Eventos tectônicos recurrentes impressos no arcabouço estratigráfico do Grupo Itararé na região de Vila Velha, Estado do paraná

Abstract

This paper describes the tectonic control on the depositional and post depositional evolution of the late Carboniferous glacial Itararé Group in the eastern flank of the Paraná Basin, southeast Paraná State. Emphasis was given on the structural and stratigraphić organization of the Vila Velha sandstone, an outcrop analogue to subsurface reservoirs in the Ponta Grossa - Itararé petroleum system. The study was based on satellite image and digital elevation model analysis, aerial photograph interpretations (1:25.000 and 1:10.000), detailed vertical stratigraphic profiles, descriptive, kinematic and dynamic analysis of deformational structures and geological mapping. The results suggest a series of tectonic events related to Phanerozoic evolution of the South American Platform that can be observed in the Vila Velha sandstone. In the studied area, the Itararé Group was deposited unconformably on a Devonian basement affected by tectonism triggered by the Eo-Hercynian orogeny during Late Devonian to Late Carboniferous times. Distribution of the lowermost glacial facies of the Itararé Group and its spatial relationship with major tectonic features suggest tectonic control during the first depositional phase in the Late Carboniferous. The second depositional phase was marked by deposition in marine, glaciomarine and shoreline environments due to deglaciation. This episode produced a 100 m thick and highly heterogeneous sand-rich succession (Vila Velha sandstone). Structural analysis showed that these sandstones were affected by at least three brittle deformational events, which appear as fracture systems and fault zones visible on remote sensing images and direct outcrop observation. The first deformation event generated north-northeast fracturing and northeast sinistral strike-slip faulting, exemplified by the Fortaleza Fault, probably related to Fini-Hercynian intraplate stress propagation induced by the Permian La Ventana-Cabo orogeny recorded in the Sierras Australes of Buenos Aires. The second event is recorded by northwest fractures and normal faults clearly related to the Early Cretaceous extensional and magmatic event due to the South-Atlantic rifting. This event produced the uplift of the Ponta Grossa Arch and the development of regional northwest structures that cross almost the entire basin, like the Rio Alonzo lineament. Patterns of sedimentation and superimposed tectonic deformations observed in the Vila Velha sandstone provide a stratigraphic/structural anisotropy that control flow units and fluid circulation within the porous media.