G Model CRAS2A-3299; No. of Pages 11 C. R. Geoscience xxx (2016) xxx–xxx Contents lists available at ScienceDirect Comptes Rendus Geoscience ww w.sciencedirect.com Tectonics, Tectonophysics Early–Middle Miocene subtle compressional deformation in the Ebro foreland basin (northern Spain); insights from magnetic fabrics a, a,b b c Ruth Soto *, Juan C. Larrasoan˜a , Elisabet Beamud , Miguel Garce´s a Instituto Geolo´gico y Minero de Espan˜a (IGME), Unidad de Zaragoza, C/Manuel Lasala, 44, 9B, 50006 Zaragoza, Spain b Laboratori de Paleomagnetisme CCiTUB-ICTJA CSIC, Institut de Cie`ncies de la Terra ‘‘Jaume Almera’’, Sole´ i Sabarı´s, s/n, 08028 Barcelona, Spain c Departament d’Estratigrafia, Paleontologia i Geocie`ncies Marines, Universitat de Barcelona, Martı´ i Franque`s s/n, 08028 Barcelona, Spain A R T I C L E I N F O A B S T R A C T Article history: The results of anisotropy of magnetic susceptibility analyses of 19 sites carried out on Received 28 September 2015 magnetostrigraphically-dated, Lower to Middle Miocene (20.4 to 13.7 Ma) ‘‘non- Accepted after revision 23 October 2015 deformed’’ mudstones from the central part of the Ebro basin reveal the presence of a Available online xxx subtle tectonic overprint lasting at least until the Langhian (Middle Miocene) in the southern Pyrenean foreland. Magnetic ellipsoids show a sedimentary fabric in 42% of sites Handled by Marguerite Godard and a weak and well-defined magnetic lineation in 47% and 11% of sites. The magnetic lineation is roughly oriented around the east–west direction, compatible with a very weak Keywords: deformation occurring there and related to the north–south compression linked to the Anisotropy of Magnetic Susceptibility (AMS) Ebro foreland basin convergence between Europe, Iberia and Africa during the Early–Middle Miocene. A slight Subtle deformation variation of the magnetic parameters Km, Pj, and T exists through time, probably due to changes in the sedimentary conditions in the basin. ß 2015 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved. 1. Introduction Garcı´a-Castellanos et al., 2003), its basement mainly dips northwards indicating the Pyrenees as the main contributor The Ebro foreland basin, located on the northeastern to tectonic load (Gaspar-Escribano et al., 2001; Milla´n et al., region of the Iberian plate, has been extensively studied 1995). Subsurface data show the existence of several during the last decades as a natural example that enables structures affecting the Paleozoic and Mesozoic sequences analysing the links between thrust belt kinematics, orogenic below the Cenozoic horizontal deposits outcropping in the loading, flexural subsidence and basin erosion (Desegaulx Ebro basin (Arlegui and Simo´ n, 2001), which were still active and Moretti, 1988; Garcı´a-Castellanos and Larrasoan˜a, during the Early Miocene (Klimowitz, 1992). These structu- 2015; Garcı´a-Castellanos et al., 2003; Gaspar-Escribano res have been interpreted as accommodation structures (i.e. et al., 2001; Hoth et al., 2008; Jones et al., 2004; Milla´n et al., forced folds, primary salt welds, and salt collapses) relatedto 1995; Verge´s et al., 1998; Zoetemeijer et al., 1990). Despite the Late Jurassic–Early Cretaceous rifting that occurred in the multivergent character of the tectonic loading of the the northern Iberian plate and the presence of Triassic Ebro foreland basin (coming from the Pyrenees, Iberian and evaporites (Butille´ et al., 2012). Through the Cenozoic, in Catalan Coastal Ranges, e.g., Desegaulx and Moretti, 1988; response to the African–Iberian–European convergence, a sequential evolution in the main deformational stage existed from the Pyrenees, where the main stage of thrusting occurred during Late Eocene–Early Oligocene to intraplate * Corresponding author. E-mail address: [email protected] (R. Soto). mountain belts as the Iberian Ranges, where the maximum http://dx.doi.org/10.1016/j.crte.2015.10.009 1631-0713/ß 2015 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved. Please cite this article in press as: Soto R, et al. Early–Middle Miocene subtle compressional deformation in the Ebro foreland basin (northern Spain); insights from magnetic fabrics. C. R. Geoscience (2016), http://dx.doi.org/10.1016/ j.crte.2015.10.009 G Model CRAS2A-3299; No. of Pages 11 2 R. Soto et al. / C. R. Geoscience xxx (2016) xxx–xxx tectonic activity occurred during the Late Eocene–Early magnetostratigraphic studies) as Late Oligocene–Early Miocene, coinciding with the decline of activity in the Miocene at its southern deformation front (Arenas et al., Pyrenees (Casas-Sainz and Faccenna, 2001). 2001; Garcı´a Senz and Zamorano, 1992). A few very young The Anisostropy of Magnetic Susceptibility (AMS) is a (Middle Miocene) thermochronology data (AFT and AHe recognized indicator of deformation, even in very subtle ages) have been interpreted as recording late out-of- deformed rocks (e.g., Kissel et al., 1986). AMS analysis has sequence thrusting in two massifs from the internal part of been applied during the last decades to characterize the chain (Gibson et al., 2007; Jolivet et al., 2007). In the deformation in fold-and-thrusts belts and/or sedimentary Iberian Range, most compressional structures formed basins (e.g., Cifelli et al., 2004; Mattei et al., 1997; Pare´s, between the Late Eocene and the Early Miocene, as dated 2015; Soto et al., 2007 and references therein). Despite that also by tectonic–sedimentary relationships (Casas-Sainz it has not been extensively used in foreland basins, several and Faccenna, 2001). works have demonstrated the potential of AMS to detect The margins of the Ebro basin display thick conglom- very weak tectonic magnetic fabrics in the Ebro foreland erate sequences recording the main tectonic events of the basin (Oliva´n et al., 2008; Pare´s et al., 1999; Pueyo- Pyrenees, Iberian and Coastal Ranges. Toward the central Anchuela et al., 2010; Sans et al., 2003; Soto et al., 2009) part of the basin, conglomerates grade to sandstones and and in the northern Chinese Tarim basin (Charreau et al., mudstones of alluvial and fluvial origin. Such fluvial 2006; Huang et al., 2006, 2010). The origin of the preferred systems converged into the internal sector of the basin, orientations of magnetic grains in these scenarios has been where palustrine areas and extensive freshwater and related to the existence of compressive tectonic strain at saline lake systems developed depending on climate the foreland basin and/or layer parallel shortening conditions (Alonso-Zarza et al., 2002; Arenas et al., extending well beyond the deformation front of the 2001; Pardo et al., 2004). With the exception of its orogen. In the Tarim basin, AMS data are complemented westernmost sector, where the Ebro basin displays a with magnetostratigraphic studies that have permitted to symmetric filling coming from its northern and southern constrain accurately the age of the tectonic imprint margins (Mun˜oz-Jime´nez and Casas-Sainz, 1997), its recorded in rocks and to relate it to the Late Cenozoic sedimentary thickness reaches more than 5500 m at its Tian Shan uplift (Charreau et al., 2006; Huang et al., 2006). northern (Pyrenean) margin, in contrast with up to 3000 m In this work, a total of 19 sites were sampled on Lower to at its southern (Iberian) margin (Alonso-Zarza et al., 2002; Middle Miocene (20.4 to 13.7 Ma) lacustrine mudstones Pardo et al., 2004). This sedimentary asymmetry, together outcropping at the central part of the Ebro foreland basin. with the northward dipping of its basement, have An accurate chronology for these mudrocks has been traditionally led to consider the flexural subsidence of established by means of magnetostratigraphic analyses the Ebro basin mainly formed in response to the loading of (Pe´rez-Rivare´s et al., 2002). The goal of this work is to the Pyrenees (Gaspar-Escribano et al., 2001; Milla´n et al., analyse late compressional deformation recorded in 1995; Mun˜oz, 1992; Naylor and Sinclair, 2008). sediments apparently undeformed from the Ebro foreland In the Ebro foreland basin, deformation associated with basin and to give clues regarding the origin of tectonic thrusting and folding in the autochthonous Cenozoic series magnetic fabrics in foreland basins. is only visible at surface at its margins. This deformation varies from thin- to thick-skinned deformation in the 2. Geological setting northern (Pyrenean) and southern (Iberian and Catalan) margins, respectively. In the central part of the Ebro basin, The triangular-shaped Ebro basin, located in the the Oligocene and Miocene materials define a very gentle northeastern Iberian Peninsula, constitutes the foreland syncline, the Ebro syncline (Arlegui, 1996; Quirantes, basin of three Alpine ranges: the Pyrenees to the north, the 1978), oriented N110E (Fig. 1), and whose wide hinge Iberian Chain to the south, and the Catalan Coastal Ranges coincides with the studied area. This syncline has been to the east (Fig. 1). Its formation started during the interpreted as a bending fold created to accommodate the Palaeocene by flexural subsidence related to the growth of subtle reactivation of WNW–ESE basement faults in these ranges. Between the Late Eocene and the Late response to the lithosphere flexure of the Ebro basin Miocene, the Ebro basin constituted an internally drained linked to isostatic rebound (Arlegui and Simo´ n, 2001). In depression (Alonso-Zarza et al., 2002; Costa et al., 2010; the Ebro basin, by the Late Miocene, sedimentation Garcı´a-Castellanos et al., 2003), which resulted in the diminished drastically and large erosion surfaces devel- accumulation of a continuous sequence of Latest Eocene, oped at its central part (Soriano, 1990). Thermochronology Oligocene and Miocene continental sediments (Alonso- and numerical modelling data also support a Late Miocene Zarza et al., 2002; Arenas et al., 2001).