Discussion of the article “Controversial epiglyptic thrust sheets: The case of the Daroca Thrust (Iberian Chain, Spain)” by Simón et al. (2021) (Full article in Spanish)
by Ferran Claudin & Kord Ernstson (April 2021)
Abstract
Simón et al. (2021), argue for an origin linked to a thrust under surface conditions (epiglyptic), in which the thrusting part lies on a base coincident with the land surface. They discard the hypotheses of Guimerà (1988, 2013) and Gutierrez et al. (2020) that consider a paleoslip (with differences between both hypotheses) to explain the frontal segment of the alleged Daroca thrust. They base this on the existence of recumbent folds in the competent Cambrian dolomites, on the existence of a damage zone with foliated fault rocks, the physical continuity between the headwall and the main thrust ramp and on the transport directions to the NNE and the E. For Claudin & Ernstson (2012, 2020 and 2021), the alleged Daroca dipping fault is not such and corresponds in reality, together with those located at Murero, Baguena, Burbáguena and Luco de Jiloca, to a set of blocks ejected during the impact that gave rise to the Azuara event. This is based on: the existence of a root zone (outcrops) of Cambrian dolomites on the SW edge of the Azuara impact structure that has been “emptied” by the aforementioned impact; the presence of high confining pressure characteristics in the alleged fault flours incompatible with epiglyptic conditions (at depths less than 2 km); the practically negligible damage in the Paleocene materials, incompatible with the conditions that are supposed to have given rise to the fault flour by epiglyptic thrusting; the presence in practically all Ribota dolomites and Paleozoic rocks of a texture that implies the action of a large confining pressure, again incompatible with epiglyptic conditions; the presence of fluid structures – compatible with a mass transport – in the contact zone between Cambrian and Ramblian materials (Upper Oligocene-Lower Miocene) of Gutierrez et al. (2020).