Cerro do Jarau, RS, Brazil, is a bona fide impact structure – Not a cryptoexplosion structure as alleged. [Comment on “Resurfaced paleodunes from the Botucatu erg amid Cretaceous Paraná volcanics” by , Geomorphology (2021), doi:10.1016/j.geomorph.2021.107893

Abstract

Hartmann and Cervo-Alves (2021) recently discussed the Inhandui Paleodune Field in the southern Paraná Basin of southern Brazil. They particularly emphasized the Cerro do Jarau structure of 13 km diameter, which they interpreted as a “compound paleodune”. The established shock deformation in arenites from this structure (of a minimum of 10 GPa, Reimold et al., 2019) was interpreted by them as caused by explosive hydrothermalism, that means jets of a hot water-sand mixture. This process had also been responsible for widespread silicification of Cerro do Jarau rocks. These authors alleged that such a process could generate the shock pressures in the order of 10 GPa constrained from observations of bona fide planar deformation features, in contrast to our interpretation that this evidence represents firm evidence for Cerro do Jarau is a confirmed impact structure. Lithostatic pressures of the order of 10 GPa or more in the uppermost crust cannot be achieved, so that any endogenic degassing/hydrothermal venting model is unrealistic. This apparent contradiction of hypotheses requires a detailed look at the evidence for an impact cratering origin of Cerro do Jarau, which necessarily results in the complete rebuttal of this “explosive” hydrothermalism hypothesis.