Abstract Despite the intriguing correlation between continental flood basalt provinces and environmental crises, little is known about how the local/regional sedimentary systems and environment respond to flood basalt volcanism. Active sedimentary systems, and their interaction with volcanism, provide an important rock record to understand palaeoenvironments in volcanic settings. The Paraná–Etendeka Igneous Province is a well-known example of a continental flood basalt emplaced on a dry desert environment, but evidence has also shown the existence of humid conditions during the volcanic episode. This work describes and interprets non-volcanic sedimentary and volcaniclastic rocks interbedded with Paraná–Etendeka Igneous Province lavas in southernmost Brazil to better understand the palaeoenvironmental process and changes during the onset of volcanism. Non-volcanic sedimentary rocks record the existence of ephemeral sheet-like flows and ponds/lakes while volcaniclastic rocks document hydromagmatic activity, supporting a change to more humid conditions. Stratigraphic constraints indicate that this change started with the onset of volcanism and affected the whole province. We suggest that SO 2 degassing from the Paraná–Etendeka province may have caused a net global surface cooling, resulting in precipitation redistribution and a local increase in rainfall. This hypothesis may help explain the cooling and increased humidity observed elsewhere to be closely related to the Paraná–Etendeka emplacement.

Abstract The lake sediments are preserved as two separate layers interleaved with Early Jurassic Kalkrand flood basalts (Duncan et al., 1984; Cerschutz, 1996) and are best exposed around Hardap reservoir, 15 km north of Mariental town in southwestern Namibia (Figure1). The 55-300 m thick volcano-sedimentary sequenceun conformably oversteps underlying Triassic(Stormberg) and latest Carboniferous-Early Permian(Dwyka and Ecca) sediments in the east onto latest Proterozoic-Early Cambrian (Nama) basement toward the west (Heath, 1972; Schalk and Germs,1980). The top of the sequence is defined by the erosive Cretaceous land surface with continental sediments of the Cenozoic Kalahari thermal sag basin draped thinly over the top. The 183.0 0.6 Ma to 186.0 0.8 Ma dated olivine-tholeiitic basalts (Duncanet al., 1997) of the Kalkrand Formation were extruded during extensional rifting between South America and Africa (Miller, 1992; Dingle, 1993). This was one of a series of early rifting episodes from the Permian onward (Figure 2) prior to ultimate extensional rift phases during the Early Cretaceous. The latter caused extrusion of the Etendeka-Parana flood basalts and onset of South Atlantic oceanic opening(Hawkesworth et al., 1992; Renne et al., 1996; Gladczenkoet al., 1997). Extensional tectonism was experienced in the study area along a northerly trending set of extensional167faults dipping toward the east. This is inferred (Stollhofenet al., 1998) to be conjugate to a westerly dipping break-away detachment system that connected with the more major detachment toward the west,along which oceanic opening was eventually effected(Maslanyj et al., 1992; Light et al., 1992, 1993).The Hardap area is therefore characterized by