PALAEOSURFACE ANALYSIS ON THE CRETACEOUS BASALTIC PLATEAU ON THE UPPER RÍO URUGUAY BASIN (NE ARGENTINA AND SOUTHERN BRAZIL)

Daniela KRÖHLING, Ernesto BRUNETTO, Gabriel GALINA, M. Cecilia ZALAZAR

Resumo


First results of a geomorphological research on the Cretaceous basaltic plateau of the Upper Río Uruguay basin (NE Argentina and southern Brazil) are presented. DEM data from SRTM and field data were used for the morphometric analysis. Generation of hypsometric curves in five representative tributary basins of the Río Uruguay basin and also in one small basin tributary of the Río Paraná permitted to identify, classify and map the main Cenozoic palaeosurfaces of the plateau. Other morphometric parameters such as longitudinal profiles and isobase lines were produced also to delimit such surfaces. The identification of palaeosurfaces was extended on the Paraná and Uruguay rivers watershed in order to identify palaeosurface remnants and to correlate them to those described previously in southern Brazil. Palaeosurfaces 1 and 1b in this work are equivalent to King's "Sul-American Surface". Both surfaces 1 and 1b (>; 883 m a.s.l.) are well represented in the Río Pelotas sub-basin. If the Upper Río Uruguay basin corresponded to the lower segment of the palaeosurface, a predicted base level value would be estimated around 840 m a.s.l. The higher remnant surface of the plateau at the northeastern area of the province of Misiones (Argentina) is interpreted as Palaeosurface 2b (676-883 m a.s.l.). King's "Velhas Palaeosurface" is correlated with Palaeosurface 2, which in Misiones comprises the plane-top watershed between the Paraná and Uruguay river basins (436-676 m a.s.l.). This surface is widespread in the Upper Río Uruguay basin in Brazil and it is represented by< a landscape of gentle and well rounded hills. The identified lower surfaces 3 and 4 correspond to the Apóstoles Surface (around 200 m a.s.l.), which would be generated by King's Paraguaçú cycle, represented by valley incision.

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