O vulcanismo Serra Geral em Torres, Rio Grande do Sul, Brasil: empilhamento estratigráfico local e feições de interação vulcano-sedimentar

Abstract

At the mounts found in the city of Torres, southern Brazil, three facies associations were identified (i) basalts, (ii) sandstones and (iii) features of volcanic-sedimentary interaction. From field and petrographic descriptions it is possible to suggest the genetic mechanisms of the volcanicsedimentary interactions. The striations on top of sandstones are produced by the flow of lava over unconsolidated sand. The clastic dikes are produced by the infilling of aeolian sand in the disjunctions of the basalt, or the injection of sand towards the lava while it is still flowing. This mechanism of injection, when dealing with plastic lava, leads to the formation of peperite, which is also found as a result of traction and fragmentation of the front and base of the lava flow. It is possible to identify, at Torres, three individual lava flows, each one of them defining a distinct stratigraphic level. These levels are composed by a cycle of events, initiated by the lava flow, which is responsible for the formation of peperite, and this succession is recovered by aeolian deposition of sand. With the definition of these levels it becomes clear that the sandstone outcropping at Morro das Cabras (Guarita Park) is intertrapic sandstone from the Serra Geral Formation, and does not belong to the underlying Botucatu Formation. Key words: Serra Geral volcanism, stratigraphy, volcanic-sedimentary interactions, peperite.