Potential palaeoenvironmental information of C24 to C36 mid-chain diols, keto-ols and mid-chain hydroxy fatty acids; a critical review

The environmental occurrence of long-chain mid-chain diols, keto-ols and mid-chain hydroxy fatty acids is reviewed. The published information is heavily biased towards organic-rich sediments, which strongly hampers interpretation. The composition of positional isomers of these compounds differs remarkably between cultures of microalgae from the genus Nannochloropsis, and sediments, suggesting that these algae are not the major sources for the compounds to the sediments. The composition of diols and keto-ols differs substantially between marine and freshwater environments, and between marine environments themselves. These observations may be useful in palaeoenvironmental reconstruction, particularly in identifying freshwater influx. Lack of overlap in the composition of positional isomers suggests that keto-ols do not originate from diols diagenetically, but are derived from as yet unknown organisms.