Chemostratigraphic evidence of higher-plant evolution in the Taranaki Basin, New Zealand

Correlation between palynological and biomarker records of higher-plant development during the Cretaceous and Paleogene in Taranaki Basin, New Zealand is good. Gymnosperms, particularly podocarps, were the chief members of coastal plain swamp flora during the Late Cretaceous, and contributed significant quantities of diterpanes, often dominated by isopimarane, to organic-rich sediments. Angiosperms increased in relative abundance through the Paleocene and became the dominant higher plants in the Eocene; their contributions to coaly sediments are characterized by various triterpanes, particularly 18α(H)-oleanane and its C24 A-ring degraded counterpart. This change in dominance of higher-plant groups can be followed by the use of an angiosperm/gymnosperm index (AGI) based on the relative concentrations of selected triterpanes and diterpanes in m/z 191 and m/z 123 mass chromatograms. Plant biomarker distributions do not provide as precise age indications as do pollen assemblages, but they may be more representative of the vegetation growing in a particular area of a peat swamp.