Carbon isotopic evidence for rapid methane clathrate release recorded in coals at the terminus of the Late Palaeozoic Ice Age.

The end of the Late Palaeozoic Ice Age (LPIA) ushered in a period of significant change in Earth's carbon cycle, demonstrated by the widespread occurrence of coals worldwide. In this study, we present stratigraphically constrained organic stable carbon isotope (δ13Corg) data for Early Permian coals (312 vitrain samples) from the Moatize Basin, Mozambique, which record the transition from global icehouse to greenhouse conditions. These coals exhibit a three-stage evolution in atmospheric δ13C from the Artinskian to the Kungurian. Early Kungurian coals effectively record the presence of the short-lived Kungurian Carbon Isotopic Excursion (KCIE), associated with the proposed rapid release of methane clathrates during deglaciation at the terminus of the Late Palaeozoic Ice Age (LPIA), with no observed disruption to peat-forming and terrestrial plant communities. δ13Corg variations in coals from the Moatize Basin are cyclic in nature on the order of 103-105 years and reflect changes in δ13Corg of ~±1‰ during periods of stable peat accumulation, supporting observations from Palaeozoic coals elsewhere. These cyclic variations express palaeoenvironmental factors constraining peat growth and deposition, associated with changes in base level. This study also demonstrates the effectiveness of vitrain in coal as a geochemical tool for recording global atmospheric change during the Late Palaeozoic.

Direct Rubidium-Strontium Dating of Hydrocarbon Charge Using Small Authigenic Illitic Clay Aliquots from the Silurian Bituminous Sandstone in the Tarim Basin, NW China.

Illitic clay is ubiquitous in clastic hydrocarbon reservoirs, and the host for several radiometric isotopes such as the potassium-argon (K-Ar) and rubidium-strontium (Rb-Sr) systems. This study applied the isotope-dilution thermal ionization mass spectrometry technique for small samples (3-4 mg) to conduct illite Rb-Sr isotope dating of five illitic clay samples from the Silurian bituminous sandstone (SBS) intersected by five drillholes in the Tarim Basin, NW China. The 87Rb/86Sr ratio of clays is fractionated mainly by the addition of Rb during the illitization of mixed-layer illite/smectite (I/S), which is the dominant clay species in the Tarim Basin samples. The subsample-scale Rb/Sr isotope values suggest that each subsample may contain I/S particles of slightly variable degrees of illitization. Three of the analyzed samples (H6, KQ1 and TZ67) generated Rb-Sr isochron ages of 141 ± 61 Ma, 332 ± 32 Ma and 235 ± 8 Ma (errors quoted at 2σ), respectively. These results are similar to the corresponding K-Ar ages (125 Ma, 389 Ma and 234 Ma). The isotopic ages are consistent with the timing of hydrocarbon charge which varies in different drillholes as constrained by basin modelling, indicating that a closed-system behavior is attained by the hydrocarbon charge that inhibits the illitization of I/S. The Rb-Sr isotope analyses of the other two samples (YM35-1 and Q1) that did not yield isochron ages suggest the conditions for producing isochrons were not satisfied, which may be caused by disturbance of the isotope system by a post-charge hydrothermal event. The outcomes of this study show the robust potential of Rb-Sr clay subsample geochronology for cross-checking isotopic ages yielded by other systems (e.g. K-Ar system) and constraining the timing of hydrocarbon charge.

Methodology to determine the extent of anaerobic digestion, composting and CH4 oxidation in a landfill environment.

An examination of the processes contributing to the production of landfill greenhouse gas (GHG) emissions is required, as the actual level to which waste degrades anaerobically and aerobically beneath covers has not been differentiated. This paper presents a methodology to distinguish between the rate of anaerobic digestion (rAD), composting (rCOM) and CH4 oxidation (rOX) in a landfill environment, by means of a system of mass balances developed for molecular species (CH4, CO2) and stable carbon isotopes (δ13C-CO2 and δ13C-CH4). The technique was applied at two sampling locations on a sloped area of landfill. Four sampling rounds were performed over an 18 month period after a 1.0 m layer of fresh waste and 30-50 cm of silty clay loam had been placed over the area. Static chambers were used to measure the flux of the molecular and isotope species at the surface and soil gas probes were used to collect gas samples at depths of approximately 0.5, 1.0 and 1.5 m. Mass balances were based on the surface flux and the concentration of the molecular and isotopic species at the deepest sampling depth. The sensitivity of calculated rates was considered by randomly varying stoichiometric and isotopic parameters by ±5% to generate at least 500 calculations of rOX, rAD and rCOM for each location in each sampling round. The resulting average value of rAD and rCOM indicated anaerobic digestion and composting were equally dominant at both locations. Average values of rCOM: ranged from 9.8 to 44.5 g CO2 m-2 d-1 over the four sampling rounds, declining monotonically at one site and rising then falling at the other. Average values of rAD: ranged from 10.6 to 45.3 g CO2 m-2 d-1. Although the highest average rAD value occurred in the initial sampling round, all subsequent rAD values fell between 10 and 20 g CO2 m-2 d-1. rOX had the smallest activity contribution at both sites, with averages ranging from 1.6 to 8.6 g CO2 m-2 d-1. This study has demonstrated that for an interim cover, composting and anaerobic digestion of shallow landfill waste can occur simultaneously.

Genome-Centric Analysis of Microbial Populations Enriched by Hydraulic Fracture Fluid Additives in a Coal Bed Methane Production Well.

Coal bed methane (CBM) is generated primarily through the microbial degradation of coal. Despite a limited understanding of the microorganisms responsible for this process, there is significant interest in developing methods to stimulate additional methane production from CBM wells. Physical techniques including hydraulic fracture stimulation are commonly applied to CBM wells, however the effects of specific additives contained in hydraulic fracture fluids on native CBM microbial communities are poorly understood. Here, metagenomic sequencing was applied to the formation waters of a hydraulically fractured and several non-fractured CBM production wells to determine the effect of this stimulation technique on the in-situ microbial community. The hydraulically fractured well was dominated by two microbial populations belonging to the class Phycisphaerae (within phylum Planctomycetes) and candidate phylum Aminicenantes. Populations from these phyla were absent or present at extremely low abundance in non-fractured CBM wells. Detailed metabolic reconstruction of near-complete genomes from these populations showed that their high relative abundance in the hydraulically fractured CBM well could be explained by the introduction of additional carbon sources, electron acceptors, and biocides contained in the hydraulic fracture fluid.

Methane metabolism in the archaeal phylum Bathyarchaeota revealed by genome-centric metagenomics.

Methanogenic and methanotrophic archaea play important roles in the global flux of methane. Culture-independent approaches are providing deeper insight into the diversity and evolution of methane-metabolizing microorganisms, but, until now, no compelling evidence has existed for methane metabolism in archaea outside the phylum Euryarchaeota. We performed metagenomic sequencing of a deep aquifer, recovering two near-complete genomes belonging to the archaeal phylum Bathyarchaeota (formerly known as the Miscellaneous Crenarchaeotal Group). These genomes contain divergent homologs of the genes necessary for methane metabolism, including those that encode the methyl-coenzyme M reductase (MCR) complex. Additional non-euryarchaeotal MCR-encoding genes identified in a range of environments suggest that unrecognized archaeal lineages may also contribute to global methane cycling. These findings indicate that methane metabolism arose before the last common ancestor of the Euryarchaeota and Bathyarchaeota.

Simultaneous determination of delta33S(V-CDT) and delta34S(V-CDT) using masses 48, 49 and 50 on a continuous flow isotope ratio mass spectrometer.

A new, fast, continuous flow technique is described for the simultaneous determination of delta33S and delta34S using SO masses 48, 49 and 50. Analysis time is approximately 5 min/sample with measurement precision and accuracy better than +/-0.3 per thousand. This technique, which has been set up using IAEA Ag2S standards S-1, S-2 and S-3, allows for the fast determination of mass-dependent or mass-independent fractionation (MIF) effects in sulfide, organic sulfur samples and possibly sulfate. Small sample sizes can be analysed directly, without chemical pre-treatment. Robustness of the technique for natural versus artificial standards was demonstrated by analysis of a Canon Diablo troilite, which gave a delta33S of 0.04 per thousand and a delta34S of -0.06 per thousand compared to the values obtained for S-1 of 0.07 per thousand and -0.20 per thousand, respectively. Two pyrite samples from a banded-iron formation from the 3710 Ma Isua Greenstone Belt were analysed using this technique and yielded MIF (Delta33S of 2.45 and 3.31 per thousand) comparable to pyrite previously analysed by secondary ion probe.