RESPONSE OF REEF GROWTH TO SEA-LEVEL CHANGES (LATE MIOCENE, FORTUNA BASIN, SOUTHEASTERN SPAIN)

Response of reef development to sea level is well displayed in the 70-m-thick upper Miocene El Desastre reef complex, Fortuna basin (Murcia Province, southeastern Spain). Conglomerates that show evidence of subaerial exposure characterize the sea-level low stand; reefs ag-graded as relative sea level rose tens of meters. The reef developed on an erosional platform (about 1.5 km(2)) carved into older reef-slope sediments. It exhibits evidence of start-up, catch-up, and Keep-up patterns of growth. Rapid relative sea-level rise flooded the platform to depths as great as 25 m. Prior to initiation of reef sedimentation (start-up phase), a lag phase of unknown duration occurred during which foraminifer wackestones and packstones accumulated. Following the lag phase, reef sedimentation yielded 20 to 40 m of fossiliferous packstones. Corals proliferated and eventually caught up to the sea-level surface, henceforth, the keep-up pattern of reef growth prevailed. Growth rates of branching-corals reflected chan,bes in sea level, which rose episodically producing distinct layers of corals and coralline algae up to 1.5 m thick. Seaward, a poorly developed algal ridge formed. The layers of flat-topped corals and algal ridges precisely record successive Miocene sea levels. The keep-up phase failed and the reef reverted to a catch-up style of growth, perhaps clue to accelerated sea-level rise, foul wafers, or isolation by a seaward barrier. Studies of similar-age reefs in the area and their inferred sea-level curves could shed light on the relative importance of eustatic and tectonic influence on sea-level change in the western Mediterranean during the late Miocene.