Abstract
The northern part of the eastern margin of the extensional Neogene Teruel Basin (central-eastern Spain) consists of a non-linear, zigzag fault zone made of alternating ca. 2 km long, NNW-SSE trending segments and shorter NNE-SSW ones. Good outcrop conditions made possible a comprehensive integrated stratigraphic and structural study, especially focused on coarse clastic sediments deposited along the basin margin. Well-exposed stratal relationships with boundary faults, allowed the analysis of tectonic influence on sedimentation. Synsedimentary deformation includes growth faulting, rollover anticlines, and monoclines and associated onlap stratal terminations, angular unconformities, and other complex growth strata geometries. One of them is the onlap-over-rollover bed arrangement described here for the first time, which reveals the competition between tectonic subsidence and sedimentary supply. Both, the structural inheritance (dense Mesozoic fracture grid) and the dominant, nearly ‘multidirectional’ (σ1 vertical, σ2 ≈ σ3), Pliocene extensional regime with σ3 close to E-W, are considered to have controlled the margin structure and evolution. Tectono-stratigraphic evolution includes: (i) reactivation of inherited NNW-SSE faults and development of W-SW-directed small alluvial fans (SAF) while NNE-SSW segments acted as gentle relay ramp zones; (ii) progressive activation of NNE-SSW faults and development of NW-directed very small alluvial fans (VSAF); during stages i and ii sediments were trapped close to the margin, avoiding widespread progradation; (iii) linking of NNW-SSE and NNE-SSW structural segments, overall basin sinking and widespread alluvial progradation; (iv) fault activity attenuation and alluvial retrogradation. The particular structure and kinematic evolution of this margin controlled alluvial system patterns. Size of alluvial fans, directly set up at the border faults, was conditioned by the narrowness of the margin, small catchment areas, and proximity between faults, which prevented the development of large alluvial fans. The size of the relay zones, only a few hundred meters wide, acted in the same way, avoiding them to act as large sediment transfer areas and large alluvial fans to be established. These features make the Teruel Basin margin different to widely described extensional margins models.
Highlights
Water flows from feeder channels lost their confinement after reaching the basin and resulted in high-energy flash floods that rapidly decrease in energy and transport capacity
1) The eastern active margin of the northern Neogene Teruel Basin is made of a dense network of NNESSW and NNW-SSE faults that are derived from the main sets of inherited Mesozoic fractures
The margin evolution was characterised by a selective reactivation of previous faults under a favorably orientated stress field (σ3 close to E-W), a process easier than the formation of new faults directly controlled by the remote stress field or the kinematics of the fault zone
Summary
Increasing knowledge of tectono-sedimentary evolution of basin margins characterised by coalescent oblique fault sets that form a continuous zigzag has developed in the last two decades (e.g., Gupta et al 1999; Gawthorpe and Leeder 2000; Younes and McClay 2001, 2002; Gawthorpe et al 2003a, b; Pascucci et al 2006; Moustafa and Khalil 2017a, b). Some works focus on faulting geometries in linkage zones (Walsh et al 1999), while others regard as important the role of stress perturbations near fault tips and their influence on length–displacement ratios and displacement gradients (Willemse et al 1996; Crider and Pollard 1998; Gupta and Scholz 2000) Most of these models assume an undeformed rock massif in which new fault systems develop. Such a role has been proved by means of (i) serial cross-sections and 3D modelling, in e.g., Suez Gulf area (Moustafa 1997; Moustafa 2002), Vallès-Penedès Fault, Spain (Belenguer Oliver et al 2012) and Malawi Rift (Mortimer et al.2016), or (ii) analogue and numerical modelling (e.g., McClay et al 2002; Hus et al 2005; Corti et al 2007)
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