Between 5 and 6 m. y. ago, at the climax of an episode of evaporite deposition, a series of events occurred on the floor of the Mediterranean Sea which left a fossil imprint reminiscent of a parched salina. The primary evidence of this unexpected happening was unearthed in the uppermost layers of a bedded sequence of evaporite salts of late Miocene age which were retrieved from beneath the present sea floor during Leg 13 of the Deep Sea Drilling Project. In continuous sections of core the shipboard scientific team discovered a remarkable transition from sterile chemical precipitates (gypsum, anhydrite, and halite) to deep-sea pelagic sediment. At all the sites drilled, the transition occurred between Miocene salts and Pliocene biogenic ooze.

In the eastern Mediterranean, the transition consisted of a 10-cm thick zone of dolomite gravel containing littoral benthonic fauna. Beneath the Balearic abyssal plain in the western Mediterranean, the corresponding zone is a 2-m thick bed of flat-pebble conglomerate directly overlying a massive unit of current-bedded gypsiferous sandstone. In the central Tyrrhenian basin the transition involved a pebbly breccia composed of lateritic soils, strikingly similar in lithology to the limons rouges of littoral sequences in North Africa and Italy.

The most plausible explanation of these findings is that a once actively precipitating deep brine basin became choked off from the open ocean and evaporation continued to the point of desiccation. Thereafter, the newly formed desert disappeared under a major marine inundation.

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