Restricted utility of the pristane/phytane ratio as a palaeoenvironmental indicator?

Abstract

The acyclic C₁₉ and C₂₀ isoprenoid hydrocarbons, pristane (Pr) and phytane (Ph), respectively, have been widely assumed to be diagenetic products of the phytyl side chain of chlorophyll¹⁻³, although alternative sources of precursors have been suggested. The ratio of these two compounds is usually interpreted to be an indicator of the oxicity of the environment of deposition. Recent advances in organic geochemistry in combination with geological constraints lead us to suggest that the Pr/Ph ratio cannot be used as an indicator for oxygen levels. However, in hypersaline environments of deposition the rationale behind a low Pr/Ph ratio is easier to understand, and in these environments application of the Pr/Ph ratio can be expected to be successful.