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Abstract
A 30−cm sediment core dating back about 300 years was collected from Lake Schrader in Alaska. The core was segmented, dated, and analyzed for three- to six-ring polycyclic aromatic hydrocarbons (PAHs) by gas chromatography/mass spectrometry (GC/MS). The PAHs analyzed were found to be distinctively different in composition from PAHs in environmental samples contaminated by anthropogenic activities. The major PAHs in polluted samples consist of over a dozen parental PAHs with typical composition profiles indicating combustion origins. In the Lake Schrader sediment, the presence of combustion derived PAHs is overwhelmed by the presence of a number of biogenic PAHs. The major biogenic PAHs found to be present are phenanthrene, alkylated phenanthrenes, alkylated tetra- and octa-hydrochrysenes, and perylene from diagenesis of natural biological products. Their original biological precursors were traced by their preserved carbon skeletons, and their depth profiles reflected the rate of the diagenetic processes. Diagenesis is the first stage of transformation which carries the original biological lipids toward the maturation to fossil fuel formation. The biogenic PAHs entrained in petroleum, which originated in the catagenesis second stage, can be useful biological markers in petroleum geochemistry.
