Indigenous Organic Matter Research Articles

Detection of indigenous organic matter in rocks from the interpretation of carbon molecular forms in the laser-induced plasma

Detection of indigenous organic matter (IOM) in rocks using molecular-laser-induced breakdown spectroscopy (LIBS) is reported. IOM refers to carbon-based compounds of variable complexity intimately associated with mineral and amorphous phases both in condensed phases and in a dispersed state spatially associated to mineral aggregates. The presence of IOM may provide valuable information in astrobiology about the possibility of past or present life on planetary bodies. Kerogen, charcoal, bitumen, and graphite are only some examples of IOM that may appear in rocks. This paper reports the detection of kerogen in oil shale (a sedimentary rock also containing dolomite, calcite, pyrite, quartz, and albite) from the LIBS study of CN and C2 emissions under simulated Martian conditions. A set of oil shale samples with variable concentrations of total organic carbon (TOC) ranging from 2.78% to 12.74% were analyzed. A careful LIBS analysis of molecular species associated within hydrocarbons confirmed the presence of organic matter derived from kerogen. A linear correlation between the CN and C2 emissions and the %TOC was observed. Using a simulated Martian atmosphere as surrounding gas, the limit of detection for organic matter was calculated in 0.42% TOC. Additionally, the potential interferences in geological samples for LIBS detection of molecular species were also evaluated. Results demonstrate that common elements in rocks such as Ca, Fe, K, Mg, Na and Si do not interfere with the detection of organics. In contrast, Ti at concentrations above 0.4% may induce false positive results using the CN emission at 388.34 nm. To overcome this inconvenience, the CN emission at 387.14 nm may be used which, although less sensitive, is free from titanium interference.

Does anoxia promote the mobilization of P-bearing colloids from dam reservoir sediment?

In the context of a reservoir, the anoxia that develops in the bottom sediment induces the release of phosphorus (P) into the overlying water, thus supporting eutrophication. Most studies focusing on P dynamic in an aquatic environment fail to consider the “truly” dissolved and colloidal fractions, hence the colloidal P has gone largely unexplored. The aim of this study was to investigate the release of sedimentary P under oscillating aerobic, anoxic and aerobic conditions, in taking into account the colloidal (10 kDa–1 µm) and truly dissolved (< 10 kDa) fractions. Laboratory incubations of wet sediment originating from a dam reservoir were performed over 63 days, consisting of 25 days of aerobic conditioning (lasting 2 periods) and 38 days of anoxia. Results showed that oxic conditions induced a very limited release of phosphorus, both in truly dissolved and colloidal forms. In turn, the development of anoxic conditions caused a large release of P, mainly in the colloidal fraction, representing about 90 % of the total water-mobilizable P (PWM < 1 µm). The initial release of truly dissolved P during the anoxic stage gradually diminished over time, possibly due to the formation of secondary minerals or re-adsorption processes. Approximately half of the PWM released during anoxia persisted under subsequent oxic conditions and consisted solely of colloidal P. The dynamics of PWM were primarily influenced by two main factors: (i) the reductive dissolution of iron, which released both dissolved and colloidal P, and (ii) the release of indigenous organic matter, which impacted the stability of the released colloids through bridging mechanisms.

The method of determination of the kerogen and bitumoids content in the Artinskian sediments of an oil and gas field of the Orenburg region by well logging data

The lithological and geochemical studies of the Artinskian carbonate sediments of one of the gas and oil fields in the southwest of the Orenburg region revealed a significant amount of indigenous organic matter in the productive intervals of the section. The study of thin sections established that the organic matter content in the examined rocks reaches 3.75 wt%, with the average value of this parameter being 1.05 wt%. The article is devoted to the development of methods for estimating the content of kerogen and bitumens in rocks according to well logging data.

Stable Carbon Isotopic Composition of Selected Alkylnaphthalenes and Alkylphenanthrenes from the Tarim Oilfields, NW China

The present study aimed firstly to use a set of crude oil samples and a dataset to provide new evidence for source input contribution in selected aromatic isomers for discrimination of oils from three oilfields from Tarim Basin and identify the key factor (s) controlling the isotope composition. Thus, the present research showed that the δ13C values of alkylnaphthalenes and alkylphenanthrenes plotted against P/DBT and Ga/C30H ratios is a reliable and convenient tool for discrimination of organic matter variations in different oilfields. More importantly, molecular ratios and different diagram plots revealed that the selected oil samples would be derived from a mixing of indigenous organic matter from the terrestrial (in Kuqa area) and marine (in the cratonic area) depositional environments prior the apparition of the Yakela Faulted Uplift. Thus, Daolaoba, Yakela, and Tahe oils were made up of organic materials from both marine and terrestrial sources. Furthermore, marine organic matter input dominates oils from the Tahe and Yakela, with a minor input from terrestrial sources. The oils from Daolaoba were assigned to be from a mixing of marine and terrestrial material inputs. The controlling factors assessment revealed that biodegradation has an insignificant effect on the set of oils; however, the source input and the thermal maturity together control the isotopic compositions of individual aromatic isomers from these three oilfields.

Exceptional molecular preservation in the Late Jurassic Claudia palaeo-geothermal field (Deseado Massif, Patagonia, Argentina)

Gas chromatography–mass spectrometry was applied to samples collected from an exceptionally well-preserved Late Jurassic (∼150 Ma) sinter complex of the Claudia palaeo-geothermal field, Deseado Massif geological province, Argentinean Patagonia, which, despite its age, has never been deeply buried. Results indicate that the distal sinter apron has a much higher preservation potential for indigenous organic matter (OM) than the more proximal (vent area) facies of this palaeo-geothermal field. Specifically, homohopane ratios show that the OM of the proximal apron is of mixed thermal maturities and is in low abundance. In contrast, the OM extracted from the distal apron contains highly abundant, thermally immature biomarkers, the presence of which are consistent with the lower original fluid temperatures of the distal spring facies. Moreover, despite indications of the presence of some thermally mature aromatic compounds, hopane and sterane ratios confirm that the distal apron samples are extremely thermally immature and thereby constitute an area of exceptional molecular preservation. From an astrobiological viewpoint, these results suggest that silica sinter can preserve abundant organics over millions of years in palaeoenvironmentally conducive settings, and that sample-site selection within a hot spring facies-model framework may be critical in the successful search for ancient extra-terrestrial life.

Impact of siderite on Rock-Eval S3 and oxygen index

Over the past four decades Rock-Eval pyrolysis has become a common means to type organic matter. The modified van Krevelen diagram, using the hydrogen and oxygen indices, has become a commonly used tool for organic matter classification. It assumes that the components used to calculate the two indices are representative of the indigenous organic matter, which is especially the case for the oxygen index. This study provides a series of experimental results that further characterize the impact of siderite on the hydrogen and oxygen index values, which decrease and increase, respectively, with increasing mineral content. This work suggests that the changes in hydrogen index values are a result of the interaction between the mineral phase and the generated hydrocarbons, where hydrocarbons may be adsorbed on to the mineral surfaces and not fully released. The increase in the oxygen index appears to be a result of mineral decomposition and the release of CO2. The oxygen index was found to be particularly sensitive to the presence of siderite in the sample. Siderite decomposition was found to occur at temperatures below often published decomposition temperatures and at or below the S3 peak trapping temperature (390 °C). Thus, the impact of organic carbon content and mineral interaction need to be taken into consideration when characterizing organic matter, especially when siderite and to a lesser extent other carbonate minerals are present. At lower organic carbon levels, organic matter will appear more gas-prone and would suggest that the organic matter has been strongly oxidized. Although corrections have been proposed in the literature they reduce the value of the Rock-Eval “quick” screen by adding additional analyses or data treatment. It is further suggested that the effect may be sensitive to the early diagenetic environment as well as cation substitution.

Indigenous carbon-rich matter associated with unusual aqueous alteration features in Nakhla: Complex formation and preservation history

While indigenous organic matter has been previously reported in the Mars meteorite Nakhla, little is known as to either its form or distribution. A notable feature of Nakhla is the prevalence of secondary phases associated with aqueous alteration. By analogy with the terrestrial environment, our objective was to determine whether Martian secondary minerals could also act to accumulate and preserve such organic matter. Through a multidisciplinary approach, we have characterized the nature of carbonaceous matter and spatially associated phases within the Martian meteorite Nakhla using a wide-ranging suite of analytical instrumentation including optical microscopy, laser Raman spectroscopy, focused ion beam microscopy, secondary ion mass spectrometry, and scanning and transmission electron microscopy. In freshly fractured chips of Nakhla, we found carbonaceous phases intimately associated with secondary aqueous alteration phases, both mineral and amorphous, interpreted to have formed through the low-temperature aqueous dissolution of the host basalt while on Mars. The carbonaceous matter is present both in condensed phases and in a dispersed state spatially associated with secondary alteration phases. In the former, we identified discrete refractory micron to submicron assemblages that appear macromolecular in nature and, in several cases, associated with fluorine and, in one case, significant nitrogen. Textural, chemical, mineralogical and isotopic considerations argue for a non-terrestrial origin of this carbonaceous matter. Additionally, we report the presence of the ferrous hydroxycarbonate mineral chukanovite (Fe2OH2CO3) within some of the secondary mineral aggregates studied. Neither the intimate association of carbonaceous matter with secondary phases nor the identification of chukanovite have been previously reported in any of the Martian meteorites. In this regard, we note such microscale features within alteration phases would most likely be lost in the preparation of conventional polished thin sections and thus explain why they have not been previously reported. In lieu of sample return, the sui generis nature provided by Mars meteorites provide insight to alteration processes on Mars currently denied to robotic exploration and remote sensing. Our results show a variety of habitability-related sample attributes, formed hundreds of millions of years ago near Mars’ surface, have persisted there until very recently and may be more widespread in the surface regolith than previously thought. This may have implications in sample selection criteria for Mars sample return.

Comprehensive analysis of chemical and biological problems associated with browning agents used in aquatic studies

AbstractInland waters receive and process large amounts of colored organic matter from the terrestrial surroundings. These inputs dramatically affect the chemical, physical, and biological properties of water bodies, as well as their roles as global carbon sinks and sources. However, manipulative studies, especially at ecosystem scale, require large amounts of dissolved organic matter with optical and chemical properties resembling indigenous organic matter. Here, we compared the impacts of two leonardite products (HuminFeed and SuperHume) and a freshly derived reverse osmosis concentrate of organic matter in a set of comprehensive mesocosm‐ and laboratory‐scale experiments and analyses. The chemical properties of the reverse osmosis concentrate and the leonardite products were very different, with leonardite products being low and the reverse osmosis concentrate being high in carboxylic functional groups. Light had a strong impact on the properties of leonardite products, including loss of color and increased particle formation. HuminFeed presented a substantial impact on microbial communities under light conditions, where bacterial production was stimulated and community composition modified, while in dark potential inhibition of bacterial processes was detected. While none of the browning agents inhibited the growth of the tested phytoplankton Gonyostomum semen, HuminFeed had detrimental effects on zooplankton abundance and Daphnia reproduction. We conclude that the effects of browning agents extracted from leonardite, particularly HuminFeed, are in sharp contrast to those originating from terrestrially derived dissolved organic matter. Hence, they should be used with great caution in experimental studies on the consequences of terrestrial carbon for aquatic systems.

Mineralogy of the 2019 Aguas Zarcas (CM2) carbonaceous chondrite meteorite fall

AbstractThe 2019 Aguas Zarcas CM2 meteorite is the most significant carbonaceous chondrite CM2 fall since Murchison in 1969. Samples collected immediately following the fall and studied here provide the rare opportunity to analyze the bulk mineralogy of a CM2 largely free of terrestrial contamination. Bulk samples were analyzed by powder X-ray diffraction (XRD), thermal gravimetric (TG) analysis, evolved gas analysis (EGA), and scanning electron microscopy (SEM) with an electron-probe micro-analyzer (EPMA). Water-extracted salts were analyzed by XRD. In hand specimen, the stones are brecciated and dominated by chondrule-rich and chondrule-poor lithologies, and locally, a matrix-rich lithology. Powder XRD patterns from multiple stones are dominated by reflections from serpentine group minerals, on which are superimposed reflections for ferrotochilinite, 1:1 regularly interstratified ferrotochilinite/cronstedtite, anhydrous silicates, calcite, pentlandite, pyrrhotite, and minor phases. Reflections for magnetite are present only from a metal-rich breccia clast. The serpentine XRD reflections from the chondrule-rich and chondrule-poor lithologies match those from 1T cronstedtite, whereas those from the matrix-rich lithology match the 1M polytype. Patterns with the 1M polytype also show a distinct low-angle scattering to the serpentine basal reflection centered near 8.6 Å, the origin of which is obscure. Further matching of the known serpentines to the Aguas Zarcas data shows that cronstedtite accounts for a subordinate amount of the clays, and at least three other chemically and structurally distinct serpentines are likely present. A typical fragment of Aguas Zarcas yielded 0.6 wt% water-extractable salts. The powder XRD pattern of the dried water extract shows reflections for halite = NaCl; chlorartinite = Mg2(CO3)(OH)Cl·2H2O; thenardite = Na2SO4; and sodium chlorate = NaClO4. The TG mass losses of 11.4 to 14.7 wt% are consistent with other CM2 chondrites. The gases detected by EGA are dominated by H2O and CO2, largely derived from the dehydroxylation and decomposition of serpentine and calcite, respectively. Also detected are gases with masses matching SO2/S2 and H2S, which are primarily released below 480 °C, and a mass of 30, which matches the molecular weight of formaldehyde and ethane, shows a maximum at 376 °C. These organic gases likely derive from the pyrolysis of indigenous organic matter. Taken together, the millimeter-scale mineralogical study of Aguas Zarcas reveals a complex breccia dominated by CM2-like clasts. The detailed study of this meteorite, together with similar studies from a range of carbonaceous chondrites, provides the foundations for studying and interpreting the samples returned from the NASA OSIRIS-REx and JAXA Hayabusa2 missions.

Influence of Calcium Perchlorate on Organics Under SAM‐Like Pyrolysis Conditions: Constraints on the Nature of Martian Organics

AbstractMost of the organics detected on Mars so far are aliphatic and aromatic organo‐chlorine compounds. The smallest were first identified by the thermal treatment of the solid samples by Viking in 1976; although at the time, they were attributed to contamination. Since 2012, a larger variety of structures have been identified by the Sample Analysis at Mars experiment aboard the Curiosity rover. Evidence suggests that the chlorohydrocarbons formed during pyrolysis of sedimentary materials. Laboratory experiments show that heating of samples containing oxychlorines, such as chlorates (ClO3−) and perchlorates (ClO4−), along with organic matter present at Mars' surface is the logical source of these compounds. Nevertheless, this discovery of indigenous organic matter in the Mars regolith raises important questions: How do the oxychlorines influence the pyrolysis of organics? What are the organics precursors of the organo‐chlorinated molecules detected on Mars? Is there a way to identify the parent molecules in a sample after pyrolysis? This paper presents the results of systematic laboratory experiments of the products formed during the pyrolysis of organic compounds from three chemical families—polycyclic aromatic hydrocarbons, amino acids, and carboxylic acids—in presence of calcium perchlorates. Results show that the polycyclic aromatic hydrocarbon parent molecules and most of the carboxylic acids are still detectable after pyrolysis in presence of calcium perchlorate and that the degradation and/or evolution of all parent molecules mostly depends on their chemical nature. In addition, we demonstrate that the chlorohydrocarbons detected on Mars by the Sample Analysis at Mars instrument could come from the three chemical families studied.

Effects of Oxygen-Containing Salts on the Detection of Organic Biomarkers on Mars and in Terrestrial Analog Soils.

The detection of chlorinated hydrocarbons by Curiosity on Mars has been attributed to the presence of unidentified indigenous organic matter. Similarly, oxychlorines on Earth have been proposed to be responsible for the apparent lack of organics in the Atacama Desert. The presence of perchlorate (ClO4-) poses a unique challenge to the measurement of organic matter due to the oxidizing power of oxychlorines during commonly used pyrolysis-gas chromatography-mass spectrometry (py-GC-MS) methods. Here, we show that perchlorates and other oxyanion salts inhibit the detection of organic compounds but that removing these problematic species prior to pyrolysis by using an optimal sample extraction duration and suitable ratios of water to sample mass enables analysis. We have characterized leached and unleached samples containing perchlorates from the Atacama Desert and have found that after leaching, the py-GC-MS chromatograms of the dried mineral residues show identifiable biomarkers associated with indigenous cyanobacteria. Samples which were pyrolyzed without leaching showed no detectable organic matter other than background siloxane and very weak or no trace of detectable polychlorinated benzenes. Dried sample residues remaining after leaching, the mineral matrix and water-insoluble organic matter, showed a strong organic response in all cases when analyzed by py-GC-MS. These residues are most likely the product of the pyrolysis of water-insoluble organics originally present in the samples. In addition, our results imply that previous soil analyses which contained high levels of oxyanions and concluded that organics were either not present or were present at extremely low levels should be reexamined.

Influence of igneous intrusions on thermal maturity and optical texture: Comparison between a bituminous marl and a coal seam of the same maturity

The impact of a 120 cm thick dike on dispersed organic matter in the Triassic Marry Harbour (MH) bituminous marl in the Raanes Peninsula, Ellesmere Island, Arctic Canada, was studied using reflected light microscopy and Rock-Eval pyrolysis. Results were compared to a coal seam of similar maturity that was thermally altered by an igneous intrusion. The MH bituminous marl is mature and within the oil window (Ro = 0.94%), whereas the coal is high-volatile B bituminous rank (Ro = 0.80%). Thermal alteration impacted differently the organic-rich marl than the coal seam. Most of the heat generated by the intrusive emplacement in contact with coal is spent transforming coal to coke in the plastic layer/zone, similar to the process that coal undergoes in industrial coking operations. In contrast, the thermal alteration of sedimentary rocks occurs over longer distances as a result of the absence of a plastic layer/zone. The impact zone of the 120 cm thick igneous intrusion was greater in the MH bituminous marl, which became thermally altered (Ro = 2.34%) at 190 cm from the contact with the dike. On the contrary, the coal became thermally altered (%Ro = 5.0%) by a 240 cm alkali-basalt intrusion (twice the thickness of the MH dike) and its impact zone was only 65 cm. Heat and hot volatile matter produced by the thermal decomposition of organic matter and minerals (carbonate, dehydration of clay minerals) in contact with the igneous intrusion body is transferred through the sedimentary rock matrix by convection through fractures. This transformation is evident by the occurrence of the pyrolytic carbon at various distances in the fractured MH marl from contact. The hydrogen index (HI) shows a similar trend to that of the remaining source potential (S2). Both parameters decrease systematically toward the dike, and go through a minimum at 20 cm from the dike contact, as the indigenous organic matter is converted to hydrocarbons or devolatilized. At the dike contact, both S2 and HI have higher values. These trends are similar to those of the volatile elements H and Cl in the intruded coal seam. The free hydrocarbons (S1) showed a slightly different trend than S2 and HI. It increased initially from 300 cm and reached a maximum at about 190 cm from the dike contact before decreasing continually and reaching a minimum at 20 cm from the contact. At the dike contact, the S1 increased slightly, similar to the HI and S2. The presence of oil droplets trapped in carbonate concretions, in combination with the highest value of oil expelled from the source rock (based on S1/TOC) at distance of 190 cm from dike, is an indication of the influence of contact metamorphism on oil generation locally. Furthermore, it indicates that intrusion of igneous dikes into the bituminous MH marl resulted in an increase of organic matter maturation locally and in hydrocarbon generation.

Water-Rock Interactions in Outer Solar System Bodies: Evidence from the Coordinated Analysis of Interplanetary Dust

NASA has an ongoing program of collecting interplanetary dust particles (IDPs) in the stratosphere using high altitude research aircraft. The collected IDPs are derived from asteroids and comets and here we report studies of a subset of hydrated IDPs rich in carbonaceous matter that are proposed to have a cometary origin. Our studies are aimed at understanding the evolution of oxygen reservoirs in the Solar System and their interaction with cometary minerals and organic matter. The small size (<20 μm) and fragility of these IDPs present a number of analytical challenges. We have pioneered techniques for performing chemical, mineralogical, isotopic, and spectroscopic measurements on the same sample in a carefully coordinated sequence. Coordinated analyses of nanogram-size samples is made possible by several delicate sample preparation techniques. To avoid organic contamination, we embed IDPs in elemental sulfur and use ultramicrotomy to partly section the particles (the first few micrometers). Multiple thin sections (50-70 nm thick) are placed on different substrates depending on the analysis technique. We use a JEOL 2500SE scanning, transmission electron microscope (STEM) to determine the mineralogy, microstructure, and elemental compositions of constituent minerals in the thin sections through a combination of high resolution imaging, electron diffraction, quantitative energy-dispersive x-ray mapping, and electron energy-loss spectroscopy. Following the STEM analyses, we use a NanoSIMS 50L for high spatial resolution isotopic measurements of H, C, N, and O to search for presolar grains and to understand the origin of the indigenous organic matter. The isotopic analyses are performed on the same sections analyzed in the STEM in order to correlate isotopic properties with the elemental and mineralogical data. We reserve other thin sections for non-destructive analyses utilizing synchrotron-based techniques including Fourier-transform infrared (FTIR) micro-spectroscopy and X-ray absorption near-edge structure (XANES) analyses, especially for functional group analysis of organic matter in the particles. The remainder of the IDP is extracted from the sulfur bead that was used for microtomy and is pressed into Au foil for quantitative analysis (including light elements) using a JEOL 8530F field emission electron probe microanalyzer (EPMA). After the EPMA measurements, high precision oxygen isotopic analyses are obtained using Cameca IMS1270/1290 instruments at UCLA. The hydrated IDPs in this study are dominated by saponitic clays, with minor magnetite, carbonate and abundant organic matter. The remarkable oxygen isotopic compositions, high carbon contents, and the abundance of isotopically anomalous organic matter, together suggest that the high carbon, hydrated IDPs are derived from primitive sources not yet represented in meteorite collections such as outer main belt P- and D-type asteroids or comets.

Preserved organic matter in a fossil Ocean Continent Transition in the Alps: the example of Totalp, SE Switzerland

Evidence from ultraslow spreading mid-ocean ridges and both fossil and present-day Ocean–Continent Transitions (OCT) demonstrates that mantle serpentinization resulting from the interaction of mantle rock and water during tectonic exhumation is widespread. Observations at white smokers in modern ocean settings suggest that methane produced by serpentinization can support methanotrophic bio-systems, which use methane as the only source of carbon. An important question is whether such bio-systems are more generally pervasive in their association with serpentinized mantle in the subsurface. In this study, we examined whether there is evidence for such a methanotrophic system in exhumed serpentinized mantle at a magma-poor rifted continental margin, by probing for characteristic biological markers in these and associated sedimentary rocks in the Totalp unit of SE Switzerland. This unit represents a remnant of the former OCT of the southern Alpine Tethyan margin and was chosen because of its mild Alpine tectonic and low-grade metamorphic overprint during Alpine orogeny, hence giving potential for the preservation of indigenous organic matter (OM). Totalp samples are characterized by low organic carbon contents of 11–647 ppm. The majority of the samples contain hydrocarbons in the form of n-alkanes in the range C17–C36. Some sediments contain isoprenoids, for example pristane and phytane and a suite of steranes that are consistent with a marine origin for the OM preserved in the rocks. Traces of marine planktonic and bacterial OM are preserved in the serpentinized mantle and overlying sediments of this ancient Tethyan OCT, but there is no evidence that the OM has been generated from methanotrophic bio-systems.

Gas cluster ion beam for the characterization of organic materials in submarine basalts as Mars analogs

The solar system contains large quantities of organic compounds that can form complex molecular structures. The processing of organic compounds by biological systems leads to molecules with distinctive structural characteristics; thus, the detection and characterization of organic materials could lead to a high degree of confidence in the existence of extra-terrestrial life. Given the nature of the surface of most planetary bodies in the solar system, evidence of life is more likely to be found in the subsurface where conditions are more hospitable. Basalt is a common rock throughout the solar system and the primary rock type on Mars and Earth. Basalt is therefore a rock type that subsurface life might exploit and as such a suitable material for the study of methods required to detect and analyze organic material in rock. Telluric basalts from Earth represent an analog for extra-terrestrial rocks where the indigenous organic matter could be analyzed for molecular biosignatures. This study focuses on organic matter in the basalt with the use of surface analysis techniques utilizing Ar gas cluster ion beams (GCIB); time of flight secondary ion mass spectrometry (ToF-SIMS), and x-ray photoelectron spectroscopy (XPS), to characterize organic molecules. Tetramethylammonium hydroxide (TMAH) thermochemolysis was also used to support the data obtained using the surface analysis techniques. The authors demonstrate that organic molecules were found to be heterogeneously distributed within rock textures. A positive correlation was observed to exist between the presence of microtubule textures in the basalt and the organic compounds detected. From the results herein, the authors propose that ToF-SIMS with an Ar GCIB is effective at detecting organic materials in such geological samples, and ToF-SIMS combined with XPS and TMAH thermochemolysis may be a useful approach in the study of extra-terrestrial organic material and life.

Incorporation of 13C labelled shoot residues in Lumbricus terrestris casts: A combination of transmission electron microscopy and nanoscale secondary ion mass spectrometry

Earthworms transform organo-mineral associations in soil, especially by incorporating fresh residues inside casts where the microbial abundance and activity are enhanced. The heterogeneous distribution of organic carbon in these structures influences decomposition levels at the microscale. The incorporation of 13C labelled plant residues by Lumbricus terrestris inside cast was investigated, through the innovative combination of two fine scale imaging techniques: transmission electron microscopy and nanoscale secondary ion mass spectrometry (NanoSIMS). The association of these methods sheds new lights on organo-mineral structures. Different types of organic matter (plant residues, microbial remains) were identified in the casts and the freshly incorporated residues could be differentiated from the indigenous organic matter thanks to δ13C NanoSIMS mapping. 13C labelled bacteria and fungi abundance and diversity highlight their preeminent role in litter decomposition within casts. Labelled plant residues observed at various stages of decomposition and microorganisms presented highly variable δ13C values, emphasizing the complexity of organic matter dynamics and the importance of microscale analyses to describe this variability. Thus, the combination of NanoSIMS and TEM shows great potential to relate organic matter stages of decomposition with their 13C signature.

Cyanobacterial Inhabitation on Archean Rock Surfaces in the Pilbara Craton, Western Australia.

High abundances of 7- and 6-monomethylalkanes as well as C17 n-alkane, indicative of cyanobacteria, have been discovered near the surfaces of Archean carbonate rocks of the Fortescue Group in the Pilbara region, Western Australia. The presence of cyanobacterial biomarkers is mostly limited to the surface layer (<1 cm thickness) of the rocks, indicating that the cyanobacteria are an endolithic species. Biomarkers are found in bitumen I (solvent-extracted rock) and also in bitumen II (solvent-extracted decarbonated rock). The abundance of biomarkers is generally the same between both bitumen fractions in the surface layer, which suggests that the cyanobacteria penetrated into the carbonate minerals. Trace amounts of the biomarkers have also diffused into a deeper part of the rocks, but this influence is only seen in bitumen I. This implies that hydrocarbons moved toward the inside of the rock through pores and fissures in the rock fabric. In contrast, hydrocarbons in bitumen II, which mainly come from within the carbonate minerals, are isolated from the hydrocarbon migration from the outside of the rock and may be ancient indigenous organic matter. To the best of our knowledge, this is the first report of the past or modern inhabitation of cyanobacteria on Archean rocks in the Pilbara region for which hydrocarbon biomarker analyses was used.

The impact of exotic forest plantations on the chemical composition of soil organic matter in Southern Brazil as assessed by Py–GC/MS and lipid extracts study

This study evaluated the effects of Acacia and Eucalyptus plantations on the soil chemical properties and molecular composition of soil organic matter (SOM) in Cambisol profiles in Southern Brazil over 7years. Control soil profiles were collected from neighboring areas that corresponded to the initial soil conditions predating the forest plantations. Soil exchangeable cations, total N, available P and K, soil pH, and the molecular composition of SOM were determined. The molecular composition of SOM was assessed by performing pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) analysis of the soil samples and GC/MS analysis of the Soxhlet-extracted free lipid composition. The Acacia plantation was associated with reductions of available P and K+, exchangeable Ca2+ and Mg2+ as well as soil pH down to depths of 40cm, whereas only the available K+ content was reduced in the Eucalyptus plantation as compared with their respective control areas. The nitrogen (N) content was depleted in the superficial soil (5cm) in both plantations, whereas no change was found in the soil carbon (C) content for the entire soil profile (0–80cm). Alterations of the SOM composition occurred in both plantations at a molecular level. Analytical pyrolysis revealed a relative enrichment of polysaccharide-derived compounds in the soil under the Acacia plantation. Together with the increase in high molecular weight n-alkanes from lipid extracts, this result suggests the input of biomass from the new forest vegetation. Increase in the proportions of degraded compounds from lignin was observed in the SOM from Eucalyptus plantation, suggesting the degradation of the indigenous organic matter which promoted the change of the SOM composition.

Mixture design and treatment methods for recycling contaminated sediment

Conventional marine disposal of contaminated sediment presents significant financial and environmental burden. This study aimed to recycle the contaminated sediment by assessing the roles and integration of binder formulation, sediment pretreatment, curing method, and waste inclusion in stabilization/solidification. The results demonstrated that the 28-d compressive strength of sediment blocks produced with coal fly ash and lime partially replacing cement at a binder-to-sediment ratio of 3:7 could be used as fill materials for construction. The X-ray diffraction analysis revealed that hydration products (calcium hydroxide) were difficult to form at high sediment content. Thermal pretreatment of sediment removed 90% of indigenous organic matter, significantly increased the compressive strength, and enabled reuse as non-load-bearing masonry units. Besides, 2-h CO2 curing accelerated early-stage carbonation inside the porous structure, sequestered 5.6% of CO2 (by weight) in the sediment blocks, and acquired strength comparable to 7-d curing. Thermogravimetric analysis indicated substantial weight loss corresponding to decomposition of poorly and well crystalline calcium carbonate. Moreover, partial replacement of contaminated sediment by various granular waste materials notably augmented the strength of sediment blocks. The metal leachability of sediment blocks was minimal and acceptable for reuse. These results suggest that contaminated sediment should be viewed as useful resources.

Biogeochemical controls on biodegradation of MC252 crude oil in coastal wetland systems

The persistence and fate of MC252 oil as well as the presence of nutrients and their effect on biodegradation were studied in both an oil-contaminated marsh and a nearby oil-contaminated mangrove site near Port Fourchon, Louisiana as well as a second marsh site in Barataria Bay adjacent to Bay Jimmy. High-resolution nutrient profiles were obtained at different locations at each site during winter and summer using dialysis samplers. Areas of sulfate depletion were observed in the top 20 cm of dialysis samplers in the Fourchon marsh and mangrove sites. When sulfate depletion was observed, it was accompanied by an increase in the ammonia and/or phosphorous concentration signifying an anoxic zone in the sediment. This anoxic zone was found more frequently in summer sampling compared to winter sampling. Flux chamber were installed at each site to capture evolved CO2 to determine if carbon from the MC252 oil was being mineralized at each site. Carbon derived from oil and carbon derived from indigenous organic matter was differentiated using the stable carbon isotope ratio. d13C signatures of the bulk soil, root matter, and soil with roots removed were measured at depth to compare contaminated sites to nearby inland sites with little to no oil contamination. A d13C signature of −24.8 ± 0.8 ‰ was observed in the bulk soil of the contaminated shoreline site in the Port Fourchon Marsh while an adjacent uncontaminated inland bulk soil sample had a d13C signature of −17.3 ± 0.8 ‰. d13C signatures were measured for sample before and after being washed with a hexane acetone solvent which removed oil. The signature of the samples became less negative after being washed with the solvent. To supplement the field findings, a laboratory microcosm study was performed to observe the effects of adding nutrients to a wetland soil/water/oil mixture. The study focuses on 5 different treatments: natural attenuation, sulfate amended, ammonia amended, sulfate and ammonia amended, and a killed control. A second set of microcosm experiments were conducted in triplicate under aerobic conditions along with a kill control sample. There was no observed degradation in the anaerobic microcosm experiments for any of the treatments during the time of the study. Aerobic microcosm results are still pending. Of particular interest are petrogenic PAHs (i.e, C1-phenanthrenes, C2-dibenzothiophenes, and C3-dibenzothiophenes) since there is little information in the peer-reviewed literature on the effectiveness of biostimulation in marsh systems.