Layers of fibrous aragonite cement up to 2 cm thick, developed on aragonitic corals and micritic cements, occur in outcrops of Miocene coral reefs in western Sicily. These aragonitic fabrics show only minor amounts

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of corrosion after subaerial exposure for at least 3 m.y. Their preservation is attributed to encasement by subsequent gypsum cements. Although these botryoidal, banded aragonite cements are strontium-rich (7,000 ppm) and resemble modern marine examples, they were precipitated in secondarily enlarged pores that formed during erosional episodes. Multiple cycles of enrichment in oxygen and carbon stable isotopes are recorded in the aragonite cement layers. The ^dgr¹⁸O values of these cycles range from -0.9 to + 6.8^pmil, whereas the ^dgr¹³C values range from +0.6 to + 3.8^pmil (PDB). These cyclic variations, indicated by isotopic data together with the petrology of the cements, are believed to record major changes in salinity, temperature, and organic productivity f the Mediterranean waters during the Miocene-Pliocene transition. These Messinian reefs were subaerially exposed and later onlapped by the upper evaporite unit with multiple cycles of marine hypersaline carbonate and evaporite deposition separated by periods of erosion. Aragonite cements formed in the enlarged cavities of the lower Messinian reefs during time of deposition of the upper evaporite and recorded the changes in Mediterranean water chemistry. This cementation is believed to have continued into the early Pliocene when colder Atlantic waters invaded the Mediterranean, ending reef growth and evaporite deposition.

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