Maleimides in the Cretaceous/Tertiary boundary sediments at Kawaruppu, Hokkaido, Japan

抄録

Maleimides were detected in organic solvent extracts and chromic acid oxidation products of the Cretaceous/Tertiary boundary sediments at Kawaruppu. Free (organic solvent extractable) maleimides consisted of 2, 3-dimethylmaleimide and 2-methyl-3-ethylmaleimide, and bound (oxidatively extractable) maleimides of 2-methylmaleimide and its 3-n-alkyl homologs up to C₄, benzomaleimide (phthalimide) and its methyl homologs. The total concentrations of free and bound maleimides ranged from n.d. to 10 and from 4 to 49 nmol g^-1, respectively. The most abundant compound was 2-methyl-3-ethylmaleimide both in free and bound forms in all the sediments, indicating that the maleimides detected were very likely degradation products of porphyrins and/or chlorophylls. The concentrations of both forms of alkylmaleimides were significantly smaller in the boundary claystone than the sediments above and below it. Their depth profiles agreed with those of pristane plus phytane and n-alkanes, indicating smaller inputs of chlorophylls into the claystone, which relates to the large bio-mass extinction at the end of Cretaceous. The Kawaruppu sequence afforded the first case in which 2-methylmaleimide was the second most abundant maleimide, indicating a mild thermal history of the sediments. The ratios of 2, 3-dimethyl- to 2-methyl-3-ethylmaleimide of both free and bound forms showed constant values above and below the boundary claystone, reflecting the uniform diagenesis experienced by the sediments. The ratios exhibited larger values within the claystone, which is possibly related to different precursor chlorophylls caused by the massive extinction of organisms.