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The impact of rapid heating by intrusion on the geochemistry and petrography of coals and organic-ri
bne: The impact of rapid heating by intrusion on the geochemistry and petrography of coals and organic-rich shales in the Illinois Basin February 2018 International Journal of Coal Geology 187 Mohammad Wahid RahmanMohammad Wahid RahmanSue RimmerSue RimmerHarry RoweHarry Rowe Igneous intrusion into organic-rich sedimentary rocks and coals has been suggested as a factor in the large-scale release of ¹³C–depleted thermogenic CH4, which may have led to global warming and mass extinction events in the geologic past. If a significant release of ¹³C–depleted thermogenic CH4 results from the intrusion of coal or organic-rich rocks, then it should produce ¹³C–enriched residual coal and dispersed organics in rocks adjacent to the intrusion due to the release of isotopically lighter CH4 gas. A review of the literature suggests only minor changes in the δ¹³Corg of coals adjacent to intrusions; however, a few studies have shown that changes in δ¹³Corg in intruded shales may be slightly more pronounced. The current study further evaluates the geochemical, isotopic, and petrographic changes that result from contact metamorphism and specifically compares the intrusion of coal to that of an organic-rich shale collected from the same general vicinity. Data for two different transects of intruded Pennsylvanian coal (Danville (No. 7) Coal) and an intruded organic-rich shale in the southern part of the Illinois Basin are presented. Both transects show similar increases in mean vitrinite reflectance (Rr); reflectance increases from background levels of 0.66% to 4.40% in the Danville (No. 7) Coal and 0.71% to 4.78% in the organic-rich shale. In addition, both transects show the formation of isotropic coke, and even development of fine circular mosaic anisotropic coke structure at and near the contact with the intrusion, along with the visual loss of liptinites at higher reflectances. In the Danville Coal transect, volatile matter, N, H, S, and O decrease whereas fixed carbon, C, and ash increase approaching the intrusion. The coal shows a marked decrease in remaining hydrocarbon potential (S2) and hydrogen index (HI) and an increase in Tmax (°C). Trends in most of the Rock-Eval parameters for the organic-rich shale are less clear due to variations in the amount of organic matter present, but a significant increase in thermal maturity (Tmax, ⁰C) is observed. No systematic changes in δ¹³C occur in the No. 7 Coal transect as the intrusion is approached, with δ¹³C varying between − 25.4‰ and − 24.8‰. The organic-rich shale transect shows a minor 1.2‰ enrichment in δ¹³C (from − 25.2‰ to − 24.0‰) within 2 m of the intrusion. These isotopic shifts are not of a magnitude that would be expected if associated with a large-scale release of thermogenic CH4. In addition, no evidence exists in either transect for ¹³C–depleted condensed gas or pyrolytic carbon at the intrusion contact that could have moderated the isotopic signature. These data agree with those reported previously that indicate no clear isotopic evidence for large-scale CH4 generation due to rapid heating by igneous intrusion into coals or sedimentary rocks.
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B_N_E_8: Complex subsurface hydrothermal fluid mixing at a submarine arc volcano supports distinct and highly diverse microbial communities Abstract Hydrothermally active submarine volcanoes are mineral-rich biological oases contributing significantly to chemical fluxes in the deep sea, yet little is known about the microbial communities inhabiting these systems. Here we investigate the diversity of microbial life in hydrothermal deposits and their metagenomics-inferred physiology in light of the geological history and resulting hydrothermal fluid paths in the subsurface of Brothers submarine volcano north of New Zealand on the southern Kermadec arc. From metagenome-assembled genomes we identified over 90 putative bacterial and archaeal genomic families and nearly 300 previously unknown genera, many potentially endemic to this submarine volcanic environment. While magmatically influenced hydrothermal systems on the volcanic resurgent cones of Brothers volcano harbor communities of thermoacidophiles and diverse members of the superphylum “DPANN,” two distinct communities are associated with the caldera wall, likely shaped by two different types of hydrothermal circulation. The communities whose phylogenetic diversity primarily aligns with that of the cone sites and magmatically influenced hydrothermal systems elsewhere are characterized predominately by anaerobic metabolisms. These populations are probably maintained by fluids with greater magmatic inputs that have interacted with different (deeper) previously altered mineral assemblages. However, proximal (a few meters distant) communities with gene-inferred aerobic, microaerophilic, and anaerobic metabolisms are likely supported by shallower seawater-dominated circulation. Furthermore, mixing of fluids from these two distinct hydrothermal circulation systems may have an underlying imprint on the high microbial phylogenomic diversity. Collectively our results highlight the importance of considering geologic evolution and history of subsurface processes in studying microbial colonization and community dynamics in volcanic environments. Аннотация Гидротермально активные подводные вулканы - это богатые минералами биологические оазисы, вносящие значительный вклад в химические потоки в глубоком море, но мало что известно о микробных сообществах, населяющих эти системы. Здесь мы исследуем разнообразие микробной жизни в гидротермальных отложениях и их физиологию, основанную на метагеномике, в свете геологической истории и возникающих путей гидротермальных флюидов в недрах подводного вулкана Братьев к северу от Новой Зеландии на южной дуге Кермадек. Из геномов, собранных в метагеномах, мы идентифицировали более 90 предполагаемых геномных семейств бактерий и архей и почти 300 ранее неизвестных родов, многие из которых потенциально эндемичны для этой подводной вулканической среды. В то время как гидротермальные системы подверглись магматическому влиянию на вулканических возрождающихся конусах вулканов Братьев, гавани сообществ термоацидофилов и различных членов супертипа «DPANN», со стенкой кальдеры связаны два разных сообщества, вероятно, сформированные двумя разными типами гидротермальной циркуляции. Сообщества, филогенетическое разнообразие которых в первую очередь совпадает с разнообразием конусов и магматическим влиянием гидротермальных систем в других местах, характеризуются преимущественно анаэробным метаболизмом. Эти популяции, вероятно, поддерживаются флюидами с большим магматическим входом, которые взаимодействовали с различными (более глубокими) ранее измененными минеральными ассоциациями. Однако проксимальные (на расстоянии нескольких метров) сообщества с предполагаемым геном аэробным, микроаэрофильным и анаэробным метаболизмом, вероятно, поддерживаются более мелкой циркуляцией с преобладанием морской воды. Более того, смешение флюидов из этих двух отдельных гидротермальных циркуляционных систем может иметь основной отпечаток на высоком филогеномном разнообразии микробов. В совокупности наши результаты подчеркивают важность рассмотрения геологической эволюции и истории подземных процессов при изучении микробной колонизации и динамики сообществ в вулканических средах.
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