Silvia Césari, Sergio Archangelsky, Liliana V. de Seoane


A taxonomic and biostratigraphic study of palynological assemblages found in the well SH-Las Mochas x- I is presented. This well is located in Santa Fe province where the Chacoparanense basin, comprising a thick Late Paleozoic sequence was developed. Eighty one species have been identif ied, some being new: Gondisporites serrulatus , Lundbladispora areolata, Protohaploxypinus paucitaeniatus, Scheuringi pollenites circularis and Cycadopites alhuampai, Brevitritetes irregularis (Nahuys, Alpern et Ybert), Diatomozonotriletes subbaculiferus (Nahuys, Alpem el Ybert), Horriditriletes superbus (Foster), and Distriomonosaccites crucistriatus (Ybert), are new combinations. Twenty one species are mentioned for the firsl lime in this basin, although some are known lo occur in the neighbouring Brazilian Paraná Basin. The distribution of the most important species along the section shows a significant compositional change at the 10p ofthe sequence that is considered to be an important zone boundary. It may be equivalent to a similar change that was previously recorded in this basin by several authors. Contrasting spore-pollen group percentages are also consistent with this interpretation. The thickest part ofthis succession is correlated with the known Cristatisporites Zone (Early Perrnian) while the basal strata are probably representing the Potonieisporites-Lllndbladispora Zone (Late Carboniferous). Although it is possible to recognize a subdivision of the Cristatisporites Zone into three subunits, as suggested recently by Vergel (1993), there is no coincidence with taxa used by this author to define those subunits because most are lacking in Las Mochas well. However. there are some taxa with coincident ranges that suggest a threefold subdivision of this Zone. It is concluded that different plant cornrnunities may have been present reflect in variable ecological conditions, These conditions may well have been responsible for the differences in composition of the observed subunits in the Cristatisporites Zone.

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