Structural analysis of the Aghajari and Pazanan anticlines, Dezful Embayment, SW Iran

Abstract

In the present study, seismic profiles and well data were used to provide detailed deformational patterns through the Aghajari and Pazanan anticlines located in the Zagros fold and thrust belt. A suite of 32 and 26 seismic profiles obtained from the Aghajari and Pazanan anticlines, respectively were examined. Furthermore, some 50 well data upon top of drilled formations were applied to prepare depth contour map of the relevant formations in these two anticlines. These asymmetric anticlines with a northwest-southeast trend and en-echelon pattern host considerable oil reserve in the Dezful Embayment. The fold axis of these anticlines are not identical above and below the upper detachment level (the Middle Miocene Gachsaran Formation). Progressive deformation caused thinning and escape of incompetent layers of the Gachsaran Formation from the crest of the anticlines toward adjacent synclines. A main deep-rooted fore-thrust within middle detachment level (the Lower Cretaceous Garu Formation) also cuts up-section toward the foreland and flattens in the Gachsaran detachment. Furthermore, a back-thrust cuts up from the main thrust into the hinterland. The shortening percentage was estimated in 58 seismic profiles across the Pazanan and Aghajari anticlines, by averaging of the Asmari, Sarvak and Fahlian Formations’ top restoration. The maximum and minimum amount of shortening is about 11.1 and 8.5 percent, respectively which is slightly less than those reported along the Dezful Embayment. The Hendijan High is the most important structure between the Aghajari and Pazanan anticlines which imparted considerable changes in basin fill facies. These changes presumably affected the folding geometry of the area, since it is similar to the fault bend folding geometry through the Hendijan High wherein exhibit fault propagation folding geometry on its both flanks. There is an anomaly and discontinuity in the depth contour maps of the Asmari and Fahlian formations which separated the northwest termination of the Pazanan anticline from the rest of the structure. Reasonably, it is better to consider it as southeast continuation of the Aghajari anticline, which is similar to the most anticlines with en-echelon pattern.