Abstract
Diamondoid hydrocarbons have been identified in Toarcian black shale alternated with bedded chert from Unuma-Hosekiji, Gihu, central Japan. The thickness of the black shale was 60cm, and seven samples were collected vertically. 73 adamantanes, 21 diamantanes and 6 triamantanes were identified in this black shale. Five diamondoid hydrocarbon ratios have been used as maturity and source rock parameter to compare each sample. These parameters indicate that the maturity levels of the black shale were increased with depth, and the influence of marine and carbonate source material were also increased with depth, although all samples were expected to indicate same values. The reason of the change of parameters is not clear, but the causes seem to be (1) the difference of contents of catalysis such as clay minerals and zeolites, (2) the migration of organic matter from radiolarian mud during early diagenesis, (3) the change of oxic/anoxic environment during the black shale accumulation.
