Geological and geochemical anomalies of gas hydrate in permafrost zones along the Qinghai-Tibet Railway, China

The authors made field observations of the phenomena of frozen mound upheaving, collapse and cold venting and performed geochemical analyses of gases in different media such as the lower atmosphere, cold spring gas, superficial frozen sediments and underground ice at key sites in permafrost zones along the Qinghai-Tibet Railway. Based on these observations and analyses, they found pronounced geological-geochemical anomalies in some frozen areas such as Tuojiu Mountain, the Kunlun Pass and Yanshiping. These gas geochemical anomalies were probably mainly produced by the rise of gas from the deep level to shallow frozen sediments via faults of different types in permafrost zones on the Qinghai-Tibet Plateau, and some of them are probably related to transformation of organic matter at the shallow level to hydrocarbon or to redistribution of gas accumulations caused by glacier displacement; the geological anomalies are likely to be related to tectonothermal activities or gas hydrate formation and evolution. A comparison with the previous modeling calculation shows that these geological and geochemical anomalies are situated in places where the permafrost depth is enough to meet the temperature and pressure conditions for the formation of gas hydrate, suggesting that these anomalies are possibly associated with gas hydrate occurrence in this region.