Geochemical facies of sediments and soils (the chemical indicators of the environment) provide geologists with a means to reconstruct fossilized environments of past ages. Facies diagnosis may be based on analysis of fossil bionomy, paleobiochemistry, or geochemistry. Geochemical facies diagnosis may be based on main constituents (lithology, sedimentology, and soil profile); minor components (concentrations in the order of 10−2or 10−3, or less: salinity, ion concentrations of Cl, Br, I, F, and P; Ca: Sr and12C:12C as well as18O:16O ratios, and indications on redox potentials), or the type and nature of organic substances preserved (C: N ratios, biochemistry of carbohydrates, and enrichment in certain elements of coals, oil, and gas). Analysis of chemical facies from remains in lithified sediments should incorporate the physical chemistry of the compounds studied, as well as the changes that will take at high burial pressures and possible increase in temperature.