Deformation bands are common subseismic structures in porous sandstones that vary with respect to deformation mechanisms, geometries and distribution. The amount of cataclasis involved largely determines how they impact fluid flow, and cataclasis is generally promoted by coarse grain size, good sorting, high porosity and overburden (usually >500–1000 m). Most bands involve a combination of shear and compaction, and a distinction can be made between those where shear displacement greatly exceeds compaction (compactional shear bands or CSB), where the two are of similar magnitude (shear-enhanced compaction bands or SECB), and pure compaction bands (PCB). The latter two only occur in the contractional regime, are characterized by high (70–100°) dihedral angles (SECB) or perpendicularity (PCB) to σ1 (the maximum principal stress) and are restricted to layers with very high porosity. Contraction generally tends to produce populations of well-distributed deformation bands, whereas in the extensional regime the majority of bands are clustered around faults. Deformation bands also favour highly porous parts of a reservoir, which may result in a homogenization of the overall reservoir permeability and enhance sweep during hydrocarbon production. A number of intrinsic and external variables must therefore be considered when assessing the influence of deformation bands on reservoir performance.

The Paraná Basin is a key locality in the context of the Late Paleozoic Ice Age (LPIA) because of its location east of the Andean proto-margin of Gondwana and west of contiguous interior basins today found in western Africa. In this paper we document the sedimentary record associated with an ice margin that reached the eastern border of the Paraná Basin during the Pennsylvanian, with the aim of interpreting the depositional environments and discussing paleogeographic implications. The examined stratigraphic succession is divided in four stacked facies associations that record an upward transition from subglacial to glaciomarine environments. Deposition took place during deglaciation but was punctuated by minor readvances of the ice margin that deformed the sediment pile. Tillites, well-preserved landforms of subglacial erosion and glaciotectonic deformational structures indicate that the ice flowed to the north and northwest and that the ice margin did not advance far throughout the basin during the glacial maximum. Consequently, time-equivalent glacial deposits that crop out in other localities of eastern Paraná Basin are better explained by assuming multiple smaller ice lobes instead of one single large glacier. These ice lobes flowed from an ice cap covering uplifted lands now located in western Namibia, where glacial deposits are younger and occur confined within paleovalleys cut onto the Precambrian basement. This conclusion corroborates the idea of a topographically-controlled ice-spreading center in southwestern Africa and does not support the view of a large polar ice sheet controlling deposition in the Paraná Basin during the LPIA.

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