Substantial maturity influence on carbon and hydrogen isotopic composition of n-alkanes in sedimentary rocks

Carbon (?13C) and hydrogen (?2H) compound-specific isotope analyses on sedimentary hydrocarbons are widely used for ecological reconstructions oil-source rock or oil-oil correlations. However, the effects of thermal alteration isotopic composition not fully understood, potentially imparting a bias interpretation older more mature sequences. We measured ?13C ?2H n-alkanes in 23 extracted bitumens from 1.64 Ga Paleoproterozoic Barney Creek Formation southern McArthur Basin, Australia. The samples cover wide range maturities with calculated vitrinite reflectance (Rc) values 0.4% to 1.3%. Our results illustrate that while kerogen remains relatively constant, have strong positive correlation maturity. Average ?13Calk increase by 6.8‰ ?2Halk 69‰ among analysed maturity range. At same time, carbon offset between (??13Calk–ker) climbs 1.3‰ 8.5‰ increasing Therefore, substantial influence stable isotopes must be considered palaeoecological petroleum studies. In initial stages maturation, display increasingly “isotope slopes” plots against number. further slopes became negative. slope inversion indicates dominant mechanisms n-alkane generation degradation changed during progression early diagenesis metagenesis. Numerical models suggest formation negative may driven balance their subsequent degradation, dependence rate constant k chain length.