Early diagenetic alterations of organic matter from conifers were simulated at low temperature of 80°C for five and a half years. Their diagenetic products of aliphatic hydrocarbons were identified and quantified. The results reveal that in the early sedimentation of organic matter from conifers, n-alkanes have developed; natural terpenoids have transformed into diagenetic terpenoids, in which some seldom reported evolutionary intermediates-two cadinatetraenes, three norabietatetraenes and one

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... bietatetraene-were detected and identified. The diagenetic pathways for cadalane-type sesquiterpenoids and abietane-type diterpenoids are proposed. The experimental data also show that the diagenesis of aliphatic hydrocarbons is influenced by different inorganic environments. The influences can be concluded as follows: high salinity is propitious to generate and expulse aliphatic hydrocarbons; iron may promote the increase of alkanes, but interrupt the alterations of terpenoids; gypsum, when not coexisting with metal, may slow the degradation from long chain alkanes to short ones; and heavy metal probably delays the early diagenesis of both alkanes and terpenoids. These influences observed under low temperature may enrich studies on early diagenesis of organic matter from higher plants.