Novel cyclised and aromatised diagenetic products of β-carotene in the Green River Shale

A suite of novel diagenetic products of β-carotene has been identified in an extract of a sample from the Green River Shale. Identification is mainly based on comparison of mass spectra with those of diagenetic products of another carotenoid, isorenieratene. These compounds were formed by (i) cyclisation and aromatisation of the polyene isoprenoid chain, (ii) explusion of toluene and m-xylene from the polyene isoprenoid chain, and (iii) aromatisation of the 1,1,5-trimethylcyclohex-5-enyl moieties resulting in 1,2-dimethylbenzene end groups. Reduction of the double bonds of β-carotene is the most important diagenetic process, however, as judged from the high relative amount of β-carotane (63% of quantified diagenetic products of β-carotene). These results indicate that the fossilisation potential of carotenoids is greater than previously thought.