NOVEL CYCLIZED AND AROMATIZED DIAGENETIC PRODUCTS OF BETA-CAROTENE INTHE GREEN RIVER SHALE

A suite of novel diagenetic products of beta-carotene has been identif ied in an extract of a sample from the Green River Shale. Identificati on is mainly based on comparison of mass spectra with those of diagene tic products of another carotenoid, isorenieratene. These compounds we re formed by (i) cyclisation and aromatisation of the polyene isopreno id chain, (ii) expulsion of toluene and m-xylene from the polyene isop renoid 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-caro tane (63% of quantified diagenetic products of beta-carotene). These r esults indicate that the fossilisation potential of carotenoids is gre ater than previously thought. (C) 1997 Elsevier Science Ltd.