Paleoclimate reconstructions using lake sediments are based on the study of climate proxies. This thesis explores the potential of Fe-minerals to record climate-driven processes and their stability throughout burial and reevaluates Rock-Eval pyrolysis to asses organic matter-related proxies, using End-Member Analysis. We described the Fe-mineral assemblage through sequential extraction in a 100 meters-long core from lake Towuti, Indonesia, and from a 40 centimeters-long core from lake Fagnano, Argentina. We investigated the coevolution of chemical and isotopic signatures (δ56Fe) in reactive ferric (Fe-(oxyhydr)oxides) and ferrous (siderite and magnetite) phases. The isotopic correlation between ferric and ferrous phases in Towuti sediments reveals slow dissolution of Fe-oxides and the formation of diagenetic siderite. The high mobility of iron during diagenesis limits its use as a proxy for water column redox conditions. These transformations can substantially occur at the redox boundary, a few centimeters below the sediment surface, as in lake Fagnano.