Figure F27. Methane (C₁) and dissolved sulfate (SO₄^2-) concentrations and methane vs. ethane plus propane ratio (C₁/C₂+C₃) from headspace gas analysis at Site 1172. Dashed lines = biogenic and thermogenic fields on the C₁/C₂+C₃ plot. Lithostratigraphic and preliminary biostratigraphic units are on the right side of the diagram.