RELATION BETWEEN PALEOCEANOGRAPHIC CIRCULATION INTO THE WESTERN PALEO-MEDITERRANEAN SEA AND FACIES OF AN UPPER MIOCENE CARBONATE RAMP AND PLATFORM, MELILLA BASIN, NE MOROCCO

Upwelling of cool seawater, paleoceanographic circulation, paleoclimate, local tectonics and relative sea-level change controlled the lithofacies and sequence stratigraphy of a carbonate ramp and overlying platform that are part of a temporally well-constrained carbonate complex in the Melilla basin of northeastern Morocco. From oldest to youngest, a third-order depositional sequence within the carbonate complex contains (1) a transgressive, retrogradational, warm temperate-type rhodalgal ramp; (2) an early highstand, progradational, bioclastic platform composed mainly of a temperate-type, bivalve-rich molechfor facies; and (3) late highstand to forced regressive, progradational to downstepping, subtropical/tropical-type chlorozoan fringing Porites reefs. The change from rhodalgal ramp to molechfor platform occurred at about 7.0 Ma, near the Tortonian/Messinian boundary. A transition from temperate-type molechfor facies to subtropical/tropical-type chlorozoan facies occurred during a late stage in the development of the bioclastic platform and is bracketed by chron 3An.2n (~6.3 to 6.6 Ma).

Comparison of the Mellila basin ramp and platform to a well-dated carbonate complex located in southeastern Spain at Cabo de Gata suggests that upwelling of cool seawater influenced production of temperate-type limestone at Melilla during postulated late Tortonian-early Messinian subtropical/tropical paleoclimatic conditions in the western Paleo-Mediterranean region. The upwelling of cool seawater across the bioclastic platform at Melilla could be related to the beginning of “siphoning” of deep, cold Atlantic waters into the Paleo-Mediterranean Sea at 7.17 Ma. The facies change within the bioclastic platform from molechfor to chlorozoan facies may be coincident with a reduction of the siphoning of Atlantic waters and the end of upwelling at Melilla during chron 3An.2n.