Stoer Group and Sibley Group nitrogen geochemistry in red beds

Nitrogen abundances in red shales are shown to be suitable as a biosignature that may be applicable to red beds on Mars. The data set includes organic carbon and nitrogen abundances and isotopic ratios, carbonate carbon and oxygen isotope ratios, and metal abundances. We evaluate potential abiotic effects and discuss diagenetic scenarios that lead to an enrichment of ammonium in clay minerals.