High Organic Carbon Research Articles

Soil Carbon: Pool, Loss, Emission and Climate Change Sources and Knowledge Level of Some Land Use Systems in Sudan Savanna, Kwara State

This research work was carried out in Sudan savanna of Kwara State to determine the effects of land use types on soil carbon pool, loss, emission and to determine the farmer’s knowledge level and sources of information on climate change. Six villages were selected randomly and in each Local Government Area, three villages were visited and three farms planted each with maize/cassava intercrop, cashew plantation and natural forest were sampled. Soil samples were collected from the farmland randomly at the depth of 0–20cm and analysed for physical and chemical properties in the laboratory. Carbon pool index was higher under cashew plantation. The mass of carbon lost recorded was higher under maize/cassava intercrop and cashew plantation recorded the lowest mass of carbon lost. Equivalent Carbon dioxide emitted recorded was lower under cashew plantation and maize/cassava intercrop recorded higher equivalent of carbon dioxide emitted. Natural forest had the highest organic carbon. Simple random sampling of 126 respondents were interviewed. Results revealed majority (71.4%) are willing to invest in residue retention and 92.9% are willing to engage in climate change mitigation practices free of charge. Maize/cassava intercrop recorded the lowest carbon pool due to burning of plant residues and the use of tillage practices. The highest carbon pool index recorded under cashew plantation was due to leaves litter decomposition. Carbon emitted was generally higher under maize/cassava intercrop as a result of continuous and vigorous cultivation leading to loss of carbon. Some farmers are not fully aware of climate change mitigation practices, therefore, more observation should be given to afforestation scheme to mitigate climate change and government and nongovernmental organization (NGOs) should educate and encourage farmers to practice crop residue retention and also minimize bush burning.

CONTRIBUTION OF PETROGRAPHIC AND GEOCHEMICAL ANALYSES OF THE KIPALA SHALE (CENTRAL BASIN, DRC) TO THE ASSESSMENT OF ITS POTENTIAL AS A HYDROCARBON SOURCE ROCK

A geological study of the Kipala region, in the "Cuvette Centrale" of the Democratic Republic of Congo, has identified two groups of shales: the dark greasy facies, interbedded with the brownish-gray facies. Their high Total Organic Carbon (TOC) content (11 % TOC on average for the dark greasy shales, compared with 8 % for the second group) classifies them as very good hydrocarbon source rocks, according to the criteria of Epistalie et al. Field and laboratory data suggest that the rocks studied were deposited in a lagoon connected to the sea by an intermittently closing channel.

The dual roles of dissimilatory iron reduction in the carbon cycle: The "iron mesh" effect can increase inorganic carbon sequestration.

Dissimilatory iron reduction (DIR) can drive the release of organic carbon (OC) as carbon dioxide (CO2 ) by mediating electron transfer between organic compounds and microbes. However, DIR is also crucial for carbon sequestration, which can affect inorganic-carbon redistribution via iron abiotic-phase transformation. The formation conditions of modern carbonate-bearing iron minerals (ICFe ) and their potential as a CO2 sink are still unclear. A natural environment with modern ICFe , such as karst lake sediment, could be a good analog to explore the regulation of microbial iron reduction and sequential mineral formation. We find that high porosity is conducive to electron transport and dissimilatory iron-reducing bacteria activity, which can increase the iron reduction rate. The iron-rich environment with high calcium and OC can form a large sediment pore structure to support rapid DIR, which is conducive to the formation and growth of ICFe . Our results further demonstrate that the minimum DIR threshold suitable for ICFe formation is 6.65 μmol g-1 dw day-1 . DIR is the dominant pathway (average 66.93%) of organic anaerobic mineralization, and the abiotic-phase transformation of Fe2+ reduces CO2 emissions by ~41.79%. Our findings indicate that as part of the carbon cycle, DIR not only drives mineralization reactions but also traps carbon, increasing the stability of carbon sinks. Considering the wide geographic distribution of DIR and ICFe , our findings suggest that the "iron mesh" effect may become an increasingly important vector of carbon sequestration.

High‐frequency palaeoenvironmental changes in the mixed siliciclastic–carbonate sedimentary system from a lower Permian restricted basin (West Gondwana, southern Brazil)

ABSTRACTGlobal climatic and palaeogeographical changes generated a siliciclastic–carbonate system with high organic matter accumulations in a shallow sea during the lower Permian in Western Gondwana. The 60 m thick mixed siliciclastic–carbonate succession (Irati Formation and the base of the Serra Alta Formation) from the Paraná Basin represents a singular record of the interplay between carbonate production and siliciclastic input, providing a window of opportunity to integrate large‐scale depositional architecture with facies and geochemical analyses. The detailed study of cores supported by outcrop columnar sections revealed a siliciclastic‐dominated, retrogradational to aggradational facies, and a carbonate‐dominated, mixed aggradational to progradational facies composing three depositional sequences that record an outer‐ramp and mid to upper‐ramp. An integrated approach based on the description of facies and microfacies, organic geochemistry and mineralogical composition, indicated high‐frequency palaeoenvironmental changes during the evolution of this restricted basin. Climate changes, resulting in humid and dry phases, produced ideal conditions for high organic matter production and dolomite formation. The high organic matter production (humid phases) in addition to the restricted condition was responsible for the anoxic bottom waters that were widespread due to the low angle and homoclinal platform. Nutrient‐rich freshwater inflows in the anoxic and hypersaline restricted basin created a density‐stratified water column causing low‐salinity surface and anoxic bottom water, which allowed planktonic life, typical of lakes, such Botryococcus braunii, to flourish in the photic zone and sulphur bacteria to populate below the chemocline. Microbial activity induced primary dolomite precipitation (dry phases) and widespread formation of synsedimentary dolostone. Freshwater inflow and marine incursions are reflected in the organic matter accumulation (kerogen types I and II, respectively), generating bituminous shale with high total organic carbon (5 to 27 wt.%).

An isotope study on nitrogen and phosphorus use efficiency and movement in soil in a mimicked vermicompost‐based organo‐mineral fertilizer

AbstractVermicompost (VC), a stabilized organic material with high organic and humic carbon, and favorable aggregation properties, was tested as a fraction of organo‐mineral fertilizers (OMFs), where organic and mineral fractions interact in hotspot areas with surrounding soil. Solutions containing 33P radioisotope and 15N‐labeled mineral fertilizers were combined with VC at two ratios of organic carbon (Corg) to mineral nitrogen (N) and phosphorus (P) (OMF7.5C and OMF15C) to simulate OMF granules. Control treatments included unfertilized soil (N0P0), mineral fertilizer (MFNP), and sole VC at two rates (OF7.5C and OF15C). Nitrogen and P uptake by Italian ryegrass (Lolium multiflorum) were measured over in 8 weeks. Furthermore, MFNP, OMF7.5C, and OMF15C treatments were incubated for 10 days without plant to measure atom% 15N excess and 33P radioactivity, as indicators of N and P movement from two soil layers (surrounding fertilizer hotspot and below it). In the pot study, OMF15C caused 24% lower biomass and less nutrient recovery derived from fertilizer (N, 11% and P, 8.5%), compared to MFNP. In the incubation study, OMF15C exhibited +19% atom% 15N excess in the combined two soil layers, relative to MFNP, and +28% 33P radioactivity in the soil surrounding the hotspot, and −89% in the soil below it. We interpreted this as a reduction in nutrient availability of the combined VC + mineral fertilizers, due to lower P mobility in soil. The combination of VC with mineral fertilizers can reduce P movement in soil. A higher Corg:N:P ratio resulted in lower nutrient use efficiency in 2 months.

Investigating Soil Water Retention and Water Content in Retrogressive Thaw Slumps in the Qinghai-Tibet Plateau, China

Retrogressive thaw slumps (RTSs) are becoming more common on the Qinghai-Tibet Plateau as permafrost thaws, but the hydraulic properties of thaw slumps have not been extensively studied. To fill this knowledge gap, we used the “space-for-time substitution method” to differentiate three stages of RTSs: original grassland, collapsing, and collapsed. Our study included on-site investigations, measurements in the laboratory, and measured and simulated analyses of soil water retention curves and estimated hydrological properties. Our findings show that the measurements and simulated analyses of soil water retention were highly consistent across RTSs, indicating the accuracy of the Van Genuchten model in reproducing soil hydraulic parameters for different stages of RTSs. The original grassland stage had the highest soil water retention and content due to its high soil organic carbon (SOC) content and fine-textured micropores. In contrast, the collapsed stage had higher soil water retention and content compared to the collapsing stage, primarily due to increased proportions of soil micropores, SOC content, and lower bulk density (BD). From original grassland stage to collapsed stage, there were significant changes on the structure of each RTS site, which resulted in a decrease in SOC content and an increase in BD in general. However, the absence of soil structure and compaction led to the subsequent accumulation of organic matter, increasing SOC content. Changes in field capacity, permanent wilting point, and soil micropore distribution aligned with variations in SOC content and water content. These findings highlight the importance of managing SOC content and water content to mitigate the adverse effects of freeze-thaw cycles on soil structure and stability at different thaw collapse stages of RTSs. Effective management strategies may include incorporating organic matter, reducing soil compaction, and maintaining optimal water content. Further research is needed to determine the most suitable management practices for different soil types and environmental conditions.

Physical Properties, Chemical Components, and Transport Mechanisms of Atmospheric Aerosols Over a Remote Area on the South Slope of the Tibetan Plateau

AbstractThe physicochemical properties and origins of atmospheric aerosols in the Tibetan Plateau (TP) region are a research topic of great interest, but an in‐depth understanding of this topic is challenging, partially due to a lack of intensive in situ observations. Thus, a field campaign was conducted over Yadong, a remote area on the south slope of the TP from June 11 to 31 August 2021. The aerosol loading was low, with a black carbon mass concentration of 147.4 ± 98.4 ng·m−3. Aerosol single‐scattering albedo was low (0.73 ± 0.11 at 550 nm) and increased from 450 to 700 nm wavelength. Organic matter (OM) accounting for 69.6% of the total aerosol mass and relatively high secondary organic carbon ratios, highlighting the importance of secondary formation. An interesting phenomenon observed was that the evolution of aerosols was mainly characterized by diurnal variation, which could not be explained by large‐scale atmospheric processes such as Indian summer monsoon. Instead, it was found that regional mountain‐valley winds between the Himalayas and South Asia transported polluted air masses toward the TP, especially in the afternoon when regional valley wind are expected to be the strongest and the boundary layer in South Asia is deepest. Additionally, daytime local valley wind further elevated these aerosols to higher altitudes on the TP. This paper provides insights into the transport mechanisms of aerosols from South Asia to the TP. These findings are of great importance since aerosols exhibit significant diurnal variations in the TP region.

Organic carbon burial and their implication on sea surface primary productivity in the middle Okinawa Trough over the past 200 ka

The long-term burial of organic carbon in marginal seas plays a critical role in Earth’s carbon cycle and climate change. However, the mechanism of organic carbon (OC) burial in the Okinawa Trough (OT) during glacial-interglacial timescales remains unclear. In this study, we analyzed the foraminiferal carbon isotopes, total organic carbon (TOC), and δ13C-TOC over the past 200 ka in core Z1 collected in the central OT. We aimed to reveal the history of OC burial in the middle Okinawa Trough during the past 200 ka, and we combined our findings with relevant paleoenvironmental indices to reveal underlying mechanisms. We found reduced surface primary productivity during MIS 6, which may indicate changes in the pathways of the Kuroshio Current (KC). Furthermore, we observed decoupling between high TOC flux and low OC burial during glacial periods. We proposed that the dilution effect caused by the high sedimentation rate and poor OC preservation during the glacial period resulted in the low TOC content. Ventilation of the North Pacific Intermediate Water (NPIW) regulated the redox conditions of the intermediate water in the Okinawa Trough. Additionally, the intensified Kuroshio Current during interglacial phases led to water column stratification, creating reducing conditions in the bottom water and facilitating improved OC preservation. Subsequently, the enhanced water column oxygenation resulting from the oxygen carried by the intensified glacial NPIW weakened the burial of OC. This study sheds new light on our understanding of the carbon cycle in marginal seas on a glacial-interglacial timescale.

Influence of Date Palm-Based Biochar and Compost on Water Retention Properties of Soils with Different Sand Contents

Generally, soils of arid and semi-arid regions have low water retention properties due to high sand and low organic carbon contents. This study aimed at quantifying the effect of date palm-based organic amendments (OAs) on the water retention properties of two soils (sandy loam and silty loam), as well as the influence of sand supplementation (0.5–2 mm) on the magnitude of the effect of OAs. Different grain size distributions were obtained by adding sand to natural soils. For this purpose, sand was added to the two soils (1/3 and 2/3) and different soil-OA combinations were tested at a dose of 3% by mass: compost alone, biochar alone and a mixture of biochar and compost (50:50 in mass), in addition to unamended control soils. Soil water contents were measured at nine matric potentials ranging from the saturation to the permanent wilting point. Biochar was more efficient than compost at improving soil water retention. The effect of organic amendments on water retention increased with sand content. In most cases, soil water content values were significantly higher for biochar-amended soils than for unamended or compost-amended soils. The weakness of the effect of compost addition (if alone) was probably due to its properties and notably its high mineral content and electrical conductivity. Soil sand supplementation led to higher differences between the OA-amended soils and unamended soils. Changes in available water capacity reached +26% and +80% in a sandy loamy soil enriched with 2/3 sand and amended with compost and with biochar, respectively, compared to the unamended soil. These results show that sand content (and more generally, soil texture) influences the effect of OA application. Thus, the application of biochar from date palm residues in soil seems to be an effective solution to improve the water retention properties of coarse textured soils and contribute to optimizing the use of water resources in irrigated areas.

Effects of intercropping on soil greenhouse gas emissions - A global meta-analysis

Diversified cropping systems, such as intercropping, have shown multifunctionality in agronomic productivity promotion, pest control, and soil health improvement. However, the intense interaction between crop species stimulates soil carbon and nitrogen turnover, and intercropping systems cause inexplicit effects on soil greenhouse gas emissions (GHG). Therefore, a comprehensive meta-analysis using 52 published articles (531 paired observations) was conducted to elucidate the effects of intercropping on soil N2O, CO2, and CH4 emissions under different environmental conditions and field practices to identify the primary driving factors, such as climate, soil and field practices. The results showed that intercropping treatment had a non-significant impact on the three GHG emissions on average. However, using a cereal-legume intercropping regime, adopting moderate N application rate or intercropping in alkaline soils could significantly mitigate soil N2O emission. Additionally, intercropping in soils with high soil organic carbon reduce soil CH4 emission. On the contrary, increasing intercropping duration, or adopted in soils with moderate soil total N tended to stimulate CO2 emission. The mixed-effect model selection indicated that initial soil pH, MAP, MAT, tillage regime, and intercropping duration and type were significant moderators in regulating soil GHG emissions. Our findings explicitly elucidated soil GHG responses to intercropping practice. Further studies are warranted on the evaluation of long-term intercropping effects to improve the comprehensive understanding of C and N balance and global warming potential under intercropping.

Atividade residual e adsorção do tebuthiuron em diferentes solos

ABSTRACT Applications of tebuthiuron can increase the risks of environmental contamination and hinder the cultivation of sensitive species in succession. The objective of this work was to assess the residual activity and sorption of the herbicide tebuthiuron in soils with different physical and chemical attributes. The experiments were conducted in a completely randomized design with four replicates. The experiment for determining residual activity was conducted in a 2 × 7 factorial arrangement consisted of two herbicide doses (0.6 and 1.2 kg a.i. [active ingredient] ha-1) and seven sowing times (0, 60, 120, 180, 240, 300, and 360 days after herbicide application) in sandy loam and sandy clay loam soils. The experiment for evaluating sorption was conducted in a sandy loam soil and two clay loam soils with applications of increasing tebuthiuron doses (0.025, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.50, 0.60, 0.70, and 0.80 kg a.i. ha-1). Regarding residual activity, the herbicide’s effect of the decreased over time, with no toxicity detected 360 days after application (DAA), regardless of the soils and doses used. Sandy loam soils had lower sorption, resulting in lower shoot dry weight and plant height and in higher phytotoxicity 21 days after emergence. Residual activity was detected 360 DAA in the studied soils. Tebuthiuron sorption was higher in soils with higher organic carbon and clay contents.

Geochemistry and Reservoir Properties of the Upper Jurassic Formations, in Selected Oilfield Central Iraq

Geochemical analysis of subsurface organic matter in the most productive source rocks, the Sargelu and Naokelekan formations, has provided insight into the potential of hydrocarbon production in the Jurassic strata of the selected oil field in central Iraq.The aim of this study is to conclude if the source rock can provide reservoir properties such as porosity and permeability. This attempt is made to support petroleum production from both reservoir and source rocks. The cause of this idea was adopted due to some of very good source rock were kept the produced hydrocarbons within the thin impermeable layers.Rock Eval pyrolysis returned high total organic carbon ranging from 0.55 to 34.82 wt%, Type II kerogen with a hydrogen index of up to 368 mg HC/gTOC, and a rock potential of 0.58 to 50.9 kghc/ton rock. Mature organic material was found in both formations, with a Tmax between 434 and 450 °C. This study of source rock properties shows that the rocks have good properties that need to be considered as the Sargelu and Naokelekan formations are the main sources of hydrocarbons in the studied area.The multi-story source-reservoir rocks are represented in this secession. The reservoir properties of the Naokelekan Formation are impressive in that it can draw crude oil from the underlying Sargelu Formation, which produces oil and releases it into the local petroleum system. The effective porosity in the Naokelekan Formation reached 14% in the main reservoir area, while permeability values mostly reached 4 mD. This indication potentially underscores the objective of this study to upgrade the oil-producing source rock into reservoir intervals.

Typhoon Chan-Hom (2015) induced sediment cross-shore transport in the mud depo-center of the East China Sea inner shelf

The erosion, transport, and deposition processes of sediments that are influenced by typhoons are significant constituents of the sedimentary source-sink processes in marginal seas. Nevertheless, the genesis of storm deposit layers in the continental shelf and their subsequent development and preservation after typhoons have not been comprehensively investigated. In this study, we have conducted a systematic investigation of the processes related to sediment transport and deposition, which were primarily induced by Typhoon Chan-Hom, and analyzed the evolution and preservation of storm deposits utilizing grain-size analysis, radionuclides (137Cs, 210Pbex and 7Be), and organic geochemistry (TOC, TN and δ13C). Sedimentary 137Cs, 210Pbex, and 7Be inventories measured three days after the typhoon suggest that the sediments in the water depth < 30 m were eroded, resuspended, and then transported offshore to deposit in the deeper areas (water depth > 50 m) of the Muddy Deposition Center of Zhejiang-Fujian Coast (MDC-ZFC), resulting in the formation of significant storm deposits (thickness of 8–16 cm) with high 210Pbex and 7Be. In addition to sediment transport, the offshore area also received organic matter generated by typhoon-induced phytoplankton blooms. Hence, in the present study area, the features of marine organic matter that possess high total organic carbon (TOC) content (>0.4%), low carbon to nitrogen (C/N) ratio (<7.5), and high δ13C value (> − 22‰) are crucial for identifying the storm deposit formed by cross-shore sediment transportation. In contrast, the commonly used indicators for identifying typhoon sedimentary records that rely on grain-size coarsening are not suitable for identifying storm deposits at the MDC-ZFC edge due to the influence of relict sands. Furthermore, the radionuclides and organic geochemical signals of the sediments revealed that no significant disturbance or transport of the storm sediments occurred three weeks after the passage of Typhoon Chan-Hom due to the high water depth, indicating that these storm deposits could be effectively preserved in this area. This study provides a valuable basis and reference for accurately identifying and interpreting typhoon sedimentary records in the MDC-ZFC.

Soil buffering capacity enhances maize yield resilience amidst climate perturbations

CONTEXTMaize production in China is facing a multitude of challenges such as climate change, increasing demand, and limited cropland availability. Soil properties, beyond supporting crop growth and development, can play a critical role in buffering the impacts of climate crisis on crop yields. However, little information is known about such buffering capacities and their spatial distributions of soil properties in buffering the impacts of climate perturbations on maize yields in China's maize belt (CMB). OBJECTIVEThe objective of this study was to identify the responses of different regions within the CMB to climate perturbations in terms of maize yields, as well as their spatial differences and magnitudes. Additionally, we aimed to quantify the capacities of soil properties in buffering the impacts of climate perturbations. METHODSWe quantified the impacts of climate perturbations (climate fluctuations deviating from the mean state) on maize yields using the APSIM across the China's maize belt. We then used the random forest model to interpret the buffering effects of typical soil properties to the adverse impacts of climate perturbations. RESULTS AND CONCLUSIONSOur results reveal that temperature variability was the predominant climatic perturbation affecting maize yields, with rising temperature leading to significant yield losses in most regions. Perturbations in solar radiation and precipitation exhibited relatively stronger positive yield impacts only in areas with inadequate solar radiation and dry conditions, respectively. Notably, soil properties explained ∼40% to ∼70% of the spatial variations for the impacts of climate perturbations. Soils with high soil organic carbon content (SOC) can significantly reduce the negative impacts of temperature increase, highlighting the crucial buffering effect of SOC in response to global warming. Soil texture, field capacity and bulk density were also critical soil buffering properties for interpreting the spatial patterns of the impacts of climate perturbations. SIGNIFICANCEOur results underscore the importance of soil quality improvement to ensure stable food production, which is an effective strategy for enhancing agricultural system resilience amidst future climate crises.

High organic carbon content constricts the potential for stable organic carbon accrual in mineral agricultural soils in Finland

Sequestering carbon into agricultural soils is considered as a means of mitigating climate change. We used agronomic soil test results representing c. 95% of the farmed land area in Finland to estimate the potential of the uppermost 15 cm soil layer of mineral agricultural soils to sequester organic carbon (OC) and to contribute to the mitigation of climate change. The estimation of the maximum capacity of mineral matter to protect OC in stable mineral-associated form was based on the theory that clay and fine-sized (fines = clay + silt) particles have a limited capacity to protect OC. In addition, we used the clay/OC and fines/OC ratios to identify areas with a risk of erosion and reduced productivity, thus indicating priority areas potentially benefitting from the increased soil OC contents. We found that 32–40% of the mineral agricultural soils in Finland have the potential to further accumulate mineral-associated OC (MOC), while in the majority of soils, the current OC stock in the uppermost 15 cm exceeded the capacity of mineral matter to protect OC. The nationwide soil OC sequestration potential of the uppermost 15 cm in mineral agricultural soils ranged between 5 and 10 Tg, which corresponds to less than the annual greenhouse gas emissions in Finland. The fields with the highest potential for SOC accrual were found in the southern and southwestern parts of the country, including some of the most intensively cultivated high-clay soils. Although the nationwide potential for additional OC sequestration was estimated to be relatively small, the current OC storage in Finnish arable mineral soils (0-15 cm) is large, 128 Tg. Farming practices enabling maximum OC input into the soil play an important role as a tool for mitigating the loss of carbon from high-OC soils in the changing climate. Furthermore, especially in high-clay areas with potential for MOC accrual, efforts to increase soil OC could help improve soil structural stability and therefore reduce erosion and the loss of nutrients to the aquatic environments.

Utilization of banana waste biochar to reduce heavy metal contamination in soil and maize plants

There are indications of heavy metal contamination in soil and agricultural products on paddy fields in Subak Kerdung, Bali. Soil amendments are needed to reduce heavy metal content in contaminated soil to minimize heavy metals in plants. Biochar that contains high organic carbon material and is highly resistant to decomposition is claimed to inhibit and reduce the content of heavy metals in soil and plants. Banana wastes containing cellulose and lignin are considered good as biochar raw materials. This research that aimed to observe the ability of banana waste biochar to reduce heavy metals in soil taken from Subak Kerdung, Bali, was conducted in a greenhouse using maize plants as control plants. The treatments tested consisted of two factors. The first factor was the type of banana waste as biochar-making material consisting of banana stem biochar, banana peel biochar, banana fruit bunch biochar, and mixed biochar (banana stem + banana peel + banana fruit bunch). The second factor was the biochar dosage, which consists of four contents, namely 0 t/ha, 5 t/ha, 10 t/ha, and 15 t/ha. All treatment combinations were arranged in a two-factor, randomized block design with three replications. The results showed that mixed biochar (banana stem + banana peel + banana fruit bunch) effectively reduced Pb and Cu in maize plants. In contrast, banana peel biochar could optimally reduce Cd content in soil and its content in plants. Based on the dose, 15 t/ha of mixed biochar reduced Pb and Cd contents, while 10 t/ha of mixed biochar reduced Cu content.

PALYNOFACIES AND ORGANIC GEOCHEMISTRY OF LACUSTRINE SOURCE ROCKS: THE POTRERILLOS – CACHEUTA SOURCE ROCK SYSTEM IN THE TRIASSIC CUYO BASIN, WEST‐CENTRAL ARGENTINA

This study presents an integrated investigation of the Upper Triassic Potrerillos – Cacheuta lacustrine source rock in the Cuyo Basin of western Argentina. Data came from palynofacies analyses, organic petrography, Rock‐Eval pyrolysis and mineralogical studies based on X‐ray diffraction analyses. An 80 m thick outcrop section was studied and is interpreted to represent the transition from shallow‐lacustrine sediments influenced by fluvial discharges (uppermost Potrerillos Formation) to the deposits of a deep, permanent lake (Cacheuta Formation). Three palynofacies were defined. Palynofacies I is characterized by shallowing‐upward cycles with abundant woody material, and was deposited under an oxic, disturbed water column. Palynofacies II and III occur in laminated shales rich in amorphous organic matter (AOM) and freshwater algal material (Botryococcus) respectively, which were deposited under oxygen‐depleted conditions. In general, the detrital material present suggests an input derived from fluvial discharges; however, interbedded tuffs altered to analcime and smectite suggest the transformation of vitric material in pyroclastic ash under saline to alkaline water conditions. Kerogen Types II/III and III with high total organic carbon values indicate a moderate oil‐ and gas‐prone source rock whose thermal maturity varies from immature to the early oil window (Tmax: 430‐438 °C; vitrinite reflectance: 0.59‐0.67 % VRo; and thermal alteration index: 2‐2+).This study demonstrates the importance of palynofacies analyses for the interpretation of depositional changes and associated controls in lacustrine shale successions. When integrated with data from organic geochemistry, palynofacies analysis is an important tool in the evaluation of a source rock's thermal maturity and hydrocarbon generation potential.

Trace-metal enrichment mechanisms in Bakken Formation black shales, Williston Basin, North Dakota, USA

The Bakken black shales represent a unique sedimentary system characterized by high total organic carbon contents (TOC; Lower Bakken shale = 10.8 and Upper Bakken shale = 11.8 avg. wt%) and enrichment factors (EF) of various trace metals (TMs) such as Cu (6.2–7.7), Mo (219.7–237.8), Ni (9.4–10.2), U (20.6–29.3), V (9.9–14.2), and Zn (10.4–12.2) that are considerably higher than many other Devonian-Mississippian (D–M) black shales. In this study, raw distributions of elemental concentrations combined with bivariate and principal component analysis (PCA) were used to clarify processes that contributed to high TM EF values in the Bakken shales. Total organic carbon shares heavier PCA component loadings (>0.445) and stronger Pearson correlation coefficients (r) with Cu, Mo, Ni, U, V, and Zn than with pyrite-associated (As, Co, Fe, and S) elements, suggesting that organic matter (OM) played a primary role in the scavenging and accumulation of TMs in the sediments. Reducing conditions within bottom waters or sediment pore waters may have accelerated the accumulation of redox-sensitive Cu, Mo, Ni, V, and Zn introduced into the sediments via an OM detritus host and most likely played a secondary role in their enrichment. Deep-water renewal times for the Bakken have been estimated to be ∼10–30 yrs. based on Mo/TOC results. The high TM EF values observed in the Bakken shales may reflect frequent resupply of TMs into basin waters, enhanced primary productivity that is necessary in scavenging TMs from the water column, the presence of H2S within sediment pore or bottom waters, or possibly secondary processes associated with basin-wide fluid and hydrocarbon migration. High TOC concentrations may be the result of a possible shallow water column (∼150 m), which would limit exposure time of OM to oxidation and degradation, coupled with intermittent fluctuations between dysoxic and anoxic/euxinic bottom-water redox conditions, the latter of which would reduce rates of OM degradation by benthic organisms.

Geochemical Reactions of High Total Organic Carbon Oil Shale during CO2 Treatment Relevant to Subsurface Carbon Storage

Geochemical Reactions of High Total Organic Carbon Oil Shale during CO₂ Treatment Relevant to Subsurface Carbon Storage

Variação espaço-temporal da comunidade bentônica do rio Itajaí-Mirim, Itajaí (SC), nos canais original e retificado

The rectified channel was installed in the Itajaí-Mirim river in the mid-1960s to increase the river flow in the urban area of Itajaí, which suffers from flooding and inundation during periods of high precipitation. The present study aimed to evaluate the spatio-temporal variations of the benthic macrofauna of the Itajaí-Mirim river, in the original and rectified channels. The distribution of organisms was evaluated with samples collected at four points, two located in the natural channel and two in the rectified channel, during the four seasons of 2021. At each sampling point, with a van Veen dredge, three samples were collected for macrofauna and one for granulometric characterization. In total, 715 individuals were identified, and distributed in eight taxa. PERMANOVA revealed that the differences observed in the abundance of organisms considering seasonality were not significant, however, they were significant between the channels. The rectified channel exhibited 67% of the total abundance of the analyzed fauna. In this region, the organic matter and CaCO3 exhibited the highest concentrations and the sediment was classified as silt, while in the natural channel, the granulometry varied between fine sand and silt. The oligochaete Tubificida was the most abundant organism, representing 97% of the fauna. Considered tolerant, this organism inhabits freshwater sediments with low oxygen concentration and high organic carbon load. The low richness of the community and the high dominance of Tubificida characterized the evaluated region as a highly altered environment.