Sedimentology
Navid Qavim; Najmeh Etemad-Saeed; Mahdi Najafi
Abstract
The Mahneshan Basin is one of the syntectonic Neogene sub-basins of the Central Iran. The basin is filled by about 4 km of the Miocene Upper Red Formation deposits, showing a combination of halokinetic and growth strata patterns. To assess the provenance evolution of sediments in north of the Mahneshan ...
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The Mahneshan Basin is one of the syntectonic Neogene sub-basins of the Central Iran. The basin is filled by about 4 km of the Miocene Upper Red Formation deposits, showing a combination of halokinetic and growth strata patterns. To assess the provenance evolution of sediments in north of the Mahneshan basin named the Hesar section, we conducted remote sensing mapping, field survey, as well as petrographical and modal analyses of sandstones. Our results reveal that the sandstones are fine to medium-grained sedarenites (Q46F10Rf44) and mainly derived from fine-grained siliciclastics, metamorphic, carbonate, chert and andesitic volcanic rocks, which were exposed in an orogenic tectonic setting (Qm34F10Lt56 and Qt49F10L41). The combination of provenance data and northeastward paleocurrent direction, reflect that the sediments mainly supplied from basement rocks of the Takab Complex and Qom Formation in southwest of Mahneshan Basin. The unchanged provenance of sediments along the studied succession, indicate that regional shortening and uplift of parent rocks has begun before deposition of the Upper Red Formation (Miocene) and continued during deposition of these sediments. This is in agreement with previous age assumption for exhumation of Takab Complex during Oligocene time.
Sedimentology
Najmeh Etemad-Saeed; Mahdi Najafi; Navid Zeinolabedin Qavim; Ghods Abdolreza
Abstract
The present study provides a detailed facies and depositional environment analyses of the Neogene sediments in the northern Dezful embayment, footwall of the Zagros Mountain Front fault. The Neogene sediments in this area, including the Mishan, Aghajari, and Bakhtyari formations, constitute the thickest ...
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The present study provides a detailed facies and depositional environment analyses of the Neogene sediments in the northern Dezful embayment, footwall of the Zagros Mountain Front fault. The Neogene sediments in this area, including the Mishan, Aghajari, and Bakhtyari formations, constitute the thickest Zagros foreland succession, with more than 5 km of thickness. As these sediments were deposited synchronous with the main phase of the Zagros orogeny, they have recorded the history of deformation events. During the current study, 9 lithofacies have been identified on the basis of lithology, grain size, sedimentary structures, and bed geometry, which can be classified into three facies assemblages including: gravel dominated (Gm, Gp), sand dominated (Sh, St, Sp, Sr), and mud dominated (Fm, Fl). Furthermore, two major marine ichnofacies, the skolithos and the Cruziana ichonafacies, have been identified at the base of the Aghajari Formation. As the results indicated, the vertical stacking of facies represents an overall shallowing-upward succession that was deposited in marginal marine (Mishan), siliciclastic shoreline (base of Aghajari), meandering river (top of Aghajari) and braided river (Bakhtyari) depositional environments, from base to top respectively. Considering eustatic sea-level fluctuations in the deposition period (13 to 3 Ma), these results propose that evolution of the Neogene sedimentary basin in the North Dezful likely controlled by tectonic folding and faulting.
Tectonics
Ali Taghavy; Mahdi Najafi; Najmeh Etemad-Saeed; Mohammad Seddigh
Abstract
A synthesis of 2-D seismic interpretation, exploration well data and field survey permit us to decipher the structural evolution history in the front of Fars paleo-high area, located in SE Zagros fold-and-thrust belt. In the current study, a structural evolution model is proposed for the region, according ...
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A synthesis of 2-D seismic interpretation, exploration well data and field survey permit us to decipher the structural evolution history in the front of Fars paleo-high area, located in SE Zagros fold-and-thrust belt. In the current study, a structural evolution model is proposed for the region, according to a sequential restoration, which was performed based on the growth stratal unit’s pattern, together with constant length and area assumptions. The result of the sequential restoration indicated that in the late Eocene time, Tanbak anticline incepted on the hangingwall of the inverted mountain front basement fault, as an out of sequence forced fold. Although, thin-skinned detachment folding initiated in the lower Miocene, shortening and amplification of anticlines did not accelarated until the late Miocene time, when thrust faults formed on the limb of growing anticlines while Dashtak middle detachment thickened in the fold crestal areas, likely due to an intensified regional shortening.
M Najafi; A Yassaghi; A Bahroudi; SH Sherkati; J Vergés
Abstract
The long-lived Fars paleo-high, located in SE Zagros Mountains is a prolific hydrocarbon province as it contains 15% of the world’s proven gas reserves. Subsurface data sets acquired during the recent hydrocarbon exploration in the region indicated fold style variation and structural complexity ...
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The long-lived Fars paleo-high, located in SE Zagros Mountains is a prolific hydrocarbon province as it contains 15% of the world’s proven gas reserves. Subsurface data sets acquired during the recent hydrocarbon exploration in the region indicated fold style variation and structural complexity deep in the sedimentary cover, understanding of which is essential for petroleum system modelling and selection of new targets for gas at depth. In order to analyse the fold style in Fars paleo-high, this study presents a new regional balanced cross-section with a length of ~130 km and a depth of 12 km, across the Fars paleo-high. The section was constructed using seismic profiles, exploration wells and field data. The results show that variation of fold style happens in accordance to variation in mechanical properties of rock units across the Fars paleo-high, as well as from surface down to the depth of sedimentary cover. Detachment folding, followed by limb thrusting, which happens above 8-12 km below sea level, is the main deformation mechanism of sedimentary cover. In the middle of sedimentary cover, however, tectonically over-thickened Triassic evaporitic rocks efficiently decouple the geometry of post Triassic succession with respect to the underlying Permo-Triassic reservoir carbonates. Restoration and balancing of the regional cross-section indicated 20% of shortening across the Fars Paleo-high, accommodated by folding and thrusting. Abrupt change in the level of synclines accompanied with trends of seismicity and linear exposure of old geological units, proposes involvement of at least two main basement reverse faults in the deformation of cover sequence.
M Najafi; A Yassaghi; A Bahroudi
Abstract
Mechanical characterizations of sedimentary cover, especially presence of ductile rock units is a major controlling parameter on deformation style within fold and thrust belts. Interpretation of seismic profiles as well as scaled analogue modeling allows us to determine the influence of ductile levels ...
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Mechanical characterizations of sedimentary cover, especially presence of ductile rock units is a major controlling parameter on deformation style within fold and thrust belts. Interpretation of seismic profiles as well as scaled analogue modeling allows us to determine the influence of ductile levels on structural style in the Central Zagros folded belt. Seismic interpretation indicates that the Miocene Gachsaran Formation forms a major median detachment level decoupling fold geometry in surface structures from Pre-Miocene units below it. In addition, the Infra-Cambrian Hormoz salt or equivalents decouple the folded sedimentary cover from basement. To evaluate the significance of multiple detachment levels, a scaled analogue model was set. Two layers of silicon putty, with thicknesses equal to 15% of total cover thickness, were placed at the base and in the middle of sedimentary cover. The rest of the sedimentary cover was simulated using dry loose sand. The result of modeling supports seismic interpretation of the Central Zagros proposing that thick middle detachment layer totally decouples structural style at surface from depth. However, the open synclines with long wavelength and low angle thrusting are developed at surficial levels, and duplex thrust systems are formed between two detachment levels. Therefore, the role of ductile detachment levels should be obtained before exploring deep hydrocarbon targets in the Zagros fold belt.
