Mineralization Controls Informative Biomarker Preservation Associated With Soft Part Fossilization in Deep Time

Diagenetically mineralized fossil tissues represent invaluable paleobiological evidence of past life. Lipid biomarkers may be identified alongside fossils, yet the relationship between localized, diagenetic mineral precipitation, and lipid preservation remains underexplored. Coprolites (fossilized feces) attract a unique diversity of early diagenetic minerals including carbonates and phosphates, within individual samples, mediating molecular preservation of soluble lipid biomarkers alongside exceptional morphological preservation. Analysis of a well-preserved coprolite from the Carboniferous (307 ± 0.1 Ma) Mazon Creek assemblage, USA via time of flight-secondary ion mass spectrometry (ToF-SIMS) spatial compound mapping demonstrated the association of 5α,14α,17α(H) 20R cholestane, a C₂₇ dietary sterane, with iron carbonate (and some pyrite) rather than phosphate minerals. Furthermore, Raman spectroscopic fingerprinting of a suite of organic-rich fossils spanning a number of biological species and preserved across the Mazon Creek site and other depositional settings was utilized to explore whether the localized preservation of steroids in carbonate phases represents a lagerstätten-specific or generalizable pattern. Our spectroscopic analyses demonstrate a significant positive correlation between signatures of lipid biomarkers and carbonates rather than phosphates across all soft-part samples at the Mazon Creek site and throughout Phanerozoic time and space. Early diagenetic carbonate measurably immobilizes otherwise labile lipid biomarkers and shields them against diagenetic stressors. Localized preservation identifies carbonate phases as a preferential resource for lipid-based biological information and reveals organomineral associations as a new frontier in understanding the survival of molecules in deep time.