Paraffinic hydrocarbons from supercritical-gas extracts of coal as organic geochemical markers

PARAFFINIC hydrocarbons have been proposed as indicators of the conditions obtaining during the deposition and subsequent maturation of sediments1–4. We consider here the relationship between the rank (as measured by carbon content) of coals and analytical results for the alkane fractions obtained by a novel extraction procedure (under investigation for the derivation of liquid fuels and feedstocks from coal5,6) which uses super-critical gases (SCG). We first discuss the limitations of n-alkane distributions and then deal with acyclic isoprenoids, drawing particular attention to the ratio of pristane to phytane.