Diagenesis Of Organic Matter Research Articles

Kinetic Characteristics of Kerogens in the Kuonamka Complex, Lower and Middle Cambrian of the Siberian Platform

Abstract —The kinetic characteristics of kerogen (activation energy and frequency factor distributions of the initial generative potential) determine the dynamics of naphthide generation during catagenesis. In the previous studies on quantitative modeling of naphthidogenesis in the Kuonamka source rocks, the kinetic characteristics were taken by analogy with the known kerogens from other complexes and provinces. It seems relevant to determine the effective kinetic characteristics of the kerogen from the Kuonamka source rocks from experimental data. To estimate the kinetic parameters, specialized multi-rate pyrolysis studies were performed. The variations in pyrolysis data was reported to be presumably associated with the conditions of kerogen and source rock formation during accumulation and diagenesis of organic matter. The effect of carbonate and organic carbon contents on the temperature range of the second pyrolysis peak is recorded. Reconstruction of the average (effective) kinetic characteristics of kerogens from the Kuonamka source rock, was conducted using data on kerogens from Serkinsky-5 and 10 and Tit-Ebya-6 wells, which are less degraded than kerogens from Ust’-Maiskaya-366 well and probably attained the early mesocatagenesis grades. The current average effective kinetic characteristics of kerogen were estimated and corrected for the possible partial degradation of reference samples. The obtained effective kinetic models of kerogen are compared with models of kerogens of various genetic types known from the literature. The estimated effective kinetic characteristics of kerogens or Menil-1 and Type B kerogens with similar characteristics are to be taken, as a first approximation, in regional historical-genetic (basin) modeling of naphthide generation in the Kuonamka source rock.

Formation and diagenesis of authigenic silicates in the Late Paleozoic alkaline lake deposits, Junggar Basin, NW China

Authigenic silicates are typical minerals of alkaline lake deposits. Their mineral composition and lateral distribution can be used for reconstructing paleoclimates, paleoenvironments, and diagenetic subsidence histories of hydrocarbon reservoirs. In particular the examples of pre-Mesozoic alkaline lake deposits were widely missing in the literature. To unveil this, a basin-wide high-resolution mineralogical investigation is conducted on the Late Paleozoic volcanic-related alkaline lake deposit of the Fengcheng Formation in the NW Junggar Basin, NW China. The investigated Late Paleozoic shales mainly contain stable silicates like K-feldspar, albite and reedmergnerite. Laterally, the authigenic silicates are mostly distributed in the lake-central and transitional zones and are especially abundant in organic-rich shales. Authigenic K-feldspar and albite were mainly formed by replacing detrital clay minerals and K-feldspar or directly precipitating from alkaline porewaters. Reedmergnerite was later formed by replacing acid-sensitive carbonate or feldspar minerals when organic matter was mature. Organic matter thermal maturation and hydrocarbon generation helped lower porewater pH and periodically open diagenetic systems. These processes facilitated fluid migration and element exchanges and promoted the transformation of thermodynamically unstable silicates and acid-sensitive carbonates to more stable silicates and quartz. A main result of this study is thus to emphasize the control of organic matter diagenesis and temperature on authigenic silicate evolution. This model can help revisit the genesis of the dominant felsic shales in alkaline lake deposits.

The climate benefit of seagrass blue carbon is reduced by methane fluxes and enhanced by nitrous oxide fluxes

Blue carbon is carbon stored long-term in vegetated coastal ecosystems, which constitutes an important sink for atmospheric carbon dioxide (CO2). However, because methane (CH4) and nitrous oxide (N2O) have higher global warming potentials (GWP) than CO2, their production and release during organic matter diagenesis can affect the climate benefit of blue carbon. Here, we present a meta-analysis synthesizing seagrass CH4 and N2O fluxes and long-term organic carbon burial rates, and use these data to estimate the reduced climate benefit (offsets) of seagrass blue carbon using three upscaling approaches. Mean offsets for individual seagrass species (34.7% GWP20;1.0% GWP100) and globally (33.4% GWP20;7.0% GWP100) were similar, but GWP20 offsets were higher, and GWP100 offsets were lower than globally, for the Australian region (41.3% GWP20;1.1% GWP100). This study highlights the importance of using long-term organic carbon burial rates and accounting for both CH4 and N2O fluxes in future seagrass blue carbon assessments.

Biogeochemical Controls on Methane Generation: A Review on Indian Coal Resources

Coal bed methane (CBM) extraction has astounding effects on the global energy budget. Since the earliest discoveries of CBM, this natural gas form has witnessed ever-increasing demands from the core sectors of the economy. CBM is an unconventional source of energy occurring naturally within coal beds. The multiphase CBM generation during coal evolution commences with microbial diagenesis of the sedimentary organic matter during peatification, followed by early to mature thermogenic kerogen decomposition and post-coalification occurrences. Indeed, the origin of the CBM and, moreover, its economically valuable retention within coal seams is a function of various parameters. Several noticeable knowledge gaps include the controls of coal make-up and its physico-chemical position on the CBM generation and genetic link through fossil molecular and stable isotopic integration with the parent coal during its evolution. Therefore, this manuscript reviews the origin of CBM; the influences of coal properties and micropetrographic entities on CBM generation and storage; and its genetic molecular and stable isotope compositions in India and the world’s major coal reservoirs. Moreover, analyses of and outlooks on future development trends in the exploration, production, and application of coalbed methane are also addressed. Finally, as India has the fifth largest proven coal reserves, this brief review of the recent CBM discoveries and developments provides a plausible scope for microbially enhanced CBM production from these basins.

Temporal evolution of shallow marine diagenetic environments: Insights from carbonate concretions

Early diagenesis of marine organic matter dramatically impacts Earth’s surface chemistry by changing the burial potential of carbon and promoting the formation of authigenic mineral phases including carbonate concretions. Marine sediment-hosted carbonate concretions tend to form as a result of microbial anaerobic diagenetic reactions that degrade organic matter and methane, some of which require an external oxidant. Thus, temporal changes in the oxidation state of Earth’s oceans may impart a first-order control on concretion authigenesis mechanisms through time. Statistically significant variability in concretion carbonate carbon isotope compositions indicates changes in shallow marine sediment diagenesis associated with Earth’s evolving redox landscape. This variability manifests itself as an expansion in carbon isotope composition range broadly characterized by an increase in maximum and decrease in minimum isotope values through time. Reaction transport modelling helps to constrain the potential impacts of shifting redox chemistry and highlights the importance of organic carbon delivery to the seafloor, marine sulfate concentrations, methane production and external methane influx. The first appearance of conclusively anaerobic oxidation of methane-derived concretions occurs in the Carboniferous and coincides with a Paleozoic rise in marine sulfate. The muted variability recognized in older concretions (and in particular for Precambrian concretions) likely reflects impacts of a smaller marine sulfate reservoir and perhaps elevated marine dissolved inorganic carbon concentrations. Causes of the increase in carbon isotope maximum values through time are more confounding, but may be related to isotopic equilibration of dissolved inorganic carbon with externally derived methane. Ultimately the concretion isotope record in part reflects changes in organic matter availability and marine oxidation state, highlighting connections with the subsurface biosphere and diagenesis throughout geologic time.

Structural-morphological features and crystallization environment of quartz in shungite rocks of the Onega basin

The article reports the results of a study of quartz in shungite rocks of the Shunga, Zazhogino and Maksovo deposits in the Onega Paleoproterozoic Basin located in the Karelian Craton in the southeastern part of the Baltic Shield. Silica is one of the main components of shungite rocks (Corg 35–80 %) and lydites (Corg up to 5 %), in which it forms two morphological types: epigenetic vein quartz and authigenic quartz. The rocks retain signs of delayed diagenesis of organic and siliceous matter: high dispersion of mineral segregations, dyscrystalline mineral matter, globular and other metacolloidal forms of segregations, which indicates the colloidal origin of authigenic quartz. The values of the (O/Si)at ratio were determined for morphologically different segregations of quartz in shungite rocks. The results of the study suggest that the structural features of authigenic quartz arose during the early stages of lithogenesis in the context of active interaction with organic matter. Most likely, the organic matter partially or fully retained its bondage to the siliceous matter of shungite rocks in the process of catagenetic transformations.

Occurrence, Diversity, and Genomes of "Candidatus Patescibacteria" along the Early Diagenesis of Marine Sediments.

The phylum "Candidatus Patescibacteria" (or Candidate Phyla Radiation [CPR]) accounts for roughly one-quarter of microbial diversity on Earth, but the presence and diversity of these bacteria in marine sediments have been rarely charted. Here, we investigate the abundance, diversity, and metabolic capacities of CPR bacteria in three sediment sites (Mohns Ridge, North Pond, and Costa Rica Margin) with samples covering a wide range of redox zones formed during the early diagenesis of organic matter. Through metagenome sequencing, we found that all investigated sediment horizons contain "Ca. Patescibacteria" (0.4 to 28% of the total communities), which are affiliated with the classes "Ca. Paceibacteria," "Ca. Gracilibacteria," "Ca. Microgenomatia," "Ca. Saccharimonadia," "Ca. ABY1," and "Ca. WWE3." However, only a subset of the diversity of marine sediment "Ca. Patescibacteria," especially the classes "Ca. Paceibacteria" and "Ca. Gracilibacteria," can be captured by 16S rRNA gene amplicon sequencing with commonly used universal primers. We recovered 11 metagenome-assembled genomes (MAGs) of CPR from these sediments, most of which are novel at the family or genus level in the "Ca. Paceibacteria" class and are missed by the amplicon sequencing. While individual MAGs are confined to specific anoxic niches, the lack of capacities to utilize the prevailing terminal electron acceptors indicates that they may not be directly selected by the local redox conditions. These CPR bacteria lack essential biosynthesis pathways and may use a truncated glycolysis pathway to conserve energy as fermentative organotrophs. Our findings suggest that marine sediments harbor some novel yet widespread CPR bacteria during the early diagenesis of organic matter, which needs to be considered in population dynamics assessments in this vast environment. IMPORTANCE Ultrasmall-celled "Ca. Patescibacteria" have been estimated to account for one-quarter of the total microbial diversity on Earth, the parasitic lifestyle of which may exert a profound control on the overall microbial population size of the local ecosystems. However, their diversity and metabolic functions in marine sediments, one of the largest yet understudied ecosystems on Earth, remain virtually uncharacterized. By applying cultivation-independent approaches to a range of sediment redox zones, we reveal that "Ca. Patescibacteria" members are rare but widespread regardless of the prevailing geochemical conditions. These bacteria are affiliated with novel branches of "Ca. Patescibacteria" and have been largely missed in marker gene-based surveys. They do not have respiration capacity but may conserve energy by fermenting organic compounds from their episymbiotic hosts. Our findings suggest that these novel "Ca. Patescibacteria" are among the previously overlooked microbes in diverse marine sediments.

Organic matter diagenesis and precipitation of Mg-rich carbonate and dolomite in modern hypersaline lagoons linked to climate changes

Lipid-biomarkers have been used to reconstruct environmental changes in lacustrine systems on a range of time scales. Lake sediments are excellent archives to apply these tools due to their rapid and amplified response to environmental pressures. For the past thirty years, the hypersaline lagoons of the Rio de Janeiro coastal plain have been studied as natural laboratories for the observation of the biogeochemical processes involved in modern dolomite precipitation. Here, we apply a multiproxy approach to characterize two depositional stages during the Holocene that may have triggered primary dolomite formation in these lagoonal environments. A first stage, with two sub-stages (1A − 6.1 to 4.2 kyr. BP; 1B − 4.2 to ∼3.6 kyr. BP) was deposited during the sea-level rise, with sediments containing an abundance of long-chain n-alkanes with 2H-depleted (δ2Hn-alk) signatures indicating riverine inputs of terrestrial organic carbon during prevailing wet conditions. A second stage (<∼3.6 kyr. BP), comprising lacustrine facies, was characterized by high amounts of authigenic carbonate precipitates (calcite, Mg-calcite, Ca-dolomite, and dolomite). The carbonates are the result of physico-chemical changes in the water after the isolation of the lagoons from both the Atlantic Ocean and the neighboring Lagoa de Araruama due to a fall in sea level and aridification associated with intensification of the coastal upwelling after 2.2 kyr. BP. The n-alkanes deposited during this phase contain variable proportions of long and short-chain homologues indicating a mixed source of organic matter (terrestrial higher plants and microorganisms), as well as changes in vegetation associated with the driest conditions, inferred from the 2H-enriched n-alkane homologous. These results clearly demonstrate a climatic influence on dolomite formation in coastal hypersaline environments linked to sea-level change and coastal upwelling phenomena. With these observations, we hypothesize that the existence of similar palaeoceanographic and environmental conditions in the geologic past may have triggered the formation of extensive microbial dolomite deposits. This study provides new elements to interpret the formation of massive dolomite deposits in the geological record, for example, along the Late Triassic Tethys margin.

Preliminary study of organic matter diagenesis in the Majerda delta (old and new mouths)

Preliminary study of organic matter diagenesis in the Majerda delta (old and new mouths)

The hysteresis of asphaltene-trapped saturated hydrocarbons during thermal evolution

Asphaltene-trapped (adsorbed or occluded) biomarkers are considered a valid source of information for crude oil with severe secondary alterations. However, thermal stress might change asphaltene-trapped hydrocarbons to some extent. Therefore, it is indispensable to investigate the thermal evolution behavior of asphaltene-trapped biomarkers. In this study, low-maturity bitumen from the Kuangshanliang area of the Sichuan Basin (China) was selected as a sample. The thermal evolution behavior of free and asphaltene-trapped saturated biomarkers was investigated by thermal simulation experiments. The results revealed, in addition to normal biomarkers, also a series of even carbon number n-alk-(1)-enes in asphaltene-occluded hydrocarbons. All of them were hardly influenced by secondary alterations. Moreover, due to the restriction of macromolecular structure, the thermal evolution of asphaltene-trapped biomarkers lags behind that of free biomarkers. Most biomarker parameters of occluded hydrocarbons changed little with increasing maturity. In particular, the distributions of occluded terpanes or steranes retained the characteristics of early diagenesis of organic matter, even if they suffered from strong thermal alteration.

Revisiting the Carbonate Chemistry of the Sea of Japan (East Sea): From Water Column to Sediment

In this study, we investigated the carbonate system in sediments and water columns from five stations in the Sea of Japan (East Sea) (JES) during the R/V Hakuho Maru KH-10-2 research cruise in the summer of 2010. The total alkalinity (TA) and pH were measured. Adopting a saturation degree of 91% and 80% for the lysocline depth and calcite compensation depth (CCD), respectively, we found that those depths corresponded to 1360 and 1980 m. A comparison of the calcite saturation depths, lysocline depths, and CCD depths obtained for 1999 and 2010 suggests that acidification of the interior of the JES occurred. Sediment cores were retrieved using a multi-corer. In the sediment cores, a sharp decrease in the pH by 0.3–0.4 pH units was observed in the subsurface horizons (0–10 cm) compared with the pH of the seawater from the bottom horizons. The TA in the porewaters was significantly higher than that in the overlying seawater. The anaerobic degradation of organic matter is probably the main cause for the increasing TA in the sediments. The porewaters were significantly undersaturated with calcite and aragonite, except in that from the shallowest station, where the sediments below 7.5 cm were saturated, and even supersaturated, with calcite and aragonite. A linear correlation between the dissolved inorganic carbon and the TA for sediments with a slope of 0.9993 was found, despite there being potentially different ways for the diagenesis of the organic matter to occur. The diagenesis of organic matter in the top sediments of the JES forms gradients of TA and CO2* concentrations on the interface of “bottom water–sediments”. Averaged fluxes of TA and dissolved inorganic carbon (DIC) from the sediments to the bottom waters estimated by means of Fickian diffusion were calculated as 44 and 89 mmol/(m2 year) for TA and DIC, respectively.

Effects and mechanisms of organic matter regulating the methylmercury dynamics in mangrove sediments

Mangrove ecosystems serve as an important carbon sink but also could be a hotspot that produces neurotoxic methylmercury (MeHg). Although many studies have focused on mercury (Hg) contamination in this carbon-rich ecosystem, our understanding of the effects and mechanisms of the organic matter (OM) regulation of MeHg production in mangrove sediments is still limited. Here, we examined the effects of Hg contamination and OM enrichment on MeHg production in anoxic mangrove sediments and identified the major microbial guilds attending this process. The mangrove sediments possessed a high potential for producing MeHg, but this was counterbalanced by its rapid degradation. Sulfate-reducing bacteria (SRB) such as Desulfobacterales, Desulfovibrionales, and Syntrophobacterales were the major methylators. OM diagenesis significantly changed the biogeochemical conditions, accelerating MeHg degradation in the sediments. The enhanced MeHg degradation could be attributed to the abundant sulfide produced during OM decomposition, which could potentially inhibit the Hg methylation by immobilization of inorganic Hg, abiotically degrade MeHg, and favor the non-mer-mediated degradation of MeHg by SRB. Our study provides both geochemical and microbial clues that can partly explain the low MeHg levels widely observed in mangrove sediments.

Assessment of the Physiological Groups of Bacteria from Salt Lakes and Euxinic Sediments Involved in Sulfur Cycle, Therapeutical Mud Formation, and Regeneration

The biogeochemical cycle of sulfur is important in the diagenesis of organic matter sedimented in saline and euxinic lakes leading to sapropel formation. The study aimed to determine the numerical densities of physiological groups of sulfur bacteria in water and sediment samples from five Romanian saline and euxinic lakes with therapeutical properties in order to assess their peloidogen regeneration potential. Bacterial communities that metabolize sulfur compounds were monitored in lakes with different salinity values: Techirghiol, Amara, Sovata-Black Lake, Ursu Lake, and Braila Salt Lake by multiple tube method. Statistical results revealed the interdependence between sulfoxidizing bacteria/SO42- in sediments, while the reductive microorganisms fraction/metabolic products (H2S/Corg./Norg) separately evolved in the economy of peloidogenic ecosystems. In the lakes, Techirghiol, Amara, and Braila Salt Lake, the dominant role in the specific microbiota belonged to sulfate/sulfur-reducing bacteria, and the formed peloid was sulfurous-sapropelic in Techirghiol Lake or sulfurous-mineral in Amara Lake and Braila Salt Lake. In the hypersaline, meromictic, and heliothermal lakes of Sovata, the sulfur metabolism was predominantly oxidative, made by sulfoxidizing bacteria in higher numerical densities, with the accumulation of SO42- ions in the strongly hydrated aqueous phase of mineral sediments.

Organic Matter Redox State Driven by Specific Sources in Mangrove Sediments: A Case Study from Peruvian Ecosystems

In order to determine the organic matter redox state in relation to specific sources in mangrove sediments, two 60 cm-long sediment cores were collected from mangrove-covered and mudflat zones within a mangrove forest in Peru. Sediment subsamples from these cores were analyzed to determine δ13C values and C:N ratios, whereas two redox indices, namely, electrochemical (fEAOM) and spectroscopical (A1650/A3400) indices, were taken from a previous study and correlated with the geochemical indices obtained from this work. These indices may provide accurate information on sedimentary organic matter diagenesis by oxidative processes through its redox state. The results show that the electrochemical index (fEAOM) and the spectroscopical index (A1650/A3400) for mangrove-covered sediments exhibited a positive correlation with δ13C values and a negative correlation with C:N molar ratios. These correlations suggest that the more labile sedimentary organic matter derived from non-terrestrial sources is in a more oxidized state than that derived from mangrove vegetation. However, this was not valid for mudflat zones, where non-significant correlations between geochemical indices were observed. Furthermore, the results suggest that the redox state of the organic matter deposited over time is dependent on source mixing influences, being better preserved in the presence of mangrove-derived organic matter.

Petrophysical properties of a siltstone reservoir - An example from the Montney Formation, western Canada

The detrital grain size of siltstone reservoirs occupies a middle ground between sandstones and shales, both of which are better understood in terms of their petrophysical properties. Because siltstones can be important hydrocarbon reservoirs, we examine controls on petrophysical properties in the Lower Triassic Montney Formation in western Canada, which hosts world-class reserves of gas, gas liquids and oil. We focus on the effects of rock fabric (including grain size) and composition on pore system characteristics and permeability, drawing contrasts between the three reservoir types.The Montney Formation is an unconventional reservoir through most of its subcrop, with porosities ranging from ∼3 to 7.5% and permeabilities in the micro to nano Darcy range (6.5*10−6 mD to 5.6*10−2 mD). Shale reservoirs worldwide are characterized by similar porosity and permeability values, with porosity of up to 8% (rarely up to 15%) and permeability in the nano to micro-Darcy range.Quartz, clay, and organic matter abundance influence the petrophysical properties of the Montney siltstone. Quartz content exerts a positive control on both porosity and permeability by strengthening the rock framework and reducing porosity loss due to compaction. Elevated clay content is also associated with higher porosity and permeability, in part because of a depositional association with quartz, and in part because clays locally shelter interconnected primary porosity that promotes permeability. Organic matter content is negatively correlated to porosity and permeability despite the presence of organic matter porosity because relict oil (now solid bitumen) occludes primary pores and because other pore types contribute a greater fraction of the total pore volume. Lithofacies, characterized in four cores, are indistinguishable on the basis of petrophysical properties, due to their similar grain size and composition and the massive overprinting by shallow burial diagenesis.While the pore system evolution of sandstones is mainly controlled by the mechanical compaction of hard grains and cementation, pore system evolution of shales is primarily controlled by compaction of ductile grains and diagenesis of primary organic matter, in addition to cementation. Porosity and permeability values of the Montney siltstones are similar to those of shale formations, but the controls on pore system evolution of this intermediate grain size reservoir are predominantly controlled by processes similar to sandstones: compaction, cementation, and cement dissolution. Minor contribution from secondary porosity in bitumen affects some sections of the reservoir in a way that is similar, but not identical, to shale reservoirs.

Geochemical Characteristics and Origin of Formation Water From the Upper Triassic Xujiahe Tight Sandstone in the Xiaoquan-Fenggu Structural Belt, Western Sichuan Depression, China

Formation water represents an important driving force and carrier for the migration and accumulation of oil and gas; thus, research on its origin is a hot spot in petroleum geology. The Upper Triassic Xujiahe Formation in the Xiaoquan-Fenggu Structural Belt in the western Sichuan Depression, China, has developed thick tight sandstone gas reservoirs. However, previous studies have provided different conclusions on the origin of the formation water in the Xujiahe tight sandstone reservoir. In this paper, the origin of the formation water in the Xujiahe Formation was determined based on the latest major and minor elemental concentration data, hydrogen and oxygen isotopes data of formation water, and carbon and oxygen isotope data of carbonate cements. The results show that the salinity of the formation water of the Xujiahe Formation in the study area is generally greater than 50 g/L. The water type is mainly the CaCl2 type, although a small proportion of NaHCO3 type water with high salinity is observed, which is related to hydrocarbon expulsion by overpressure. Moreover, the formation water in the sandstone of the Xujiahe Formation is obviously rich in Br, which is related to membrane infiltration, overpressured hydrocarbon expulsion of shale and diagenesis of organic matter. The composition of Cl− and Na+ ions in the formation water in the Xujiahe tight sandstone reservoir is consistent with the seawater evaporation curve, which deviates significantly from the freshwater evaporation curve. The hydrogen and oxygen isotopes of condensate water in the Xujiahe Formation tight sandstone are similar to those of atmospheric precipitation water, while the hydrogen and oxygen isotopes of the formation water in the Xujiahe Formation show that it is of seawater origin. Therefore, to use hydrogen and oxygen isotopes to determine the origin of formation water, condensate water must be accurately differentiated from formation water. Otherwise, if the condensate water is misjudged as formation water, then incorrect conclusions will be drawn, e.g., that the formation water of the Xujiahe Formation originated from fresh water. Affected by organic carbon, the carbon isotope Z value of the carbonate cements in the Xujiahe Formation is low (mainly distributed between 110 and 130). A Z value of less than 120 does not indicate that the ancient water bodies formed by cements were fresh water or mixed water bodies. However, Z values greater than 120 correspond to a formation temperature lower than 80 C, which indicates that carbonate cement was not affected by organic carbon; thus, the Z value can reflect the origin of ancient water bodies. The results of this study indicate that the formation water of the Xujiahe tight sandstone in the study area is of seawater origin. The determination of the origin of the formation water and seawater of the Xujiahe Formation provides strong evidence for the determination of the marine sedimentary environment of the Xujiahe Formation in the study area, and can provide scientific guidance for the search for high-quality reservoirs.

Sulfate reduction and its important role in organic carbon mineralization in sediments of the Pearl River Estuary

The sulfate reduction process plays an important role in the early diagenesis of organic matter in the estuarine and coastal sediments. In this study, the sulfate reduction rates (SRR) were determined by the 35SO42− radioactive tracer method, and the SO42−, CH4, Cl− of sediment porewater and total organic carbon (TOC), temperature, and redox potential (Eh) of sediment were determined simultaneously at three stations (QA, HQ, and GS) in different sedimentary environments of the Pearl River Estuary to study the sulfate reduction process and its important role in organic matter mineralization. The results show that SRR was mainly controlled by the content and availability of organic matter in sediments of the Pearl River Estuary. The consumption of sulfate mainly included the organic matter mineralization on the upper sediments and the anaerobic oxidation of methane (AOM) driven by sulfate in the sulfate-methane transition zone (SMT), which formed two peaks in the SRR profile, respectively (stations HQ and GS). Affected by physical disturbance, there was only one SRR peak formed above the SMT at station QA. The results of flux calculations for AOM and sulfate reduction show that the contributions of AOM to total sulfate reduction were 7.04 %, 5.46 %, and 42.0 % at stations QA, HQ, and GS, respectively, which were also controlled by the content and availability of organic matter in sediments. The depths of SMT in sediments of stations QA, HQ, and GS were 25, 30, and 213 cm, respectively, which were controlled by the input of organic matter and sulfate concentration in sediments. The calculation results show that total fluxes of sulfate reduction were 22.7, 35.3, and 3.9 mmol m−2 d-l at stations QA, HQ, and GS, respectively, and the rates of organic carbon mineralization by sulfate reduction were 45.4, 70.6, and 7.8 mmol m−2 d-l. In the estuarine mouth (station GS) with relatively weak hydrodynamic force and deep water, the burying efficiency of organic matter in sediment was higher than that in the brackish coast (station HQ); whereas the burial efficiency of organic matter in sediment cannot be comprehensively estimate in the upper estuary (station QA) due to the existence of the fluid mud layer. These findings contribute to a comprehensive understanding of the biogeochemical cycling process of sulfate and methane in sediments of the Pearl River Estuary.

Modeling Small Scale Impacts of Multi-Purpose Platforms: An Ecosystem Approach

Aquaculture and marine renewable energy are two expanding sectors of the Blue Economy in Europe. Assessing the long-term environmental impacts in terms of eutrophication and noise is a priority for both the EU Water Framework Directive and the Marine Strategy Framework Directive, and cumulative impacts will be important for the Maritime Spatial Planning under the Integrated Maritime Policy. With the constant expansion of aquaculture production, it is expected that farms might be established further offshore in more remote areas, as high-energy conditions offer an opportunity to generate more power locally using Marine Renewable Energy (MRE) devices. A proposed solution is the co-location of MRE devices and aquaculture systems using Multi-Purpose Platforms (MPPs) comprising offshore wind turbines (OWTs) that will provide energy for farm operations as well as potentially shelter the farm. Disentangling the impacts, conflicts and synergies of MPP elements on the surrounding marine ecosystem is challenging. Here we created a high-resolution spatiotemporal Ecospace model of the West of Scotland, in order to assess impacts of a simple MPP configuration on the surrounding ecosystem and how these impacts can cascade through the food web. The model evaluated the following specific ecosystem responses: (i) top-down control pathways due to distribution changes among top-predators (harbor porpoise, gadoids and seabirds) driven by attraction to the farming sites and/or repulsion/killing due to OWT operations; (ii) bottom-up control pathways due to salmon farm activity providing increasing benthic enrichment predicated by a fish farm particle dispersal model, and sediment nutrient fluxes to the water column by early diagenesis of organic matter (recycled production). Weak responses of the food-web were found for top-down changes, whilst the results showed high sensitivity to increasing changes of bottom-up drivers that cascaded through the food-web from primary producers and detritus to pelagic and benthic consumers, respectively. We assessed the sensitivity of the model to each of these impacts and the cumulative effects on the ecosystem, discuss the capabilities and limitations of the Ecospace modeling approach as a potential tool for marine spatial planning and the impact that these results could have for the Blue Economy and the EU’s New Green Deal.

Source rock maturity evaluation and its implications for regional petroleum charge, Sirt Basin, Libya: Insights from regional geochemical assessments and modelling study

Six marine and lacustrine source rocks were studied to define their thermal maturation levels in the largest, youngest, and most productive petroliferous sedimentary basin in Libya (Sirt Basin). From the oldest to the youngest, the studied source rock formations were: 1) Middle Nubian; 2) Etel; 3) Rachmat; 4) Sirte; 5) Kalash; and 6) Hagfa. The calibrated basin modelling studies (1D, 2D, and 3D) were used to generate regional maturation maps for each source rock in the basin. Thermal maturity calibration was carried out at different levels utilising measured and simulated vitrinite reflectance (VRo), pyrolysis Tmax data, and 39 typical wells for burial history modelling and geochemical screening. Corrected bottom hole temperature data were used to obtain the geothermal gradient and heat flow throughout the basin. The thermal gradient and heat flow analyses results indicated that the Sirt Basin has an average geothermal gradient of approximately 1.58 °F/100 ft and an average heat flow of 72 m.W.m−2 with a systematic heat flow increase toward the basin platforms and a decrease toward the basin troughs. The conducted assessments in the Sirt Basin presented different levels of source rocks thermal maturity due to variable burial depths, with an average VRo range of 0.35%–2%. The lower Cretaceous source rocks were subjected to higher degrees of diagenesis of organic matter (i.e. mid-to over-mature rocks), with an average VRo of 0.9%–2%. In contrast, the Upper Cretaceous source rocks demonstrated a wide range of thermal maturity (from marginally to late mature) in the deepest part of the Sirt Basin (Ajdabiya trough), whereas the late Palaeocene source rocks entered the mid-to late-maturity levels in the Wadayet trough (North Ajdabiya trough).

Organic Carbon and Carbonate System in the Bottom Sediments of Shallow Bights of the Peter the Great Bay (Sea of Japan)

Abstract—The diagenesis of organic matter (OM) is studied in bottom sediments taken in February, 2018 from therapeutic mud deposits of the Uglovoi Bay and Voevoda and Ekspeditsiya bights (Peter the Great Bay, Sea of Japan). The carbonate system of bottom sediments and pore water were analyzed for the contents of nutrients, dissolved organic carbon, humic substance, and concentrations of sulfates and chlorides. The concentrations of organic carbon, chlorophyll-a, humic and fulvic acids, and mobile sulfide species are measured in a solid phase of sediment. Underwater photographing shows that sampling localities are covered by Zostera marina meadows in the Voevoda and Ekspeditsiya bights and by diatom mats in Uglovoi Bay. The proportions between dissolved inorganic carbon and alkalinity, as well as data on sulfate–chlorine ratios and mobile sulfide species indicate that the OM degradation in bottom sediments is mainly controlled by sulfate reduction. The Uglovoi Bay and Voevoda and Ekspeditsii bights are characterized by different values of bioturbation coefficients: 3.0, 107.6, and 14.5 cm2/day, respectively. The estimated fluxes of organic carbon from water into sediment and of dissolved inorganic carbon from sediment into water significantly differ. The disbalance between organic and inorganic carbons can be caused by the following reasons: (a) ignored CO2 flux released by marine organisms from bottom sediments through their siphonal system; (b) partial OM consumption in food with its subsequent deposition in it.