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

In this study, Shahbazan Formation has been studied from the perspective of diagenetic processes and paragenetic sequences. This formation extends to the middle to late Eocene age in a large area of Lorestan sedimentary basin. In this area, a 62-meter-thick surface section has been selected in 10 km northwest of Poldokhtar city. Shahbazan Formation in the study area is located on the Kashkan detrital Formation and is covered by carbonates of Asmari Formation as a continuous discontinuity. Petrographic studies have been performed on thin sections and SEM studies have been performed on 10 samples of dolomites. Petrographic studies led to the identification of several diagenetic processes such as micritization, neomorphism, cementation, compaction, dissolution and replacement, which finally determined the diagenetic model. Based on the petrographic evidence, the paragenetic sequence of the Shahbazan Formation deposits in this section has been interpreted in four marine environments, freshwater, burial and uplift, and during three stages of diagenesis, namely primary diagenesis (Eogenetic), middle diagenesis (Mesogenetic) and late diagenesis (Telogenetic) has been determined. The most important diagenetic process in the studied section is dolomitization, which is formed both primary and secondary. Primary dolomites have low amounts of Fe and high amounts of Sr and Na, while secondary dolomites have high concentrations of Fe and lower amounts of Sr than primary dolomites, indicating a diagenetic burial environment. Shallow to medium for secondary dolomites.

Shahbazan Formation is one of the Eocene carbonate units of Lorestan region. In present study, dolomitization models this formation were investigated by petrographic and geochemical (EDS) methods. The section under study is 71 m in the thickness and located at 65 km southwest of Khorramabad including carbonate and dolomitic carbonate rocks, and dolomite. The dolomites based on the texture are categorized into dolomicrite, dolomicrosparite, dolosparite, and filling of fractures, which except dolomicrite, the others are secondary. Dolomites of first type represent the formation in the tidal zone environment. In most cases, these dolomites are seen at the end of upwardly shallowing sequences, which indicate a drop in sea level. The secondary dolomites were formed in a shallow to medium burial digenesis environment as a result of seepage of evaporated basin floor sediments into the carbonate platform of the Shahbazan Formation. Low amounts of Fe and high amounts of Sr and Na in dolomicrites, high concentration of Fe and Mn in dolomicrosparites and doloasparites along with evidences such as algal laminae, intraclasts, fenestral porosity and absence of evaporate minerals indicate the formation of this dolomite from the model of tidal, seepage and the following shallow to medium burial. Low values of Sr and high concentration of Fe and Mn in coarse crystal dolomites can indicate the increase in the size of dolomite crystals and their recrystallization during burial. The absence of saddle dolomites probably indicates the non-interference of hydrothermal solutions and fluids during the process of dolomitization of Shahbazan Formation carbonates.

Bitumen is a mixture of oxidized hydrocarbons with color, hardness, specific gravity and various metamaterials that are in solid or semi-solid forms and can be dissolved in Carbon disulfide (CS2). To evaluate the physical and chemical characteristics of bituminous deposits in Lorestan sedimentary basin (a part of the Folded Zagros zone), 6 fresh and non-weathered bitumen samples were collected from the veins and inside the mines of three areas with high potential of bitumen, including the northern region of Kohdasht, western Poldokhtar and southeastern Sepiddasht. The surface studies of above mentioned area, indicates the appearance of bitumen (tar mats) occurred in Amiran Formation. According to the analysis, the average amount of oxygen, nitrogen and carbon in the studied samples is 6.30%, less than 1% and 74.47% respectively, the average percentage of mineral ash and moisture of the samples is 6.4% and 0.8 percent respectively which indicates the very favorable quality of the studied bitumens .The solubility of studied bitumens in CS2, benzene and ethanol solvents shows that most of these bitumens have compounds with high molecular weight (asphaltene molecules) and low amounts of hydrogen (average 6.02). This example is also consistent with this conclusion. X-ray fluorescence analysis (XRF) on 6 bitumen samples from the studied area shows that Al2O3, SiO2 and Fe2O3 oxides are more abundant than other oxides. This issue can be due to the formation of this mineral in the host rock of the Amiran shale formation, which is rich in the mentioned elements. The values of CaO and K2O in the analyzed bituminous samples can be due to the formation of this mineral from the underlying formations (Ilam and Gurpi) which have found their way into the Amiran formation after formation and migration. The ratio of Ni vs V of the samples of the studied area is low (Ni/V <1) and has an average of 0.57%, so their rock of origin was somewhat carbonate-shale. The current studies reveal that, the origin of the studied bitumen started from deeper and older shale sediments (Ilam and Gurpi Formations), in which the deeper bitumen has migrated upward and washed the younger hydrocarbons to shallower formations and earth surface accumulation.

The aim of this research is to investigate the primary mineralogy and the type of diagenesis systems in the south-west of Lorestan based on elemental geochemistry. The Talezang F ormation is formed in this section with a thickness of 84.5 meters and the predominant lithology is limestone and sandy limestone. From this section , 20 samples were selected for EDS and EPMA analysis. The change trend of Sr element to Na compared to Mn showed that the studied samples are in the range of Gordon aragonite limestones of Tasmania . Also, the trend of changes of Mn element against Sr in the studied samples showed that are in the same range as the primary mineralogy of the aragonite of the Mo zdooran Formation, which is a proof of the aragonite mineralogy of the primary limestones of the formation. The high ratio of strontium to manganese (average 63.70) strontium to calcium (average 21.01), low amounts of iron elements (average 1.75 ppm) manganese (average 24.70 ppm), the high concentration of Sr (average of 750.35 ppm) in the studied samples and the plotting of Sr / Ca values ​​against Mn , Mg, Fe indicate a closed to slightly open diagenesis system with exchange of water to rock bottom. (W/R) is for carbonates of Talezang Formation. The relatively open diagenesis system in this formation can be due to the influence of atmospheric fluids due to the presence of an erosional discontinuity that is at the top of the Talez ang Formation.

The world is diverse in all dimensions and the natural diversity of the planet can be divided into two categories: geodiversity and biodiversity. In fact, geodiversity is referred to as the diversity of non-living factors on Earth, which has certain services and functions. Areas with high geodiversity and geomorphodiversity are the main parts of the geological heritage; Hence, they must be preserved for future generations. Geodiversity provides the elements and conditions necessary for plant growth and development, so it has become an important issue in global conservation issues. In order to successfully protect the biodiversity and especially the characteristics and diversity of vegetation in an area, it is necessary to assess the geodiversity and pay attention to geoconservation. Therefore, this study intends to investigate the relationship between geodiversity and vegetation characteristics of a protected area to achieve comprehensive and complete natural protection.

Oshtorankuh Protected Area is located in the west of Iran and in the east of Lorestan province; In order to analyze the relationship between geodiversity and vegetation characteristics, various indicators were used in this research. First, the geodiversity of the study area was evaluated, which was divided into three classes: low, medium and high. Then, based on the geomorphological map prepared from the protected area of Oshtorankuh, the results were verified and then the types of vegetation in this area were divided into five classes using spectral unmixing method and based on morphological classification, and finally It was compared and analyzed with the results of geodiversity assessment. In order to determine the spatial distribution pattern of vegetation types and follow the spatial distribution pattern of geodiversity classes, the soil adjusted vegetation index was used.

The results of the geodiversity assessment showed that the northern parts of the Protected area, and in particular the northern slopes of the Oshtorankuh mountain range on the third floor of the geodiversity (high diversity); The northern and southern parts of sabz mount, Negar valley and Chalmiron mount due to the passage of Doroud strike-slip fault and various fault landforms, Alluvial–Fluvial sediments leading to the eastern valley of Gohar Lake, numerous landslides and diversity in evaporitic formations, in The second class was geodiversity and geomorphodiversity. The western parts of the Oshtorankuh Protected Area and the major parts of priz mount are also located on the first floor of Geodiversity and Geomorphodiversity. After evaluating the geodiversity of Oshtorankuh Protected Area, the types of vegetation formations in this area were identified and the space and coverage percentage of each type of vegetation in accordance with the geodiversity classes were calculated and analyzed. After that, the spatial distribution pattern of geodiversity classes was studied with the spatial distribution pattern of different vegetation formations and similarities were observed. After that, the spatial distribution pattern of geodiversity classes was studied with the spatial distribution pattern of different vegetation formations and similarities were observed.

Studies have shown that the density, pattern and area of spatial distribution and the type of vegetation formations in the protected area of Oshtorankuh follow the geodiversity classes. Thus, the meadow with tree formation had the highest adaptation to the third class of geodiversity (high diversity) compared to other groups. Shrub formation also had the highest adaptation to the second class of geodiversity (medium diversity) compared to other types of coatings. From shrub formation to pasture and meadow, the process of adapting the covered area to the first floor is increasing and to the second floor is decreasing geodiversity. According to the above, rich geodiversity is an important factor in determining the pattern, density and type of vegetation formations in an area, and therefore to succeed in the conservation of biodiversity, especially vegetation in protected areas, proper attention to geoconservation is essential.

The study area is a part of Zagros Folded zone and located in the Lorestan sedimentary basin. In this regard, three areas with high bitumen potential were selected, which include the northern area of Kuhdasht, northeast of Poldokhtar and southeast of Sepiddasht. In the study areas, bitumens are exposed as veins between the fractures and as interlayers with host rock that the thickness of these veins is between 10 cm to more than 1.5 meters. Field studies showed that the studied bitumens have developed in the shales of Amiran Formation. Based on the results of organic geochemistry, 80.10 to 93.60% of the extractable saturated compounds are in the category of asphalts and have a very good quality in terms of thermal maturity (maturity of organic matter). The studied samples are formed in a reducing to slightly reducing sedimentary environment. Drawing the diagram of C34/C35 Homohopane vs. C29/C30 Hopane for the studied bitumens showed that the generating rocks of the studied samples are carbonate and detrital in nature. This can be explained by the lithology of bituminous formations such as Ilam and Gurpi formations in the study areas. The triangular diagram of regular streams (m/z = 217) for the studied bitumens showed that the source of organic compounds of the studied bitumens is mostly marine with a small amount of entry from dry environments. Severe depletion of the carbon isotope (average -28.83 per mill) indicates organic origin and biomass in these samples. On the other hand, sulfur compounds with depletion (-12.16  per mill) indicate formation in a reduced to semi-regenerated sedimentary environment and oxygen isotope data (+15.03  per mill) indicate the formation of organic matter of sedimentary origin.

In order to understand the sedimentation history of carbonate rocks of Asmari Formation, a 145 m thick stratigraphic section was selected in the south of Lorestan. The lithology of this periodic formation is from thin-layer, middle-layer limestones, thick to very thick-layered. The samples taken from this section are 145 samples that were examined in terms of sedimentary environment and diagenetic processes based on field evidence and studies of thin microscopic sections and due to the absence of evidence such as the construction of bird eyes. , Stromatactis cavities, Typical structures, Intracellular components, Evaporative minerals and the absence of traces and structures resulting from sediment drying as well as the absence of slippery and sedimentary sediments (turbidites, intraclasts and sections) Finally, it led to the identification of 7 micro-defects related to 4 lagoon facies belts, dam, restricted section (middle ramp) and internal ramp. In this section, several diagenetic processes such as micriticization, morphology (increasing and decreasing), cementation (coaxial cement, fibrous thickness, dimensional, block, joint and kilotopic dynamics), compaction (mechanical and chemical), dissolution (dependent To fabric and non-fabric dependent), substitution (pyritization, silicification and dolomitization) and diagenetic modeling. Based on petrographic evidence, the paragenetic sequence of Asmari Formation deposits in this section has been interpreted in four marine environments, freshwater, burial and uplift. Three stages of diagenesis, namely primary diagenesis (eogenesis), middle diagenesis (mesogenesis) and final diagenesis (telogenesis) have been determined for the studied deposits.

Shahbazan Formation with Eocene age is widely developed in Lorestan basin. In the study section, this formation with a thickness of 62 meters is located on the Kashkan Formation and is discontinuously below the Asmari Formation. The lithology of Shahbazan Formation in the study area includes dolomitic carbonate rocks. In order to study micro-facies, 60 samples of this section were collected and 20 samples were selected for elemental analysis. Based on field observations, lithographic and geochemical evidences based on elemental analysis by (EPMA) and (EDS) methods, two groups of dolomite were identified. Primary dolomites include dolomicrites in size between 4 to 10 microns that represent the formation of a tidal zone environment. Secondary dolomites include dolomicrosparite in size between 10 to 20 microns, dolosparites larger than 50 microns that is formed in a shallow to medium burial diagenesis environment due to the seepage of evaporated basin floor brines in to the carbonate platform on Shahbazan Formation in the study area. Low values of Fe versus high values of Sr and Na in dolomicrites, and high concentration of Fe in dolomicrosparite and dolosparite with some evidence such as intraclast, fenestral prosity and lack of evaporative minerals, indicate that these dolomites have been formed from the tidal model, seepage and then shallow to moderate burial. Geochemical evidence showed that the studied dolomites are non- stoichiometric, which can be explained the age of Shahbazan Formation.

The Ilam Formation is one of the important reservoir units in the Zagros area. Integrated sedimentological and petrophysical studies have been used to evaluate its depositional and diagenetic history, sequence stratigraphy and, finally, reservoir quality in an oilfield in the Lurestan area. Facies analysis has resulted in the recognition of 4 microfacies including pelagic mudstone/marl, planktonic foraminifera mudstone/wackestone, microbioclast wackestone to packstone, and oligosteginids planktonic foraminifera wackestone/packstone. Petrophysical logs of two wells A and B (Neutron, Sonic, Gamma-ray, and Resistivity( are used to define lithology, porosity and water saturation in the Ilam Fm. Clean to argillaceous limestone was the main lithology of the Ilam Fm. in studied wells. The formation has microscopic pores (up to 15%) as dominant pore types. Based on the MRGC method, 5 electrofacies have been defined and correlated with core-based microfacies. Finally, six integrated reservoir zones have been differentiated and correlated in a sequence stratigraphic framework.

In the present study, the limestone unit of the Pabdeh Formation was investigated in Bankul  stratigraphic section in the northeast of Ilam and compared with other outcrops of this unit. The studied unit is 73m in thickness and formed by thin to medium -bedded limestone. According to the identified index microfossils, four biozones were recorded: 1) Assemblage Zone 1, which is equivalent to the upper part of Acarinina topilensis Partial Range Zone; 2) Morozovelloides lehneri Partial Range Zone; 3) Orbulinoides beckmanni Taxon Range Zone. As a result of this study and based on the identified planktonic foraminifera, the age of the middle part limestone of the Pabdeh Formation is Lutetian –Bartonian and correlated to the Shahbazan Formation. The sedimentation of this unit has been contemporary with global temperature decrease and eustatic sea level decrease. Meanwhile, the limestone unit at the base of the Pabdeh Formation in the Early Eocene age in the south of Lorestan has a shallow facies and is equivalent to global warming and rising eustatic water level. This was the same condition in Izeh zone. In the north of Dezful, there was the opposite of these conditions, so that in the Middle Eocene, the limestone unit of Pabdeh Formation had a shallow facies. This difference in facies has probably been influenced by various tectonic movements in the Lorestan foreland zone.

The Pillow lava and diabase dykes of the southwestern region of Aleshtar are host different species of zeolites and secondary minerals. Zeolites are formed by the cavities and veins and decomposed from primary minerals. Based on field studies, X-ray diffraction (XRD) and Electron Microprobe Analysis (EPMA), natrolite zeolites (most abundant zeolites), mesolite, scolecite and analcime have been identified in the pillow lava and diabase dykes in the study area. The average Si/Al ratios for natrolite, mesolite, scolecite and analcim are 1.46, 1.49, 1.62 and 2.29, respectively. These zeolites are formed during two stages of metamorphic hydrothermal fluids, during fractures and in the cavities of host rocks and at temperatures below 250 °C. The investigation of the geochemical properties of zeolites host rocks, shows that their magmatic series is calc-alkaline to tholeiitic and their tectonic environment depends on the mid-ocean ridges (MORB).

In the present study, a stratigraphic section was selected on the Poshte-Jangal anticline in the southwestern part of Khorramabad to study the microbiostratigraphy of the Cretaceous sediments. This Section with a thickness 190 meters consists of invariable thin to Medium bedded limestones with Middle Turonian to Late Santonian age which were deposited in a continues sedimentation process. Both lower and the upper boundaries of this formation with The Surgah and Gurpi formations are conformable, respectively. In the present study of the Ilam Formation, 12 genera, 40 species and 4 biozones of the planktonic foraminifera were recognized. Based on the stratigraphic distribution of the introduced species and identified biozones the Middle Turonian to Late Santonian age is suggested for deposits of the Ilam Formation in this stratigraphic section.

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.

Taleh Zang Formation is shallow carbonate facies of the Paleogene Zagros Basin. According to the area, including depth, tectonic and sedimentary sedimentation rate and other factors of the formation with Kashkan and Shahbazan sometimes with different thicknesses of semi-deep and deep Papdeh facies were deposited locally. According to the study Taleh Zang Formation calcareous stratigraphic section thickness of 185 meters (true thickness) were measured from 15 genera and 10 species of 110 sample benthic foraminifera identified by study and introduced 3 biozones 2 Assemblage zone and a Acrozon, late Paleocene (thanetian) and lower Eocene (ypresian) is intended for the stratigraphic section.

This research has been carried out in order to understand geometric and kinetic analysis of the khaneh Sorkh folding and its structural style. Khaneh Sorkh folding is a long and narrow anticline that is formed due to sleep in the Garau Formation which is located in the Lorestan region. The Garau Fomation is the intermediate detachment layer in the Lorestan. In order to carry out geometric analysis, three structural cross sections were drawn perpendicular to the axial surface trace on this anticline. Thus, based on the analysis of the geometry of cross sections and comparing parameters with variety of models, it could be suggested that the Khaneh Sorkh Anticline is a detachment fold in the thrust fault-related folds. Finally,geometry of faulted detachment fold and analysed  kinetic evolution is valid for Khaneh Sorkh Anticline based on the proposed  model.

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 Sarvak Formation is mainly composed of limestone and is one of the most important rock reservoirs in the Zagros sedimentary basin. This formation has been studied extensively in many parts of the Zagros; however the information about various aspects of this formation in northern Lorestan is limited. Due to the discovery of a pycnodont fish tooth plate from Aleshtar area, and because of scarce data on Cretaceous deposits in this region, we conducted this research.
Material &

In order to study the age, sedimentary environment and sequence stratigraphy of the Sarvak Formation, field and microscopic studies of 100 thin sections from an outcrop near Aleshtar (north of Lorestan) has been carried out.
Discussion of Results &

The Sarvak Formation in the studied section is Cenomanian in age and is 835 meters thick. It is bounded by Garu and Surgah formations at the base and top respectively. It is mainly composed of thick, medium, and thin bedded limestone rich in chert nodules, bioturbation and rudists. The studied outcrops can be subdivided into four units litho-stratigraphically. The first unit is 200 meters of thick, grey limestone with benthic foraminifera and echinoids. Second unit is 320 meters of mainly grey, medium bedded limestone with reddish intercalation of shale, containing benthic foraminifera, rudist debris and bioturbation. 180 meters of thick bedded, grey limestone with rudist and other bivalve debris forms the third unit. The last litho-stratigraphic unit consists of 135 meters of medium to thin bedded, grey limestone with interlayers of dolomitic limestone and rudist/bivalve debris and bioturbation. Benthic foraminifera are less abundant here.
Our study led to the identification of 12 microfacies and 3 facies-belts, which belong to tidal flat, lagoon, and open marine environments. These microfacies are differentiated based on abundance and diversity of skeletal and non skeletal remains and rock texture. These facies, ordered from shallower to deeper environments, include: bioclastic stromatolite wackestone to bindstone, and pisoid rudstone in tidal-flat facies belt; bioclast peloid intraclast grainstone, bioclast green algae wackestone to packstone, peloid ooid grainstone to packstone, bioclast echinoderm benthic foraminifera wackestone, rudist benthic foraminifera wackestone, orbitolina miliolid wackestone to packstone, bioclast miliolid wackestone, and benthic foraminifera rudist floatstone to rudstone in lagoon facies belt; and rudist floatstone to rudstone, and bioclast oligosteginid wackestone within open marine facies belt.
According to type and gradual changes of microfacies in lower parts of the Sarvak Formation, and compared to abrupt changes of microfacies and presence of extensive rudists in the upper parts of this formation, lower and upper parts of the Sarvak Formation are deposited in two different sedimentary environments. Presence of micrite in most of microfacies, formation of sedimentary textures such as wackestone to packstone and absence of traceable reefs on the ground, shows that the carbonate sediments of the Sarvak Formation in the lower parts in the studied section were deposited in a ramp carbonate platform. Widespread distribution of rudists in the field, abundance of oligosteginids, and abrupt changes of microfacies along the section; like alteration of pisoid and stromatolite facies to oligosteginids in a short interval, indicates that the upper parts of the studied section were deposited in a carbonate shelf.
Three third-order depositional sequences were determined based on the deepening and shallowing trend of facies. The transgressive systems tract consists mainly of microfacies belonging to the lagoon and open marine sedimentary environments, which contain the benthic foraminifera, echinoids and oligosteginids. The highstand systems tract consists mainly of microfacies belonging to the lagoon with green algae and the benthic foraminifera, and also to the microfacies belonging to the tidal flat, which contain stromatolite and pisoid. The maximum progression level in sediment sequences 1 and 2 was determined by microfacies rich in echinoid and rudist debris. In sedimentary sequence 3 it is identified with oligosteginid rich microfacies.

Sedimentary setting and paleoecology of the rudist-bearing Upper Cretaceous strata were studied in three sections in Khorram abad. The sections include: Tang Shabi Khone, Cham Sangar (Tarbur Formation) and Pir Shams Eldin (upper part of Amiran Formation). The Tang- E Shabi Khone and Chamsangar sections are located in Zagros Trust zone while, the Pir Shams Eldin in Lorestan zone. On the basis of the recognized fossils, the three sections are assigned to the Late Cretaceous (Middle to Late Masstrichtian) and are comparable to Omphalocyclus- Loftusia Assemblage Zone. The petrography study showed that the three sections contain nine microfacies that deposited in an open marine, shoal and restricted marine that based on rudist sedimentary models, are comparable to the Inner- shelf basin prograding margin complexes (Tarbur Formation) and the low- angel open shelf margin complexes (Amiran Formation). Probably, Sepid Kuh Fault was detaching the these settings. Augmentation of entering the detrital and silica due to river injection and runoff and consequently to the eurotrophic conditions in the Tnage Shabi Khone and Pir Shams Eldin, frequency of agglutinate foraminifera were increased but in the chamsangar section due to oligotraphy condition , frequency of hyaline foraminifera is increased. Distribution of the foraminifera and algae indicated that the Tarbur Formation is deposited in a photic zone though, some parts of the carbonates of the Amiran Formation were deposited in a aphotic zone.