Tertiary bauxites in subsidence areas and associated laterite derived sediments in Northwestern India

The bauxite-bearing laterites in Kutch/India are presented as an example for bauxites on downwarping platforms along passive shelves. During the tilting of the platform, the marine transgression and the rising of the groundwater level, the bauxite formation started. At the same time, their equivalents in the uplifted hinterlands were reworked, and the resulting products were deposited mainly in flood plains. They formed specific sediments called ? laterite-derived facies? = LDF. The formation of in-situ bauxites and associated laterite-derived sediments was connected with tectonic activities and related marine trans- and regressions. The short period of a few millions of years during the Lower Eocene was sufficient for a very effective mineralogical and geochemical reorganisation of the weathering profiles and sediments producing laterite and finally bauxite. The results of mineralogical and chemical investigations of saprolite-bauxite profiles and the sedimentary LDF are presented to characterize the unique surface processes occurring in the marine- terrestrial transition zone.