A memory of Paleozoic to Quaternary Greenhouse climates recorded in Southern African regolith

Abstract In this article, we explore the potential of iron-rich duricrust regoliths from old erosional anorogenic surfaces to record clues of the long-term continental paleoclimatic evolution. We coupled geochemical, mineralogical and geochronological analyses on iron oxides and oxyhydroxides (i.e. hematite and goethite) from iron-rich duricrusts collected on the ~2000 m elevation pre-glacial surface of Nyika, in Malawi, a surface isolated since at least the Permian. Here we show that the studied samples are the remnants of dismantled tropical regoliths and contain clasts with complex mineralogical, geochemical and (U-Th)/He geochronological characteristics. The iron oxides and oxyhydroxides present continuous ages range from 397 ± 40 Ma to 1 Ma that correlate with clear geochemical trends. It allows to extract three main periods of iron oxides and oxyhydroxides crystallization during the Devonian, Late Cretaceous and Quaternary. Mixing of minerals generations reveals here some of the main periods of warm and wet climate that affected the Southeastern African continent during the last 400 Myr.