Shale Deposits Research Articles

Dramatic attenuation of continental weathering during the Ediacaran-Cambrian transition: Implications for the climatic-oceanic-biological co-evolution

The Ediacaran–Cambrian (E-C) transition witnessed dramatic tectonic, climatic, oceanic, and biological co-evolutions at the dawn of the ‘Cambrian explosion’. Although glaciations were reported in some mid-high-latitude continents during this interval, large uncertainties remain concerning timing and extent, as well as their effect on the entire Earth's surface system. We here report magnesium (Mg) isotopic compositions, along with chemical index of alteration (CIA), Al/Ti ratios from a time-dated, nonglacial E-C boundary section on the mid-low-latitude Yangtze Block, South China, to constrain chemical weathering intensity and associated climatic, oceanic and biological co-evolution during this critical interval. Our data demonstrate a rapid and significant negative δ26Mg excursion (from +1.28 to −0.34‰) along with similar CIA and Al/Ti decreases across the E-C boundary, reflecting an apparent attenuation in chemical weathering intensity likely in response to severe climate cooling. This finding further affirms the far-field glaciation reported in the mid-high-latitude continents during the E-C transition. Under this condition, the intense climate cooling could have enhanced oceanic circulation and/or upwelling, and simultaneously caused prominent variations of seawater geochemistry (including alkalinity elevation) and nutrient flux as well as ecological stresses on metazoans. All these could reasonably account for extensive deposition of phosphorites and organic-rich black shales, and faunal turnover (extinction of Ediacaran fauna and appearance of skeletonized small shelly fauna) across this interval. These novel datasets thus shed new insights into the climatic-oceanic-biological interactions and time-specific deposition around the E–C transition at the prelude of the Cambrian explosive bioradiation.

Controls on silica enrichment of lower cambrian organic-rich shale deposits

The factors controlling silica enrichment of the Lower Cambrian sedimentary succession have been disputed for a long time. This paper describes results of a petrological and geochemical investigation of Lower Cambrian shale deposits of the intraplatfrom basin of the Yangtze Block, South China, with the goal of elucidating potential controls on silica enrichment of these deposits. Excess silica (Sixs) concentrations in the studied deposits suggest that silica was generally enriched in Lower Cambrian units, including the Maidiping Formation (MDP) and the overlying Qiongzhusi Formation (QZS). Greater excess silica concentrations in the MDP relative to the QZS may reflect the influence of three factors: continental weathering, aeolian input, and biological activity. Corrected chemical index of alteration (CIAcorr) values and Ti/Al ratios of the MDP suggest that strong chemical weathering increased the delivery of dissolved silica to the global ocean during the episodes of warm, humid paleo-climate conditions. This, in tandem with diminished aeolian input that accompanied the humid climate, favored establishment of a silica-rich ocean during Fortunian and early Stage 2 time. The presence of coeval massive chert-phosphorite deposits may be attributed to blooms of phytoplankton and siliceous organisms (mainly sponge spicules) induced by upwelling of nutrient-rich bottom waters (e.g., Si and P). However, the abundance of low-diversity sponge spicules was likely insufficient to achieve silica supersaturation of seawater by itself so that direct precipitation of aqueous silica from Si-enriched seawater and pore water may have partly contributed to silica enrichment of the MDP. Diminished CIAcorr values and elevated Ti/Al ratios of the QZS suggest the increased terrestrial and aeolian inputs into the global ocean under a relatively cool, arid paleo-climate condition during middle Stage 2 to the Stage 3 time thereby reducing aqueous silica concentrations. The present study suggests that the interaction among paleo-climate fluctuations, increased delivery of nutrients to the ocean, and redox variability was critical to the diversification of sponge spicule and the appearance of radiolarian during the Cambrian Explosion.

Sedimentary Evolution Characteristics of Fine-Grained Lithofacies under the High-Resolution Isochronous Shelf System: Insights from the Wufeng-Longmaxi Shales in the Sichuan Basin

Abstract The deposition and evolution of fine-grained sediments is a hot topic in fine-grained sedimentary rock studies and is important for accurately evaluating shale gas sweet spots. In this paper, the fine-grained deposition and evolution characteristics of the Wufeng-Longmaxi shales, major targets for Chinese shale gas exploration, were studied by using core observations, thin section analyses, scanning electron microscopy, geochemical analysis, and fossil identification. This work accurately identified six typical lithofacies; among them, the organic matter-rich siliceous shale facies (OMRSSF), the high-organic matter siliceous argillaceous shale facies (HOMSASF), and the medium-high organic matter low calcareous siliceous shale facies (M-HOMLCSASF) are favorable facies for shale gas exploration. The high-resolution isochronous unit in the shelf fine-grained sedimentary system was established, and the differential evolution of lithofacies in the system tract was discussed. The lithofacies deposition and differentiation in the transgressive system tract were controlled by the transgressive scale and tectonics under increasingly shallow water conditions. The lithofacies deposition and differentiation in the regressive system tract were controlled by tectonics and the preexisting lithofacies. The lithofacies in the regressive system tract had more frequent facies transitions and greater differentiation than those in the transgressive system tract, and they exhibited significant spatiotemporal inheritance. Sequential differential sedimentary sequences and symmetric differential sedimentary sequences were distinguished in the continental shelf sedimentary system. The lithofacies depocenters and subsidence centers were consistent in the transgressive system tract, while the tectonically active paleocontinent was important in the regression system tract. This study is of great significance for further high-resolution exploration of marine shale and improvement of the theory of shelf fine-grained sedimentary systems.

INSIGHTS OF SHALE GAS EXPLORATION AND DEVELOPMENT IN INDIA: REVIEW

Encouraging results of shale gas production in different countries viz. USA, China and Australia, India is also inspired to explore shale gas resources, which may not only support meeting the growing energy demand but also assist to reduce the import of hydrocarbons. This paper aims to review the current status of shale gas exploration programs in various sedimentary basins in India for a better understanding of the prospect of shale gas. The signicant thickness of organic-rich shale deposits is reported in various Gondwana and Tertiary sedimentary basins including Damodar valley, Krishna-Godavari, Cauvery, Cambay, Assam-Arakan, Ganga and Vindhayan basins. The geochemical properties like TOC and thermal maturity, Organo-inorganic mineral compositions, pore-network system, and depth of shale deposits are favoring the potential prospect of shale gas in India. Several agencies namely EIA, ONGC, USGS, Schlumberger, and CMPDI reported enormous resources of shale gas in its various sedimentary basins.

Evaluation of the Shale Oil Reservoir and the Oil Enrichment Model for the First Member of the Lucaogou Formation, Western Jimusaer Depression, Junggar Basin, NW China

The Lucaogou Formation (Fm) in the Jimusaer depression is the first large-scale development of a terrigenous clastic sedimentary shale oil reservoir in China. Nearly one billion tons of shale oil resources have been discovered. However, the current exploration and development is concentrated in the eastern part of the sag. The limited geological understanding in the western area has restricted the prediction and development of “sweet spots” for shale oil. To help rectify this, we have studied the petrology, geochemistry, oil content, and pore properties of the second part of the first member (Mbr) of the Lucaogou Fm (P2l12) in a typical well (Ji-X) in the western part of the sag. The results show that P2l12 in the Jimusaer sag is a mixed fine-grained sedimentary system composed of sandstone, mudstone, and carbonate, which can be divided into seven types: dolomitic mudstone, calcareous mudstone, mudstone, mixed fine-grained rock, argillaceous limestone, sandstone, and argillaceous dolomite. The organic matter type of P2l12 in well Ji-X is dominated by types I and II, and this is the best source rock in the whole exploration area of the Jimusaer sag. The overall oil saturation is relatively high, but the maturity of crude oil is low, and the overall oil quality is heavy, which is mainly controlled by the sedimentary environment and maturity of source rocks. Lithology and reservoir physical properties are the key to control oil content. The high-quality light oil reservoir lithology is argillaceous dolomite and sandstone. The higher the content of macropores and mesopores, the weaker the heterogeneity of the pore structure, and the better the oil content in the reservoir. There are four light oil sweet spots in the upper part (burial depth less than 4366 m), and there are excellent source rocks with high HI and high organic matter content near each sweet spot. This discovery of shale oil enrichment regularity will effectively guide the development of shale oil in continental lacustrine basins in other parts of the world.

Comparative Assessment of Hydrocarbon Generation Potential of Organic Matter from Shale Sediments along Isugwuato – Okigwe Axis, Anambra Basin, SE Nigeria

TRACT: The Cretaceous sediments in the Anambra Basin (SE Nigeria) consist of a cyclic succession of coals, carbonaceous shales, silty shales and siltstones interpreted as deltaic deposits. The objective of this study is to compare the hydrocarbon generation potential of organic matter from shale sediments along Isugwuato-Okigwe axis in the Anambra Basin, Nigeria. Data obtained indicates the presence of Type III kerogen with Tmax values are between 424 and 441ºC indicating that the shales are thermally immature to marginally mature with respect to petroleum generation. Hydrogen Index (HI) values range from 14 to 388.9mgHC/gTOC while S1 + S2 yields values ranging from 0.2 to 1.0mgHC/g rock, suggesting that the shale have gas generating potential. The TOC values rangesfrom 1.3 to 3.0%, an indication of a good source rock of terrestrially derived organic matter. The high oxygen index (OI) (16.3 mgCO2g-1TOC), TS (1.35) and TOC/TS (1.5) suggest deposition in a shallow marine environment. Based on the kerogen type, shales from the studied area will equally generate oil and gas if its organic matter attained sufficient thermal temperature.
 Keywords: Shale, kerogen type, maturity, oil generation.

Geochemical characteristics and mechanism of organic matter accumulation of marine-continental transitional shale of the lower permian Shanxi Formation, southeastern Ordos Basin, north China

The marine-continental transitional shale is widely distributed in the Lower Permian Shanxi Formation of the southeast Ordos Basin. The primary factors controlling organic matter accumulation of the Shanxi shale are still obscure. In this study, we used mineralogy and organic geochemistry, coupled with major and trace element geochemistry to analyze the paleoenvironment and their effects on organic matter enrichment, and established the accumulation model of organic matter in the Shanxi transitional shale. Results show that the mineralogical composition of the Shanxi shale is dominated by clay and quartz (averaging of 62.8 and 33.3%, respectively). The Shanxi shale has relatively high TOC contents and thermal maturity (Ro) (averaging of 1.25% and 2.66%, respectively), and predominantly contains type III kerogen. The significantly low paleoproductivity indicates that this factor plays not the primary role of organic matter accumulation. Ti and Al concentrations indicate a strong terrestrial input, simultaneously bringing abundant terrestrial organic matter, which is favourable for its enrichment. The warm and humid climate condition enhanced higher plant growth and provenance weathering. The δU, U/Th, V/Cr and Ni/Co values show dysoxic-oxic environments, suggesting relatively poor preservation conditions for organic matter. Comprehensive analysis shows that the terrestrial organic matter input, paleoclimate and redox conditions are the primary factors controlling the organic matter accumulation of the Shanxi shale. • The paleoproductivity is significantly low during the Shanxi shale deposition. • The terrestrial detrital input is strong, carrying abundant terrestrial organic matter. • The paleoclimate and redox conditions triggered organic matter accumulation to some extent. • An accumulation model of organic matter in the Shanxi Formation was established.

Sedimentary environment and organic enrichment mechanisms of lacustrine shale: A case study of the Paleogene Shahejie Formation, Qikou Sag, Bohai Bay Basin

Recent Chinese shale oil (or gas) exploration efforts have focused on the Shahejie Formation of Bohai Basin. However, this work has been handicapped by a lack of state-of-the-art investigations of the targeted shale. Specifically, there is a need for an improved understanding of the role that paleoenvironmental aspects of the basin played in the organic enrichment of these deposits. The present study provides the insights into the paleoenvironmental and depositional history of various of shales of the Es1 Member of Paleogene Shahejie Formation, Qikou Sag, Bohai Basin, and addresses the controlling factors of organic matter (OM) accumulation and preservation in these deposits based on petrographic characteristics, organic geochemistry, and major and trace elements data. Our results suggest that the organic-enriched Es1 oil shale is a desirable exploration target, especially felsic and mixed shale. The felsic shale, mixed shale, dolostone and carbonate shale accumulated under relatively humid climatic conditions but in saline lacustrine environment. Climate, salinity, and redox conditions appear to have varied at least three times during the depositional history of the studied interval. Paleoenvironmental conditions favored stable productivity levels and only a modest supply of clastic detritus sediment resulting in a diminished rate of deposition. Felsic and mixed shale deposits that have the greatest source potential accumulated under more humid atmospheric and oxygen-depleted environmental conditions than dolostone and carbonate shale. The present study suggests infers that organic carbon content of the Es1 oil shale was controlled principally by salinity and secondarily by primary productivity and redox conditions.

A peculiar fusuline assemblage from the Tanes locality, Campo de Caso section (Pennsylvanian, Upper Moscovian; Cantabrian Zone, Spain)

The Campo de Caso section (eastern part of the Cantabrian Zone, NW Spain) exposes a middle to upper Moscovian (Middle Pennsylvanian) succession, up to 3500-m thick, consisting of marine shelfal and deltaic siliciclastic and shale deposits with numerous intercalated fossiliferous limestones. A limestone outcropping in the upper part of this section, close to the village of Tanes, has yielded a fusuline assemblage composed of species of the genera Eostaffella, Pseudonovella, Ozawainella, Pseudostaffella, Neostaffella, Schubertella, Fusiella, Taitzehoella, Fusulinella, Beedeinaand Putrella. The specific composition of these genera, considered as a whole, indicates an early to mid- Myachkovian age; however, some of the taxa exhibit rare aspects, among which are the occurrence of pseudostaffellids having a “primitive” appearance recalling that of the Bashkirian Pseudostaffella, and a Putrella species exhibiting a wall that, at first glance, resembles the schwagerinid wall. Data gathered during this study question the validity of the genus Quasistaffella Solovieva 1986 and point to consider it as a junior synonymous of Pseudostaffella Thompson 1942.

Compositional Simulation of Geological and Engineering Controls on Gas Huff-n-Puff in Duvernay Shale Volatile Oil Reservoirs, Canada

Duvernay shale is a world class shale deposit with a total resource of 440 billion barrels oil equivalent in the Western Canada Sedimentary Basin (WCSB). The volatile oil recovery factors achieved from primary production are much lower than those from the gas-condensate window, typically 5–10% of original oil in place (OOIP). The previous study has indicated that huff-n-puff gas injection is one of the most promising enhanced oil recovery (EOR) methods in shale oil reservoirs. In this paper, we built a comprehensive numerical compositional model in combination with the embedded discrete fracture model (EDFM) method to evaluate geological and engineering controls on gas huff-n-puff in Duvernay shale volatile oil reservoirs. Multiple scenarios of compositional simulations of huff-n-puff gas injection for the proposed twelve parameters have been conducted and effects of reservoir, completion and depletion development parameters on huff-n-puff are evaluated. We concluded that fracture conductivity, natural fracture density, period of primary depletion, and natural fracture permeability are the most sensitive parameters for incremental oil recovery from gas huff-n-puff. Low fracture conductivity and a short period of primary depletion could significantly increase the gas usage ratio and result in poor economical efficiency of the gas huff-n-puff process. Sensitivity analysis indicates that due to the increase of the matrix-surface area during gas huff-n-puff process, natural fractures associated with hydraulic fractures are the key controlling factors for gas huff-n-puff in Duvernay shale oil reservoirs. The range for the oil recovery increase over the primary recovery for one gas huff-n-puff cycle (nearly 2300 days of production) in Duvernay shale volatile oil reservoir is between 0.23 and 0.87%. Finally, we proposed screening criteria for gas huff-n-puff potential areas in volatile oil reservoirs from Duvernay shale. This study is highly meaningful and can give valuable reference to practical works conducting the huff-n-puff gas injection in both Duvernay and other shale oil reservoirs.

Nannoplankton and 13C and 13O stable isotope stratigraphy record of the mid Cretaceous sequences, Zagros Basin (western Iran)

Deposition of black shales and dark argillaceous limestones across the Cenomanian to Turonian interval has been recorded in many parts of the world. In this regard, a stratigraphic section in the Iran's hydrocarbon field in the Kermanshah region in the Zagros Basin has been studied in detail to reconstruct palaeoceanographic conditions under a reliable biostratigraphic framework. Biostratigraphy based on calcareous nannofossils integrated with high resolution carbonate and oxygen stable isotope analyses were carried out on the Cenomanian-early Turonian interval of the upper part of Garau Formation. In this formation, 24 species of calcareous nannofossils were identified in the pelagic marine deposits. Our study allowed the definition of nannoplankton bio zones from the upper part of Eiffellithus turriseiffelii Zone to the lower part of Quadrum gartneri Zone in the mid Cretaceous. This research first recorded the upper part of the Garau Formation at site and it is consistent with the previous bio zones identified in the Tethyan domain in the region. The middle Cretaceous events of calcareous nannofossils proposed here correlate with the isotope global profile for the early Cenomanian-earliest Turonian interval and with those, reported for the southeastern France and south England reference curves, represented by the positive Cenomanian to Turonian δ13C excursion. Thus, the sequences of dark argillaceous limestone rich in organic matter in Kermanshah region can be considered as a continuation of the global trend in the Tethyan domain, where the Cenomanian-Turonian Oceanic Anoxic Event constrained to about 91.5 ± 8.6 millions of years, occurred in an anoxic pelagic sedimentary environment correlates with both, global and local sea-level rises, represented in this study by the characterization of the nannoflora assemblage reflected in a variety of widespread paleoenvironmental changes that coincides with significant shifts in the stable carbon and oxygen isotope signature.

First evidence of the early cretaceous oceanic anoxic events (MBE and OAE1a) in the southern Tethyan margin (NE-Tunisia): biostratigraphy and shale resource system

The Jebel Oust region (north-eastern Tunisia) recorded two levels of marine black shale in the Lower Cretaceous marly series. Geodynamic evolution, biostratigraphic and Rock–Eval analysies allow classifying those black shales as unconventional shale oil resource systems that were deposited during two oceanic anoxic events: the Middel Barremian Event "MBE" and the Early Aptian Event "OAE1a". Paleogeographic evolution highlights two transgressive–regressive cycles: the first one is Valanginian-Early Barremian, and the second is Late Barremian–Early Aptian. Each black shale deposit occurs at the end of the transgression that coincides with the highest sea level. During the Barreman–Aptian interval, sedimentation was controlled by extensional faults in a system of tilted fault blocks which were reactivated several times. Kerogen is of type I, II origin in black shales and of type III origin in marls. Tmax values indicate "oil window" stage. Average transformation ratio is around 67% and 82%, respectively, in the Lower Aptian and Middel Barremian source rock related to the relatively high thermal maturity degree due to the deep burial of the later. Estimated initial hydrocarbon generation potential is moderate to high. Oil saturation index records an "oil crossover" indicating expelled and migrated hydrocarbons from the organic-rich to the organic-poor facies. The petroleum system of the two mature source rocks with a high hydrocarbon generation potential enclose all elements characterizing a "shale oil hybrid system with a combination of juxtaposed organic-rich and organic-lean facies associated with open fractures".

Energy and environment policy in Poland: Various aspects in the context of shale gas extraction

This article outlines the social approach of meeting the challenges of energy policy in Poland in the context of potential shale gas extraction, focused on social perception and environmental protection policy. While Poland holds promising shale gas resources, the state of current technology indicates that shale gas exploitation is not imminent. However, shale deposits are still considered a potential future resource that could play a central role in diversifying energy sources, developing the economy, and potentially increasing the country’s energy security. This paper presents energy opportunities of Poland, a review of Polish society opinion about energy and environment security. This study shows that Polish society sees a connection between energy, environment and policy problems, as well as potential benefits in the context of shale gas, based on research results of various institutions, including the European Commission. The author draws attention to tasks before the economic exploitation of shale gas in order to optimizing socio-economic benefits, and short- and long-term impacts. Since we are a common Europe, a common space for people, we can create an energy policy. It is the way the topic of energy diversification opportunities in Poland and the building of consistent energy and environmental protection policy is still an important issue to discuss in humanistic and economic fields.

Elemental composition, environment of deposition of the lower Carboniferous Emma Fiord formation oil shale in Arctic Canada

The sedimentary succession of 51-m consisting of a thin coal seam (1 m) and oil shale with a marlstone and carbonate-mudstone matrix of the Lower Carboniferous (Viséan) Emma Fiord Formation located on the Grinnell Peninsula, Devon Island, Arctic Canada was examined. The techniques used include reflected light microscopy, and instrumental neutron activation analysis (INAA) for elemental concentration, and inductively coupled plasma emission spectrometry (ICPES) for boron concentration.The coal and oil shale was deposited in a lacustrine, freshwater environment. Due to the climatic variation, two types of oil shale were developed based on the amount of precipitation. One with carbonate-mudstone matrix, with high calcite (75%) and low TOC (1.14–1.87%) content. The other a marlstone-dominated matrix with high aluminosilicate (64%) and TOC (16.4–53.6%) content.Oil shale from Emma Fiord experienced a slow rate of sedimentation and terrestrial flux as determined using Th/K/ Na/K, ratios Mn/Ca ratio to Ca respectively, and compared to the oil shale of Carboniferous age deposited in a lacustrine environment with a regular rate of recharge/discharge. The redox conditions for the Emma Fiord oil shale indicate anoxic to dysoxic conditions based on the variation of Cr and V + Ni.Thorium and U systematics indicate that U is more concentrated in oil shale with marlstone matrix and is associated with clay minerals and organic matter (OM), similar to the Carboniferous oil shale from the Big Marsh. The authigenic U is associated with TOC content and is higher for oil shale with the marlstone matrix.The variation of U with TOC indicates both paleo-productivity and preservation and is higher for oil shale with the marlstone matrix.The concentration of rare earth elements (REEs) is 95% due to the presence of light rare earth elements (LREEs) in both oil shale with marlstone and carbonate-mudstone matrices.The REES were normalized to the post-Archean average shale (PAAS). The high volatile bituminous coal at the base of the oil shale sections displays a flat, featureless pattern. The oil shale with a carbonate matrix decreases slightly from light rare earth elements (LREEs) to heavy rare earth elements (HREES). In contrast, the REEs concentration for oil shale with the marlstone matrix decreases more sharply from the LREEs (La-Eu) to HREEs (Tb-Lu). It displays a weak negative Eu anomaly typical of the upper continental crust.

Controls on U enrichment in organic-rich shales from the Triassic Yanchang Formation, Ordos Basin, Northern China

The Chang 7 lacustrine organic-rich shale in the Upper Triassic Yanchang Formation has high U contents, with a mean of 10.2 ppm. Previous studies have proposed that the redox conditions and high total organic carbon (TOC) content provide advantageous physical-chemical conditions for syngenetic U enrichment; however, the processes, mechanisms, and factors controlling U enrichment are still unclear. In this study, we examined the relationships between TOC and major, and trace element concentrations to better understand the factors that control U enrichment. Results indicate that U enrichment in the Chang 7 organic-rich shale is mainly controlled by redox conditions, sources of U, and sedimentation rate. Under oxic conditions, U is predominantly enriched in authigenic phosphate nodules; however, under anoxic conditions, it is mainly enriched in organic matter. Therefore, organic matter plays a more important role in controlling U enrichment than once thought due to its high content in the Chang 7 organic-rich shale, although the authigenic phosphate nodules have a higher enrichment efficiency. In addition to favorable redox conditions, deep hydrothermal fluids and volcanic ash can provide sources for U, and low sedimentation rate during shale deposition may create an environment conducive to U enrichment. The results of this study provide critical information about U enrichment in organic-rich shales and provide guidance for further research on the coexistence of U enrichment and high organic matter contents in source rocks.

Factors Controlling the Lower Radioactivity and Its Relation with Higher Organic Matter Content for Middle Jurassic Oil Shale in Yuqia Depression, Northern Qaidam Basin, China: Evidence from Organic and Inorganic Geochemistry.

Organic-rich oil shale with unusual lower radioactivity (expressed by GR) was found in Member 7 of Dameigou Formation, middle Jurassic (J2d7) in Yuqia depression of northern Qaidam Basin, China. In order to systematically and contrastively investigate the factors controlling the lower GR and its relation with higher organic matter (OM) content (expressed by total organic carbon, abbr. TOC), organic and inorganic geochemical analyses were performed on samples consisting of oil shale and the underlying conformable contact dark shale from Well YQ-1Y. Our study shows that GR of J2d7 oil shale is mainly derived from uranium and thorium. Compared with dark shale, oil shale is characterized by higher OY and TOC, lower GR, and clay mineral content. During oil shale deposition, the paleoclimate was relatively arid, indicated by a decreased C value and siderite content as well as an increased carbonate content and Classopollis. Under such paleoclimate conditions, sedimentary water became more anoxic, suggested by higher V/(V + Ni), pyrite content and lower pristane/phytane (Pr/Ph). From oil shale to dark shale deposition, according to analyses of Al2O3/TiO2, TiO2 versus Zr, La/Sc versus Th/Co, La/Th versus Hf, and La–Th–Sc, the felsic igneous rock could always be deduced as the parent rock of provenance; however, the increasing arid paleoclimate resulted in weakened chemical weathering of provenance, inferred by relatively low chemical index of alteration, chemical index of weathering, and plagioclase index of alteration corresponding to the input degree of radioactive materials and other terrigenous detrital materials (TDMs), evidenced by Ti and Al contents and terrigenous (%). Meanwhile, the relatively high P/Ti and Ba/Al both indicated increased primary paleoproductivity. Together with the maximum flooding stage of oil shale deposition, the relatively low radioactivity tends to be associated with the inhibited input of clay minerals and radioactive materials, largely caused by increasing arid paleoclimate. The accompanying decreased TDM benefited primary paleoproductivity and anoxic conditions; their combined influence could induce sapropelic OM accumulation.

Geochemical characteristics of marine shale in the Wufeng Formation–Longmaxi Formation in the northern Sichuan Basin, South China and its implications for depositional controls on organic matter

Marine black shales of Upper Ordovician Wufeng Formation–Lower Silurian Longmaxi Formation in the Sichuan Basin are considered as excellent source rocks in South China. According to the geochemical characteristics of source rocks, the formation and preservation conditions of organic matter in source rocks are showed. In order to study the aggregation mechanism of organic matter, geochemical proxies were proposed, including redox proxies (V, V/Al, U, U/Al, Mo, and Mo/Al), paleoproductivity proxies (P, P/Ti, Ba, Ba/Al, and SiXS), paleoclimate proxies (CIA), and terrigenous flux proxies (Al, Zr, and Zr/Al). At present, the average content of TOC in Wufeng Formation is 3.63 wt%, which is in the range of 2.59–4.22 wt%. The average content of TOC in Longmaxi Formation is 1.02 wt%, and ranges from 0.45 to 2.07 wt%. The redox proxies show that the Wufeng shale is mainly accumulated under anoxic conditions. Longmaxi shale is mainly accumulated under suboxic-oxic conditions. The P/Ti and excess silicon (SiXS) values indicated that the whole sedimentary sequence had high paleoproductivity, but it was reduced to some extent in the Longmaxi Formation. The reduced Corg/Ptot ratios implies that the decrease of productivity may be caused by the increase of P (phosphorus) burial. The restricted degree of watermass shows that Wufeng shale deposits under strongly restricted watermass, while Longmaxi shale deposits under weakly restricted watermass. During the sedimentary period of the Wufeng Formation, the strongly restricted of the ocean circulation of the northern Sichuan Basin and the effective stratification of water column is beneficial to the preservation of organic matter. During the Longmaxi shale sedimentary period, tectonic movement and global sea level changes controlled the production and preservation of organic matter, affecting terrestrial clastic material flux, redox conditions and nutrient cycling.

The impact of volcanic activity on the deposition of organic-rich shales: Evidence from carbon isotope and geochemical compositions

The organic-rich black shales from the Late Ordovician and early Silurian were identified as essential source rocks for shale gas exploration and development in South China. To investigate the influence of volcanic activity on the deposition of organic-rich shales in the Wufeng and Longmaxi formations, this study presents the carbon isotope and geochemical compositions of the Upper Ordovician-lower Silurian succession of the Yangtze Platform. The organic-rich Wufeng and lower Longmaxi shales are characterized by isotopically negative carbon shifts; however, obviously high δ13Corg values are shown in the organic-poor shales of the upper Longmaxi Formation. The negative δ13Corg excursion is attributed to 12C-depleted CO2 sourced from volcanic activity. Furthermore, the positive δ13Corg excursion in the upper Longmaxi Formation occurs because a large amount of 12C was removed from the ocean-atmosphere system through continuous burial of organic carbon. The biogenic silica (Sibio) contents and (Cu + Ni)/Al ratios in the lower Longmaxi Formation display higher values than those in the upper Longmaxi Formation, suggesting that the primary productivity gradually decreased from the Wufeng Formation to the Longmaxi Formation. This study proposes that high primary productivity was related to accelerated chemical weathering and release of micro-nutrients. The former emphasizes that high pCO2 and globally high temperatures can enhance chemical weathering, so that more nutrients are transported from continents to oceans (Yan et al., 2010, 2019). The latter highlights that volcanic material input can act as fertilizer by releasing many nutrients. Moreover, the values of UEF and MoEF are higher in the Wufeng and lower Longmaxi formations than in the upper Longmaxi Formation, suggesting that the oxygen concentration increased upward through the section. Given the positive correlations between indicators of productivity and redox conditions, the constantly high primary productivity would consume much O2, resulting in anoxic conditions in the Wufeng and lower Longmaxi formations. Overall, this study considers that volcanic activity-driven primary productivity is the first-order control for organic matter (OM) enrichment.

Fugitive road dust alters annual plant physiology but perennial grass growth appears resistant

Dust is a feature of the natural environment that can be exacerbated by anthropogenic activities. A range of physiological impacts have been attributed to dust deposition on plant leaves, including altered gas exchange and reduced photosynthetic activity—traits associated with yield and overall productivity. Substantially increased traffic along rural unpaved roads following the development of shale petroleum deposits in the Bakken region of North Dakota, USA, prompted us to investigate the effect of heavy dust exposure on economically important annual crops and perennial forage grasses. In a greenhouse study, we exposed six species of annual plants (barley Hordeum vulgare, durum wheat Triticum durum, maize Zea mays, sorghum Sorghum bicolor, lentil Lens culinaris, pinto bean Phaseolus vulgaris, sunflower Helianthus annuus) and eight species of perennial grasses (creeping bentgrass Agrostis stolonifera, crested wheatgrass Agropyron cristatum, intermediate wheatgrass Thinopyrum intermedium, tall fescue Schedonorus arundinaceus, Bermuda grass Cynodon dactylon, blue grama Bouteloua gracilis, buffalograss Bouteloua dactyloides, switchgrass Panicum virgatum) to 40 g of scoria road dust every other day for 10 and 14 days, respectively, resulting in cumulative dust exposure of 200 g/m $$^{2}$$ for annual plants and 280 g/m $$^{2}$$ for perennial grasses. Chlorophyll concentration tended to increase in all annual plants within 1–2 h of dust exposure, which remained high (along with photosynthetic yield) over the duration of the study. Stomatal conductance tended to decrease over the 2-week study period, which was expected, while leaf temperature also decreased for most species, which was contrary to previous research. Conversely, we found little evidence that high levels of dust reduce the ability of perennial grasses to recover from repeated defoliation, regardless of photosynthetic pathway or functional group. While perennial grass growth appears unaffected by the heavy dust emissions produced by traffic associated with energy extraction, the effect on annual plants is difficult to determine because dust might actually have a positive, light-scattering effect that improves plant performance.

Bulk pyrolysis and biomarker fingerprints of Late Cretaceous Galhak Shale Formation in the northern Melut Basin, Sudan: implications on lacustrine oil-source rock

Organic-rich shale samples from the Late Cretaceous Galhak Formation were collected from one well location in the northern Melut Basin, Sudan, and analyzed by integrated organic geochemical and microscopic techniques. The study investigates the nature and preservation conditions of the organic facies and their relevance to petroleum resource potential. Judging from the high total organic contents (total organic carbon (TOC) > 2%), the analyzed Galhak shales are organically rich and include favorable source rocks. The organic richness in these shale sediments may be attributed to enhance the preservation of organic matter under suboxic conditions as implied from the n-alkanes and isoprenoid biomarkers. Biological markers, including of n-alkanes, isoprenoids, terpanes, and steranes, further suggest that the Galhak shale sediments were deposited in a relatively fresh lacustrine environment and received largely aquatic organic matter of plankton and bacteria with little terrestrial plant input. An abundance of aquatic-derived organic matter is consistent with types I and II kerogen as indicated by high Rock-Eval HI values of more than 400 mg HC/g TOC. The hydrogen-rich kerogen types I and II in the analyzed samples suggests an oil-prone source. According to the optical and geochemical maturity indicators, the organic matter in the Galhak oil shale is thermally immature; thus, they have not reached sufficient oil-window maturity for commercial oil generation. Therefore, the deeper parts of the Melut Basin, where the Galhak Formation reached high mature of peak-oil generation window, are recommended for further petroleum exploration and production.