Geodynamics of Bauxites in the Tethyan Realm

Bauxites, particularly the karst-type deposits, are closely related to the history of the Tethys. Four main modes of origin can be distinguished: autochthonous, parautochthonous, parallochthonous, and allochthonous. A simple classification of the deposits is proposed according to their location in relatively high level, intracontinental domains, on pericontinental lowlands or on insular platforms. The secondarily redeposited bauxite accumulations are considered a separate group. Bauxite formation in the Tethys area was a discontinuous process, which began during the Late Permian in the area of the present Middle East and progressed westward following the gradual separation of Laurasia and Gondwana. It reached a peak during the Mid-Cretaceous and two minor peaks in the Malm and the Paleocène. A further major peak occurred during the Late Miocene in the Caribbean area. Study of these periods shows that several favorable factors promoted the formation of bauxite: 1.Tropical and subtropical, humid, monsoon climate, a low equator-to-pole temperature gradient, and a high atmospheric CO₂ and O₂ content.2.High eustatic sea level, leading to the submergence of the coastal lowlands and contributing to the development of a humid climate.3.Tectonic instability. Most bauxite deposits in the Tethys area are allochthonous. The instability favored the erosion of the weathering profiles and the accumulation of clastic bauxitic material.4.Paleogeography. The distribution of the bauxite deposits followed the opening of the Tethys sea in a westerly direction. The wedge-shaped coastline guided the warm ocean currents and the clouds westward, where the carbonate platforms and the bauxite deposits could form under the most favorable climatic conditions.