| Formation mechanism | Precusor | Reaction fluid/liquid | Fe-oxide mineralization | Fe state | |
| ① Chan et al. model | Goethite precipitation by redox-oxic reaction | None | Buoyant, reducing fluid due to hydrocarbon | Precipitation of goethite (not clear for crust formation) | Fe2+ |
| ② Loope et al. model | Siderite formation and microbial oxidation | Siderite (not found) | Reducing groundwater with methane dissolved | Internal Fe source (siderite) | Fe2+ |
| ③ Our proposed model | Calcite-acid reaction by pH buffering | Calcite (found) | Penetration of CO2-charged acidic groundwater | Inward precipitation of goethite by Fe-rich acidic water from outside | Fe3+ |