To　examine　the　abundance　and　speciation　of　iron,　six　iron　species　(poor　crystalline　Fe(III),　crystalline　Fe(III),　non-sulfidic　Fe(II),　porewater　Fe2+,　FeS,　and　FeS2)　were　investigated　in　a　cross　transect　(span=250m,　depth=~1.2m)　in　a　tidal　marsh　of　the　Min　River　Estuary　in　the　East　China　Sea.　The　results　suggested　that　sediment　characteristics,　pH,　redox　condition,　conductivity,　chloride,　sulfate,　and　organic　matter　create　a　highly　heterogeneous　geochemical　framework　in　the　cross　transect.　Correspondingly,　the　zonation　of　iron　species　differed　significantly　across　the　tidal　marsh.　Poor　crystalline　Fe(III)　(48±24μmolg-1)　and　crystalline　Fe(III)　(75±32μmolg-1)　accumulated　on　the　surface　of　the　high-tide　zone　and　decreased　with　elevation.　The　non-sulfidic　Fe(II)　minerals　(140±61μmolg-1)　accounted　for　the　largest　proportion　of　the　six　iron　species.　The　porewater　Fe2+　was　enriched　within　the　deep　layer　of　the　upland　region　(pH=6.2-6.5)　and　exhibited　a　maximum　of　11.49mM.　The　aqueous　sulfide　concentration　was　below　detection.　FeS　(39±6μmolg-1)　and　FeS2　(57±25μmolg-1)　accumulated　closer　to　the　lower　extremity.　Tidal　water　brought　O2　and　removed　certain　amounts　of　dissolved　organic　carbon,　dissolved　inorganic　carbon,　and　Fe(III)-bearing　particles　in　an　element　budget　during　tidal　inundation.　Variations　of　topography,　tidal　hydrology,　seawater　intrusion,　and　organic　matter　altered　the　dominant　organic　matter　oxidation　pathway　and　further　affected　iron　mineralization.　©　2014　Elsevier　Ltd.