Minor Limestone Research Articles

Geologic causatives of the stratigraphic and structural heterogeneties of Baharyia formation, based on their seismic interpretation, Razzak field, Western Desert, Egypt

Evaluation of seismic attributes and seismic reflection characteristics analysis of Razzak Field was undertaken by subdividing the study area rock units. There are four seismo-facies units of varying parameters from top to bottom. These units are comparable to the Apollonia and Khoman Formations; the Abu-Roash Formation; Baharyia Formation and Alamein Formation. The seismo-facies unit 1 of the Apollonia and Khoman Formations reveal parallel to sub-parallel layering, with thickness increases northwards. The lithological distribution consists of limestone with minor clay intercalations with facies varying from middle neritic graded to outer neritic. Unit 2 of the Abu-Roash Formation shows divergent layering, with a thickness increasing gradually northwards and eastwards. The lithological distribution shows predominance of carbonate, sandstone occurring in minor portions and laterally graded into shale with littoral facies ranging to inner and middle neritic facies. Unit 3 of the Baharyia Formation reveals chaotic and oblique layering with a time thickness increases towards northeast and southwest parts, the lithological distribution exhibited sand and shale with minor limestone streaks, with facies varied changed from continental to inner-middle neritic, unit 4 of the Alamein Formation shows variation from parallel-subparallel orientation to oblique and chaotic with thickness increasing towards northwards and eastwards, the lithological distribution exhibited dolomitic limestone with minor streaks of limestone with facies varied from middle neritic facies to outer neritic and bathyal. Finally, the results are integrated to build up a seismo-stratigraphic model of the evaluated area of the northwestern Desert of Egypt. Seismic interpretation involves the construction of structure contour maps, in terms of time and depth, on the tops of the Apollonia, Abu-Roash, Baharyia and Alamein Formations. These maps show three structural closures, due to folding, that are dissected by NW–SE faults, analysis of relevant structural and stratigraphic seismic attributes such as root-mean-square amplitude, local structural dip, variance, ISO frequency component, sweetness and acoustic impedance average energy applied on reservoir tops, to enhance the visibility of faults, geological interpretation and the physical parameters of the subsurface related to lithology and stratigraphy for reservoir characterization. Finally, the results obtained are used to construct a seismic structural model. Integration of seismic and stratigraphic data is used to build a geological model of the northwestern Desert of Egypt.

Reservoir characterization, in relation to the petrophysical modeling of Baharyia formation, Razzak field, northern western desert, Egypt

The present work aims to investigate the reservoir characterizations of the Lower Cenomanian Baharyia Formation by creating isoparametic maps to calculate the petrophysical parameters and detect the favorable parts for oil accumulations using the available well logging data. Baharyia Formation is one of the main hydrocarbon sandstone reservoirs in the northern Western Desert of Egypt. About 90% of the Western Desert field produces form Baharyia sandstone Formation. This has been achieved through the analyses of the conventional wireline logs and petrophysical modeling. The Baharyia Formation comprises a complex of depositional lithofacies such as interbedded siltstone, shale, sandstones and pebbly sandstones. Petrophysical modeling of the Baharyia Formation was performed, based on the interpretation of complete wireline logs from five wells in Razzak oil field, north Western desert, Egypt. Petrophysical analysis accomplished, such as: shale volume, total and effective porosities, water saturation and hydrocarbon saturation, were deduced and utilized in the petrophysical subdivision of the Baharyia Formation. Relations between theses petrophysical parameters are established to define the implications of such parameters on the Baharyia Formation. Iso-parametric and litho-saturation crossplots are used to delineate variations in petrophysical parameters across the area. The obtained petrophysical results reveal that, the Baharyia Formation have a good reservoir quality, with high effective porosity values exceeding 18%,volume of shale about 30% and low water saturation values of 25%. The rock genetic types of the Baharyia Formation deduced form the log curve shapes proved that the Baharyia Formation was deposited from fluvial to marine environments passing through the tidal flood plain conditions. However, the lithology of the Baharyia Formation composed of sandstone, siltstone, shale and minor limestone inter-beds.

Evolution of diagenetic fluids in the deeply buried, upper Ediacaran Dengying Formation, Central Sichuan Basin, China

Deeply buried Precambrian carbonate reservoirs host economic petroleum reserves. The upper Ediacaran Dengying Formation (maximum burial depth >8 km) is predominantly composed of dolostone with porosity ranging from 2 to 4%, and minor limestone with a porosity of <2%. Detailed petrological observations and high-resolution geochemical analyses show the evolution from depositional fluids to late diagenetic fluids. Dolostone is subdivided into dolo-mudstone, dolo-laminite, stromatolitic dolostone, thrombolitic dolostone and oncoidal dolostone. These dolostones were precipitated from the Ediacaran seawater and yield rare earth elements and yttrium (REY) patterns similar to those of modern seawater. In the early diagenetic regimes, fibrous dolomite cement, characterised by superchondritic Y/Ho ratios, was first precipitated from marine porewaters, and then fine-crystalline dolomite cement, characterised by low Y/Ho ratios, was formed during meteoric diagenesis. Bladed dolomite cement was subsequently precipitated from (modified) seawater-dominated porewaters. In the intermediate burial regimes, medium- to coarse-crystalline dolomite cement was formed during reduction of Mn oxides. In the deep-burial regimes, saddle dolomite was precipitated from hydrothermal fluids and yields REY patterns characterised by MREE enrichment. Its superchondritic Y/Ho ratios were likely caused by the fractionation between Y and Ho during the co-precipitation of fluorite. Calcite cement has similar parent fluids to those of saddle dolomite. These dolomite phases have similar δ13C values, while their δ18O values gradually decrease during the paragenetic sequence. Multiphase dolomitisation led to the increase in Ca/Mg ratios of formation water and reservoir performance. This study is significant for those concerned with the deeply buried dolostone reservoirs. KEY POINTS Microbialites and five types of dolomite cements have different REY patterns. Co-precipitation of fluorite led to the superchondritic Y/Ho ratios of dolomite. Dolomite and calcite grains show micro-scale geochemical variations. This dolostone reservoir underwent multiphase fluids, including meteoric water, seawater and hydrothermal fluid.

Recent water disposal and pore pressure evolution in the Delaware Mountain Group, Delaware Basin, Southeast New Mexico and West Texas, USA

Study regionA flat, large, semi-arid plateau in the southwest United States (west Texas and southeast New Mexico) underlain by a deep Paleozoic sedimentary basin, the tectonic Delaware Basin, host of intensive hydrocarbon production. Study focusImpacts of injection of large volumes of water produced from oil and gas wells and injected through 1000 + disposal wells, in particular, pressure buildup, induced seismicity and their potential consequences, in a formation underlying fresh-water aquifers but separated from them by thick layers of evaporites. The target formation is the Delaware Mountain Group (DMG) of Permian age and consisting of up to 4500 ft (~1400 m) of mostly fine-grained, deepwater siliciclastic slope and basin deposits (sandstones, siltstones, and minor limestones). A flow model was developed and calibrated from well log data, stratigraphic data, petrophysical analyses, and core data (123 ×170 mi2 - 1 ×1 mi2 grid size) complemented with dynamic injectivity information based on surface injection pressures and rates of the disposal wells. New hydrological insights for the regionInjection of 5.8 billion barrels (0.92 billion m3) of waste water has generated regional pressure increases in the DMG mostly in the 100–400 psi (0.7–2.8 MPa) range: (1) creating strong artesian conditions that, combined with the presence of numerous historical boreholes, could connect DMG and fresh-water aquifers; and (2) generating conditions leading to actually observed moderate induced seismicity.

Sedimentary environment and tectonic setting of the clastic formation of the Tanjianshan Group in the Tuomoerrite area, North Qaidam

柴北缘构造带断续出露的寒武-奥陶纪滩间山群火山-沉积岩系是早古生代时期原特提斯洋俯冲造山作用的产物，也是中国西部块状硫化物和造山型金矿床的重要含矿岩系。前人已对滩间山群火山岩组开展了大量的地球化学和同位素年代学研究，而碎屑岩组的沉积序列和沉积相研究相对薄弱。我们在柴北缘托莫尔日特地区地质填图过程中，对该地区的滩间山群碎屑岩组开展了系统的沉积组合序列和沉积相研究。托莫尔日特地区滩间山群碎屑岩组是由富含火山碎屑物质的含砾砂岩、砂岩、粉砂岩、泥岩、沉凝灰岩、硅质凝灰岩、硅质岩及少量砾岩共同组成。可分为下岩性段和上岩性段，其中下岩性段为一套形成于海底扇外扇环境以沉凝灰岩为主的沉积组合；上岩性段包含海底扇内扇、中扇和外扇沉积，且以中扇环境的沉积为主。垂向上，它们呈现出粒度向上逐渐变细特征；空间上，具有向北西方向火山物质成分逐渐增多、砾岩和砂岩厚度变薄且砾岩消失的变化特征。砂岩主要为岩屑长石杂砂岩，其中岩屑主要是安山岩和少量玄武岩、英安岩、凝灰岩；长石主要为斜长石；石英碎屑相对缺失。砾岩中砾石以安山岩和硅质岩为主，并含有少量灰岩和凝灰岩砾石。底冲刷面、正粒序、平行层理和波纹层理等沉积构造普遍发育，呈现出典型的浊流沉积特征；同时在局部露头见有滑塌构造和波痕。区域上，这套沉积组合序列位于寒武-奥陶纪岛弧火山岩的南侧；古水流分析显示，它们的碎屑物质主要来自于其北东方向。这些结果表明，柴北缘构造带东段的滩间山群碎屑岩组是一套成熟度极低且与寒武-奥陶纪岛弧火山活动密切相关的沉积组合。;Volcano-sedimentary system of the Cambrian-Ordovician Tanjianshan Group in the northern margin of Qaidam basin was formed by the subduction of the Proto-Tethys Ocean during Early Paleozoic and hosted massive sulfides and orogenic gold deposits in western China. Much attention had been paid to geochemistry and isotopic dating of the volcanic Formation of the Tanjianshan Group, but the sedimentary sequence and facies of the associated clastic rocks received less care. Systemic studies on the sedimentary sequence and facies in the processes of the geological mapping demonstrate that the clastic Formation in the Tuomoerrite area consists of pebbly sandstone, sandstone, siltstone, mudstone, tuffite, siliceous tuff, chert and minor conglomerate. This formation can be subdivided into two lithologic units. The lower unit is mainly dominated by tuffite deposited in the lower submarine fan environment, whereas the upper unit is deposited in the upper, mid, and lower fan environments. In contrast, the rock assemblages of the upper unit are mainly composed of the mid-fan deposits. The upper unit is characterized by fining-upward sequence and increasing abundance of volcanic composition northwestward, but the thickness of sandstones decreases and conglomerate disappears to northwest. Sandstones mainly comprise lithic greywacke. Lithic fragments contain andesite, basalt, dacite, and minor tuff and limestone. Feldspar fragments are dominated by plagioclase grains, and less monocrystalline quartz grains with an igneous origin occur in several samples. Clasts of conglomerates are dominated by angular andesite, chert and minor limestone and tuff. Irregular basal erosional surface, normal grading, parallel laminations and ripples are widespread show typical of turbidite. Slumping folds and wave marks can also be observed in the local outcrops. Regionally, volcano-clastic rocks distributed in the southern margin of Cambrian-Ordovician Keke island arc with a southwestward paleocurrent. These results demonstrate that the clastic formation is closely related to the Cambrian-Ordovician island arc.

Lithofacies and petrochemical characterization of volcano-sedimentary sequence of Chandil Formation around Kharidih-Bareda area, Seraikela-Kharsawan District, Jharkhand: implications for uranium mineralization

Mesoproterozoic Chandil Formation (ca. 1600 Ma) of North Singhbhum Mobile Belt record numerous features of felsic volcaniclastics and felsic to intermediate volcanics preserved in the central sector of the fold belt around Kharidih-Bareda area, Seraikela-Kharsawan district, Jharkhand. The felsic volcanic rocks exhibit flow bands, autoclasts and layering of crystal mushes revealing viscous nature of eruptives. The volcaniclastic sediments comprise of significant proportion of volcanic epiclasts and accidental lithic fragments. These volcaniclastics have been categorized into five prominent lithofacies viz, stratified lapilli tuff, banded tuff, tuff with penecontemporaneous deformation, welded lapilli stones, vitric tuff and volcanic bombs by field and petrographic studies of outcrops and subsurface borehole cores. The welded lapilli tuffs display fiamme and eutaxitic texture. Interlayering of the volcaniclastics, which are most often pyrite-rich, with psamo-pelitic lithology like carbonaceous phyllite, variegated phyllite, quartzite and minor limestone is suggestive of marine euxenic depositional environment. Petrographic study of the volcaniclastics indicated presence of glass shards, garnet phenocrysts, spherules of tremolite, ovoid to lenticular accretionary lapilli along with devitrified glassy material. Compositionally these felsic volcanics and volcaniclastics are rhyodacitic to andesitic in nature with peraluminous to meta aluminous in character. A/CNK values vary from 0.52 to 2.42 in felsic volcanics and from 0.12 to 1.63 in volcaniclastics. Signatures of arc magmatism is indicated by low concentration of HFS elements such as Nb (5-17 ppm), Ga (11-17 ppm) and Y (5-28 ppm). Elevated intrinsic content of uranium (3-8 ppm), Th/U ratio ranging from 1.2 to 13.2, presence of metamict allanite and zircon in volcanics and volcaniclastics reveal their suitability as a prospective source for search of uranium mineralization. The volcanic-volcaniclastic-clastic association of the Chandil Formation provides an ideal situation where provenance and province both are available. Thus, suitable litho-structural locales such as the concealed shear zones sympathetic to the Dalma thrust and South Purulia Shear Zone within the volcano-sedimentary package of Chandil Formation may be targeted as preferable sites for locating concealed uranium mineralization.

Iron-nickel metallic components bearing silicate-melts and coesite from Ramgarh impact structure, west-central India: Possible identification of the impactor

The Ramgarh structure (rim-to-rim diameter ~2.4 km) in the Vindhyan Supergroup of sedimentary rocks (including sandstone, shale and minor limestone) of the Mesoproterozoic age in the west-central India, is India’s third confirmed asteroid impact crater. This eroded structure is roughly rectangular in shape and resembles to the Barringer Crater, USA. The presence of central peak and its current crater diameter/depth ratio of ~12 well corroborate the range (10–20) of terrestrial complex asteroid impact craters. The mm-sized, iron-rich (FeO ~50 wt.% in average), spherule-like particles, recovered from the alluvium inside the Ramgarh structure, have internal morphology similar to those of the accretionary lapilli described in known impact craters. The in-situ LA-ICP-MS analyses also suggested high Co–Ni (up to 13,000 and 2500 ppm, respectively)-rich areas locally within these spherules/lapilli. A few non-in-situ, mm-sized particles, recovered from the rim of the structure show the presence of coesite, one of the diagnostic indicators of shock metamorphism. A few fragments of iron-rich, Ca–Al–silicate glasses recovered from the soil inside the structure and outside of the western crater rim include the presence of dendritic magnetite with occasional inclusions of relict native iron. Our microprobe analyses confirm that these metallic irons contain high proportions of Co (~350–3000 ppm), Ni (~200–4000 ppm) and Cu (~2200–7000 ppm) and possibly could be the relict component of a Cu-rich iron meteorite impactor. The field observation and relative enrichment of compatible and incompatible trace elements in the spherule-like substance (recovered from the alluvium inside the Ramgarh structure) as compared to target rocks suggests that hydrothermal activity played an important role in the evolution of the crater.

Cobar Deposits - Structural control

The Cobar Superbasin is located in the Central Subprovince of the Lachlan Orogen in the central part of New South Wales, about 700km northwest of Sydney. The Cobar Superbasin is the most mineralised Palaeozoic sedimentary basin in Lachlan Orogen. It has an estimated pre‐mining resource of 202 t of Au, 4.597 t Ag, 2.5 Mt Cu, 4.8 Mt Zn and 2.8 Mt Pb metals. The term ‘Cobar Superbasin’ is introduced to refer to a series of deep-water troughs/basins, inferred to have formed as half graben and shallow water shelfs. Its northern portion is dominated with siliciclastic sedimentary sequences whilst the southern portion comprises sediments, volcaniclastics, volcanic rocks, granites and minor limestone. The basin formed in the Early Devonian by NE-SW transtension and was closed by NW transpression in Late and Middle Carboniferous. The overall inversion structural style is NW-SE folding, overprinted by NE-SW trending and NNW-trending eastwards oblique left-lateral reverse faulting, in a combined thick- and thin-skinned tectonic environment. The Cobar Style mineralisation is a common name for mineral deposits hosted in the Cobar Superbasin and includes massive sulphides (VMS), clastic hosted Pb-Zn mineralisation and epithermal gold. In the Cobar Superbasin, the primary location of mineral deposits is controlled by basement architecture and then overprinted and modified with secondary controlling factors of inversion tectonics. Primary control is related to the location of mineral deposits within basin architecture and directly depends om major basement structures such as: - basin marginal growth fault; - intersection of growth and transform/transfer faults; and - intersection transform/transfer faults. Secondary control is related to deposit geometry and is direct consequence of invasion tectonic such as: - intersection termination and deflection of strike-slip faults; - overlap of en-echelon strike-slip; and - junction of major faults. Cobar Style mineralisation occurs in form of sheeted veins characterised by narrow width (5m - 10m), short strike (50m – 10m) and a significant depth extension (> 2000m). The deposits occur as a group of lenses in an en-echelon array with a steep plunge

Facies and petrophysical modeling of the Upper Bahariya Member in Abu Gharadig oil and gas field, north Western Desert, Egypt

The Upper Bahariya Member represents an argillaceous sandstone reservoir and it is one the Late Cretaceous units. There is a need for understanding the detailed facies and petrophysics of this member and identifying whether its petrophysical parameters are related to the facies changes or the present structures. Therefore, the present study aims at determining the facies and petrophysical characteristics of the Upper Bahariya Member and their distribution in the Abu Gharadig field. This field is located in the central portion of Abu Gharadig basin in the northern part of the Western Desert of Egypt. The available data for the present study includes four digital well logs, twenty 2D seismic sections and a checkshot survey. This is achieved through building the 3D facies and petrophysical models using Petrel™ Schlumberger Modeling software. These models were built on a predefined 3D stratigraphic and structural framework. The interpreted lithology of the Upper Bahariya Member is represented by sandstone cemented by argillaceous and/or calcareous materials, siltstone, shale and minor limestone inter-beds. A new lithofacies subdivision for the Upper Bahariya is introduced in the present study through the study area. This subdivision is represented by three lithofacies (an upper shale-silt-carbonate lithofacies, a middle sand-silt lithofacies and a lower shale-silt lithofacies). The Upper Bahariya Member is evaluated as a good quality reservoir and it exhibits rapid variations in the conditions of deposition, from continental fluvial to marine passing through the tidal flood plain conditions. The sandstone source is mainly from the southeast and southwest directions. The vertical and lateral changes of the different petrophysical parameters are directly related to vertical and lateral facies changes.

Characterization of the Permo-Triassic upper Khuff reservoir, central Saudi Arabia: An integrated core plugs, petro-fabrics and mercury injection analysis

The present work aims to characterize the reservoir properties of the upper Khuff Formation using integrated core plugs, petro-fabrics and Mercury injection analyses. A thirty four rock samples are picked up from the exposure of the upper Khuff Formation (Khuff A Member) at Al-Qassim province. These samples are subjected to a verity of laboratory measurements including core plugs, thin sections and mercury injection as matched with well log and crude oil analyses. Good porosity and permeability ranges (4–18% and 5–20 mD) are indicated, especially at the lower part with a uni-modal pore size distribution. The lithology is mainly dolomitic with minor limestone. Some fractures, cemented pores and dissolution process are indicated at the middle and upper parts of the section, respectively. Autopore-based mercury injection is performed to determine the volume of intrusion, touristy, pore size distribution and diameter. Total intrusion volumes of 0.352, 0.137 and 0.036 ml, threshold pressures of 127.44, 146.04 and 216.00 psi and tortuosities of 40.01, 75.19 and 60.26 are indicated for the analyzed samples, respectively. The results of the logging analyses are matched with the laboratory ones. Good hydrocarbons content is recognized in the middle part of the section. The analysis of crude oil sample indicates medium oil with high carbon content of 81.29 wt% and average specific gravity of 0.886 gm/cc. In conclusion, this integrated study indicates that the lower part of the Khuff A Member attains the best reservoir properties among the studied section.

Pedogenic record of climate change across the Pennsylvanian-Permian boundary in red-bed strata of the Cutler Group, northern New Mexico, USA

The Upper Pennsylvanian to lowermost Permian El Cobre Canyon and Arroyo del Agua formations are well exposed in a 250+ m section in the Chama Basin in northern New Mexico. This is one of the few known successions of fossiliferous red-bed siliciclastic sediments encompassing the Pennsylvanian-Permian boundary in the American Southwest and thus may inform questions regarding changing paleoclimate in tropical Pangea across the Pennsylvanian-Permian boundary. The section consists mainly of silty mudstones and sandstones with sheet-like to ribbon geometry and very minor limestones and records an upward transition from mainly braided stream deposition in the El Cobre Canyon Formation to anastomosing stream deposition in the Arroyo del Agua Formation.We recognized multiple paleosol types within these strata, including calcic Protosols, calcic Argillisols, argillic Calcisols and Calcisols, all generally consistent with the interpretation of a seasonal sub-humid to semi-arid climate. The calcretes in these paleosols occur primarily as truncated profiles. Although Calcisols occur in both formations, we note that Protosols are more common in the El Cobre Canyon Formation, and Argillisols dominate in the Arroyo del Agua Formation. Also, we find that the calcretes in the Arroyo del Agua Formation are generally thicker than those in the underlying El Cobre Canyon Formation. The difference in calcrete maturity could be explained by changes in source-area relief and sedimentation rate. However, stable isotope analyses of pedogenic carbonate indicate that a significant enrichment of δ18O occurs near the transition between the two formations, which approximates the Virgilian-Wolfcampian (equals Gzhelian-Asselian) boundary. Although the δ13C data suggest that pCO2 remained stable during the interval of deposition, the δ18O data are consistent with the interpretation of climate aridification across the Pennsylvanian-Permian transition, potentially related to the onset of Gondwanan glaciation in the earliest Permian.

Geodynamics of Late Carboniferous–Early Permian forearc in north Chile (28°30′–29°30′S)

A large section of the Late Palaeozoic forearc is exposed along the coastal ranges of north–central Chile (28°–29°30′S). This is characterized by three lithotectonic units: (1) the Punta de Choros Metamorphic Complex (basal accretion series), composed mostly of micaschists and metabasites; (2) the Chañaral Epimetamorphic Complex (frontal accretion series), formed by metaturbidites and metasediments; (3) the Llano del Chocolate Beds (forearc basin deposits), composed of a sedimentary sequence of clastic sedimentary rocks with minor limestones and acidic volcanic rocks. Within the basal accretion series, two distinctive blocks of garnet-bearing schists with amphibolite-facies metamorphism have been preserved, recording early stages of the subduction system. The stratigraphic record and the U–Pb dating of igneous (291–318 Ma) and detrital zircons (maximal deposition ages between 273 and 292 Ma) in the forearc basin deposits, coupled with 40 Ar/ 39 Ar ages for metamorphic rocks (319–280 Ma), indicate that forearc sedimentation was broadly contemporaneous with metamorphism and exhumation of the basal accretion series. The radiometric dating on garnet-bearing rocks indicates that the onset of the subduction system took place in the Mississippian, at a high thermal gradient. These conditions were responsible for generation of limited volumes of acidic melt, now recognized as acidic domes and tuffs within the forearc basin stratigraphy. Supplementary material: Tables of sedimentary facies, U-Pb geochronological analyses and Ar-Ar geochronological data are available at: http://doi.org/10.6084/m9.figshare.c.2868307 .

Geochemistry characteristics and hydrocarbon-generating potential of lacustrine source rock in Lucaogou Formation of the Jimusaer Sag, Junggar Basin

There are a mass of transitional types of rock including proportionally-predominated shales, secondary siliciclastic sandstones, and carbonate rocks which are in small proportion (major dolostone and minor limestone) in Lucaogou Formation of the Jimusaer Sag of Junggar Basin.These rocks were deposited in brackish lacustrine environment under alkaline to weak alkaline conditions. The various rock types were all formed in reduction environment, but there is the broadest oxidation–reduction varying condition for the shale, and environmental reductivity where dolostones deposited is stronger than that of sandstones. The organic matter in source rocks comes from either aquatic organism or terrestrial organism. As reservoir, parts of sandstones and dolostones contain more primitive solid organic matters which might act as the hydrocarbon-generating material base.Parent material types of source rocks in different lithologies are mainly mixed type of type II2-I and have oil-prone characteristic. In the study area, the Ro value corresponding to oil generation peak for source rock is Ro=0.9%, lower than the classic model oil peak Ro=1.0% and thermal maturity of source rocks in multifarious types fall in the stage of oil generation.Determined by relationships of TOC content vs. Bitumen/TOC and TOC content vs. HCI, the lower TOC limit for active rocks is around 1.0%, hereby, about 90% of the shales, all of the limestone, and a third of the dolostone and sandstone are active source rocks.Therefore, there are preferable oil-generating potential of lithologically different source rocks in Lucaogou Formation of the Jimusaer Sag. The shales are chiefly oil-prone source rock and parts of dolostone, sandstone and limestone also have a contribution to the oil reservoirs.

Mineralization and trace element distribution in pyrite using EMPA in exploration drill holes from Cheshmeh Zard gold district, Khorasan Razavi Province, Iran

ناحیه مطالعاتی در شمال استان خراسان رضوی و 45 کیلومتری جنوب نیشابور قرار دارد. رگه های طلادار درون سنگهای گرانیت، گرانودیوریت، گرانودیوریت پورفیری، آندزیت، برش و توف نفوذ کرده اند. رگه ها از جنس کوارتز و کلسیت هستند. مناطق اصلی دگرسانی شامل منطقه سرسیتیک، سیلیسی، پروپلیتیک و منطقه کربنات است. کانی زایی به‌طور نزدیکی با دگرسانیهای سیلیسی و سرسیتیک به شکل رگه‌چه و با منطقه پروپلیتیک به شکل افشان همراه است. کانی شناسی کانیهای باطله کوارتز، کلسدونی، سرسیت، آدولاریا، کلسیت، دولومیت، ایلیت، دیکیت، آلبیت، کائولینیت و کلریت است. کانی زایی رگه ای عمدتا با رگه‌چه ها، برش، افشان و استوک ورک همراه هستند. رگه‌چه ها از پیریت، مارکازیت، آرسنوپیریت و کمتر کالکوپیریت، اسفالریت، گالن، مگنتیت و هماتیت تشکیل شده اند. بیشترین عیار طلا در رگه های سیلیسی دیده می شود. پیریت کانی سولفیدی اصلی در کانی سازی اولیه است. سه نوع پیریت بر اساس ترکیب شیمیایی شناسایی شده است: پیریت خالص، پیریت غنی از آرسنیک و پیریت تیتانیوم- وانادیوم دار. تجزیه های ریزکاوشگر الکترونی بیشترین غلظت آرسنیک، تیتانیوم و وانادیوم را به ترتیب 62/3، 91/3 و 53/0 درصد وزنی در پیریتهای رگه های طلادار نشان می دهند. طلا معمولا همراه با پیریت آرسنیک دار و پیریت تیتانیوم- وانادیوم دار است. براساس مطالعه بافت و ترکیب پیریتها، رگه‌چه‌های پیریت آرسنیک دار همراه با کانیهای سولفیدی آرسنوپیریت، کالکوپیریت، گالن، اسفالریت در دمای بالا و با کاهش دما و فشار، پیریتهای فرامبوئیدال با حاشیه حاوی آرسنیک و طلا شکل گرفته اند و در ادامه پیریتهای درشت تیتان دار به‌وجود آمده اند. پیریتهای خالص و تأخیری درشت بلور آخرین فاز کانی ساز در منطقه هستند.

Stratigraphic characterization and structural analysis of the northwestern Hazara Ranges across Panjal Thrust, northern Pakistan

The study area is a part of the Western Himalayan fold-and-thrust belt in northern Pakistan and lies in the hanging wall of Panjal Thrust between Hazara-Kashmir and Indus syntaxes (Fig. 1). The present study uses stratigraphic appraisal and structural analysis to understand the tectonic evolution of the western Hazara Ranges. Based on detailed field mapping and structural analysis, the Western Hazara Ranges are broadly divisible into three structural domains: Sherwan, Aluli, and Pind Khan Khel. Each of these three structural domains comprises a major synclinal fold structure that exposes the Early Cambrian Abbottabad Formation in the core and Precambrian Tanawal Formation in the limbs. The syncline folds are doubly plunging and upright in nature. The basement rocks in the hanging wall of Panjal Thrust belong to Tanawal Formation which dominantly comprises of quartzites in the study area but changes to quartz schists and garnetiferous schists in the northern parts of the Hazara arc, while in the footwall, the Hazara Formation which is dominantly slates with some minor limestone is present as a basement sequence. Both blocks with different basement rocks are overlain by similar Early Cambrian Abbottabad Formation. This study attempts to explain the difference of basement rocks across Panjal Thrust through a tectonic evolution model, which suggests that the Pan-African orogeny is responsible for the basement stratigraphic changes while the Himalayan orogeny folded the Early Cambrian sequence in broad synclines and anticlines. The present exposures of Early Cambrian sequence in the core of synclines resulted due to subsequent erosion of anticlines and preservation of synclines.

Lower Triassic mixed carbonate and siliciclastic setting with Smithian–Spathian anoxic to dysoxic facies, An Chau basin, northeastern Vietnam

In the An Chau basin in northeastern Vietnam, the Olenekian (Lower Triassic) stage comprises mixed carbonate and siliciclastic shallow marine to marginal basin deposits that extend into the southern Nanpanjiang basin in South China. The upper Lang Son Formation, which is dominated by siliciclastic facies, is composed of storm- and wave-influenced shallow marine and slope deposits. The overlying and interfingering Bac Thuy Formation consists of tidal flat, wave-influenced carbonate platform, slope, and marginal basin plain deposits. The tidal flat deposits are composed mainly of lenticular, wavy-bedded, or thin flat-bedded carbonates containing desiccation cracks and ripples that are indicative of bidirectional paleocurrents. The platform carbonates are characterized by wave ripples, ooids, and abundant marine mollusks and microfossils; the molluscan fossil assemblage primarily contains Smithian ammonoids such as Owenites koeneni. The slope deposits are characterized by limestone breccia and slump beds. The marginal basin plain deposits consist of classical turbidite beds, minor limestone breccia, and hemipelagic mudstone and marl containing the Spathian ammonoids Tirolites and Columbites. The turbidite sets may represent frontal splay environments in the marginal basin plain. These Olenekian carbonate and siliciclastic facies are typical of a transgressive succession.The Smithian–Spathian boundary and the anoxic to dysoxic facies of the latest Smithian are characterized by organic-rich dark gray limestone and mudstone deposits intercalated in the succession of slope to marginal basin plain facies, which are composed mainly of gravity flow and hemipelagic deposits. The organic-rich deposits show no evidence of bioturbation and are characterized by low-diversity fauna. Clastics in the marginal basin plain deposits were apparently supplied from the west; hence, the paleocurrent direction of the siliciclastic gravity flows was approximately eastward.

Kolosjoki Sedimentary Formation: A record in the aftermath of the Paleoproterozoic global positive δ13C excursion in sedimentary carbonates

The Kolosjoki Sedimentary Formation of the Pechenga Greenstone Belt, north eastern Fennoscandia, records the aftermath of the Paleoproterozoic global positive δ13C excursion in sedimentary carbonates (the Lomagundi-Jatuli isotope excursion). The goals of this research were to provide detailed new data on the δ13C trend in the Kolosjoki Sedimentary Formation and generate a secular δ13C curve for the time period immediately succeeding the Lomagundi-Jatuli isotope excursion. For these purposes, sedimentary carbonate samples from two new drillcores representing the Kolosjoki Sedimentary Formation were collected. In total 88 whole-rock samples and 67 micro-drilled subsamples (ca. 1–3mg) were analyzed for the isotope composition of C and O, the whole-rock elemental abundances, and for the composition of the acid-soluble fraction. The Kolosjoki carbonate rocks are dolostone or calcitic dolostone (Mg/Ca=0.50–0.67) with minor limestone (Mg/Ca=0.04–0.06). Only weak correlation was observed between the Mn/Sr ratios and the δ13C and δ18O values, and the carbonate samples have likely retained their near-primary δ13C values. The sedimentary carbonate rocks show first low δ13C values at −2 to −1‰ and then a subtle, upward increasing δ13C trend from ca. 1 to 3‰. The increasing δ13C trend is interpreted to record a recovery from a δ13C minimum following the Lomagundi-Jatuli isotope excursion.

The record of the Late Palaeozoic active margin of the Palaeotethys in NE Iran: Constraints on the Cimmerian orogeny

The Cimmerian orogen resulted from the collision and accretion of several Perigondwanan blocks to the southern margin of Eurasia between the Late Triassic and Early Jurassic, following the closure of the Palaeotethys ocean. Remnants of this orogen discontinuously crop out in N (Alborz range) and NE Iran (Mashhad–Fariman area) below the syn- to post-collisional clastic successions of the Shemshak Group (Upper Triassic–Middle Jurassic) and the Kashaf Rud Formation (Bajocian). In NE Iran rock associations exposed in the Binalood Mountains, Fariman and Darreh Anjir areas include mafic–ultramafic intrusive rocks, basalts, silicoclastic turbidites and minor limestones, which have been interpreted in the past as ophiolitic remnants of the Palaeotethys ocean. Original stratigraphic, structural, geochemical and geochronological data, described in this paper, suggest a different interpretation. The volcano-sedimentary units of Fariman and Darreh Anjir complexes where deposited during Permian in a subsiding basin were siliciclastic turbidites, derived from the erosion of a magmatic arc and its basement, interfinger with carbonates and basaltic lava flows with both transitional and calc-alkaline affinity. The coexistence of magmatic rocks with different geochemical signature and the sedimentary evolution of the basin can be related to a supra-subduction setting, possibly represented by a fault-controlled intra-arc basin. The Fariman and the Darreh Anjir complexes are thus interpreted as remnants of a magmatic arc and related basins developed at the southern Eurasia margin, on top of the north-directed Palaeotethys subduction zone long before the collision of Iran with Eurasia. They were later involved in the Cimmerian collision during the Triassic. New radiometric ages obtained on I-type post-collisional granitoids postdating the collision-related deformational structures suggest that the suture zone closed before mid-Norian times. Deformation propagated later northward into the Turan domain involving the Triassic successions of the Aghdarband region.

Lower palaeozoic stratigraphy of murchisonfjorden and sparreneset, nordaustlandet, svalbard

Stouge, S., Christiansen, J.L. and Holmer, L.E., 2011. Lower Palaeozoic stratigraphy of Murchisonfjorden and Sparreneset, Nordaustlandet, Svalbard. Geografiska Annaler: Series A, Physical Geography, 93, 209–226. DOI: 10.1111/j.1468‐0459.2011.00433.xThe Lower Palaeozoic stratigraphy of the Kap Sparre Formation of Kulling (Hecla Hoek Succession) from Murchisonfjorden and eastern Nordaustlandet of Svalbard is described based on new field observations in the region. The investigated sedimentary succession is referred to the Upper quartzite series and Upper dolomite series of the Kap Sparre Formation. The observed sequence resembles that of the Oslobreen Group from central and northeastern Ny Friesland and the formal and well‐established and more detailed stratigraphical framework used in Ny Friesland may apply for the strata at Sparreneset and in Murchisonfjorden, western Nordaustlandet. The lower Palaeozoic succession overlies the uppermost Precambrian sediments (Dracoisen Formation = the lower part of Kap Sparre Formation sensu Kulling) of the Polarisbreen Group with a cryptic unconformity, and a regional stratigraphical gap spanning the late Ediacaran developed on the platform.Additions to the previous descriptions of some of the existing units are presented. The new lithostratigraphical unit: Black shale and limestone unit is proposed informally. It is a Lower(?) to Middle Cambrian black shale with limestone nodules and lenses that is exposed on the northwest coast of Krossøya in Murchisonfjorden, Svalbard. In addition, a Dolostone‐limestone unit, Middle(?) Cambrian to Lower Ordovician, composed of dolostone and dolomitized limestone and minor limestone, and a Limestone unit (Lower to Middle(?) Ordovician), which overlies the Upper dolomite series are added to the succession.The deposits as a whole show the development of an environmentally controlled carbonate platform that marked the transition from the inner to the outer shelf that evolved during the opening and spreading of the Iapetus Ocean.

U–Pb and Hf isotopic study of detrital zircons from the Yejishan Group of the Lüliang Complex: Constraints on the timing of collision between the Eastern and Western Blocks, North China Craton

The Trans-North China Orogen is a recently recognized continent–continent collisional belt along which the discrete Eastern and Western Blocks amalgamated to form the coherent basement of the North China Craton. However, there is a hot debate on the timing of the collision between the two blocks, with one school of thought arguing the collision occurred at 2.5 Ga, whereas others believe it took place at ~ 1.85 Ga. U–Pb ages and Hf isotopic data of detrital zircons from foreland basins in the Trans-North China Orogen can provide rigorous constraints on this controversial issue. One of such foreland basins is represented by the Yejishan Group in the Lüliang Complex in the middle sector of the western margin of the Trans-North China Orogen. The group consists of conglomerates, quartz wackes, sandstones and minor limestones, most of which contain large amounts of detrital zircons. CL images reveal that nearly all detrital zircons from the Yejishan Group possess oscillatory zoning, with Th/U ratios of 0.2–2.34, typical of an igneous origin. The 207Pb/ 206Pb ages of detrital zircons range between 3.24 and 1.81 Ga, with most having Paleoproterozoic ages, of which the youngest group ages are around 1.87–1.81 Ga. This indicates that the foreland basin in which the Yejishan Group was deposited must have formed not earlier than 1.87–1.81 Ga, thus supporting the collision between the Eastern and Western Blocks at ~ 1.85 Ga, not at ~ 2.5 Ga.