The surveyed microflora was recovered from six cores from the Tonono x-1 well in northwestern Argentina. Most of the studied interval corresponds to the Tonono Formation, i.e., the upper part to the Jollín Member and the basal part of the interval may be related to the Michicola Formation. The microflora totals 73 species represented by trilete spores (35 species), microplankton (30 species) including prasinophycean, acritarch and chlorophycean algae and chitinozoans (8 species). The stratigraphic distribution of these species allowed the definition of three associations. The palynoassemblage To1 (3946,5 – 3638,5 m) is characterized by species such as Grandispora douglastownense Mc Gregor, Dibolisporites eifeliensis (Lanninger) McGregor, Verrucosisporites sp. cf. V. loboziakii Marshall and Fletcher, Alpenachitina matogrossensis Burjack and Paris, Alpenachitina sp. cf. A. eisenacki Dunn and Miller and Ancyrochitina simplex Grahn, Bergamaschi and Pereira suggesting a late Eifelian to earliest Givetian age. Based on the presence of Geminospora lemurata Balme, Aneurospora greggsii (McGregor) Streel, Biharisporites parviornatus Richardson, Raistrickia aratra Allen and Leiotriletes balapucencis di Pasquo a Givetian age is proposed for palynoassemblage To2 (3367,35 – 3285 m). Palynoassemblage To3 (3073,2 – 3137,5 m) is predominantly composed of marine elements together with AOM. Few key species are recognized; however the presence of Acinosporites sp. cf. A. eumammillatus Loboziak, Streel and Burjack together with the chitinozoans Angochitina katzeri Grahn and Melo and Angochitina mourai Lange support an early Frasnian age. The distinctive increase of marine elements and AOM between To2 and To3 suggests that a maximum flooding event would have occurred there during this period.