted through time, the recorded river influence varied stratigraphically. The facies yielding the fossils correspond to the most distal part of the system, likely in prodelta/offshore to shelf environments with limited oxygen conditions, where mud settling and low-density turbidity currents influenced deposition, thus aiding the exceptional preservation of the Cabrières Biota.