6. Rotational kinematics of the Boltaña anticline - Instituto Geológico ...

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Boltaña kinematics Mochales, 2011 Figure 2. Geological map of the studied area, modified from Barnolas et al. (in press a and b). Formal and nonformal units have been individualized according their local use. UTM coordinates European datum ED50, zone 30T. 33
Boltaña kinematics Mochales, 2011 In the following sections, sampled formations will be marked in bold; nevertheless, we briefly describe all the units represented in the study area. Among them, the pre-tectonic units that can be distinguished are: Triassic: Middle-Upper Triassic rocks constitute the detachment level for the thrust sheets and associated folds involved in the study area. It consists of shales with thin layers of coastal plain and lagoonal evaporites, limestones and dolostones from shallow marine environments. Its thickness is difficult to determine, Alastrué et al., (1957) estimates around 250 m in outcrops in the core of the Mediano anticline, in the SE corner of the study area. Cretaceous: Cenomanian-Santonian (Upper Cretaceous) limestones and dolostones lie unconformably over Triassic rocks. A subsequent regional uncorformity evidences the beggining of the tectonic inversion (from extensional to compressive regimes) in the Southern Pyrenees. All this together, with the Campanian-Maastrichtian limestones and sandstones of the Marboré Fm, is almost 400 m thick in the Mediano anticline (Garrido-Megías, 1973) but can reach more than 3 km in the Cotiella unit (García Senz, 2002) in the NE edge of the study area. Paleocene: It can be found in the north of the study area and locally in the south near the Mediano Reservoir. Dolostones (Fm Salarons, Van der Velde, 1967), limestones and sandy limestones with tidal structures (Fm Gallinera, Van der Velde, 1967) represent the Paleocene Lower Ilerdian: The Alveolina Limestones (Mey et al., 1968), term equivalent to upper Gallinera Fm or Navarri Fm (Garrido-Megías and Ríos-Aragüés, 1972), represents the Lower Ilerdian in the Aínsa Basin. It is the consequence of an extensive transgression in the Pyrenean domain leading to the sedimentation of shelf-carbonated facies, as reflected by the stratigraphic discontinuity pointed by an erosive surface (Robador, 1991). It is composed of quartzite, quartz-gravelly limestones and limestones with chert nodules; its thickness ranges from 70 to 150 m (Fernández-Bellón, 2004). It represents the last quiescence stage before the development of the Aínsa foreland basin in the footwall of the SPCU (Garrido-Megías and Ríos-Aragüés, 1972; Nijman and Nio, 1975; Farrell et al., 1987; Vergés and Muñoz, 1990; Teixell and Muñoz, 2000) or the Montsec thrust sheet (Arbués et al., 1998; Fernández-Bellón, 2004; Fernández et al., 2004). It crops out in the cores of the Boltaña and Mediano anticlines (Figures 3 and 4). Middle-Upper Ilerdian: The Millaris Fm (Van der Velde, 1967; Van Lunsen, 1970) represents distal ramp, deeper facies that conformably overlie the Alveoline Limestones. Marls and marly limestones with thin layers of fine-grained siliciclastic turbidites (tempestites) appear in its upper part (Barnolas and Gil-Peña, 1991). Its age is Middle Ilerdian (Barnolas and Gil-Peña, 2001; Mochales et al., 2011). It crops out in the cores of the Boltaña and Mediano anticlines. Total thickness ranges from 70 to 200 m although the section studied in this work covers 100 m. The Metils Fm (Van Lunsen, 1970) overlies the Millaris Fm and is laterally equivalent to its upper part in some sectors. This unit is Middle Ilerdian in age (Barnolas and Gil-Peña, 2001; Mochales et al., 2011). It represents the progradation of carbonate ramp facies as evinces the decimetric limestone layers interlayered with thinner marl beds with abundant fossils (sponges, bryozoans and echinoderms). It thickens northwards, reaching 180 m in the Ara River section. 34
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