Siderite in sedimentary siderite deposits has been widely accepted as a consequence of microbe-mediated reduction of precursor Fe-oxides during diagenesis. Similar to the well-known dolomite problem, nucleation of siderite from seawater is kinetically unfavorable, and by now no robust case has been reported. In this work, we report a convincing example of abiotic siderite from a Devonian giant sedimentary siderite deposit. Petrological and geochemical evidence indicates that siderite in this deposit was directly precipitated from ferruginous seawaters in the presence of suitable clay substrates. This finding highlights the potential of siderite as a primary Fe-sink in ferruginous seawaters and may have implications for the formation pathways of sedimentary Fe deposits, especially the Precambrian banded iron formations (BIFs). 

siderite, abiotic, sedimentary Fe deposits