The Cabrières Biota inhabited a polar wave-influenced delta

The recent discovery of the Cabrières Biota provides a unique insight into a complex, polar community of the Early Ordovician. This biota was found in the southeastern part of the Montagne Noire, in the Landeyran Formation, 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 its lifetime, which may have influenced its ecological distribution and preservation, remain unknown. In this study, we examined a stratigraphical succession from the nearby 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. The facies yielding the fossils correspond to the most distal part of the system, likely in prodelta/offshore to shelf environments, where mud settling and low-density turbidity currents influenced deposition, thus aiding the exceptional preservation of the Cabrières Biota.