The Kuche Depression is considered as the most important gas resource potential and gas exploring area with great gas resource potential and prospect in the Tarim Basin. Based on geochemical experimental analyses and comprehensive geological studies, the general geochemical characteristics of molecular and isotope compositions of rare gases as well as hydrocarbon gases and nonhydrocarbon gases are comparatively studied in the Kuche and Southwestern Depressions. Then, their genetic types are separately identified and gas originations are comprehensively discussed. The main results are as follows. (1) Gas fields in the Kuche Depression have a higher methane abundance, accompanied with low N2 and CO2 abundances, but the Akemomu gas field in the Southwestern Depression has a relatively lower average methane abundance, accompanied with high average N2 and CO2 abundances. The helium abundance of natural gases in gas fields from the Kuche Depression general has 1 order of magnitude higher than the air value. Comparatively, it has more than 2 orders of magnitude higher than the atmospheric value in the Akemomu gas field from the Southwestern Depression. The neon, argon, krypton, and xenon abundances in both Kuche and Southwestern Depressions are lower than the corresponding air values. (2) Natural gases from gas fields in the Kuche Depression and the Southwestern Depressions are generally typical coal-formed gases. The rare gases in the Kuche Depression have typical crustal genesis, mainly deriving from the radioactive decay of elements in the crust, while in the Akemomu gas field from the Southwestern Depression, the rare gases have main crustal genesis with a proportion of 92.5&#x0025;, probably accompanied with a little mantled genetic contribution. (3) Natural gases in the Kuche Depression are generally derived from coal measure source rocks of Jurassic and Triassic, which principally originated from Jurassic in strata period and coals in source rock types. The Jurassic source rocks account for 55&#x0025;-75&#x0025; and the Triassic source rocks account for 25&#x0025;-45&#x0025; approximately, while coals occupy 68&#x0025; and mudstones occupy 32&#x0025; separately. Natural gases from the Akemomu gas field in the Southwestern Depression mainly originated from humic mudstones of marine and continental transitional source rocks of Carboniferous to Permian.

Xiaobo Wang

Caineng Zou

Jian Li

Guoqi Wei

Jianfa Chen

Zengye Xie

Zhisheng Li

Jianying Guo

Shiguo Lin

Songqi Pan

Aisheng Hao

Chunlong Yang

Xuening Qi

Comparison on Rare Gas Geochemical Characteristics and Gas Originations of Kuche and Southwestern Depressions in Tarim Basin, China

Thoron&#x2019;s (220Rn) contribution to &#x03B1;-radiation exposure is usually considered negligible compared to that of 222Rn (radon). Despite its short half-life of 55.6 seconds, thoron can be exhaled from porous surface layers of building materials into indoor air where people subsequently inhale radioisotopes, including metallic radioactive progeny. Bare surfaces of dry porous soil with relatively high 232Th content can pose a thoron radiation hazard in indoor air. On northern Vietnam&#x2019;s &#x0110;&#x1ED3;ng V&#x0103;n karst plateau, the spatial distribution of thoron was determined in indoor air of traditional earthen and other types of dwellings using portable RAD7 and SARAD&#x00AE; RTM 2200 detectors. &#x201C;Mud houses&#x201D; are constructed with local compacted soil and typically do not have any floor or wall coverings (i.e., no plaster, wallpaper, or paint). Detailed measurements in a mud house revealed levels of thoron in room air averaging &#x003E;500&#x2009;Bq&#x2009;m-3. The spatial distribution of &#x03B1;-radiation from thoron in indoor air at a distance of about 1&#x2009;m from interior walls was fairly homogeneous and averaged &#x007E;200&#x2009;Bq&#x2009;m-3. Most concerning, from a human health perspective, were the high thoron concentrations of up to 884&#x2009;Bq&#x2009;m-3 in sleeping areas near mud walls. The average annual thoron radiation dose to inhabitants of mud houses was estimated based on 13 hours of daily occupancy, including daily activities and sleeping. The estimated average thoron inhalation dose of 27.1&#x2009;mSv a-1 during sleeping hours near mud surfaces accounts for nearly 75&#x0025; of the total estimated radon and thoron inhalation dose of 37.4&#x2009;mSv a-1 from indoor mud house air. Our conservative annual radiation dose estimates do not include subsequent radiation from inhaled metallic progeny of thoron. Our data demonstrate a significant human health risk from radiation exposure and a critical need for remediation in traditional northern Vietnamese mud house dwellings.

D&#x01B0;&#x01A1;ng Nguy&#x1EC5;n-Thu&#x1EF3;

H&#x01B0;&#x1EDB;ng Nguy&#x1EC5;n-V&#x0103;n

Jan P. Schimmelmann

Nguy&#x1EC7;t Th&#x1ECB; &#x00C1;nh Nguy&#x1EC5;n

Kelsey Doiron

Arndt Schimmelmann

220Rn (Thoron) Geohazard in Room Air of Earthen Dwellings in Vietnam

Gas hydrates, acting as a dynamic methane reservoir, store methane in the form of a solid phase under high-pressure and low-temperature conditions and release methane through the sediment column into seawater when they are decomposed. The seepage of methane-rich fluid (i.e., cold hydrocarbon seeps) fuels the chemosynthetic biota-inhabited surface sediments and represents the major pathway to transfer carbon from sediments to the water column. Generally, the major biogeochemical reactions related to carbon cycling in the anoxic marine sediments include organic matter degradation via sulfate reduction (OSR), anaerobic oxidation of methane (AOM), methanogenesis (ME), and carbonate precipitation (CP). In order to better understand the carbon turnover in the cold seeps and gas hydrate-bearing areas of the northern South China Sea (SCS), we collected geochemical data of 358 cores from published literatures and retrieved 37 cores and corresponding pore water samples from three areas of interest (i.e., Xisha, Dongsha, and Shenhu areas). Reaction-transport simulations indicate that the rates of organic matter degradation and carbonate precipitation are comparable in the three areas, while the rates of AOM vary over several orders of magnitude (AOM: 8.3-37.5&#x2009;mmol&#x00B7;m-2&#x00B7;yr-1 in Dongsha, AOM: 12.4-170.6&#x2009;mmol&#x00B7;m-2&#x00B7;yr-1 in Xisha, and AOM: 9.4-30.5&#x2009;mmol&#x00B7;m-2&#x00B7;yr-1 in Shenhu). Both the arithmetical mean and interpolation mean of the biogeochemical processes were calculated in each area. Averaging these two mean values suggested that the rates of organic matter degradation in Dongsha (25.7&#x2009;mmol&#x00B7;m-2&#x00B7;yr-1) and Xisha (25.1&#x2009;mmol&#x00B7;m-2&#x00B7;yr-1) are higher than that in Shenhu (12&#x2009;mmol&#x00B7;m-2&#x00B7;yr-1) and the AOM rate in Xisha (135.2&#x2009;mmol&#x00B7;m-2&#x00B7;yr-1) is greater than those in Dongsha (27.8&#x2009;mmol&#x00B7;m-2&#x00B7;yr-1) and Shenhu (17.5&#x2009;mmol&#x00B7;m-2&#x00B7;yr-1). In addition, the rate of carbonate precipitation (32.3&#x2009;mmol&#x00B7;m-2&#x00B7;yr-1) in Xisha is far higher than those of the other two regions (5.3&#x2009;mmol&#x00B7;m-2&#x00B7;yr-1 in Dongsha, 5.8&#x2009;mmol&#x00B7;m-2&#x00B7;yr-1 in Shenhu) due to intense AOM sustained by gas dissolution. In comparison with other cold seeps around the world, the biogeochemical rates in the northern SCS are generally lower than those in active continental margins and special environments (e.g., the Black sea) but are comparable with those in passive continental margins. Collectively, &#x007E;2.8&#x2009;Gmol organic matter was buried and at least &#x007E;0.82&#x2009;Gmol dissolved organic and inorganic carbon was diffused out of sediments annually. This may, to some extent, have an impact on the long-term deep ocean carbon cycle in the northern SCS.

Yanping Zhang

Min Luo

Yu Hu

Hongbin Wang

Duofu Chen

An Areal Assessment of Subseafloor Carbon Cycling in Cold Seeps and Hydrate-Bearing Areas in the Northern South China Sea

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Geofluids

Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China

Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China

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<div>The most recent advances in fluid geochemistry provide new tools to gain insight into a variety of natural and anthropogenic processes.The management of volcanic and seismic risks is heavily based on findings gathered by fluid geochemistry and advanced techniques for natural hydrocarbon exploration, as well as industrial processes for oil refining. Advancements in planetary science investigations are made possible by using results from noble gas geochemistry. Important information on extreme environment conditions is gained by the latest applications of environmental and radioactive gas geochemistry on dissolved and free gases.The aim of this special issue is to collect contributions on the most recent advances in gas geochemistry. We encourage the submission of articles covering a wide spectrum of gas geochemistry applications. We welcome the submission of research presented at the 14th International Conference on Gas Geochemistry (<a href="https://icgg2017.uni.wroc.pl/">https://icgg2017.uni.wroc.pl/</a>), as well as papers from any contributor.Potential topics include but are not limited to the following:<ul class="li_special"><li>Noble gas geochemistry</li><li>Gas geochemistry in volcanic systems</li><li>Gas geochemistry over seismic areas</li><li>Radioactive gas Geochemistry</li><li>Environmental gas geochemistry</li><li>Gas geochemical processes in reservoirs</li><li>Gas geochemistry in petroleum basins</li></ul></div>

Geofluids

New Applications in Gas Geochemistry

New Applications in Gas Geochemistry

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Comparison on Rare Gas Geochemical Characteristics and Gas Originations of Kuche and Southwestern Depressions in Tarim Basin, China

²²⁰Rn (Thoron) Geohazard in Room Air of Earthen Dwellings in Vietnam

An Areal Assessment of Subseafloor Carbon Cycling in Cold Seeps and Hydrate-Bearing Areas in the Northern South China Sea