Pillow lavas and fluvio-lacustrine deposits in the northeast of Paraná Continental Magmatic Province, Brazil

Abstract

The northeast edge of the Paraná Continental Magmatic Province was marked by a topographical barrier that gave rise to a predominantly peridesertic environment. This high allowed the recurrent of above-average rainfall in this area of the Province, in contrast with other areas where many evidences indicate that lava flows have settled in an arid climate, in a desert environment. As a result, alluvial-fan debris flows and fluvio-lacustrine systems developed occasionally. This paper presents one of these sequences, which is remarkable for the presence of sedimentary rocks and two sets of pillow lavas. Both sets of pillow lavas show interaction with the fluvio-lacustrine sediments with distinctive grain size (from pebbly sand to clay) that locally preserve the original sedimentary structures such as bedding and lamination. This interaction gives rise to peperites, which show a diversity of textures for different sedimentary granulometries. Hyaloclastites and fragments of lava also occur in the interpillow material and may be intricately mixed with sediment. These features, based mainly on detailed field observations in the northeastern region, demonstrate that the palaeorelief, sedimentary environment, stratigraphy and morphology of sedimentary units and basaltic flows are contrasting from the central and southern regions of the Paraná Continental Magmatic Province.