Detection of retene in Proterozoic strata: a new understanding of its environmental indicator significance

Abstract Retene is generally recognized as a diagenetic product of abietane-structured diterpenoids originating from terrestrial higher plants (such as conifers) that evolved after the Devonian period. In this study, retene was detected in the Proterozoic strata of the Tarim Basin and the Western Hubei area of the lower Yangtze Platform in China. A gas chromatography-mass spectrometry analysis of 28 Proterozoic (Sinian and Nanhua system) sediment samples collected from China demonstrates that these Proterozoic marine carbonate strata, although absent of input from higher plants, were rich in retene compounds. This finding indicates that diterpenoids, a type of retene precursor, can also be synthesized by Proterozoic algae and bacteria and that terrestrial higher plants are not the only sedimentary provenance of retene. So, retene can no longer serve as a biomarker to distinguish marine and continental sedimentary environments. However, no known retene precursors, such as dehydroabietin, dehydrabietane, simonellite, and tetrahydroretene, were detected in the samples. Therefore, the existence of other unknown types of retene precursors derived from algae or bacteria remains to be investigated.