The Mio-Pliocene fossil woods from Nkondo (Lake Albert, Uganda), mineralogical composition and formation.

The fossil wood samples found in the Mio-Pliocene lacustrine sediments of t he Nkondo Formation, on the eastern shore of Lake Albert (Uganda), have und ergone different mineralisations. The first epigenetic replacement by hemat ite, goethite and apatite preserved the plant structures, whereas subsequen t: replacement by goethite erased it. Some precipitations likely to be of m icrobial origin are associated with the epigenesis in apatite. The characte ristics of the different mineralisations reveal that the fossilisation of t he wood samples started with their transportation into the lake and continu ed after their deposition into the ironstone levels that have yielded the f ossil woods. (C) 2000 Academie des sciences/Editions scientifiques et medic ales Elsevier SAS.