Characterization of dicarboxylic acids in the Cretaceous/Tertiary boundary sediments at Kawaruppu, Hokkaido, Japan, and comparison with those of carbonaceous chondrites

Abstract

Twenty-seven C 2 to C 9 dicarboxylic acids were identified in the Cretaceous/Tertiary (K/T) boundary sediments at Kawaruppu, Hokkaido, Japan. These dicarboxylic acids included normal, branched, and unsaturated forms. Their concentrations were lowest (17, 0.40, and 0.71 nmol g −1 for normal, branched, and unsaturated, respectively) at the lowest horizon (0–0.8 cm) of the boundary claystone, reflecting the minimal biomass production due to the massive extinction of organisms at the boundary. However, the concentrations were higher at the other horizons (0.8–13.7 cm) within the boundary claystone than above (40–495 cm) or below (−395–0 cm) it. In general, the normal dicarboxylic acids showed a roughly logarithmic decrease in concentration with increasing carbon number. Only methylsuccinic acid among the branched dicarboxylic acids could be shown to be racemic, because only in this case was enough material present in the sediments for analysis. Unsaturated dicarboxylic acids showed an apparent cis-form predominance over trans with C 4 and C 5 isomers. The logarithmic decrease, the presence of racemic methyl succinic acid, and the cis-form predominance can be explained as a result of the 65-million-year diagenesis of the sediments. These characteristics were compared with those found in the Murchison and Yamato-791198 carbonaceous chondrites (Shimoyama and Shigematsu, 1994) in order to seek evidence for a contribution of dicarboxylic acid(s) of extraterrestrial origin to the K/T boundary sediments at Kawaruppu; however, the observed dicarboxylic acids in the sediments could not be attributed to an extraterrestrial origin.