Dating petroleum emplacement by illite ~(40)Ar/~(39)Ar laser stepwise heating

摘要

The timing of petroleum emplacement is crucial in understanding petroleum-forming processes and predicting new prospecting regions. This study investigates the possibility of determining the age of petroleum emplacement by an illite ~(40)Ar/~(39)Ar laser stepwise heating technique. A specially designed apparatus has been used to clean up the organic gases in samples contaminated with residues from oil or gas fields, resulting in credible ~(40)Ar/~(39)Ar data. The sandstone samples are from the Zhuhai and Zhujiang formations in the Huizhou sag in the Pearl River Mouth Basin, South China Sea. Illite ~(40)Ar/~(39)Ar laser stepwise heating consistently yields gradually rising age spectra at the low-temperature steps until reaching age plateaus at high-temperature steps. The first-step apparent ages of the six samples from the Zhujiang formation give a weighted mean age of 11.4 ± 0.5 Ma (1σ), in agreement with an age of 12.1 ± 1.1 Ma in the first three steps of the sample from the Zhuhai Formation.