STRATIGRAPHIC AND GEOCHRONOLOGICAL EVIDENCE FOR THE AGE OF AN IMPACTOGENIC THE ARAGUAINHA IMPACT STRUCTURE IN CENTRAL BRAZIL: AN END-PERMIAN IMPACTOGENIC TSUNAMI?

Recent studies of the Araguainha impact structure indicate an age contemporaneous with the end-Permian mass extinction, which is speculatively linked to the impact event through release of methane from oil shales of the Paraná Basin. We conducted field investigations of the stratigraphic record of the Araguainha impact in the Paraná Basin, and report the occurrence of seismites, i.e., clastic dikes and breccias at distances 50–1000 km from the 40 km Araguainha impact structure. Seismites are overlain by a ≤4.5 m-thick debrite known as the ‘Porangaba bed’, which is a poorly-mixed conglomerate with floating clasts up to 50 cm in length, and two fining-upward sequences. We interpret this bed as a tsunami deposit within the shallow Paraná Basin. Samples of the Porangaba bed located 50 to 800 km from the center of the impact structurecontain zircons that exhibit potential shock features in polished grain mounts. Shock features will be confirmed by EBSD. The presence of probable shocked material demonstrates a causal link to the impact event. A SHRIMP study of detrital zircons from the event bed identified the youngest population (n=12) of detrital zircons, providing a maximum depositional age of 253.0 ± 3.0 Ma. These findings demonstrate that the Araguainha impact structure was a catastrophic event that defines the P–T boundary in Brazil and created one of the world’s most extensive seismite–tsunamite couplets.