Controversial epiglyptic thrust sheets: The case of the Daroca Thrust (Iberian Chain, Spain)

摘要

Epiglyptic thrusts can be misinterpreted as paleolandslides since they underwent displacement on the Earth surface. The Daroca Thrust has been object of controversial interpretations owing to (i) the particular style of its frontal structure (a thin slab of Cambrian dolostones overthrusting syntectonic Miocene deposits), and (ii) its relatively young age with respect to the overall compressional building of the Iberian chain. While several authors have interpreted its frontal flat as a synsedimentary landslide, a number of key features evince that it represents an epiglyptic thrust: (i) recumbent folds in competent Cambrian dolostones; (ii) thick damage zone with foliated fault rocks; (iii) physical continuity between the frontal flat and the main thrust ramp; (iv) transport directions towards NNE and E consistently recorded in both of them. Geometric reconstruction in cross section indicates that the syntectonic deposits of the Daroca area lie below the well-dated succession of the Aragonian stratotype (Middle Miocene). Nevertheless, by extrapolating the age model resulting from the complete succession of mammal sites, it can be inferred that the slip on the Daroca Thrust still took place during Middle Aragonian time.