Quaternary Palaeoenvironmental Reconstruction Based On Fossil Imprints and Palynological Data From Villa Escolar, Eastern Chaco Plain, Argentina

CONTRERAS, SILVINA A.

Foz Iguazu

Congreso; The Meeting of the Americas; 2010

The AGU

The Quaternary paleoflora of Argentina is poorly studied; particularly no data is available about the paleoflora of the Chaco plain. This plain is a great sedimentary basin limited by the Andes and the Brazilian craton. The Paraguay and Paraná rivers run along the eastern boundary, and four aloctone rivers (Parapetí, Pilcomayo, Bermejo, and Juramento-Salado) cross the Chaco from northwest to southeast. Along the plain, in correlation with climatic and edaphic xericity, the vegetation changes from xeromorphic forest and thickets in the northwest (Western Chaco) to semideciduous forest intermingled with extensive palm-savannas in the southeast (Eastern Chaco). The vegetation of the banks of the main rivers and their western tributaries is usually a gallery forest. Such patterns of vegetation of the Chaco have been proposed to be the result of the Pleisto?Holocenic alluvional dynamics of the plain and of the intensive migration of the fluvial belts of the main rivers. In a recent survey in the Bermejo river banks (Formosa, Argentina), some fossils imprints together with molluscan and ostracod evidences of Holocene? age were found. The reconstruction of Quaternary palaeoenvironments may contribute to interpret the role of the Quaternary episodes in shaping plant distributions and evolution in the Eastern Chaco. Thus, in order to provide insights into the environmental history of the region, in this study the fossils imprints and palynomorphs recovered from two sections (A and B) in the banks of the Bermejo river (Villa Escolar, Formosa) are analyzed. The results obtained constitute the first descriptions of the paleoflora for the Eastern Chaco. Among fossils imprints there were found stems of Equisetum sp., leaves and fruits of Dicots, as well as stems and spikelets of Poaceae. The palynomorphs spectra show a high contribution of pollen of Poaceae and Asteraceae, among other families, as well as spores of Pteridophytes and fungus. Both sections showed different species composition suggesting that a mosaic of savanna and forest occupied the landscape. In section A, an important Poaceae diversity might have developed as part of savanna-like vegetation; while in section B, the abundance of Dicots elements representing the forest are in agreement with a gallery forest environment. The information from fossils imprints and palynomorphs in combination with the paleofauna evidences of both sections suggest that, the paleoenvironment in the Quaternary sediments of Villa Escolar are comparable to those of the extant Eastern Chaco flora.