While there is increasing knowledge on microbial effects on the primary precipitation of carbonates, the subsequent alteration of trace element and stable isotope signals in ordinary carbonate muds during early diagenesis is still poorly understood. CHARON TP7 applies a combined approach of NGS-based metagenomic analyses and pore water, mineralogical and isotope analyses to trace changes in fine-grained primary carbonates at shallow sediment depth in a tropical lagoonal setting on the Aldabra Atoll, Seychelles. Samples were taken inside the lagoon and at landlocked pools on the island ring. They include sediments from up to 50cm deep push cores, water samples, microbial mats, biofilms and bacterial isolates.