A set of Silurian black shales from Sierra de Albarracín (NE Spain) corresponding to two different sections was studied to determine the relative influence of diagenesis, igneous activity, and regional tectonics on the clay-mineral genesis. The coexistence of pyrophyllite, I-S interstratifications (R1), ammonium-rich illite, potassium illite, kaolin, and chlorite is not the result of prograde evolution during diagenesis – very low-grade metamorphism. Three different stages may be inferred: (1) sedimentation of black shales (Aeronian, Lower Silurian, to basal Ludfordian, Upper Silurian) and the subsequent diagenetic process producing the coexistence of quartz, illite, kaolinite, organic matter, etc.; (2) intrusion of andesitic sills producing hydrothermal alteration and crystallization of pyrophyllite, ammonium-rich illites, smectite, I-S R1 phases and jarosite; and (3) and folding of shales and sills and development of penetrative schistosity during the late Variscan leading to illite and paragonite recrystallization reaching the anchizone grade.

F. J. Gracia, F. Gutiérrez & M. Gutiérrez comment: In a recent paper, Rubio & Simón (2007) propose that the origin of the Jiloca Depression (Iberian Range, NE Spain) is primarily due to extensional neotectonics and estimate a Plio-Quaternary vertical offset of 350–400 m on the basin-bounding master fault. However, these authors omit crucial evidence presented in previous papers that contradict their model and derive interpretations from ambiguous or erroneous data. This discussion presents the main objections to their model and supports the mixed erosional (karstic) and tectonic origin proposed in previous research articles.