جستجوی مقالات مرتبط با کلیدواژه « تاقدیس » در نشریات گروه « زمین شناسی »

The Sarkan anticline is located in the Lurestan sedimentary-structural zone and in the Zagros fold and thrust belt. Geometry and kinematic of the fold in this zone are controlled by thrust faults and detachment levels. The exposed formations in this anticline include the upper Cretaceous and Cenozoic formations. In this research, geometry and deformational style analysis of the anticline and the role of the detachment levels on folding style are investigated using drawing four structural cross-sections, interpretation of the seismic profiles and calculation of geometric parameters. The structure of this anticline is affected by two detachment horizons, which comprises the Amiran flysch, and the shaley Garu formations as the upper and middle detachment levels, respectively. The high thickness of the upper detachment level caused southwestward displacement of the surface anticline axis with respect to the deep anticline axis. The study of geometrical parameters and structural cross-sections of the Sarkan anticline represent that this structure is an asymmetric and noncylindrical anticline. From tightness and dimentional ratio view, it is ranked in the open to gentle and wide category, respectively.

1-Introduction The Zagros fold and thrust belt with NW–SE trend is located in the Alpine–Himalayan orogeny, resulting from the Late Cretaceous to Cenozoic convergence between the Arabian and Eurasian plates (Berberian and King, 1981; Alavi, 1994). The northeastern boundary of this belt is the structural style, and sedimentary history divides the Main Zagros Reverse Fault into several structural zones. The Zagros fold and thrust belt can also be divided, along strike from east to west, into the Fars, Izeh, Dezful embayment and Lurestan zone. The Lurestan zone has a long history of hydrocarbon exploration, and production, and only a few wells have been successful. Seismic and well data in the area indicate that folding style has the primary role in the exploration and production of the hydrocarbon. Also, in this belt, thrust faults and detachment horizons have the main character in geometry and kinematics of the folded structures. The Sargelan anticline is one of the main folded structures in the Lurestan zone. So, in this research, deformational pattern and structural geometry of the Sargelan anticline have been studied using the interpretation of five 2D seismic profiles, drawing of structural cross-sections, drilling well data in the adjacent anticline and detailed analysis. 2-Methodology The Zagros fold and thrust belt with NW–SE trend is located in the Alpine–Himalayan orogeny, resulting from the Late Cretaceous to Cenozoic convergence between the Arabian and Eurasian plates (Berberian and King, 1981; Alavi, 1994). The northeastern boundary of this belt is the anticlines in the Lurestan zone host the hydrocarbon reserves in the west of Iran, hence are well-acknowledged regarding the style of folding and their response to appropriate detachment levels. This research indicates the results of a detailed study of the Sargelan anticline, based on field surveys, seismic profiles interpretation, well data, and drawing four structural cross-sections. We will successively focus on the upper (Amiran Formation) and middle (Garu Formation) detachment levels and deep-rooted thrust faults, causing the disharmonic folding beneath and above the upper detachment level restoration of each structural cross-section. At last, restoration of each structural cross-section obtained by a shortening percentage. 3-Results and discussion Recent studies indicate that mechanical stratigraphy has the main role in folding style in the Lurestan zone (Casciello et al., 2009; Farzipur-Saein et al., 2009). In the study area, full upper detachment level causes a reduction in wavelength of overlying anticlines and formation of disharmonic folding. So, in this research four structural cross-sections (from SE to NW: AA´, BB´, CC´, DD´) across the Sargelan anticline has been drawn transecting the anticline from the NE to SW to illustrate the vertical variations in folding style. Interpretation of seismic profile indicates that along the AA´ section deep thrust fault has not formed in the southwest limb. Also, regarding the geometrical parameters and the drawing the folding stereograph, the axial trend of the Sargelan anticline is 115/0, and its axial plane is 030/86 degrees. The BB´ structural cross-section indicates that in the southern part of the deep Sargelan anticline, another anticline is formed, which is introduced as the South Sargelan anticline. Along the South Sargelan anticline, a deep thrust fault rooted within the Garu Formation (middle detachment level) and cuts up-sections of the southern limb and flattens in the Amiran Formation (upper detachment level). In addition to the deep thrust fault, a low angle shallow thrust rooted within the upper detachment level (Amiran Formation) caused displacements and deformations in the post-Amiran formations. Along the CC´ cross-section, disharmonic folding caused the formation of the deep-seated Sargelan anticline beneath the surface syncline. The structure suggests that the deep-seated Sargelan anticline is formed along the s cross-section and continues to the north. The DD´ structural cross-section drew along the Sargelan, South Sargelan, Darreh-Baneh, and Chahar-Qaleh anticlines. Along with this structural cross-section, the Sargelan and South Sargelan anticlines have formed between the upper and middle detachment levels. Therefore, the study of these four structural cross-sections indicates that the deep-seated Sargelan anticline continues more than about 10 km just beneath the surface syncline. The reason for the formation of disharmonic folding is the high thickness of the upper detachment level (Amiran Formation) in the study area. 4- Conclusions The interpretation of structural profiles indicates two upper (Amiran Formation) and middle (Garu Formation) detachment level. Detachment levels and thrust faults have a significant influence on the geometry and kinematics of the structures, as the southwest limb thrust has formed and begin to ramp. Displacement of this thrust transported the anticline upward, and so the Sargelan anticline is a transported detachment folding. The high thickness of the upper detachment level cased formation of disharmonic folding that the deep Sargelan anticline continues to the northwest more than about 10 km and beneath the surface syncline. Measurement of the geometrical parameters indicates that the Sargelan anticline is an asymmetric, cylindrical fold, and concerning the aspect ratio and bluntness is fold-wide and semi-circle respectively. Interpretation of seismic profiles indicates that a deeper anticline is formed parallel to the Sargelan anticline, under the upper detachment level and it is introduced as the South Sargelan anticline in this study. References Alavi, M., 1994. Tectonics of the Zagros orogenic belt of Iran: new data and interpretations. Tectonophysics 229, 211–238. Berberian, M., King, G.C.P., 1981. Towards a paleogeography and tectonic evolution of Iran. Canadian Journal of Earth Sciences 18, 210–265. Casciello, E., Verges, J., Saura, E., Casini, G., Fernandez, N., Blanc, E., Homke, S., Hunt, D.W., 2009. Fold patterns and multilayer rheology of the Lurestan Province, Zagros simply folded Belt (Iran). Journal of Geological Society 166, 947–959. Farzipour-Saein, A., Yassaghi, A., Sherkati, S., Koyi, H., 2009. Basin evolution of the Lurestan region in the Zagros fold-and-thrust belt, Iran. Journal of Petroleum Geology 32, 5–19.

The East Darreh-Baneh anticline is located in the Lurestan structural zone, west of the Zagros fold and thrust belt. In this zone thrust faults and detachment horizons have a main role in geometry and kinematic of the folded structures. In this research, deformational pattern and structural geometry of the East Darreh-Baneh anticline have been studied using interpretation of five 2D seismic profiles, drawing of structural cross sections, drilling well data in the adjacent anticline and related analysis. Accordingly, the East Darreh-Baneh anticline is a detachment folding, in which two upper and middle detachment levels is affected its structural geometry. In the study area, the shaly Garu and the flysch Amiran formations caused deformations as a middle and upper detachment levels, respectively. The high thickness of the upper detachment level caused formation of the anticlines in surface with low wavelength and amplitude and formation of the surface disharmonic folding on deep-seated anticlines. Also, geometrical parameters analysis of the East Darreh-Baneh anticline indicate that this anticline is an asymmetric and noncylindrical fold and from tightness view is open to gentle with wide aspect ratio

 The impact of past processes on development of Qazvin and Eshtehard plains is quite visible in the region’s landforms. Being the function of geological structure, tectonic movements and geomorphological processes, these effects have shaped the geomorphology of the region in a way that Eshtehard plain forms a saline depression with a gentle slope entering from the south into another hole via Shoor River that reaches the end of Mahdasht alluvial fan. In the middle of this depression, parallel hills can be seen drawn from west to the east. The existence of eroding loose hills in a low slope area covered in evaporite sediments and water stroke in southern hole, has formed the geomorphic features of the region in a way that is not justified with the current situation. Researchers who have studied this region, have achieved different results. Sadough et al (1396) have concluded thattectonic movements caused by Eshtehard Fault and the development of Mahdasht alluvial fan, have changed Shoor River’s direction towards south. Ramesht et al (1393) have concluded that there has been a paleo-lake behind Mahdasht Alluvial fan and its overflow, has caused the lake to tear through Mega-Floods. It seems that to explain the paleo-geomorphology of the area the evidence of the upstream location of these events should be investigated with a wider look to the region. Resources used in this research, include two categories of documentary and library sources including articles, books, sites, theses, all written resources and field data including field visit, sampling and investigating geomorphological evidence. The tools used in this research include two groups as well. Physical instruments like maps, diagrams, laboratory tools and field sampling equipment, conceptual tools such as ArcGIS software, GRADISTAT, Google Earth and etc. First, geomorphology map of the area was created and the history of past processes was identified. Then landforms of area were sampled. Samples were transferred to the laboratory in order for some experiments to be done, such as granulometry for extracting statistical parameters of sediments, morphoscopy to identify the amount of rounding, origin and sedimentation process, hydrometry for indentifying particle diameter in silt and clay size. At the end by connecting the results, the evolution process of Qazvin and Eshtehard Plains, was explained. The results showed that the existence of stretched and fine-grained hills in the north of Qazvin Plain and Eshtehard, represents a relatively stable environment in the past and cutting it down by water-ways, shows a change in situation from sedimentary environment to erosion environment. Earth’s current surface in the area is lower than the past sedimentary floor and the little difference between the heads of northern and southern hills indicates that there has been a paleo-lake in this region with an insignificant slope from north to the south. Forming alluvial terraces in south-western part of the basincould be related with changing the river base level, in addition to climate change. This is because the reverse and gentle slope of sedimentary layers indicates a very slow tectonic movements in southern mountains. Because of that, forming of terraces in relation with baseline changes could be considered as sign of descending in lake level in the current location of Qazvin Plain. The sign of water in the southern slopes of halghedar anticline are seen like significant water strokes. The existence of clay hills in Qazvin Plain and waterstrokes in Eshtehard Plain indicate that full opening of the lake which has been situated in the north of halghedar hills, has occurred in transition from glacier to inter-glacier. Buried sand hills and gypsum crystallized particles among the sediments confirms the existence of an evaporate environment  in the studied area. The obtained sedimentary evidence indicates periodicity of high and low water courses in a closed sediment basin. These evidence include layered fine grained deposits, also layers with coarser sediments, evidence of the formation of sand dunes in the region and the presence of crystalline particles of salt and gypsum among the sediments. Terraces of Kharroud River in  southwestern part of the basin show the change in base level. Loose and parallel clay hills, can prove that these sediments have been deposited in a calm and closed area. Water strokes in southern slope of Halghedar anticline shows the sudden exit of water from the area and the formation of a lake in the southern depression. Thus, the results of this study proves the existence of a lake in Qazvin plain in the last glacial period and shows that in transition from glacier to inter-glacier period, as the ice melted in heights and mega-floods occurred, the  lake’s water level rised and overflowed from the southern heights, and meanwhile a part of anticline eroded. This causes a reduction in depth of the lake and in inter-glacier period, when the weather was much warmer, evaporation created playa environment in the lake and this happened frequently until the front of lake is completely open in the last period of transition from glacier to inter-glacier.

The Kupal oil anticline is one of the most important structures in Dezful embayment that is located in northeast of the Ahvaz city and north of the Marun oil field. Recent deposits and Lahbari member of the Aghajari formation have formed the surface outcrops, and the Asmari formation with 7 reservoir layers is the main reservoir rock in this oil field. In this research fractures of the Asmari formation in this anticline have been analyzed based on well data, subsurface maps and seismic profiles. The Kupal oil anticline is a fault-related (detachment fold) and asymmetric fold, in which the middle parts have been distinguished as potential zones of of dense fractures development due to longitudinal curvature. The southwest limb in much parts and northeast limb in middle parts indicate zones with high fracture density, and the axial bending of the Kupal anticline is a result of movement of deep faults.

Situated 15 km NW of the Izeh city, Tukak and Kamarun anticlines are located in northwest of the Izeh zone in the Zagros fold-and-thrust belt. The Tukak anticline measures about 17 km length by 3.3 km width on the Asmari formation outcrop, while the Kamarun anticline shows a maximum length and width of about 15 km and 3.5 km, respectively, on the same formation. The SE termination of the Kamarun anticline and the NW termination of the Tukak anticline form together an en-echelon array. Both anticlines represent nearly symmetrical box-fold geometry, in which the Pabdeh formation is the oldest outcrop in each anticlinal core and the Asmari formation constitutes most of their surface outcrop. Based on surface geology, 4 cross-sections across the Tukak anticline and 3 cross-sections across the Kamarun anticline (D-D' is a common section crossing the en-echelon plunges), and one longitudinal section through both structures were constructed. Since the Bangestan horizon is taken to indicate a position upper than sea level, the cross-sections were used to construct the UGC map on the Upper Khami horizon. In Tukak anticline, which is bigger than the Kamarun anticline, the UGC map of the Upper Khami horizon illustrates vertical and horizontal closures of 250 m and about 4.3 km2, respectively.