The 18O/16O and 13C/12C ratios of about 250 dolomite and limestone samples from the Malm of Southern Germany were measured and the results have been compared with information obtained from microscopic studies.The dolomites were formed by dolomitization of marine limy sediments, more or less penecontemporaneously with the precipitation of the calcitic sediments, i.e. during Jurassic time. During post-Jurassic time these dolomites were partly dedolomitized. The distinction between a centrifugal and centripetal dedolomitization was possible and both occurred under the influence of circulating fresh-water. Centripetal dedolomitization leads very often to the formation of saccharoidal limestones, a process which probably is still going on today.

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