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30th International Meeting on Organic Geochemistry (IMOG 2021)
- Conference date: September 12-17, 2021
- Location: Online
- Published: 12 September 2021
101 - 150 of 279 results
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Experiences in Finding End Members for Production Monitoring and Allocation of a North Sea Oil Field Using Petroleum Geochemistry
Authors T. Garlichs, R. Patience and G. HansenSummaryExperiences to find adequate End members for production monitoring and allocation of an oilfield in the Norwegian North Sea. Samples from exploration, appraisal and development making up the sample set with sample dates from the 1980s to 2020. Several test fluid samples were collected and analyzed by a range of standard analytical methods. As a result of this work, a number of positive learnings, as well as pitfalls, emerged.
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A New Method for Rapid Analysis of Polar Molecular Markers of Biomass Burning in Air and Water Filters
Authors N. Davtian, J. Villanueva, N. Penalva Arias, P. Comes Bordas and A. Rosell MeléSummaryMonosaccharide anhydrides (MAs) are routinely analysed to track modern and past biomass burning. While liquid chromatography (LC) methods are promising, MA compounds (galactosan, levoglucosan and mannosan) are typically not well separated. This shortcoming results in a cumbersome and time-consuming isotopic characterization of MAs. Here we describe novel liquid chromatography-electrospray ionization-tandem mass spectrometry and liquid chromatography-isotope ratio mass spectrometry methods for rapid analysis of MAs. We also developed a simple protocol for MA extraction and workout from air and water filters. In addition to their simplicity and the rapid analysis of MAs, our new methods have several advantages. First, we extract and separate MA compounds only with ultrapure water, which enables compound specific isotopic analysis under ideal conditions. Second, we use small solvent volumes for MA extraction to limit sample dilution. Third, we achieve baseline separation of all MAs. Fourth, we achieve detection and quantification limits as small as 50–100 pg of injected MA compounds with post-column ammonia addition and MA analysis in multiple reaction monitoring mode. Therefore, our methodological developments further demonstrate that LC methods compare favourably with gas chromatography methods for the analysis of MAs in environmental samples.
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A Regional Geochemical Assessment of Lower Carboniferous and Permian Source Potential in the UK Southern North Sea
Authors E. Donoghue, H. Bosscher, D. Den Hartog Jager and M. De KeijzerSummaryA regional source rock and fluid evaluation has been carried out for the UK Southern North Sea (SNS) basin in support of Shell’s UK exploration activities. While traditional plays in the SNS basin have targeted gas sourced from the Upper Carboniferous (Westphalian) coals ( Kombrink et al., 2010 ), this study focuses on the quality and generation potential of the Lower Carboniferous (Namurian, Visean) and Permian (Zechstein) source intervals. In combination with regional basin modelling work, the likelihood of generating and trapping additional hydrocarbon volumes from these intervals is evaluated.
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Using supervised and unsupervised statistical approaches to elucidate the presence of environmental brGDGTs clusters that reflect different bacterial producers.
Authors C. De Jonge and Z. LandrySummaryRecently, local environmental gradients were targeted [temperature; Iceland, De Jonge et al. (2019) and pH; The Netherlands, Scotland, Iceland (in review)], to elucidate the effect of bacterial communities composition on the distribution of brGDGTs in the environment. Indeed, local thresholds in temperature and pH cause the bacterial community composition (16S rDNA based) to change. Across these local thresholds, we observe that the environmental dependencies of brGDGTs change, resulting in a change in the temperature proxy MBT’5ME. While the local studies present interesting initial results, that can tentatively be extrapolated to the global scale (i.e. De Jonge et al., 2019 ), it has not been independently confirmed that these clusters (and their impact on the MBT’5ME values) are also present on a global scale.
By leveraging existing datasets of globally distributed soils and lake surface sediments, we aim to test the performance of several statistical clustering approaches, both supervised as unsupervised. Furthermore, supervised (e.g. partial least squares) and unsupervised (e.g. non-negative matrix factorization [NMF]) methods will be used to analyse the variation present in the global soil and lake datasets. We are confident that using these new statistical approaches is needed to accommodate the changing framework of brGDGTs interpretation as climate proxies.
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MOVABLE HYDROCARBON EVALUATION OF LACUSTRINE SHALE OIL: A CASE STUDY OF TRIASSIC CHANG7 SHALE FROM ORDOS BASIN, CHINA
By W. YangSummaryMovable hydrocarbons evaluation is important for shale oil exploration, two feasible and practical experiment-technologies were discussed in this study. One is the method of three-section Rock-Eval pyrolysis, which provides a prediction procedure on light hydrocarbon recovery, so the movable hydrocarbon contents of common cores could be calculated by developed formulas. Another technique is extraction of shale samples by petroleum ether. Contrast between the extraction components by different solvents including chloroform, dichloromethane and petroleum ether, and produced oil from shale reservoirs demonstrated that petroleum ether extraction is optimal. Results of the two methods are similar with an average around 0.5% of the movable hydrocarbons, pointing out that shale oil potential resources of Chang7 organic-rich sediments would be huge with a bright prospect of exploration and development.
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CYANOBACTERIAL HETEROCYST GLYCOLIPIDS ASSOCIATED WITH THE FLOATING MACROALGA SARGASSUM
Authors N. Bale, M. Konst, L. Amaral-Zettler, E. Zettler, E. Hopmans and S. SchoutenSummarySpecies of the floating macroalga Sargassum occur in a range of marine settings, in particular the tropical North Atlantic. Recently, inundations of Sargassum washing ashore particularly in the Caribbean, have been a socio-economic and ecological concern. Since abundance records of floating Sargassum are limited, geological sediment cores could provide clues as to the causes of the accumulations and help with predicting future growth dynamics. Open-ocean Sargassum sinks as it ages with remnants observed both on the seabed and buried in sediments. Floating Sargassum provides a habitat for many microorganisms, including N2 fixing cyanobacteria. Heterocyst glycolipids (HGs) have proven to be highly specific biomarkers for heterocystous N2 fixing cyanobacteria. HGs with hexose (C6) head groups are generally associated with free-living cyanobacteria while those with pentose (C5) head groups have been found mainly in endosymbiotic species (found within diatoms). These HGs have been used to trace the cyanobacterial occurrence and activity back in the geological record. We hypothesize that past occurrence of Sargassum can be traced in the sediment record using HGs as a quasi-biomarker for Sargassum. In this study, we looked at the HG distribution in two Sargassum species collected across the tropical North Atlantic and in associated underlying surface sediments.
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Marine and Terrestrial Nitrifying Bacteria are Sources of Diverse Bacteriohopanepolyols
Authors F.J. Elling, T.W. Evans, J.D. Hemingway, J.J. Kharbush, V. Nathan, B. Bayer, A.E. Santoro, E. Spieck, R.E. Summons and A. PearsonSummaryHopanoid lipids and their derivatives, bacteriohopanepolyols, are membrane components of some bacteria that are commonly used as biomarkers for specific bacterial groups or biogeochemical processes in the geologic record ( Newman et al., 2016 ). However, the sources of hopanoids to marine and freshwater environments remain largely unconstrained. Recent marker gene studies suggest widespread capacity for hopanoid biosynthesis in marine bacterioplankton, including nitrifying (i.e., nitrite- or ammonia-oxidizing) bacteria ( Kharbush et al., 2018 ).
To explore their hopanoid biosynthetic capacities, we studied the distribution of hopanoid biosynthetic genes in the genomes of cultivated and uncultivated ammonia-oxidizing (AOB) nitrite-oxidizing (NOB) bacteria. We found that hopanoid biosynthesis is common among seven of the nine presently cultivated clades of AOB and NOB. Hopanoid biosynthesis pathways are also conserved among the diverse lineages of AOB and NOB detected in environmental metagenomes.
Distinct carbon isotopic signatures of biomass, hopanoids, and fatty acids suggest operation of distinct carbon fixation pathways among nitrifying bacteria. Accordingly, nitrifying bacterial contributions to the geologic record of hopanoids could be estimated by their carbon isotopic compositions. The ubiquity of nitrifying bacteria in the ocean today and the antiquity of this metabolic process suggest the potential for significant contributions to the geologic record of hopanoids.
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Comparison Between Extraction Procedures for the Recovery of Polyfunctionalized Biohopanoids
Authors P. Schaeffer, R. Schwartz-Narbonne, P. Adam, D. Rush and M. RohmerSummaryFour extraction procedures (i.e., Bligh and Dyer, direct acetylation, CH2Cl2/CH3OH extraction and methanolysis) were tested for the recovery of biohopanoids from bacterial cells of a model bacterium (K. xylinus) and yielded similar amounts of bacteriohopanetetrols whatever the procedure used, without significant loss in the aqueous phase in the case of the Bligh and Dyer extraction. In contrast, the recovery of composite bacteriohopanepolyols (cyclitol ether derivatives) was shown to depend on the procedure used, with harsher conditions (i.e., methanolysis and direct acetylation) leading to higher yields. In the case of the Bligh and Dyer extraction, a significant part of the composite biohopanoid pool is lost in the aqueous phase, suggesting that the latter procedure should be avoided if optimal extraction of composite hopanoids is required.
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Rapid Evaluation of Organic and Pyritic Sulfur Content in Sedimentary Rocks by Rock-Eval 7S Analyser
Authors H. Cohen-Sadon, A. Amrani, S. Feinstein and Y.O. RosenbergSummaryEvaluating individual sulfur (S) fractions in rocks (e.g., pyrite, organic-S) provides essential information about depositional environments and petroleum systems potential. However, the common method for quantifying individual S-fractions in rocks is highly time-consuming (weeks) and labor-intensive. A more tractable approach may be the pyrolysis of the rock and gradual release of S-fractions based on their thermal stability. We have developed a method to identify and quantify the organic and pyritic-S using the rapid analysis (∼one hour) of the new Rock-Eval 7S analyzer (RE-7S, Vinci Technologies) based on an empirical relationship. The empirical relationship was established on nine different source rocks and was confirmed on 11 more samples relative to reference data obtained by the traditional wet chemistry procedure. The precision of organic and pyritic S values achieved by the new method is between 2 to 8 % for an S-fraction above 0.03 wt. % (of the bulk rock), and requires ∼60 mg rock. The fraction separation accuracy was assessed relative to wet chemistry separation and is better than 10 %.
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Diamondoids in Hydrocarbon Fluids from the Central North Sea — Implications for Maturity and Source Assessment
Authors R. Van der Ploeg, J. Pureveen and P. Van BergenSummaryDiamondoid analysis has become a well-established technique for investigating hydrocarbon fluids over a large maturity range, owing to the great thermal stability of diamondoids and their progressive enrichment with increasing maturity levels. This study presents the first detailed compilation of diamondoids results for hydrocarbon fluids from the North Sea. The data clearly reveals how diamondoid distributions can be used to disentangle maturity and source effects both on a regional as well as a field scale, which provides valuable insights for ongoing exploration efforts as well as further development optimization.
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Rapid Evaluation of D34S Values in Sedimentary Rocks by Rock-Eval 7S Analyser Coupled to a Mc-Icpms
Authors H. Cohen-Sadon, Y. Rosenberg and A. AmraniSummarySulfur isotopic ratio (d34S) is commonly used to reconstruct paleoenvironment conditions of sediment deposition and diagenesis, and for oil-oil and oil-source rock correlations. However, determination of the OM and pyrites d34S values requires a tedious and time-consuming (weeks), step-wise wet chemistry procedure followed by analytical d34S measurement by different instruments. A more rapid and simple technique can thus enhance the studies in this field. This study presents a rapid method for d34S values analysis of organic-S and pyrite-S by a Rock-Eval 7S analyzer, coupled to MC-ICPMS (RE/MC-ICPMS). The system was calibrated relative to the international standard V-CDT and achieved accuracy and precision better than ±1‰. The results suggest that isotopic fractionation between the pyrolysis products and the bulk fractions (organic and pyritic S) is minor in the majority of the samples. Thus the coupling of RE-7S to MC-ICPMS was conducted only for the pyrolysis cycle. The proposed method is a simple, robust, and rapid technique to measure the main S fractions d34S values in sedimentary rocks.
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Combined Pyrolysis Methods to Mitigate Sorbed Hydrocarbon Effect on Kinetic Response: A Case Study from Albian Units, Sw Iran
Authors A. Baniasad, F. Froidl and R. LittkeSummaryOrganic matter-rich, oil-prone, marine Albian units are the main source rock for the Upper Cretaceous-Tertiary reservoirs in southwest Iran and adjacent offshore areas. Its paleo-depositional environment encompasses a variety of coastal plain to inner and outer shelf settings resulting in temporal and spatial variations in source rock quality and quantity and presumably the kinetic response. This study attempts to add new bulk and molecular geochemical characteristics for these Albian units as well as its kinetic response considering the variations in the paleo-depositional environment employing different techniques, PY-GC-MS, GC-FID, GC-MS, and GC-IRMS.
The results indicate prominent temporal and spatial organofacies variations in the region which is in line with petrographic investigations and bulk and molecular properties of the samples. It also indicates the importance of geological process modeling and preparation of organofacies extension maps for implementing the Albian kinetic response in the regional basin modeling study.
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TRACKING SOURCES AND DYNAMICS OF DISSOLVED ORGANIC MATTER (DOM) IN AN ALLUVIAL PLAIN IN CONTRASTED HYDROLOGICAL SITUATIONS
Authors E. Parlanti, M. Sourzac, F. Baratelli, G. Varrault and N. FlipoSummaryUV/visible absorbance and excitation-emission matrix (EEM) fluorescence spectroscopy coupled to parallel factor analysis (PARAFAC) have been used to characterize dissolved organic matter (DOM) in surface and groundwater of a natural alluvial plain of the Seine River which is one of the most important regional and national wetlands in France. This work showed contrasting DOM optical properties between the three studied compartments of the system (river, alluvial aquifer, chalk regional aquifer) and between two hydrological periods (flood and low waters). During flood, DOM exhibited low molecular weights while groundwater was characterized by higher molecular sizes and biological activity. DOM optical characteristics for flood samples pointed out dominant terrestrial sources for river waters, a high biological activity and low terrestrial inputs in the chalk regional aquifer and mixed sources in alluvial aquifer. Whereas in low water, DOM molecular weights were generally lower with DOM characteristics for surface and groundwater still distinct, but with lower terrestrial inputs and higher autochthonous sources in rivers. Tracking DOM optical properties finally helped to understand the functioning of each of the three compartments and to identify possible connections and exchanges between the river, the alluvial aquifer and the underlying chalk regional aquifer depending on hydrological situations.
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OIL AND GASES OF THE KRASNOLENINSKY FIELD AND THE SEARCHING FOR THEIR SOURCE ROCKS (WESTERN SIBERIA, RUSSIA)
Authors N. Oblasov, I. Goncharov, I. Eftor, M. Veklich, M. Chudinova, A. Zherdeva, S. Fadeeva and V. SamoilenkoSummaryThe main purpose of the work was to search for source rocks that formed oil and gas deposits in the Jurassic section of the Krasnoleninsky field. Using GC, GC–MS, GC–MS/MS, IR-MS and Rock-Eval methods we studied 163 samples of oils, 144 gases and 1000 source rocks and reservoirs from the wells of this field. According to our results, the most significant source of hydrocarbons are rocks of the Bazhenov Horizon (Tutleim Formation). We allocated one large source of hydrocarbon generation within the Krasnoleninsky field, where rocks of the Bazhenov Horizon have released their source potential from 0 to 84%. The largest realization of source potential has occurred on the territory of Kamennaya, Palyanovskaya and Em-Egovskaya areas. The second most important source rock of hydrocarbons located in the complex of the Lower Middle Jurassic rocks with a high content of organic matter. these rocks contain typical non-marine organic matter, which accumulation proceeded mainly under oxidizing conditions. According to the complex of molecular and isotopic characteristics, we estimated the contribution of fluids generated by different types of source rocks.
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Aryl Isoprenoids of Paleozoic Oils of Southeastern Western Siberia (Russia)
Authors S. Fadeeva, I. Goncharov, A. Litvinova, N. Oblasov, M. Veklich, V. Samoilenko and A. ZherdevaSummaryArylisoprenoids (m/z 134) were found in the Paleozoic oils of southeastern West Siberia (Russia). Our studies have shown absent of arylisoprenoids in the oils and sediments of the Togur and Bazhenov Formations. This indicates a different composition of bioproducers and sedimentation conditions of organic matter. The presence of arylisoprenoids in the composition of the studied Paleozoic oils is evidence of periodic occurrence of anoxic conditions in the photic layer of paleobasin waters. The degree of anoxia of the photic layer during the formation of the organic matter by the arylisoprenoid index (AIR) was estimated for Paleozoic oils. Also, relative arylisoprenoid content (arylisoprenoid/n-alkanes ratio) was estimated for Paleozoic oils. The values of the arylisoprenoid index in the studied Paleozoic oils are determined not only by the conditions of formation of syngenetic organic matter of the source rock but also by the processes of catagenesis.
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Abrupt Mid-Holocene Cooling — Insights from Sub-Annually Resolved Reconstructions of Alkenone Lake Temperature
Authors M. Zwick, L. Wörmer, P.R. Leavitt, J. Wendt, B. Cumming, B. Wissel, K. Hinrichs and J.L. ToneySummaryImproved knowledge of past abrupt climate transitions on regional scales is essential for understanding current abrupt climate change and its repercussions. In the Northern Great Plains, we lack highly sensitive temperature proxies and validated records of past environmental change.
In this study, we develop and apply a new, quantitative, high-resolution algal paleothermometry approach based on analysis of lacustrine alkenones preserved in sediments using Mass Spectrometry Imaging (MSI). We demonstrate that the alkenone summer temperature proxy and MSI technology a) offer unprecedented insights during an abrupt climate event (5500 BP) and b) perform well in modern validation exercises.
Sub-annual resolution of the mid-Holocene Cooling (MHC, ∼5500 ka BP) with MSI alkenone paleothermometry offered unprecedented insights that would have remained hidden with conventional biomarker analysis.
Application of additional high-resolution proxies including X-Ray Fluorescence and conventional biomarker analysis also captured the general pattern of environmental changes during the MHC phase but lacked evidence of a marked increase in variability characteristic of sudden state change.
This study presents the first fully calibrated, high-resolution, lacustrine alkenone record of past lake water temperature. These analyses allow the development of better analogs for current climate change, especially in context of tipping points and climate system state change.
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The Use of Long-Term Climate Change Experiments for Improved Interpretation of Paleoenvironmental Records
Authors G. Wiesenberg, C. Zosso, N. Ofiti and M. SchmidtSummaryThe environmental impacts of increasing temperature have strong effects of organic matter production, incorporation and degradation in terrestrial ecosystems, which complicate the limitation to individual factors, such as only changing temperature, which is often associated with changing water availability. As a consequence, drawing general conclusions with respect to the impact of, e.g., temperature and CO2 concentration on plant molecular composition seems premature. We conclude, that paleoecological conclusions based on space-for-time approaches should be re-evaluated with the help of long-term field trials before they are transferred to paleoenvironmental records.
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Integration of Isotopic Data from Different Laboratories / Technologies. The Interest - or Necessity - of Regular Intercalibration Tests.
Authors Y. Poirier, D. Duclerc, I. Mitteau and M. LoriauSummaryMore and more laboratories/contractors are engaged in this molecular and isotopic compositions activity. The integration of isotopic composition of gases from different laboratories / technologies request comparable results and well-defined analytical uncertainties. In order to re-examine the actual situation, 6 different external laboratories used by TOTAL around the world were selected. Internal standard gases were sent for molecular and isotopic measurements (blind test). We will present the comparison of these results. The analytical uncertainties provided by the laboratories will be also compared. The impact on organic geochemistry fluid interpretation studies will be evaluate.
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Petroleum Systems Characterization Based on Organic Geochemistry Interpretation in Gabon, Lower Congo and Kwanza Basins
More LessSummaryRegional geochemical synthesis study in Lower Congo, Kwanza and Gabon basins resulted in oil families identification and petroleum systems characterization
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High Resolution Mapping of PO14C in the Northwest African Upwelling System Off Mauretania
Authors H. Grotheer, G. Fischer, T. Gentz, M. Iversen, K. Zonneveld and G. MollenhauerSummaryHere we report on the radiocarbon composition of particulate organic matter (POC) collected on four shelf (∼100 m water depth) to open ocean (∼2700 m water depth) transects in the northwest African upwelling system off Cape Blanc. Data show complex, seasonaly variable features of highly depleated POC in the water column sugguesting remobilization of pre-aged sediments.
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Car and Truck Tire Wear Particles in Environmental Samples –A Comparison With “Traditional” Microplastic Mass Loads
Authors I. Goßmann, M. Halbach and B.M. Scholz-BöttcherSummaryTire wear particles (TWP) are assumed to be the most dominant source of microplastics (MP). In environmental samples TWP particles occur as heteroaggregates with road material and particles. Combined with their variable composition both points lead to the fact that reliable determination methods for TWP are rare.
Therefore, identification and quantification of TWP was implemented in an existing pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) method for MP determination. The resulting TWP mass loads were compared to “traditional” MP shares. The latter included polymers such as PE, PP, PS, PET and PVC.
The widely held belief of TWP being the most dominant source of MP applies to sites in direct vicinity to TWP sources, only. An increasing distance to these sources leads to a decrease in TWP concentration in respective environmental samples. This points to a low long-distance transport potential of TWP compared to “traditional” MP which occurred ubiquitous.
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Modes of Soil Organic Carbon Sequestration and Carbon Use Efficiency Determined by Soil Aeration Status
Authors T. Meador, J. Niedzwiecka, S. Jabinski, T. Picek, R. Angel and H. ŠantrůčkováSummaryMicrobes regulate key ecosystem functions and global estimates of microbial activity in any habitat invoke on one or more scaling factors, including cell abundance, size, carbon content, and carbon use efficiency (CUE). Choice of CUE can sway C flux estimates by approximately one order of magnitude and propagate high uncertainty into global C budgets. Moreover, microbial CUE studies have focused on aerobic metabolisms and must still address the intensifying hydration-desiccation cycles that alter soil aeration status and prevalent anaerobic microniches in soils, where terminal electron acceptors such as iron may influence CUE. Here we employed a stable isotope labeling approach to follow the fate of ¹³C-glucose amended to two forest soils (100 μmol g-1; AT% = 3) with varying iron content and incubated under different oxygen levels, taking multiple channels of C assimilation into account.
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Formation of liquid hydrocarbons in bituminous coals: Natural observations and experiments
Authors L. Zieger, R. Littke and C. Hartkopf-FröderSummaryThe potential of forming liquid hydrocarbons for Pennsylvanian bituminous coals from Germany was studied, combining a set of organic-petrological and organic-geochemical methods as well as pyrolysis experiments.
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STRUCTURAL VARIATION AND PROVENANCE OF SULFUR-RICH ORGANIC MATTER IN NÖRDLINGEN POST-IMPACT SEDIMENTS
More LessSummaryThe Nördlinger Ries crater in southern Germany was formed by a meteorite impact 14.6±0.2 Ma ago and contains a sequence of Miocene post-impact lacustrine sediments. A suite of bulk rock and kerogen samples from exploration well Nördlingen-1973 (18–260 m depth) has been analysed in terms of bulk geochemical composition, organic petrology, online Curie Point-pyrolysis gas chromatography-mass spectrometry and attenuated total reflectance Fourier-transform infrared spectroscopy for getting insights into the chemical composition and structural evolution of the kerogen up the sedimentary sequence in relation to sources for organic matter.
The results show that hydrogen- and sulphur-rich kerogen prevails in the post-impact sediments, having abundant aliphatic and thiophenic constituents, which is proved by high H/C (1.6 on average), intensive aliphatic CH stretching vibration bands at 2700–3000 cm-1 in ATR FT-IR spectra, abundant aliphatic and thiophenic pyrolyzates. The OM mainly originates from algal and microbial material as suggested by prominent n-alkane/-alkene doublets and iso-alkanes. Type III kerogen occurs in the uppermost unit, containing more aromatic and phenolic constituents with abundant phenolic and aromatic pyrolyzates, in which OM is partly of higher land plant origin with ample vitrinite and inertinite particles.
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Seasonal to Decadal Sea Surface Temperature Changes During the Younger Dryas/Holocene Transition in the Tropics
Authors L. Wörmer, J. Wendt, B. Boehman, G. Haug and K. HinrichsSummaryWe explored how the Younger Dryas (YD)/Holocene transition impacted tropical sea surface temperature (SST) by evaluating marine sedimentary archives at scales unattainable for conventional molecular stratigraphy. In sediments from the Cariaco Basin, we analysed the well-established UK’37 SST proxy via mass spectrometry imaging, and obtained 2D-images of sedimentary proxy distribution at 100 µm resolution and corresponding downcore SST profiles with subannual resolution.
SST in the Cariaco Basin remains relatively constant over the YD/Holocene transition, suggesting a decoupling from the major environmental change associated to this event, i.e. the northward shift of the intertropical convergence zone. However, we were able to reveal a short-lived ∼50 year episode of abrupt warming during which average SST increased about 1°C. This episode is synchronous with the Preboreal Oscillation cooling, that led to drier, colder conditions in Europe and North America.
The comparison of proxy values, elemental composition and sediment colour from every µm-sized spot further provides clues on SST seasonality and its modulation across the YD/Holocene transition.
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Sedimentary Branched Tetraethers in an African Lake Record 170 KYR of Tropical Temperature Change: Assessment of Calibrations
Authors A. Baxter, F. Peterse, D. Verschuren and J. Sinninghe DamstéSummaryIn order to improve our understanding of Earth’s climate history, proxies that accurately reconstruct past temperatures are needed. The distribution of branched glycerol dialkyl glycerol tetraethers (brGDGTs), the membrane lipids of certain bacteria, is correlated to temperature in modern settings, and therefore is at the basis of several paleothermometers. Here we apply several brGDGT based temperature calibrations developed specifically for lakes to the sediment sequence from Lake Chala, in equatorial East African, to generate temperature records which cover the last 170 kyr in unprecedented high temporal resolution (210 years on average). Surprisingly, application of the recently developed East African lake calibration leads to ambiguous results. By contrast applying a calibration created before the discovery of 5- and 6-Me brGDGT isomers produces a temperature record strongly reminiscent of established climate records such as the isotope records from Antarctica and contains periodicities relating to orbital precession and obliquity. Therefore it appears that 6-Me brGDGTs are key to the temperature signal archived in Lake Chala. In Lake Chala today, 5- and 6-Me brGDGTs generally occupy different parts of the water column, and thus their relative abundance may be indirectly related to temperature through changes in lake depth or seasonal mixing.
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Polymer Characterization by the Rock-Eval® Device for Identification of Plastics in Sediments
Authors M. Romero-Sarmiento, H. Ravelojaona, D. Pillot and S. RohaisSummaryIn this work, artificial thermal degradation experiences using the Rock-Eval® device were performed on selected polymer microsphere samples. The main idea of this work is to create a database of different polymer standard responses (PE, PE100, PA6, PA11, PFA and PET) using the specific Rock-Eval® FID peak signals. This study attends to demonstrate if this quick thermal degradation method can be also used to characterize the plastic contents (detection, type, quantity) in sedimentary samples
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PAIRED SUB-ANNUAL BIOMARKER AND ELEMENTAL CLIMATE PROXIES REVEAL MONTHS OF CLIMATE SIGNAL INTEGRATION IN THE ARABIAN SEA
Authors T. Napier, L. Wörmer, J. Wendt, A. Lückge and K. HinrichsSummaryLaminated Pakistan Margin (northeastern Arabian Sea) marine sediments provide excellent, continuous archives of past climate conditions that can be used to reconstruct the variability of the Southwest (summer) and Northeast (winter) monsoons of India. Sea surface temperatures (SSTs) were reconstructed using UK'37 and CCaT proxies, with a resolution of 0.1-year. Both proxies reconstruct reasonable SSTs compared to the instrumental range, but neither proxy captures the full ∼6°C annual cycle. However, there is coherence on interannual to decadal timescales between instrumental SSTs and proxy-derived SSTs, indicating the proxies capture the same climatic cyclicity as instrumental SSTs. In particular, the UK'37 and instrumental SSTs have similar interannual to decadal trends, which is apparent when comparing UK'37 SSTs with an 11-month moving mean of the instrumental SSTs. The proxy SST signal is a temporal integration of SSTs from up to several months. We posit that this may be linked to variable sinking flux throughout the year. The sinking flux of these organisms increases during periods of high productivity (spring-summer, winter) or high lithogenic flux. These organisms likely remain in suspension when sinking flux is low, which may last several months; subsequent aggregation then integrates their SST signals.
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Occurrence of Human-Excreted Contaminants Within a Decantation Tank: A Clue of Their Historical Consumption?
Authors T. Thiebault, L. Fougère, A. Simonneau, E. Destandau, C. Le Milbeau and J. JacobSummaryThis study investigated the occurrence of drug target residues (DTR) in a decantation tank. This installation trapped the coarse fractions of a unitary sewer system, collecting both stormwater and wastewater. While this 17 m deep underground building could constitute a nonesuch opportunity to study the historical evolution of illicit and licit drug consumption in the catchment, the deposition processes and the record of DTRs remain largely unknown at present. Five cores were acquired from 2014 to 2017. 152 sediment samples were extracted using a mixture of water:methanol (1:1) prior to the DTRs quantification in the extracts. Several classical sedimentological analyses such as total organic carbon, facies description and granulometry were also performed on these samples, in order to understand the most important factors impacting their deposition.
The key-role of the speciation of DTRs was highlighted by the higher contents in neutral and anionic DTRs in organic layers, whereas only cationic DTRs were found in mineral layers. The considerable modifications in the sediments’ properties are therefore the most important driver impacting their DTR concentrations in decantation tank sediments. Further research remains necessary to fully understand the deposition process, but this study provides new clues explaining these temporal evolutions.
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New Insights into Microbial Wax Ester Biosynthesis, Natural Occurrence and Adaptive Role
By G. VincentSummaryWax esters (WE) are a major class of storage lipid compounds synthesized by bacteria in which they can have different physiological functions. So far, the potential for WE biosynthesis by prokaryotes has been mostly investigated in aerobic bacteria, and this metabolic capacity is considered not to have arisen in archaea. Additionally, the use of WE in geochemical and environmental studies has been overlooked due to their apparent rapid hydrolysis during early diagenesis. However, some reports have documented a possible formation of WE by facultative or phototrophic anaerobic bacteria, and WE have been reported in up to 40,000 years old lacustrine sediments, suggesting their possible formation in anoxic environments and preservation in the geological record under adequate conditions. Here, we present a combination of recent laboratory and field studies demonstrating that WE can be biosynthesized in various anoxic environments by several families of anaerobic bacteria and that such storage lipids may be specifically important for some microbial communities to survive in environments experiencing harsh environmental conditions. Our data also describe original interactions between abiotic and biotic processes that can occur during OM diagenesis and show that WE can constitute an interesting molecular tool to decipher carbon transformation pathways in the geosphere.
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Lake Dziani Dzaha (Mayotte, Indian Ocean): A Modern Analogue for Type I Kerogen Formation
Authors I. Jovovic, V. Grossi, P. Adam, M. Ader, F. Baudin, I. Antheaume, D. Jézequel, F. Arnaud, E. Malet, E. Bard, M. Capano, L. Simon, S. Mignard, P. Cartigny and F. GelinSummaryIn the past, highly productive (hyper)saline and alkaline environments have proved propitious for large accumulation of sedimentary OM that led to the formation of Type I kerogens, such as those of the Green River Formation.
A sediment core that covers most of the history of Lake Dziani Dzaha, a hypereutrophic saline, alkaline and mostly anoxic crater lakewhich waspostulatedto be a modern analogue of such environments, has been investigated using several analytical approaches comprising bulk (Rock-Eval and C, N, S elemental analyses), isotopic (δ13,14C, δ15N, δ18O, δ33,34,36S), and sedimentological descriptions.
This study revealed that, despite strong environmental changes undergone by the lake since its formation, the conditions prevailing in the lake supported by a continuous high primary production have led to an excellent preservation of OM and to early diagenetic reductive and sulfurization processes which have yielded an exceptionally reduced character of the OM with respect to its short diagenetic history (< 6 ky).
The similarities observed between the sediments of Lake Dziani Dzaha and some source rocks associated to Type I kerogens suggest that early diagenetic processes can have a strong and rapid impact on the accumulation of OM in some (semi)closed and highly productive aquatic ecosystems.
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Role of Ecosystem Engineers on the Organic Matter Characteristics in the Northern Intertidal Zone of the Seine Estuary (Nw France)
Authors A. Huguet, J. Morelle, C. Anquetil, M. Sourzac, K. Judith, J. Lebrun-Thauront, J. Maubert, F. Orvain and E. ParlantiSummaryIntertidal zones have a key ecological role in estuaries. The area covered by the intertidal mudflats in the Seine estuary (NW France) was divided by 3 over the last centuries. The preservation of these areas is a priority but requires a detailed understanding of their functioning. The latter is complex and notably depends on the presence and activity of benthic macrofauna, which can act as ecosystem engineers, strongly affecting the other organisms.
The aim of this study was to assess the influence of the two predominant ecosystem engineers in the Seine Estuary mudflats (Hediste diversicolor and Scrobicularia plana) on the dissolved and sedimentary organic matter (OM) quality. The role of the ecosystem engineers on the quality of the sedimentary OM was evaluated through the analysis of complementary lipid biomarkers. The characteristics of the dissolved OM (DOM) from the corresponding interstitial waters were concomitantly determined by spectroscopic analyses.
Even though it was shown that H. diversicolor and S. plana play a major role on the microphytobenthos dynamics, the seasonality was shown to have a more pronounced effect on the sedimentary OM characteristics than benthic organisms. In contrast, the DOM was suggested to be sensitive and reactive to the ecosystem engineer activities.
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APPLICABILITY OF INFRARED ALIPHATIC STRETCHING REGION FOR CHARACTERISATION OF OILS OF THE SAME GENETIC TYPE
Authors J. Stevanovic, A. Rakitin and K. StojanovicSummaryThe work focuses on the applicability of infrared (IR) aliphatic stretching region for characterisation of oils of the same genetic type. Paraffinic oils (56 samples) from the Turija-Sever oil field were studied. The oils are similar originate from mixed aquatic/terrestrial sources and were generated from Tertiary source rocks in an early stage of oil window. However, slight differences among the oils were observed. They are reflected in a higher contribution of algal organic matter (OM) to the group I oils formed in more reducing environment (western part of the field), compared to the oils from eastern part (group II). The IR CH2/CH3 branching factor segregates oils into two identical groups (I and II) established based on biomarkers and aromatic hydrocarbons. The group I oils showed lower values of CH2/CH3 factor than group II oils. Enhanced CH2/CH3 ratio for group II oils indicate that in the case of uniform maturity greater average length of polymethylene fragments results from a higher content of long chain n-alkanes signifying an increased impact of terrigenous OM (land plant waxes). Correlation between the normal to isoprenoid alkanes sum ratio and the CH2/CH3 factor is useful for detecting slight differences between oils of the same genetic type.
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Subsurface Lithoautorophy Revealed Through Unique Biomarker Distributions and Compound-Specific Carbon Isotopes
Authors M. Selensky, A. Masterson, J. Blank, S. Lee and M. OsburnSummaryThe shallow subsurface spans the transition between the deep subsurface and surface biospheres. Microbial communities in the subsurface are known to subsist on organic carbon transported from the surface and/or carbon fixed in situ via chemolithoautotrophy. However, the relative balance between these two sources is unknown. Cave environments fortunately present opportunities to directly interrogate shallow subsurface microbial ecology. Here, we explore the lipid biomarkers and carbon sources used by microbes in the lava caves of Lava Beds National Monument, CA, USA. To accomplish this, we extracted intact polar lipid (IPL)-derived fatty acids from cave biofilms, speleothems, and surface soils. We observe 127 discrete compounds in total, including 36 branched isomers. Whereas soils are dominated by straight-chain fatty acids and dicarboxylic acids, bacterial branched and trans-unsaturated fatty acids are particularly abundant in cave biofilms. Compound-specific stable carbon isotope analysis (CSIA) revealed very negative δ13C values in such biofilm fatty acids (down to −47.8‰ vs. VPDB). By comparing these values to the isotopic compositions of dissolved organic (−29.8 +/− 2.0‰) and inorganic carbon (−6.0 +/− 1.9‰) in water entering the caves as drips, we infer that biofilm microbes source a significant portion of their biomass from in situ fixation of previously-respired carbon.
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Subsurface Microbial Communities Utilise a Wide Range of Aromatic Compounds in Anoxic Coal Seams
Authors B. Campbell, S. Gong, P. Greenfield, D. Midgley, I. Paulsen and S. GeorgeSummaryCoal bed methane is a key source of energy in the transition from fossil fuels to renewables. Although a large proportion of this methane is generated via subsurface biological processes, little is known about the degradation pathways and microbial communities responsible. Previous literature has identified many of the microbial communities present in methane-producing coal seams and speculated as to which of these microbes are responsible for possible coal-to-methane degradation processes in situ.
Anoxic microcosms were established with a range of different monoaromatic and polyaromatic compounds as sole sources of carbon. These microcosms were inoculated with a coal seam microbial community sourced from a methane-producing well in the Surat Basin, Queensland, Australia. After incubation, community amplicon sequencing of the 16S rRNA gene revealed the identities of microbes that increased in relative abundance on each of the aromatic substrates. Putative degradation pathways for the substrates were hypothesized, along with which microbes are likely to be active in different parts of the degradation pathways, based on both these analyses and pre-existing literature on anaerobic degradation of aromatic compounds from non-coal environments.
This research provides valuable insights into the catabolism of organic matter in coal in situ.
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Fires Support Biome Shifts in E Siberia? Interglacial Fire-Vegetation-Climate Feedbacks Reconstructed from MIS-11-Sediments of Lake El’gygytgyn
Authors E. Dietze, A. Andreev, K. Mangelsdorf, M. Theuerkauf, C. Kraamwinkel, M. Melles, H. Meyer, T. Tessendorf, V. Wennrich and U. HerzschuhSummaryThe ongoing spread of forest fires in the Siberian Arctic raises concerns on how far increasing temperatures and fire occurrence lead to biome shifts from tundra to summergreen or evergreen boreal forest. Here, we investigate vegetation and fire regime shifts during late MIS 12 and MIS 11 c. 390–430 kyrs ago using sedimentary charcoal, anhydrosugars and pollen from Lake El'gygytgyn, NE Siberia. We find different types of centennial-to-millennial-scale biome shifts, partly accompanied by fire regime shifts. We assess the role of fire in driving and/or responding to biome changes, especially periods of abrupt warming, to gain understanding of what we can expect during the ongoing warming of the high-northern latitudes.
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Application of Mc-Icp-Ms Method for Sulfur Isotopic Analysis in Reservoir Rocks
Authors B. Gareev, G. Batalin and A. ChugaevSummaryWe have developed a technique for determination of 34S/32S isotopic ratio in pyrite using multiple-collector inductively coupled plasma mass-spectrometer NEPTUNE PLUS equipped with J-interface and desolvating nebulizer sample injection system (Aridus II). This configuration of the NEPTUNE PLUS, as well as a high-resolution mode, made it possible to significantly reduce (>10000 times) major isobaric interferences by 32 mass from O2+. For mass bias correction, standard-sample bracketing was applied.
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Decadal Sea Surface Temperature Variability in the Eastern Mediterranean During the Last Interglacial
Authors I. Obreht, D. De Vleeschouwer, L. Wörmer, M. Kucera, D. Varma, M. Prange, T. Laepple, J. Wendt, S.D. Nandini-Weiss, H. Schulz and K. HinrichsSummaryUnderstanding the climate variability from geological periods with warmer-than-present climate is of great relevance for understanding the climate of the future warmer world. The Last Interglacial (LIG; ∼130,000 to 116,000 years ago) is the most recent geologic period with warmer-than-present climate, where climate reconstructions from the LIG provide an opportunity to evaluate climate variability from a warmer world. However, conventional analytical methodology applied on classical geological archives does not provide access to information on annual and decadal patterns of climate variability. In this study, we apply novel analytics on a unique marine geological archive to generate the first annually to subdecadally resolved continuous millennial-scale record indicative of Earth's climate variability during the last warmer-than-present interglacial. We will examine the naturally occurring cyclicity and variability of sea surface temperature and constrain the rate of SST change on decadal to centennial time-scales in the warmer-than-present LIG in the Eastern Mediterranean.
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Impact of Oxyegn Level on the Distribution of Branched Tetraethers in Soil Profiles
More LessSummaryThe influence of oxygen level on brGDGT-based proxies was evaluated by studying GDGTs in three soil profiles with contrasting oxygen level.
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Realizing the Full Potential of Lipidomics: A New Protool for an Improved Extraction of the Intact Polar Lipids of Archaea
Authors T.W. Evans, F.J. Elling, Y. Li, A. Pearson and R.E. SummonsSummaryThe investigation of intact polar lipids (IPLs) is a powerful tool for investigating the physiology of Archaea in cultures and their prevalence in environmental samples. IPLs are typically extracted using the Bligh and Dyer protocol. However, recent studies have exposed both, bias and a low extraction efficiency for archaeal lipids obtained by this technique. Here, we tested different solvent mixtures, mechanical rupture techniques and chemical detergents/enzymatic lysis buffers for their potential to destroy the cell envelope and thus increase the extraction efficiency of archaeal IPLs in pure cultures and environmental samples. The tests with different solvent mixtures revealed highest IPL yields when samples were extracted with a monophasic solvent system that included a trichloroacetic acid buffer. Freeze-thaw cycles prior to the extraction after Nishihara and Koga (1987) enhanced the extraction efficiency by 1.7-times, while other investigated mechanical rupture techniques (bead beating and osmotic shock) showed no increase. The use of chemical detergents in combination with freeze-thaw cycles resulted in significantly higher IPL yields than the experiments without the pre-treatment.
The results demonstrate that the novel protocol results in significantly higher archaeal IPL abundances than the Bligh and Dyer protocol, suggesting that earlier studies may have overlooked the majority of IPLs.
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MICROBIAL METHANOGENESIS ASSOCIATED WITH BROWN AND BITUMINOUS COALS IN THE BOHEMIAN MASSIF: ISOTOPIC AND METAGENOMIC EVIDENCE
Authors J. Francu, J. Šerá, M. Koutny, F. Koutny, P. Parizek, P. Jirman and Z. VilhelmSummaryMicrobial methane occurrence associated with brown and bituminous coals in the Bohemian Massif is documented by chemical and isotopic composition and by metagenomics analysis. New methane shows were found recently in the Lower Miocene Most basin in the NW Czech Republic in drillings to deeper horizons with unmined coal seams. Gas evolved from formation water contains up to 27 % methane of δ13C-CH4 ‐73.1 ‰ and 33% of CO2 of δ13C-CO2 ‐8.0 ‰. The microbiological investigations found the presence of archaeal methanogens. In fluids and muds closer to surface microbial communities were found capable of degrading complex organic compounds and methane oxidation. Bituminous coals mined in the Upper Silesian Coal Basin in the NE Czech Republic contain gas with up to 94% of microbial methane of δ13C-CH4 ‐64 to -68‰ and up to 5% CO2 of δ13C-CO2 ‐14 to -47‰. The gas data suggest active and fossil methanogenesis, microbial methane oxidation associated with surface water infiltration and widespread sorption of both gases on coal seams. The bacterial communities in the bituminous coals are dominated by organisms specialized on fermentative degradation of complex organics considered as the prerequisite for microbial methanogenesis. Archaeal methanogens were identified by metagenomic analysis.
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HEMICELLULOSE REMNANTS IN SEDIMENTARY ORGANIC MATTER DETECTED USING METHANOLYSIS GC-MS
More LessSummaryOur results show that not only cellulose, but also hemicelluloses can persist for millions of years under favorable conditions with only minor structural changes due to slow microbial and/or diagenetic decay. In fossil wood, types of hemicellulose can help assess whether the ancient plants were related to gymnosperms or angiosperms.
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Geochemical Evidence of KaČÁk event in Eastern Gondwana, Ponta Grossa Formation, ParanÁ Basin, Brazil
Authors L. Rocha, E. Soares de Soua and H. J. P. Severiano RibeiroSummaryThe Ponta Grossa Formation is one of the sedimentary sequences belonging to the Paraná Basin. Inside the strata of this formation, in the Eastern portion of the Gondwana continent, occupy the time interval known as Devonian, in which several significant events occurred: like the event named Kačák associated with a rise in sea level. This event caused drastic changes to the environment. This present work aims to characterize the organic matter input variation along with the description of the depositional paleoenvironment over the related geological time and the influence of the Kačák event. For this purpose, were conducted GC/MS saturated biomarker analyses of 15 samples, collected from very known outcrops in the stratigraphic interval that goes from the Early to the Middle Devonian.
The differences observed in the geochemical parameter values are possibly related to the latest Eifelian Kačák Event. This event affected a large part of marine species. However, the recovery of fauna and flora already could be observed in the Givetian. The Kačák event was a landmark of biotic crisis and extinction of the Devonian period and is well registered in the strata of the Paraná Basin in the Grossa Formation.
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In-Situ Shale Oil Conversion Potential of the Nenjiang Formation Organic-Rich Shale With Low Maturity in Northern Songliao Basin
More LessSummaryThe Nenjiang 1st-2nd members of Songliao Basin were deposited during large-scale lake transgression with marine incursion and the paleo-lake covered more than 0.2 million km2. The deep water with salinity stratification favored organic matter preservation and source rocks developed in this two members are excellent. Most source rocks are in immature to low mature stage and the burial depth is relatively shallow, implying a large scale of in-situ conversion shale oil potential (ICP). Organic-rich shales are widely distributed and the thickness of shale with TOC greater than 4.0% is 10–30m in K2n1, and 6∼12m in K2n2. The TOC of organic rich shale of K2n1 and K2n2 members is 4%∼13.97%, with the maximum hydrocarbon potential of 92.31mg/g, the maximum HI of 922mg/gTOC. Hydrous pyrolysis result shows the maximum oil yield is 424 ∼451 mg/gTOC at temperature 375℃. It is suggested that organic-rich shales of K2n1 and K2n2 members have great oil generation potential and the total oil yield can be 52–59% of the original HI. The estimated in-situ conversion oil resource of K2n1 and K2n2 members is over 20 billion tons.
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DEMIXING OIL-BASED DRILLING MUD AND RESERVOIR OILS FROM DRILLING CUTTINGS USING ULTRAHIGH RESOLUTION MASS SPECTROMETRY
Authors M. Yin, H. Huang and T. OldenburgSummaryThis study uses ultrahigh resolution mass spectrometry techniques, namely Fourier transform ion cyclotron resonance mass spectrometry (FTICR–MS) to deconvolve and characterize reservoir oils encountered by drilling cuttings that are contaminated by oil-based drilling mud. The hydrocarbon species are ineffective to separate the drilling fluids and the reservoir oils in the cuttings. However, in the non-hydrocarbon fraction, the disappearance of the N1 class monitored in the electrospray negative ion mode and great abundances of the NxOy classes in the DM and the cuttings alike suggest severe contamination of these cuttings by the drilling fluids. In contrast, the N1 class containing cuttings indicate presence of authentic reservoir oils. The triangle plot of the relative proportions of the DBE 9, 12, and 15 groups of the N1 class suggests a PM level range of 1–5 of authentic reservoir oils as well as non-biodegraded reservoir oils contained in the cuttings.
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Hyrous Pyrolysis of Source Rock Plugs: Geochemical and Visual Investigations and Implications for Primary Mirgation
Authors S. Grohmann, G. Gaus, J. Klaver, I. Abu-Mahfouz, V. Vahrenkamp, T. Patzek, J. Urai and R. LittkeSummaryType II-S kerogen source rock plugs with high TOC contents (10 to 20 wt.%) were investigated in their initial immature state as well as in different thermal maturities induced by hydrous pyrolysis under both unstressed and stressed conditions in order to investigate hydrocarbon generation and primary migration. Applied methods comprise organic geochemical investigations to assess the state of kerogen conversion as well as visual techniques such as reflected light microscopy and BIB-SEM to investigate the distribution and evolution of kerogen, solid bitumen and pore space within these rocks. Our first results indicate that primary migration within such high TOC rocks occurs along an interconected porenetwork that evolves upon kerogen conversion rather than due to the buildup of overpressure and microfracturing.
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ROCK-EVAL PYROLYSIS ON MICRO-PLUGS TO INVESTIGATE SOLID BITUMEN DISTRIBUTION AT DIFFERENT THERMAL MATURITIES
Authors S. Grohmann, S. Grohmann, R. Littke, M. Dörner and M. ErdmannSummaryThe distribution and type of solid bitumen at different thermal maturities is characterized by a combined approach of organic geochemical and petrographic investigations. Different maturities are present as both naturally achieved as well as by open system pyrolysis of small rock pieces placed into Rock-Eval crucibles. Our first results show, that a certain fraction of the bitumen has a high thermal stability and is detected as the S2 peak rather than S1. Further, the isothermal temperature of 300°C for 3 minutes is not able to fully extract the observable solid bitumen from the rock pieces. In contrast, the amount of solid bitumen in pores increases as well as its reflectivity, indicating remigration from the inner part of the rock towards its surface. Pyrolysis at higher temperatures also creates new solid bitumen filling pores that have been empty in the initial state.
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The Characteristics of Biomarkers Under the Superimposed Influences of Biodegradation and Thermal Alteration
More LessSummaryTo elucidate whether and how petroleum biomarkers could be altered under the superimposed influence of successive biodegradation and thermal alteration, a sequence of oil and oil sands that are at different biodegradation levels were artificially matured via closed-system pyrolysis. The distributions of biomarkers in the variably biodegraded oil samples and corresponding pyrolyzates were compared. The results showed that the presence of normal alkanes in crude oil does not necessarily excludes the possibility of previous moderate–severe biodegradation as n-alkanes can be further generated under advanced thermal stress. Most source related parameters based on steranes and terpanes seem to be reliable only when the oil reservoir has suffered biodegradation not beyond moderate level and the maturity of the crude oil is below 0.91 Easy%Ro. The TT23/(TT23+TT24) ratio, however, was found to remain constant even after severe biodegradation and thermal alteration, making it applicable in oil-source correlation in superimposed oil reservoirs. In addition, isomerization-based maturity parameters such as methylphenanthrene index of crude oils are reliable if subsequent thermal alteration reached above 0.91 Easy%Ro despite prior moderate–severe biodegradation, because the related isomerization reactions would approach the same level observed for the non-biodegraded oil after subsequent thermal alteration.
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ISOTOPIC COMPOSITION AND NATURE OF GASES IN THE NORTH OF WESTERN SIBERIA
Authors M. Veklich, I. Goncharov, A. Zherdeva, N. Oblasov and V. SamoilenkoSummaryWere determined the carbon isotopic composition (δ13C) of methane and its homologues (C2-C5) for more than 150 gas samples from 26 different fields in the North of Western Siberia (Gydanskaya and Nadym-Pur-Tazovskaya oil and gas bearing areas).
Several genetic types of gases were identified based on the obtained results.
First group - gases directly from the Bazhenov Formation (Upper Jurassic source rock which content marine type of organic matter) have a sublinear view and C1-C5 components have the same origin.
Second group - gases that were generated by source rocks, where the organic matter had been formed mainly in the lake-marsh facies of the Lower and Middle Jurassic.
Third group - microbial gases and gases genetically related to the nonmarine organic matter of the Jurassic, another group of gases is found in the Upper Cretaceous rocks (Turonian, Cenomanian). A distinctive feature of these gases is the abnormally light isotopic composition of ethane (-54...-51‰) and propane (-45...-43‰).
Fourth group - biodegraded gases. A distinctive feature of these gases is heavy isotopic composition of propane and butane carbon.
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Petroleum Generation and Migration in the South of Western Siberia, Russia
Authors V. Samoilenko, I. Goncharov, P. Trushkov, N. Oblasov, M. Veklich, S. Fadeeva, R. Kashapov and A. LitvinovaSummaryA detailed study of petroleum and source rock extract data confirms that the Bazhenov source interval is the main source of all reservoired petroleum found in the region. Lower Cretaceous petroleum deposits are found at distances up to 100 km from the mapped Bazhenov kitchen areas. Petroleum deposits in Upper Jurassic reservoirs have been generated in local kitchens or have migrated over short distances only (10–20 km). The largest regional spread is seen in Bazhenov-generated petroleum in Middle Jurassic Tyumen reservoirs, which are found in deposits along migration routes from the kitchen areas towards the south and which can reach up to 150–200 km.
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