Fig. 7
From: Timing and origin of natural gas accumulation in the Siljan impact structure, Sweden
Gas composition discrimination diagrams. (a) δ13CCH4 versus C1/(C2 + C3). (b) δ2HCH4 versus δ13CCH4. (c) δ13CCH4 versus δ13CCO2 (adapted from32). Position of the gases from boreholes VM2 (diamonds = gas samples, triangle = water samples), VM5 (square) and drinking water well (circle) are shown. Genetic gas field abbreviations denote: CR CO2 reduction, F methyl-type fermentation, SM secondary microbial, EMT early mature thermogenic, OA oil-associated thermogenic, LMT late mature thermogenic gas. Gas data were extracted from the database of AB Igrene (Supplementary Data 8), and from45 (drinking well at Gulleråsen close to Solberga, δ13CCH4: −60.3‰, δ2HCH4: −269‰). The sampling site of the gas data in borehole VM2 corresponds to the uppermost 13C-rich calcites in this borehole, whereas the other gas-sampled borehole (VM5) is just adjacent to other boreholes sampled for calcite (VM- and 01-boreholes). Errors (2σ) are within the size of the symbols
