I am searching for information concerning the oldest confirmed occurrence of pedogenic siderite, eg. sphaerosiderite. There are numerous reports from Phanerozoic, but what about Neoproterozoic? Pedogenic siderite forms in reducing, water-logged soils, where degradation of organic matter takes place. It requires high atmospheric pCO2 and accumulation of organic matter on land. Is it possible that such conditions developed in Neoproterozoic?