Facies analysis and depositional environments of the OligoceneeMiocene Asmari Formation,Zagros Basin,Iran

The Asmari Formation(a giant hydrocarbon reservoir)is a thick carbonate sequence of the Oligocenee Miocene in the Zagros Basin,southwest of Iran.This formation is exposed at Tang-e-Lendeh in the Fars interior zone with a thickness of 190 m comprising medium and thick to massive bedded carbonates.The age of the Asmari Formation in the study area is the late Oligocene(Chattian)eearly Miocene(Burdigalian).Ten microfacies are defned,characterizing a gradual shallowing upward trend;the related environments are as follows:open marine(MF 8e10),restricted lagoon(MF 6e7),shoal(MF 3e5),lagoon(MF 2),and tidal fat(MF 1).Based on the environmental interpretations,a homoclinal ramp consisting of inner and middle parts prevails.MF 3e7 are characterized by the occurrence of large and small porcelaneous benthic foraminifera representing a shallow-water setting of an inner ramp,infuenced by wave and tidal processes.MF 8e10,with large particles of coral and algae,represent a deeper fair weather wave base of a middle ramp setting.     

Sedimentary facies and sequence stratigraphy of the Asmari Formation at Chaman-Bolbol, Zagros Basin, Iran

The Oligocene–Miocene Asmari Formation of the Zagros Basin is a thick sequence of shallow water carbonate. In the study area, it is subdivided into 14 microfacies that are distinguished on the basis of their depositional textures, petrographic analysis and fauna. Based on the paleoecology and lithology, four distinct depositional settings can be recognized: tidal flat, lagoon, barrier, and open marine. The Asmari Formation represents sedimentation on a carbonate ramp. In the inner ramp, the most abundant lithofacies are medium grained wackestone–packstone with imperforated foraminifera. The middle ramp is represented by packstone–grainstone to floatstone with a diverse assemblage of larger foraminifera with perforate wall, red algae, bryozoa, and echinoids. The outer ramp is dominated by argillaceous wackestone characterized by planktonic foraminifera and large and flat nummulitidae and lepidocyclinidae. Three third-order depositional sequences are recognized from deepening and shallowing trends in the depositional facies, changes in cycle stacking patterns, and sequence boundary features.     

Biostratigraphy,Microfacies and Depositional Environment of the Sarvak Formation at the Pyun Anticline (Zagros Basin,Southwest of Iran)

The Sarvak Formation is a carbonate sequence of Late Albian–Early Turonian age in Zagros Basin in Iran. In this investigation, the Sarvak Formation at the Pyun Anticline section (Izeh Zone) has been studied. It consists of 797 m thick limestone which overlies the Kazhdumi Formation conformably and underlies the Gurpi Formation unconformably at the Pyun Anticline. A very rich fossil association (85 genera and 132 species) characterizes the Pyun section. Based on the stratigraphic distribution of diagnosed foraminifera, five biozones are established: 1, Muricohedbergella-Globigerinelloides sp. assemblage zone (Late Albian); 2, Praealveolina iberica-Chrysalidina gradata interval zone (Early Cenomanian); 3, Chrysalidina gradata-Cisalveolina fraasi (fallax) and C. lehneri interval zone (Middle Cenomanian); 4, C. fraasi (fallax) and C. lehneri-Praetaberina bingistani assemblage zone (Late Cenomanian); 5, Nezzazatinella picardi-Mangashtia- Dicyclina assemblage zone (Early Turonian). Based on the petrographic and sedimentological analyses, some 13 carbonate microfacies were identified. The investigated microfacies confirm a ramp-type paleoenvironment. These microfacies, from distal to proximal environments, consist of: MF1: planktonic foraminifera wackestone-packstone; MF2: Oligostegina planktonic foraminifera wackestone to packstone; MF3: planktonic-benthic foraminifers sponge spicules wackestone-packstone; MF4: rudist floatstone; MF5: rudist rudstone; MF6: bioclast intraclast grainstone; MF7: peloid intraclast grainstone; MF8: benthic foraminifers rudist grainstone-packstone; MF9: peloid bioclast grainstone-packstone; MF10: bioclast (benthic foraminifers) wackestone-packstone; MF11: peloid bioclast packstone; MF12: dacycladacea benthic foraminifera packstone-wackestone; MF13: miliolids wackestone-packstone.     

Microfacies and geochemistry of the Ilam Formation in the Tang-E Rashid area, Izeh, S.W. Iran

The Ilam Formation (Santonian–Campanian in age), part of the Bangestan Group, is disconformably overlain by the Sarvak Formation and underlain by the Gurpi Formation in the Tang-E Rashid, Peyon area, Izeh (Zagros), southwest of Iran.Facies analyses indicate that the Ilam carbonates formed in four microfacies belts: tidal flat, lagoon, shoal and open marine, in a platform ramp environment. Major and minor elements and carbon and oxygen isotope values were used to determine the original carbonate mineralogy of the Ilam Formation. Petrographic evidence and elemental and oxygen and carbon isotope values indicate that aragonite was the original carbonate mineralogy in the Ilam Formation. The elemental and isotopic compositions of the Ilam carbonates also illustrate that they have stabilized in the marine phreatic environment. Variations of Sr/Ca and δ¹⁸O values versus Mn suggest that diagenetic alteration occurred in a closed system. Temperature calculation based on the oxygen isotope value of the least-altered sample indicates that the very early shallow burial fluid temperature was around 28 °C.Recognition of the exact boundary between the Ilam and Sarvak Formations is difficult, due to similar lithologies and the absence of the Surgah Formation in the study area. However, elemental and oxygen and carbon isotope analysis were used to determine the boundary between these formations. The δ¹⁸O and δ¹³C values, along with elemental results, clearly indicate a subaerial exposure surface, below which meteoric diagenesis affected the sediments.     

The Aghajari (Upper Fars) Formation in the Folded Zagros Zone, Iran:Insights to Identify Facies, Architectural Elements, Fluvial Systems,Petrography and Provenance

The Aghajari Formation, called also the Upper Fars, develops throughout the Folded Zagros Zone and its thickness in the type section in southwest of Iran is 2966 meters. To analyze the sedimentary basin of this Formation, lithofacies, architectural elements and petrofacies of the related deposits in a section in southeast of Sarvestan in Fars Province of Iran with a thickness of 2221.45 meters were examined. Microscopically studying thin sections, the petrography and the occurrence of the deposits were determined. In this section, 16 lithofacies, 10 architectural elements and 2 sandstone petrofacies were identified. The lithofacies were divided into two major and minor groups, in which the major lithofacies consist of coarse-grained (Gh, Gp, Gt and Gm), medium-grained (Sh, Sp, St, Sl, Sm, Sr and Ss and fine-grained ones (Fm, Fl and Fsm), and the minor lithofacies were evaporative and mixed silisiclastic-carbonate. The identified architectural elements are CH, SB, GB, LA, DA, CR, CS, LV, LS, CH (FF) and FF. By combining evidences from facies analysis and architectural elements together, the Aghajari Formation was divided into three parts in which the related sedimentation environments, from top to bottom, are gravel, gravel-sand and fine-grained meandering river respectively. There have also been playas and shoreface in the lower part. Based on petrography, the sandstones of this formation were classified into two groups: litharenite and sublitharenite. The origin of these deposits (sandstones) was appointed to the recycled orogeny and the source of quartz is low and medium to high metamorphic rank. Using the field evidences, the paleocurrent direction was achieved indicating the direction of the paleocurrent from northwest to southeast at the time of deposition. It is hoped that these data can be used in the interpretation of the basin and reconstruction of the paleogeography in the local and regional scales.     

Provenance, Tectonic Setting and Geochemistry of Ahwaz Sandstone Member (Asmari Formation, Oligo-Miocene), Marun Oilfield, Zagros Basin, SW Iran

The Asmari Formation deposited in the Zagros foreland basin during the OligoceneMiocene. Lithologically, the Asmari Formation consists of limestone, dolomitic limestone, dolomite, argillaceous limestone, some anhydrite(Kalhur Member) and sandstones(Ahwaz Member). This study is based on the analysis of core samples from four subsurface sections(wells Mn-68, Mn-281, Mn-292 and Mn-312) in the Marun Oilfield in the Dezful embayment subzone in order to infer their provenance and tectonic setting of the Ahwaz Sandstone Member. Petrographical data reveal that the Ahwaz Sandstone comprises 97.5% quartz, 1.6% feldspar, and 0.9% rock fragments and all samples are classified as quartz arenites. The provenance and tectonic setting of the Ahwaz Sandstone have been assessed using integrated petrographic and geochemical studies. Petrographic analysis reveals that mono- and poly-crystalline quartz grains from metamorphic and igneous rocks of a craton interior setting were the dominant sources. Chemically, major and trace element concentrations in the rocks of the Ahwaz Sandstone indicate deposition in a passive continental margin setting. As indicated by the CIW′ index(chemical index of weathering) of the Ahwaz Sandstone(average value of 82) their source area underwent "intense" recycling but "moderate to high" degree of chemical weathering. The petrography and geochemistry results are consistent with a tropical, humid climate and low-relief highlands.     

伊朗扎格罗斯造山带构造演化与成矿

扎格罗斯造山带是特提斯构造域的重要组成,其内赋存有世界级规模的金属矿产资源。本文综述了扎格罗斯造山带构造格架、物质组成、矿床分布及特征,讨论了该区构造演化与成矿。扎格罗斯造山带由南至北由扎格罗斯褶皱冲断带(ZFTB)、萨南达杰-锡尔詹岩浆变质带(SSZ)、乌尔米耶-达克塔尔火山岩浆带(UDMA)和伊朗中部地块四个构造单元组成。新元古代—早寒武世时,萨南达杰-锡尔詹带和伊朗中部地块位于冈瓦纳大陆北缘,受始特提斯洋盆俯冲影响,边缘发育大陆岩浆弧。晚石炭世—二叠纪萨南达杰-锡尔詹带和伊朗中部地块与冈瓦纳大陆裂解,新特提斯洋盆形成。三叠纪伊朗中部地块与北侧的欧亚大陆汇聚,古特提斯洋盆闭合。侏罗纪—白垩纪新特提斯洋盆向北侧的萨南达杰-锡尔詹带俯冲,形成弧岩浆岩及弧后盆地,其中弧前蛇绿岩中发育铬铁矿床,弧后盆地双峰式火山岩中产有块状硫化物矿床,碳酸盐岩内发育梅迪阿巴德密西西比河谷型超大型铅锌矿床。白垩纪末—新生代初洋壳向萨南达杰-锡尔詹带仰冲,含铬铁矿的蛇绿岩就位。始新世末—渐新世新特提斯洋闭合,南侧的阿拉伯板块与北侧的萨南达杰-锡尔詹带和中伊朗地块所在的欧亚大陆碰撞,在阿拉伯板块前缘形成扎格罗斯褶皱冲断带,在欧亚大陆南缘形成乌尔米耶-达克塔尔火山岩浆带。伴随碰撞,在萨南达杰-锡尔詹带的碳酸盐岩中形成类密西西比河谷型铅锌矿床,中中新世以来扎格罗斯地区进入后碰撞阶段,在乌尔米耶-达克塔尔带内发育了包括萨尔切实梅和松贡超大型矿床在内的众多斑岩型铜矿床。     

Dinoflagellate and foraminiferal biostratigraphy of the Gurpi Formation (upper Santonian–upper Maastrichtian), Zagros Mountains, Iran

A rich dinoflagellate cyst assemblage has been recovered from an outcrop of the Gurpi Formation, the hydrocarbon source rock in the South Iranian Basin. Key dinoflagellates recorded in the section studied provide a means of correlation with zonation schemes for Australasia and north-west Europe. These include Eucladinium kaikourense, Nelsoniella aceras, Odontochitina spp., Cannosphaeropsis utinensis, Palaeocystodinium denticulatum and Dinogymnium spp. The assemblage points to a late Santonian–late Maastrichtian age for the Gurpi Formation. Dinoflagellate and planktonic foraminiferal evidence indicates the presence of a hiatus spanning the uppermost Maastrichtian to at least the lowermost Danian at the base of a glaucony-rich layer separating the Gurpi Formation from the overlying Pabdeh Formation. Palynofacies and lithofacies profiles suggest that the sediments were deposited in an open, relatively deep marine outer ramp environment belonging to ramp facies 8 and 9.     

Impacts of Depositional Facies and Diagenesis on Reservoir Quality: A Case Study from the Rudist-bearing Sarvak Formation, Abadan Plain, SW Iran

An integrated geological-petrophysical analysis of the rudist-bearing sequence of the Cretaceous Sarvak Formation is given one giant oilfield, and provides an improved understanding of this main reservoir in the Abadan Plain, in the Zagros Basin, SW Iran. The main objective of this study is to evaluate reservoir potential of the Sarvak Formation, and then to utilize the calibrated well log signature to correlate reservoir potential in un-cored wells. Eight main facies are recognized and categori...     

Revision of the age of the Qom Formation in the Central Iran Basin, Iran

The Qom Formation in the Central Iran Basin contains not only relatively abundant calcareous nannofossils and a small number of dinoflagellate cysts, but also a number of stratigraphically significant benthonic foraminifers and ostracods. Calcareous nannofossils reported for the first time from this formation include Coccolithus pelagicus, Cyclicargolithus abisectus, C. floridanus, Dictyococcites bisectus, D. scrippsae, Helicosphaera euphratis, Ericsonia fenestratus, Pontosphaera sp., Reticulofenestra dictyoda, R. minuta and Sphenolithus moriformis. Dinoflagellates include Homotryblium plectilum, Hystrichokolpoma rigaudiae, Operculodinium centrocarpum, Palaeocystodinium golzowense, Spiniferites pseudofurcatus and Thalassiphora pelagica. Benthonic foraminifers include Assilina aff. spira, Discocyclina sp., Neodiscocyclina cf. barkeri, Nummulites aff. variolarius, Operculina sp. and Orbitolites sp. Among the ostracods recovered are Alocopocythere dhansariensis, Asymmetricythere samalutensis, Bairdia montiformis, Cytherella jonesiana, Cytheretta virgulata, Cytheridea cf. bundensis, C. cf. scruposa, C. sp., Eopaijenborchella sp., Hermanites cf. grafica, Krithe oryza, K. cf. pernoides, Loxoconcha sp., Paracypris sp., Propontocypris zongbuensis, P. sp. and Xestoleberis sp. This assemblage indicates that the Qom Formation is Eocene in age instead of Middle-Late Oligocene to Early Miocene as previously determined.     

Biostratigraphy and depositional environment evolution of the Asmari Formation at the Shajabil anticline,Iran

In the present research, biostratigraphy and paleoecology of the Asmari Formation at the Shajabil anticline, northwest Yasuj in the Izeh zone are discussed. The Asmari Formation at the studied area is Rupelian–Chattian to Burdigalian in age. In the study, 18 genera and 29 species of benthic foraminifera have been identified. Besides, the following biozones which reflect Rupelian–Chattian to Burdigalian age are identified for the Asmari Formation: (1) Lepidocyclina–Operculina–Ditrupa; (2) Archaias asmaricus–Archaias hensoni–Miogypsinoides complanatus; (3) Peneroplis farsenensis_Elphidium sp.14–Miogypsina sp.; (4) Borelis melo–Borelis melo curdica. Relying on fossils, Coral and Corallinacea have been detected depositional environment. The paleo-ecological factors are identified for the Asmari Formation at the study area: water salinity, 34 to more than 50 psu; water depth of 90 to 0 m; water temperature of 14 °C to more than 27 °C in a subtropical to tropical environment, oligotrophoic to mesotrophic conditions.     

A dye-tracing test as an aid to studying karst development at an artesian limestone sub-aquifer: Zagros Zone,Iran

A dye-tracing test is employed to study the karst development and flow regime at an artesian limestone sub-aquifer, the Khersan3 Dam site, Zagros Zone, Iran. Tracer breakthrough curves showed an early dominant peak followed by a pronounced tailing effect. The peak concentration was a response to induced pressure during dye injection. The results suggest that the dye was pushed into the small pores and fissures around the injection point during dye injection. Hence, the dye moved out as a result of matrix and fissure diffusive processes and created a long pronounced tailing. The maximum flow velocity in the upper artesian sub-aquifer ranged from 0.97 to 2.9 m/h. However, the mean tracer velocity ranged from 0.19 to 0.51 m/h based on the mean residence tracer time; consequently, the flow regime in the artesian sub-aquifer was determined to be mainly diffusive. The results reveal (1) a low hydraulic gradient from upstream of the dam axis to downstream; consequently, there is no considerable flow; (2) poor karst development and diffuse flow at the tracing test area; (3) a discharge zone at a location downstream of the dam axis which is the main terminal of general flow direction at the dam site.     

鄂尔多斯盆地北部山西组页岩沉积相及其对页岩储层的控制作用

鄂尔多斯盆地北部山西组页岩气储层与煤层共生,页岩有机质含量较高,具有较大的资源勘探潜力。为精细表征控制山西组页岩储层分布的沉积微相,根据测井数据、录井数据、岩芯观察描述、薄片分析、粒度分析、X射线衍射全岩分析以及总有机碳含量(TOC),研究了山西组页岩储层岩相与沉积微相类型,在山西组识别出(灰)黑色碳质页岩、(灰)黑色含碳质页岩、(灰)黑色含碳质(粉)砂质页岩、(深)灰色含碳质页岩、(深)灰色页岩、(深)灰色(粉)砂质页岩和含钙质页岩7种岩相。这些岩相沉积在富植沼泽、贫植沼泽、三角洲平原分流间洼地、曲流河河间洼地、天然堤与决口扇远端微相环境,其中富植沼泽、贫植沼泽与成煤的泥炭沼泽、泥炭坪环境比邻共生,且在山二段时期更发育。富植沼泽和贫植沼泽微相控制了具有较高TOC的(灰)黑色碳质页岩、(灰)黑色含碳质页岩、(灰)黑色含碳质(粉)砂质页岩和(深)灰色含碳质页岩的分布,是控制山西组页岩储层分布的有利微相。     

Mineralogical and geochemical investigations of the Mombi bauxite deposit,Zagros Mountains,Iran

The Mombi bauxite deposit is located in 165 km northwest of Dehdasht city, southwestern Iran. The deposit is situated in the Zagros Simply Fold Belt and developed as discontinuous stratified layers in Upper Cretaceous carbonates (Sarvak Formation). Outcrops of the bauxitic horizons occur in NW-SE trending Bangestan anticline and are situated between the marine neritic limestones of the Ilam and Sarvak Formations. From the bottom to top, the deposit is generally consisting of brown, gray, pink, pisolitic, red, and yellow bauxite horizons. Boehmite, diaspore, kaolinite, and hematite are the major mineral components, while gibbsite, goethite, anatase, rutile, pyrite, chlorite, quartz, as well as feldspar occur to a lesser extent. The Eh–pH conditions during bauxitization in the Mombi bauxite deposit show oxidizing to reducing conditions during the Upper Cretaceous. This feature seems to be general and had a significant effect on the mineral composition of Cretaceous bauxite deposits in the Zagros fold belt. Geochemical data show that Al₂O₃, SiO₂, Fe₂O₃ and TiO₂ are the main components in the bauxite ores at Mombi and immobile elements like Al, Ti, Nb, Zr, Hf, Cr, Ta, Y, and Th were enriched while Rb, Ba, K, Sr, and P were depleted during the bauxitization process. Chondrite-normalized REE pattern in the bauxite ores indicate REE enrichment (ΣREE = 162.8–755.28 ppm, ave. ∼399.36 ppm) relative to argillic limestone (ΣREE = 76.26–84.03 ppm, ave. ∼80.145 ppm) and Sarvak Formation (ΣREE = 40.15 ppm). The REE patterns also reflect enrichment in LREE relative to HREE. Both positive and negative Ce anomalies (0.48–2.0) are observed in the Mombi bauxite horizons. These anomalies are related to the change of oxidation state of Ce (from Ce³⁺ to Ce⁴⁺), ionic potential, and complexation of Ce⁴⁺ with carbonate compounds in the studied horizons. It seems that the variations in the chemistry of ore-forming solutions (e.g., Eh and pH), function of carbonate host rock as a geochemical barrier, and leaching degree of lanthanide-bearing minerals are the most important controlling factors in the distribution and concentration of REEs. Several lines of evidences such as Zr/Hf and Nb/Ta ratios as well as similarity in REE patterns indicate that the underlying marly limestone (Sarvak Formation) could be considered as the source of bauxite horizons. Based on mineralogical and geochemical data, it could be inferred that the Mombi deposit has been formed in a karstic environment during karstification and weathering of the Sarvak limy Formation.     

Boundary Between Upper Cretaceous and Lower Paleocene in the Zagros Mountain Ranges of Southwestern Iran

In the present study, over 3000?m of Upper Cretaceous sediments (Tarbur Formation) in seven stratigraphic, columnar sections were studied. The area is located in the Zagros mountain ranges of southwestern Iran, attributed to the converging continental Arabian Shield, and is interpreted as the result of subduction and collision. Based on foraminiferal studies of the Tarbur Formation in the sections, we have established many new biozones in the stratigraphic sections. However, investigations of the biozones indicate that there is no lithostratigraphic variation between the Upper Cretaceous and Lower Paleocene sediments in some of the studied sections. The concept of widespread formations and lithologic correlations is not applicable in this area, probably as a result of the tectonic unrest at that time. The biostratigraphic boundary between the Cretaceous and the Lower Paleocene is nevertheless well defined by the intraformational boundary in the sections.     

Appraisal of relative tectonic activity along the Kazerun Fault Zone,Zagros Mountains,Iran: insight from spatial analysis of geomorphic indices

This paper investigates the impact of active tectonics on the geomorphic processes and landscape evolution along the Kazerun Fault Zone (KFZ) in the Zagros Mountains of Iran using spatial analysis of geomorphic indices. We document how topography and morphology are influenced by active tectonic deformation. The Zagros fold–thrust belt is an area of active crustal shortening where northwest–southeast oriented fault‐related folds become younger from north to south and from southeast to northwest. This temporal and spatial evolution of the belt was tested using geomorphic indices of active tectonics that include mountain front sinuosity index (Smf), the valley width/height ratio (Vf), drainage basin asymmetry factor, hypsometric integral, drainage basin shape ratio and mean axial slope of the channel. Change in the geomorphic indices is the result of active fold growth and change in the uplift rate. Decreasing Smf and Vf values from north (Smf = 2.01; Vf = 0.5) to south (Smf = 1.12; Vf = 0.2) and from southeast (Smf = 1.84; Vf = 0.8) to northwest (Smf = 1.54; Vf = 0.1) points to a migration of the active crustal shortening towards W–SW. The combined geomorphic (field evidences) and morphometric data (quantitative analysis of geomorphic indices) provide evidence of relative variation in the tectonic activity along the Kazerun Fault Zone and related landforms. The utilization of geomorphic parameters with comparison to the field observations exhibits change in relative tectonic activities mostly corresponding to the change in mechanism of the prominent fault zones in the study area. Copyright © 2014 John Wiley & Sons, Ltd.     

伊朗Kashan地区库姆组沉积相及其对储层的控制作用

伊朗Kashan地区库姆组形成于混水碳酸盐岩台地沉积环境,以碳酸盐岩与陆源碎屑岩的混合沉积为主,沉积特征受陆源碎屑的影响较大.库姆组自身储集条件偏差,裂缝和溶孔在储集空间中占绝对优势,断裂活动及相伴生的溶蚀活动是控制储层发育的主要因素,而沉积相则为之提供物质基础.有利储集相带主要分布在应力集中区域和岩石破裂地区,其中局限台地滩相和三级层序界面之下的岩溶带是最佳储层发育位置.     

湖北省栖霞组沉积环境-沉积旋回及层序地层划分

根据岩石结构、构造及生物碎屑含量等特征,将本区栖霞组分为3类微相:A.生物碎屑灰岩;B.灰泥岩;C.具水平层纹的含炭质泥质细生物屑灰岩(泥灰岩).在剖面上,这3类微相组合成CA、CB或以C微相为主的韵律.不同韵律纵向上有规律的叠置常构成厚约10余米的沉积旋回.根据沉积旋回在垂向上的更替,在本区栖霞组内可识别出4次较大的海平面变化,周期约3My.通过与同期泛大陆北方各大陆上所发育的旋回层的对比,作者认为本区栖霞组内的4次海平面变化属三级海平面变化,对应4个三级层序,为全球冰川性海平面变化的结果,可与同期北美大陆上海平面变化曲线对比.     

鄂尔多斯盆地中东部奥陶系马家沟组沉积相演化模式研究

通过野外露头、岩心和薄片观察,结合测井资料,综合古气候、古沉积格局分析,系统地总结了鄂尔多斯盆地中东部奥陶系马家沟组沉积微相类型,并建立了沉积相演化模式。研究表明:(1)鄂尔多斯盆地中东部马家沟期具有"隆洼相间型"和"平底锅型"两种古沉积格局并存的特征;(2)主要发育9种微相类型,根据不同海平面高度的沉积微相平面组合类型,可将一个完整的海侵—海退旋回细分为海侵初期、中期和末期,海退初期、中期和末期等6个演化阶段;(3)古气候、古沉积格局和海平面升降变化共同控制了马家沟组生储盖分布,指出位于海侵期的东部隆起带及邻近区域发育的颗粒滩和白云岩坪,具有良好的成藏条件,有望成为一个碳酸盐岩勘探新领域。     

Revised age of proximal deposits in the Zagros foreland basin and implications for Cenozoic evolution of the High Zagros

The regionally extensive, coarse-grained Bakhtiyari Formation represents the youngest synorogenic fill in the Zagros foreland basin of Iran. The Bakhtiyari is present throughout the Zagros fold-thrust belt and consists of conglomerate with subordinate sandstone and marl. The formation is up to 3000 m thick and was deposited in foredeep and wedge-top depocenters flanked by fold-thrust structures. Although the Bakhtiyari concordantly overlies Miocene deposits in foreland regions, an angular unconformity above tilted Paleozoic to Miocene rocks is expressed in the hinterland (High Zagros).

The Bakhtiyari Formation has been widely considered to be a regional sheet of Pliocene–Pleistocene conglomerate deposited during and after major late Miocene–Pliocene shortening. It is further believed that rapid fold growth and Bakhtiyari deposition commenced simultaneously across the fold-thrust belt, with limited migration from hinterland (NE) to foreland (SW). Thus, the Bakhtiyari is generally interpreted as an unmistakable time indicator for shortening and surface uplift across the Zagros. However, new structural and stratigraphic data show that the most-proximal Bakhtiyari exposures, in the High Zagros south of Shahr-kord, were deposited during the early Miocene and probably Oligocene. In this locality, a coarse-grained Bakhtiyari succession several hundred meters thick contains gray marl, limestone, and sandstone with diagnostic marine pelecypod, gastropod, coral, and coralline algae fossils. Foraminiferal and palynological species indicate deposition during early Miocene time. However, the lower Miocene marine interval lies in angular unconformity above ~ 150 m of Bakhtiyari conglomerate that, in turn, unconformably caps an Oligocene marine sequence. These relationships attest to syndepositional deformation and suggest that the oldest Bakhtiyari conglomerate could be Oligocene in age.

The new age information constrains the timing of initial foreland-basin development and proximal Bakhtiyari deposition in the Zagros hinterland. These findings reveal that structural evolution of the High Zagros was underway by early Miocene and probably Oligocene time, earlier than commonly envisioned. The age of the Bakhtiyari Formation in the High Zagros contrasts significantly with the Pliocene–Quaternary Bakhtiyari deposits near the modern deformation front, suggesting a long-term (> 20 Myr) advance of deformation toward the foreland.