Structural and Faunal Evolution of Chattian — Miocene Reefs and Corals in Western France and the Northeastern Atlantic Ocean
Bruno Cahuzac, Christian Chaix, 1996. "Structural and Faunal Evolution of Chattian — Miocene Reefs and Corals in Western France and the Northeastern Atlantic Ocean", Models for Carbonate Stratigraphy from Miocene Reef Complexes of Mediterranean Regions, Evan K. Franseen, Mateu Esteban, William C. Ward, Jean-Marie Rouchy
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Chattian and Miocene coral reefs and faunas of the western France basins are reviewed within a paleogeographic context. Several new outcrops have been discovered, and extensive new and historic collections have been studied. Coral diversity was very high in the Aquitaine basin during the Chattian(1) (ca. 150 species) and a little less so during the Early Miocene (110 species); during these times, relatively small reefal buildups formed in a tropical climate. The Mid-Miocene coral faunas show a marked decrease in diversity (some 75 species in all), with "subreefal" facies in the Langhian of southwestern and northwestern France. The Upper Miocene fauna is even poorer (just about 20 species) and only known in northwestern France. Throughout the Miocene, the proportion of hermatypic taxa also decreased notably; in the coral assemblages, these species were strongly predominant from Chattian to Burdigalian. Afterwards, the ahermatypic taxa became progressively predominant. Other northeastern Atlantic areas (Portugal, Morocco) are also investigated. Some biogeographic data sketch the evolutionary trend of these coral communities. During the Chattian, an (eastern and western) Atlantic-Mediterranean bioprovince was differentiated. During the Early Miocene, this bioprovince was restricted to eastern Atlantic and Mediterranean. From the Mid-Miocene, the coral faunas were disconnected from the Mediterranean, and an impoverished eastern Atlantic bioprovince became established without real renewal. A comparison with Mediterranean reefs shows that maximum coral building took place within the Mid-Miocene in the Mediterranean realm (with continuation of reefs in the Late Miocene), instead of Chattian (and Early Burdigalian) as in the Atlantic areas.
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Miocene carbonates are intensively explored and locally exploited for hydrocarbons in parts of the Mediterranean regions. The outcrop models presented in this publication provide excellent analogs for the highly productive Miocene carbonates from Iran, Iraq and Gulf of Suez and for smaller reservoirs in other localities. Lessons learned in the outcrops of the Mediterranean regions are applicable as well to Miocene carbonate reservoirs. The Miocene outcrops in Mediterranean regions can serve as models for the relationships between carbonate reservoirs, pre-evaporitic basinal sediments, and overlying evaporites. Additionally, the Miocene carbonate rocks exposed in the Mediterranean regions serve as important analogs for ancient carbonate-rimmed basins with or without basinal evaporites.