Geolipidomics: Non‐Targeted Analysis of Rapidly Heated Geologic Samples With Gas‐Chromatography‐Mass Spectrometry

Abstract Lipids are powerful tools for reconstructing paleoenvironments and geologic processes because of their ubiquity and preservation in the rock record. Traditionally, organic geochemistry studies are targeted analyses of known biomarker compounds with known responses to past environmental conditions or geologic processes. With the recent development of the lipidomics field in the biological sciences, there is an opportunity for non‐targeted analysis to identify new biomarkers. However, lipids in the rock record integrate processes from biologic to geologic (i.e., diagenesis, heating, catagenesis) resulting in more chemically complex matrices than biological samples. As non‐targeted “‐omics” approaches are transferred from biology and applied to sediment, soil, and rock samples to perform geolipidomics, they must be evaluated and potentially adapted for geologic samples. Here we compare four non‐targeted methods of extracting features consisting of a peak area and spectrum from raw gas chromatography mass spectrometry data. We compare targeted data from hydrous pyrolysis experiments of Woodford Shale to non‐targeted features extracted with each method. These comparisons illuminate the pitfalls and/or potential advantages of the different computational approaches when applied to complex matrices. Only one method, MSHub, robustly recreates the targeted data, including a thermal maturity index based upon methylphenanthrenes. Exploration of the MSHub results revealed a wide range of features affected by temperature rise. We illustrate a systematic way to identify new thermal maturity indices in this non‐targeted feature space. Geolipidomics approaches could be broadly applied to generate new hypotheses and novel, robust biomarkers for organic matter sources and Earth‐system processes.