Lateritic bauxite in central Germany and implications for Miocene palaeoclimate

Intense chemical weathering during middle Miocene times led to the formation of deep ferralitic weathering profiles on the Vogelsberg basaltic massif. Saprolite more than 50 m thick, was formed and, in its higher parts, bauxite concretions developed by absolute accumulation of aluminium. The tops of the profiles consist mostly of allochthonous, lateritic bauxite which has been mined intensively in the past. r high latitude bauxites occur on the Paleogene basalts of Ireland. These formed during a phase of recognized greenhouse conditions with a climatic optimum near the Paleocene-Eocene boundary, while during the Miocene the climate was already changing toward Quaternary icehouse conditions. r, the occurrence of deep weathering profiles with lateritic bauxite at the high palaeolatitude of 45°N may be interpreted as pointing to extreme climatic conditions also during the middle Miocene. The associated laterites and bauxites on middle Miocene basalts (17-15 Ma) provide evidence for a global climatic optimum around 17-14.5 Ma. Reduced uplift rates of the Himalayan-Tibetan Plateau and associated reduced CO2 consumption, coupled with additional volcanogenic CO2 production could have induced high atmospheric CO2 and an intensification of the global greenhouse effect. This may be reflected in accelerated chemical weathering and bauxite formation. Basalt volcanism has thus provided both a source (eruption) and a sink (via weathering) of CO2.