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30th International Meeting on Organic Geochemistry (IMOG 2021)
- Conference date: September 12-17, 2021
- Location: Online
- Published: 12 September 2021
201 - 279 of 279 results
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Organic Matter Input to Marine Sediments off East Antarctica
Authors Z. Li, S. George and H. SadatzkiSummaryTo investigate the organic matter input to the East Antarctic sea floor during marine isotopic stages (MIS) 1 to 3, twenty samples from two kasten cores, KC02 (0–230 cm) and KC04 (0–245 cm) from the continental slope close to the Sabrina Coast were studied for their organic geochemical characteristics. The aliphatic and aromatic compounds all indicate a strong terrigenous organic matter input with a minor marine algal contribution. The transportation of organic matter by glaciers from the Antarctic land-mass and dust deposition could be possible explanations for such a significant terrigenous and allochthonous input.
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Under Low Oxygen Conditions, Ascomycete Fungi Blur Their Ergosterol Biosignature by Taking Up Sterols from the Environment
Authors C. Heim and C. BeimfordeSummaryStromatolithic Fe-oxide precipitating biofilms living in the subsurface at 160m depth of the Äspö Hard Rock Laboratory were investigated for their biomarker content and the inhabiting microbial community. Analytic microbial, molecular and biochemical methods, amongst next generation sequencing and biomarker studies (GC-MS), allowed a detailed characterization of the microbial community inhabiting the biofilms which surprisingly concisted of bacteria, archaea and fungi. Biomarker studies of the fungal isolates implicate that ascomycete fungi produce ergosterol under ideal oxygen conditions. In natural environments with low oxygen conditions, like in the investigated biofilm, fungi are able to take up sterols from the environmental food source, thereby blurring their conventional biomarker signature. Due to the ubiquity of the analysed ascomycetes in sediments, our results imply that fungi may simply be overlooked if we just rely on the classical ergosterol biomarker.
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The Kupferschiefer in Spremberg, East Germany: Signals of Organic Matter Alteration from Hydrogen Isotopes and Nso Compounds
Authors S. Poetz, Y. Liu, A. Vieth-Hillebrand, S. Yang, J.M. Magnall, S.A. Gleeson and H. SchulzSummaryOre forming processes in sediment-hosted sulfide deposits are widely regarded to involve organic matter (OM). However, the precise nature of interactions between OM and hydrothermal fluids are still debated as well as how the interconnected reactions develop over geological timescales. Here, we present results from an advanced characterization of organic matter in the Kupferschiefer from Spremberg in Northeast Germany with a focus on NSO (organonitrogen, sulfur and oxygen compounds) and compound specific hydrogen isotopes.
The observed strong enrichment of D in the n-alkanes that is not linked with thermal maturity likely occurred due to intensive hydrogen exchange with an evaporitic brine with an initial high δD value. Signals of slight degradation and oxidation argue against interaction of the organic matter with strongly oxidizing and hot metal bearing brines. Further work is required to assess if the fluids have become less oxidised and cooler due to water-rock interactions during migration (and yet maintained copper in solution) or if different fluids were involved in the mineralization of the Spremberg Kupferschiefer.
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Combined Source and Maturity Influence on Molecular Tracers and Implications For Oil-Source Correlation in Deep Reservoirs
More LessSummaryIn this study, geochemical characteristics of two Devonian oil families in Western Canada Sedimentary Basin (WCSB) will be used as an example, to demonstrate the source affected trends in thermal maturation of common biomarker compounds in crude oils. Our results suggest that deconvolution of the possible source and maturity effects is necessary to ensure the effective application of molecular tracers in oil-source correlation of the deep petroleum systems. Comparison of the molecular parameters for the three sample sets reveals several distinct compositional straits for the evaporate and carbonate sourced oils. The most important feature of the chemical composition and molecular distributions for these oils is the significant variation in the concentrations of sulfur containing compounds and the abundance of 17(H)-hopanes relative to other terpenoid components such as 8,14-secohopanes, C23 tricyclic terpane, C24 tetracyclic terpane, 18(H)-22,29,30-trisnorneohopane (Ts) and 18(H)-30-norneohopane (C29Ts). These oils form several continuums between the extreme end members of terpane and sterane distributions likley reflecting the inherited differences in source character, diagenetic change, and thermal cracking effects between the sulfate and iron-rich source rocks. Recognizing lithofacies signature and matrix effects is important for deep reservoired fluids, as it could signficantly increase the confidence of biomarker data interpretation.
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Basin scale evaluation: Organic geochemical characteristics of northern Perth Basin (Early Triassic)
Authors T. Taniwaki, C. Elders and K. GriceSummaryBiomarker analysis has been conducted on rock samples of the Late Permian to Early Triassic Kockatea Shale containing microbial mats in the northern Perth Basin. The northern wells of the northern Perth Basin exhibit darker shale horizons and contain microbial mats. These horizons contain abundant carotenoid biomarkers attributed to PZE and microbial mats. Such biomarkers are however, not identified in the southern wells of the northern Perth basin which are deposited under more oxic conditions in a tidal regime. In the northern wells, there are fluctuations of PZE conditions intruded by oxic conditions, caused by fluctuations of the chemocline. Elevated 2α-methylhopanes index and higher renieratane and renierapurpurane/isorenieratane ratio are identified in the microbial mats formed under oxic conditions. In addition, the higher proportion of both okenane against chlorobactane and isorenieratane and C33 n-alkylcyclohexane ratio (n-C33 ACH ratio) are identified in the microbial mat facies.
The combination of organic geochemistry (biomarker analysis) and geology (core observation, well analysis and seismic interpretation) show a strong relationship between basin morphology, paleogeography and paleoenvironmental conditions. The southern wells experienced higher influence of fluvial input (oxic conditions). The northern wells, which are far north of the fluvial input show evidence for PZE conditions.
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THE DIFFERENCES IN THE YIELD, PARAMETERS AND CARBON ISOTOPES OF LIGHT HYDROCARBONS OBTAINED BY TWO COLLECTION METHODS
More LessSummaryIn this study, two liquid hydrocarbon collection methods were used to collect light hydrocarbons generated from the cracking of crude oil in closed system, and the characteristics of the products collected were compared. Relative to the liquid nitrogen direct freezing collection (LNDF) method, the traditional liquid hydrocarbon collection (TLH) method can cause the yield loss of 10%-75% of light hydrocarbons, especially low carbon number light hydrocarbons (such as nC6, nC7, benzene, toluene, and 3-methylhexane). Because the TLH method can lead to various degrees of loss for different compounds in light hydrocarbons, it can also lead to the deviation of some light hydrocarbon parameters representing oil-oil correlation, indicating the maturity of crude oil and reflecting secondary alteration of crude oil. In addition, the δ13C values of nC6, nC7, benzene, toluene and 3-methylhexane collected by TLH method are heavier. These compounds with heavier δ13C values are the ones that have suffered the most yield loss in the TLH method. Therefore, the LNDF method can more accurately reflect the yield, parameters and carbon isotopes of light hydrocarbons in closed system pyrolysis.
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Mobilization of pre-aged organic carbon in the Nile-River watershed linked to hydologic changes during the past 20ka
Authors V. Meyer, G. Mollenhauer and E. SchefußSummaryThis project seeks to detect perturbations in the carbon cycle in large (sub-) tropical watersheds during the last deglaciation and the Holocene and to understand their climatic controls. It is generally assumed that in tropical regions, the fluvially exported organic matter is rather young due to rapid carbon turnover and often dense vegetation in the catchments. However, evidence for mobilization of pre-aged organic carbon in tropical regions has recently been obtained from the Congo-River catchment. Hydrology is suggested as a major control on the mobilization of pre-aged organic matter mediating the carbon storage in river-associated wetlands. Yet, the link between hydrology and the mobilization of old carbon in tropical regions as well as the associated climate feedbacks remain poorly constrained. Here, we investigate whether hydrologic changes affected the re-mobilization of pre-aged terrigenous organic carbon in the Nile-River watershed during the past 20ka. We present biomarker data from a sediment core recovered from the Mediterranean. Applying compound-specific radiocarbon analysis on terrigenous biomarkers we identify intervals of intensified mobilization of pre-aged terrigenous organic matter. We combine these data with compound-specific stable hydrogen isotope compositions of the same compounds to reconstruct past hydrologic conditions and their effects on mobilization of pre-aged organic matter.
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NOVEL INSIGHTS INTO PALEOVEGETATION RECONSTRUCTION OF THE BEERBERG PEAT SEQUENCE (THURINGIA, GERMANY) THROUGH THE USE OF MULTIPLE PROXIES
Authors C. Thomas, M. Galka, S. Czerwiński, K. Knorr, E. Van Loon, B. Jansen and G. WiesenbergSummaryUsing a core from the Beerberg peatland, we investigated the paleovegetation through multiple proxies including macrofossil, pollen, and biomarkers. The biomarker results, including n-alkanes, n-alcohols, and n-fatty acids, were used with the VERHIB model to estimate vegetation composition. The macrofossil and pollen results were used to calibrate and verify the model.
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Organic Geochemistry Studies of Carbonate-Evaporative Sourced Oils in the Southernmost Gom
Authors A.F. Cedeño Motta, S. Ohm and A. EscalonaSummaryOils derived from carbonate-evaporative sources are characterized by low API gravities, and overall low amounts of hydrocarbons as compared to polars and asphaltenes ( Orr, 1996 ). These aromatic-asphaltic oils originate from sulfur-rich type I-IIS kerogens at low levels of thermal stress ( Orr, 1996 ). The Peten-Corozal Basin in Guatemala and Belize lies at the southernmost end of the Mexican Gulf of Mexico (GoM) and hosts the most proximal areas of a mid-Cretaceous carbonate-rich platform, which is known to contain several source rock intervals. Bulk geochemical and biomarker data are used here to characterize the organic facies generating the oils found in the Peten-Corozal Basin.
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Carbon and Hydrogen Isotopic Analyses of Bacterial Lipids Reveal Dramatic Biogeochemical Responses to Ancient Warming
Authors R. Pancost, D. Naafs, J. Blewett, G. Inglis, V. Lauretano, X. Dang, S. Xie, A. Pearson, F. Elling and L. KatteinSummaryHere, we explore the use of bacterial and archaeal lipid carbon and hydrogen isotopic compositions to explore carbon cycling processes in modern settings and in response to ancient warming events. Investigations of Holocene peat and Eocene lignites reveal both stability over long time-scales but rapid, transient responses to climate perturbations.
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Pyrolysis of an Artificially Matured Shale Havning Type Ii Kerogen and Its Retained Oil: Implications for Late Gas Potential
More LessSummaryWe present the results of the pyrolysis using shale powder to see whether the presence of minerals and/or water has significant effects on the kerogen-oil interactions and related late gas generation. The results indicates minor effects of minerals and water in the shale on the gas generation processes under the employed conditions in this study. The oil expulsion has played an important role in enhancing late gas generation, which may be associated with the changes in the kerogen structure.
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Flame Extinguished! End-Triassic Mass Extinction Polycyclic Aromatic Hydrocarbons Reflect More Than Fire
Authors C. Fox, J.H. Whiteside, P.E. Olsen and K. GriceSummaryWidespread biomass burning events during the end-Triassic mass extinction are supported by combustion-derived polycyclic aromatic hydrocarbons (PAHs) from European and Greenland sections. However, our investigation into a range of PAHs from focal end-Triassic extinction outcrops in the southwest UK reveals otherwise. We find major discrepancies in combustion-derived PAHs that support ETE biomass burning events were more localised. In addition, we find evidence of soil erosion during the newly proposed marine expression of the end-Triassic extinction and no evidence of biomass burning. Finally, below the extinction horizon good correlation between increases in combustion-derived PAHs and low molecular weight S- and O-containing PAHs associated with the terrestrial realm suggest that increased continental run off could account for changes in pyrogenic PAHs given their degraded but pyrogenic source.
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Molecular Characterization of Dissolved Organic Matter in Deep Geothermal Fluids
Authors A. Leins, A. Vieth-Hillebrand, S. Regenspurg, F. Eichinger and S. PötzSummaryWithin the Horizon 2020 REFLECT project (Redefining geothermal fluid properties at extreme conditions to optimize future geothermal energy extraction), organic compounds in deep fluids from geothermal sites are being characterized and interpreted with regard to numerous site parameters. DOC concentrations and the relative abundance of DOC fractions from fluid samples of two sites located in Austria and Germany were analyzed via Liquid Chromatography - Organic Carbon Detection (LC-OCD). Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS) with Electrospray (ESI) and atmospheric pressure photoionization (APPI) has been applied to characterize DOM on a molecular level and its changes of time and flow path. The Austrian site Bad Blumau is located in Styrian Basin and uses deep fluids from a Palaeozoic carbonate reservoir (104°C). Samples were taken from production and injection side, as well as from the heat central. The Berlin drill site is part of the North German Basin and targets a limestone formation (Muschelkalk) with a reservoir temperature of 32°C. Samples were taken during a lift test over a period of 25 hours. A better understanding of the role of organic compounds in geothermal fluids might help to optimize present and future geothermal energy extraction.
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STRATIGRAPHIC CHANGES OF GEOCHEMICAL SIGNATURES OF THE CENOZOIC BALINGIAN COAL, SARAWAK, MALAYSIA.
Authors N.S. Zainal Abidin, K.A. Mustapha, W.H. Abdullah and M.H. HakimiAbstractThe thick coal seams of the Cenozoic Balingian coals in the Liang Formation, Sarawak, Malaysia are of interest in the present work. Through this paper, the genesis of the environmental conditions of thick coal seams in relation to their ancient peat and paleomires were investigated in vertical profile. A total of 40 coal samples were prepared and characterised based on organic geochemical analysis. The TOC content range is 40.5 to 58.2 wt.%, and the HI values range from 43 to 441 mg HC/g TOC in the samples tested. Collectively, the analysed coal samples were characterised by mixed Type II-III kerogen and predominantly Type III kerogen and demonstrated the ability to produce substantial gas and some oil generation potential. The carbon/nitrogen ratio of over 20, notable odd-over-even predominance, high long chain C25–35 n-alkanes (mean 79%), moderate ratios of pristane/phytane (mean 1.37) and diterpenes (mean 1.06), moderate carbon preference index (CPI, mean 1.98), high Tm/Ts (mean 2.52), high C29 norhopane/ C30 hopane (mean 3.21) and high C29 steranes (mean 63%) of the studied coals indicate the dominance of terrestrial source inputs. The ratio of C27/C31 (0.06 – 3.64) may further indicates a decrease in woody vs. herbaceous input characterised the upward trend. Peat’s doming is a significant factor of lowered in ash, and sulphur. The mildly influenced of brackish water in the ombrogenous peat were observed by slightly increase of C27, C28 steranes and decrease of C29 steranes and slightly increase of sulphur content. The ancient peat and mires are subjected to ever-wet climates, however an alternance relatively wet and dry episodes were deduced from the variation of n-alkanes, pristane/phytane and diterpanes ratios. The biomarker signatures, furthermore, indicative of oxygen-deficient and water-saturated conditions in the precursor mires due to seasonal dry/wet climates by high and reduced rainfall during peat growth.
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Organic Matter Distribution is Controlled by Sedimentological Parameters in Marine Oxygen Minimum Zone
Authors E. Bruni, T.M. Blattmann, N. Haghipour, D.B. Montlucon and T.I. EglintonSummaryOrganic matter (OM) in marine sediment is usually associated with mineral surfaces because it offers protection from degradation. As the amount of OM on a particle increases, so does its grain size, but its density decreases. The reduced density of the surface sediment results in a high propensity for resuspension, therefore aggregate transport represents an efficient way to relocate OM to offshore sites and depocentres on the continental slope. This process has significant effects on reconstructing past environments as OM is laterally displaced from where it was produced.
OM abundance in sediments is negatively correlated to oxygenation state; hence, oxygen minimum zones are often characterised by a soft, soupy sediment surface. We study samples from the Benguela upwelling system offshore Namibia, where widespread lateral transport has been described and significant age differences are reported between compounds (alkenones, crenarchaeol), calcareous shells, and bulk organic carbon. Working with the comprehensive dataset on environmental tracers on the Benguela upwelling system, we use bulk molecular tracers on core-top samples and their respective grain size and density fractions to trace resuspension effects on sedimentary OC ageing in anoxic and oxic water condition.
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Geochemical Fluid Classifications Using Supervised Machine Learning Techiniques
Authors G. Spaak, R. Van der Ploeg, J. Weijers, S. Van den Boorn, S. Bierman and O. PodlahaSummaryThis study explores the use of novel data analysis techniques such as supervised machine learning algorithms to unlock the full potential of large geochemical datasets
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Oil and Gas Potential Source of the Lake Baikal Sediments: Gas-Geochemical and Biomarker Study
Authors O. Vidishcheva, M. Delengov, N. Fadeeva, E. Poludetkina, E. Bakay, G. Akhmanov, A. Mazzini, N. Morozov and O. KhlystovSummaryThis paper presents the results of surface geochemical exploration of Lake Baikal bottom sediments. Such studies provide information on the quality, thermal maturity, age, and distribution of the underlying source rock in under-explored and poorly understood basin. The studies presented in the work were obtained during the Class@Baikal expeditions (2014–2020).
Gas-geochemical and biomarker study permit determine that the initial organic matter of both gas and oil source rocks has a mixed origin with a predominance of the terrestrial component.
Most of the samples of organic matter from the bottom sediments showed a severe biodegradation process. The samples from the oil seep present a unimodal distribution with n-C23 to n-C25 as the major peaks. The CPI values ∼ 0.97, and the Pr/Ph ratio is close to 1 indicating an input of algal/microbial organic matter with a significant input of terrestrial matter.
Biomarkers evidence the high maturity of initial organic matter (end of the oil generation zone - the beginning of the gas generation zone). Thus, the ratio Ts / (Ts + Tm) up to 0.78 (Parameter MPI-1 up to 1.59).
The δ13C isotopic composition ranges between −26 and −28‰ indicates a terrestrial organic matter origin.
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Development of Organic Matter Porosity During Thermal Maturation: Study on the Example of the Bazhenov Formation Source Rocks
Authors T. Karamov, E. Leushina, E. Kozlova, T. Bulatov and M. SpasennykhSummaryThe porosity of shales consists of mineral matrix voids and pores in organic matter. Since organic matter occupies up to 50% of source rock volume and most of the pores are connected, this type of porosity may considerably contribute to saturation of rocks by hydrocarbons. The study is devoted to the investigation of organic matter (kerogen) porosity development during thermal maturation of source rocks using SEM. On the example of the Bazhenov Formation source rocks, we have demonstrated the presence of nano- and micropores in solid organic matter at the beginning of the oil window and a developed porous structure at the end of the oil window with organic matter porosity of more than 50% of kerogen volume. The obtained results expand existing knowledge on void space volume of the Bazhenov formation and show that organic matter porosity of mature kerogen may several times exceed intergranular porosity of rock.
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New Frontiers in Compound-Specific δ2H Analysis
Authors S. Lengger, S. Kelly, K.W.R. Taylor, Y. Weber, S. Kopf, R. Berstan, M. Seed, I. Bull, J. Meyser, W. Leavitt, J. Blewett, A. Abrahim, A. Cannavan, A. Pearson and R. PancostSummaryElementar UK Ltd present present two pioneering new techniques for the analysis of larger and/or more polar organic molecules of biogeochemical interest which are traditionally considered unamenable for gas chromatography stable isotope ratio mass spectrometry (GC-IRMS) analysis, which have been developed by and in collaboratoration with Elementar GC-IRMS users from a variety of laboratories. This includes a rapid one-step derivatization procedure for the isotope analysis of the non-exchangeable hydrogen in mono and disaccharides and subsequent conversion to H2 by chromium reduction ( Abrahim et al, 2020 ), and the development of a high-temperature GC-IRMS (HTGC-IRMS) methodology employed for the analysis of a suite of compounds of interest ( Lengger et al., 2021 ).
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Preliminary Ams 14C Measurements from Holocene-Age Carbonate Concretions
Authors A. Mojarro, B. Uveges, M. Roberts, J. Vinther and R. SummonsSummaryIn order to better constrain the timescale and mechanisms for concretion formation, we have analysed two Holocene-age concretions from contrasting depositional environments which display divergent levels of soft-tissue preservation. Inorganic carbon samples (carbonate) were taken at successively greater distances from the center of the concretion for accelerator mass spectrometry (AMS) 14C dating.
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USING BACTERIAL HOPANOIDS TO FINGERPRINT PEAT-DERIVED ORGANIC MATTER ALONG THE TERRESTRIAL-AQUATIC CONTINUUM
Authors G. Inglis, B.D.A. Naafs, R. Pancost, J. Toney and J. BendleSummaryPeat is a heterogeneous mixture of (partly) decomposed plant material that forms large carbon stores. However, if peat-derived organic carbon (OCpeat) is eroded and transported along the terrestrial-aquatic continuum, it may act as a source of carbon to the atmosphere. Modern observational evidence suggests that carbon losses from peatlands are significant and an increasing component of the global carbon cycle ( Moore et al., 2013 ). Although relatively well-constrained at present, the transfer of OCpeat along the terrestrial-aquatic continuum remains poorly constrained in ancient settings. Radiocarbon measurements can be used to distinguish between fresh OC and older peat-derived OC ( Moore et al. 2013 ). However, because the half-life of 14C is relatively short, this approach cannot be used beyond ∼50,000 years and alternative techniques are needed to probe this during different climate states, e.g. greenhouse climates of the Eocene. Here we explore whether the stereochemical properties of bacterial hopanoids can be used to fingerprint peat-derived OM along the terrestrial-aquatic continuum.
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USING BACTERIAL HOPANOIDS TO FINGERPRINT PEAT-DERIVED ORGANIC MATTER ALONG THE TERRESTRIAL-AQUATIC CONTINUUM
Authors G. Inglis, B.D.A. Naafs, R. Pancost, J. Toney and J. BendleSummaryPeat is a heterogeneous mixture of (partly) decomposed plant material that forms large carbon stores. However, if peat-derived organic carbon (OCpeat) is eroded and transported along the terrestrial-aquatic continuum, it may act as a source of carbon to the atmosphere. Modern observational evidence suggests that carbon losses from peatlands are significant and an increasing component of the global carbon cycle ( Moore et al., 2013 ). Although relatively well-constrained at present, the transfer of OCpeat along the terrestrial-aquatic continuum remains poorly constrained in ancient settings. Radiocarbon measurements can be used to distinguish between fresh OC and older peat-derived OC ( Moore et al. 2013 ). However, because the half-life of 14C is relatively short, this approach cannot be used beyond ∼50,000 years and alternative techniques are needed to probe this during different climate states, e.g. greenhouse climates of the Eocene. Here we explore whether the stereochemical properties of bacterial hopanoids can be used to fingerprint peat-derived OM along the terrestrial-aquatic continuum.
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Evidence for the Role of Water in Ch4 Generation from Long-Term, Low Temperature Experimental Maturation of Immature Shales
Authors K. Doiron, P. Sauer, A. Schimmelmann, M. Mastalerz, A. Drobniak and S. BrassellSummaryThe conventional paradigm for generation of economically viable petroleum reserves involves thermal cleavage of C-C bonds within sedimentary organic matter. However, there is evidence for alternative chemical pathways yielding non-microbial methane generation at low temperatures. In addition, assessing the role of water in methane generation at temperatures lower than those required for it to form by thermal cracking represents a critical step for evaluating processes likely involved in catalytic methanogenesis. Previous pyrolysis experiments of source rocks in the presence and absence of water have yielded insights on the role of water in CH4 generation at a range of maturities including late-stage thermogenesis. Our studies explore the role of catalytic pathways in CH4 generation by experiments simulating maturation of immature source rocks at temperatures insufficient to achieve thermal cleavage of C-C bonds. These hydrous maturation experiments demonstrate that immature shales can generate CH4 at temperatures (80–100 °C). They establish the potential to yield δ13C values <-70 ‰ commonly associated with microbial gas by early CH4 generation at low maturity levels. Incorporation of 2H derived from 2H-enriched water in these hydrous maturation experiments confirms the role of water in catalytic processes generating CH4 at low temperatures.
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Trace Elements in Antarctic Algae and Moss
Authors S. Chatterjee, S. Das, A. Chakraborty and S. PalchaudhurySummaryConcentrations of Al, Fe, Co, Cu, Mn, Ni, Zn and V, were measured in algal and moss samples collected from areas surrounding different freshwater lakes in Larsemann Hills of East Antarctica. This study focuses on the relative distribution of these elements within these organisms, and the extent of bioaccumulation occurring in the algal and moss samples.
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Assessment of Sedimentary Botryococcenes in Vietnamese Maar Lakes as Paleoclimate Proxies
Authors K. Doiron, L. Stevens and S. BrassellSummaryIn contemporary settings, suites of C30-C37 hydrocarbons with botryococcene-related structures, including monocyclic and bicyclic components, have been identified in East African maar lakes and in the Everglades. The sedimentary concentrations of these compounds can be substantive, dwarfing other aliphatic hydrocarbon constituents. Distributions of botryococcenes in sediment samples spanning the past 32 kyr from Lake Masoko, Tanzania, reveal temporal variations attributed to variations in dominant strains of B. braunii rather than a response to changing environmental and climate conditions. Recognition of similar suites of botryococcenes in Vietnamese maar lakes with records that extend back past the Last Glacial Maximum now affords the opportunity to further assess the possibility that botryococcene distributions may record climatic information in these settings. The relative abundances of C34:2 botyrococcene (A) and C34:3 monocyclic botyrococcene (M) in a sediment core from Lake Ia M’He in the Central Highlands of Vietnam, expressed as % M/(A+M), reveals a progressive decrease in the proportions of the monocyclic component relative to the acyclic botyrococcene from the last glaciation to the recent past. These data suggest that assessment of links between the distribution of these specific botyrococcene components in Lake Ia M’He sediments and changes in climate is merited.
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Unsupervised and Supervised Machine Learning to Classify Oils from the Norwegian Continental Shelf North of 62°N
Authors J. Rinna, P. Aursand and B. LerchSummaryUnsupervised and supervised machine learning algorithms were applied on two large geochemical data sets, one from the Norwegian Sea and an other from the Barents Sea. Data bases were thoughtfully examined with regard to sample type, contamination, and data integrity, respectively. The purpose of this work is to compare both traditional and machine learning approaches for oil-oil and oil-source rock correlation on two large datasets on the Norwegian Continental Shelf. Unsupervised clustering of oil samples produces classes that are, overall, consistent with geological understanding of the origin of the oils. We established a workflow using supervised learning that enables an expert to infer oil types and source rock correlation in an immature (low confidence) area given available samples in a mature (high confidence) area. We emphasize through examples the importance of data quality and data consistency when using machine learning for automatic oil typing.
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Characteristics of dissolved organic matter released by hot-water extraction of organic-rich Guaymas Basin sediments
Authors J. Brünjes, M. Seidel, A. Teske and F. SchubotzSummaryThe Guaymas Basin (GB) in the Gulf of California is a young rift system where hot basaltic sill intrusions into unconsolidated organic-rich sediments lead to the generation of complex petroleum compounds and discharge of bioavailable dissolved organic matter (DOM) into the overlying water column. However, the contribution of hydrothermal heating to the release of recalcitrant DOM, for instance polycondensed aromatic compounds (PCAs), has not been studied yet. PCAs such as dissolved black carbon in marine DOM are thought to be mainly derived from incomplete combustion of terrestrial organic matter on land and accumulate in the oceanic carbon reservoir over thousands of years. Recent research, however, points to additional sources with a marine isotopic signature, for instance petrogenic carbon.
In our study, we investigate whether hydrothermally heated sediments release DOM that can contribute to the recalcitrant oceanic DOM pool. We simulated hot-water discharge events by Soxhlet extraction of sediment core samples from GB sites with in situ temperatures up to >105°C and analyzed DOM by ultra-high resolution mass spectrometry (FT-ICR-MS) and optical spectroscopy. Our preliminary results suggest that hydrothermal mobilization of DOM from organic-rich sediments can release aromatic and sulfur-enriched compounds that may contribute to the recalcitrant deep oceanic DOM pool.
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DEEP MICROBIAL SIGNATURES IN TERTIARY SEDIMENTS OF THE HARTOUŠOV CO2 MOFETTE SYSTEM, NW BOHEMIA
Authors K. Mangelsdorf, K. Adler, Q. Liu, H. Kämpf, R. Bussert, B. Plessen, H.M. Schulz, D. Lipus, P. Krauze, F. Horn, D. Wagner and M. AlawiSummaryPast and present microbial signatures were investigated in deep sedimentary successions of the Hartousov CO2 mofette system (NW Bohemia, Czech Republic). In about 78 m depth a CO2 reservoir was penetrated by the Hartousov borehole leading to a CO2 blow out. This core interval was selected for further analysis to test whether this section could represent a specific habitat stimulating a deep CO2-related microbial ecosystem. We applied organic geochemical, biogeochemical and microbiological approaches to characterize the deep mofette ecosystem. Necrotic microbial biomarkers reflect the microbial biomass during time of deposition and are not suitable to trace the deep biosphere at the Hartousov site. Common intact phospholipid life markers (IPLs) were not detected in significant amounts. However, two clusters of unknown lipids presumably with a sulfonic head group and ether side chains with different chain length could be identified, which might represent specific mofette related bacteria. Microbiological analysis point to a low abundant but characteristic microbial community consisting of Acidovorax, Aquabacterium, Hydrogenophaga, Sulfuricurvum and unknown genera of the family Comamonadaceae. Overall, although there is an adapted deep microbial community in the CO2 reservoir of the mofette system, this interval does not seem to represent a specific hotspot for deep microbial life.
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Arctic Alaska Petroleum Systems: Characterizing Mixtures and Charge History Using Advanced Geochemical Technologies
Authors P. Botterell, J.M. Moldowan, D. Houseknecht, S. Barbanti, J. Dahl and P. LillisSummaryThe Arctic Alaska petroleum province is geologically and geochemically complex. Mixed hydrocarbon charge from multiple source rocks and/or levels of thermal maturity is common within an individual oil pool. Molecular fingerprinting tools are used in the present study to characterize and establish genetic relationships among a suite of oils sampled from multiple discoveries and fields across the North Slope. Applications of Advanced Geochemical Technologies (AGTs) are utilized to identify and correlate fluids generated from deep sources, determine co-sources for oil mixtures, and ascertain controls on hydrocarbon provenance ( Dahl et al., 1999 ; Moldowan et al., 2015 ). The AGTs presented here comprise quantitative diamondoid analysis (QDA), quantitative extended diamondoid analysis (QEDA), compound specific isotope analysis of diamondoids (CSIA-D), biomarker assessments by gas chromatography-tandem mass spectrometry (GC-MS-MS), CSIA of hopane and sterane biomarkers (CSIA-Bh and CSIA-Bs, respectively), and CSIA of n-alkanes (CSIA-Ac). Diamondoid analyses reveal mixed-oil accumulations in most sampled reservoirs and allow the source(s) of both post-mature and oil-window maturity charge contributions to be identified. Age-diagnostic and source-sensitive biomarker parameters provide an assessment of age ranges and depositional environmental constraints of the sources of the oil-window components. Results of CSIA-Bh, -Bs, and -Ac provide greater insight into paleoenvironments of the generative sources.
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Testing the Sponge Biomarker Hypothesis Through Identification of 24-Isopropenylcholesterol Biosynthesis Enzymes
Authors M. Brown, H. McShea, B. Olagunju, J. Giner and P. WelanderSummaryIn order to improve interpretations of the demosponge biomarker 24-isopropylcholestane (24-ipc), we examine the biosynthesis of side chain alkylated sterols, including 24-isopropenylcholesterol, through functional analysis of sterol methyltransferases (SMTs). We experimentally demonstrate sponge SMTs are capable of multiple rounds of methylation as previously hypothesized. We also identify functional SMTs of probable bacterial origin capable of producing 24-methyl, 24-ethyl, and 24-isopropyl sterols, suggesting bacteria may be an overlooked source of side chain alkylated steranes in the geologic record, including 24-ipc.
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Pyrolysis-Compound Specific Isotope (δ13C, δ2H) Analysis (PY-CSIA) of Lignin Phenols in Soils from a Mediterranean Agro-Ecosystem
SummaryThis communication describes and validates a methodology based on analytical pyrolysis for the direct measure of lignin-derived phenols δ13C and δ2H isotope composition. The technique combines Py-GC with combustion (for C) and high-temperature conversion (for H) reactors and a continuous flow isotope ratio mass spectrometer (IRMS) (Py-CSIA).
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Cholesterol Production by the Bacterium Enhygromyxa Salina
Authors P. Welander and A. LeeSummaryWe demonstrate the production of cholesterol by Enhygromyxa salina, a heterotrophic marine bacterium. Cholesterol is a highly modified sterol that is preserved as cholestane in the rock record. Cholestane is often indicative of heterotrophic microbial eukaryotes. The production of cholesterol by E. salina is the first reported instance of cholesterol synthesis by a bacterium. Through genomic analyses, we show that E. salina has cholesterol biosynthetic genes that are homologous to the eukaryotic cholesterol pathway. However, we do observe some biosynthetic proteins that are unique to E. salina. Further, extensive lipid analyses demonstrate that cholesterol in this organism is conjugated to either a lipid or protein moiety and does not exist as a free sterol. Conjugated sterols play significant physiological roles in eukaryotes and understanding the nature of conjugated cholesterol in E. salina may provide insight into the physiological roles of these lipids in bacteria. Through these studies, we should be able to better assess what implications, if any, cholesterol production by bacteria has on our interpretation of sterol biomarkers in the rock record.
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Organic Carbon Aging as Recorded in Marine Sediments from the Cabo Frio Upwelling System (South-Eastern Brazil)
Authors M. Ceccopieri, A.L. Albuquerque, D. Lessa, R. Carreira and G. MollenhauerSummaryThe ¹⁴C-age offset between the organic matter (OM) and carbonates buried in marine sediments of the Cabo Frio upwelling system during the past 6.5 kyr was investigated. The ¹⁴C-ages of the OM were 787 ± 166 years older than those of foraminifera, which might be indicative of a long-term storage and re-processing of the OM on the mid-shelf sediments caused by local upwelling-related hydrodynamic processes. A gradual increase up to the maximum ¹⁴C-offset from 5.8 to 4.0 cal kyr BP may be a response to the intensification of the Brazil Current activity over the shelf, extending the sediment translocation and, consequently, the OC aging. Also, an intensification of the South American monsoon during this period might had favored the input of pre-aged terrigenous OM. Between 4.0 and 2.0 cal kyr BP the ¹⁴C-offset decreases, possibly due to a subsequent weakening in the bottom currents. After 1.8 cal kyr BP, a slightly increase in the ¹⁴C-offset could be caused by an upwelling enhancement. These results reinforce the existence of a temporal decoupling between the organic proxies commonly used in paleoceanographic studies and the correspondent age models applied, which highlights the need to interpret proxy-based information with caution, especially in upwelling regions.
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Calibration of Bacterial 3-Hydroxy Fatty Acid-Based Paleoclimate Proxies in Global Soils, Marine Sediments and Lakes
Summary3-Hydroxy fatty acids (3-OH-FAs), derived from Gram-negative bacterial outer membranes, have received recent attention for their potential as both: a) terrestrial temperature and pH palaeoclimate proxies; and b) marine sea-surface temperature proxies. However, the distribution and performance of 3-OH-FA based proxies at a global scale and in lake sediments remains largely unknown. This is a critical gap in knowledge as lake sediments are the most common terrestrial archive for paleoclimate. Here we explore (including the application of machine learning tools) 3-OH-FA lipid distributions in 186 globally distributed soils. We also investigate co-located lake sediments and catchment soils in China and the USA. We find that the ratio of anteiso to normal 3-OH-FAs of the C15 or C17 homologues (RAN15 or RAN17) shows a significant linear relationship with mean annual air temperature (MAAT) in global soils. However, in lakes these do not appear to be suitable for temperature calibration. Analysis of gene community composition reveals that Gram-negative bacterial populations from lake sediments are distinct from both soils and marine sediments (but are closer to the former). We find strong relationships between alternative 3-OH-FA based proxies and MAAT in lakes. Thus 3-OH-FA geochemical tools continue to show promise for palaeoclimate reconstruction.
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Pore water concentrations of low-molecular-weight organic acids – effects of thermal generation and decomposition
Authors O. Helten and C. Ostertag-HenningSummaryAt elevated temperatures e.g. caused by heat-emitting, high-level radioactive waste, low-molecular-weight organic acid (LMWOA) generation and decomposition from organic matter take place simultaneously. In the process, the generation can exceed the decomposition for individual compounds – and vice versa. As a result, concentrations of LMWOA in aqueous geological fluids undergo constant, temperature-dependent changes. This study presents hydrous pyrolysis data for the generation of three LMWOA (formate, acetate, and oxalate) from a natural claystone (Opalinus Clay). Experiments were conducted between 80–200 °C and at 20 MPa over 504 to 906 hours. Thus, the material was exposed to conditions resembling diagenesis to catagenesis. The results clearly show individual generation and decomposition behaviors. As an example, at 200 °C, acetate was continuously generated, whereas formate experienced rapid generation and successive decomposition. Oxalate decomposition outcompeted its generation, which resulted in concentrations below the limit of quantification after 48 hours. The observations are consistent with calculations using kinetic parameters for thermal LMWOA decomposition. This study emphasizes the importance of simultaneous thermal LMWOA generation and decomposition in the context of mineral dissolution, metal-ion and radionuclide complexation, for sorption processes and as a pathway to sustain microbial communities e.g. in the deep biosphere.
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An Overture to the Anthropocene: Isotopic Evidence of Strong CO2 Modulation of the Tropical Monsoon at the Dawn of Dinosaurs
Authors J. Whiteside, M. Schaller, P. Olsen, M. Margulis-Ohnuma and J. YagerSummaryGlobal climate model experiments predict that greenhouse-induced warming results in an intensification of the hydrological cycle, with amplification of the effects of astronomically paced precipitation cycles. Extreme high-CO2 intervals during the hothouse Early Mesozoic provide a test bed for this warming-induced hydroclimate hypothesis and a potential analog for our future. Here we present leaf wax n-alkane hydrogen isotope ratios, as well as lithological, plant structural forms, carbon isotope ratios, and the soil carbonate proxy for atmospheric pCO2, from non-marine strata in eastern North America, and marine strata in Peru for the hothouse world of the Late Triassic and Early Jurassic (232-200 million years ago). We place these data in the context of the modulation of the tropical monsoon by pCO2 and the ecological ascent of dinosaurs at the end-Triassic mass extinction.
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Intact Coenzyme-A-Thioester Analysis as a Tool to Characterize Bacterial Metabolism of Single Substrates and Crude Oil
More LessSummaryThis presentation reports on the development of a sensitive screening method for the detection of intact coenzyme-A-thioesters in microbial samples and its application to the study of an anaerobic n-alkane-utilizing bacterium growing under different substrate conditions. In particular, we report for the first time the coenzyme-A-thioester pattern occurring during growth of a bacterium with crude oil as a complex substrate mixture. The study reveals that intact coenzyme-A-ester analysis is a promising tool for the detection and characterization of active metabolism in microorganisms. The sensitivity of the newly developed method allows screening and identification of coenzyme-A-thioesters in microbial samples even if they occur in strongly differing abundances. We envisage that this approach can also be applied to natural samples for tracing ongoing metabolic processes.
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Deciphering the Input from Fossil and Recent Organic Carbon to Soils in Recultivation Sites in Lusatia, Germany
By S. IsmailSummaryPrevious studies from the recultivated open-cast mining sites of Lusatia differentiate only between the organic carbon pools. This enabled a rough estimation of the individual contributions but did not allow describing molecular differences between the pools nor molecular changes over time. Therefor our work aims to use Ultrahigh resolution mass spectrometry (Fourier transform ion cyclotron resonance mass spectrometry, FT-ICR-MS). It allows a deeper insight into the molecular composition of the different soil carbon pools in the recultivated open-cast mining sites. Negative ESI FT-ICR-MS measurements of the solvent extracts reveal a strong dominance of organo-oxygen compounds representing components with varying carboxylic and hydroxyl groups. The differences in the chemical compositions of the soil extracts from Bär-1 site allowed tracking the changes of the molecular composition of organic matter fractions. Higher amounts of lignite-derived compounds found in the lower part of the profile point to a reduced supply of recent organic carbon into the deeper parts of the profile and a low transformation of the recalcitrant lignite-derived OM at a depth below 40 cm due to missing melioration treatment and/or lacking roots. At Bär-2 site, the compositional inventory of the soil lipids is rather constant with depth completely lacking condensed aromatics.
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Investigating the Intramolecular Isotopic Structure of Isoprenoids Using Orbitrap Mass Spectrometry
By M. ÖztoprakSummaryIsoprenoids are a class of ubiquitous organic compounds constructed from C5 isoprene units. Pathways for their biosynthesis are highly conserved and distinct among the Domains of Life. Since the intramolecular isotopic composition of molecules strongly depends on the pathways by which they are synthesized, as well as the degree of conversion of their intermediates and the sources of their substrates, characterization of intramolecular isotopic signatures may allow for the recapitulation of these processes. Chemical and NMR methods for the study of intramolecular isotopic signatures, however, require large quantities of analyte (∼mmol), which is generally not feasible for geological samples. Here, we investigate the intramolecular carbon isotopic structure of phytane from chlorophyll of the cyanobacterium Anacystis nidulans (MEP phytane) and archaeol from the archaeon Halobacterium sp. NRC-1 (MVA phytane) at natural abundance (∼10 nmol). Orbitrap measurements were standardized relative to a commercially available phytane of unknown petrogenic origin and compared for bulk compound specific isotopic values via GC-irMS. Although intramolecular isotopic differences between analytes were not significant for mass fragment 85 m/z, our results demonstrate for the first time the accurate and precise detection of intramolecular isotopologues of large biomarker compounds at natural abundances using Orbitrap mass spectrometry.
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Microbial Membrane-Spanning Lipids: Determination of Biological Sources and Evolutionary Implications
SummaryBacterial membrane lipids are composed of a glycerol-3-phosphate backbone attached via ester bonds to fatty acid molecules, while those of Archaea have a glycerol-1-phosphate backbone linked to isoprenoids via ether bonds. The cytoplasmic membrane is generally organized as a bilayer, however the majority of archaeal membranes are organized as membrane-spanning lipids (MSLs), forming a monolayer of isoprenoidal glycerol dialkyl glycerol tetraethers (isoGDGTs). Some bacterial species produce lipids similar to the archaeal MSLs but non-isoprenoidal, i.e., branched glycerol dialkyl glycerol tetraethers (brGDGTs) that are likely produced by soil bacteria. During the past decade, these types of MSL have been increasingly used in molecular proxies. Some isoGDGTs are used in the paleotemperature proxy TEX86 to reconstruct past sea surface temperatures, while the BIT index evaluating terrestrial input is based on isoGDGTs and brGDGTs. Recently, novel GDGTs have been detected in various environments and proposed to have biomarker potential, however little is known about their sources, which is instrumental for their application as paleoproxies. Here, we investigated the biosynthetic pathway leading to the formation of bacterial MSLs by using cultivation and genomic analyses. In addition, we also investigated two anoxic and highly sulfidic environmental settings to determine the biological sources of specific isoGDGTs.
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Assessing Source Rock Organofacies Using the Ft-Icr Ms Amenable Nso-Compounds Inventory of Pyrolysates
Authors N. Mahlstedt, M. Noah and B. HorsfieldSummaryOpen-system pyrolysates of fourty-three immature source rock and coal samples covering all depositional environments and geological ages were prepared and analysed using Fourier transform-ion cyclotron resonance-mass spectrometry (FT-ICR MS) in connection with an electrospray source run in negative-ion mode to asses the fraction of acidic NSO compounds. The aim was to establish proxies based on the NSO inventory of pyrolysates for kerogen and petroleum type organofacies typing. The main result is that different depositional environments/ organofacies can be characterized using bulk NSO elemental and compound class distributions in combination with DBE class and Carbon number distributions. The feasability of the approach is demonstrated by Principal Components Analysis, whereas the geochemical background of the used loadings is discussed in detail in the paper/presentation.
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Physical Simulations of Petroleum Changes Related to Interaction with CO2 and CH4
Authors J.P. Lopes, A.J.M. Vieira and H.L.D.B. PenteadoSummaryDifferent accumulations in Brazilian marginal basins have CO2 contents varying between 0 to 80 mol %. Where the CO2 values reach their maximum, two distinct fluids were observed at the reservoir: a rich gas-condensate at the top, and a heavy oil at the bottom. The main objective of this study was to evaluate the compositional changes of oil due to the contact with CO2, in order to understand the alterations of the PVT and geochemical properties. It is evident that the mixing sequence (CO2-oil or oil-CO2) significantly alters not only the distribution of the components, but also the composition of the phases.
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Giant deep-sea Foraminifera are enriched in Archaea and associated lipid biomarkers in their agglutinated tests
Authors J. Bösche, J. Wendt, J. Lipp, S. Goffredi, L. Levin, E. Cordes, J. Cortes Nunez, K. Hinrichs and V. OrphanSummaryAs agglutinated Foraminifera, Xenophyophores inhabit the deep ocean floor and build their tests from particles of the environment. Despite their diversity and abundance, especially in areas of commercial interest for polymetallic nodules, the role of Xenophyophores in the deep-sea ecosystem and their physiology is still poorly understood. Previous studies hypothesized that their tests provide a habitat for deep-sea microbes. To further investigate Xenophyophores and associated microbes, we analyzed diverse Xenophyophores from the Quepos plateau and seamounts off Costa Rica for their lipid biomarkers and microbial 16S rRNA gene diversity.
In our data we identified archaeal glycerol dialkyl glycerol tetraethers with a high content of intact polar lipids and substantial amounts of the thaumarchaeal biomarker Crenarchaeol. This data is suggestive of a thaumarchaeal assemblage, which was independently confirmed through Illumina 16S rRNA amplicon sequencing. The spatial distribution of biomarkers we observed with mass spectrometry imaging in a section through a Xenophyophore test shows a heterogeneity, which we interpret as differences in activity, community composition and/ or growth stages of the archaeal community members.
Our lipid biomarker and molecular data suggests that Thaumarchaea are associated with diverse Xenophyophores and that their tests can provide a newly discovered micro-niche for these microbes.
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Properties and Transport of Organic Matter from the Inland to the Ocean - Influence of Coastal Wetlands.
Authors J. Gensel, M. Humphries, D. Sebag, M. Zabel and E. SchefußSummaryTo assess the influence of sub-tropical coastal wetlands on organic matter transport by rivers in southeastern Africa we conducted a multi-timescale study by characterising the current status, the recent past (∼2000years), and the time since the formation (∼6000 years) of South Africa's largest Freshwater Wetland System (MKhuze Wetland System, KwaZulu Natal). This approach and the application of multiple proxies such as plant-wax derived n-alkanes, their compound specific isotope composition, bulk organic matter parameters, Rock-Eval analyses, and persistent organic pollutant quantification enable us to decipher the three main drivers which can cause alteration in biomarker signals: (i) natural development of the system, (ii) adaptation/response to climatic events, and (iii), especially during the Late Holocene, anthropogenically induced changes. The combination of the present status (predominant vegetation, organic matter transport pathways and characteristics) with the decadally resolved records and a centennial archive promise to provide a comprehensive clarification of the evolution of a subtropical wetland in a coastal watershed and its response to climatic conditions.
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CARBON ISOTOPIC COMPOSITION OF LEAF WAX n-ALKANES OF MANGROVE PLANTS DISTRIBUTED ALONG A LATITUDINAL GRADIENT IN BRAZIL
Authors M. Ceccopieri, R. Carreira, A. Scofield, L. Almeida, C. Hamacher, C. Farias, M. Soares and A. WagenerSummaryHere we present baseline data of δ¹³C of n-alkanes (δ¹³Cn-alkanes) from leaf waxes of mangrove trees – Avicennia schaueriana, Rhizophora mangle and Laguncularia racemosa – distributed along a latitudinal gradient in Brazil. The objective was to evaluate the influence of trees physiology, local hydrology and climatic factors upon the molecular and isotopic signature of the leaf wax n-alkanes. Higher weighted average δ¹³Cn-alkanes (δ¹³CWA), average chain lenght (ACL25-35) and carbon preference index (CPI24-36) for R. mangle and A. schaueriana contrasting with lower values for L. racemosa seem to be linked to physiological characteristics of each species regarding intrinsic water use efficiency under the specific tidal flooding regime of mangrove forests. About the plant’s response to local environment influence, inverse correlations between all δ¹³Cn-alkanes values (δ¹³C₂₇, δ¹³C₂₉, δ¹³C₃₁, δ¹³C₃₃ and δ¹³CWA) and mean annual precipitation were found for the A. schaueriana samples. For the R. mangle species, a relationship between ACL25-35 and mean annual potential evapotranspiration and between CPI24-36 and mean annual temperature were observed. The different molecular and isotopic footprints of the three mangrove species presented here have potential to be used in future interpretations of n-alkanes as biomarkers in biogeochemical and paleoclimate studies near mangrove-dominated coastal regions.
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Quantifying Microplastics in Complex Environmental Samples: Py-Gc/Ms vs. Hyperspectral Ftir – Potential and Limitations
Authors S. Primpke, M. Fischer, C. Lorenz, G. Gerdts and B. Scholz-BoettcherSummaryIn a proof of principle, FTIR and PY-GC/MS are applied subsequently on identical filter for microplastics identification and quantification. Both approaches are of complementary scientific value since they result in particle numbers and sizes or polymer masses, respectively. Although the combined use of both methods is ideal, the transferability of particle related data, by far more referred in literature, into masses is an often-asked question.
The filter represented different complex environmental samples (waters from wastewater treatment plants, North Sea sediments and water) prior treated for selective MP pre-concentration. Associated with data evaluation, a general harmonization step regarding distinct polymer clusters of both methods was performed. A comprehensive data comparison revealed that FTIR and Py-GC/MS resulted in polymer types and qualitative distribution. This is attributed mainly to the size-influenced detection of both methods resulting in deviant quantitative calculations. The determined polymer mass is increasing with particle size. Consequently, the impact of few big particles is high regarding relative calculations for Py-GC/MS. In contrast, an inverse effect occurs in FTIR since particle counts ascend with decreasing particle size. Any calculative might lead to overestimation. A complementary use of both methods is highly recommended for reliable data generation.
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Evolution of Organic Matter Using Rock-Eval® Pyrolysis in Beech Forest Soils After Their Particle Size-Fractionation
Authors D. Sebag, E. Verrecchia, I. Kowalewski, T. Adatte, M. Aubert, G. Cailleau, T. Decaëns, J. Trap, F. Bureau and M. HeddeSummaryThis study presents the evolution of organic matter content using Rock-Eval® pyrolysis in Beech forest soils after their particle Size-fractionation. The amount of C in soil depends in microbial and physicochemical interactions between various biomass affecting its accumulation and its stability. As far as thermal stability of soil OM is supposed to mimic its biogeochemical stability, Rock-Eval® pyrolysis method is an efficient tool to quantify the organic and mineral carbon. To this end, litter and topsoil samples from a beech forest located in Normandy (France) were selected and fractionated by sieving from large debris to A-fine fractions. The TOC decreases from large debris to A-medium and drops in A-fine. Thermal stability inputs are highlighted through RE parameters when comparing litters and particle size fractions separated from topsoil samples (increase of TpS2 and OI, decrease of HI with decreasing fraction size in A horizons). Three distinct thermal stability C pools are identified
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Non-Pyrogenic Formation of Condensed Aromatic Compounds in Iron-Rich Environments
Authors P. Hatcher, A. Goranov and H. ChenSummaryExamination of wood decking that has been subjected to environmental change for about a decade in contact with Fe nails in the absence of sunlight shows significant modification due to active Fenton chemistry. The wood is blackened and the analysis of benzenepolycarboxylic acids shows that polycondensed aromatic molecules, commonly associated with black carbon from pyrogenic sources, are formed from the lignin abiotically and without pyrolysis. Because this transformation process occurs globally in soils, these results indicate that black carbon found globally in soils and other natural environments may not be exclusively from pyrogenic sources and that Fenton oxidation of wood is capable of producing black carbon. Such a finding will have an impact on the validity of global estimates of pyrogenic black carbon inputs to the environment.
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A Closer Look at 15N in Relation to Climate Change: Example from the California Current System
Authors Z. Erdem, P. Riekenberg, M.T.J. Van der Meer, N. Ohkouchi, N. Ogawa and D. RushSummaryThe nitrogen isotopic ratio of bulk sedimentary organic matter (δ¹⁵Nsed) has been an important tool to investigate biogeochemical dynamics in relation with the climate change. However, its signal could be altered during sinking and burial processes. In past decades new approaches were introduced in paleo-N investigations including compound-specific analysis. In this study, we present results of two approaches; N-isotopes of individual chlorophyll-derivatives (δ¹⁵Nchl) as well as amino acids (δ¹⁵NAA), to a sedimentary record collected from offshore California (ODP Site 1012). The region is characterized by strong upwelling in the surface, enhanced oxygen limitation, and denitrification in the subsurface waters, thus a suitable location to test these proxies. Here, we present the δ¹⁵Nsed and δ¹⁵NAA results covering the first 120 kyr whereas δ¹⁵Nchl measurements are covering the last 22 kyr of the record. The overall δ¹⁵NAA trend is following the δ¹⁵Nsed throughout the record with more-or-less stable offset as well as the interglacial-glacial variability suggesting that the nitrogen dynamics offshore California is mainly driven by climatic forces over time. At specific periods, compound-specific ¹⁵N divert from δ¹⁵Nsed suggesting more local changes and/or isotopic alterations.
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A Geochemical Context for Stray Gas Investigations in the N. Appalachain Basin: An Update of Analyses of Natural Gases
Authors F. Baldassare and E. ChapmanSummaryNatural gas production in the Marcellus Formation in NE Pennsylvania, USA has matured in the Northern Appalachian Basin. Our evaluation of time-series gas geochemistry data provides additional insight into the complexities of gas origin and migration.
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Differential organic matter enrichment of lacustrine fine-grained rocks: Jurassic Da’anzhai Member, central Sichuan Basin, China
Authors Ziyi Liu and Dongxia ChenSummaryIn the Da’anzhai member, fine-grained sediments consist of siliceous shales, argillaceous shales, mixed shales, muddy shell limestones and crystalline shell limestones. The total organic carbon (TOC) in these fine-grained sediments varies significantly (0.11 wt% - 3.11 wt%). Generally, paleoredox conditions, paleoclimate, paleoproducticity, clastic input, and sedimentation rate control the preservation and accumulation of OM. Low Mo, U, and V concentrations and mainly euhedral pyrites in fine-grained sediments indicate oxic conditions in the study area. In addition, less change in the chemical index of alteration (CIA) and relatively low value of biological barium (Babio) data may suggest the lower change in paleoclimate and relatively low paleoproductivity in the Da’anzhai member. Meanwhile, relatively weak correlations existed between the TOC and these indicators of the sedimentary paleoenvironment, implying that they may not be the main reason for differential OM enrichment in the study area. However, only when the clastic input matches the sedimentary rate can there be a chance of high-rich OM in fine-grained sediments. Fine-grained sediments with high TOC are located in the OM enrichment area controlled by sedimentary rate and clastic input, which avoids clastic dilution or OM oxidation.
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Sapropel for Soil Remediation: A Comparative Study
Authors Z. Vincevica-Gaile, K. Stankevica and M. KlavinsSummaryOne of the gentle soil remediation methods in situ involves the use of amendments for biodegradation of hazardous substances or mobility and bioavailability reduction of contaminants in soil and food chain. The study involved treating historically polluted soil by amending with peaty, blue-green algae, green algae, carbonate, organic/blue-green algae, organic/silicates and diatomaceous sapropel. For comparison, gravel sediments, natural and modified quaternary illite clay and KH2PO4 were used. Use of any of the tested soil amendments in application to polluted soil led to positive results in remediation if the soil is polluted with metals. Among all tested amendments, sapropel-containing additives revealed the most efficient influence on plant development and increased biomass when plants were grown in polluted soil. However, not in all cases, solely sapropel is the best choice for soil remediation if the following three targets have to be achieved: to improve plant development, to increase biomass, to reduce metal transfer from soil to plants. The results indicate that gentle remediation using sapropel as a component of soil amendments can be promising and might be significant for resolving complex contamination issues related to heavy metal pollution in urban areas, industrial sites, wastelands, etc.
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Application of Time Lapse Geochemistry to Better Understand the Barriers to Fluid Flow in a Reservoir
More LessSummaryThe paper describes the application of the technique of time lapse geochemistry to a reservoir in Naharkatiya oilfield in Upper Assam, India to understand the barriers to fluid flow in different parts of the reservoir under dynamic conditions. Naharkatiya oilfield is a mature oilfield and under consideration for implementation of enhanced oil recovery (EOR) technique, namely, carbon dioxide (CO2) flooding. Dynamic simulation study of the reservoir has identified two inverted five spot patterns for implementation of CO2 EOR.
Well head crude oil samples from the five producing wells in the reservoir were collected in 2017 and 2019 and their detailed fingerprinting was carried out using a Gas Chromatograph. The study identified subtle differences in composition of the oils, if any, collected at the same time and at different times.
The interpretation of the data led to the conclusion that there is poor connectivity between a particular well, that is part of the both the EOR patterns, and other nearby wells. On the hand, there is good connectivity among other four wells that were studied. The knowledge of the fluid flow barrier in the reservoir has significant implication to the implementation of EOR in the reservoir.
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Diagenetic fate of glycerol ethers in seep carbonates revealed by two novel isoprenoid hydroxyphytanyl-glycerol monoethers
Authors Lanfang Xu, Hongxiang Guan, Zheng Su, Lihua Liu and Jun TaoSummaryStudying the diagenetic fate of mono- and dialkyl glycerol ether lipids (MAGEs and DAGEs) are of a broad geochemical significance, since they are potential powerful biomarker for specific environments and not limited in cold seep ecosystems. There are several creative findings in our studies as follows: (1) Novel 13C depleted hydroxyphytanyl-glycerol ethers and hydroxyphytanol were found. (2) Hydroxyphytanyl-glycerol ethers and hydroxyphytanol were hydrolyzed form di-hydroxyarchaeol. (3) The short-chain alcohols were most likely hydrolysis products of MAGEs. (4) Degradation from glycerol ethers to respective alcohols might be common and highly underestimated in cold seep ecosystems.
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Biomarker insights into a methane-enriched Holocene peat-setting from “Doggerland” (Central North Sea)
Authors M. Blumenberg, S. Schlömer, L. Reinhardt, G. Scheeder, M. Krüger, K. Heeschen and M. RömerSummaryWidespread peat formed early after the Last Glacial Maximum (LGM) in what is today’s Central North Sea. Here, we present insights into peat cored at 43 m water depth in the German exclusive economic zone (EEZ). Peat layers of generally a few centimeters thickness were recovered from multicores and from one gravity core at three sites. Porewaters in these samples document a slight hydrocarbon enrichment in the peats. Ethane, propane and butane were also found and may either document paleoseepage from an underlying oil-mature source rock and adsorption in the peat organic matter or, likely, peat-specific gases. The latter hypothesis is supported by accompanying abundant unsaturated analogues (i.e., ethene and propene). Peats were formed in a variable environmental setting with the majority of extractable organic matter consisting of higher plant wax material. However, in two samples also different amounts of a C20 highly branched isoprenoid (HBI) were found, which likely records abundant diatoms typical for an oligotrophic lake environment. In addition, all peat samples contained a suite of bacterial hopanes, hopenes and fernenes, recording strongly fluctuating methane-flux and methane-turnover during peat-formation with partially high 13C-depletions of <-60 ‰ VPDB in hopene and fernene biomarkers (hop-17(21)-ene, diploptene, fern-7(8)-ene).
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Experimental investigation of oil expulsion within organic-rich laminated lacustrine shale: Based on closed hydrous pyrolysis of Lucaogou Formation
Authors Guangqing Yang and Jianhui ZengSummary- Fine and thick laminae development in the Lucaogou organic-rich shale is a hybrid shale-oil system in the microscale.
- The great quantities of generated CO2 during hydrous pyrolysis might contribute to desorbing NSOs and hasten its expulsion.
- Fine lamination development can promote more total hydrocarbon expelled.
- Thick lamination development might avoid phase separation and dent the compositional fractionation effect in the microscale.
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Insight into Enhancement of CO2 Captured by Clay Minerals
Authors M. Abdalqadir, P. Adzakro, T. Pak and S. Rezaei GomariSummaryClimate change and global warming recently became significant concerns due to the massive emissions of greenhouse gases into the atmosphere, predominantly CO2 gases. Therefore, it is necessary to find sustainable and inexpensive methods to capture the greenhouse gasses and protect the environment for live species. The application of naturally available and cheap adsorbents of carbon such as clay minerals became a great interest. However, the minerals prone to low storage capacity despite their high affinity to adsorb carbon. This paper aims to explore ways to improve the pore volume and surface area of two selected clay minerals, ‘montmorillonite and kaolinite’ by acid treatment to overcome their low storage capacity.This study concludes that clay minerals are inexpensive and available material sources to model the realistic conditions and apply the results of carbon capture to prevent global warming, which is one of the most critical and urgent problems in the world.
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Determining Hydrocarbon Source and Thermal Maturity by Integrating Kerogen and Reservoir Gas Geochemistry
More LessSummaryAn source-reservoir ends integrated approach and case study for petroleum system analysis
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New Interpretation of the Nature and Origin of Carbonate-Derived Oil in Seram Basin, Eastern Indonesia
Authors B.M. Hartono, E.A. Subroto, A.H.P. Kesumajana, R. Andrianto, G. Malvinas, J. Wahyudiono and B. PriyantoSummarySeram Basin is a petroliferous basin in Eastern Indonesia with a complex geological setting. The crude oils in Seram Basin have been known to be originated from Triassic marine carbonate source rock that is composed by type II organic matter. However, carbonate rock could be divided into several organofacies that will expel crude oil with a distinctive character. Therefore, the depositional environment of the probable carbonate source rock is comprehensively studied and divided into several organofacies. This study found that several biomarkers are sensitive to carbonate facies change in Seram Basin, which are the ratio of C24/C23 tricyclic terpane, C26/C25 tricyclic terpane, hopane/sterane, C29/C27 sterane, and the composition of C27 and C28 steranes. Therefore, the carbonate-sourced oils in Seram Basin could be further divided into Subfamily A, possibly derived from deep marine carbonate (basinal), and Subfamily B, possibly derived from shallow marine carbonate (shelf edges). This study significantly renew and improved the previous 1980s concept that has been widely accepted for Seram Basin. Moreover, this study gives huge implications for further paleo-reconstruction study and possible exploration play in Seram Basin and adjacent areas.
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Evidence of Gymnosperm-Dominant Forests in the Early Paleocene of Western India Based on Lipid Biomarkers
Authors Rimpy Chetia, Runcie Paul Mathews and Prakash K. SinghSummaryThe geoterpenoid composition of the Paleocene sediments from the Barsingsar lignite mine of Bikaner-Nagaur Basin (Rajasthan) have been studied with the help of gas chromatography-mass spectrometry (GC-MS) to understand their botanical origin. The terpenoids include sesquiterpenoids, diterpenoids and few triterpenoids. The sesquiterpenoids and terpenoids indicate higher plant-derived. The diterpenoid primarly comprising of abietane, phyllocladane, kaurane, pimarane/isopimarane and podocarpane-class compounds show affinities to Southern Hemisphere conifer families, Podocarpaceae and Araucariaceae. The tetracyclic diterpenoids include 18-norkaurane, ent-beyerane, ent-16ß(H)-kaurane and 16a(H)-phyllocladane. The tricyclic diterpenoid, rosane and its derivative are identified. Exceptional void of phenolic abietanes and labdane derivatives rules out the probability of Pinaceae being the source. Low abundance in pentacyclic terpenoids like oleananes and their degraded forms suggest a negligible angiosperm contribution . The average value of pr/phy in the realm is 1.8 indicating dysaerobic depositional setting. The ar-AGI values for the samples range from 0.01 to 1. The t-AGI 1 and t-AGI 2 values range from 0.009 to 1.23 and 0.002 to 0.34 respectively indicating low angiosperm input. This work provided evidence of the occurrence of a gymnosperm dominated tropical rainforest as refugia in the midst of emerging angiosperms and a probable clue to biotic exchange out-of-India during the Paleocene.
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Controls on Thermal Maturation – Insights from Artificial Maturation of Organic Rich Shales
Authors C. Onwumelu, S.H. Nordeng and G.P. MuscioSummaryThe presence of the secondary compensation effect in kinetic analysis was used as a means of establishing the equivalence between the natural and experimental maturation. Consequently, influence of source rock bitumen on natural and experimental mature samples was examined by using a dean stark extractor to extract bitumen from the materials. Crushed and homogenized Bakken Shale samples were artificially matured by exposing them to 340 C in an oven for 0, 12, and 48 hours. Analyses include source rock analysis using source rock analyzer (Rock Eval equivalent), kinetic analysis and petrographic analysis. Results demonstrated that thermal maturation has a significant influence on the total organic carbon (TOC) content and reactive organic matter (Rock Eval S2). Our research findings established the foundation for calibrating kinetic parameters (Ea and A), as well as other organic geochemical parameters and indices, to various degrees of thermal stress.
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Microbial Community Variations Recorded by Biomarkers in a Tropical Peatland During the end Permian Mass Extinction
Authors Jiaqi Wu and Genming LuoSummaryTerrestrial ecosystem is a particularly important type of ecosystems on the earth, especially on the extreme climate periods, such as the end Permian mass extinction (EPME). It also can affect the marine ecosystem directly, such as large nutrient inputs induced by terrestrial weathering. Studying the changes of it can provide a way to understand the mechanism of the EPME. Current understanding of terrestrial ecosystem crisis is often based on plant fossils. However, studies of fossil-based terrestrial ecosystem are limited, e.g., the absence of record of lower organisms, including microorganisms. The microbial changes, which are always associated with contemporaneous environmental changes, can be traced by lipid biomarkers. Here, we provide a systematic investigation on the lipid biomarkers from a paleo-tropical peatland in southwest China to explore the contemporaneous environmental changes. Our lipids biomarker data identifies that terrestrial ecosystem had begun to become unstable prior to the extinction of conventional wisdom. Our records also reveal two episodes of elevated bacterial contribution relative to eukaryotes and massive soil erosion, which may be caused by two different events: the former was related to wildfires and the latter was related to Siberian Trap intrusions.
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Subsurface CO2 Level Prediction: Workflow, Uncertainties and Mitigation Approach
By S. MehaySummarySubsurface CO2 level prediction is best performed using a petroleum system model in which the various CO2 formation processes are considered. A major source of uncertainty is the identification of CO2 formation processes and the calibration of the model to known CO2 levels in the area of interest. In the presented approach, the key steps in processing and interpreting archived rock and fluid data to decipher the CO2 formation processes, establish CO2 levels and major controlling factors are described. This approach effectively mitigates the uncertainties associated with predicting subsurface CO2 level.
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Source Rock Distribution in the Drava Depression, Pannonian Basin, Croatia
Authors T. Troskot-Čorbić and K. KrizmanićSummaryThe DR-02 exploration area is extremely heterogeneous in terms of environment and facies due to its extremely dynamic position in the geological past. The overall source rock average TOC is relatively low. The HI values vary in an extremely wide range (from less than 10 to 700 mg HC/ g TOC) as a reflection of organic matter type and/or thermal maturity. Source rock distribution, types of organic facies as well as redefined hydrocarbon potential are demarcated throughout DR-02 sedimentological model. The facies of the source rocks are related to marine (shallow and deep-water), transitional and lake (brackish-freshwater) environments. Lithologically they are dominated by marls, calcite-rich marls and mudstones. The variable relations of aquatic and terrestrial organic matter reflect these environments and conditions during deposition.
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Tracing Soil Pollution Sources through Forensic Geochemistry
SummaryThe main objective of this work is to identify sources and patterns of organic and inorganic pollutants along soils of a heavily industrialized town. To this scope, 15 samples from soils in the town and its surroundings were collected. All samples were meshed (< 2 mm), dried and milled (<100 µm) prior being analysed, They were subjected to aqua regia digestion and analysed by means of inductively coupled plasma mass spectrometry (ICP-MS) for PTEs quantification, whereas aliquots were extracted and then injected in a gas chromatography–mass spectrometry (GC-MS) device to assess total petroleum hydrocarbons (TPH), PAHs and BTEX. Tools for environmental assessment included uni- and multi-variate statistics, statistical interpolations and molecular diagnostic ratios for PAHs.
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Key differences between laminated and massive lacustrine source rock during primary migration across oil window
SummaryThe role played by laminae development during gas expulsion in closed-hydrous pyrolysis is negligible and the expelled C2+ content gases are higher than methane.
The great quantities of generated CO2 from laminated shale during hydrous pyrolysis might contribute to desorbing NSOs and hasten its expulsion.
Laminae’s development might avoid phase separation and dent the compositional fractionation effect in the microscale.
Laminae development has a positive effect on primary migration across oil window.
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Geochemical assessment of reservoir continuity for an oilfield in the U.S. Gulf of Mexico
Authors A. Martín Monge, N. Marcano and R. ToccoSummaryA geochemical assessment of reservoir continuity is presented for an oilfield in the U.S. Gulf of Mexico. The field produces from several zones within the lower Miocene section. The distribution and extent of these units are complex introducing, together with the existence of potentially sealing faults, large uncertainties with regards to reservoir continuity.
Crude oils from the different producing zones collected from four wells across the field were investigated using bulk fraction characterization, stable carbon isotope analyses, whole oil high-resolution gas chromatography and gas chromatography–mass spectrometry of the saturate and aromatic fractions.
The results of these analyses offer insights for a better reservoir characterization at a field scale, supporting the presence of separate units both vertically within the investigated wells and laterally within the same unit. This contribution summarizes the main findings of this work.
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Study of supramolecular structure of humic acids
Authors D. Širůček, M. Kalina and M. KlučákováSummaryThe aim of this study was focused on the investigation of supramolecular structure of humic acids (HA). This issue was studied on a number of HA samples which differed in source matrix (lignite, leonardite, biochar, soil, peat and compost). For these purposes, methods of size exclusion chromatography coupled with UV-VIS, MALS (multiangle light scattering) and dRi (differential refractometry), as well as dynamic and electrophoretic light scattering and UV-VIS spectrometry were used. In order to better understand the formation of the supramolecular structure of HA, the ways of its stabilization and how it was influenced by the change in pH, individual HA samples were studied in three pH-varying mediums (3,5; 7 and 12).
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Biochar – A Promissing Soil Conditioner for Agriculture
Authors S. Sovova, M. Kurkova, N. Storkova, V. Enev and M. KalinaSummaryThe contribution describes the use of biochar as promissing soil conditioner. Physico-chemical characterization of used soils was performed. Also, the effect of biochar was studied during the cultivation experiment of model Plant Zea mays.
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Sources and Spatial Variations of Particulate Organic Matter in the Seine Estuary (NW France)
Authors Zhe-Xuan Zhang, Edith Parlanti, C. Anquetil, M. Sourzac and Arnaud HuguetSummaryEstuaries are essential from ecological, economical and biogeochemical points of view. Constraining the organic matter (OM) origin in such ecosystems is challenging, as estuarine OM can originate from rivers, coastal ocean or be produced within the estuary itself. This complexity can limit the use of bulk proxies for distinguishing OM sources in such zones. To overcome the limitations of bulk geochemical proxies, several proxies such as the Branched and Isoprenoid Tetraether (BIT) index based on branched glycerol dialkyl glycerol tetraethers (brGDGTs) and crenarchaeol have been applied for estimating the relative contribution of terrestrial OM ( Hopmans et al., 2004 ). However, the applicability of GDGT-based proxies in estuaries remains poorly understood because of the multiple sources of GDGTs and their complex transport processes from the land to sea ( Cheng et al., 2021 ). Here, we combined bulk and molecular biomarker approaches to investigate the sources and spatial variations of particulate organic matter (POM) in the Seine Estuary (NW France). We showed that d13Corg and BIT are both applicable as proxies of terrestrial OM inputs. Besides, our results showed the spatial variability of the brGDGT composition in POM from the Seine Estuary, with significant differences between the upstream and downstream parts of the latter.
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Reconstruction of Past Environmental Variations in the Semi-Arid Brazilian Nordeste Through Last Interglacials
Authors L. Rouyer, A. Govin, I. Bouloubassi, A. L. S. Albuquerque, T. T. Nguyen Tu, M. Mandeng-Yogo and A. HuguetSummaryBrazilian Nordeste is a semi-arid region that is a key area for future South American climate. Climatic conditions of Nordeste strongly depends on nearby western Atlantic parameters (Temperature, Salinity, etc.). This work aims to improve the understanding of the Nordeste response to hydroclimate and vegetation changes over past interglacial periods (known as odd Marine Isotope Stage, MIS) based on a 17 m long marine sedimentary core (GL1180) collected on the eastern Brazilian continental margin. A multi-proxy approach will be developed by analyzing sedimentary organic matter (OM) at the bulk and molecular levels. Here we present the first results of bulk OM analysis for 135 selected depths with a higher temporal resolution during interglacial periods.
Bulk elemental and isotope analyses of OM in sediments from the GL1180 core revealed that the Brazilian Nordeste area experienced notable changes in humidity conditions over the last 300 kyr BP. Complementary lipid biomarker analyses of these samples are in progress to help in the reconstruction of past vegetation and hydroclimate conditions in northeastern Brazil.
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Compositional Fingerprinting for Geochemical Insights from Two-Dimensional Gas Chromatography
Authors Julia C. Forsythe, Tetsushi Yamada, Guillaume Vidal and Shawn David TaylorSummaryAutomated workflow that integrates compositional analysis of petroleum from comprehensive two-dimensional gas chromatography (GCxGC) data for cross-comparative analysis of oils based on concentrations of select individual chemical groups. Six oils with different APIs evaluated and differences between the oils are shown based on five different chemical groups.
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GDGT-based determination of paleoenvironments via machine learning
Authors P. Martínez-Sosa, J. Tierney, L. Pérez-Angel, I. Stefanescu, J. Guo, F. Kirkels, J. Sepúlveda, F. Peterse, B. Shuman and C. RoutsonSummaryGlycerol Dialkyl Glycerol Tetraethers (GDGTs) are a group of molecules that have been successfully used for paleoclimate reconstructions in a wide range of environments.
GDGTs have shown to be useful biomarkers as they are widely available, and their structure is relatively resistant to diagenetic alteration. Specific GDGTs are associated with particular environments, which suggests that they could potentially be used to classify ancient depositional conditions in cases where the exact paleoenvironment is not known.
In this work we present a comprehensive branched and iGDGT dataset from published and novel analyses, with more than 1000 modern samples from marine, lake and river sediments as well as soils and peat samples. Unsupervised and supervised machine learning techniques were applied to this dataset to generate GDGT and environmentally based clusters and train a classification algorithm. The trained algorithm has the potential to be applied to samples formed in unclear or transitional depositional environments, allowing us to identify the potential environment in which they were formed. Furthermore, the classification model can help determine which environmental calibration is most appropriate for the setting, thereby improving paleoenvironmental reconstructions.
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Petroleum Geochemistry of Oil and Gas from Lacustrine and Fluvio-Lacustrine Source Rocks, Thailand Tertiary Basins
Authors K. Jankaew, S. Wooding, M. Mesdakom and R. NoosriSummaryWe report character of oil and gas produced from selected Tertiary basins in Thailand. Previously, only limited published data are available for oils generated from lacustrine and fluvio-lacustrine source rocks in Thailand basins. We conclude that shallow water fluvio-lacustrine environment deposited sources receiving fluctuating contribution of terrestrial organic matter input as well as variation in micro-algal communities appear to be the main source type in basins we have studied. This source type is perhaps under-estimated in terms of importance across Sundaland. We believe that a better, more profound understanding of the nature of source rocks within classic Sunda fluvio-lacustrine depositional systems is still needed as they are difficult to delineate, more variable in quality and often occur as local discrete beds in thick sequences.
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Sedimentary and Geochemical Characterization of Miocene Siliceous Formations in Akita Prefecture (Northern Japan)
Authors P. Martizzi, S. Chiyonobu and H. AratoSummarySilica-rich diatomaceous sediments deposited during the Cenozoic are widely distributed in the North Pacific sea region and they represent an important source rock for oil and gas in several sedimentary basins located in California, Sakhalin, and the Sea of Japan. In this study, we are going to present results from the analysis of the middle to late Miocene Iwaya Formation siliceous mudstones, distributed in the Gotanzawa area, in central Akita Prefecture. These analyses include the Rock-Eval pyrolysis and the observation of framboidal pyrite size distributions.
Samples are composed of light gray and dark gray mudstones. Rock-Eval pyrolysis data revealed that light gray horizons are poorer in TOC than the dark gray ones. Similarly, the high HI in the dark gray mudstones suggests a better preservation of the organic matter in these layers than in the light grey. Although the dark gray mudstones could represent a potential source rock for hydrocarbons, the Tmax value indicates that these mudstones are immature for the generation of hydrocarbons.
The massive lithofacies and the diameter of the framboidal pyrite suggest that these sediments deposited under oxic-dysoxic bottom waters. However, the TOC in the dark gray mudstones may indicate that OM was preserved from bacterial degradation.
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Evaluation of Gas Maturity Parameters from the Hydrous Pyrolysis of Different Source Rocks
Authors A.A. Ferreira, A.L.D. Spigolon and A. PrinzhoferSummaryA preliminary application of the hydrous pyrolysis technique to assess some gas maturity parameters (based on chemical and carbon isotopic composition) from the evaluation of 4 distinct source rocks. A starting point to better understand the influence of the composition of different source rocks on the hydrocarbons´ formation/thermal maturation, and to provide additional insights on the source of hydrogen and olefins commonly generated in the process, also present during the drilling of wells under specific circumstances (a phenomenon known as “bit metamorphism”).
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Geochemical evaluation of produced petroleum from the Middle Permian Lucaogou reservoirs Junggar Basin and its implication for shale oil play
Authors Yazhou Liu, Jianhui Zeng, Guangqing Yang and Shu’ning LiuSummaryThe Lucaogou Formation develops two sweet spots, the upper (P2l22) and lower (P2l12) sweet spots, which are not more than 150 m apart. Interestingly, oils produced from the deep Lucaogou Formation (the lower sweet spots) have higher densities and viscosities than those in the shallow Lucaogou Formation (the upper sweet spots). In this paper, geochemical data from 78 source rock solvent extracts and 17 oil samples from different depths were carried out to clarify unconventional petroleum systems and the cause of high viscosities. Oils produced from the P2l12 interval are characterized by abundant polar compounds, which are derived from the P2l12 and P2l11 intervals source rocks with relatively high marine sources contribution. Oils in the P2l22 interval are generated from the P2l22 interval source rocks with relatively high terrigenous-marine sources contribution. Migration from sources to reservoirs in the Lucaogou shale oil systems is short-distance given thermal maturity considerations. The sources and thermal maturities are the primary reasons for the high viscosities of the crude oils produced from the P2l12 interval. This research also indicates the Lucaogou shale petroleum system could be divided into two subsystems, and different strategies are required for the exploration and development of different unconventional petroleum subsystems.
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GDGT-Based Temperature and Precipitation Proxy Calibration for the South American Lowlands
SummaryWe present results from a proxy calibration study on br- and isoGDGTs in soils from tropical South America. Our study includes both surface soil samples as well as vertical profiles. We find that the brGDGT based temperature proxy is depending on vegetation type and introduce an improved tropical calibration. In addition to the aridity dependence of the ratio between br- and isoGDGTs, we also find that the isoGDGT distribution is aridity dependent, allowing for improved precipitation reconstructions. Finally, we find that the down-profile distribution of brGDGTs remains relatively stable, while large variations in isoGDGT distributions indicate potential biogeochemical-driven changes in archaea communities.
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