A Permian-Triassic extensional wedge in northern Patagonia related to the Gondwanide post-orogenesis

Abstract

We have studied a syn-rift sedimentary wedge corresponding to Puesto Piris Formation deposited in a half-graben related to the post-orogenic Gondwanide extension during Changhsingian (late Permian) to Triassic in the northeastern Patagonia. The sedimentary succession is in a half-graben depocentre covering a Palaeozoic basement that was probably exhumed during the late Permian. The basal section of the Puesto Piris Formation contains thick levels of conglomerates, almost exclusively composed of basement fragments. The succession continues with arenites, tuffites, and limestones that conformably overlie the conglomerate beds. Red layers of conglomerates and sandstones that are rich in volcanic fragments culminate the succession. We linked the changes in texture and composition along with the sedimentary succession with variations in the tectonic activity of a master fault delimiting the half-graben depocentre. In addition, new U-Pb zircon ages allowed us to constrain the sedimentary and tectonic processes from Wuchiapingian to Olenekian, possibly extending to Anisian (late Permian to Early Triassic, probably early Middle Triassic). This age range is consistent with the new founding of cf. Dicroidium fossil remains in the lower section of the Puesto Piris Formation. The age and provenance of the Puesto Piris Formation resemble other contemporaneous basins in southern Pangea, suggesting a generalised extensional setting (rifting) linked to active volcanism as part of the post-orogenesis and ending of the Gondwanide Orogen during the Pangea assembly.