High Total Organic Carbon Research Articles

Depositional settings of the Eocene Suhostrel bituminous coal, SW Bulgaria, inferred from organic petrology and molecular proxies

The paper reports results from organic petrological and geochemical characterization of Suhostrel bituminous coal deposit, SW Bulgaria. Three high ash (21–47 wt%) and thin (up to 0.6 m) coal seams, representing splits from a locally compact coal bed (∼1.8 m thick), were formed around the southern and south-western rim of the Padesh Graben during its Eocene evolution. High total organic carbon contents (avg. ∼86 wt%, daf), vitrinite reflectance (avg. Ro = 1.05%) and Tmax (avg. 457 °C) argue for high vol. A/medium vol. bituminous coalification rank. Maceral composition is dominated by vitrinite (avg. ∼ 95 vol%), accompanied by small amounts of liptinite (avg. ∼ 5 vol%). Apart from few occurrences of funginite, inertinite is not present. The organic matter is mostly represented by detrovitrinite and collotelinite, the latter generally occurring in the form of gelified leaf-derived tissues. Liptinite is mainly represented by cutinite and microsporinite and display no evidence for organic matter contribution from algae. Low TPI and VI indices indicate peat formation from vegetation with poor preservation potential. Insignificant contents of gelovitrinite, coupled with high GI indices denote greater importance of the geochemical processes for the gelification of the organic matter. Striking predominance of mid- and long-chain n-alkanes argues for peat formation from a mixture of aquatic macrophytes and terrestrial vegetational communities. Presence of oleanane, albeit in low concentration, provides robust argument for contribution from angiosperm plants, whereas absence of resin-derived sesqui- and diterpenoid hydrocarbons denotes insignificant role of conifers during peat accumulation. Reconstructed depositional settings indicate organic matter accumulation under marginal aquatic, marsh/fen-type peatland with meso- to rheotrophic characteristics (GWI > 0.5). High mineral matter contents, coupled with the abundance of siliciclastic grains, imply hydrologically active environment. Plant remains deposited under oxidizing conditions (Pr/Ph = 1.5–2.5), but because of high water table were likely subjected to frequent (perhaps seasonal) changes in Eh settings. The resultant limited aerobic biodegradation of the plant remains is evidenced by low concentrations of hopanoid biomarkers and their diagenetic degradation products – drimane-type sesquiterpenoids. Post-depositional marine influence and downward infiltrating sulfate-rich waters is considered responsible for the presence of dibenzothiophene derivatives in Suhostrel coal.All molecular maturity-related ratios (e.g. CPI, Ts/(Ts + Tm), βα/(αβ + βα) C30 hopanes, ββ/(ββ + αα) C29 steranes, MPI-1, etc.) are fully compatible with the bulk geochemical parameters (e.g., TOC, Tmax, Ro) and confirm the bituminous coalification rank of the coal. Based on this data, temperatures of ∼130–140 °C were likely reached during burial of the sediments in a zone, characterized by high thermal influx (geothermal gradient ∼43–47 °C/km).

Sheepfolds induce significant increase of seasonal CO2, CH4 and N2O emissions in temperate steppes of Inner Mongolia

IntroductionThe changes in grassland management and grassland types are strongly linked with dynamics in soil physico-chemical properties and vegetation attributes, with important implications for carbon/nitrogen cycling and greenhouse gas (GHG) fluxes. However, the seasonal variations of GHG emissions from sheepfolds, and the underlying biotic and abiotic drivers affecting GHG exchanges across different steppe and management types remain largely unclear.MethodsTaking the Inner Mongolian grassland as a model system, we measured the fluxes of CO2, CH4 and N2O, as well as soil and vegetation variables, in three contrasting grassland management areas (grazing, sheepfold, enclosure) and in three representative (wet typical, dry typical, desert) grassland ecosystems in July, September and November 2016.ResultsOur results showed that: (1) GHG fluxes were mostly higher in the plant growing season (July and September) than in the nongrowing season (November); sheepfold area had significantly higher GHG emissions (in July and mean over the season) than enclosed and grazing areas, with the effects being most pronounced in dry typical steppe. (2) The high GHG emissions in dry typical steppe were closely associated with the interactions among favorable soil temperature and moisture, high total organic carbon (TOC) content, and high aboveground biomass. The important predictors for CO2 emission were soil TOC and pH, whereas that for CH4 and N2O emissions were soil temperature and moisture content, in sheepfold areas. (3) Three GHG emissions were negatively affected by species richness across all steppe and management types, which might be a consequence of indirect effects through the changes in soil TOC and total nitrogen (TN).DiscussionThese results indicate that sheepfold areas are intensive hotspot sources of GHGs in the steppes, and it is of great importance to help to account GHG emissions and develop mitigation strategies for sheepfold areas for sustainable grassland management in the natural steppe based pastoral production ecosystems.

Pore structure characteristics and organic carbon distribution of soil aggregates in alpine ecosystems in the Qinghai Lake basin on the Qinghai-Tibet Plateau

Soils in alpine ecosystems serve as important carbon sinks. Soil aggregates provide physical protection to soil organic carbon (SOC) and pore networks of them can greatly influence SOC sequestration. However, previous studies mainly focused on SOC dynamics at ecosystem or regional scale in cold alpine regions. The lack of quantification of alpine soil aggregate pore structure limits our understanding of SOC sequestration mechanisms of alpine soil. In this study, three typical alpine ecosystems in the Qinghai Lake basin of Qinghai-Tibet Plateau (QTP) were selected: Kobresia pygmaea meadow (KPM), Potentilla fruticosa shrubland (PFS), and Achnatherum splendens steppe (ASS). Soil pore structure, SOC and their relationships in aggregates were examined through sieving procedure and X-ray computed tomography (CT) scanning. The results showed that the mass proportion of small macroaggregates (SMA, 0.25–2 mm) was highest and they accounted for 36–51% of all aggregate fractions in the above three alpine ecosystems. The pores of soil aggregate were found to be dominated by micropores (<30 μm), which accounted for over 90% of the pore numbers. Aggregates of the ASS ecosystem had highest mean pore volume (7.761 × 10³ μm3 in average) while soil aggregates of the KPM ecosystem had the highest pore number density (4.137 × 10-5 no. μm−3 in average). The highest total organic carbon (TOC) content was mostly observed in the mA (microaggregates, 0.053–0.25 mm) fractions in the three ecosystems. Particulate organic carbon (POC) content was higher than mineral-associated organic carbon (MAOC) content of aggregates. Pores of < 15 μm served as indirect indicators for SOC protection in soil aggregates. Pores of 15–30 μm in aggregates might provide voids for SOC decomposition. TOC and MAOC content were positively correlated with pore surface area density while POC content was positively correlated with pore equivalent diameter and mean volume of aggregates. SOC was mainly affected by soil water content (SWC) in KPM and PFS ecosystems while it was mainly affected by soil particle compositions in the ASS ecosystems. Our results revealed the structural characteristics of aggregates of alpine soil and their relationships with the carbon storage function, which are helpful to understand the micro-scale mechanism of carbon sink of alpine soil.

Response of stream macroinvertebrate communities to forest harvesting in the Piedmont region of North Carolina

Forest disturbances have significant effects on water quality and quantity, river geomorphology, and the ecology of receiving waterbodies. Riparian forests provide numerous functions for aquatic communities including retaining fine sediments and nutrients, controlling water temperature, and providing food sources and habitat for aquatic organisms. Forestry Best Management Practices (BMPs) use riparian forests as buffers to mitigate potential sources of disturbance to aquatic ecosystems from forest management. The objective of this study was to quantify the impacts of timber harvest on stream macroinvertebrates in the Piedmont region. We assessed the changes in macroinvertebrate communities and identified their relationships with specific hydrologic and water quality parameters. We used a paired watershed approach to quantify the response of watershed hydrology and water quality to clearcut forest harvesting with the use of BMPs in the Hill Demonstration Forest and Umstead Research Farm in central North Carolina. We sampled macroinvertebrates and monitored water quality in the first-order streams, and surveyed vegetation within riparian zones one year preharvest (2010) and four years postharvest (2011–2014). We found more sensitive species (indicated by biotic index classifications), scrapers, and Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa from the harvested watershed than in the reference watershed at the Umstead Research Farm site. No differences were detected between the reference and treatment watersheds at the Hill Demonstration Forest site. More sensitive species were present in watersheds with the highest pine basal area and in-stream total organic carbon (TOC) loads. More scrapers were present in watersheds with low hardwood basal area, high stream flow, and more vines. EPT abundance was higher in watersheds with high stream flow, large pine trees, and thick leaf litter layer. EPT abundance was lower in watersheds with large hardwood trees and high TOC loads. Overall, sensitive species, scrapers, and EPT abundance were lower in the Umstead Research Farm reference watershed than in any other watershed. We conclude that, in contrast to similar studies in the region, clearcut harvesting with the use of BMPs did not cause detectable negative effects on macroinvertebrate communities. Moreover, water quality as determined by macroinvertebrates may even be improved in some cases following clearcutting. This study provides a better understanding of how macroinvertebrate communities in Piedmont streams change after harvesting and what watershed characteristics may be driving these changes. This information is useful in characterizing macroinvertebrates in headwaters in the Piedmont, and helps land managers protect aquatic resources across the region.

Treatment of Effluent Containing p-Cresol through an Advanced Oxidation Process in a Batch Reactor: Kinetic Optimization

The present research is related to the study of p-cresol oxidation reaction in aqueous phase. Firstly, the conventional advanced oxidation process (AOP) in a lab-scale batch reactor was used, seeking to identify the most impacting process variables and then to propose an optimization approach for ensuring the complete p-cresol degradation and the highest total organic carbon (TOC) conversion. In the AOP with the use of hydrogen peroxide as the oxidizing agent, the oxidation reaction was optimized with the aid of a factorial design, and a maximum TOC conversion of 63% was obtained. The Lumped Kinetic Model (LKM) was used to describe the profile of residual TOC concentration due to chemical species, which were categorized into two groups (refractory and non-refractory compounds). The model was able to satisfactorily describe the profile of the residual fractions of these two classes of organic compounds and allowed estimating the related kinetic constants (k) at two different temperatures, namely (a) 3.19 × 10−1 and 2.82 × 10−3 min−1 for non-refractory and refractory compounds at 80 °C and (b) 4.73 × 10−1 and 5.09 × 10−3 min−1 for the same compound classes at 90 °C, while the activation energy (Ea) of the process was 42.02 and 62.09 kJ mol−1, respectively. The kinetic modeling of organic pollutants oxidation in liquid effluents would allow to perform in situ seawater treatment on vertical reactors installed in offshore platforms and to properly release treated water into the oceans. In this way, ocean contamination caused by the exploration on offshore platforms of oil and natural gas, the main energy sources and vectors in the current world, may be remarkably reduced, thus favoring a more eco-friendly energy production.

Basin-wide unconventional potential of the Doig Formation, Triassic of the Western Canada Sedimentary Basin

The Doig Formation is a Lower to Middle Triassic fine-grained unit of the Western Canada Sedimentary Basin, which includes a phosphate-bearing basal unit informally defined as the Doig Phosphate Zone (DPZ). The DPZ is recognized as a significant source of hydrocarbons hosted in conventional reservoirs in the basin. Phosphatic mudstones are uncommon and studies of their source-rock potential are scarce. The regional distribution of the Doig Formation source-rock properties across its entire stratigraphic and spatial range is poorly understood. In this study, we characterize the source-rock potential of the Doig Formation through an integrated assessment of thickness, organic content, kerogen type and thermal maturity. A new method for estimating the relative contribution of kerogen type and its original hydrogen index pseudo-van Krevelen, is introduced. The method assumes a binary mixture of kerogen types and requires an assumption for the initial value of immature kerogen from each end-member. The Doig Formation thickens southwestwards from the eastern erosional edge towards the deformation front to a maximum thickness of 229 m. The upper Doig and DPZ have distinct thickness distribution patterns, which suggests a transition from a tectonically-influenced sedimentation marked by uplifting, faulting and erosion, to the start of physiographic healing and a return to large-scale subsidence. The source-rock generative potential of the Doig Formation is fair to good, containing kerogen Types II and III. The DPZ has higher total organic carbon (TOC) content, of up to 12.2% and a higher proportion of Type II kerogen than that the upper Doig, where the maximum TOC content is 8.4 wt%. Original TOC was higher in the northern part of the lateral extent, which is likely related to a connection with open ocean; and in a linear trend through the center of the basin, which represents the trough of a marine fore-arc basin. Thermal maturity increases to the southwest, from early oil to dry gas windows, in a trend that approximately correlates to gas wetness and liquid yield. A zone of dry gas occurs near the eastern edge, however, which may be explained by preferential updip migration of thermogenic methane generated at greater depths, or mixing of thermogenic and biogenic gas.

Main controlling factors of natural fractures in tight reservoirs of the lucaogou formation in the jimsar sag, Xinjiang, China

Natural fractures act as critical flow channels and reservoir space in the Lucaogou Formation tight reservoir of the Jimsar Sag. It is essential to identify the main controlling factors of natural fractures in order to achieve efficient development of tight oil in this area. There are mainly three types of natural fractures, including tectonic fractures, diagenetic fractures, and abnormal overpressure-induced fractures. Diagenetic fractures are predominantly bedding seams. The fracture development is affected by multiple factors including brittle minerals, lithology, tectonic stress, bed thickness, and total organic carbon (TOC). Large tectonic stress, smaller bed thickness, and higher total organic carbon are all favorable for the development of tectonic fractures and bedding seams. The controls of brittle minerals and lithology on fracture development are different for tectonic fractures and bedding seams. Specifically, carbonate minerals stimulate the tectonic fracture development, while brittle minerals have no control over the bedding seam development; tectonic fractures are most developed in the dolomitic rocks, while bedding seams are most developed in the argillaceous rocks. The calculated fracture density variation coefficients reveal that tectonic stress and brittle minerals are the main controlling factors of tectonic fracture development; total organic carbon and lithology are the main control factors of bedding seam development.

Soil factors that contribute to the abundance and structure of the diazotrophic community and soybean growth, yield, and quality under biochar amendment

BackgroundA 2-year field trial was conducted to test the effect of biochar addition (0, 15, 30, and 45 t hm−2) on soil properties, nutrients, diazotrophic community diversity, abundance, and structure, and soybean growth, yield, and quality. Furthermore, we aimed to explore the responses of diazotrophs, grain yield, and quality to nine soil environmental factors. Rhizosphere soil and plant samples were collected after harvest.ResultsBiochar application resulted in a lower soil bulk density (γd) but higher total organic carbon (TOC), effective phosphorus (AP) and total nitrogen (TN). Compared with untreated soil, the diversity index of diazotrophic bacteria in biochar-amended soil decreased, but the abundance of diazotrophic bacteria increased. The microbial community remained stable when a small amount of biochar was applied but changed as biochar amount increased. Furthermore, biochar reduced the proportion of unique nitrogen-fixing bacteria, but did not affect that of common nitrogen-fixing bacteria between biochar-amended and untreated soils, and increased the relative abundance of Bradyrhizobium (B9 vs. B0) and Sinorhizobium (B18 or B21 vs. B0) involved in symbiotic nitrogen fixation. The main components and content of fatty acids (except for stearic acid) and the content of protein and soybean oil remained stable under biochar application. The low biochar treatment (15 t hm−2) promoted soybean growth and yield. Redundancy analysis suggested that TN greatly influenced the diazotrophic community structure at the phylum and genus levels, and that pH, TOC, and NO3−-N greatly influenced grain yield and quality.ConclusionsSoil diazotroph environment can be improved by targeted farmland implementation based on changes in soil physicochemical properties, which would benefit biological N fixation in agricultural soils and further increase economic benefit.Graphical

Geochemical characteristics of coal measure source rocks of Upper Carboniferous Benxi Formation in Daning-Jixian area, eastern margin of Ordos Basin

The Carboniferous-Permian in Daning-Jixian area of Ordos Basin is a typical marine-continental transitional facies deposit, with many sets of organic-rich shales, and abundant shale gas resources. Through unremitting exploration, the shale gas exploration of Shanxi Formation has achieved a major breakthrough, but the related research of Benxi Formation remains to be further studied. Therefore, based on the test and analysis of total organic carbon (TOC) content, rock pyrolysis, kerogen stable carbon isotope (δ13CPDB) and vitrinite reflectance (Ro), this paper systematically discusses the geochemical characteristics and hydrocarbon generation potential of Benxi Formation coal-bearing source rocks, in order to grasp their exploration prospect. The results show that the shale of Benxi Formation has high TOC content (averaging 5.13%) and high Ro (averaging 2.75%), showing good hydrocarbon generation potential. In addition, shale, coal and sandstone are interbedded and superimposed, which can realize the combined production of three gases, improve the yield and benefit, and further promote the exploration process of marine-continental transitional shale gas.

Distribution characteristics of organic matter in the Fengcheng Formation in Mahu Sag, Junggar Basin: implications for hydrocarbon generation model in alkaline lacustrine deposition

Alkaline lacustrine deposits are known for their high primary productivity, unique aquatic environments, and sedimentary patterns, which are conducive to the formation and preservation of organic matter. Consequently, related source rocks have significant hydrocarbon generation potential. The study of hydrocarbon source rocks in the Fengcheng Formation of the Mahu Sag in the Junggar Basin serves as a good example for understanding organic matter enrichment and hydrocarbon generation characteristics of such alkaline lacustrine deposits source rocks. However, the characteristics of organic matter and hydrocarbon generation model in the source rocks of Fengcheng Formation lack systematic research, thus hindering exploration planning and favorable area selection. In this study, analysis of mineral content based on X-ray diffraction and organic geochemical analysis were employed, along with systematic observations of bio-precursor types under fluorescence microscopy. Based on mineral identification and quantitative statistics, the Fengcheng Formation was classified into three zones according to different alkaline mineral assemblages: an inner zone dominated by sodium carbonate minerals, a transitional zone with higher borosilicate mineral content, and a marginal zone characterized by abundant calcite deposition. The inner zone is characterized by the presence of lamalginite and telalginite, which are influenced by high pH values and changes in water depth, and exhibit high maturity characteristics. The transitional zone exhibits high total organic carbon (TOC) values, with predominantly type I and type II1 kerogen. Under fluorescence, the main components were observed to be lamalginite and telalginite, with their distribution being influenced by high salinity and ash supply. The marginal zone has relatively lower TOC than the previous two zones, which is dominated by type II2 kerogens, and contains a certain quantity of terrigenous inertinite supply. The hydrocarbon generation patterns of lamalginite and telalginite are consistent with the bimodal efficient hydrocarbon generation model observed in the source rocks of Fengcheng Formation, revealing the unique hydrocarbon generation model of organic matter in alkaline lacustrine source rocks. This research has significant implications for the exploration strategy of the alkaline lacustrine deposits in the Fengcheng Formation and similar oil- and gas-bearing basins.

Factors determining the distribution of Erica patches on the Sanetti Plateau, Bale Mountains, Ethiopia

In the Bale Mountains, the ericaceous belt ranges between 3200 and 3800 m asl. Studies indicate an expansion on the Sanetti Plateau at the end of the Late Glacial and during the early Holocene. Currently, only patches of Erica growing between boulders are found on the Plateau, while most of the landscape above 3800 m asl is covered by afro-alpine plants. Driving factors for Erica patches above the upper ericaceous ecotone is a matter of debate. This study evaluates site variables and biogeochemical properties of soils under Erica patches and nearby Erica-free control to understand the environmental conditions responsible for the patchy occurrence of Erica on the Sanetti Plateau. Except for the boulder richness, Erica and control plots have comparable topography, soil texture, and electrical conductivity. However, soils below Erica patches have higher total organic carbon, nitrogen, carbon-to-nitrogen ratios, and black carbon contents than the control plots indicating fresh organic matter input and availability of combustible fuel. This implies that Erica did not fully cover the control plots in former times. Carbon and nitrogen stocks were slightly higher in control plots due to the lower stone contents of the profiles. In addition, soils of the Erica plots showed more positive δ13C values than the control soils, possibly attributed to water stress. In general, the relief and soil conditions of control plots may support the growth of Erica. However, Erica growing between boulders seems to benefit from the favorable microclimate and physical protection against grazing and fire.

High-quality source rocks in an underexplored basin: The upper Carboniferous–Permian succession in the Zaysan Basin (Kazakhstan)

The Zaysan Basin is a petroliferous basin in eastern Kazakhstan. Its upper Carboniferous–Permian sedimentary succession outcrops in the Kenderlyk Trough and includes, from base to top, the Kenderlyk, Karaungur, Tarancha, and Maychat formations, which contain 5 to 65 m-thick oil shale deposits—the principal subject of this study. Results from 49 outcrop samples show high total organic carbon (TOC) contents (1.2–21%, mean 7.8%), extract yields (1.2–15 mg HC/g rock, mean 6.8 mg HC/g rock), and ultimate expulsion potential (UEP; up to 23 mmboe/km2), making these oil shale deposits among the best source rocks in the world. Sedimentological, organic geochemical and organic petrographic analyses suggest an overall evolution of the basin from a deep/semi-deep lake during deposition of the Kenderlyk, Karaungur, and Tarancha formations to a deltaic setting during deposition of the Maychat Formation. The organic material in the Kenderlyk, Karaungur, and Tarancha formations is predominately composed of Type I and mixed I/III kerogens with high hydrocarbon generation potential (S1 + S2; up to 172.8 mg HC/g rock), high hydrogen index (HI; up to 838 mg HC/g TOC), and low oxygen index (OI; < 60 mg CO2/g TOC). The sporadic influx of terrigenous organic matter resulted in layers with lower HI and higher OI index, and increased inertinite and vitrinite contents. The Maychat Formation includes hydrogen-poor Type III kerogen with low HI (< 200 mg HC/g TOC) and high OI index (> 60 mg CO2/g TOC) in the Kenderlyk Trough. While a highly oxidizing environment during deposition of the Maychat Formation is postulated for the Kenderlyk Trough, it is likely that oxygen-depleted conditions in the depocenter of the Zaysan Basin favored accumulation of Type I kerogen. The oil-source correlation shows that the produced oils are chemically distinct from the source rock extracts of the Kenderlyk, Karaungur, and Tarancha formations. We propose that these source rocks are “massive”, where the retention of generated oil is too high, causing the hydrocarbons to “bleed” from the source rock's edge only. The expelled oil has probably charged the lower Permian deposits, which have not yet been explored. Regional geological cross-sections and seismic lines allow for selecting sweet spots, characterized by high TOC, yields, and temperatures needed for oil generation and unconventional hydrocarbon resource development.This study provides the play concept and a risk assessment analogue for tectonically and magmatically dynamic settings and basins with multiple organic rich strata. Furthermore, the results and proposed concepts may play a significant role in future petroleum exploration and development activities in the Zaysan Basin. In addition, this highly multidisciplinary study emphasizes the significance of integrating several data sources and weighing contradictory information to get the most reasonable conclusion.

Role of physical processes in regulating the biological responses in the Eastern Arabian Sea during the late southwest monsoon

Understanding physical properties and associated biological responses in the marine ecosystem is critical for fisheries and assessing the ocean’s role in determining the fate of anthropogenic carbon dioxide emissions. This study reports the different roles of southwest monsoon (SWM) upwelling, oceanic fronts, and mesoscale eddies in supplying nutrients and fueling phytoplankton production in the eastern Arabian Sea (EAS). In-situ measurements of physical parameters along with the distribution of biogeochemical parameters in the 100 m water column over a wide latitudinal transect from 8°N to 21°N (Station II-1 to II-14 at 1° interval) along the 68°E were carried out during the late SWM (September 11–19) of 2017. We found distinct features in the study area from the in-situ measurements and satellite data. Primarily, oceanic fronts along with higher instabilities caused vertical mixing at stations II-6, and II-10 (13°N and 17°N). Secondly, eddy-induced lateral advection of high productive water from the Western Arabian Sea (WAS) resulted in high phytoplankton biomass at stations II-7, and II-8 (14°N and 15°N), which led to high concentrations of pigments (chlorophyll-a (Chl-a) and fucoxanthin). SWM upwelling induced higher phytoplankton biomass at northern stations II-13 and II-14 and is evident from the higher total organic carbon (TOC), high total bacterial count (TBC) and Chl-a concentration (up to 0.371μg/L at II-14). The difference in time lag for vertical mixing at II-6 and II-10 are responsible for the contrasting biological responses in these stations. The present study showed that along with SWM upwelling, eddy-induced lateral advection from WAS and oceanic fronts are also increasing phytoplankton biomass in the EAS. The present study suggests that the high phytoplankton biomass prompted by upwelling, oceanic fronts, and mesoscale eddies can influence CO2 sequestration and the prevailing subsurface oxygen minimum zone in the EAS.

Multiple geological events controlling rock types development: A case study of Wufeng-Longmaxi formation in southern Sichuan Basin, China

During Late Ordovician to Early Silurian, global geological events such as volcanic activity, glaciation, and mass extinction affected sedimentary environments and organic matter (OM) accumulation, and controlled the development of organic-rich shales. Taking the Wufeng-Longmaxi Formation (WF-L Fm) shales in southern Sichuan Basin as the research object, based on the core, thin section and scanning electron microscopy (SEM) observations, combined with X-ray fluorescence (XRF) two-dimensional element distribution maps, X-ray diffraction (XRD), trace elements, carbon isotope composition and total organic carbon (TOC) data, the relationship between geological events and sedimentary environments, OM accumulation as well as rock types development are analyzed, and the sedimentary environments response to geological events is elaborated. Eight rock types have been identified, and the minerals occurrence model has been characterized. By using Cu content, Mo content, δ13C and TOC to measure paleoproductivity, Sr content and Sr/Cu to judge paleoclimate, Sr/Ba to measure paleosalinity, and U/Th, V/Cr, V/Ni, and Ni/Co to analyze redox conditions, the sedimentary environments of the WF-L Fm shales can be furtherly divided into 7 intervals. In general, the deep water hypoxic-anoxic environments from Interval Ⅰ to Interval Ⅴ is conducive to the formation of organic-rich shales. The organic-rich shales formed in the anoxic environments from Interval Ⅰ to Interval Ⅴ are related to the fact that volcanic activities not only release a large amount of nutrients, promote biological prosperity and improve productivity, but also make the water in a sulfide anoxic environment, which is conducive to the preservation of OM. The rapid rise and fall of sea level caused by the Hirnantian glaciation harmed the living environments of organisms, led to the mass extinctions and provided material sources for OM accumulation, resulting in high TOC in the rock types of Interval IV. Irregular gravity flow can enhance terrigenous input in deep water for a short time and dilute OM, which is one of the reasons for the low TOC in the rock types of Interval Ⅵ to Interval VII. Upwelling current enhances nutrient flux in surface water and improves primary productivity of water, thus affecting the development of WF-L Fm organic-rich shales. Based on the aforementioned interpretations, the sedimentary model of the southern Sichuan Basin was established.

Multi-analytical Approach (FTIR, XRF, XRD, GC-MS) Characterization of Source Rocks from the Anza Basin, Kenya

Potential source rocks from three wells (Chalbi-3, Sirius-1, and Ndovu-1) in the Anza Basin of northeastern Kenya were analyzed using elemental carbon-hydrogen-nitrogen analysis, and mineralogical characterization by X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM-EDX).)&lt;strong&gt;. &lt;/strong&gt;A Gas Chromatography-Mass Spectrometry (GC-MS) analysis of the saturated aliphatic biomarkers was carried out to illuminate the organic matter source. The analytical results revealed that the source rocks have moderate to high total organic carbon (%TOC) content, suggesting conditions in the Basin favor organic production and preservation. The Hydrogen Indices (HI: 0.19–0.60 atomic ratios) typify a predominance of mixed type II/III (oil/gas-prone) with more type III (gas-prone) and less II (oil-prone) kerogens. The FTIR, XRF, and XRD results reveal that the studied source rock samples comprised mainly of quartz, followed by silicate-clay minerals and calcite minerals. The solvent-extractable organic matter investigation revealed biomarker distributions of n-alkanes and isoprenoids (pristane/ phytane ratios), suggesting that source rocks were derived from algae and bacteria deposited weakly anoxic and low toxic environmental conditions, with minimal contribution from terrestrial organic matter sources. Consequently, all three wells have hydrocarbon generation potential, particularly Ndovu-1, which displays good organic matter content to produce oil and gas. The hydrocarbon potential is excellent and capable of making expulsions of oil and/or gas from the wells at sufficient depths.

Climate plays a dominant role over land management in governing soil carbon dynamics in North Western Himalayas

The soil carbon (C) dynamics is strongly influenced by climate and land-use patterns in the Himalayas. Therefore, soils under five prominent land use [e.g., maize (Zea mays), horticulture, natural forest, grassland, and wasteland] were sampled down up to 30 cm depth under two climatic conditions viz., temperate and subtropical to assess the impacts of climate and landuse on soil C dynamics. Results demonstrated that irrespective of land use, temperate soil contains 30.66% higher C than subtropical soils. Temperate soils under natural forests had the higher total organic carbon (TOC, 21.90 g kg−1), Walkley-Black carbon (WBC, 16.42 g kg−1), contents, and stocks (TOC, 66.92 Mg ha−1 and WBC, 50.24 Mg ha−1), and total soil organic matter (TSOM, 3.78%) concentration as compared to other land uses like maize, horticulture, grassland, and wasteland. Under both climatic conditions, maize land use had the lowest TOC 9.63, 6.55 g kg−1 and WBC 7.22, 4.91 g kg−1 at 0–15 and 15–30 cm soil depth, respectively. Horticulture land use had 62.58 and 62.61% higher TOC and WBC over maize-based land use under subtropical and temperate climatic conditions at 0–30 cm soil depth, respectively. However, soils of maize land use under temperate conditions had ∼2 times more TOC than in subtropical conditions. The study inferred that the C-losses is more in the subtropical soil than in temperate soils. Hence, the subtropical region needs more rigorous adoption of C conservation farming practices than the temperate climatic setting. Although, the adoption of C storing and conserving practices is crucial under both climatic settings to arrest land degradation. Horticultural land uses along with conservation effective soil management practices may be encouraged to restore more soil C and to improve the livelihood security of the hill populace in the North Western Himalayas.

Carbon stability and morphotype composition of biochars from feedstocks in the Mekong Delta, Vietnam

This study investigates carbon stability of biochars produced from wood, herbaceous, and fruit agricultural waste products from southern Vietnam. The biochars were produced by pyrolysis to 500 °C, 700 °C, and 900 °C at a heating rate of 10 °C/min. Organic geochemistry and petrology have well-established measurable parameters that define degree of preservation of organic carbon in the Earth's crust. These parameters are utilized, comparatively, to infer the organic carbon stability in biochars relative to that preserved in the geological carbonaceous rocks. The stability of carbon was assessed by measuring incident-light random reflectance (%Ro) to determine the degree of thermally induced aromatization/ordering of the biochar carbon molecules. Additionally, the organic carbon content of the biochars was quantitatively separated into reactive and non-reactive carbon fractions based on thermodynamic stability of CH and CO bonds. The results show increasing carbon stability with increasing pyrolysis temperature and indicate high stability has been achieved at 700 °C and 900 °C where the biochars have the highest total organic carbon (TOC) contents and lowest Hydrogen Index values. Occurrence of a small quantity of readily degradable, labile free hydrocarbons (soluble organic matter; SOM) is due to condensation of the thermally generated hydrocarbons on the surfaces of the biochars. This fraction is minimized in the biochars produced at 700 °C and 900 °C due to volatilization of the free hydrocarbons at higher pyrolysis temperatures. The relatively substantial content of labile hydrocarbons associated with particulate organic matter (POM) in the 500 °C produced biochars is attributed to the incomplete pyrolyzation of the feedstock at this temperature. This fraction declines to near zero at 700 °C and 900 °C as complete carbonization is achieved at these higher temperatures. The overall carbon budget within the biochar shows that irrespective of the biochar type, over 97% of the TOC consists of highly refractory, residual carbon that geochemically is considered to possess long-term stability (“inert”). This is further underpinned by a pronounced increase in biochar mean random reflectance from <2.33% at 500 °C to >4.35% when pyrolyzed at 700 °C, indicating a highly polyaromatized condensed carbon structure. Rice husk is an exception as it yields a mean reflectance of 4.55% at 500 °C suggesting that pyrolysis temperature is not the only factor controlling %Ro and hence carbon stability. Furthermore, the biochar compositions show a relationship between feedstock and pyrolysis temperature. The biochar morphotype composition changes significantly with increasing temperature, but the analyzed biochars are all dominated by fusinoid/solid (primarily fusinoid) morphotypes with the highest initial quantity recorded at 500 °C. This quantity decreases with increasing pyrolysis temperature while porous morphotypes (tenuinetwork, crassinetwork, mixed porous, mixed dense) increase. Variations in morphotype composition observed between the biochars is attributed to the structural nature of the feedstocks.

Pore Fractal Characteristics of Lacustrine Shale of Upper Cretaceous Nenjiang Formation from the Songliao Basin, NE China

The evaluation of pore characteristics in lacustrine shales is of significance for shale oil and gas exploration in terrestrial sedimentary basins. However, due to the complex depositional environments, there have been few reports on the quantitative evaluation of lacustrine pores. In this study, we carry out experiments, e.g., scanning electron microscopy (SEM), nitrogen adsorption, X-ray diffraction (XRD), and rock pyrolysis, on sixteen lacustrine shale core samples of the Late Cretaceous Nenjiang Formation (K2n1+2) in the Songliao Basin. At the same time, we bring in the fractal dimensions to quantitatively characterize the pores of shale samples in K2n1+2. The kerogen type of shales in the Nenjiang Formation is mainly type Ⅰ. The shales of K2n1+2 develop a large number of mineral intergranular pores and a small number of organic pores and mineral intragranular pores. The primary minerals of the samples are clay minerals and quartz. The total organic carbon (TOC) has a correlation with the pore physical parameters, whereas the content of minerals does not correlate significantly with pore development. The average pore fractal dimensions obtained from the analysis of nitrogen adsorption data are D1 = 2.5308 and D2 = 2.6557. There is a significant negative correlation between the fractal dimensions (D1 and D2) and the TOC content: the lower the fractal dimensions, the higher the TOC, and the more the free oil. In low maturity shales with higher TOC content, due to hydrocarbon generation, larger pores with a regular shape (small fractal parameters) can be produced, which can store more free oil. The shale reservoir evaluation of K2n1+2 in the Songliao Basin should be focused on shales with higher TOC and lower pore fractal parameters. Our work provides a reference for the shale oil evaluation of K2n1+2 in the Songliao Basin and complements studies on lacustrine pore characteristics.

Metal-free electro-Fenton degradation of perfluorooctanoic acid with efficient ordered mesoporous carbon catalyst

Heterogeneous electro-Fenton with in situ generated H2O2 and •OH is a cost-effective method for the degradation of refractory organic pollutants, in which the catalyst is an important factor affecting its degradation performance. Metal-free catalysts can avoid the potential risk of metal dissolution. However, it remains great challenge to develop efficient metal-free catalyst for electro-Fenton. Herein, ordered mesoporous carbon (OMC) was designed as a bifunctional catalyst for efficient H2O2 and •OH generation in electro-Fenton. The electro-Fenton system showed fast perfluorooctanoic acid (PFOA) degradation with kinetics constant of 1.26 h−1 and high total organic carbon (TOC) removal efficiency of 84.0 % after 3 h reaction. The •OH was the main species responsible for PFOA degradation. Its generation was promoted by the abundant oxygen functional groups such as C-O-C and the nano-confinement effect of mesoporous channels on OMCs. This study indicated that OMC is an efficient catalyst for metal-free electro-Fenton system.

Geochemical conditions regulating chromium preservation in marine sediments

In the marine sediment record, concentrations and isotope ratios of chromium (Cr) can be used to reconstruct ocean biogeochemical conditions. These reconstructions rely on a detailed understanding of the chemical pathways that Cr undergoes as it is transferred from the water column to the sediment record. We examined Cr concentrations in marine pore fluids and sediments from six continental margin sites, which can be grouped into two basic environments: (1) sites where sediments are oxygenated and rich in solid phase Mn (herein termed oxic), and (2) sites where sediments are organic C (Corg)-rich and oxygen is depleted (anoxic). We found Cr concentrations to be lower (maximum of 12 nM in pore fluids and 124 ppm sediment solid phase) at oxic sites compared with anoxic sites (maximum of 77 nM and 184 ppm). Our findings confirm previously published interpretations of dissolved Cr in pore fluids (Brumsack and Gieskes, 1983; Shaw et al., 1990). In oxic surface sediments, particulate Cr(III) can be oxidised by Mn oxides, which leads to elevated concentrations of dissolved Cr co-occurring at the same depth as elevated Mn concentrations in the sediment. Under these oxidising conditions, down-core sediments contain relatively low solid-phase Cr concentrations. In oxic sediments, Cr speciation reveals that most of the pore fluid Cr is in the Cr(VI) state. At the site where Mn oxide-rich sediments rest below an oxic water column, oxidative loss of Cr from the sediment to the bottom water leads to the lowest estimated Cr burial efficiency of the sites examined here. Under anoxic Corg-rich conditions, both pore fluids and sediment solid phases contain high Cr concentrations, with 40–80% of dissolved pore fluid Cr present as Cr(III). This enrichment of Cr appears to be tightly linked to the presence of high total organic carbon (TOC) content and scavenging of Cr by (organic) particles in the water column. Combined, these data highlight the strong dependence of Cr on both sedimentary redox conditions as well as biological productivity. Based on the data from modern continental margin sediments, we propose that Cr concentrations and isotope compositions of the authigenic sediment fraction may record a combination of redox conditions and biological productivity in the water column. If confirmed by Cr isotope analyses, these findings will add support for the notion that Cr may serve as a proxy for ocean biological and chemical sedimentological conditions. Thus, careful assessment of the impact of organic matter on Cr is required for reconstructions of redox conditions with sedimentary records.