Preservation Of Organic Matter Research Articles

Controlling Factors of Organic Matter Enrichment in Marine–Continental Transitional Shale: A Case Study of the Upper Permian Longtan Formation, Northern Guizhou, China

The marine–continental transitional shale of the Upper Permian Longtan Formation in northern Guizhou is an important source rock in the upper Yangtze region of China, and it holds significant potential for the exploration of shale gas. To investigate the correlation between sedimentary conditions and the accumulation of organic matters in marine–continental transitional shale, this paper performed an extensive analysis using organic geochemical testing, organic petrology examination, a cross-section polisher–scanning electron microscope (CP-SEM), and geochemical analysis. The Jinsha and Dafang drilling cores were selected as the research subjects. The results showed that the TOC of the Longtan Formation in the study area was relatively high, and the TOC content of the tidal flat–lagoon environment (average of 8.37%) was significantly higher than that of the delta samples (average of 2.77%). The high content of Al2O3 (average of 17.41% in DC-1, average of 16.53% in JC-1) indicated strong terrigenous detrital input. The proxies indicated that the Longtan Formation shale in northern Guizhou was deposited in a climate that was both warm and humid, with oxic–dysoxic sedimentary water characterized by high biological productivity and a rapid sedimentation rate. The organic-rich shales during the marine and continental transitional phases were affected by various factors, including the paleo-climate, water redox properties, paleo-productivity, sedimentation rate, and other variables, which directly or indirectly impacted the availability, burial, and preservation of organic matter.

Biochar – a sustainable soil conditioner for improving soil health, crop production and environment under changing climate: a review

Land degradation and climate change, two intricately intertwined phenomena, demand appropriate management solutions to effectively tackle the escalating issues of food and nutritional security. In this context, the realm of agriculture confronts formidable challenges in its pursuit of soil resource reclamation, improving water quality, mitigating climate change, and maintaining soil and natural resources for posterity. Central to these aspirations is the preservation of an optimum organic matter, serving as a linchpin threshold is crucial for protecting the physical, chemical, and biological integrity of the soil, while simultaneously sustaining agricultural productivity. To address these multifaceted challenges, the introduction of diverse organic amendments has emerged as a crucial strategy. Noteworthy among these is the application of biochar, which functions as a soil conditioner capable of bolstering soil health, mitigating the impact of climate change, and securing global food security. Biochar is a carbon-enriched substance produced through pyrolysis of assorted biomass waste. It has a larger surface area, higher cation exchange capacity, and an extended carbon storage capability. The strategic integration of biochar production and subsequent soil application engenders an array of benefits, encompassing the amelioration of soil physical properties, augmented retention and the availability of nutrients, and the enhancement of biological activity, resulting in higher agricultural yields and societal benefits through the curtailment of soil to atmosphere greenhouse gas emissions. Additionally, biochar demonstrates its efficacy in the realm of environmental restoration by serving as a medium for extraction and elimination of heavy metals, which often pervade aquatic ecosystems and soil matrices. This review addressed the need for biochar production, characterization, soil health, the possibility for environmental restoration, and crop yield fluctuations owing to climate change.

The relationship between total organic carbon and bottom water redox state in North American black shales

It is clear from modern analogue studies that O2-deficient conditions favor preservation of organic matter (OM) in fine-grained sedimentary rocks (black shales). It is also clear that appreciable productivity and OM flux to the sediment are required to establish and maintain these conditions. However, debates regarding redox controls on OM accumulation in black shales have mainly focused on oxic versus anoxic conditions, and the implications of different anoxic redox states remain unexplored. Here, we present detailed multi-proxy sedimentary geochemical studies of major Paleozoic and Mesozoic North American black shale units to elucidate their depositional redox conditions. This is the first broad-scale study to use a consistent geochemical methodology and to incorporate data from Fe-speciation – presently the only redox proxy able to clearly distinguish anoxic depositional conditions as ferruginous (H2S-limited) or euxinic (H2S-replete, Fe-limited). These data are coupled with total organic carbon (TOC), programmed pyrolysis, and redox-sensitive trace element proxies, with almost all measurements analyzed using the same geochemical methodology. Consistent with expectations based on previous geochemical and paleontological/ichnological studies, these analyses demonstrate that the study units were almost exclusively deposited under anoxic bottom waters. These analyses also demonstrate that there is wide variance in the prevalence of euxinic versus ferruginous conditions, with many North American black shale units deposited under predominantly ferruginous or oscillatory conditions. TOC is significantly higher under euxinic bottom waters in analyses of both preserved (present day) TOC and reconstructed initial TOC values, although sediments deposited under both redox states do have economically viable TOC content. While this correlation does not reveal the mechanism behind higher organic enrichment in euxinic environments, which may be different in different basins, it does open new research avenues regarding resource exploration and the biogeochemistry of ancient reducing environments.

Paleoceanographic Significance of Calcareous Nannofossil Assemblages in the Tropic Shale of Utah during Oceanic Anoxic Event 2 at the Cenomanian/Turonian Boundary

Oceanic Anoxic Event 2 (OAE2) at the Cenomanian/Turonian Boundary (CTB: 93.9Ma) involved the global deposition of organic carbon-rich sediments, a distinctive positive shift in carbon isotope values, and significant species turnover, including changes in calcareous nannofossil assemblages. While it is thought that volcanism triggered organic C-rich sediment deposition during OAE2, it is unclear whether enhanced productivity, increased stratification, of some combination of the two increased organic matter preservation. Calcareous nannofossil assemblages have the potential to qualitatively assess changes in ocean nutrient and temperature conditions to disentangle such ecological dynamics during OAE2. Here we study an expanded section of the Tropic Shale in a drill core in southern Utah near the western margin of the Western Interior Seaway (WIS) to understand how circulation changed during the event and how this may have influenced primary productivity and organic carbon burial. Relative abundance data of well-preserved nannoplankton are complemented with measurements of trace metal, and organic carbon and carbonate concentrations to determine changes in temperature and water column structure, as well as controls on surface water productivity. Detailed statistical analysis helps refine species paleoecologies combined with information from planktic and benthic foraminiferal assemblages and organic biomarkers. Changes in calcareous nannofossil assemblages indicate that near the start of OAE2 the western WIS surface ocean actually cooled for a short time. Following this, surface waters became warmer and more stratified as a Tethyan water mass invaded the seaway. Assemblages suggest that warmth persisted for much of the OAE2 interval, while stratification waxed and waned. The local seaway cooled near the end of OAE2 as Boreal water masses streamed along the western margin. Variations, including the decrease in the abundance of Biscutum constans and short-lived peaks in the abundance of Eprolithus spp. are super regional or possibly global in extent. There is no correlation between calcareous nannofossil assemblages and trace metal concentrations, suggesting they were unaffected by volcanism-related nutrient inputs. Assemblages support other data that suggest increased stratification influenced organic carbon burial in the Western Interior Seaway, and possibly elsewhere, during OAE2.

Geochemical Modeling and Hydrocarbon Generation Potentiality of Source Rocks of the Oligocene to Miocene Succession in the Temsah Area, Eastern Nile Delta, Egypt

Geochemical investigation of the Temsah-4 well (T-4) in Temsah gas fields at the eastern offshore Nile Delta differentiate into two categories of OM (organic matter) which are kerogen types II and III within the boreholes penetrated Oligocene-Miocene source rocks. The geochemical and lithological characteristics of the OM-bearing formations in the investigated borehole recognized four thick organic matter-rich intervals (OMRI) in well T-4. The OMRI considers a part of formations that are believed to be considered a real source rock that comprises approximately 66.68% of the Wakar, 65.17% of Sidi-Salem, and 100% of Qantara Fms in the T-4 well. They comprised intervals depths of 3120m-3150m and 3300m-3559.4m belonging to Wakar Fm, from 3580m- 3870m belonging to Sidi-Salem Fm and from 3977m- 4170m belonging to Qantara Fm. The geochemical data reveals that Wakar Fm in the T-4 well considers immature source rock. While mature OMRI within Sidi-Salem and Qantara Fms in the T-4 well represented as effective mature source rocks. Construction of a TOC map in two dimensions throughout the studied areas shows a trend of increasing the quantity of OM eastward during the deposition of Sidi-Salem and Wakar Fms. The improvements of the richness (relatively high TOC) toward the eastward suggested a favorable condition for preservation and accumulation of OM toward the east than the west drilled boreholes. Based on the relative hydrocarbon potential (RHP) the suggested expulsion threshold depths appear to be shallower at 3700m in T-4. Burial history diagrams of studied T-4 wells based on geochemical results postulate that Tineh Fm enters the early mature stage at 2.8Ma. The maturity continues till the recent periods to enter the Qantara and most of Sidi-Salem Fms the same main-oil window at the T-4 area.

The source and preservation of lacustrine shale organic matter: Insights from the Qingshankou Formation in the Changling Sag, Southern Songliao Basin, China

Organic-rich shale in the Cretaceous succession of the large non-marine Songliao Basin in northeastern China, especially the Qingshankou Formation of the Turonian and Coniacian stages, provides a unique record for studying the role of global climate control on organic matter accumulation. Organic enrichment in the Qingshankou Formation along the Southeastern Uplift of the basin has been widely reported and is implicated in the formation of algal blooming and a saline anoxic water environment. However, studies on the Qingshankou Formation in the Changling Sag are relatively few, which leaves a significant gap to understand the controlling factors of organic enrichment at a basin scale. In this study, the sedimentary environment of the first member of the Upper Cretaceous Qingshankou Formation (K2qn1) is reconstructed from petrological and geochemical data to discuss the sources and preservation mechanisms of lacustrine shale organic matter in the Changling Sag (southern Songliao Basin). The K2qn1 is subdivided into three stratigraphic units: Sq1 phase, Sq2 phase, and Sq3 phase. Biomarker (abundance of tricyclic terpane and regular steranes) and petrographical (maceral composition) data indicate that the organic matter in K2qn1 was mainly from terrigenous plants, with some algal input. Inorganic minerals (major and trace elements) and petrological (framboidal pyrite size) data suggest a humid climate and saline anoxic water environment at the Changling Sag during the most organic-rich Sq1 phase. During the Sq2 and Sq3 phases, a relative low lake level and semi-arid climatic conditions likely prevailed. Moreover, these results imply that apart from a saline anoxic water environment, the persistence of continentally derived organic matter in lacustrine shale is mainly controlled by clay minerals. Accordingly, this study proposed a new enrichment model for lacustrine shale organic matter. The new model complements existing lacustrine shale sedimentary models for sources of organic matter and emphasizes the role of clay minerals in preserving organic matter.

Origin and Formation Mechanism of the Late Permian Black Siliceous Rocks in the Lower Yangtze Region.

The Late Permian witnessed a Permian Chert Event (PCE) and distinctive oceanic geochemical fluctuations, such as an ocean acidification event, large-scale volcanic eruption, and rapid global warming. However, the links between siliceous rock formation mechanism, ocean, and climate changes are rarely discussed. In this article, two well-preserved deeper-water sections of the Dalong Formation from the Lower Yangtze region in southeast China are selected for analysis. To document the coeval oceanic changes, we present thin section authentication, scanning electron microscope (SEM) observation, and multiple geochemical proxies, including total organic carbon contents (TOC), major element contents, trace element contents, and rare earth element contents (REEs). The results show that siliceous rocks are mainly of biological origin in this region. The low content of MgO (0.10-0.94%, mean = 0.36%) in the Fantiansi section of Tongling area indicates that it is affected by regional hydrothermal fluids. The correlation between Al2O3/TiO2, Al2O3 versus SiO2 /Al2O3, and TiO2/ΣREEs indicates that the Late Permian was greatly influenced by the continuous input of terrigenous materials. The correlations of MnO/TiO2, LaN/CeN, Ce/Ce*, and LREE/HREE imply that the Dalong Formation siliceous rocks were deposited in a continental margin setting. Redox geochemical data (EFU, EFMo, and EFV) imply the water column experienced widespread anoxic/euxinic during the Late Permian, which aided in the preservation of organic matter following biological decay. The accumulation of siliceous rocks is related to South China experiencing a hot tropical climate, coastal upwelling and continental weathering-enriched marine nutrients, fostering high primary productivity, and benefiting abundant siliceous zooplankton. Volcanic and regional hydrothermal activity further enhanced nutrient flux, and the simultaneous ocean acidification event provided favorable chemical conditions for the preservation of silica, leading to the formation of siliceous rocks in the Dalong Formation.

Constraints on hopanes and brGDGTs as pH proxies in peat

pH is one of the major parameters governing peat functioning, and pH variations in modern peatlands affect carbon and methane production and consumption. Paleo-pH reconstructions have been limited thus far, but they could help to better understand peat functioning in variety of settings and also serve as an indirect proxy for climatic and environmental variations such as precipitation. Bacterial hopanes and branched Glycerol Dialkyl Glycerol Tetraethers (brGDGTs) were investigated in a 10-ka peat record from North-East Cameroon (NGaoundaba, Western Central Africa). Recently developed pH proxies using the hopane ββ/(αβ + ββ) ratio and the brGDGT cyclization ratio (CBTpeat) were applied and compared with previously published bulk organic data from the same core. Different hypotheses are usually proposed to explain the high abundance of the “thermally mature” C31 αβ hopane in peats: acid-catalyzed isomerization of ββ to αβ isomers with or without biological mediation or the direct input of C31 αβ hopanes by bacteria. In the NGaoundaba peat deposit, the opposite variation in the ββ/(αβ + ββ) ratio of C30 and C31 hopanes and the carbon isotopic composition of C31 ββ and αβ hopanes suggest that an eventual transformation of C31 ββ to αβ isomers is not possible without biological mediation. A linear correlation between hopane- and brGDGT-reconstructed pH is observed, suggesting a similar response to environmental changes for these two independent proxies. A large increase in reconstructed pH values coincides with changes in vegetation and precipitation at the end of the African Humid Period (AHP). Lower pH values are observed during the AHP, coinciding with a period of increased precipitation and consistent with bulk organic data and slightly higher C31 ββ hopane δ13C values compared to middle and late Holocene. Bulk organic data indicate an interruption of the AHP by a drier intermission that coincides with a decrease in reconstructed pH values, probably reflecting a decrease in evapotranspiration. Variations in pH values could be interpreted in terms of preservation of peat organic matter and might reflect past changes in methane cycling in the investigated peatland. The present study reinforces the idea that reconstruction of pH in peat deposits represents a promising proxy of environmental change, enabling a better understanding of changes in peat functioning over large timescales and various locations.

Multiple enrichment mechanisms of organic matter in the Fengcheng Formation of Mahu Sag, Junggar Basin, NW China

Based on core and thin section data, the source rock samples from the Fengcheng Formation in the Mahu Sag of the Junggar Basin were analyzed in terms of zircon SIMS U-Pb geochronology, organic carbon isotopic composition, major and trace element contents, as well as petrology. Two zircon U-Pb ages of (306.0±5.2) Ma and (303.5±3.7) Ma were obtained from the first member of the Fengcheng Formation. Combined with carbon isotopic stratigraphy, it is inferred that the depositional age of the Fengcheng Formation is about 297–306 Ma, spanning the Carboniferous–Permian boundary and corresponding to the interglacial period between C4 and P1 glacial events. Multiple increases in Hg/TOC ratios and altered volcanic ash were found in the shale rocks of the Fengcheng Formation, indicating that multiple phases of volcanic activity occurred during its deposition. An interval with a high B/Ga ratio was found in the middle of the second member of the Fengcheng Formation, associated with the occurrence of evaporite minerals and reedmergnerite, indicating that the high salinity of the water mass was related to hydrothermal activity. Comprehensive analysis suggests that the warm and humid climate during the deposition of Fengcheng Formation is conducive to the growth of organic matter such as algae and bacteria in the lake, and accelerates the continental weathering, driving the input of nutrients. Volcanic activities supply a large amount of nutrients and stimulate primary productivity. The warm climate and high salinity are conducive to water stratification, leading to water anoxia that benefits organic matter preservation. The above factors interact and jointly control the enrichment of organic matter in the Fengcheng Formation of Mahu Sag.

Depositional Model and Controlling Factors of High-Quality Shales of the Wufeng and Longmaxi Formations in Western Chongqing, Sichuan Basin, China.

The enrichment of organic matter is the foundation for a high-quality shale deposition. It is generally believed that high productivity and persistent anoxic conditions facilitate the preservation and enrichment of organic matter. However, there is a lack of investigation into how the dynamic combination of productivity and anoxia affects organic matter enrichment. Here, the black shales of the Wufeng Formation and Longmaxi Formation in the western Chongqing area were selected, where oceanic anoxia and high productivity evolved as a function of the water depth. The main findings were as follows: (1) the distribution of high-quality shales in the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation is closely related to the oxygen minimum zone (OMZ), indicating that the physicochemical conditions within the OMZ zone facilitated the development of high-quality shale; (2) in the late period of the Wufeng Formation, intense ocean upwelling in the middle shelf and outer shelf regions caused high productivity where thick-bedded high-quality shales were deposited; and (3) in the early period of the Longmaxi Formation, ocean upwelling weakened, accompanied by the expansion of the OMZ to shallow water regions, and high-quality shales were widely distributed. Based on the above findings, two depositional models were proposed to account for the formation of high-quality shales, and it is suggested that intense ocean upwelling during the late period of the Wufeng Formation and OMZ expansion during the early period of the Longmaxi Formation played crucial roles in facilitating the formation of high-quality shales. These two models present the spatial and temporal variability of high-quality shale development for the first time and can guide shale gas exploration and development strategies.

Environmental conditions in the Massif Central during the Upper Palaeolithic using stable isotope tracking (13C, 15N) of bone collagen from large herbivores

ABSTRACTThe environmental conditions experienced by hunter‐gatherers during the second part of the Upper Palaeolithic (ca. 28 000–15 000 cal bp) are poorly known in the mid‐elevation volcanic mountains of the Massif Central in southern France. The stable isotope ratios of carbon and nitrogen (13C/12C and 15N/14N expressed as δ13C and δ15N values) in bone collagen of large herbivores can track their diet and habitat, reflecting local abiotic conditions (temperature, aridity, altitude). Due to poor preservation of skeletal organic matter in the region, new radiocarbon dating was conducted on a limited number of quality‐controlled collagen samples, based on a minimum carbon content of 30%. They document three main phases of occupation corresponding to the Final Gravettian, the Badegoulian and the Magdalenian, each of which is represented in different regions of the Allier and Loire valleys. Over time, a decrease in horse δ15N values, the best documented species of large herbivores, is found between the Final Gravettian (ca. 26 700–25 600 cal bp), around the Last Glacial Maximum and the Badegoulian (ca. 21 900–19 200 cal bp), followed by an increase in δ15N and δ13C values during the Magdalenian (ca. 19 100–16 600 cal bp). During the Badegoulian, the δ15N values of the horses were lower than those of their counterparts in southwestern France, testifying to harsh climatic conditions favourable to a tundra‐like landscape, also reflected in the higher horse and reindeer δ13C values in the Allier valley compared to those in southwestern France. The relatively high δ13C and low δ15N values of a Final Gravettian wolf from the Allier valley suggests reindeer as a preferred prey, in line with their high abundance in the archaeological sites. Game access, rather than climatic conditions or lithic resources, seems to have motivated human groups to occupy the Massif Central during the Upper Palaeolithic.

Organic Petrologic Characterization and Paleoenvironmental Analysis of Permian Shale in Northeast Sichuan Province, China

The Permian shale in Northeast Sichuan is an important shale oil and gas resource potential area, and the study of its organic matter characteristics and paleoenvironmental analysis is of great significance for revealing the shale oil and gas formation mechanism and resource evaluation. In this study, the organic matter of Permian shales in northeast Sichuan was carefully studied based on various analytical tools, such as petrology, laser Raman, microscopy, and principal trace elements, and the paleoenvironmental parameters of the shales were comprehensively analysed. A detailed study of the organic matter characteristics of Permian shales in northeast Sichuan reveals important features such as organic matter fractions, structural characteristics, maturity and sources. The results show that the organic matter of the shale consists mainly of solid bitumen, putrescine group, specular group and multicellular planktonic algae. Petrological observations and laser Raman analyses indicate a high maturity of the organic matter and a high content of organic carbon (TOC), showing good hydrocarbon potential. In this study, we reconstructed the palaeoenvironmental parameters and inferred the palaeoenvironmental evolution through palaeoenvironmental analyses of Permian shales in northeast Sichuan. The results of the comprehensive multi-indicator study show that the type of palaeoenvironment at the time of shale deposition was mainly an anoxic-reducing environment, and the depositional conditions were favourable to the enrichment and preservation of organic matter. In summary, the organic matter characteristics and paleoenvironmental analyses of the Permian shales in Northeast Sichuan provide important geological background information for an in-depth understanding of the formation mechanism, exploration potential and development prospect of shale hydrocarbons in this area. The results of this study can provide a scientific basis for the evaluation and development of shale oil and gas resources in this area, which is of great significance to geologists and the energy industry.

Organic matter preservation through complexation with iron minerals in two basins of a dimictic boreal lake with contrasting deep water redox regimes

The biogeochemical cycles of iron and organic carbon (OC) are closely interconnected in terrestrial and aquatic systems. In ocean waters, the concentration of reactive Fe is tightly controlled by soluble organic ligands. In soils, Fe stabilizes OC by forming aggregates that shield OC from degradation. In lake sediments however, the role of Fe in the preservation of OC has not been explored as extensively yet. We investigated Fe-OC interactions in sediment collected from Lake Tantaré, in which two basins are characterized by contrasting redox conditions. These contrasting redox conditions provide an opportunity to assess their importance in the formation of stable Fe-OC complexes. On average, 30.1 ± 6.4 % of total OC was liberated upon reductively dissolving reactive iron. The Fe-associated and the non-Fe-associated OC pools were characterized at the elemental (OC, TN), isotopic (δ13C, δ15N) and functional group (FTIR) levels. Large differences in OC:Fe and TN:Fe ratios between the two basins were found which were not linked to OM chemical composition but rather to differences in reactive iron concentrations stemming from the higher abundance of iron sulfides in the anoxic basin. Nevertheless, since the affinity of OM for iron sulfides is lower than that for iron hydroxides, using OC:Fe and TN:Fe ratios as a diagnostic tool for the type of OM-Fe interactions should be done with care in anoxic environment. Same caution should be considered for oxic sediments due to the variation of the proportion of iron hydroxides associated with OM from sample to sample.

Palynological, palynofaciological and organic geochemistry analysis of oligocene microclastics sediments from the tremembé formation - São Paulo State, Brazil

Samples of outcrops from the mining companies Extrativa Santa Fé Ltda and Aligra - Indústria e Comércio de Argila Ltda provided the base material for this investigation into palynological, palynofaciological and organic geochemistry analyses of the Taubaté Basin, São Paulo State. The sediments belong to the Tremembé Formation and comprise microclastic rocks. The Tremembé Formation is known for its rich fossil record and clay mineral content, widely used as raw material for various industrial processes. The generating potential of the sediments was evaluated through qualitative and quantitative analyses of organic content, percentage of total organic carbon (TOC), and Rock-Eval pyrolysis.Furthermore, using transmitted light optical microscopy, observation of the palynological content allowed the identification of characteristic species in terms of age and thermal maturation through the Spore Color Index (SCI) and depositional paleoenvironment.Palynofacies were individualized via reflected light optical microscopy, and together with Rock-Eval pyrolysis data, the quality and type of kerogen were determined. The organic content of the two mining companies shows a predominance of amorphous, globose, and dispersed organic matter of lacustrine origin. Moreover, it is composed mainly of the genera Botryococcus and Pediastrum algae. Palynological associations allowed the section to be temporally positioned in the Oligocene.The abundance of bisaccate pollen grains attributable to conifers, represented mainly by the species Podocarpidites marwickii and Dacrydiumites florinii, combined with the presence of spores, suggests a temperate paleoclimate with humid niche conditions. The pyrolysis results and microscopic observation of the organic content in fluorescence mode show that deposition occurred under anoxic conditions, allowing better preservation of organic matter with high potential for generating hydrocarbons.

Investigating organic sulfur in estuarine and offshore environments: A combined field and cultivation approach

Estuarine-offshore sediments accumulate substantial particulate organic matter, containing organic sulfur as a key component. However, the distribution and sources of organic sulfur in such environments remain poorly understood. This study investigated organic sulfur in the Yangtze River Estuary and adjacent East China Sea. Dissolved organic sulfur varied from 0.65 to 1.99 μmol/L (molar S:C 0.006–0.018), while particulate organic sulfur ranged from 0.42 to 2.69 μmol/L (molar S:C 0.007–0.082). Sedimentary organic sulfur exhibited a similar molar S:C ratio (0.014–0.071) to particulate organic sulfur in bottom water, implying that particulate matter deposition is a potential source. Furthermore, sediments exposed to frequent hypoxia harbored significantly higher organic sulfur and S:C values compared to non-hypoxic areas. Laboratory incubation experiments revealed the underlying mechanism: sustained activity of sulfate-reducing bacteria in hypoxic sediments led to a substantial increase in sedimentary organic sulfur (from 15 to 53 μmol/g) within 600 days. This microbially driven sulfurization rendered over 90 % of the organic sulfur resistant to acid hydrolysis. Therefore, this study demonstrates that, alongside particle deposition, microbial sulfurization significantly contributes to organic sulfur enrichment and likely promotes organic matter preservation in estuarine-offshore sediments, particularly under hypoxic conditions. This finding advances our understanding of organic sulfur sources in these vital ecosystems.

Nitrification-induced acidity controls CO2 emission from soil carbonates

Nitrification acidifies soil, and the produced H+ are neutralized by inorganic carbon (C) in soil leading to irreversible CO2 emissions. CO2 released by nitrogen (N) fertilizer-induced acidification is partitioned between solid (CaCO3 re-precipitation), liquid (dissolved HCO3− and CO32−) and gaseous (CO2) phases. Therefore, quantifying the effects of N fertilization on CO2 emissions from soil inorganic C is an enormous challenge. 14C-labeled CaCO3 was used as a model inorganic C to trace the released CO2 caused by acidification by five fertilizers: chicken manure, urea, KNO3, NH4NO3, and (NH4)2SO4 added at three N rates. Cropland soil was homogenously mixed with Ca14CO3 powder and fertilizers, and the emitted CO2 was trapped in NaOH solution to determine total CO2 and 14CO2 efflux originated from inorganic C. Fertilization, particularly ammonium-based fertilizers ((NH4)2SO4, NH4NO3), strongly decreased soil pH by 0.35 units over 40 days. All fertilizers except KNO3 increased total CO2 emissions by 21%–490% compared to the unfertilized control soil. The fertilization effects on cumulative 14CO2 emission induced by CaCO3 neutralization, corresponded to acidification and decreased in the order (NH4)2SO4 > NH4NO3 > urea > KNO3 > chicken manure. Ammonium-based fertilizers induced the strongest CO2 emissions originated from inorganic C, emitting 1.6–4.5 times more 14CO2 than non-fertilized soils during the first nine days. The total CO2 emissions from SIC were proportional to the fertilizer dose applied. Therefore, we conclude that both the choice of N fertilizers and their application rates need to be considered to control CO2 emissions originated from inorganic C. The soil inorganic C losses should be prevented not only because of their irreversible contribution to atmospheric CO2, but also to safeguard ecosystem services of CaCO3, such as organic matter preservation, soil structure stabilization, and C sequestration.

Abrupt intensification of AMOC and monsoonal winds during mid-MIS4 (Heinrich Event 6) in the western Arabian Sea

In the Arabian Sea (AS), higher organic matter preservation and biological productivity are observed during the summer due to strong southwest monsoonal winds. Centennial and millennial-scale fluctuation in the geochemical and relative abundance of foraminifera species are widely used to study the past preservation and productivity variation reconstruction in the Western Arabian Sea (WAS). The sediment records from the AS also show similarities with the North Atlantic and Greenland mainly during Heinrich events (HEs) which is related to the atmospheric and oceanic teleconnections of the AS with the higher latitude climate perturbations. In this context, we used a sediment core VM3504-PC from the WAS to understand the long-term changes in productivity and organic matter preservation using Globigerina bulloides (G. bulloides) relative abundance, total organic carbon (TOC) content, and calcium carbonate (CaCO3) wt%. The TOC and G. bulloides shows a positive correlation, while significantly negative correlation is recorded in the TOC % and CaCO3 wt% datasets during interglacial periods (MIS5e-b, MIS3, and MIS1). Our results show evidence of CaCO3 dissolution and intense summer monsoon induced upwelling related productivity in core location during interglacial periods (MIS5e), based on higher relative abundance of G. bulloides (%), higher TOC content, and lower CaCO3 wt%. Interestingly, higher preservation of organic matter and increased productivity/nutrient concentration during mid-MIS4 suggesting stronger upwelling/winter convective mixing together with higher aeolian transport from adjacent landmasses. The abrupt weakening in the Atlantic Meridional Overturning Circulation (AMOC) synchronized with low productivity due to weak monsoon during HEs except for H6 and H4 in the tropical Indian Ocean. The H6 coincides with mid-MIS4 is showing abnormal preservation. Thus, AMOC and the summer monsoon significantly regulate primary productivity in the WAS. It is interesting to note that possibly well‑oxygenated deep-water masses do not penetrate up to surface water and/or ballistic effect (indicated by moderate sedimentation rate), preventing organic matter degradation on the seafloor during mid-MIS4.

Paleoenvironmental reconstruction and organic matter accumulation of the paleogene shahejie oil shale in the Zhanhua Sag, Bohai Bay Basin, Eastern China

The controlling factors of organic-rich shale accumulation is essential for the exploration and development of shale oil and gas resources. The sedimentary environment plays a vital role in the formation of organic-rich sediments in lacustrine facies. This article unravels the mineralogy, geochemistry, and paleoenvironmental evolution during the deposition of the Paleogene Shahejie Formation (Es3L). It discusses the effects of paleoclimate, paleosalinity, paleoredox conditions, paleowater depth, and paleoproductivity on organic matter (OM) enrichment. Finally, the OM enrichment model was established. The results show that the mineralogical compositions are mainly composed of calcite (avg. 40.13%), quartz (avg. 21.64%) and clay minerals (avg. 24.07%), accompanied by dolomite (avg. 7.07%), feldspar (avg. 6.36%) and pyrite (avg. 2.95%). The Es3L shale has a high abundance of OM, with total organic carbon (TOC) ranging from 1.07% to 5.12%. The organic matter type is mainly composed of type Ⅰ-Ⅱ1 kerogen, which is generally considered a good-quality source rock. The source of OM is a mixture of lower bacteria, algae, and plants. During the early sedimentary period, the paleoclimate was dry and cold, with high salinity, intense reducibility, and relatively low productivity. During the late sedimentary period, the climate became warmer and more humid. As a result, the salinity decreased to a level that was suitable for biological reproduction, and productivity increased gradually due to the input of terrigenous plants. Paleosalinity and paleoclimate determined the environment of the sedimentary period, in addition, paleoproductivity and paleoredox condition indicated the formation and preservation conditions of OM. The warm and humid climate, brackish water, suitable reduction conditions and high productivity are the favorable conditions for the generation and preservation of organic matter. The research results may have implications for the genetic mechanisms of organic matter accumulation. They will provide theoretical and technical insights into the exploration and development of shale oil.

Composition and distribution of sedimentary organic matter in nearshore Berriasian strata (“German Wealden”) of the eastern Lower Saxony Basin, NW Germany

Abstract In the Lower Saxony Basin (LSB) of Northern Germany, the earliest Cretaceous (Berriasian, “German Wealden”) is represented by organic-rich shales assigned to the Isterberg Fm., which have been deposited under brackish-lacustrine conditions in a partially restricted basin. Towards the southern basin margin, these shales interfinger with nearshore sandstones sourced from the Deister-Hils delta. In order to better understand the environmental conditions and depositional dynamics of the Isterberg Fm., the sedimentary organic matter (OM) has been studied with a combined approach including bulk rock organic geochemistry and palynofacies analysis. The lower part (W1–W3) is interpreted to reflect very shallow water conditions and episodic emergence, indicated by multiple occurrences of palaesol horizons, rhizoliths and intercalated coal beds formed within a mud-dominated and protected domain of the delta plain. The overlying sand-rich interval represents a nearshore deltaic setting. A distinct change is observed in the upper part (W4), indicating more distal conditions characterised by clay dominated sedimentation, abundant lumachelle interbeds and a predominance of aquatic-derived OM. The newly acquired data fill a gap in the record between proximal and distal strata of the Berriasian LSB and provide new insights into the accumulation and preservation of OM within this exceptional depositional setting. Supplementary material at https://doi.org/10.6084/m9.figshare.c.7093491

Depositional mechanism of Duwi Formation organic-rich rocks in anoxic Campanian-early Maastrichtian condensed sections in the Qusseir–Safaga region in Eastern Desert of Egypt and their economic importance

The organic-rich rocks of the Duwi Formation have gained much attention in recent years because of the growing demand for their utilization as energy and metal sources. A depositional model for these important rocks is delineated in the present study based on multiple analytical approaches. Samples from these organic-rich rocks were collected from eight mines in the Qusseir-Safaga region along the Red Sea coast in the Eastern Desert of Egypt. These mines are located at El Nakheil, Younis, El Beida, Atshan, Hamadat, Tundub Bahri, Tundub Qubli, and Zog EL Bahr. The depositional model is based firstly on organic geochemical and petrographical analyses of the organic matter to identify its enrichment, composition, hydrocarbon potential, types and origin, and their relationship to rock minerals. Secondly, the inorganic geochemical analysis, including mineralogy and trace elements, is integrated to explore the lithological characteristics and to confirm the results obtained from other analyses. Only the El Nakheil, Atshan, Tundub Bahri, and Tundub Qubli mines are found to have total organic carbon content above 10 wt%. These mines contain hydrogen-rich organic matter that reached a maximum in the El Nakheil Mine as reflected in the Rock-Eval parameters of S2 (137.95 mg HC/g rock) and hydrogen index (HI of 707 mg HC/g TOC). The organic matter is composed mainly of large sheet-like alginite particles and prasinophytes that are finely laminated with minerals, planktonic debris of fish bones, and foraminifera without any sign of the presence of benthic organisms or bioturbation. This lamination is attributed to the occurrence of condensed sections in the studied mines. In addition, the high organic enrichment in terms of quantity and quality is accompanied by enriched metal composition including trace elements that signify anoxic conditions and low sedimentation rates. This composition points to the occurrence of prominent anoxic conditions that are stabilized by a slow sea level rise, which inhibits water circulation and water column stagnation in a restricted basin. The depositional model emphasizes the optimal balance between anoxia, sedimentation rate, and paleoproductivity that resulted in enhanced organic matter preservation in a condensed section. The deposition of the organic-rich rocks is situated in the deep parts of the basin or depocenters that reached their present-day distribution by topographic inversion. The organic and metalliferous reserves in these organic-rich sediments are calculated in the studied mines. The estimation of these reserves is found to be economic for many trace metals in an ore reserve that reached 151742 tons in one bed alone within the Duwi Formation.