The roles of complex mechanical stratigraphy and syn-kinematic sedimentation in fold development: insights from discrete-element modelling and application to the Pico del Águila anticline (External Sierras, Southern Pyrenees)

Abstract

A 2D discrete-element modelling technique is used to explore the effects of complex mechanical stratigraphy and syn-kinematic sedimentation in the development of the Pico del Águila anticline (External Sierras, Southern Pyrenees). The stratigraphy (Middle Triassic–Oligocene in age) involved in this structure is characterized by a gross interlayering of competent and incompetent units, which leads to a striking variation in outcrop-scale deformation of the units observed in the field. The numerical model attempts to reproduce the stratigraphic variation seen in the field by using a mechanical stratigraphy that contains a complex interlayering of competent/incompetent units. Two experiments are presented. Model 1 tests the response of this complex mechanical stratigraphy to shortening under conditions that lead to the formation of a detachment fold. This experiment shows that folding mechanisms vary abruptly depending on the mechanical properties of the materials involved: the incompetent units are strongly internally deformed, accommodating much layer-parallel shearing; the competent units deform by rigid-body translation/rotation, localized faulting and minor internal shearing. Model 2 tests the effect of syn-kinematic sedimentation under identical boundary conditions: these sediments stabilize the fold against gravitational instabilities and cause a concentration of deformation in the core of the structure, leading to a tighter, narrower fold.

Syn-kinematic strata influence the structural evolution of emergent fold–thrust belts

“…These two sections show the same tectonic contraction (so would be numerical models (e.g. Strayer et al 2004;Vidal-Royo et al 2011;Hughes et al 2014). Analogue models show that the spacing and geometry of imbricate thrusts, together with their relative timing and activity, change depending on syn-kinematic sedimentation (Storti & McClay 1999;Bonnet et al 2008;Barrier et al 2013).…”

Impact of synkinematic sedimentation on the geometry and dynamics of compressive growth structures: Insights from analogue modelling

“…They demonstrate that erosion facilitates and prolongs the activity of thrusts without changing their geometry (Raleigh and Griggs, 1963;Elliott, 1976;Johnson, 1981;Price and Johnson, 1982;Willemin, 1984;Merle and Abidi, 1995). They also highlight that sedimentation affects the geometry and dynamics of thrusts and folds (Tondji-Biyo, 1995;1999;Casas et al, 2001; Barrier et al, 2002;Gestain et al, 2004;Strayer et al, 2004;Pichot and Nalpas, 2009;Vidal-Royo et al, 2011). However, the influence of synkinematic deposits on compressive growth structures has not yet been systematically explored according to the different sedimentation modes (a slow or rapid sedimentation rate that is constant or changing in space and time) that can occur in natural systems.…”

Seismic Imaging of Salt-influenced Compressional Folds

“…Hence, the displacement path, and kinematic evolution of the system can be recognized at any phase of the model (Vidal-Royo et al, 2011). For these reasons, this method has been used in many geological problems, especially involving the analysis of highstrain brittle deformation in the sedimentary cover such as normal faulting in layered sequences (Schöpfer et al, 2006(Schöpfer et al, , 2007a(Schöpfer et al, , 2007bEgholm et al, 2008;, fault bend folding (Strayer et al, 2004;Benesh et al, 2007), fault-propagation folding (Finch et al, 2003(Finch et al, , 2004Cardozo et al, 2005;Hardy andFinch 2006, 2007) (Hardy and Finch, 2005), and doubly vergent thrust wedges (Hardy et al, 2009), to name some examples.…”