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

A suite of novel diagenetic products of beta-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) expulsion 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 beta-carotene is the most important diagenetic process, however, as judged from the high relative amount of beta-carotane (63% of quantified diagenetic products of beta-carotene). These results indicate that the fossilisation potential of carotenoids is greater than previously thought. (C) 1997 Elsevier Science Ltd.