Dolinas em arenitos da Bacia do Paraná: evidências de carste subjacente em Jardim MS e Ponta Grossa PR

Abstract (English)

In the Paraná Basin, dolines in sandstones occur in the Aquidauana Formation in Jardim (MS) and in the Furnas Formation in Ponta Grossa (PR). In the Ponta Grossa region, the retreat of arenitic rocks is marked by the “Furnas Formation Escarpment”, whereas in Jardim there is no associated escarpment. The dolines of the Jardim are generally extensive and shallow, and those of the Ponta Grossa deep and scarped. In Ponta Grossa, the dolines have had their origin associated, in most studies, with the subsurface erosion of sandstones, due to the presence of ruiniform relief features, the proximity of escarpments and the mistaken absence of carbonatic rocks in the basement of the basin. The Jardim and Ponta Grossa dolines are collapse phenomena generated by a piping process, brought about by the development of a subjacent karst system, at depth, in a phreatic environment, in the carbonatic basement rocks. The role of subjacent karst in doline formation in sandstones is demonstrated by: 1) rather than being distributed along all the arenitic units of the Paraná Basin, dolines are restricted to only those locations with carbonatic rocks in the basement structures of the basin; 2) ruiniform relief features are surface structures originating from erosive or weathering processes in sandstones and can be attributed to pseudokarst, having no direct relationship with the dolines, which even when present at the surface, represent points of injection of meteoric water, connected at depth to the karst system; 3) besides being evidence of structural control in the sandstones, the alignment of surface features shows the direction of karst conduits at depth. The “Vila Velha Depression”, described for the first time in this study, which includes the dolines in the Ponta Grossa region, is a reflection of the piping process brought about by the subjacent karst. In the exposed karst area typical features are not very frequent or evident, due to dolomitic composition, and the dolines are more evident in sandstones than the actual carbonate rocks. However, in Jardim, the gradual geomorphological transition between sandstones and carbonate rocks makes the subjacent karst more visible, which exposed the karst features, in a different manner to the Ponta Grossa region, where the karst is encountered at a distance from the dolines and at greater depth.