Here, we present a geochemical study of the soil above a plugged oil well ('Elwerath'), which was drilled in the early 1920s and is located near Hannover (Germany). At this site similar to 40 mg methane per hour is emitted. Geochemical analyses of the soil gas confirm the presence of thermogenic natural gas (with up to 8 % methane and 600 ppm ethane in the soil gas) and the delta C-13 of the methane indicates that most of the emitted methane is thermogenic (delta C-13 -47.1 parts per thousand VPDB). In addition to natural gas, we also found petroleum in the soil, accounting for up to 80 % of the total soil organic carbon. Detailed soil gas and organic geochemical analyses of extracts from the soil confirm a strong similarity with the old petroleum reservoir. Our data suggest a complex mosaic of gas-altering effects that cannot be explained by admixture with biogenic methane alone, but are rather dominated by microbial degradation of oil and natural gas components (e.g. propane oxidation). Most likely O-2 availability controls the microbial degradation of petroleum close to the 'Elwerath' well, because the strongest degree of degradation, with the lowest petroleum content, is found in the upper, well aerated soil horizons. The gas geochemistry and isotopic composition of the soil gases also indicate anaerobic processes, such as methanogenesis, probably with petroleum as carbon source. These processes must have taken place significantly deeper than the top meter sampled, where O-2 was still detectable. CO2 emissions appear to be negatively affected by the oil contamination, most likely due to the inhibition of natural microbial respiration by toxic effects. While processes in the deeper biosphere appear to play a role here, it is clear that the microbial processes in the soil surrounding the well also regulate the composition and quantity of oil and gas. In conclusion, (i) the high degree of degradation of natural gas and oil in the soil, and (ii) the low methane emissions, indicate that only little hydrocarbon is leaking and that a 'microbial hydrocarbon filter' is established and active.

Dilute sediment gravity flows transporting fine-grained sediments such as silt or clay in suspension are thought to be the principal carriers of organic carbon into the deep sea. However, observations from submarine fan datasets show that plant debris can also be accumulated in a range of coarser (sandy) facies, which suggests that organic carbon buried in sand-prone turbiditic environments could make a significant contribution to the total amount of sequestered organic carbon in submarine fans. Here, we present insights on the distribution of organic carbon in relation to grain size and facies from slope deposits of the Arro System, A & iacute;nsa Basin (Spain). Evaluation of total organic carbon (TOC) content from 82 samples (canyon-fill, channel-overbank, mass-transport intraslope-lobe and slope deposits) shows that there are distinct partitioning patterns of organic carbon between different deposits depending on facies, grain size and depositional sub-environment. The main outcomes of this study are: (1) fine-grained sandstones are relatively enriched in organic carbon (average of 0.78 wt% TOC) compared to silt-prone deposits (average of 0.45 wt% TOC); (2) non-channelised turbiditic and hemipelagic slope deposits (0.38 wt% TOC) are not the main depocentre of organic carbon, which is preferentially stored within the channelised turbidite system; and (3) deposits exhibiting sinusoidal stratification show the highest organic carbon content independent of grain size. Sinusoidal stratification indicates high rates of aggradation by quasi-steady supercritical turbidity flows, allowing for the preservation of organic material in stable antidune deposits with a record of high suspension-load sedimentation. This study shows that the partitioning of organic carbon within slope deposits is controlled by depositional flow regimes and aggradation rates. Therefore, these depositional dynamics need to be considered to understand the variability of carbon sequestration within deep-marine sediments.

Natural hydrocarbon seepages constitute a substantial influx of oil and gas into hydrosphere and atmosphere, impacting the environment and greenhouse gas budgets. The Lusi seepage system (Indonesia) is one of the Earth's largest surface hydrocarbon manifestations, and is intrinsically associated with the interaction of organic-rich sedimentary rocks and recent magmatism. Previous ground-based and satellite measurements revealed that Lusi is a mega emitter of thermogenic methane, releasing similar to 0.1 Mt methane per year. Here, linking the quantification of mud flow rates with oil concentration data, we estimate that Lusi released similar to 0.22-0.28 Mt of oil over 13 years of continuous fluid discharge. This emission is of the same order of magnitude as the Deepwater Horizon spill. The oil discharge into the Porong River and Madura Strait poses an environmental threat to aquatic ecosystems of north-east Java. Combining flux and concentration data, we have also estimated a release into the atmosphere of similar to 8-10 kt of ethane and similar to 6-8 kt of propane per year. Over 18 years, Lusi has already injected into the atmosphere more than 20 times the amount of ethane released by the 2015 Aliso Canyon gas storage accident (California), considered as one of the largest gas leaks in U.S. history.

Alkyl benzenes and toluenes are common in petroleum and shales. In addition to the series of n-alkylated benzenes and toluenes, the phytanyl toluene (and-benzene) is often abundant. In the present study, n-alkyl toluenes and phytanyl toluene were detected in more than 180 petroleum oils with different maturation histories and from two different source rocks, the Jurassic Posidonia Shale and the Cretaceous Wealden Shale (from the Lower Saxony Basin; Germany). A novel ratio of C22-C24 meta-substituted n-alkyl (combined in the ratio as "n") to phytanyl ("iso") toluenes is proposed as a thermal maturity indicator. Our data show that the relative proportion of phytanyl toluene to n-alkyl toluenes systematically decreases with maturity and therefore the "n/(n + iso)" toluene index increases. The relative change is due to both the processes of catalytic formation of n-alkyl toluenes and destruction of phytanyl toluene. The applicability of this ratio was confirmed using closed gold capsule pyrolysis maturation experiments with Posidonia Shale (for a maturation range from EASY%Ro of 0.78 to 1.4 %). The correlation is most pronounced in petroleum produced from the Posidonia Shale. For oils from the Wealden shales, the correlation is less clear due to the generally low phytanyl toluene contents. Comparisons of the "n/(n + iso)" toluene index with maturity-dependent biomarker ratios indicated its potential to record thermal maturity over a wide range. The occurrence of phytanyl toluene also appears to record a poorly understood (microbial) source, which was more abundant in the marine-euxinic depositional system of the Posidonia Shale than that of the brackish-marine Wealden shales.

The Paleocene-Eocene Thermal Maximum (PETM) and early Eocene hyperthermal events were characterized by a Hothouse climate state. Our understanding of the climatic impact of these hyperthermals is currently biased toward marine settings and the mid-latitudes. Here we present organic geochemical data from Stenkul Fiord, Ellesmere Island, Arctic Canada. This organic rich formation was deposited in a high northern latitude wetland setting during the late Paleocene to early Eocene, spanning the PETM and subsequent ETM-2 hyperthermals. Biomarker data (e.g., diterpenoids), combined with published palynological data from the site, indicate Cupressaceae-dominated vegetation. Biomarkers suggest that land plant composition remained fairly unchanged across the two hyperthermal events. Increases in abundance and 13C-depletion of hopanoid biomarkers (minima <-50 parts per thousand (VPDB)) highlight periods of enhanced bacterial methane consumption, particularly during the PETM. However, periods of low hopanoid delta 13C values were also found outside the hyperthermal intervals. Relatively low delta 2H values of higher plant n-alkanes (average delta 2H values of n-C25, n-C27, n-C29 similar to -230 to -270 parts per thousand (SMOW)) indicate that deposition formed during times with enhanced precipitation. The wettest intervals, as identified by the lowest delta 2H n-alkane values, contain high abundances of hopenes, indicating enhanced bacterial turnover. At Stenkul Fiord, high temperatures and CO2 concentrations likely fostered the growth of widespread wetland forests that became a CO2 sink and may have played an important role in carbon drawdown during the Early Paleogene.

During the Middle to Late Berriasian (so called “German Wealden”) a large lake system developed in the Lower Saxony Basin (LSB; in northwestern Germany) of which the eastern part is characterized by varying fluvial and lacustrine influences. The changeable situation through the earliest Cretaceous, particularly in the eastern LSB, is relatively understudied and a recently drilled well (KB-Rehburg 2; R-2) can help shedding light on these variations. R-2 covers the Berriasian ostracod zones Wealden 1 to 4 (Wd1 to Wd4), and palynomorphs presented in another study record stages with fluctuating predominantly terrigenous or aquatic organic matter. Short-term marine ingressions (MI) and more extensive transgressive events (TE) during that time interval have been reported, but some remained questionable. We here present novel organic geochemical data (including Rock–Eval and biomarkers) from R-2 showing a low maturity in terms of organic geochemical stress (Rock–Eval Tmax 435 to 445 °C) and bulk geochemical and biomarker data support the fluctuation in the sources of the predominating organic matter. In addition to the recently published marine influx events recorded in R-2, a significant decrease in pristane/phytane and increase in dinosterane index biomarker ratios demonstrate the previously unclear TE2 at the beginning of zone Wd4. While dinoflagellate cysts during that stage were reported to occur only sporadic, the dinoflagellate-specific dinosterane biomarker became highly abundant [“dinosterane/(regular steranes + dinosteranes)” ratio up to 0.15]. It demonstrates that dinoflagellates also flourished at R-2 during zone Wd4. This palynomorph/biomarker mismatch may be explained by the prevalence of non-cyst forming, or less likely, non-preservation of cells of dinoflagellates. Our data from R-2 also points at a likely widespread and general complication for palaeoreconstructions because we observed a slight lag between first records of palynomorphs used for TE and MI event identification compared to changing biomarker ratios and bulk organic geochemistry. We hypothesize that while the first likely demonstrate first occurrences of pioneer organisms, which mark events best, organic geochemical data appear to be more integrating and record changes only after establishment of a palaeoenvironment.

Extraction of plastic particles from soil is challenging and, thus, exceptionally little spatial information on plastic distribution at the field scale has been gathered. However, for environmental risk assessment, adequate sampling should complement coherent plastic profiling. In this study, we investigated the spatial distribution of mesoplastics (MePs; from >5 mm up to 130 mm) in arable soil (Haplic Cambisol) managed intensively by 12 years of compost application. Geo-referenced samples (n = 128) and five different sampling designs (n = 45) of variable sampling volume (from 2 to 300 L) were collected at a three hectare study site in Northern Germany (0-30 cm soil depth). Soil properties such as pH and soil organic carbon (SOC) were measured to evaluate dispersion measures of these data. In total, we found 259 MePs with a predominance of transparent packaging foils made of polyethylene and coloured fibres of polypropylene. Average particle metrics were a projection area of 47 (3-400) mm2, a Feret diameter of 18.5 (5.4-130) mm and a mass of 1.89 (0.11-221) mg. Caution is advised when measuring the particle mass due to still strongly adhering soil material, especially for fibre bundles with 0.544 mg soil mg-1 particle. We recommend using a 0.1 mol L-1 tetrasodium pyrophosphate solution to purify MePs by removing attached soil before weighing for further environmental risk assessment. The MePs count with a median value of 0.50 (0-3.2) particles kg-1 and median mass of 2.26 (0-221) mg kg-1 featured the highest coefficient of variation (CV) with 103% and 187%, respectively. This is 10-20 times larger in comparison to the CV of SOC (9.2%) and even 50-93 times larger than CV of soil pH (2.2%). This leads to the need of larger sample numbers to delineate plastic metrics in comparison with soil properties to identify a reliable mean value of the field within a predefined allowable error. Mesoplastics in the soil were characterized by a pure nugget effect variogram (no spatial correlation), revealed no intrafield variability and the sample volume yielded inconclusive results. Sampling for plastics in soil should either (i) drastically increase the sample number for a single field or (ii) communicate transparently that the allowable error is by far enhanced in comparison with classical soil properties like pH and SOC. More systematic studies featuring geo-spatial analysis of MePs and smaller-sized plastics in soils are required to propose adequate sampling designs across multiple land uses and plastics fingerprints. A larger database would, thereupon, pave the way for best-practice guides on how to treat 'outliers' and search for robust estimators for spatial mapping of plastics in soils.

Since 2015, the determination of microplastics (MPs; < 5 mm) in soil has gained increasing attention. However, usual analytical protocols still render a comparison of results challenging. This structured review integrates an in-depth screening of scientific articles ( n = 106; from 1980 to 2022) that focused on determining MPs in soils. The different studies were divided into groups regarding (i) MPs input pathways, (ii) study site information, (iii) sampling design, (iv) sample preparation, and (v) analytical methods for MPs detection. Most of the studies (63%) focused on a defined study site influenced by a known point source, whereas 37% measured MPs background contents related to delocalized MPs emission sources. Even though soil was the target compartment, only 26% classified the soil type, mostly using the World Reference Base (WRB) as a classification system. Additional information on soil properties was supplied within only 20% of the studies. However, this information is mandatory for evaluation of MPs recovery tests and analytical results. In nearly all studies, the mass of the single samples equaled the final mass of the composite sample, with a mean of 1.32 kg ± 1.07 kg. However, other procedures that involve a larger sample mass seem promising but are still seldom applied. Our structured review revealed that a standard operation procedure with harmonized methods is urgently needed with a coherent and comprehensive workflow, including field sampling and sample preparation. Such a procedure would ensure the reproducibility and representativeness of analytical results, which are mandatory for evaluating and restricting MPs pollution in soils in the future. Graphical Abstract

Alkyl benzenes and toluenes are common constituents in thermally matured shales, kerogens and petroleum. In addition to the series of n-alkylated benzenes and toluenes formed by catalytic kerogen cracking, especially contents of the single isoprenoid phytanyl toluene (and-benzene) are often elevated. Sources of these compounds and the geochemical information from their occurrence are still under discussion and a subject of paleoreconstruction- and applied petroleum research (e.g., Solli et al., 1980 ; Sinninghe Damsté et al., 1993 ; Moura et al., 2019 ). Recently, for example, enhanced concentrations of phytanyl toluene in rocks of the Permian-Triassic boundary, a critical interval in Earth History, have been demonstrated ( Grotheer et al., 2017 ). In the study presented here, variations in contents of n-alkyl toluenes and phytanyl toluene were analysed for more than 100 oils of two different petroleum source rocks, the Lower Jurassic Posidonia Shale and the Lower Cretaceous Wealden shales, both from within the Lower Saxony Basin (Northern Germany). Based on this dataset, a ratio of C22–C24 meta-substituted n-alkyl toluene to phytanyl toluene was developed and its changes with maturity and source rock characteristics are discussed. The ratio had to be based on combined abundances of alkylated toluenes in both, the aliphatic and aromatic fractions, as due to the intermediate polarity, the compound class eluted into both fractions with differing phytanyl/alkyl toluene ratios.

There is a lack of knowledge about the fate and impact of microplastics (MPs) and nanoplastics (NPs), as well as their potential uptake and impact on plants and microorganisms. The predicted environmental concentrations (PEC) of frequent polymers in soils are low, and therefore, difficult to detect with the available techniques, which explains the knowledge gaps. Therefore, model particles (polystyrene particles (PS-P), 343 nm) and palladium (Pd) nanoparticle-doped polystyrene particles (PS-Pd-PS-P, 442 nm) were synthesized, characterized, and subsequently applied to agricultural soils (Cambisol, Podzol, PS target contents: 25 mg kg-1, 75 mg kg-1, 225 mg kg-1). A combination of different techniques, such as inductively coupled plasma-mass spectrometry (ICP-MS), pyrolysis-gas chromatography-mass spectrometry (Pyr-GC-MS), dynamic light scattering (DLS), and scanning electron microscopy (SEM), were used to characterize the particles in the dispersions, soils and plants. The spiked soils were applied to a chronical plant toxicity test with oat (Avena sativa). The applied particle contents could be recovered from both soils by ICP-MS (Pd, 89% - 99%), and Pyr-GC-MS (PS, 73% - 120%). Moreover, non-aggregated particles in soils and on oat roots were visualized through SEM. The ratio obtained for the Pd contents in oat roots to that in the Cambisol (2.2-2.7) and the Podzol (2.3-2.6) implied that particles accumulated on the root surface or in the roots. No Pd was detected in the oat shoots, which indicated that no translocation occurred from the roots to the shoots. Despite particle accumulation at or in the roots, no clear effects on plant growth were observed. Furthermore, the soil microorganisms (Podzol) and the soil water repellency (Cambisol, Podzol) showed no clear monotone concentration-response relationship after exposure to PS-P and PS-Pd-PS-P. The findings are complex and illustrate the urgent need for further sophisticated experimental studies to elucidate the impacts of NPs on physicochemical soil function, plants, and soil organisms. The model PS-P doped with Pd nanoparticles significantly enhanced the development and validation of methods for investigating MPs and NPs in environmental matrices, highlighting their considerable potential for further studies.

Peats formed widespread early after the Last Glacial Maximum around the coast of the Dogger Bank, the central high of the now flooded “Doggerland” (central North Sea). Here we present biomarker and gas geochemical insights into near-surface peat cored at 43 m water depth. Based on their probable age of ~10 ka before present (BP), the peats are likely part of the so-called basal Holocene peats. Pore waters in the samples document slight methane enrichments in peat layers (up to 250 nM methane vs 60 nM above the peat layer) and δ13C-values of methane ranging between ca. −46‰ and −60‰ PDB. Ethane, propane, and n-butane were also found and may either document upward migration of thermogenic hydrocarbons in the past or, more likely, peat-specific gases, which is indicated by accompanying abundant unsaturated analogs (i.e. ethene and propene). High concentrations of elemental sulfur (up to 19 wt.%) and sulfur-specific transformation products of plant triterpenoids (Des-A-triterpenoids) point to microbial generation during and/or slightly after peat-formation as hydrocarbon source. Biomarkers indicated that peats were formed in a variable environment with high contributions from higher plant wax material. However, a C20 highly branched isoprenoid (HBI) likely records abundant diatoms typical of an oligotrophic lake environment. In addition, all samples contained a suite of bacterial hopenes and fernenes (hop-17(21)-ene, diploptene, fern-7(8)-ene). A strongly fluctuating methane-flux and/or -turnover during peat formation is recorded in partially high 13C-depletions of <−60‰ PDB of these biomarkers. This underlines the importance of peat layers for methane generation and consumption on “Doggerland” during the Holocene.

Numerous hydrocarbon seep sites at the continental shelf, slope, and in the deep water basin are known to feed the Black Sea water reservoir of dissolved methane. In this study, we identified the likely sources of gas and oil that are emitted at four sites located on the continental slope offshore Georgia in the Eastern Black Sea at 830 to 1,140 m water depth ? an area with gas seepage only (Batumi seep area) and three areas of coupled gas and oil seepage (Iberia Mound, Colkheti Seep, and Pechori Mound). The geochemistry of bulk parameters, organic fractions and individual hydrocarbon biomarkers in near-surface sediments and of gas/oil expelled from the seafloor was analyzed and jointly interpreted to assign most likely hydrocarbon source rocks in the studied region. Presence of oleanane in shallow oil-impregnated sediments and oil slicks attests that the source rock at all sites is younger than Mid Cretaceous in age. We conclude that hydrocarbons ascending at all the four seepage areas originate from the Eocene Kuma Formation and/or the Oligocene?Lower Miocene Maikop Group, which are considered the principal hydrocarbon sources in the Eastern Black Sea region. Distributions of crude oil biomarkers in shallow sediments suggests moderate to heavy biodegradation. C1/C2+ ratios (10?4,163) along with stable C and H isotopic ratios (813C?CH4 -46.3 to -53.1.3%o V-PDB; 82H?CH4 -159 to -178%o V-SMOW) indicate gas mixtures of oil-associated thermogenic and secondary microbial light hydrocarbons that are discharged from the four seep sites. Light hydrocarbons discharged at the Batumi Seep area are characterized by significant enrichments of methane, but have almost similar 813C?CH4 values if compared to the other study sites. Such methane enrichments likely result from a comparably higher degree of petroleum degradation and associated formation of secondary microbial methane.

The maximum burial depth and thermal maturity of a hydrocarbon source rock controls the generation of petroleum, and data on rock maturity are necessary for an understanding of a petroleum system. RockEval pyrolysis is an established method to assess the hydrocarbon generation potential, the type of organic matter (kerogen type), but also the thermal maturity of hydrocarbon source rocks. Data on the thermal maturity of source rocks and/or of the generated hydrocarbons are, however, often lacking either, because (i) the source rock itself is not available or (ii) today's maturities cannot be directly linked to a generated petroleum, because petroleum generation and expulsion may have taken place at an earlier and less mature stage of the source rock. Indirect records of source rock maturities can be inferred from the physical properties of petroleum (e.g, API gravity), from biomarker abundances or from individual hydrocarbon ratios (including biomarkers). Using an adapted direct Rock-Eval pyrolysis approach for petroleum samples we present data from oils from the BGR petroleum archive. We distinguish between two hydrocarbon release-stages during Rock-Eval pyrolysis of which the first represents a vaporizable midmolecular (S1(oil)) fraction (< 400 degrees C; n-C-15 -> n-C-40) and the second (S2(oil)) fraction (> 400 degrees C; > n-C-40) most likely represents a residual higher-molecular weight petroleum fraction generating hydrocarbons by pyrolytic destruction. Using this program, we calculate an "Oil Composition Index" (OCI). Unless processes like biodegradation, evaporation or migration can affect OCI values, in a relatively well known petroleum system without major influences from these processes (the Gifhorn Trough in the Lower Saxony Basin [LSB] in Northern Germany), our data indicate that maturity of the source rock during expulsion is key for OCI. Application of Rock-Eval on a large set of oils from the entire LSB demonstrates that OCI values further hold information on the kerogen-type of the source rock (Wealden vs. Posidonia shales). (C) 2020 The Author(s). Published by Elsevier Ltd.

Conventional studies of petroleum basins associate oil generation with the gradual burial of organic-rich sediments. These classical models rely on the interplay between pressure, temperature, and the time required for organic matter transformation to oil and gas. These processes usually occur over geological timescales, but may be accelerated by rapid reactions when carbon-rich sediments are exposed to migrating magmatic fluids. The spectacular Lusi eruption (north-east Java, Indonesia) is the surface expression of the present-day deep interaction between volcanic and sedimentary domains. Here we report the ongoing generation of large amounts of hydrocarbons induced by a recent magmatic intrusion from the neighbouring Arjuno-Welirang volcanic complex. We have investigated a unique suite of oil and clast samples, and developed a detailed conceptual model for the complex hydrocarbon migration history in this part of the basin by integrating multidisciplinary techniques. Our results show that palynology, organic petrology, and chlorite microthermometry are the most sensitive geothermometers for basins affected by recent magmatic activity. These findings further our understanding of the driving mechanisms fueling the world’s largest active mud eruption and provide a unique dataset to investigate modern hydrocarbon generation processes.

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Geochemical analyses were used to classify 39 Zechstein (Late Permian, Lopingian) Main Dolomite (Ca2) crude oil samples from fields in the eastern and southern sector of the Southern Permian Basin (SPB) of Europe and to provide new insights into the origin of the oil. Geochemical data indicate that Ca2 oils were generated in the early-to-late oil window and are mostly non-waxy oils. Various biomarker and stable carbon isotopic ratios were used to identify source and depositional settings for source rocks of Ca2 oils arranged within 10 distinct oil groups. Specifically, the geochemical analyses and oil-oil correlations revealed a set of characteristic biomarkers including an even-over-odd predominance (EOP) for the C20-30 n-alkanes, C40 carotenoid occurrence (isorenieratane, chlorobactane, β-isorenieratane), bisnorhopane/hopane (BNH/H) ratios >0.1, high abundances of C35 homohopanes and elevated concentrations of C32 and C34 homohopanes, a predominance of C29 homologues among 4-desmethyl steranes in the majority of oil samples, and a high abundance of diasteranes. Stable carbon isotopes and biomarkers provided ample evidence that Ca2 oils were generated from predominantly algal-rich marly carbonate/evaporite source rocks located in the lower slope/shallow-basin and lagoonal facies of the Ca2 basin, all deposited under suboxic-anoxic (euxinic) conditions. In the case of all higher maturity oils, the source rocks could not be reliably identified but high (>2) C24Tet/C23 values suggest a carbonate-evaporite depositional setting.