Paleoclimatical significance of the paleosol levels occuring in the Miocene-Pleistocene stratigraphy of the Manonga-Wembere Valley in Central Tanzania

Abstract

Micromorphological characteristics of four paleosol levels of the Manonga - Wembere deposits in Central Tanzania indicate periods of wetter climate in the Pliocene than at present. The stratigraphy of the studied section shows a series of lacustrine calcareous clay sediments alternating with gravel, sand and silt. The sediments are believed to have been deposited in the Manonga - Wembere paleolake environment. Paleosols intercalate these sediments and were formed when stable landscapes developed on former lake beds during regression periods. Micromorphological features of the paleosols indicate strong clay illuviation of red to yellow typic clay coating and some Fe-Mn hydoxide hypocoatings in voids and channels. The groundmass consists of either an accumulation of bioturbated yellow to red clay coating fragments or an argillic red to yellow groundmass of clay mass. Such an illuviation and its associated groundmass is comparable to intense clay illuviation fronts that are found in present-day calcareous sediments of warm and wet climates. The paleosol levels therefore represent wetter climatic conditions than today in the area during the Lower Pliocene.