Irreversible contamination of Precambrian kerogen by 14C-labelled organic compounds

Abstract

Abstract Kerogen isolated from stromatolitic, microfossiliferous chert of the Paradise Creek Formation (ca. 1500 m.y. old; Queensland, Australia) was exposed to 14 C-labelled organic compounds (hexadecane, heptanoic acid, ribose, or serine) at elevated and room temperatures for periods up to four days. The labelled compounds were then extracted and the kerogen was analyzed to determine the amount of radioactivity remaining. Results show that kerogen can be irreversibly contaminated by younger organic compounds. The level of contamination was highest with the hydrocarbon, followed by the amino acid and the sugar; there was no irreversible contamination by the fatty acid. The maximum observed contamination level was 60 μg hexadecane/g kerogen; calculations suggest that similar contamination levels may occur under natural conditions, especially in clastic sediments. Contamination levels of this magnitude are insufficient to affect isotopic or major elemental analyses of kerogens significantly, but could produce spurious results in analyses (in the ppm range) of the organic chemical composition of kerogens.