Purpose <p>When sediments are deposited on land, large themodynamic disequlibria are induced. We studied early pedogenesis of sediments deposited between 1971 and 2016 in a depot with a well-known history to characterize transformation processes and estimate their rate of transformation into Technosols.</p> Methods <p>Total and extractable concentrations of elements were determined in samples from several depths of four sampling pits. Surface samples were subjected to mineralogical investigations and weathering cell test. Investigations focused on sulfur (S) dynamics, but iron (Fe) and manganese (Mn) transformation and trace metals were also studied.</p> Results <p>Concentrations of soluble salts were low in leachates from older sediments. Oxidation progressed downwards through the profiles converting sulfides to&#xa0;sulfates (SO₄²⁻)&#xa0;at a rate of about 6–10&#xa0;cm per year and this was faster in sediments with high sand content. There were significant amounts of S left in the sediments also after depletion of leachable SO₄²⁻ but weathering cell tests indicate that this pool is not reactive. Leaching of trace metals was generally low and did not increase with sulfide oxidation, indicating that released metals redistributed quickly to scavengers, probably newly formed Fe and Mn (hydr)oxides and organic matter.</p> Conclusion <p>The first processes occurring after sediment deposition are the release of soluble salts, including SO₄²⁻ kinetically controlled by the oxidation of sulfides. The evolution during this critical stage may not be fully captured by the total trace metal content and simple leaching tests. For sediment managers, we recommend complementing sediment assessment with analysis of total S and in the case of high S content with the weathering cell test.</p>