Data report: solid-phase major and minor elements and iron and sulfur species in sediments of the Anholt Basin, Baltic Sea collected during IODP Expedition 347

Abstract

In this report, we present bulk solid-phase major and minor element contents and Fe and S species in sediments from IODP Expedition 347 Site M0060 in the Anholt Basin recovered during Integrated Ocean Drilling Program Expedition 347 to the Baltic Sea. Site M0060 is characterized by alternating sand- and clay-/silt-dominated sediment sequences that indicate deposition under brackish-marine and limnic conditions, respectively. We use Al-normalized elemental ratios and transition metal data to characterize the different sediment sequences and to study the impact of early diagenetic processes on the abundance and reactivity of Fe oxide and Fe sulfide mineral phases across lithologic boundaries. Ratios of Fe/Al and Mn/Al exceed the continental crustal average in the clay-/silt-dominated sequences, whereas low ratios are associated with the sandy units. About 10%–20% of the total bulk Fe content is associated with Fe oxides and Fe sulfides, whereas the major Fe fraction is bound in clay minerals. The transition metals (V, Ni, Cr, and Co) correlate with the depth profile of Fe/Al, which indicates that they are adsorbed onto Fe oxides and concomitantly deposited. Sequential leaching reveals that magnetite is the most abundant Fe oxide phase. Leached contents approach 1 wt% followed by crystalline and easily reducible Fe oxides. Pyrite is the dominant Fe sulfide phase and is enriched at several lithologic boundaries that can likely be associated with the formation of pyrite. Pyrite is formed through the reaction of Fe monosulfides with (1) polysulfides and/or S0 in zones dominated by organoclastic sulfate and Fe oxide reduction and (2) sulfide released during the anaerobic oxidation of methane.