This present study describes the acritarch assemblages from the siltstone and claystone of the Landeyran Formation of southern Montagne Noire, France displaying the Early Ordovician Cabrières Biota, and from the coeval Landeyran section. The moderately to well-preserved organic-walled microfossils allow the identification of a rich and diverse palynoflora bearing different important biostratigraphical and palaeobiogeographical markers. The presence of typical Early Ordovician index species, such as Coryphidium bohemicum, Ampullula spp., Barakella spp., together with the absence of the genera Arkonia, Frankea, Orthosphaeridium and Dicrodiacrodium, allow an assignment to the late-middle to early-late Floian (transition Fl2 to Fl3), confirming biostratigraphical data from trilobite and graptolite biozonations. The presence of the genera Acanthodiacrodium, Arbusculidium, Coryphidium and Striatotheca enables the attribution of the southern Montagne Noire area to the peri-Gondwana acritarch province in high southern latitudes. The presence of the genus Ampullula in the late Floian in the southern peri-Gondwana province allows a modification of its First Appearance Datum in this province where it was previously only recorded from the early Darriwilian.
Caillaud et al. (Mon,) studied this question.