Thermochemical sulfate reduction in fossil Ordovician deposits of the Majiang area: Evidence from a molecular-marker investigation

The main reservoirs of Majiang fossil deposits consist of the Silurian Wengxiang group, dominantly sandstones, and the Ordovician Honghuayuan formation, dominantly carbonate rocks, and the Lower Cambrian Niutitang Formation mudstones serve as the major source rocks. Thermochemical sulfate reduction (TSR) might have taken place in the Paleozoic marine carbonate oil pools, as indicated by high concentrations of dibenzothiophenes in the extracts (MDBT=0.27-4.32 µg/g extract, and MDBT/MPH= 0.71-1.38). Hydrocarbons in the Pojiaozhai Ordovician carbonate reservoirs have undergone severe TSR and are characterized by higher quantities of diamondoids and MDBT and heavier isotopic values (δ13C=-28.4‰). The very large amounts of dibenzothiophenes might be products of reactions between biphenyls and sulfur species associated with TSR

Evolutionary Origin, Gradual Accumulation and Functional Divergence of Heat Shock Factor Gene Family with Plant Evolution

Plants, as sessile organisms, evolved a complex and functionally diverse heat shock factor (HSF) gene family to cope with various environmental stresses. However, the limited evolution studies of the HSF gene family have hindered our understanding of environmental adaptations in plants. In this study, a comprehensive evolution analysis on the HSF gene family was performed in 51 representative plant species. Our results demonstrated that the HSFB group which lacks a typical AHA activation domain, was the most ancient, and is under stronger purifying selection pressure in the subsequent evolutionary processes. While, dramatic gene expansion and functional divergence occurred at evolution timescales corresponding to plant land inhabit, which contribute to the emergence and diversification of the HSFA and HSFC groups in land plants. During the plant evolution, the ancestral functions of HSFs were maintained by strong purifying pressure that acted on the DNA binding domain, while the variable oligomerization domain and motif organization of HSFs underwent functional divergence and generated novel subfamilies. At the same time, variations were further accumulated with plant evolution, and this resulted in remarkable functional diversification among higher plant lineages, including distinct HSF numbers and selection pressures of several HSF subfamilies between monocots and eudicots, highlighting the fundamental differences in different plant lineages in response to environmental stresses. Taken together, our study provides novel insights into the evolutionary origin, pattern and selection pressure of plant HSFs and delineates critical clues that aid our understanding of the adaptation processes of plants to terrestrial environments

A GCxGC-ToFMS Investigation of the Unresolved Complex Mixture and Associated Biomarkers in Biodegraded Petroleum

Heavy biodegraded crude oils have larger numbers of coeluting compounds than non- biodegraded oils, and they are typically not resolved with conventional gas chromatography (GC). This unresolved complex mixture (UCM) has been investigated using comprehensive two- dimensional gas chromatography-time-of-flight mass spectrometry (GCxGC-ToFMS) within a set of biodegraded petroleums derived from distinct sedimentary basins, including northwestern Sichuan (Neoproterozoic, marine), Tarim (Early Paleozoic, marine), Bohai Bay (Eocene, saline/brackish) and Pearl River Mouth (Eocene, freshwater). In general, the hydrocarbons that constitute the UCM in petroleum saturate fractions can be classified into three catalogues based on the distributions of resolved compounds on two dimensional chromatograms. Group 1 is composed mainly of normal and branched alkanes, isoprenoid alkanes and monocyclic alkanes; Group 2 comprises primarily terpanes ranging from two to five rings, and Group 3 is dominated by monoaromatic hydrocarbons such as tetralins and monoaromatic steranes. In addition, the UCM is source dependent and varies between oil populations. i.e., the UCM of petroleum derived from Precambrian and Early Paleozoic marine, Eocene saline/brackish and freshwater source rocks is specifically rich in higher homologues of A-norsteranes, series of 1,1,3-trimethyl-2- alkylcyclohexanes (carotenoid-derived alkanes), and tetralin and indane compounds, respectively

Influencing factors and significance of organic and inorganic nitrogen isotopic compositions in lacustrine sedimentary rocks

Comprehensive nitrogen biogeochemical cycle has been reconstructed for representative lacustrine organic-rich sedimentary rock in China, namely the Triassic Yanchang Formation (YF, 199–230 Ma) in Ordos and the Cretaceous Qingshankou Formation (QF, 86–92 Ma) in Songliao basins, by evaluating the organic and inorganic nitrogen isotopic compositions rather than only organic or bulk nitrogen isotopic compositions. The results indicate that the nitrogen isotope values of bulk rock (δ15Nbulk) in the non-metamorphic stage are significantly different from that of kerogen, which challenge the conceptual framework of sedimentary nitrogen isotope interpretation. The δ15Nbulk from the YF and QF were lower than their respective the nitrogen isotope values of kerogen (δ15Nker), with offsets up to ∼5.1‰, which have the inverse relationship for the metamorphosed rock. Thermal evolution did not significantly modify the δ15N of bulk rock and kerogen. The δ15N of sediments from the YF (δ15Nbulk, 1.6‰–5.6‰) were lower than that of rock from the QF (δ15Nbulk, 10.2‰–15.3‰). The nitrogen isotope values of silicate incorporated nitrogen (δ15Nsil) were slightly lower than those of the δ15Nker in the YF and obviously lower for the QF. The fact that different nitrogen cycles occur in the YF and QF due to the different depositional redox conditions leads to different isotopic results. The YF water environment dominated by oxic conditions is not conducive to the occurrence of denitrification and anammox, and no abundant N2 loss leads to the relatively light δ15Nbulk. In the stratified water for the QF, redox transition zone promotes denitrification and anammox, resulting in the heavy δ15Nbulk of rock and promotes the DNRA, resulting in heavy δ15Nker and low δ15Nsil

Progressive Degradation of Crude Oil <i>n</i>-Alkanes Coupled to Methane Production under Mesophilic and Thermophilic Conditions

<div><p>Although methanogenic degradation of hydrocarbons has become a well-known process, little is known about which crude oil tend to be degraded at different temperatures and how the microbial community is responded. In this study, we assessed the methanogenic crude oil degradation capacity of oily sludge microbes enriched from the Shengli oilfield under mesophilic and thermophilic conditions. The microbial communities were investigated by terminal restriction fragment length polymorphism (T-RFLP) analysis of 16S rRNA genes combined with cloning and sequencing. Enrichment incubation demonstrated the microbial oxidation of crude oil coupled to methane production at 35 and 55°C, which generated 3.7±0.3 and 2.8±0.3 mmol of methane per gram oil, respectively. Gas chromatography-mass spectrometry (GC-MS) analysis revealed that crude oil <i>n</i>-alkanes were obviously degraded, and high molecular weight <i>n</i>-alkanes were preferentially removed over relatively shorter-chain <i>n</i>-alkanes. Phylogenetic analysis revealed the concurrence of acetoclastic <i>Methanosaeta</i> and hydrogenotrophic methanogens but different methanogenic community structures under the two temperature conditions. Candidate divisions of JS1 and WWE 1, <i>Proteobacteria</i> (mainly consisting of <i>Syntrophaceae</i>, <i>Desulfobacteraceae</i> and <i>Syntrophorhabdus</i>) and <i>Firmicutes</i> (mainly consisting of <i>Desulfotomaculum</i>) were supposed to be involved with <i>n</i>-alkane degradation in the mesophilic conditions. By contrast, the different bacterial phylotypes affiliated with <i>Caldisericales</i>, “Shengli Cluster” and <i>Synergistetes</i> dominated the thermophilic consortium, which was most likely to be associated with thermophilic crude oil degradation. This study revealed that the oily sludge in Shengli oilfield harbors diverse uncultured microbes with great potential in methanogenic crude oil degradation over a wide temperature range, which extend our previous understanding of methanogenic degradation of crude oil alkanes.</p></div

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

Changes in group composition and biomarker ratios of crude oil during methanogenic degradation.

<p>Pr/<i>n</i>C₁₇: pristane/<i>n</i>-heptadecane; three replicates in each time points with exception of original day 0. a <i>n</i>-heptadecane was only detected in one of the three replicates; b: <i>n</i>-heptadecane was not detected above the detection limit; Sterilized-330: crude oil sampled from the sterilized control group after 330 days of incubation at 35°C, Sterilized-303: crude oil sampled from the sterilized control group after 303 days of incubation at 55°C.</p><p>Changes in group composition and biomarker ratios of crude oil during methanogenic degradation.</p

Phylogenetic affiliation of archaeal 16S rRNA gene sequences of the methanogenic crude oil-degrading consortia.

<p>A: 35°C; B: 55°C. The number in the column indicates the major OTUs represented by specific T-RFs, followed by the number in parentheses indicating the clone numbers of each OTU.</p