Evidence for pre‐folding vein development in the Oligo‐Miocene Asmari Formation in the Central Zagros Fold Belt, Iran

Abstract

[1] In order to understand the interplay between vein development and folding in the carbonates of the Oligo-Miocene Asmari Formation (one of the main hydrocarbon reservoir rocks) in Iran, several anticlines have been investigated in the central part of the Zagros folded belt. Combining observations of relative chronology between veins based on calcite-filling phases and crosscutting/abutting relationships, as well as aerial/satellite image interpretation on several anticlines allowed proposing a tectonic model highlighting the widespread development of veins and other extensional micro/meso-structures in the Central Zagros folded belt. Our data suggest that most of the veins affecting the Asmari formation predated the main Miocene-Pliocene folding episode. An early regional vein set striking N50°marked the onset of collisional stress build-up in the region. Then, N150°a nd N20°trending vein sets were initiated in response to local extension caused by large-scale flexure/drape folds above N-S and N140°basement faults reactivated under the regional NE compression. At the onset and during Miocene-Pliocene folding of the sedimentary cover, the early formed veins were reactivated (reopened and/or sheared) while duplexes, low angle reverse faults and thrusts formed. Beyond regional implications, this study puts emphasis on the need of carefully considering regional/local vein development predating folding as well as influence of underlying basement faults in models of folded-fractured reservoirs in fold-thrust belts.

Lithology effects on the fractures parameters using image log and petrophysical data

“…Folding process of this basin occurred in Miocene and Pliocene and continued until now which formed long anticlines [Ahmadhadi et al, 2008;Mottie, 1995;Twerenbold and McQuillan, 1962]. These anticlines constitute most of oil traps in this basin.…”

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

“…The ZFTB hosts more than half of the world's hydrocarbon reserves (Sepehr and Cosgrove 2005). High productivity of these reserves is related to the presence of fractures that have led to secondary effective porosity in carbonate reservoirs (Gholipour 1998;Ahmadhadi et al 2008;Mobasher and Babaie 2008;Khoshbakht et al 2009Khoshbakht et al , 2012.…”

“…The activity of preexisting north-south trending basement faults and their effect on structural and sedimentation history in the ZFTB have been documented (Berberian 1995;Hessami et al 2001a;Bahroudi and Talbot 2003;Sepehr and Cosgrove 2005;Ahmadhadi et al 2007;FarzipourSaein et al 2009aFarzipourSaein et al , 2013. While the spatial density and dispersal variation of fold-related fractures depend on the fold geometry, a fault-related fracture system is localized along isolated linear zones, possibly marking boundaries of a basement block (Stephenson et al 2007;Ahmadhadi et al 2008;Lacombe et al 2011).…”

“…In the ZFTB, fracture studies were mainly reported from the Dezful Embayment or the Fars region (Authemayou et al 2006;Wennberg et al 2006;Ahmadhadi et al 2008;Mobasher and Babaie 2008;Khoshbakht et al 2009;Lacombe et al 2011;Khoshbakht et al 2012). Some studies focused on fractures within single anticlines (McQuillan 1973(McQuillan , 1974Wennberg et al 2006;Stephenson et al 2007), while others investigated fracture sets from a regional view (Ahmadhadi et al 2008;Mobasher and Babaie 2008;Lacombe et al 2011).…”

Upliftment Estimation of the Zagros Transverse Fault in Iran Using Geoinformatics Technology

“…On the basis of the historical evidence, the Zagros Mountain indicates that a l mm/yr uplift in the Shaur anticline (in the Dezful Embayment, Zagros Foredeep) has occurred since the Late Pliocene [14]. Holocene uplift rates of 1.8-6.6 mm/yr indicate a shortening by folding of 29 mm/yr.…”