“Preliminary Studies on phytolith content on the Toropí Formation (Upper Plestocene), Corrientes, Argentina.

ERRA, G.; M. OSTERRIETH Y A. A. CARLINI.

Mar del Plata

Congreso; 7mo. Encuentro Internacional de Investigaciones Fitolíticas y 4to. Encuentro Sudamericano de Investigaciones Fitolíticas.; 2008

The Toropí stream flows into the Paraná River 10km. south of the city of Bella Vista (Dep. Bella Vista), in the province of Corrientes Argentina, 28° 36´ S and 59° 02´ W. In this province, the Upper Pleistocene is represented by two juxtaposed fossiliferous lithostratigraphic units, corresponding to the Toropí and Yupoí formations. Recent OSL datings indicate that both formations belong in the Upper Pleistocene (circa 58 ka and 28 ka BP respectively). Lithologically, the Toropí formation consists of clay sands, sandy lime mud and, in part, sandy clay, whereas the Yupoí formation has a higher content of fine sands and a lower content of clays. From an environmental point of view, these units include floodplain deposits. The evidence suggests that present day Mesopotamia used to have its own paleobiogeographic identity. This situation continued until the Upper Pleistocene since the paleozoological, paleobotanical, palynological and sedimentological evidence indicates that this area had probably developed environmental climatic processes in general more humid and warmer than those estimated for the Pampean region and the central-northern area of Argentina.This is the first approach to the analysis and interpretation of the phytoliths contained in the sediments of these two formations. In the five samples analyzed, the inorganic mineral components always exceed 50%, the highest levels being in N4 (Toropí roof) and N3 (Yupoí base), whereas the highest levels of phytholites (around 20%) appear in N5 and N2 (Toropí base in the profile analyzed and the middle section of Yupoí). These levels are also very similar in texture, with a predominance of fine materials, very fine clays and lime muds, and they show the highest levels of diatoms, especially N5 with 8%. The intermediate levels (N3·, N1 and N4) have thicker textures where the middle and fine sands predominate, but they have lower amounts of phytoliths and diatoms. Based on the general characterization of the different components of each sample analyzed in the sequence, N2 and N5 would correspond to an environment with less energy, in which fine particles, which allow a higher expression of diatom communities and better development of vegetation cover, are concentrated. These levels would have evolved under conditions of less environmental humidity and more evapotranspiration, coinciding with the presence of bilobate and cross type phytoliths (typical C4 grasses) whose evolution requires conditions of higher hydric stress, salinity and insolation. In general, the morphotypes observed in all the levels correspond to bilobate, rondel and flat elongate. Samples N1, N3·and N4, with granulometrically higher mineralogy, also included large sized elongates, bulliforms and aciculars, probably due to non-grass vegetation.The succession of these environments coincides with previous hypotheses based on the study of vertebrates which attempt to explain the presence of different adaptative types in temporal synthesis.