Ken Sawada, Hideto Nakamura, Arai Takaaki, Minoru Tsukagoshi
International Journal of Coal Geology, 107: 78-89, 2013
Publication year: 2013

Abstract

We investigated terpenoid biomarkers in muds from lignite seams, clays from porcelain clay beds that slightly contain lignite, and from a conifer cone macrofossil from the Miocene Tokiguchi Porcelain Clay Formation of the Tokai Group in central Japan, as well as extant cones. The n-alkanes, n-alkanols (suberin origin), diterpenoids (conifer origin), hopanoids (bacteria origin) and steroids were mainly present in the lignite-containing muds and clays. On the other hand, the diterpenoids, triterpenoids (angiosperm origin), hopanoids and steroids were detected as major component in the conifer cone macrofossil. In addition, the diterpenoids were mainly detected in the extant conifer cones. The low hopane isomer ratios and the detection of biosterols are confirmed to be immature in the lignite, sediment and macrofossil in the formation. The stanol/sterol ratio values of the lignite-containing muds and clays are much higher than that of the macrofossil. The higher ratios in lignite-containing muds and clays are possibly attributed to enhanced microbial reduction of organic matter under reduced condition in the swampy environments. A large amount of angiosperm-derived triterpenoids detected in the conifer cone macrofossil are considered as contaminants in the sample from sedimentary organic particles originated from detrital waxes of angiosperms. Such contamination might occur by migration of organic compounds within sediment after deposition. The angiosperm-derived polar terpenoids may be hardly affected by contamination by migration of organic matter from the adjacent sediments because these are less abundant in the conifer macrofossil. Thus, it is suggested that the polar terpenoid biomarkers are more reliable as paleochemotaxonomic and paleovegetation indicators.

Highlights

► We analyze terpenoid in sediments of Miocene lignite and clay beds, and plant fossil.

► Coniferous diterpenoid is mainly detected in sediments in the lignite and clay beds.

► Low hopane isomer ratio and biosterol detection show the lignite seams are immature.

► Lower stanol/sterol ratios of lignite seams are due to microbial reduction in swamp.

► Angiosperm-derived triterpenoids are detected as contaminant in a conifer fossil.

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