Significance of the upper miocene coral reefs of the Western Mediterranean

Abstract

Low-diversity Porites reefs of the Upper Miocene of the Western Mediterranean are more extensive and better developed than was previously thought. The distribution in time and space of different types of reefs, together with their particular ecology, leads to the concept of a retrogressive ecologic succession since the Middle Miocene in a partially isolated Mediterranean. The available data suggest that the entrance of colder Atlantic waters was the major environmental disturbance controlling the final stages (Messinian) of this retrogression. Several sea-level oscillations of a minimum of a few hundred metres are recorded in the reef complexes and related to the Messinian evaporite deposition all over the Mediterranean. The Terminal Complex, a Messinian shallow-water carbonate unit upslope equivalent to the Upper Evaporite, also contains Porites reefs. The generalized cyclic character of the Upper Evaporite is reflected by the repeated colonization of successive Porites buildings by huge stromatolites. The survival of Porites in the Terminal Complex seems quite hazardous; alternatively, the hypothetic immigration of corals from the east should be considered. The late corals of the Mediterranean are not comparable to modern tropical reefs.