Several levels of conglomerate cropping out in the Peña de Francia syncline were previously included
in the Ordovician basal unit. However, a Lower Cambrian conglomerate can be identified inside, even in
the areas where the basal Ordovician unconformity is not exposed. The Cambrian conglomerate witness
the filling of deep water channels by mass flow; whereas the Basal Ordovician conglomerate indicates the
starting of the Ordovician transgression in a coastal environment under tides and waves regime. Sedimentary
and lithological data from the conglomerates and geochemical data from interlayered slates support this
interpretatio