Here we have applied ToF-SIMS and Raman microspectroscopy to a phosphatic coprolite (fossilised faecal matter) preserved within an iron carbonate concretion from the Mazon Creek lagerstätte (306 Ma), of which the biomarker composition has been previously characterised using GC-MS. Abundant cholesteroid biomarkers were determined to represent dietary input from animals. This study aimed to spatially resolve these cholesteroid biomarkers within the coprolite specimen.

The steroid 5a,14a,17a(H) 20R cholestane was targeted for secondary ion mapping due to its abundance in the GC-MS analyses of the fossil (Tripp et al., 2022). The sterane biomarker was shown to be intimately associated with locally precipitated iron carbonate and some minor amounts of pyrite, and not associated with the phosphatised tissues. Importantly, phosphatisation is often associated with three-dimensional soft tissue preservation during earliest diagenesis, yet here does not show association with endogenous lipid biomarkers. This suggests that the factors facilitating lipid preservation in geological samples may differ to those controlling soft tissue fossilisation.