Source of soluble organic matter in Quaternary sediments in the Muli permafrost area of the South Qilian basin and its relationship to gas hydrate

Muli depression in the South Qilian basin is an area where the first natural gas hydrate sample was drilled in land area in China.Organic geochemical analysis was carried out on the soluble organic matter in the Quaternary sediments in gas hydrate-drilled area (DK well area) as well as the Quaternary sediments in adjacent Laoren lake area in the Muli permafrost area.The results show that pyrogenic organic matter obviously exists in shallow surface sediment in the DK well area, while the soluble organic matter in the sediments of Laoren Lake is mainly derived from higher plants.Compared with the characteristics of source rocks in this area, the pyrogenic organic matter mainly comes from the Middle Jurassic source rock, and the Upper Triassic Galerdesi source rock also has a certain contribution.Combined with the research results of hydrate gas source in the study area, the pyrogenic organic matter in Quaternary sediments in the DK well area is probably homologous to hydrocarbon gases that form hydrates.Oil and gas generated by thermal evolution of deep source rocks migrate upward or leak to shallow surface along channels such as faults and sandstone fissures.The light components of methane and heavy hydrocarbon gas can combine with formation water to form gas hydrate in the stable zone.The research on the source of soluble organic matter in the Quaternary sediments in the Muli area can provide a new perspective for the exploration of gas hydrate.