古代の堆積物中の陸上高等植物テルペノイドを用いた古植生解析

抄録

Terrestrial higher plant terpenoids (HPTs) occurring in ancient marine and lacustrine sediments, are more refractory and constitute a more highly diversified family of molecules than the other terrestrial higher plant biomarkers including wax compounds and lignin phenols. Therefore, this HPT biomarker can be plant biogeochemical and paleontological indicators. Triterpenes such as oleanane are derived from various biological triterpenoids synthesized by almost all angiosperms. Diterpenenes such as retene are originated from abietane-type diterpenoids, which are constituents of gymnosperm, especially conifer. In pimarane and phyllocladane type diterpenoids, their precursors, source plants, and diagenetic products have been partly known. In addition, sesquiterpenoids are derived from both angiosperm and gymnosperm biosynthesized compounds. Several researchers have suggested that the HPT distributions were useful as the paleovegetation proxies for reconstructing the relative abundance of angiosperm to gymnosperm (e.g. angiosperm/gymnosperm index; AGI). Moreover, we recently examinated applicability of the indicator for angiosperm/gymnosperm ratio by using the HPTs in ancient plant fossils. In this paper, we review such HPT biomarkers and their applicability and reliability of the indicator as plant chemotaxonomy and paleovegetation in the ancient sediments.