AUTHOR=Li Xue , Duan Xiaoyong , He Xingliang , Xie Yongqing , Yang Lei , Yin Ping , Cao Ke , Chen Bin , Gao Fei , Li Feng 

TITLE=The relationships between vertical variations of shallow gas and pore water geochemical characteristics in boreholes from the inner shelf of the East China Sea

JOURNAL=Frontiers in Marine Science

VOLUME=Volume 11 - 2024

YEAR=2024

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2024.1343701

DOI=10.3389/fmars.2024.1343701

ISSN=2296-7745

ABSTRACT=Shallow gas was widely recognized in the coastal region, especially in the estuarine delta areas with high organic matter (OM) burial flux. In this study, the vertical variations of shallow gas and the related geochemical indicators from two boreholes in the coastal region of the East China Sea (ECS) were investigated. Two gasbearing layers were identified in the sediments from the Holocene and late Pleistocene series. Both boreholes exhibit a "typical" and an "inverse" Sulfate Methane Transition Zone (SMTZ). The "typical" SMTZs (SMTZ1 and SMTZ3) were in the upper part of the gas-bearing layers, where sulfate levels decrease and methane levels increase with depth. Conversely, the "inverse" SMTZs (SMTZ2 and SMTZ4) were in the lower part of the gas-bearing layers, exhibiting an increase in sulfate levels and a decrease in methane levels with depth, a phenomenon rarely documented in previous research. The downward variations of pore water geochemical characteristics indicates that these ions