Shale Deposits Research Articles

Geochemical characteristics of organic carbon and pyrite sulfur in Ordovician-Silurian transition shales in the Yangtze Platform, South China: Implications for the depositional environment

Global climate change and tectonism are principal causes of spatial and temporal differences in Ordovician-Silurian (OS) transition sedimentary environments of China's Upper Yangtze Platform. However, the relative significance of each of these drivers is not always obvious. This paper describes results of a geochemical study of a drill core section (Well X3) recovered from Xiang'e Submarine High in the central part of the Upper Yangtze Platform. This work focused on shale deposits of the Wufeng Formation and Longmaxi Formation that accumulated during the OS transition. Geochemical characteristics, including total organic carbon (TOC), pyrite S (Spy), stable carbon and sulfur isotopes, and Mo and U enrichment values, were combined with pyrite framboid size distribution data to reconstruct the OS paleoenvironmental evolution of this region of the Upper Yangtze Platform. The studied succession appears to record the transition from lower Katian-Hirnantian shale deposited under sulfate-limited conditions to Rhuddanian organic-rich shale and finally to organic-depleted Aeronian sediment. The depositional history of these deposits was controlled by changes in water depth and watermass chemistry as a result of changing sea level. The sea-level history of the studied succession was largely controlled by global climate change related to Hirnantian glaciation and Rhuddanian warming and tectonism associated with the Kwangsian Orogeny that resulted in uplift of the Xiang'e Submarine High. Similar geochemical investigation of the Pengshui and Shuanghe sections, also in the Upper Yangtze Platform, demonstrate the dominant role of global climate change and tectonism in controlling organic carbon content and thickness of potential shale gas targets. Specifically, the low concentrations of organic carbon in thin shale deposits proximal to uplifted regions of the basin pose a major risk to shale gas exploration.

Geochemical and organic petrographic characteristics of high bituminous shales from Gurha mine in Rajasthan, NW India

A high bituminous shale horizon from the Gurha mine in the Bikaner sub-basin of the Rajasthan District, NW India, was studied using a collection of geochemical and petrological techniques. This study investigated the nature and environmental conditions of the organic matter and its relation to the unconventional oil-shale resources of the bituminous shale. The analyzed shales have high total organic carbon and total sulfur contents, suggesting that these shale sediments were deposited in a paralic environment under reducing conditions. The dominant presence of organic matter derived from phytoplankton algae suggests warm climatic marine environment, with little connection to freshwater enhancing the growth of algae and other microorganisms. The analyzed bituminous shales have high aquatic-derived alginite organic matters, with low Pr/Ph, Pr/n-C17, and Ph/n-C18 ratios. It is classified as Type II oil-prone kerogen, consistent with high hydrogen index value. Considering the maturity indicators of geochemical Tmax (< 430 °C) and vitrinite reflectance values less than 0.40%VRo, the analyzed bituminous shale sediments are in an immature stage of the oil window. Therefore, the oil-prone kerogen Type II in the analyzed bituminous shales has not been cracked by thermal alteration to release oil; thus, unconventional heating is recommended for commercial oil generation.

Unraveling a hidden Rhyacian magmatic arc through provenance of metasedimentary rocks of the Crixás greenstone belt, Central Brazil

The Crixás-Goiás Domain, Central Brazil, comprises an association of Archean TTG (tonalite-trondhjemite-granodiorite) and Archean-Paleoproterozoic greenstone belts. The Crixás greenstone belt, located in the northern part of the domain, is constituted of Mesoarchean metakomatiites and metabasalts overlaid by Paleoproterozoic carbonaceous phyllites and metagraywackes that host important gold deposits. In this work, we present new integrated petrographical, geochemical and isotopic data to investigate the provenance and tectonic setting of the metasedimentary rocks of the Crixás greenstone belt. Mineral and textural immaturities, particularly of the metagraywackes, are consistent with a proximal source area; which is also evidenced by the chemical aspects that denote absence of significant sediment sorting and recycling. Geochemical data indicate provenance from mixed mafic and felsic sources. U-Pb detrital zircon geochronology shows unimodal age spectra, with a dominant peak at ca. 2.2–2.1 Ga and minor contribution of ca. 2.7 and 2.4 Ga grains. Concordia diagrams yielded upper intercepts between 2213.4 ± 5.6 and 2162.2 ± 9.2 Ma, interpreted as the age range of the main source area. The rocks present relatively homogeneous Sm-Nd model ages (2.44 to 2.34 Ga) and slightly negative to positive ƐNd, ranging from −0.27 to +1.25. We argue that the original sedimentary protoliths were deposited in a trench or forearc basin related to a ca. 2.2–2.1 Ga island arc formed adjacent to an Archean paleocontinent constituted of TTG-greenstone terranes. Rapid erosion of the rising intraoceanic arc resulted in syn-orogenic sedimentation that started with deep ocean black shale deposition in an anoxic environment followed by episodic turbidite currents of poorly-sorted immature sands. Sedimentary rock layers were tectonically transported to the continent and preserved in the elongated keels of Mesoarchean mafic–ultramafic volcanic rocks. This orogeny can be correlated with the amalgamation of the Goiás Massif during the Siderian-Rhyacian crustal growth related to successive collage of arc-related terranes in the formation of the western margin of the São Francisco paleocontinent. Sediment provenance of the Crixás greenstone belt proved to be crucial to the recognition and characterization of Paleoproterozoic crust that are apparently no longer preserved in outcrops.

Marine osmium isotope record during the Carnian “pluvial episode” (Late Triassic) in the pelagic Panthalassa Ocean

The Carnian Pluvial Episode (CPE) was a global environmental change and biotic crisis that occurred during the Carnian (Late Triassic). The climate during the CPE was characterized by a short-lived period of extreme rainfall, and an extinction of marine taxa is known to have occurred during the latest Julian (i.e. early Carnian). Although these events are considered to have been caused by the Wrangellia Flood Basalt (FB) volcanism, existing studies have found little direct evidence to support this. We investigated the temporal relationship between the eruption of Wrangellia FB and CPE using high-resolution microfossil biostratigraphy and paleo-seawater Os isotope data of an Upper Triassic bedded chert succession from an accretionary complex in Japan, which accumulated in a pelagic deep-sea environment in an equatorial region of the Panthalassa Ocean. Our biostratigraphic analysis, based on conodonts and radiolarians, and osmium isotope data show: (i) a continuous decline of initial Os isotope ratios (187Os/188Osi) in the early Julian; (ii) low 187Os/188Osi ratios during the late Julian; and (iii) an abrupt increase in 187Os/188Osi ratios at the end of the Julian. The decrease in 187Os/188Osi ratios throughout the Julian suggests an increased input of unradiogenic Os from the eruption of the Wrangellia FB into the ocean. Moreover, redox-sensitive elements, such as V and U, increased abruptly at the end of the Julian, which is the first evidence of reducing conditions during the CPE within the pelagic deep-sea Panthalassa Ocean. Marine anoxic event in the late Julian has been recognized from widespread deposition of black shales and organic-rich marls in intermediate to shallow water Tethyan sections. Thus, oxygen-depleted conditions occurred at the Tethyan shallow continental margin, as well as in the pelagic deep-sea Panthalassa Ocean, at the end of Wrangellia FB volcanism.

New paleoenvironmental proxies for the Irati black shales (Paraná Basin, Brazil) based on acidic NSO compounds revealed by ultra-high resolution mass spectrometry

Variations of the acidic NSO (Nitrogen, Sulphur, and Oxygen) compound composition of the Lower Permian Irati black shales and Serra Alta shales were assessed by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) using electrospray ionization (ESI) in negative ion mode to test their significance for the regional paleoenvironmental reconstruction by comparison with known features in the northeastern and central-eastern Paraná Basin, Brazil. The high abundance of the S1Ox class for the basal Irati black shales in the northeastern basin reflects a sulfide-rich environment, whereas high O>2 classes in the Serra Alta shales indicate a high input of terrestrial organic matter deposited in oxic waters. Here, eight parameters based on O1 and O2 compounds are suggested as new paleoenvironmental proxies: phenol index (%DBE 4; O1 class); C27/C28 DBE 4 (O1 class); C27/C28 DBE 5 (O1 class); Even/OddFA; TARFA Odd (terrigenous/aquatic ratio); TARFA Even; C36 hopanoic acid index; and hopanoic/steranoic acids ratio. Higher values of the phenol index, the TARFA and Even/OddFA indicate higher land plant input during the final black shale deposition. Variations of C27/C28 DBE 4 and C27/C28 DBE 5, the first being based on the distribution of methylated isoprenoidyl phenols, can be used to reconstruct paleosalinity; here higher values indicate higher salinity. The C36 hopanoic acid index is higher for the marine hypersaline samples from the northeastern basin, while a significant bacterial biomass signal is stored as a higher hopanoic/steranoic acids ratio for samples from the central-eastern basin.

The birth and demise of the vast epicontinental Permian Irati-Whitehill sea: Evidence from organic geochemistry, geochronology, and paleogeography

Organic-rich shale deposits of the Irati (Brazil) and Whitehill (South Africa) formations represent the most important sedimentary remnants of a huge Permian sea that occupied an estimated 5 million km2 before drying out and disappearing. To unravel the evolution and final demise of the Irati-Whitehill sea, we present a paleogeographic and organic geochemical characterization as well as a precise tephrochronology of the sea. Constrained by new high-resolution chemostratigraphic data (biomarker data combined with carbon and nitrogen isotopes) of two boreholes from central and southern areas of the Paraná Basin (Brazil), the evolution of the sea is divided into five stages. These stages reflect the transition from a marine realm (stage I) to an environmentally restricted sea characterized by major ecosystem changes (stages II and IV) where water renewal controlled the post-salinity environmental dynamics (stages III and V). A zircon UPb TIMS age of 277.26 ± 0.62 Ma of stage V correlates with the age of the San-Rafaelic orogeny along the paleo-Pacific South American margin and the rising of the Cape Fold Belt. We conclude that the convergent tectonic dynamics may have acted as the main agent in the entrapment and disappearance of the sea, ending a history of no more than four-million-year of the Irati-Whitehill sea.

Geochemical evaluation of Campanian-Maastritchian clay-shale sediments of Patti formation, Southern Bida and Mamu Formation, northern Anambra basins

Two basins (Southern Bida and Northern Anambra Basins) were investigated to deduce weathering, paleooxygenation, provenance, depositional environment and tectonic setting, as well as to establish a relationship between the two basins. The obtained high values of calculated weathering indices such as Chemical index of alteration (CIA &gt; 90), Chemical Index of Weathering (CIW &gt; 90), Plagioclase Index of Alteration (PIA &gt; 90) and the Al2O3-(CaO + Na2O)-K2O ternary relationship for the clay – shale sediments from both basins indicate intense weathering in the source area. Important geochemical ratios such as V/Cr, Cu/Zn, Ni/Co, (Cu+Mo)/Zn, revealed predominantly oxic conditions for the clay – shale sediments from both basins, although, a more reducing or an anoxic condition cannot be ruled out for the clay – shale sediments from the Southern Bida basin due to high ratios of U/Th (1.93-5.67) and Cu/Zn (0.19-5.00). In addition, the Sr/Ba ratios (0.16–3.50) for the clay-shales from the Southern Bida basin indicated an alternated marine and continental paleo-depositional settings and only continental setting (Sr/Ba ratios = 0.22 – 0.50) for the Northern Anambra basin. The Th/Sc, La/Sc, Th/Co and the LREE/HREE ratios showed a derivation of the shale and clay deposits from similar felsic-rich source rock while the log of (K2O/Na2O) vs SiO2, revealed a Passive Margin tectonic setting for the two Basins. There is insignificant differences between the geochemical classifications, weathering, source rock/provenance and tectonic settings of clay-shale sediments of both sedimentary basins, however, there exist slight disparity in their salinity conditions and redox settings.&#x0D; Keywords: Geochemistry, Clay-shale, Provenance, Tectonic Setting, Northern Anambra and Southern Bida Basins

Assessing anoxia, recovery and carbonate production setback in a hemipelagic Tethyan basin during the Toarcian Oceanic Anoxic Event (Western Carpathians)

Abstract The chemostratigraphic record of the Toarcian Oceanic Anoxic Event (T-OAE) is generally well documented in epicontinental basins; however, the duration of anoxia and recovery remains poorly constrained in the Tethys Ocean owing to limited stratigraphic resolution of oceanic sections with hiatuses. In this paper, we describe a relatively continuous hemipelagic record in the Central Western Carpathians of Slovakia (Skladana Skala section), which contains the Pliensbachian/Toarcian boundary, the T-OAE, and the subsequent recovery phase. In our section, the Pliensbachian Spinatum Zone is represented by a ~ 7 m thick alternation of spotted, spiculitic marly limestones and limestones of the Allgau Formation that contain moderately diverse trace fossils including abundant Zoophycos, Lamellaeichnus and Teichichnus. In the uppermost part of the Spinatum Zone, a ~ 0.8‰ decline in δ13Ccarb values marks the carbon isotope excursion (CIE) at the Pliensbachian/Toarcian boundary. This isotope anomaly is overlain by a ~ 3 m-thick interval of spotted marly limestones and marls, which contains a positive CIE that represents the base of the T-OAE. The T-OAE interval comprises a 60 cm-thick pyritic black shale interval that lacks bioturbation and shows a negative CIE (δ13Corg values drop by 4–5‰), coincident with an increase in TOC values (from 0.3% to 2–3%), and a drop in CaCO3 values (from 50 to 80% to 3–7%). The black shale is overlain by ~8 m thick marls with rare intercalations of marly limestones, which show ammonites of the Exaratum Subzone in the lowermost part (~1 m) succeeded by Serpentinum Zone beds. This unit exhibits a second positive CIE (δ13Corg increases by 2.5‰ and δ13Ccarb increases by 1.5‰), significantly more negative δ18O values relative to the pre-T-OAE interval, and a low diversity of trace fossils dominated by Chondrites and extremely thin Zoophycos. Sponge spicules re-appear in the uppermost 6.5 m-thick interval of the section formed by the alternation of spotted marls and limestones, with ammonites of the Falciferum Subzone in the lower part and of the Bifrons Zone in the uppermost parts; however, diversity of trace fossils remains low. Based on these findings, we argue that the 60 cm-thick pyritic black shale that represents the T-OAE is a strongly condensed succession because it includes the onset of the negative CIE and the subsequent rebound, and thereby encompasses the full duration of the anoxic event. Anoxia in basins open to the oceanic Tethys thus coincided not only with reduced carbonate production but also with reduced siliciclastic supply, generating very thin black shale deposits. In contrast to current-swept swells where black shales associated with hardgrounds are thin or missing owing to winnowing, carbonate starvation was induced by a calcification crisis coincident with the T-OAE and siliciclastic starvation was probably induced by rapid sea-level rise. Although bottom waters were not anoxic in the aftermath of T-OAE, bioturbation remained restricted during the Falciferum Subzone in basinal settings, indicating that environmental stress induced by limited ventilation and/or high bottom-water temperatures were persistent. The reduced diversity of trace fossils and the re-appearance of sponge spicules close to the lower/middle Toarcian boundary indicate that the ecological recovery in basins open to the oceanic Tethys was delayed, a pattern similar to the epicontinental seas that experienced anoxia.

Primary productivity and basin redox conditions within the Mesoproterozoic Hongshuizhuang Formation from Chaoyang area, Liaoxi sag

The Mesoproterozoic Hongshuizhuang Formation in Liaoxi sag, northern China, is an important hydrocarbon source unit having good potentials to generate oil and gas. The total organic carbon (TOC) content ranges from 0.54% to 4.07% in the Chaoyang area. Trace element geochemistry was utilized to study the primary productivity and basin redox conditions during the deposition of Hongshuizhuang Formation black shales. The results suggest that primary productivity during the deposition of the Hongshuizhuang Formation was relatively high. The redox-sensitive elements results indicate that the Hongshuizhuang Formation was deposited under euxinic or anoxic bottom water conditions. The degree of environment restriction, diagenesis, reoxygenation, and the presence of free H2S can make some of the redox-sensitive elements proxies and primary productivity proxies not applicable. The high TOC content of the Hongshuizhuang Formation is contributed by high primary productivity in the surface water combined with euxinic/anoxic in the bottom water.

Siratur gold deposit in the black shales of the ophiolite association (the Southern Urals)

The Siratur gold deposit is located in the northern part of the South Ural segment of the Main Ural Fault. Its ore zone is confined to the area of the tectonic junction of the serpentinite of the Nurali massif and the submeridional strip of carbonaceous schists of the Ordovician Polyakovka Formation. Its composition is widely represented basalts with chemical characteristics of the main effusive rocks of the mid-ocean ridges. In the black shale deposits of the Siratur deposit, gold ore mineralization is mainly represented by the gold-sulfide vein-disseminated type, and in the listwanite-beresite complex, gold-quartz-low-sulfide vein-streaked type. Microprobe studies of zolotins showed that gold in ores of the first type has a low-qality of 670–820, and in the second — 940–970. The deposit can be attributed to the polygenic and polychronous type.

Geochemical characteristics and sedimentary setting of chang 9 shale in the Upper Triassic Yanchang Formation of southeastern Ordos Basin (NW China)

In addition to the organic-rich shale in the Chang 7 Member (Ch7 shale) of the Ordos Basin, the shale hosted in the Chang 9 Member (Ch9 shale) is another source rock and potential unconventional target. However, there is a general lack of consensus on the features and potential of the Ch9 shale. In order to determine the potential of the Ch9 shale, this study analyzes its paleoenvironment and sedimentary setting based on the integrated analysis of geochemistry and sedimentary facies. A comparison of geochemical features between the Ch9 shale and the organic-rich Ch7 shale is made to evaluate the factors controlling organic matter (OM) enrichment of the Ch9 shale. The results show that the Ch9 shale has good hydrocarbon potential, and terrestrial OM is important component of the OM in the Ch9 shale. The Ch9 shale was deposited in climatic transition period from cold and dry to warm and humid, when the water body was suboxic-anoxic and freshwater. The relatively cold and dry climate and suboxic-anoxic water condition in the Ch9 period could not provide the same excellent conditions for OM enrichment as that in the Ch7 period. The Ch9 shale is composed of sediments mixed with felsic rocks that originated from continental island arcs and active continental margins. The active tectonic setting resulted in event deposition (e.g. turbidity flows and hydrothermal fluid activity) during the deposition of Ch9 shale. The input of terrestrial OM carried by turbidity flows also promoted OM enrichment, however, the very high depositional rates caused by turbidity flows diluted the OM, which probably offset the effect of hydrothermal on OM enrichment. Our results are helpful to revealing the source potential of the Ch9 shale, providing a theoretical basis for the shale oil and gas exploration in the Ordos Basin.

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.

Reconstructing the Climatic-Oceanic Environment and Exploring the Enrichment Mechanism of Organic Matter in the Black Shale across the Late Ordovician-Early Silurian Transition on the Upper Yangtze Platform Using Geochemical Proxies.

Black shale deposited in the transitional period from the Late Ordovician to Early Silurian is the most important source rock and shale gas reservoir in the Yangtze region of South China. However, the source of these sediments is still controversial. In this paper, the changes in total organic carbon (TOC), total sulfur (TS), organic carbon isotopes (δ13Corg), biomarkers, trace elements, and rare earth elements in the Ordovician–Silurian boundary strata of the XK-1 well in northern Guizhou Province, South China, have been systematically studied. The paleoenvironmental and paleoclimatic conditions of the Late Ordovician to Early Silurian and their relationship with organic matter enrichment in the Upper Yangtze Platform have been reconstructed. The distribution of biomarkers reflects that the Late Ordovician–Early Silurian shale was deposited in the marine environment and was highly contributed by marine plankton/algae and microorganisms. Paleoclimatic proxies (Sr/Cu, δ13Corg) show that the global climate system experienced significant changes from a warm-humid climate to a brief period of cold-dry climate and then back to a warm-humid climate during the Ordovician–Silurian transition. This warm and humid climate condition helps to improve the biological productivity within the photic zone of the water column during deposition. In addition, the low oxygen (reduction) conditions during the deposition of the Late Ordovician–Early Silurian deposits are characterized by low Pr/Ph values (0.39–0.79) and relatively high elemental ratios of V/Ni (1.40–5.77) and V/(V + Ni) (0.58–0.85). This paleoredox condition contributes to the preservation of organic matter during deposition of the Late Ordovician–Early Silurian deposits. Therefore, it is demonstrated that the climate and ocean fluctuated greatly during the Late Ordovician–Early Silurian transition period, and this fluctuation provided necessary control factors for marine anoxia, primary productivity, and subsequent organic-rich black shale deposition in the Upper Yangtze region during the Late Ordovician and Early Silurian intervals.

Impact of Paleosalinity, Paleoredox, Paleoproductivity/Preservation on the Organic Matter Enrichment in Black Shales from Triassic Turbidites of Semanggol Basin, Peninsular Malaysia

Turbidite-associated black shale of the Semanggol Formation is extensively distributed in the northwestern part of the Western Belt, Peninsular Malaysia. The black shale occurs as a dark grey to black and thick to medium-bedded deposit. It represents the distal part of submarine fan system (outer-fan) overlying interbedded sandstone to shale facies of the mid-fan and conglomeratic pebbly sandstone facies of the inner-fan. Field observations and its widespread occurrence have resulted in the black shale being considered as a potential analog for a source rock in offshore Peninsular Malaysia. The present study includes detailed mineralogical (XRD, SEM, and EDX analysis), inorganic geochemical (major oxides, trace elements TEs, and rare earth elements REEs), and Rock-Eval pyrolysis analyses of the black shale samples, collected from the Gunung Semanggol, Bukit Merah, and Nami areas in northwestern Peninsular Malaysia. The primary focus of this study is to investigate the provenance, paleoredox conditions, paleoclimate, sedimentary rate, paleoproductivity, and upwelling system that would be helpful to understanding the role of these parameters in the enrichment of organic matter (OM) in the black shale. The Rock-Eval analysis shows that the black shale of the Semanggol Formation comprises type-III kerogens, which suggests organic input from a terrestrial source. The black shale also contains mature to postmature organic matter. Based on the mineralogical analysis, the mineral composition of the black shale comprises illite and kaolinite, with abundant traces of quartz and feldspar as well as few traces of titanium and zircon. Inorganic geochemical data designate black shale deposition in a passive margin setting that has experienced moderate to strong weathering, semi-arid to hot arid climate, and moderate sedimentation rate. Ratios of Ni/Co, U/Th, and V/(V+Ni) along with slightly negative to positive Ce* anomalies and UEF-MoEF cross-plot unanimously indicate anoxic/dysoxic water conditions that are suitable for organic matter preservation. Geochemical proxies related to modern upwelling settings (i.e., Cd/Mo, Co vs. Mn) show that the deep marine black shale was strongly influenced by persistent upwelling, a first-order controlling factor for organic matter enrichment in the distal part (outer fan of the submarine fan system) of the Semanggol Basin. However, productivity-controlled upwelling and a high sedimentary rate, as well as high-productivity in oxygen-depleted settings without strong anoxic conditions, has played an essential role in the accumulation of organic matter.

Public opposition to shale gas extraction in Algeria: Potential application of France's ‘Duty of Care Act’

Algeria, a former French Colony, gained independence from France in 1962. It can be argued, however, that the legacy of post-colonialism continues, particularly with respect to the extractive industries. Both France and Algeria have large unconventional shale deposits—France has the second largest shale gas deposits in Europe after Poland and Algeria has the third largest in the world. Proposals to extract shale gas have led to widespread public opposition in both France and Algeria. The protests in France arguably led to the 2011 ban on hydraulic fracturing for shale gas, followed by the 2017 decision to ban all hydrocarbon exploration and extraction (unconventional and conventional) in French territory by 2040. Hydrocarbon company Total S.A., headquartered in France, has given up on operating in France but has now focused on potential development in Algeria, arguably an illustration of the continuation of a post-colonial relationship or NIMBY'ism (Not In My Back Yard). This perspective article aims to briefly highlight issues related to unconventional hydrocarbons in Algeria and introduce an emerging regulatory mechanism that could potentially provide a remedy to protect human and environmental rights and provide a model for future legislation in other countries. France's 2017 Duty of Care Act (Devoir de Vigilance) requires companies headquartered in France of a certain size to develop a ‘plan of care’ that mandates corporate responsibility throughout the supply chain and all subsidiaries, including outside French territory, and moreover provides a mechanism for legal recourse in the event of environmental or human rights harm from business activities.

Arc-related black shales as sedimentary archives of sea-level fluctuations and plate tectonics during the late Neoproterozoic: An example from the Bohemian Massif

The late Neoproterozoic Lečice black shales and an overlying siliciclastic succession, Bohemian Massif, were deposited in a marine environment on a volcanic arc and provide insights into palaeoenvironmental conditions at the former active margin of northern Gondwana. Field relationships integrated with major/trace element and Mo–Cr–S isotope systematics in two different sections (Štěchovice and Břežany) indicate complex depositional settings intimately connected with the waning activity of the underlying volcanic arc. The Štěchovice black shales represent a deeper part of the basin and were first deposited in weakly anoxic conditions (lower stratigraphic level) with limited terrigenous supply, as reflected by their higher total organic carbon (TOC) and U contents and positive δ53Cr, but negative δ34Spyrite values accompanied by late-stage silicification by arc-related fluids. An abrupt change to oxygenated conditions and increased terrigenous flux, characterized by lower TOC, U and Mo and coupled, negative δ53Cr and δ98Mo, is documented in the upper level of the same section. By contrast, the Břežany black shales were deposited in a shallower part of the basin and their composition (e.g., low metal contents, negative δ53Cr and δ98Mo) suggests oxygenated conditions. Furthermore, the extensive syn-to post-depositional silicification by low-temperature hydrothermal fluids was associated with Si and Ba enrichment and elevated bacterial productivity leading to higher organic matter input. The black shale deposition was terminated by arc uplift, which supplied vast amounts of terrigenous material to the basin and produced a thick flysch sequence deposited at oxygenated conditions. The estimated age of the Lečice black shales (~580–560 Ma) suggests that their deposition may be linked to interactions between global eustatic sea level changes in response to the late Neoproterozoic glaciations (Gaskiers, Farquar) and dynamic arc topography.

Lake level oscillations recorded in Buracica Stage (Barremian, Early Cretaceous) of Recôncavo Basin, Bahia State (N.E. Brazil)

This work studies the Buracica Stage (Barremian, Early Cretaceous) in the Reconcavo Basin, Bahia State (N.E. Brazil), comprising the Sao Sebastiao and Pojuca formations, from the analysis of 143 well logs and outcrop records. The Reconcavo Basin is a rift basin associated with the beginning of the South Atlantic Ocean. The basin started with very slow subsidence rates, leading to the formation of shallow lakes and the deposition of shales and sandstones, which compose the Brotas Group; later, subsidence accelerated and gave rise to the formation of a deep lake. Then the deep lake basin was filled throughout six depositional episodes making up the so-called Reconcavo tectonic sequence. Previous studies divided the last depositional event of Reconcavo Basin into seven fourth-order sequences concerning the Marker Bed “1” to the Marker Bed “F” stratigraphic interval. Sequence boundaries were marked by sharp flooding surfaces related to the transgression of lacustrine system due to rapid tectonic subsidence and generation of accommodation. In turn, the sequences are divided into three systems tracts: the lake lowstand systems tract, the transgressive systems tract and the lake highstand systems tract. The maximum flood surface of the sequences generally coincides with the stratigraphic marker “B” to “F”. Depositional systems like braided-fluvial plus eolian dunes, meandering-fluvial, deltaic, or moving-lake and near-shore deposits were identified in this work. Isopach, isolith and sand percentage maps indicate depocentre and source area distribution like the previous Aratu Stage. The primary sources of the sediments are located in the west and north areas; only from the third sequence, an eastern source could be described conspicuously. The fourth-order cyclicity is controlled by lake level changes, related to climatic factors (Milankovitch cycles). The results from the studies of cyclicity confirm the proposed stratigraphic model. They indicate 43,000 years for each fourth-order sequence and 150,000 years for the third-order sequences, which provide an accumulation rate of 1200 mm per 1000 years for the studied interval.

Spatial variation of carbon isotopic compositions of carbonate and organic matter from the Late Ordovician sedimentary succession in the Yangtze Platform, South China: Implications for sea – Level eustacy and shoaling of marine chemocline

Spatial correlation of isotopic chemostratigraphy across ancient epeiric basins is of particular interest in the field of geology. This study examines the carbon isotopic compositions of carbonate and organic matter from the Late Ordovician sedimentary succession in the Yangtze Platform, including the Linxiang (LX) Formation deposited in the bottom and the Tiezufeike (TZFK)/Daduhe (DDH)/Wufeng (WF) formations in the top. Paired δ13Ccarb and δ13Corg analyses of the Upper Ordovician strata on the Yangtze Platform were recorded, and the results show that the rocks in the LX Formation have high δ13Ccarb and δ13Corg values relative to those in the DDF/TZFK/WF formations. Additionally, a variation of ~ 2‰ was found between shallow- and deep- water settings during the Late Ordovician: heavier δ13Ccarb and δ13Corg values are observed at the Wukemuchang (WKMC) and Wanhe (WH) sections, representing the shallow regions of the Yangtze Platform, relative to the Tianjiawan (TJW) and Tianba (TB) sections representing the deeper margin of the Yangtze Platform. We suggest that the variations of δ13C in carbonate and organic matter are related to the sea - level eustacy and shoaling of marine chemocline: (1) sea - level rise driven decrease in local scale carbonate weathering; (2) decreased decomposition of organic matter under anoxic conditions; and (3) incorporation of non - photosynthetic chemoautorophic bacteria living in deeper waters. The △13C (△13C = δ13Ccarb – δ13Corg) values in both the WH and WKMC sections display an increasing trend upward from the LX Formation to the overlying strata, varying from 27.8‰ to 31.2‰ and from 28.1‰ to 31.1‰, respectively. These increased △13C values are related to the enhanced nutrients and correspondingly high primary productivity, and thus that, the anoxic water conditions and high primary productivity may be the significant factors in the deposition of Late Ordovician black shales.

The experience of rational development of hydrocarbon resources in the Earth’s interior used in the new paradigm of Academician A.E. Kontorovich – the development of oil and gas complex of Russia

The Republic of Tatarstan has accumulated vast experience in the exploration and development of oil fields of various ranks – from small and smallest to giant and supergiant. Approaches for the rational development of various groups and categories of deposits have been found. The most effective methods of prospecting, exploration and additional exploration of oil fields, the most advanced hydrodynamic methods of developing fields with active and hard-to-recover reserves, including those at the late and post-late stages of development, have been worked out. Methods of enhanced oil recovery have found wide application for various geological and physical conditions, including the extraction of residual reserves from long-term exploited fields. A great deal of experience has been accumulated in the development of complex small fields with hard-to-recover oil reserves. Research work is underway to find effective methods for the development of unconventional oil deposits (high-viscosity, ultra-high-viscosity oils and natural bitumen, in shale and similar deposits), to study the phenomenon of replenishment of sedimentary cover deposits with deep hydrocarbons through the crystalline basement. This experience of advanced development of the republic helps in the formation of the principles of a new paradigm for the development of the oil and gas industry.

Major and trace element characterization of Oceanic Anoxic Event 1d (OAE 1d): Insight from the Umbria-Marche Basin, central Italy

The Pialli Level in the Umbria-Marche Basin (central Italy) correlates with the lowermost part of the positive carbon isotopic excursion characterizing the late Albian–early Cenomanian Oceanic Anoxic Event 1d (OAE 1d). High-resolution litho-, bio- and chemostratigraphic data from the Monte Petrano and Le Brecce sections allow for a bed-by-bed comparison of the two successions, and discriminate local from basin-scale signals. We present new X-ray fluorescence, ICP-MS and TOC data for both the limestones and the Pialli Level shales integrated with available carbonate carbon isotopes and nannofossil temperature and nutrient indices. Data indicate a homogenous background sedimentation dominated by pelagic carbonates, biogenic silica with little contribution by clays. The limited variation in lithogenic elements points to an essentially homogeneous detrital source area with limited fluvial terrigenous input. Higher Mn concentrations coupled with low enrichments in redox-sensitive elements, such as U, Fe, S, Re, Mo, Ag, suggest that the Pialli Level shales represent temporary suboxia without reaching anoxia. Furthermore, P, authigenic Ba, Cd and Ni enrichments, together with nannofossil nutrient index indicate generally low primary productivity conditions along the entire succession, with only minor increases for some of the black-to-dark grey shales of the Pialli Level. The nannofossil temperature index highlights a warm climate during the OAE 1d, with the warmest conditions experienced during the deposition of the Pialli Level shales. During the late Albian, the warm and humid climate was interrupted by brief episodes of relatively warmer and less saline surface waters ensuring slower rates of bottom water renewal and producing temporary suboxic conditions. Such paleoceanographic dynamics would be the continuation of episodic warmer and humid pulses characterizing the late Albian interval in the Umbria-Marche Basin. As such, the Pialli Level can be considered the result of a last episode closing a cycle before the establishment of a steadier climate during the early Cenomanian.