Alteration Of Organic Matter Research Articles

From paleolake to peatland: Paleo environmental changes over glacial and interglacial cycles (Mid-Pleistocene) in the Colônia Basin, Brazil

Diatom and geochemical elements were used to analyze the transition from lake to peatland in the Colônia basin, São Paulo, Brazil; local versus regional driving factors were examined. Sediment core COL17–1, section 1470–800 cm depth shows five distinct diatom intervals offering insights into environmental changes and ecological characteristics based on sediment sources, diatom productivity, and bog wetness. Colônia basin evolution exhibited a progressive transition from mineral elements, associated with catchment instability during the lake stage, to higher levels of organic-rich sediments towards the uppermost section of the core. This shift was accompanied by the increasing presence of elements reflecting redox/productivity dynamics under changing conditions. Simultaneously, Br concentrations increased during peat formation indicating alterations in organic matter were influenced by atmospheric circulation and precipitation. During the transition from lake to peatland, the paleolake shallowing process showed successive colonization by benthic acidophilus diatom taxa, indicating a broader littoral zone and subsequent disappearance of diatoms under dry conditions. After a benthic stage, the diatom content shifted to one of planktonic dominance characterized by Aulacoseira sp., marking the return to cold-wet conditions and a moderately deep, flooded environment. Subsequently, the basin evolved into a completely flooded, turbulent peatland dominated by the Aulacoseira granulata complex. An uppermost layer sterile in diatom was associated with warmer and drier conditions and decrease in the concentration of mineral elements. Present results compared with core CO14 and Lake Titicaca showed benthic-rich levels during the penultimate glacial period and low benthic abundances. This differed the glacial-interglacial transition from those of COL17–1, which was dominated by planktonic-rich levels, suggesting the need for either a reassessment of our age model or the influence of local factors on diatom content. These findings highlight the sensitivity of diatoms to climate shifts, particularly in tropical regions, across different glacial-interglacial cycles.

Deciphering the active bacteria involving glucose-triggered priming effect in soils with gradient N inputs

The soil priming effect, which refers to the alteration of soil organic matter (SOM) decomposition due to labile carbon (C) inputs, is widely acknowledged for its impact on C storage in terrestrial ecosystems. However, the impact of chronic nitrogen (N) fertilizer on soil priming effect, particularly in agroecological systems, remains unclear. Here, we utilized soils subjected to varying levels of N fertilization (0, 140, 280, 470, and 660 kg N ha−1 y−1), which were collected from a long-term experimental site. Enzyme activity related to C, N, and phosphorus (P) acquisition was measured using the fluorometric method. Additionally, DNA-based stable isotope probing with 13C-labeled glucose was conducted to explore the role of active bacterial communities (16S rRNA gene analysis) on the priming effect in soils with different N fertilization histories. Glucose addition enhanced the decomposition of native SOM and induced positive priming effects in all soils, which were amplified by the historical N application level. Activity of C-related enzymes essential for soil C decomposition increased following glucose addition, which was positively correlated with the soil priming effect. Active bacterial taxa, primarily Firmicutes, Actinobacteria, and Proteobacteria, were capable of assimilating exogenous glucose-C or native SOM-C. Notably, bacteria assimilating glucose exhibited higher abundance-weighted average ribosomal RNA gene operon copy number than those assimilating SOM, indicating the role of r-strategists in accelerating SOC turnover and increasing C loss. These findings highlight the role of active microbial community attributes on the soil priming effects. This study provides new insights into the intricate processes of C transformation in soils subjected to long-term N management in agroecosystems.

Molecular dynamics simulations of shale wettability alteration and implications for CO2 sequestration: A comparative study

Geological CO2 sequestration (GCS) in shale reservoirs is considered an imperative approach to reducing CO2 emissions and mitigating greenhouse gas effects, with the wettability of reservoir rocks playing a critical role in this process. In this study, we comparatively investigated the wetting characteristics of H2O on the organic matter (graphene) and inorganic matter (hydroxylated quartz) surfaces of shale in a CO2 atmosphere utilizing molecular dynamics (MD) simulations and focused on elucidating the effects of CO2 pressure, temperature, and salinity on wettability from the perspectives of the H2O droplet contact angle (CA), gas-water density distributions and interaction energy. The results demonstrate that the H2O droplet is gradually stripped from the graphene surface by CO2 with increasing CO2 pressure, inducing a wetting transition from intermediate-wet to strongly CO2-wet, while the hydroxylated quartz surface consistently exhibits a strongly H2O-wet state. This significant discrepancy in wetting behaviors can be attributed to the differential adsorption capabilities of CO2. The hydrophilicity of graphene and quartz surfaces is enhanced with increasing temperature for the given CO2 pressure condition, and the wettability alteration is more pronounced above the CO2 critical temperature for graphene, while the opposite is observed for quartz. The H2O CA in the CO2-H2O-shale systems only slightly increases with increasing salinity, which is related to the spatial effect of ions in the brine. The results of this work indicate that the CO2-wet feature of shale organic matter during GCS is favorable for the adsorption trapping of CO2 but unfavorable for capillary trapping, while the opposite is true for inorganic matter. This study sheds light on the phenomena and regularity of the wettability alterations of shale organic and inorganic matter by CO2 injection, and the results gained are expected to furnish new insights into CO2 sequestration-enhanced gas recovery (CS-EGR) and gas-water two-phase flow at the nanoscale.

Top-down control of climate on long-term interactions between fires, tree-cover and soil erosion in a Mediterranean mountain, Corsica

Fire is a potential significant driver of soil erosion in the Mediterranean area, as it results in the partial removal of vegetation and the alteration of organic matter, affecting soil structure and stability. The erosion of particle sizes is influenced by the intensity and duration of rainfall, regulated by disturbance regimes and vegetation cover. We hypothesize that, during the Holocene, high fire frequency and intensity under precipitation control may have contributed to soil erosion, while plant cover and composition could have mitigated it. This plant cover, in turn, might have been influenced by biomass burning. To test this hypothesis, we conducted a detailed analysis of sediments spanning the last 11,500 years from a small mountain lake, Corsica, situated in the black pine forest belt. The high temporal resolution analysis (∼10 years per sample), used granulometry and loss-on-ignition as proxies for erosion and ecosystem productivity in both the lake and watershed, and fire and plant macroremains as fire and tree cover proxies, respectively. The correlation between particle size and the contents of organic or mineral matter with mean fire return intervals (FRI) revealed significant patterns. Long fire intervals were associated with more fine and coarse sands, whereas short mean FRI positively correlated with clay and, fine and coarse silt, along with higher total mineral and organic matter contents. These findings suggest that fires were more frequent when rain duration was sustained but runoff intensity was lower. Conversely, wildfires were less frequent during intense runoff periods (wetter climate). Unlike fire frequency, fire severity did not correlate with erosion, and tree cover and plant richness had minimal to no effect. The 8.2 kyr event was characterized by runoff transporting primarily coarse sands, i.e. a dry period with very intense rains. This suggests that the system is primarily top-down controlled by climate. Multimillennial erosion trends are influenced by fire frequency and precipitation regimes, whereas vegetation does not seem to have a mitigating effect on this process.

Trophic niches of macrobenthos: Latitudinal variation indicates climate change impact on ecosystem functioning.

Benthic food-web structure and organic matter (OM) utilization are important for marine ecosystem functioning. In response to environmental changes related to the ongoing climate change, however, many benthic species are shifting their ranges to colder regions, which may lead to altered community composition, but it remains largely unknown how it will affect ecosystem functioning. Here, stable isotope analysis was used to study benthic OM utilization and food-web structure and to assess whether their spatial patterns reflect today's community differentiation among biogeographic regions and depth zones. Benthic fauna and OM mixtures were collected from two depth zones (100-150 m vs. 200-250 m) within a temperate, two sub-Arctic, and an Arctic fjord along a latitudinal gradient (59-78° N) that was used as a space-for-time substitution to assess the impact of climate change. Our results showed that Arctic and temperate communities are functionally different. Arctic communities were characterized by a strong resource partitioning among different feeding types, irrespective of depth zone. In contrast, all feeding types in temperate communities seemed to rely on sedimentary OM. The sub-Arctic presented a transition zone. In the sub-Arctic, shallower communities resembled Arctic communities, suggesting a functional transition between temperate and sub-Arctic regions. Deeper sub-Arctic communities resembled temperate communities, suggesting a functional transition between the sub-Arctic and Arctic regions. This implies that the regions north of the current transitions (deep Arctic and shallow sub-Arctic) are most likely to experience functional changes related to an altered OM utilization in benthic food webs in response to climate change.

Thirty years of increased precipitation modifies soil organic matter fractions but not bulk soil carbon and nitrogen in a mesic grassland

Grassland ecosystems, which are known to be sensitive to climate change, have shown minimal responses of soil carbon (C) and nitrogen (N) pools to increased moisture availability, despite moisture-induced changes in plants and soil microbes (e.g., expected drivers of soil C and N). However, it is not clear if this apparent limited response is due to an unresponsive belowground system or because alterations in multiple soil organic matter (SOM) component pools and fluxes offset each other. To investigate potential responses of C and N in SOM to decadal increases in precipitation, we sampled soils from a 30-year precipitation augmentation experiment in an annually burned mesic grassland. We measured C and N in three SOM fractions which vary in their plant and microbial controls 1) free particulate OM (fPOM), 2) occluded POM plus heavy, coarse OM (oPOM + hcOM), and 3) mineral-associated OM (MAOM), as well as amino sugars, pyrogenic C and N, and root quality metrics. We found no changes in bulk C or N under increased precipitation, but SOM fractions were modified. Altered plant inputs and soil N availability appeared to drive the responses of fPOM N and oPOM + hcOM C:N, which were increased and decreased, respectively, by increased precipitation. In contrast, the observed increase in MAOM C and N under increased precipitation could not be connected to a specific driver, suggesting additional plant, microbial, or mineral measurements may be required. Regardless, our results indicate that investigating SOM fractions may more directly connect soil C and N pools and their drivers, compared to measuring only bulk SOM. Further, our finding of greater stable OM (MAOM) under increased precipitation suggests soil C storage could provide a negative feedback to climate change with increased moisture availability, but the lack of bulk SOM response suggests that this feedback is not strong in mesic grasslands.

Alteration of Organic Matter during Wildfires in the Forests of Southern Siberia

Large areas of forests burn annually in Siberia. Pyrogenic organic matter (PyOM) generated by wildfires acts as a stable carbon deposit and plays an important role in the global carbon cycle. Little is known about the properties of PyOM formed during fires in Siberian forests. In this work, we report the results of thermogravimetry (TG), differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy applied to the study of the chemical composition, structure, and thermal stability of PyOM formed during surface and crown fires of moderate to high severity in southern Siberia. We studied the PyOM produced from the forest floor, down wood, cones, and outer bark of tree stems in Scots pine, larch, spruce, and birch forests. We calculated the thermal recalcitrance indexes (R50, Q3) based on TG/DSC data. We found that wildfires resulted in a strong decrease in thermolabile components in burned fuels, enrichment by aromatic structures, and a significant increase in thermal stability (T50) compared to unburned samples. In all the studied forests, bark PyOM revealed the highest value of T50 while forest floor PyOM had the lowest one. At the same time, our results indicated that the properties of PyOM were more strongly driven by wildfire severity than by fuel type. Overall, the thermal recalcitrance R50 index for PyOM samples increased by 9–29% compared to unburned plant residues, indicating a shift from low to intermediate carbon sequestration potential class in the majority of cases and hence less susceptibility of PyOM to biodegradation.

Yedoma Permafrost Releases Organic Matter with Lesser Affinity for Cu2+ and Ni2+ as Compared to Peat from the Non-Permafrost Area: Risk of Rising Toxicity of Potentially Toxic Elements in the Arctic Ocean.

Pollution of the Arctic Ocean by potentially toxic elements (PTEs) is a current environmental problem. Humic acids (HAs) play an important role in the regulation of PTE mobility in soil and water. The permafrost thaw releases ancient organic matter (OM) with a specific molecular composition into the Arctic watersheds. This could affect the mobility of PTEs in the region. In our study, we isolated HAs from two types of permafrost deposits: the Yedoma ice complex, which contains pristine buried OM, and the alas formed in the course of multiple thaw-refreezing cycles with the most altered OM. We also used peat from the non-permafrost region as the recent environmental endmember for the evolution of Arctic OM. The HAs were characterized using 13C NMR and elemental analysis. Adsorption experiments were conducted to assess the affinity of HAs for binding Cu2+ and Ni2+. It was found that Yedoma HAs were enriched with aliphatic and N-containing structures as compared to the much more aromatic and oxidized alas and peat HAs. The adsorption experiments have revealed that the peat and alas HAs have a higher affinity for binding both ions as compared to the Yedoma HAs. The obtained data suggest that a substantial release of the OM from the Yedoma deposits due to a rapid thaw of the permafrost might increase the mobility of PTEs and their toxicity in the Arctic Ocean because of much lesser "neutralization potential".

The effects of Jurassic igneous intrusions on the generation and retention of gas shale in the Lower Permian source-reservoir shales of Karoo Basin, South Africa

Shale gas potential of the Whitehill Formation (Permian), Karoo Basin, South Africa is strongly influenced by widespread Jurassic igneous intrusions. A high-resolution organic petrographic and geochemical study is reported here on two stratigraphic sections, the objective being to gain insights into the chemical structure and alteration of oil-prone sedimentary organic matter during contact metamorphism. One section unaffected by intrusion served as background, while the other section was intruded by two laterally continuous dolerite sills with an average thickness of 10.7 and 9.3 m, preferentially emplaced at the upper and lower contacts of the formation, respectively. Heat flow from the sills caused TOC and S2 values from programmed pyrolysis to decline over a distance of 8.7 m from 3.2 to 0.15% and 4.65 to 0.11 mg HC/g TOC, respectively, and cause the reflectance of vitrinite and solid bitumen to increase from 2.03 to 5.82% and 1.58 to 7.87%.Organic matter in the background samples is dominated by solid bitumen, a secondary thermal conversion product of oil-generative Type II kerogen. In the sill-hosting section, the thermal aureoles can be recognized by systematic changes to the optical texture and chemical structure and composition of solid bitumen. Solid bitumen particles develop anisotropy approaching the sills and become transformed into coke and pyrolytic carbon. δ13Corg values become less negative by up to 3.13‰ VPDB. These data suggest significant devolatilization of organic matter to methane and destruction of petroleum generation and retention potential in the contact aureole of the sills. The trend of these datasets, coupled with the presence of several sills and their laterally extensive nature throughout much of the study area suggests that the intrusions have been significant in increasing methane generation on a basinal scale. Together, this study indicates that the complementary application of combined light and electron microscopy (CLEM), programmed pyrolysis, and isotope ratio mass spectrometry (IRMS) is suitable for a comprehensive characterization of organic matter alteration through the maturation continuum. Results also show that contact metamorphic alteration of organic matter by intrusions produced structural and compositional changes that are distinctive from those expected from geological burial maturation where graphite is the end-product.

Soil Organic Matter of Tidal Marsh Permafrost-Affected Soils of Kolyma Lowland

Soils of the Arctic sea coasts are one of the least studied due to the complex logistical accessibility of the region, as well as the severe climatic conditions. The genesis of these soils is determined by several factors of soil formation simultaneously—cryogenesis, the influence of river alluvial processes, as well as the tidal influence of the sea. The paper presents data on the morphological structure of soils formed on the seacoast of the East-Siberian Sea (Kolyma Lowland, North Yakutia). Under the influence of cryogenesis and sea water tidal input, marsh soils are formed, with a relatively high level of salinity and the development of gleyization. Autochthonous and allochthonous soil organic matter play a leading role in marsh soil formation here, including the possible accumulation and biochemical transformation of incoming pollutants (e.g., hydrocarbons). The main objective of the study was to evaluate the soil organic matter genesis and alteration under the influence of tidal processes in coastal permafrost-affected soils as well as to obtain the previously unknown characteristics of the structural and elemental composition of different fractions of organic matter. The elemental composition and 13C NMR spectroscopy of humic acids were analyzed. It was revealed that humic acids extracted from the studied marsh soils accumulate up to 50% C and 4% N. Active processes of dehydrogenation are noted in HAs molecules, which indicates a relatively low degree of aliphatic structure development. According to 13C NMR spectroscopy, it was revealed that up to 45% of aromatic structural fragments accumulate in marsh soils, indicating a relatively high degree of organic matter stabilization and resistance to biodegradation.

Microbial alteration in marine sediments: Insights from compound-specific isotopic compositions of amino acids in subseafloor environments

The proportion of amino acids (AAs) in sediment can be used as an indicator of microbial degradation, which is primarily the product of benthic prokaryote activity. The microbial activity would be reflected with the stable isotope ratio of nitrogen (δ15N) at the time of mineralization and resynthesis of AAs. In this study, the compound-specific isotope analysis of individual AAs was used to investigate δ15N variation associated with microbial processes in marine sediment samples. Our results showed a decrease in AA concentrations in core-top sediment was accompanied by an increase in δ15N values, suggesting large 15N enrichment in buried AAs. Phenylalanine displayed an increase in δ15N from the surface to depths greater than 2 cm, whereas relatively constant δ15N values at depths below 2 cm, suggesting that microbial utilization of phenylalanine varies with depth. Glycine showed the highest relative molar contribution (from 12.1 to 36.4%), with the largest δ15N increase (from 0.8 to 8.7) in deep sediment, implying that such information can serve as a measure of AA diagenesis in sedimentary environments. Our results also indicated that the δ15N values of individual AAs in sediment reflected the microbial alteration of organic matter at water-sediment interfaces and in sub-surface environments. These findings form an important basis for interpreting the δ15N values of AAs in sediment.

The effect of Pliocene volcanic intrusive rocks and thermogenic gas generation from the Miocene Salif Formation in the offshore Tihamah Basin, Yemeni Red Sea

Organic geochemical and basin modeling methods were used to investigate the potential of thermogenic gas generation from the source rock of the Miocene Salif Formation. The analyzed Salif shales were collected close to the intrusive volcanic rocks intersected by the Kathib-01 well in the offshore Tihamah Basin, Yemeni Red Sea. Generally, the analyzed Salif shale samples have total organic matter (TOC) values up to 3.4 wt %, overall, indicating organic matter richness capable of generating hydrocarbons. The analyzed Salif shale samples have low hydrogen index (HI) values of <200 mg HC/g TOC, indicating mainly Types IV and III kerogen. These results are in contrast with the presence of dominated hydrogen-rich Type-II kerogen in the Salif shales from the close location of the exploration wells e.g., Al-Auch-01, Al-Meethag −01 and Al-Meethag −02. Therefore, the drastic alteration of the original organic matter of Type II and decreasing HI values, as a result of conversion of kerogen to HCs in the studied well, is due to the high thermal maturation as indicated from thermal maturity indicators. The Salif shale samples in the studied well have reached the main stage of the gas generation window, implying that the Salif Formation has substantial thermogenic gas generation. The increase in thermal maturity in the studied well was caused by the presence of the intrusive volcanic rocks that extruded during the Pliocene age as a result of the regional uplift of rift shoulders.Based on the burial/thermal/generation model of the Kathib-01well, the conversion of kerogen to oil and the subsequent cracking of the retained oil into thermogenic gas has been simulated. During the early to late Pliocene age (5–2 Ma), 10 to about 60% of kerogen was converted to oil, matching the peak mature to late mature of oil window (0.75–1.35 %Ro). Moreover, oil was cracked into thermogenic gas during end of the late Pliocene until the present day (2-0 Ma), indicating the beginning of the gas generation window (>1.35% Ro) with a transformation ratio (TR) above 99%. The prediction of a significant charge of thermogenic gas generation from the Salif Formation in the studied Kathib-01 well is due to the presence of the volcanic intrusive rocks extruded during the late Pliocene to present day time.

Burn Intensity Drives the Alteration of Phenolic Lignin to (Poly) Aromatic Hydrocarbons as Revealed by Pyrolysis Gas Chromatography-Mass Spectrometry (Py-GC/MS).

High-intensity wildfires alter the chemical composition of organic matter, which is expected to be distinctly different from low-intensity prescribed fires. Herein, we used pyrolysis gas chromatography/mass spectrometry (Py-GC/MS), in conjunction with solid-state 13C nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectroscopy, to assess chemical alterations from three wildfires and a long-term frequent prescribed fire site. Our results showed that black ash formed under moderate intensity burns contained less aromatic (ArH), polyaromatic hydrocarbon (PAH), and nitrogen-containing compounds (Ntg) but more lignin (LgC) and phenol compounds (PhC), compared to white ash formed under high intensity burns. Both 13C NMR and FT-IR confirmed a higher relative percentage of carboxyl carbon in white ash, indicating the potential for higher water solubility and more mobile carbon, relative to black ash. Compared to wildfires, ash from low-intensity prescribed fire contained less ArH, PAH, and Ntg and more LgC and PhC. Controlled laboratory burning trials indicated that organic matter alteration was sensitive to the burn temperature, but not related to the fuel type (pine vs fir) nor oxygen absence/presence at high burn temperatures. This study concludes that higher burn temperatures resulted in higher (poly)aromatic carbon/nitrogen and lower lignin/phenol compounds.

Signals of low grade organic matter alteration in the Upper Permian Kupferschiefer (Spremberg area, Eastern Germany) – A by-product of copper mineralization?

Organic matter (OM) is known to be an important reductant in many sediment-hosted base metal deposits. However, the precise nature of the interactions between OM and hydrothermal fluids is still debated, as is just how such interconnected reactions develop over geological timescales. We investigated the Kupferschiefer mineralization in two drill cores from the Spremberg-Graustein field in Eastern Germany focusing on the inventory of organonitrogen, -sulfur and -oxygen (NSO) compounds, which are most affected by organic–inorganic interactions with mineral surfaces, metals and aqueous fluids. Rather homogeneous deposition of type II marine organic matter, prevailing photic zone euxinia and an early oil window thermal maturity were documented using conventional hydrocarbon analysis. Furthermore, a slight level of hydrothermal alteration was detected in the lower part of drill core 121 h/72, in proximity to the epigenetic hematitic alteration zone known as ‘Rote Fäule’. A minor loss of extractable organic matter and especially long-chain n-alkanes was accompanied by significant enrichment in oxygenated compounds and increased molecular oxygen content detected by ultra-high resolution mass spectrometry (FT–ICR–MS). A strong enrichment of deuterium observed in the n-alkanes (up to −36‰) and isoprenoids (up to −20‰) indicates that hydrogen exchange with an evaporitic fluid occurred in the Spremberg Kupferschiefer over geological timescales at maximum temperatures not exceeding 110 °C. We therefore conclude that FT–ICR–MS, combined with determination of stable hydrogen isotope compositions, can provide valuable information about interaction time scales and the origin of mineralizing hydrothermal fluids.

Geology and Petrography of Uraniferous Bitumens in Permo-Carboniferous Sediments (Vrchlabí, Czech Republic)

Uraniferous bitumens found in black shales from the Permian rocks at Vrchlabí in the Krkonoše Piedmont Basin (Czech Republic) were described and characterized petrologically and mineralogically. The Permian sediments originated from weathering products in metasediments and granitoids of the Krkonoše–Jizera and Orlice–Sněžník crystalline complexes. The organic matter contained up to 4.8 wt.% uranium, as uraninite grains. Elements associated with uraninite, such as Pb, Zr, Cu, and As, may have accumulated from epigenetic fluids in layers rich in organic matter during their late diagenesis. The bitumen structures were extremely heterogeneous, a feature attributed to the radiolytic effects of uranium. Amorphous bitumens, alternating with various forms of nodular and corroded bitumen types from multiple generations, were present. Low and highly altered bitumens with weak anisotropy were recognized, together with halo zones, with reflectance up to 4.37%. The halo zones differed in size, brightness, and reflectance, increasing from the edge to the center. Halos often revealed dark rims between uraninite inclusions and clear zones, originating probably as a result of weaker alterations in organic matter due to the presence of other inorganic components. Uranium concentration was the main factor controlling the degree of radiolytic alteration. The studied uraniferous bitumens are an excellent example of multistage formation and diverse evolution during burial and diagenesis.

Elemental and Isotopic Signatures of Bulk Sedimentary Organic Matter in Shenhu Area, Northern South China Sea

Hydrate-bearing sediments provide excellent materials for studying the primary sources and diagenetic alterations of organic matter. In this study, the elemental and isotopic signatures of total organic carbon (TOC), total inorganic carbon (TIC), total nitrogen (TN), and total sulfur (TS) are systematically investigated in three hydrate-bearing sediment cores (∼240 m) retrieved from the Shenhu area, South China Sea. All sediment layers from three sites are with low TOC content (average 0.35%) with marine and terrestrial mixed sources (-23.6‰ &amp;lt; δ13Corg &amp;lt; -21.4‰). However, the generally low δ15N (2.49–5.31‰) and C/N ratios (4.35–8.2) and their variation with depth cannot be explained by the terrestrial sources (Pearl River) and marine sources, binary end-member mixing processes. Contribution from lateral allochthonous organic matter from the mountainous river is considered after excluding other possible factors and ingeniously elucidating the organic matter origins. Furthermore, specific layers in W01B and W02B exhibit elevated S/C ratios (up to 2.39), positive bias of δ34S-TS (up to +29.7‰), and negative excursion of δ13C-TIC (up to -8.29‰), which are the characteristics of sustained occurrence of sulfate-driven anaerobic oxidation of methane. The occurrence of coupled carbon–sulfur anomaly may be accompanied by deep hydrocarbon leakage and the formation of hydrate with high saturation.

Influences of microwave irradiation on pore, fracture and methane adsorption of deep shale

In order to better understand the feasibility of enhancing shale gas recovery by microwave irradiation, the influences of microwave irradiation on the pore, fracture, and methane (CH4) adsorption pertaining to shale gas production of a deep shale were fully addressed. A combination of multiple characterization methods was used, including pyrolysis, X-ray diffraction, back-scattered scanning electron microscope, probe molecule adsorption, steady-state permeability, X-ray computed tomography, and gravimetric method for measuring CH4 adsorption. Results show that microwave irradiation has no obvious impact on micropore but decreases mesoporous surface area, and volume of the shale matrix. It particularly reduces the adsorption pores for accommodating CH4 with the diameter of less than 8 nm. The nanoscale pore structure evolution is mainly associated with alterations in organic matter and inorganic minerals of the deep shale after microwave irradiation. Microwave irradiation induces the decomposition, cracking, shift, stripping and formation of minerals, as well as the formation of organic matter. Furthermore, it significantly increases fractures paralleling to bedding planes of the deep shale due to thermal stress generated within various minerals. These newly formed fractures dramatically increase the porosity and permeability of the deep shale. Finally, microwave irradiation significantly decreases the maximum CH4 adsorption capacity of the deep shale by 16.38%. In summary, this study put forward a novel method for enhancing shale gas production via simultaneously promoting CH4 migration and reforming reservoirs under controlled microwave field.

Localized alteration of ferrihydrite natural organic matter coprecipitates following reaction with Fe(II)

AbstractCoprecipitation of natural organic matter (NOM) with ferrihydrite (Fh) can alter the trajectory of Fe(II)‐catalyzed transformation. High C/Fe molar ratio Fh‐NOM coprecipitates are expected to resist transformation completely and preserve organic matter (OM). To explore how heterogeneous NOM would influence this process, we reacted low (0.8) and high (1.8) C/Fe molar ratio Fh‐NOM coprecipitates (synthesized with a 13C‐labeled plant litter extract) with 2 mM Fe(II) for 1 and 14 d under anoxic conditions and examined changes in the solid phase with Mössbauer spectroscopy (MBS) and secondary electron images using scanning transmission electron microscope. Mössbauer spectroscopy data suggests Fe(II) interaction with coprecipitates increases Fe mineral crystallinity, as did lower molar C/Fe ratios and longer aging times. However, de novo crystal phase development was only observed (via secondary electron images) in the Fe(II)‐reacted coprecipitates and only when the organic carbon (OC) loading was low. For example, the low C/Fe coprecipitate developed localized lath‐like crystal phases after 1 d of reaction with Fe(II), while the lath‐like phases only developed in the high C/Fe coprecipitates after they lost some NOM (C/Fe ratio decreased from 1.8 to 0.7) and reacted with Fe(II) for 14 d. In addition, partial exchange of coprecipitate 13C‐NOM for C in the media (likely the organic PIPES buffer) occurred in all treatments but was accentuated by reaction with Fe(II), suggesting coprecipitate OM composition likely evolves over time, especially when exposed to Fe(II). Our findings suggest that Fe(II) mediated Fh‐NOM transformation is highly dynamic and has the potential to influence the stability of NOM in Fh.

Dominant products and reactions during organic matter radiolysis: Implications for hydrocarbon generation of uranium-rich shales

Organic-rich shales are generally characterized by high uranium (U) contents. The effects of U irradiation on evolution and hydrocarbon generation of organic matter (OM) have attracted substantial attention. However, details on the generation mechanisms of products and the identification of dominant reactions occurring during OM radiolysis remain understudied. In this study, γ ray was used to irradiate immature kerogen and bitumen, and electron beam was for decane. The contents and carbon (C) isotopic compositions of gaseous products, the liquid products of decane, and the functional groups alterations of kerogens and bitumen were detected. The results showed that, the product generation corresponded well to the structural alteration of OM during radiolysis. C–H and R–CH3 rupture contributed to H2 and CH4 generation, respectively. O-containing group cleavage caused CO2 generation, and O2 presence could enhance the oxidation of OM by joining in the structure of OM or by facilitating the formation of new oxides. H2O addition could not only provide O, enhancing the oxidation of OM, but could also provide H, thus promoting H2 generation. We identified cracking, cross-linking, and oxidation reactions during the OM radiolysis. C isotopic composition changes in solid OM could facilitate identification of dominant reactions. Non-closed geological environment of shales promoted the occurrence of cracking reaction. The substantial radiation energy generated from U decay in U-rich shales was significant for OM evolution via decrease in H/C, increasing O/C, and via enhancement of dealkylation, aromatization and unsaturation, which were similar to the thermal effects. Moreover, U irradiation could also promote conventional gas and immature gas generation and could provide exogenous H for hydrocarbon generation of OM, especially for OM in an over mature stage. It is essential to consider the effects of U irradiation on the evolution, hydrocarbon generation, and resources assessment of U-rich shales.

Wood shrinkage during fossilisation and its significance for studying deep-time lignophytes

Silicified wood is one of the most frequent and insightful records of ancient life since the Devonian. Although cellular anatomy is often preserved in great detail, alterations of organic matter occur during fossilisation modifying tissue properties. Due to taphonomic pathways, plant tissues experience multiple changes, which may cause a tissue-volume reduction, including desiccation, microbial decay, charcoalification, coalification and mineralisation. Case studies from different geological ages, fossilisation backgrounds and palaeogeographic positions provide evidence of widely distributed but still underestimated shrinkage phenomena in fossil woods. Samples from seven Paleozoic to Cenozoic localities representing several geologic settings are analysed to understand putative shrinkage reasons. Volume reduction is more widespread in fossilised wood than commonly thought. Accordingly, quantitative data on cellular anatomy may be misleading, and cell size and shape modifications affect morphometric purposes, like the interpretation and identification of fossil species. Differences in preservation demonstrate the profound effects of microbial degradation, such as lacking tracheid secondary walls and decayed tissue constituents. Differential shrinkage of silicified wood and their encrustation by stromatolites help quantify volume loss during fossilisation. They provide graphically measurable, one- and two-dimensional parameters to assess percental volume loss. Our approach reveals essential shrinkage-related alterations independent of palaeoenvironment, plant material and host rock. Tissue contraction varies considerably: Unexpectedly, variability even occurs in wood from the same fossil site, the same strata and reflecting the same taphonomy. The results demonstrate that shrinkage needs to be taken into account in comparisons of morphometric data obtained from fossil and modern woods, irrespective of their particular provenance.