پديد آورندگان :
توكليان, اسلام دانشگاه تربيت مدرس - بخش زمين شناسي , يساقي, علي دانشگاه تربيت مدرس - بخش زمين شناسي , نجفي, مهدي دانشگاه تحصيلات تكميلي علوم پايه زنجان - گروه زمين شناسي , گلالزاده, عليرضا شركت ملي مناطق نفت خيز جنوب - اداره زمين شناسي - بخش ژئوفيزيك
كليدواژه :
سبك چين خوردگي , سازند گچساران , فروافتادگي دزفول جنوبي , افق جدايشي و مقدار نمك
چكيده لاتين :
The mechanical stratigraphy of the sedimentary cover sequence, especially the presence of incompetent layers that can act as detachment zones, is a vital parameter control folding style in fold-thrust belts (Cotton and Koyi 2000; Spratt et al., 2004). Intermediate Detachment layers cause structural separation and variation of the style of folding in their upper and lower units. Therefore, the shape of the folds on the surface does not exhibit deep geometry (Sherkati et al., 2006; Casciello et al., 2009). The Zagros fold-thrust belt is an appropriate area for studying the behavior of detachment layers because the sedimentary cover in Zagros consists of several competent and incompetent units, which cause a sequence with various mechanical characteristics (Sherkati et al., 2006; Motamedi et al., 2012).
Dezful embayment as a part of the Zagros folded belt zone separated by the Kazerun-Borazjan Fault and the Balarud Fault from Fars and Lorestan zones. The Hindijan-Bahrengsar fault zone (Pattinson and Jazayeri, 1972) divide l embayment internally into the northern and southern parts. Also, the Gachsaran Formation in the Dezful embayment composed of seven members acts as a detachment layer. Lithostratigraphy of the Gachsaran Formation is composed of salt, anhydrite, marl, and lime layers. The NW-trending Zagros Front Fault (ZFF) is located in the southern part of the Dezful embayment and is affected by the Nargsi, Sulabdar, Bibi-Hakimah, Pazanan, Rage-sefid, and Aghajari anticlines (Fig. 1). Aims of this study are: (1) analysis of folds’ geometry, (2) investigation on the effect of Gachsaran Formation as a detachment zone on the anticlines axial movement, and
(3) determination of the effect of the Gachsaran lithostratigraphy on the formation detachment behavior.
2-Methodologhy
The used data in this study include the present geological maps, data from field mapping, the present UGC maps of Asmari Formation, the reflective seismic lines, and drilling well data from Aghajari, Pazanan, Rage-sefid, Bibi-
Hakimah, Sulabdar, and Narges anticlines. At first, the geological maps are georeferenced to be used as a base map and then updated using field data gathered during this study. Through the Move software, the amount of displacement on the axial trace of the surface and subsurface anticline axes for each anticline is estimated. Finally, employing the wells graphic logs the Gachsaran Formation, and its salt thickness is calculated to estimate the ratio
of the thickness of salt to the total thickness of the Formation (Table 1).
3-Discussion
The folding style is mostly effected by changes in the mechanical characteristics of the sedimentary strata during folding (Cotton and koyi, 2000; Spratt et al., 2004). Zagros sedimentary cover with a thickness of 8-14 km consists of a different sedimentary sequence of competent and incompetent units (Motiei, 1995). Due to their different rheology, the mechanical characteristics of these units are not similar and change along the strike of the belt (Sherkati and Letouzey, 2004). In the study area, the disharmonic geometry of the Aghajari, Pazenan, Ragesefid, and Bibi-Hakimeh anticlines in the Asmari Horizon and the younger horizons is proposed to be the result of the detachment function of the Gachsaran Formation. According to Ramsay's (1967) classification, the study area folding style in which the fold geometry changes from the surface to the depth is of parallel folds.
