DOLOMITIZATION STAGES OF MARINE DIATOMITIC DEPOSITS FROM THE SUBMERGED PERUVIAN MARGIN

Dolomitic Late Miocene to Pleistocene diatomites have been collected d uring the Nautile cruise along the Pacific convergent margin off Peru. Petrographic studies (Cathodoluminescence, SEM, electron microprobe) reveal several stages of dolomitization of an initial siliceous mud. S everal micritic and sparitic fabric phases of the sediment are control led by the initial composition, by the early hydroplastic deformation of the soft sediment; at least three fracturation stages have been obs erved. These phases are controlled by the differential compaction of t he thick soft mudstones, siltstones and diatomitic oozes, along the sl ope. Compaction processes favoured the circulation of interstitial flu ids and the dolomitization process throughout the burial period.