Evolution of near‐surface ramp‐flat‐ramp normal faults and implication during intramontane basin formation in the eastern Betic Cordillera (the Huércal‐Overa Basin, SE Spain)

Abstract

[1] The nucleation, propagation, and associated folding of ramp-flat-ramp normal faults were analyzed from field examples developed in a brittle/ductile multilayer sequence of the Huércal-Overa Basin (SE Spain). Gently dipping sandy silt layers, which display a low cohesive strength (C 0 = 7 kPa, m = 34 ), favor the development of extensional detachments. A tectonic origin instead of a possible gravitational origin is supported by the perpendicularity between the paleoslope direction of the fluvial-deltaic environment inferred from imbricated pebbles, and the senses of movement deduced from fault slickenlines. The link between high-angle normal faults (HANFs) -formed at different levels in the layered sequence-with horizontal fault segments comes to develop ramp-flat-ramp normal faults with associated roll-over in the hanging wall. Observed extensional duplexes are formed by parallel detachments connected through synthetic Riedel faults. These Riedel faults would produce the back-rotation of the individual blocks (horses), i.e., extensional folding of the originally subhorizontal layers. There is no correlation between the analyzed ramp-flat-ramp normal faults, accommodating south-southeastward extension during Serravallian-lower Tortonian, and either the regional Alpujarride/ Nevado-Filabride west-directed extensional shear zone or the top-to-the-north detachments within Alpujarride units, which are clearly sealed by Serravallian-lower Tortonian sediments. Therefore, the studied normal faults are restricted to the brittle/ductile multilayer fluvio/deltaic sequence and accommodate moderate late extension instead of belonging to a large crustal extensional system connected with a regional detachment at depth. Therefore, the basin formed in a moderate crustal thickness context where small and medium-scale extensional systems were subordinate structures. These natural examples support the development of low-angle normal faults at very shallow crustal levels in multilayer sequences with suitable rheological conditions. Citation: Pedrera, A., J. Galindo-Zaldívar, F. Lamas, and A. Ruiz-Constán (2012), Evolution of near-surface ramp-flat-ramp normal faults and implication during intramontane basin formation in the eastern

From ductile to brittle, late- to post-orogenic evolution of the Betic Cordillera: Structural insights from the northeastern Internal zones

“…Normal faulting that occurred during sedimentation or the early diagenesis stages within the basin has already been documented in many previous studies toward which the reader is referred for more details [Briend, 1981;Briend et al, 1990;Ott d'Estevou and Montenat, 1990;Mora, 1993;Augier, 2004;Meijninger and Vissers, 2006;Pedrera et al, 2007Pedrera et al, , 2010Pedrera et al, , 2012. Only new descriptions of syn-sedimentary and stratigraphic age constraints are now presented in details.…”

“…The consistent~W-E to NW-SE orientation of the fault trace direction and the associated slickenside lineation carried by fault planes, irrespective of the delta palaeoslope Meijninger, 2006;Pedrera et al, 2007] clearly discard a pure gravitational origin as already described in deltaic context [e.g. Maloney et al, 2010;Pedrera et al, 2012].…”

“…While normal faults generally develop as 50-70 o -dipping roughly planar surfaces in the sandstone or conglomerate layers, they conversely display a gentle to flat dips in the siltstone or claystone layers. These two types of faults, both oriented W-E to NW-SE interact and often form flat-ramp-flat systems or sets of steep normal faults that bend down on a layer-parallel gently-dipping master normal faults [Mora, 1993;Augier, 2004;Meijninger, 2006;Pedrera et al, 2012]. Arguments including bed omission and rapid lateral changes of both the sedimentary facies and the thickness of the layers in the vicinity of the faults strongly argue for an extensional deformation that occurred during sedimentation [see e.g.…”

“…Basins are indeed diversely interpreted as resulting from late-orogenic extensional processes, strike-slip tectonics (e.g. pull-apart basins) or simply flexural synclines [Bousquet and Montenat, 1974;Bousquet et al, 1975;Montenat et al, 1977;Bousquet, 1979;Ott d'Estevou and Montenat, 1990;Mora, 1993;Vissers et al, 1995;Silva et al, 1997;Montenat and Ott d'Estevou, 1999;Poisson et al, 1999;Augier, 2004;Meijninger and Vissers, 2006;Pedrera et al, 2007Pedrera et al, , 2009Pedrera et al, , 2010Pedrera et al, , 2012. In order to test these various interpretations, this study explores the tectonic record of the prominent~E-W-trending Huércal-Overa and Almanzora corridor basins, lying either in the hanging wall of a major extensional shear zone (e.g.…”

Tectonic inversion of an asymmetric graben: Insights from a combined field and gravity survey in the Sorbas basin

“…The extensional regime which affected the Betic Cordillera and, in a more regional extent, the entire Alboran domain started from the late Oligocene to early Miocene (see Vergés and Fernàndez [2012] for a review of tectonic evolution) and is widely documented both offshore [Watts et al, 1993;Comas et al, 1999] or onshore [García-Dueñas et al, 1992;Galindo-Zaldívar et al, 2003], especially in the Huércal-Overa basin [Briend et al, 1990;Augier et al, 2005a;Meijninger and Vissers, 2006;Pedrera et al, 2009Pedrera et al, , 2010Pedrera et al, , 2012Augier et al, 2013]. This later displays an overall half-graben geometry accompanied by mesoscale to small-scale synsedimentary normal faults.…”