Séminaire ISTeP - Eric Verrecchia

(U. Lausanne, prof. invité ISTeP)

Can Mima-like Mounds be Vertisol relics (Far North Region of Cameroon, Chad Basin)? Implications for palaeo-reconstruction of the carbon cycle

Non-anthropogenic earth mounds, defined as mima-like mounds in this talk, have been recently observed in non-carbonate watersheds, along the Sudano-Sahelian belt in the Chad Basin. These mounds are composed of a clay-rich sediment associated with high proportions of secondary carbonate nodules and Fe-Mn micro-nodules. Observed characteristics point to vertic properties. However, these properties are altered and mima-like mounds are interpreted as degraded Vertisols. OSL and 14C dating revealed that these vertic paleosols developed during a former and wetter period than present-day and are inherited from regional climatic variations during the Late Pleistocene-Holocene (African Humid Period). In addition, Sr isotopes confirmed that they acted as a carbon sink since the in situ weathering of plagioclases provides the main source of Ca. The way such accumulations of CaCO3 may precipitate is still under debate.

29/01/2016 à 12h30, Salle Fourcade (Tour 55-56, 4ème étage)