Geometry, kinematics and fracture pattern of the Bangestan anticline, Zagros, SW Iran

Abstract

Thrust-related anticlines in the Zagros Simply Folded Belt provide excellent exposed analogue structures for fractured reservoirs located in the more external sectors of the belt. In these structures it is possible to study the fracture network attributes and understand their relationships to the folding process, thus gathering fundamental information for fracture modelling in reservoirs. In this work we analyse the mesoscopic deformation pattern of the NW–SE-trending Bangestan anticline (SW Zagros, Iran) and discuss its relationship to the kinematic evolution of the hosting structure. The deformation pattern mostly includes extensional structures and pressure solution cleavages striking parallel to the fold axial trend (i.e. longitudinal), transversal extensional structures, and N–S- and E–W-striking extensional structures (oriented oblique to the fold axis). With the aid of deep wells and a transversal reflection seismic profile, we constructed a balanced cross-section of the anticline and propose a kinematic evolution pathway constrained by the mesoscopic deformation pattern. Longitudinal and transversal deformation structures developed before and/or in the very early stages of fold growth. During this stage, the Bangestan anticline grew as a set of unconnected décollement anticlines involving the Cambrian to Pliocenic sedimentary cover. In a later stage, inherited basement faults were reactivated with a right-lateral strike-slip component and the previously developed anticlines propagated laterally up to their complete linkage and thrust breakthrough. This produced the right-lateral strike-slip reactivation of longitudinal joints and the development of N–S- and E–W-striking extensional structures, which were also frequently reworked as strike-slip faults.

Uplift-induced residual strain release and late-thrusting extension in the Anaran mountain front anticline, Zagros (Iran)

“…8B) hosted in exposed km-scale thrust-related folds involving carbonate multilayers, which indicate a pre-to syn-thrusting strike-slip stress regime, at least in the shallower portions of the thrust and fold belt, with the stress field having a subhorizontal σ1 oriented parallel to the regional shortening direction, a near-vertical σ2, and a sub-horizontal and foredeep-parallel σ3 (e.g. Ahmadhadi et al, 2008;Amrouch et al, 2011;Erslev, 2001;Lacombe et al, 2011;Quintà and Tavani, 2012;Tavani et al, 2006Tavani et al, , 2011aTavani et al, , 2011bTavani et al, , 2012.…”

“…An example of this is the mountain front of the Zagros Simply Folded Belt, where abundant studies have been carried out to provide insights on the fracture patterns in the adjacent reservoirs (e.g. Ahmadhadi et al, 2008;Awdal et al, 2013;Casini et al, 2011;McQuillan, 1974;Stephenson et al, 2007;Tavani et al, 2011a;Wennberg et al, 2006).…”

“…In addition, outer arc extension is not capable of explaining why some mountain front anticlines with a radius of curvature of many km are characterised by an intense array of extensional faults, like the Khaviz Anticline Tectonophysics 636 (2014) 257-269 (Wennberg et al, 2007), while the neighbour and more curved mountain front anticline (i.e. the Bangestan Anticline) holds mostly outcrop-scale extensional faults, even in the hinge zone between the crest and the recumbent backlimb, where the radius of curvature is less that one thousand metres (Tavani et al, 2011a).…”

Kinematics and surface fracture pattern of the Anaran basement fault zone in NW of the Zagros fold–thrust belt

“…These oblique sets include fractures striking about N-S and E-W (e.g., Amrouch et al 2010;Lacombe et al 2011), and they have been interpreted as related with the reactivation of inherited, N-S striking, basement faults (e.g., Stephenson et al 2007;Tavani et al 2011). On the other hand, occurrence and reactivation of oblique inherited faults during thrusting, can determine local perturbation of the stress field and the development of local fracture patterns.…”

Introduction: geodynamic evolution of the Zagros

“…The main insights of this modelling are the better definition of the depth to basement, and the pre-salt morphology, the geometry at depth of salt diapirs and the interaction between salt diapirism and folding. Tavani et al (2011) analyse mesoscopic deformation pattern of the Bangestan anticline (SW Zagros, Iran) and discuss its relationships with the kinematic evolution of the hosting structure. They conclude that anticlines in the Simply Folded Belt provide excellent exposed analogue structures for fractured reservoirs located in the more external sectors of the belt.…”