The organo-mineral assemblage formation from the mixture of crushed rocks and leaf compost was promoted by (i) microbial re-working of OM (indicated by lower C:N and higher δ¹³C and δ¹⁵N compared to the original leaf compost) and (ii) the supply of extractable metals (esp. oxalate-extractable Fe phase) from the rock weathering. These findings supported the organo-metallic glue hypothesis (Wagai et al., 2020) and suggest that C accretion during early pedogenesis.