Facies analysis and depositional environments of the Oligocene–Miocene 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.     

The Shishugou Fauna of the Middle–Late Jurassic Transition Period in the Junggar Basin of Western China

The Middle–Late Jurassic transition period is a critical period for the evolution of terrestrial vertebrates, but the global fossil record from this time is relatively poor. The Shishugou Fauna of this period has recently produced significant fossil remains of dinosaurs and other vertebrate groups, some representing the earliest known members of several dinosaurian groups and other vertebrate groups and some representing the best-known specimens of their group. These discoveries are significant for our understanding of the origin and evolution of several vertebrate lineages. Radiometric dating indicates that the fauna is aged approximately 159–164 Ma. Comparisons with other similarly-aged terrestrial faunas such as Shaximiao and Yanliao show both taxonomic similarities and differences between these faunas and indicate that the Junggar deposits might have preserved the most complete vertebrate fossil record for a Middle–Late Jurassic Laurasian terrestrial fauna.     

A Periglacial Palaeoenvionment in the Upper Carboniferous–Lower Permian Tobra Formation of the Salt Range, Pakistan

The Upper Carboniferous—Lower Permian(Upper Pennsylvanian-Asselian) Tobra Formation is exposed in the Salt and Trans Indus ranges of Pakistan.The formation exhibits an alluvial plain(alluvial fan-piedmont alluvial plain) facies association in the Salt Range and Khisor Range.In addition,a stream flow facies association is restricted to the eastern Salt Range.The alluvial plain facies association is comprised of clast-supported massive conglomerate(Gmc),diamictite(Dm)facies,and massive sandstone(Sm) Hthofacies whereas the stream flow-dominated alluvial plain facies association includes fine-grained sandstone and siltstone(Fss),fining upwards pebbly sandstone(Sf),and massive mudstone(Fm) Hthofacies.The lack of glacial signatures(particularly glacial grooves and striatums) in the deposits in the Tobra Formation,which are,in contrast,present in their timeequivalent and palaeogeographically nearby strata of the Arabian peninsula,e.g.the AI Khlata Formation of Oman and Unayzah B member of the Saudi Arabia,suggests a pro-to periglacial,i.e.glaciofluvial depositional setting for the Tobra Formation.The sedimentology of the Tobra Formation attests that the Salt Range,Pakistan,occupied a palaeogeographic position just beyond the maximum glacial extent during Upper Pennsylvanian-Asselian time.     

A Middle–Upper Devonian Boundary Section in the Open Platform,Platform Margin Facies of Guilin, South China

Abstract: The Caiziyan Middle and Upper Devonian boundary section is located approximately 30 km northeast of Guilin. It hosts relatively abundant benthic and common–rare pelagic fossils, including brachiopods, corals, tentaculites, and conodonts, which may serve as a better suitable section for pelagic and neritic stratigraphic correlation. In this section, 10 “standard” conodont zones are recognized across the Givetian–Frasnian boundary, including, in descending order, the Lower hassi Zone, punctata Zone, transitans Zone, the Upper falsiovalis Zone, the Lower falsiovalis Zone, disparilis Zone, the Upper hermanni–cristatus Zone, the Lower hermanni–cristatus Zone, the Upper varcus Zone, and the Middle varcus Zone, all of which are defined by the first occurrence of their defining conodont species. The Middle–Upper Devonian (Givetian–Frasnian) boundary is defined by the first occurrence of Ancyrodella pristina in accordance with the Global Stratotype Section and Point (GSSP), which is assigned at 6.2m above the base of bed 19 in the Caiziyan section.     

Lithostratigraphy, Sedimentology, and Provenance of the Balfour Formation (Beaufort Group) in the Fort Beaufort–Alice Area, Eastern Cape Province, South Africa

Abstract: The Balfour Formation has a pronounced lithological variation that is characterized by alternating sandstone- and mudstone-dominated members. The sandstone-dominated Oudeberg and Barberskrans Members are composed of lithofacies that range from intraformational conglomerates to fine-grained sediments, whereas the mudstone-dominated members (Daggaboersnek, Elandsberg, and Palingkloof) are dominated by the facies Fm and Fl. Petrography, geochemistry, and a paleocurrent analysis indicated that the source rock of the Balfour Formation was to south east and the rocks had a transitional/dissected magmatic arc signature. The sandstones-rich members were deposited by seasonal and ephemeral high-energy, low-sinuous streams, and the fine-grained-rich members were formed by ephemeral meandering streams. The paleoclimates have been equated to present temperate climates; they were semiarid becoming arid towards the top of the Balfour Formation. This has been determined by reconstructing the paleolatitude of the Karoo Basin, geochemistry, paleontology, sedimentary structures, and other rock properties, like color.     

The First Reconstructions of Vegetation and Climate Changes in the Central Part of the Oka Plateau (East Sayan Mountains) in the Middle–Late Holocene

Doklady Earth Sciences - The Central part of the Oka Plateau lying in the East Sayan Mountains is still a poorly studied area of southern Siberia as regards its paleogeography. This gap can be...     

Sedimentary and organic facies investigation of the Gurpi Formation (Campanian–Paleocene) in southwest of Zagros,Iran

The Gurpi Formation in the southwest of Iran has been studied for microfacies and bulk organic geochemistry in order to elucidate its depositional environment and petroleum source rock characteristics. The obtained results ended up with four types of organic facies and three types of microfacies through the formation. Three microfacies types differentiated including Pelagic mudstone Wackstone, microbioclast Packstone and bioclastic Packstone reflect a distal outer ramp or basinal environment. Combination of palynofacies and organic geochemistry resulted in differentiation of four organic facies corresponding to organic facies B, BC, C and CD of Jones 1987. Detailed organic facies shows that the formation is characterized by low values of TOC, high percentages of amorphous organic matter and black phytoclasts, rare marine algae thereby representing a mixture of terrestrial and marine kerogen that confirm the formation was deposited in a distal anoxic to oxic condition. The formation shallows upward to the Microbioclast Packstone facies below the Lopha Member reaching its minimum depth in boundstones of this member in uppermost Campanian and then is followed by stagnant condition and high contents of organic matter in suboxic to anoxic condition that favoured accumulation of organic matter in early Maastrichtian. Organic geochemical and petrographical data indicate that the formation is not potentially suitable for petroleum production except for the minor interval (organic facies 2) in early Maastrichtian. Tmax values vary between 340 and 440 °C confirming immaturity trends indicated by Rock-Eval data.     

Petrographic and Geochemicial Characteristics of the K?z?loren Formation (Upper Triassic-Lower Jurassic) in the Akp?nar (Konya, Turkey) Area

This paper describes the occurrence of dolomite and the mechanism of dolomitization of the Upper Triassic-Lower Jurassic K?z?loren Formation in the autochthonous Bolkardag? unit of the middle Taurus Mountains in south western Turkey. Dolomites were analyzed for geochemical, isotopic and crystallographic variation. Dolomites occur as a replacement of precursor carbonate and cement. The dolomite crystals range from <10 to ~1000 μm existing as both replacements and cements. Sr concentrations range between 84 and 156 ppm, and the molar Sr/Ca ratios of dolomitizing fluids are estimated to range between 0.0066 to 0.013 ratios. Dolomites are Ca-rich (with average CaCO3 and MgCO3 equal to 56.43 and 43.57 mol%, respectively) and they are non-stoichiometric, with an average Sr=116 ppm, Na=286 ppm, Mn=81 ppm, Fe=1329 ppm, and δ18O and δ13C ranges from –0.6‰ to –6.1‰ Pee Dee Belemnite [PDB], and +1.2 to +3.9‰ PDB. The North American Shale Composition [NASC]-normalized rare earth element (REE) values of the both limestone and dolomite sample groups show very similar REE patterns characterized by small positive Eu (mean=1.32 and mean=1.42, respectively) and slightly or considerably negative Ce (mean=0.61 and mean=0.72, respectively) anomalies and a clear depletion in all REE species. The K?z?loren Formation dolomites have been formed as early diagenetic from mixing zone fluids at the tidal-subtidal environment and at the late diagenetic from basinal brines at the shallow-deep burial depths.     

Geochronology, Geochemistry and Tectonic Setting of the Bairiqiete Granodiorite Intrusion (Rock Mass) from the Buqingshan Tectonic Mélange Belt in the Southern Margin of East Kunlun

This study focuses on the zircon U–Pb geochronology and geochemistry of the Bairiqiete granodiorite intrusion(rock mass) from the Buqingshan tectonic mélange belt in the southern margin of East Kunlun. The results show that the zircons are characterized by internal oscillatory zoning and high Th/U(0.14–0.80), indicative of an igneous origin. LA–ICP–MS U–Pb dating of zircons from the Bairiqiete granodiorite yielded an age of 439.0 ± 1.9 Ma(MSWD = 0.34), implying that the Bairiqiete granodiorite formed in the early Silurian. Geochemical analyses show that the rocks are medium-K calc-alkaline, relatively high in Al2O3(14.57–18.34 wt%) and metaluminous to weakly peraluminous. Rare-earth elements have low concentrations(45.49–168.31 ppm) and incline rightward with weak negative to weak positive Eu anomalies(δEu = 0.64–1.34). Trace-element geochemistry is characterized by negative anomalies of Nb, Ta, Zr, Hf and Ti and positive anomalies of Rb, Th and Ba. Moreover, the rocks have similar geochemical features with adakites. The Bairiqiete granodiorite appears to have a continental crust source and formed in a subduction-related island-arc setting. The Bairiqiete granodiorite was formed due to partial melting of the lower crust and suggests subduction in the Buqingshan area of the Proto-Tethys Ocean.     

Carbonate Sequence Stratigraphy of a Back-Arc Basin： A Case Study of the Qom Formation in the Kashan Area, Central Iran

The Qom Formation comprises Oligo-Miocene deposits from a marine succession distributed in the Central Basin of Iran. It is composed of five members designated as A-F. Little previous work exists on the sequence stratigraphy. Based on an integrated study of sequence stratigraphy with outcrop data, wells and regional seismic profiles, the Qom Formation is interpreted as a carbonate succession deposited in a mid-Tertiary back-arc basin. There are two second-order sequences (designated as SS1 and SS2) and five third-order sequences (designated as S1-S5). Five distinct systems tracts including transgressive, highstand, forced regressive, slope margin and lowstand have been recognized. The relationship between the sequences and lithologic sub-units has been collated and defined (S1 to S5 individually corresponding to A-C1, C2-C4, D-E, the lower and upper portions of F); a relative sea level change curve and the sequence stratigraphic framework have been established and described in detail. The coincidence of relative sea level change between that of the determined back-arc basin and the world indicates that the sedimentary cycles of the Qom Formation are mainly controlled by eustatic cycles. The variable combination of the systems tracts and special tectonic-depositional setting causally underpin multiple sequence stratigraphic framework styles seen in the carbonates of the back-arc basin revealing: (1) a continental margin basin that developed some form of barrier, characterized by the development of multiple cycles of carbonate-evaporites; (2) a flat carbonate ramp, which occurred on the southern shelf formed by the lack of clastic supply from nearby magmatic islands plus mixed siliciclastics and carbonates that occurred on the northern shelf due to a sufficient clastics supply from the land; and (3) a forced regressive stratigraphic stacking pattern that occured on the southern shelf and in basin lows due to the uplifting of the southern shelf. Thick and widespread aggradational framework limestone usually occurs in the initial sequences (S1 and S3) of the supersequence, which led to preferential oil reservoir deposition but a lack of source and cap rocks, whereas the retrogradational and progradational framework limestone usually occurs in the later sequences (S2 and S4-S5) of the supersequence, which results in two perfect sets of source, reservoir and cap rock assemblies, so that the limestone in sub-member C2-C4 and the F-Member can be predicted as important objects for oil exploration.     

Facies Analysis and Sequence Stratigraphy of Silurian Carbonate Ramps in the Turan (Kopeh-Dagh) and Central Iran Plates with Emphasis on Gondwana Tectonic Event

Two sections from the Silurian deposits in the Central Iran Micro and Turan Plates were measured and sampled. These deposits are mostly composed of submarine volcanic rocks, skeletal and non-skeletal limestone, shale and sandstone that were deposited in low to high energy conditions (from tidal flat to deep open marine). According to gradual deepening trend, wide lateral distribution of facies as well as absence of resedimentation deposits, a depositional model of a homoclinal ramp was proposed for these deposits. Field observations and facies distribution indicate that, two depositional sequences were recognized in both sections. These sections show similarities in facies and depositional sequence during the Early Silurian in the area. Although there are some opinions and evidences that demonstrated Paleo-Tethys rifting phase started at the Late Ordovician-Early Silurian, similarities suggest that the Turan and Iran Plates were not completely detached tectonic block during this time, and that their depositional conditions were affected by global sea level changes and tectonic events.     

伊朗Kashan地区古近系库姆组层序地层及盆地演化特征

库姆组沉积时期伊朗Kashan地区为中伊朗盆地库姆盆地东南方向的弧后边缘海盆地,以浅海相的碳酸盐岩和碎屑岩沉积为主.受构造运动与全球海平面旋回变化控制,大部分地区的库姆组形成了5个三级层序S1～S5,上覆上红组底部蒸发岩层,在这5个三级层序之下,盆地沉降中心位置还可见S0a和S0b层序.对格架中层序地层特征的动态演化分析后认为,Kashan地区在库姆组及其上、下地层沉积时期经历了7次重要的地层演化阶段:低水位充填期、初次海侵期、沉降充填期、孤立泻湖期、再次海侵期、构造抬升期、完全孤立期.     

Stratigraphy and ammonite fauna of the upper Shemshak Formation (Toarcian–Aalenian) at Tazareh, eastern Alborz, Iran

With a thickness of 3900 m, the Tazareh section is one of the thickest developments of the Shemshak Formation in the Alborz range. It overlies with sharp and disconformable contact the limestones and dolomites of the Lower–Middle Triassic Elikah Formation and is topped, again with a disconformable contact, by the marls and limestones of the Middle Jurassic Dalichai Formation. The nearly exclusively siliciclastic succession represents a range of environments, from fluvial channels, flood plains, swamps and lake systems to storm-dominated shelf, and a comparatively deep marine and partly dysoxic basin. The segment of the section between 2300 and 3500 m is exclusively marine and contains a moderately diverse ammonite fauna, ranging from the Middle Toarcian to the Upper Aalenian. The ammonite fauna comprises 21 taxa, among them the new genus Shahrudites with two new species, Shahrudites asseretoi and S. stoecklini from the Middle Aalenian Bradfordensis Zone. The other ammonites from the Shemshak Formation at Tazareh (as elsewhere in North and Central Iran) are exclusively Tethyan in character and closely related to faunas from western and central Europe. An ammonite-based correlation of Toarcian–Aalenian successions of the eastern Alborz with time-equivalent strata of the Lut Block, part of the Central-East Iranian Microcontinent (ca. 500 km to the south), suggests a strong influence of synsedimentary tectonics during the deposition of the upper Shemshak Formation.     

Lower Jurassic Sequence Stratigraphy and Sedimentary Facies on the North Slope of Mount Qomolangma

The Lower Jurassic is subdivided in ascending order into the Wulong, Kangdui and Yongjia Formations on the north slope of Mount Qomolangma, with a total thickness of 1362 m. They are thought to have been deposited respectively in the environments of the carbonate ramp fault-bounded basins and carbonate platform, with six sedimentary facies and six sub-facies. During the Early Jurassic, the Qomolangma area experienced strong faulting and subsidence, and was of a matured rift basin. The Lower Jurassic consists of eleven 3rd-order sequences, which can be grouped into three 2nd-order sequences and form a large transgressive-regressive cycle. The 3rd-order sequences and the corresponding sea-level changes recognized in the area can be correlated quite well with those set up in the western Tethys, and may have been caused by the eustatic fluctuations, while the 2nd-order sequences seem to be more closely related to the basement subsidence and the variation in sedimentary influx, indicating the evolution of th     

Geochemistry of lower Jurassic shales of the Shemshak Formation, Kerman Province, Central Iran: Provenance, source weathering and tectonic setting

Lower Jurassic shales of the Shemshak Formation of Kerman Province, Central Iran, were analyzed for major and selected trace elements to infer their provenance, intensity of palaeoweathering of the source rocks and tectonic setting. Plots of shales on Al₂O₃ wt.% versus TiO₂ wt.% diagram and Cr (ppm) versus Ni (ppm) diagram indicate that acidic (granitic) rocks constitute the source rocks in the provenance. Average CIA, PIA and CIW values (84%, 92%, 93%, respectively) imply intense weathering of the source material. Plots of shales on bivariate discriminant function diagram reveal an active continental margin setting for the provenance. The inferred tectonic setting for the Lower Jurassic shales of the Shemshak Formation of Kerman Province is in agreement with the tectonic evolutionary history of the Central Iran during the Jurassic period.     

鄂尔多斯盆地陇东地区延长组沉积相特征与层序地层分析

晚三叠世鄂尔多斯盆地是一个东缓西陡的不对称坳陷盆地。通过岩心、录井、测井等资料综合研究,识别出陇东地区延长组发育河流、三角洲、浊积扇和湖泊等4种沉积相类型,其中河流沉积和浊积扇发育在湖盆的西缘陡坡带,三角洲则在西缘和东部缘坡均有发育。根据层序地层学原理,将延长组划分出5个三级层序;延长组地层经历过5次大的湖泛,在层序演化上具有早期形成、中期鼎盛、晚期衰退的特点。利用恢复后的原始地层厚度,绘制的陇东地区延长组地层的F ischer图解,与本区5次显著的湖平面上升-下降旋回之间有很好的对应关系,这不仅证实了上述层序地层分析的正确性,同时揭示了F ischer图解在划分地层层序方面的潜在意义。     

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.     

伊宁凹陷金鑫煤矿侏罗系露头剖面层序地层分析

以伊宁凹陷北缘霍城县金鑫煤矿侏罗系露头地层剖面为研究对象,采用层序地层学和沉积相分析方法,对其层序界面特征、层序的构成特征和沉积相类型进行研究.结果表明,侏罗系露头剖面发育冲积扇、辫状河、曲流河、三角洲和滨浅湖等沉积相类型;层序界面以侵蚀不整合面和河道强烈侵蚀下切面为识别标志.依据确定的层序界面,在八道湾组中划分3个层序、三工河组和西山窑组中分别划分2个层序.低位体系域主要发育冲积扇和辫状河沉积体系,湖扩体系域主要发育滨浅湖沉积,高位体系域主要发育三角洲和曲流河沉积体系.泥炭沼泽主要发育于湖扩体系域和高位体系域.     

准噶尔盆地阜康凹陷东部斜坡带中侏罗统头屯河组高分辨层序与沉积微相精细分析

在岩芯观察、测井及地震资料分析基础上,应用高分辨层序地层理论对准噶尔盆地阜康凹陷东部斜坡带中侏罗统头屯河组进行划分,共识别出1个长期旋回,3个中期旋回以及10个短期旋回。概括起来有2种基准面旋回基本结构类型,多种亚类型,且旋回总体划分与地层划分基本一致。通过对试油资料的分析与总结,发现研究区油层大部分位于中期旋回MSC2中SSC4和SSC7两个短期旋回中,因此重点对两个短期旋回沉积微相特征进行详细分析,认为两个旋回都位于辫状河三角洲前缘亚相,包括水下主河道、分流河道等四个主要沉积微相。通过连井对比、等时地层格架的建立、上升相域沉积微相图编制和砂体纵向及横向分布特征的描述,总体认为SSC7旋回中所发育的有利储集体发育厚度及砂体连通性要好于SSC4旋回中砂体,并对有利储集层分布进行预测。