Geologia do Supergrupo Camaquã no Corredor do Apertado – Rio Grande do Sul

Abstract

In the region called Corredor do Apertado, located in the South-central of the Rio Grande do Sul, the Super Group Camaquã is represented by Acampamento velho, Seival, Pedra Pintada and Serra do Apertado formations, beyond the Rodeio Velho magmatism. This volcanics deposits (whit some intrusions assossieted) and sedimentars are lying over the rocks of Porongos Metamorfic Complex, undivised and cutted by Serra Geral intrusions. The studearea has 65km² and are situated at the bondary of Tapera-Emiliano fault zone south of Camaquã river comprising aproximately 6 km of North-South oriented Velhaco stream and between basement highlands Alto de Caçapava do Sul and Alto da Serra das encantadas. The main objectives in this paper was the accomplished of the geological mapping in scale 1:25000. The thechniques used were: (I)Field practices including lithostratigraphic surveys based on columnar sections and stratigraphycs fácies analises, paleocurrent, provenience and structures; and (2) Laboratory practices, petrographics and data analises. In this context, the lithologys founded in each unit was: (1) milonitc rocks and cristalin marblestones from the undivised Porongos metamorfic complex; (2) riolitic tufus from the Acampamento Velho formation; (3) conlgomerates, conglomeratics sandstone, micaceous sandstones containning levels of pelites and siltites from Seival formation; (4)Conglomeratics sandstones and well selected sandstones at Pedra Pintada formation; (5) Conglomerates and conglometes sandstones from Serra do Apertado formation; (6) Andesitic sills and pepperites assossieted whith the Rodeio Velho magmatism; and (7) Serra Geral diabasium dikes. In general, the sandstones that make up the Super Group Camaquã in the region of the Corredor do Apertado of the tight present arcosian composition varying for litoarenites. The mostly abundant detritus are at first quartz, followed by feldspar and finally litic arenites fragments. The accessories are plentyfull. The kind of matrix is pseudomatrix and the cimentation is calcium carbonate and iron oxide. The porosit of these sandstones are regular, intergranular kind, grain dissolution and fractures. About the provenance, a great amount of elements derived from granitic rocks was verified. Thus, we showed that the mapping of detail, with macro study of outcrops, local structures and microscopic petrography provide answers to specific stratigraphic problems. Finally, was accomplished the Corredor do Apertado geological map and the respectives geolocical cross section.