Dolomitic Shale Research Articles

Occurrence states and potential influencing factors of shale oil in the Permian Fengcheng Formation of Mahu Sag, Junggar Basin

Taking the Permian Fengcheng Formation of the Mahu Sag of the Junggar Basin as an example, a systematic study of shale oil was carried out for the occurrence states and potential influencing factors by integrating various data including cores, well logging, X-ray diffraction, argon ion polishing and field emission-scanning electron microscopy (FE-SEM) observations, high-pressure mercury injection (HPMI), rock pyrolysis, and two-dimensional nuclear magnetic resonance (NMR) experiments. The shale oil of the Fengcheng Formation in the Mahu Sag mainly has two modes of occurrence:film-like adsorbed oil and infilled free oil. The main constrains for shale oil occurrence state include lithofacies association, mineral composition and reservoir space. Four lithofacies associations namely dolomitic shale, sandy shale-dolomitic siltstone, dolomite rock containing alkaline mineral-argillaceous siltstone, and siliceous dolomite rock-dolomitic siltstone were recognized in the shale reservoirs of the Fengcheng Formation. The mineral composition, reservoir space, micro-pore structure and shale oil occurrence states of different lithofacies appeared to be quite different. The contents of quartz, pyrite and organic matter were positively correlated with thermal cracking hydrocarbon (S2), and the contents of feldspar and dolomite showed a weak positive correlation with free hydrocarbon (S1). The free oil was mainly stored in mesopores and large pores, such as secondary dissolution pores and residual intergranular pores. The absorbed oil was mainly stored in mesopores and small pores, such as organic pores, intercrystallite pores and the surface of mineral particles. The mineral composition and pore-throat structure were dominant factors controlling the occurrence state of shale oil.

Seismic prediction of lithofacies heterogeneity in paleogene hetaoyuan shale play, Biyang depression, China

AbstractShale lithofacies identification and prediction are of great importance for the successful shale gas and oil exploration. Based on the well and seismic fine calibration, extraction, and optimization of seismic attributes, root mean square (RMS) amplitude analysis is used to predict the spatial–temporal distribution of various lithofacies in the fifth organic-matter-rich interval, and the prediction results are confirmed by the logging data and geological background. The results indicate that in the early expansion system tract, dolomitic shale and calcareous shale were widely developed and argillaceous shale, silty shale, and argillaceous siltstone only developed in the periphery of deep depression. With the lake level rising, argillaceous shale and calcareous shale were well-developed, and argillaceous shale interbedded with silty shale or argillaceous siltstone developed in deep or semi-deep lake. In the late expansion system tract, argillaceous shale was widely deposited in the deepest sag; calcareous shale presented in eastern sag with belt distribution.

Deposition and diagenesis of the Early Permian volcanic-related alkaline playa-lake dolomitic shales, NW Junggar Basin, NW China

This study describes and interprets the mineral and facies assemblages of lacustrine shales that occurred in an ancient volcanic-related alkaline playa-lake, considering the importance of diagenetic pathways (calcification, dolomitization, borosilicate replacement, and silicification). Three laminated lithofacies (LF) have been differentiated in the Early Permian Fengcheng Formation, NW Junggar Basin: an alginite-poor, dolomite-lean, and argillaceous-rich lithofacies deposited during high lake level stages (LF-A), an alginite-moderate, dolomite-moderate, and evaporite-present lithofacies deposited during low lake level stages (LF-B), and an alginite-dense, dolomite-rich and reedmergnerite (NaBSi3O8)-rich lithofacies deposited during periods of intense hydrothermal input (LF-C). Depositional environments influenced subsequent diagenetic pathways of the three laminated lithofacies. In the shallow-water LF-B sediments, extensive evaporite crystallization, dissolution and subsequent calcification or dolomitization occurred during eodiagenesis. The deep-water LF-A sediments underwent slight eodiagenetic modifications, but developed abundant calcite-filling sub-horizontal fractures during moderate inversion and uplift in mesodiagenetic regime. With increasing depth of burial, the previous vugs-filling calcite and dolomite were preserved well or only slightly replaced by reedmergnerite in the LF-A and LF-B sediments, but intensely replaced by reedmergnerite in the LF-C sediments during mesodiagenesis. The reedmergnerite enrichment processes in the LF-C sediments were closely related to organic matter production and thermal evolution. Algae blooms induced by spring input functioned as an important media in sinking hydrothermal boron from the not very concentrated waters. Later degradation and thermal evolution of alginite released boron and organic acids into interstitial waters, which caused carbonate dissolution and promoted reedmergnerite formation. The formation of reedmergnerite during mesodiagenesis restrained silicification process of carbonate minerals in ancient volcanic-related alkaline lake deposits.

Key exploration & development technologies and engineering practice of continental shale oil: A case study of Member 2 of Paleogene Kongdian Formation in Cangdong Sag, Bohai Bay Basin, East China

Abstract Based on detailed core description and systematic joint test data, enrichment laws of continental shale oil have been examined deeply. Key technologies such as the identification and quantitative evaluation method for sweet spot, precise design and tracking of horizontal well trajectory, and the low-cost horizontal well volume fracturing technology of the whole process “slick water + quartz sand” for continental shale oil have been formed. The research results show that the enrichment of pure continental shale oil of the Paleogene Kong 2 Member in Cangdong Sag is controlled by predominant fabric facies and cross-over effect of retained hydrocarbons jointly; and there are four modes of shale oil enrichment, i.e. laminar felsic, laminar mixed, thin-layer limy dolomitic, and thick-layer limy dolomitic shales. The identification and evaluation method for shale oil sweet spots can predict sweet spots accurately. The precise trajectory design for sweet spot layer and tracking-trajectory optimization while drilling by considering geological and engineering factors have been proved effective by field application, with drilling rate of sweet spots reaching 100% and drilling rate of type I sweet spots reaching over 75%. The whole process “slick water + quartz sand” low cost volume fracturing has been proved effective in creating multi-stage fracture network in the horizontal section, and improved productivity greatly. It can lower the comprehensive engineering cost by 26.4%.

Iron-rich carbonate tidal deposits, Angepena Formation, South Australia: A redox-stratified Cryogenian basin

The Cryogenian Angepena Formation (ca. 650 Ma) of South Australia records deposition in a peritidal environment equivalent to, and landward of the Balcanoona reef complex, and offers valuable insights into shallow marine chemistry during the nonglacial interlude between two global ice ages. The sedimentary facies comprise an iron-rich marine red bed succession and include red mudcracked dolomitic shales, tepee dolostone, crossbedded intraclastic ooid grainstone, and tepee-related sheet cavities with marine cements. These facies are interpreted to have been deposited in a Cryogenian tidal flat to subtidal setting that is laterally equivalent to the reefal and back reef environments of the Balcanoona Formation. Marine cements from this environment are characterized by well-preserved, non- and bright-cathodoluminescent zoning, and strong negative to slightly positive cerium (Ce) anomalies (Ce/Ce*). We suggest that the Angepena Formation is indicative of intermittent synsedimentary iron oxide precipitation in an oxidized peritidal environment in an otherwise strongly ferruginous and anoxic oceanic setting. Large negative Ce anomalies develop over a narrower depth range when compared to modern oxic marine settings, highlighting the importance of dissolved Mn and Fe concentrations in controlling the magnitude of the negative Ce anomalies. Overall, coupled sedimentological and geochemical evidence suggest a Neoproterozoic shallow marine system at the interface of an oxidizing atmosphere and an anoxic ferruginous marine system.

Soils Developed from Dolomitic Shale in the Yichang Area, China and Adsorption Characteristics for Phenol

Recently, the problem of phenolic organics pollution has become increasingly serious. More and more strategies have been developed to remove phenolic organics from water, including oxidation, adsorption, chemical precipitation, etc. Among them, adsorption technology has attracted great attention due to its advantages of high efficiency, simplicity and easy operation. In this study, the natural shale soil without any modification was directly used as adsorbent to remove phenol from aqueous solutions. The shale soil samples were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and nitrogen adsorption-desorption isotherms. Detailed kinetics and isotherm studies of phenol adsorption onto shale were investigated. According to the results of the orthogonal test, the influence degree of the four factors on the removal of phenol by soil samples was operating temperature > adsorbent dosage > contact time > pH. The adsorption kinetics of phenols by the soil corresponded with the pseudo-second-order kinetic model. Thermodynamic studies indicated that Freundlich adsorption isotherm model could better describe phenol removal characteristics than Langmuir adsorption isotherm model. And the maximum adsorption capacity was found to be 9.68 mg/g for phenol. It is concluded that shale soil without any modification or activated methods could be employed as a low-cost alternative adsorbent for wastewater treatment.

The Influence of Injected Fluids on Microscopic Pore Structures in the Intersalt Dolomitic Shale Oil Reservoirs

Given their low porosity and permeability, intersalt dolomitic shale oil reservoirs need to be developed via large-scale hydraulic fracturing to achieve economic effects. However, various lithologies and salt materials make these reservoirs vulnerable to salt mineral dissolution and recrystallization and salt plugging during development. This study investigated the variation rules of pore structures, porosity, and permeability of intersalt dolomitic shale oil reservoirs under the influence of hydraulic fracturing fluid. Correspondingly, a series of experiments (i.e., high-temperature and high-pressure soaking experiments, focused ion beam scanning helium ion microscope analyses, and porosity and pulse permeability tests) is performed on the Qian 34-10 rhythmic intersalt dolomitic shales. Results show that distilled water dissolves the salt crystals inside the matrix pores to improve the reservoir permeability. However, the distilled water-rock interaction will cause the massive migration of salt minerals. By contrast, the supercritical CO2 can disperse salt particles, dredge the channels, and enlarge pores by expansion, but it has an overall weak capability of changing the pore structure and matrix permeability. To simulate the supercritical CO2 composite fracturing, the mixed solution of supercritical CO2 and distilled water favors the salt dissolution effect in the water-based fracturing fluid and recovery enhancement by CO2. This solution can remarkably improve the reservoir porosity and permeability and avoid massive salt mineral migration and salt crystallization damage. This study is theoretically and practically important to the effective and enhanced development of intersalt dolomitic shale oil reservoirs.

Geological characteristics and key exploration technologies of continental shale oil sweet spots: A case study of Member 2 of Kongdian Formation in the Cangdong sag in the Huanghua depression, Bohai Bay Basin

Under the general trend of stepping-up oil and gas exploration and development in China, the unconventional oil and gas resources such as shale oil and gas have become an important alternative. Abundant continental shale oil resources are developed in Member 2 of Kongdian Formation (Ek2) of the Cangdong sag in the Huanghua depression of the Bohai Bay Basin which has complex structure, strong heterogeneity, and large buried depth, thus, the geological characteristic of shale oil accumulation and key exploration technologies are investigated on base of the system coring of 635.8 m, centimeter-level fine description and analysis of over ten thousand samples, therefore, the “four accurate” technologies have been developed, including the accurate selection of sweet spot areas, accurate drilling of sweet spot layers, accurate fracturing of sweet spot layers and accurate measure of fracture-rich sections. The results show that the continental shale strata in Member 2 of Kongdian Formation can be divided into three types: felsic shale, limy dolomitic shale and mixed shale. The Member 2 of Kongdian Formation is characterized by diverse mineral components, abundant laminae, good source rocks and medium thermal evolution degree, tight reservoir with rich micropore and microfractures, high oil saturation and brittle mineral content, indicating good prospect of shale oil exploration. Through sedimentological study, TOC and Ro evaluation, brittle mineral calculation, and seismic fusion inversion, a total of 126 km2 of Class I sweet spots in Member 2 of Kongdian Formation was delineated comprehensively, which guides horizontal well deployment (Well GD1701H and Well GD1702H). The drilling rate of sweet spot of these two horizontal wells is up to 96% by tracing thin layer through fine calibration, locating compartment through fine inversion, ensuring window entry through precise positioning, and tracking sweet spot through adjustment. The "one-excellent and five-highs” criterion is used to select perforation points to realize differential designs of fracturing intervals and clusters. Micro-seismic and potentiometry monitoring show that the artificial fractures formed by volumetric fracturing are 300–400 m long and 120 m high, and control a volume of about 0.07 km3. The maximum daily oil production of two horizontal wells is 48 t and 66 t respectively to realize the economic exploitation of shale oil reserves controlled by fractures. The shale oil exploration in Member 2 of Kongdian Formation shows that the continental shale oil has great potential of exploration and development, and the above technologies are critical and effective for shale oil efficient recovery.

The Nadeiyakha Ore occurrence (Pai-Khoi, Russia): an example of ferromanganese metasediments in carbonaceous dolomitic shales

The paper presents the results of study of metalliferous (ferromanganese and manganese) rocks at the Nadeiyakha ore occurrence (Pai-Khoi) discovered in 2010. The metalliferous deposit represents a stratiform body lying conformably in the Upper Devonian carbonaceous siliceous and clayey–carbonate–siliceous shales. The ore bed occurs 180 m below the regional Famennian manganiferous rock association in Pai-Khoi. Discovery of the Nadeiyakha ore occurrence suggests the existence of an additional age interval of Mn accumulation within the Devonian sequence of this region. The studied metalliferous rocks display structures and textures typical of the metasedimentary rocks. In terms of composition, they are divided into two varieties: (i) ferromanganese (quartz–carbonate) rocks composed of quartz, dolomite, kutnahorite, rhodochrosite, siderite, and calcite; (ii) manganiferous (quartz–rhodochrosite–silicate) rocks composed of quartz, rhodochrosite, tephroite, sonolite, and pyroxmangite. The Nadeiyakha ore occurrence is marked by the abundance of dolomite in the ferromanganese rocks and host shales. In terms of the relationship of indicator elements (Al, Ti, Fe, and Mn), ferromanganese and manganese rocks are comparable with the recent metalliferous and ore-bearing sediments. The carbon isotope composition in carbonates (δ13C from –16.4 to –7.8‰ PDB) corresponds to authigenic carbonates related to the involvement of carbon dioxide produced during the microbial decomposition of organic matter at the stage of dia- and/or catagenesis. Geological and petrographic observations show that the ferruginous and manganiferous sediments were deposited synchronously with the terrigenous–carbonate–siliceous sediments. Fe and Mn could be sourced from hydrothermal solutions or interstitial diagenetic waters. The latter version seems to be more probable. Metals were accumulated in a depression-trap characterized by a periodic stagnation of bottom waters. Such sedimentation setting promoted the formation of paragenetic association of ferruginous and manganiferous sediments with the carbonaceous sediments and fostered reductive conditions during the postsedimentary mineral formation. Calcium carbonates contained in the primary rocks were subjected to dolomitization during the dia- or catagenesis. This process was promoted by the mobilization of Mg released during the transformation of clay minerals owing to the montmorillonite–illite transition. Iron and manganese carbonates were formed during the later replacement of oxides of Mn3+, Mn4+, and Fe3+. Crystallization of manganese silicates also started at early stages of lithogenesis and terminated during the regional metamorphism of metalliferous rocks.

Elaboration De La Carte Géotechnique De La Ville De Lubumbashi Guide Technique De Sélection Des Sites D’implantation D’ouvrages Du Génie Civil

Geotechnical data processing that ignores the spatial aspect leads to loss of information, specification errors, non-convergent and ineffective estimation, and prediction errors. These data often present a spatial dependence (problem of spatial autocorrelation) and a heterogeneity in space (clustering problem) and sometimes temporal. The geotechnical mapping of Lubumbashi soils based on 1672 observations according to the AASHTO classification system (designation ASTM D-3282 M145), divided these soils into 11 subgroups: A-1-a (sandy gravels with clays), A-1-b (gravelly sands with clays), A-2-4 (gravelly sands with silts), A-2-5 (sandy gravels plastic silts), A-2-6 (gravelly sands with clays), A-2-7 (gravelly sands with active clays), A-4 (silts with sands), A-5 (plastic silts with sands), A-6 (clays with sand), A-7-5 (active clays), A-7-6 (active clays). Class A-3 has not been identified. Soils with an index 5 contain clays of the illite type whereas the others consist of kaolinites on plasticity Casagrande chart. Class A-1 and A-2 are good for foundation engeneering and form the potential aquifers of the city (groundwater, drainage zone, groundwater recharge zone). They also constitute favorable sites for the implantation of the cimeteries (aerated soils) because the time necessary for the destruction of bodies is brief. In this case the rotation of 5 years can be used without problem for a city with dense population like the city of Lubumbashi. Soils A-4 and A-5 are also good for subgrade-foundations, but are highly vulnerable to erosion and liquefaction. Soils A-6 and A-7 form impervious bedrock substrates. These sites can be used as the landfill site. They are also considered clay deposits in the manufacture of ceramics and refractory products. Taking into account the nature of the source rocks, the same lithology can give several types of soils depending on the parameters influencing weathering: climate (Lubumbashi's tropical climate), pH, Eh, topography, anthropization, etc. One type of soil may also come from several rock formations. The geotechnical map developed compared to the geological map of Lubumbashi, shows that soils A-1 and A2 come from conglomerates, sandstones and the lateritization process of rock formations very rich in iron such as dolomitic shale and shale. Soils A-4 and A-5 are often alteration products of silty shales and siltstones, while soils A-6 and A-7 are derived from the alteration of clay and dolomitic rocks: shales, dolomitic shales, silty shales, limestones and dolomites. The geological map is fondamental but not sufficient document for geotechnical studies. A detailed study of the soils and the state of weathering of the different parts of a rock mass is inevitable.

Warm-humid paleoclimate control of salinized lacustrine organic-rich shale deposition in the Oligocene Hetaoyuan Formation of the Biyang Depression, East China

Lacustrine organic-rich shales are widely developed within the Oligocene Biyang Depression in the Nanxiang Basin in east China and across Southeast Asia. These shales have been proven as hydrocarbon source rocks of crude oil, as well as sources and reservoirs of shale oil. Understanding the deposition of these shales is essential to reconstruct the paleoenvironment and paleoclimate during the Oligocene in east China, as well as target the potential shale oil resources. Based on X-ray diffraction, organic and inorganic petrologic, organic and inorganic geochemical, and stable isotopic analyses, paleoenvironment, paleoclimate and hydrocarbon potential of the lacustrine organic-rich shales in the Oligocene Hetaoyuan Formation were investigated. The mineral composition of Hetaoyuan Formation organic-rich shales is dominated by clay minerals, followed by quartz, plagioclase, calcite, dolomite, pyrite and gypsum. Six lithotypes are identified, including siltstone, silty shale, clay shale, calcareous shale, dolomite shale and massive mudstone. The organic matter (OM) of the organic-rich shales is dominated by type I kerogen (lamalginite). Maturity parameters (Tmax, biomarker ratios and calculated vitrinite reflectance) suggest that the OM enters the oil window maturity. High TOC and generative potential, together with high contents of brittle minerals (including quartz, plagioclase and carbonates) reveal the Oligocene Hetaoyuan Formation hold good to very good potential of shale oil exploitation. Six organic-rich shale layers have been identified in the Hetaoyuan Formation (shale layer 1 to 6, from top to bottom). Among them shale layers 5 and 3 hold the best shale oil potential and therefore be investigated in the present paper. Shale layer 5 was deposited in a semi-deep lacustrine environment under the moderately warm-humid paleoclimate, further dividing into lower, middle and upper units. Relatively low TOC contents (av. 2.6 wt%) in the lower unit are probably caused by high sedimentation rate. High bioproductivity under favorable preservation conditions led to relatively high TOC contents (av. 3.6 wt%) in the middle unit. Less reducing conditions together with moderate-low bioproductivity resulted in relatively low TOC contents (av. 2.6 wt%) in the upper unit. Warm-humid paleoclimate prevailed during deposition of shale layer 3, deepened water depth and formed a deep lacustrine environment. The stratified water column led to stable anoxic condition and photic zone euxinia in the saline, deep lacustrine environment, which enabled the accumulation of high amounts of OM (av. 4.9 wt% TOC) under excellent preservation (av. HI: 710 mg HC/g TOC). The results of core scanning analysis indicate that formation of the laminated shales probably controlled by seasonal fluctuations of paleoclimate.

Characterization of the Lower Silurian Longmaxi marine shale in Changning area in the south Sichuan Basin, China

On the basis of the core description, thin sections, and geochemistry data, we characterized the Lower Silurian Longmaxi marine shale in the Changning area in the south Sichuan Basin. Ten lithofacies were identified in the Lower Silurian Longmaxi marine shale: (a) massive silty shale (Lithofacies A); (b) laminated siliceous calcareous shale (Lithofacies B); (c) calcareous shale (Lithofacies C); (d) silty dolomitic shale (Lithofacies D); (e) argillaceous siltstone (Lithofacies E); (f) siltstone (Lithofacies F); (g) laminated silty shale (Lithofacies G); (h) silty calcareous shale (Lithofacies H); (i) argillaceous lime shale (marl) (Lithofacies I); and (j) bentonite (Lithofacies J). Obvious heterogeneity occurred in different lithofacies in terms of mineralogy, total organic carbon (TOC) content, porosity, permeability, pore surface area, total pore volume, and total gas content. Among these lithofacies, Lithofacies B has the highest porosity (5.4%), pore surface area (12.79 m2/g), total pore volume (0.015 cc/g), TOC content (4.37%), total gas content (3.4 m3/ton), and relatively high brittle minerals, suggesting great shale gas potential. Lithofacies A, C, and D have a relatively high brittle minerals, porosity, pore surface area, total pore volume, TOC content, and total gas content, which means that these 3 lithofacies show relatively good potential for shale gas. The rest of the lithofacies have low brittle minerals content, porosity, pore surface area, total pore volume, TOC content, and total gas content, representing poor shale gas potential.

Investigation of Oil Potential in Saline Lacustrine Shale: A Case Study of the Middle Permian Pingdiquan Shale (Lucaogou Equivalent) in the Junggar Basin, Northwest China

The Pingdiquan shale (Lucaogou equivalent) is a typical saline lacustrine deposit in China and is one of the most significant petroleum source strata for the oil and natural gas fields in the Junggar Basin in northwestern China, which is widely acknowledged to have a large shale hydrocarbon potential. This article characterizes the Pingdiquan shale in the eastern Junggar Basin from the geochemical and geological perspectives, describes its oil potential, and compares the results with those from freshwater lacustrine shales. The Pingdiquan shale is highly heterogeneous in its mineral composition, with a big variation in each composition compared to that of freshwater lacustrine shales. The Pingdiquan shale can generally be classified into clastic shale and dolomite shale, where the clastic shale is distributed across the eastern Junggar Basin and thins from north to south, whereas the dolomite shale is developed only in the Jimusaer Sag and at the foot of the Kelameili Mountains. The Pingdiquan shale (both the clastic shale and dolomite shale) has a good petroleum potential and primarily consists of types II and III organic matter with thermal maturity ranging from early to late mature. The oil content (S1) of clastic shale and dolomite shale ranges from 0.01 to 4.96 mg/g and 0.02 to 3.23 mg/g, respectively. The oil content and oil saturation index (OSI) of the Pingdiquan shale reach a maximum value at the early to peak mature zone (Tmax of 445–450 °C). Similar trends can be observed in some typical freshwater lacustrine shales. In the Pingdiquan Formation, the dolomite shale has a higher total organic carbon content and genetic potential (S1 + S2) than the clastic shale; however, its oil content and OSI are lower than those of the clastic shale, as is its production index (PI). The results of one-dimensional basin modeling show that the dolomite shale and clastic shale have had almost the same petroleum transformation ratio values throughout geological history. However, the permeability of dolomite shale is orders of magnitude larger, which allows for more petroleum to be expelled from source rocks. In addition, positive correlations between specific surface areas and OSI and clay content are observed, indicating that high clay content also assists in maintaining the petroleum within the rocks. Therefore, less oil can be retained within dolomite shale than in clastic shale.

Lithogeochemical characterization of the Middle–Upper Devonian Road River Group and Canol and Imperial formations on Trail River, east Richardson Mountains, Yukon: age constraints and a depositional model for fine-grained strata in the Lower Paleozoic Richardson trough

Lithogeochemical characterization of the Road River Group and Canol and Imperial formations as exposed at an outcrop on Trail River, eastern Richardson Mountains, documents the evolution of a Laurentian-margin basin during the latest Eifelian through middle Frasnian stages. δ13Corg stable isotope data correlated to conodont-constrained global isotopic curves indicates deposition of the section from ≥387.7 to ≤376.7 Ma. The uppermost Road River Group is latest Eifelian and older in age (≥387.7 Ma) and is primarily calcareous and dolomitic shale and mudstone, representing a slope environment below a carbonate platform that experienced cyclical turbidity current deposition. A 2.3 m, metalliferous and concretionary unit lies transitionally between the Road River Group and Canol Formation and is herein designated as an informal, conformable, lithologic unit called the Road River – Canol transition zone (RCTZ), which records 4.5 Ma of condensed sediment deposition during the Givetian stage (387.7–383.2 Ma). The Canol Formation is confined to the latest Givetian to middle Frasnian stages (383.2–376.7 Ma) and consists of rhythmically bedded, biogenically sourced, siliceous shale and chert that was deposited in an anoxic (and likely euxinic) to oxic basin that evolved from moderately to strongly hydrographically restricted over time. The lowermost Imperial Formation is a siliciclastic mudstone, which documents turbidity current deposition in oxic bottom water conditions in the late Frasnian (≤376.7 Ma). Interpretation of lithofacies, whole-rock geochemistry, mineralogy, and total organic content enable the section to be grouped into eight lithochemozones that record a first-order late-stage sea-level transgression (Road River Group and RCTZ), highstand (lower Canol Formation), and early-stage regression (upper Canol Formation) followed by continued falling stage sea-level conditions with strong detrital influence from a continental collision in the high Arctic (Imperial Formation).

Mineral types and organic matters of the Ordovician-Silurian Wufeng and Longmaxi Shale in the Sichuan Basin, China: Implications for pore systems, diagenetic pathways, and reservoir quality in fine-grained sedimentary rocks

Mineral types (detrital and authigenic) and organic-matter components of the Ordovician-Silurian Wufeng and Longmaxi Shale (siliceous, silty, argillaceous, and calcareous/dolomitic shales) in the Sichuan Basin, China are used as a case study to understand the control of grain assemblages and organic matter on pores systems, diagenetic pathway, and reservoir quality in fine-grained sedimentary rocks. This study has been achieved using a combination of petrographic, geochemical, and mercury intrusion methods. The results reveal that siliceous shale comprises an abundant amount of diagenetic quartz (40–60% by volume), and authigenic microcrystalline quartz aggregates inhibit compaction and preserve internal primary pores as rigid framework for oil filling during oil window. Although silty shale contains a large number of detrital silt-size grains (30–50% by volume), which is beneficial to preserve interparticle pores, the volumetric contribution of interparticle pores (mainly macropores) is small. Argillaceous shale with abundant extrabasinal clay minerals (>50% by volume) undergoes mechanical and chemical compactions during burial, leading to a near-absence of primary interparticle pores, while pores preserved between clay platelets are dominant with more than 10 nm in pore size. Pore-filling calcite and dolomite precipitated during early diagenesis inhibit later compaction in calcareous/dolomitic shale, but the cementation significantly reduces the primary interparticle pores. Pore-throat size distributions of dolomitic shale show a similar trend with silty shale. Besides argillaceous shale, all of the other lithofacies are dominated by OM pores, which contribute more micropores and mesopores and is positively related to TOC and quartz contents. The relationship between pore-throat size and pore volume shows that most pore volumes are provided by pore throats with diameters <50 nm, with a proportion in the order of siliceous (80.3%) > calcareous/dolomitic (78.4%) > silty (74.9%) > argillaceous (61.3%) shales. In addition, development degree and pore size of OM pores in different diagenetic pathway with the same OM type and maturity show an obvious difference. Therefore, we suggest that the development of OM pores should take OM occurrence into account, which is related to physical interaction between OM and inorganic minerals during burial diagenesis. Migrated OM in siliceous shale with its large connected networks is beneficial for forming more and larger pores during gas window. The result of the present work implies that the study of mineral types (detrital and authigenic) and organic matter-pores are better understanding the reservoir quality in fine-grained sedimentary rocks.

LITHOLOGICAL VARIABILITY OF THE KUPFERSCHIEFER IN DEPRESSIONS OF THE WEISSLIEGEND RELIEF IN THE AREA OF THE RUDNA AND SIEROSZOWICE COPPER DEPOSITS

The paper presents analyses of spatial diversity of Kupferschiefer lithologies in the area of three top surface depressions of the Weissliegend relief in the central and northern part of the Rudna and Sieroszowice copper deposits. These are organic-rich (pitchy) shale, clay shale, and dolomitic shale. Sequences of author’s own lithological profiles and those received from the KGHM database were analyzed along 13 cross-section lines. Macroscopic studies were conducted on samples from author’s profiles. Eight types of lithological successions were distinguished and then the frequency of their occurrence along each cross-section and depression was analyzed. The most common sequence with organic-rich and dolomitic shale is observed both in author’s profiles as well as in the profiles received from the mine. In the profiles tested by the author, the dominant configurations were (1) organic-rich shale, clay shale and dolomitic shale (model sequence) and (2) organic-rich shale and clay shale. Such assemblages were observed in four cross-section lines on both slopes of the Northern Rudna Elevation, which suggests a local dependence between different lithological successions of shale and their location in the depression zones. Occurrences of a few profiles with non-standard shale sequences may suggest wider variability of sedimentation conditions in the north-easternmost Tarnówek Depression.

Sedimentology of the Shangoluwe breccias and timing of the Cu mineralisation (Katanga Supergroup, D. R. of Congo)

The origin of breccias in the Neoproterozoic Katanga Supergroup in D.R of Congo is still a matter of debate. At the Shangoluwe Cu deposit located in the Kambove mining district (central part of the Lufilian arc), the sedimentary breccias bearing Cu mineralisation have been investigated for lithological and sedimentological study, quantitative analysis of the breccias fragments and fault kinematic analysis in order to understand the origin of the breccias, their lithostratigraphic position and the timing of mineralisation.At Shangoluwe, three sedimentary breccias sequentially deposited within the Kundelungu rocks can be identified on the basis of the nature of the matrix and fragments; from bottom to the top, the Ferruginous Breccias, the Dolomitic Breccias and the Siliceous Breccias. These breccias were deposited as lenses. The presence of debris and grain flows, a finely laminated matrix, pseudo-stratification, normal and reverse graded-bedding, and the presence of interbedded siltstone, sandy shale, dolomitic shale, shale and dolomite, are considered as evidence of a sedimentary origin of the breccias. The log normal distribution of the fragments indicates that gravity flow was the main deposition mechanism.The Ferruginous and Dolomitic Breccias are regarded as contemporaneous with the Kundelungu Group. They were deposited as lenses interbedded in the Kanianga and Mongwe formations, both affected by the Lufilian orogeny (D1 - Kolwezian and D2 – Monwezian phases). The Siliceous Breccias are post-orogenic as shown by the presence of an erosional and angular unconformity respectively on the Dolomitic Breccias and the Kundelungu formations. Therefore, the Siliceous Breccias are attributed to the Lower Palaeozoic Biano Subgroup and the lithostratigraphy of the Biano Subgroup is proposed for revision accordingly. Copper mineralisation post-dates the deposition of the breccias, the dissolution of dolomite fragments and in-situ fragmentation. This mineralisation occurred during late- to post-orogenic extension of the Lufilian orogeny, and was remobilised during the Cenozoic.

The Late Cryogenian Warm Interval, NE Svalbard: Chemostratigraphy and genesis

The Late Cryogenian Warm Interval (LCWI) refers to a non-glacial interval that separates presumed representatives of the Sturtian and Marinoan panglaciations. Its duration is poorly constrained radiometrically and its deposits are relatively poorly known in most geographic regions. This paper aims to constrain the duration, palaeoenvironments and petrogenesis of such deposits in the classic region of NE Spitsbergen, Svalbard. The succession comprises a 200–205m dolomitic shale (Macdonaldryggen Member, known as E3, of the Elbobreen Formation) overlain by oolitic dolomite Slangen Member (E4), 15–25m thick, with limestone developed at top and base of E3 in the south of the area. The assumed age context of the succession has been confirmed by the presence of a typical Sturtian cap carbonate profile of negative to positive δ13C, and primary Sr isotope compositions of basal E3 limestones <0.7072 and of upper E3 limestones of 0.7076.At the base of E3, interstratification of cap carbonate with ice-rafted and redeposited glacial sediments occurs. Early diagenetic stabilization of carbonate mineralogy from a precursor, possibly ikaite, to calcite or dolomite is inferred. E3 is predominantly dolomitic silt-shale, with sub-millimetre lamination, lacking sand or current-related sedimentary structures. Thin fine laminae are partly pyritized and interpreted as microbial mats. Dolomite content is 25–50%, with δ13C values consistently around +4‰, a value attributed to buffering by dissolution of a precursor metastable carbonate phase. Local calcite cement associates with low δ13C values. The carbonates form silt-sized, chemically zoned rhombic crystals from an environment with dynamically changing Fe and Mn. Three-dimensional reconstructions of cm-scale disturbance structures indicate that they represent horizontally directed sock-like folds, developed by release of overpressure into thin surficial sediment overlying an early-cemented layer.A shoaling upwards unit near the top of E3 displays calcium sulphate pseudomorphs in dolomite in the north, but storm-dominated limestones in the south, both being overlain by peritidal oolitic dolomites, exposed under the succeeding Wilsonbreen glacial deposits. There is no Trezona δ13C anomaly, possibly implying top-truncation of the succession.Regular 0.5m-scale sedimentary rhythms, reflecting subtle variations in sediment texture or composition occur throughout E3 and are interpreted as allocyclic. They are thought to be mainly primary in origin, locally modified slightly during early diagenetic cementation. Rhythms are proposed to represent ca. 18kyr precession cycles, implying 6–8Myr deposition between glaciations.

Reactive transport modelling of ore mineral zoning and the paragenesis of copper sulfides in sediment-hosted stratiform ore deposits, the Katanga Copperbelt (DRC)

1. Introduction and geological settingSediment-hosted stratiform copper deposits are characterized by including several types of sulfide and oxide minerals that exhibit different zoning and paragenesis. Stratiform copper mineralization in the Katanga Copperbelt (Democratic Republic of Congo; Fig. 1) took place in the Neoproterozoic Katanga Supergroup, mainly in the Roan Group, but also in the Nguba and Kundelungu Groups. The Nguba Group overlies the Roan Group and consists at its base of the Grand Conglomerat, a glacial deposit. The Nguba Group is overlain by the Kundelungu Group, with the Petit Conglomerat at its base. The latter is also a diamictite deposit (Cailteux et al., 2005). Two main ore bodies are present in the Mines Subgroup in the lower part of the Roan Group, i.e. the Lower and Upper Orebody. Between both ore bodies, a barren or weakly mineralized member, the Roches Siliceuses Cellulaire (RSC), occurs. The host rock of the two ore bodies is formed by dolomitic shales, siltstones and stromatolitic dolomites (Cailteux et al., 2005). The latter shales and siltstones contain lenticular layers and nodules of pseudomorphs after anhydrite and very early diagenetic pyrite (Cailteux et al., 2005). The RSC is interpreted to originally represent massive stromatolitic dolomites with some interbedded dolomitic siltstone, and thus biogenic carbonates. Figure 1. Location of the Central African Copperbelt and of the most important ore deposits (after Cailteux et al. 2005).Numer

Milankovitch-driven cycles in the Precambrian of China: The Wumishan Formation

Carbonate strata of the Mesoproterozoic Wumishan Formation in the Jixian area near Tianjin are ~3300m thick and were deposited over some 100million years (from ~1310±20 Ma to ~1207±10 Ma). Metre-scale cycles (parasequences) dominate the succession. They are generally of the peritidal carbonate type, and mostly show an approximately symmetrical lithofacies succession with thick stromatolite biostromes and small thromboliteoncolite bioherms constituting the central part and tidal-flat dolomites forming the upper and lower parts. Lagoonal-supratidal dolomitic shales with palaeosol caps make up the topmost layers. The boundaries of the Wumishan cycles are typically exposure surfaces, and there is abundant evidence for fresh-water diagenesis.Widespread 1:4 stacking patterns indicate that the individual Wumishan cycles are sixth-order parasequences, with 4 parasequences constituting one fifth-order parasequence set. Locally, 5–8 beds or couplets, can be discerned in some of the cycles. The regular vertical stacking pattern of beds within the sixth-order parasequences, forming the fifth-order parasequence sets, are interpreted as the result of environmental fluctuations controlled by Milankovitch rhythms, namely the superimposition of precession, and short and long-eccentricity. The widespread 1:4 stacking pattern in the cyclic succession, as well as the local 1:5–8 stacking patterns of the beds within the cycles, suggest that the Milankovitch rhythms had similar ratios in the Mesoproterozoic as in the Phanerozoic. Based on the cycle stacking patterns, 26 third-order sequences can be distinguished and these group into 6 second-order, transgressive-regressive megasequences (or sequence sets), all reflecting a composite, hierarchical succession of relative sea-level changes.