RODRIGUES DE MIRANDA, DEBORA, Univ. of Wisconsin--Madison, Madison, WI; and A.J. SIMO, Univ. of Wisconsin--Madison, Madison, WI

ABSTRACT: What Controls Cyclicity in the Upper Cretaceous Sant Corneli Platform, South-Central Pyrenees, Spain

The Coniacian-Santonian Sant Corneli platform is characterized by a succession of meter-scale subtidal shallowing upward cycles that can be traced from shelf to basin for several kilometers. There is a lower and an upper mixed carbonate-siliciclastic interval and a middle carbonate interval. The platform shows significant thickness difference between shelf (700 m) and upper slope (200 m). Low relief rudist- and coral buildups occur on the platform and form the margin.

Each cycle of the upper mixed interval starts with a poorly sorted, skeletal-rich, thin grainstone bed, overlain by fine-grained, bioturbated peletal wackestones. Skeletal packstones deposited in foresets, with upward decreasing depositional dip and with a consistent NNE progradational direction, overlie these wackestones. The cycle top consists of cross-bedded, well-sorted grainstones. Quartz grain size and abundance increase upward. Within 50 meters (basinward), the cross-bedded grainstone bed grades laterally into foresets and then into wackestone. However, the basal poorly-sorted grainstone continues basinward, separating successions of wackestones.

Meter-scale cycles can be explained by a combination of rates of carbonate production, clastic input, and wave damping. High sediment supply and wave action caused cycle progradation. However, as the platform built out, reduced water depth and reduced potential of marine reworking slowed down progradation. The stacking pattern shows a deepening trend which suggests that although sediment accumulation and wave energy could have controlled cyclic deposition at a local scale, deposition of larger-scale intervals was controlled by rising relative sea level.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.