Queries about biogenesis of Quaternary gas in Qaidam Basin, NW China

Abstract

Abstract: Organic geochemistry of Quaternary source rocks is not favorable to the generation of natural gas, such as the low organic matter content, the thin layer, and the low ethanoic acid content in mudstones. Seven cases of natural gas occurrences show that the gas genesis cannot be recognized by the current carbon isotope compositions. Five simulation experiments show that carbon isotopic fractionation can also happen in the Fischer-Tropsch reaction. Carbon isotope is not a reliable criterion for distinguishing biogenic from abiogenic gases. Based on 2 geo-transects and electromagnetic soundings, there is an uplifting upper mantle and 3 ultra-deep faults in the deeper crust, and there is a low velocity–high conductive layer in the mid crust, which is rich in CO2 (CO) and H2. If metal catalytic elements participated, the Fischer–Tropsch reaction might have occurred and formed hydrocarbons under certain temperatures and pressures. The deep crust structure shows that abiogenic gas might exist under the Quaternary System in the Qaidam Basin. Key words: biogenic gas, carbon isotope, fractionation, Fischer-Tropsch reaction, Quaternary, Qaidam Basin