TECTONIC, SEA-LEVEL, AND PALEOECOLOGICAL CONTROLS ON CARBONATE FACIES DISTRIBUTION, SANTONIAN SANT CORNELI FORMATION, SOUTH-CENTRAL PYRENEES, SPAIN

The Santonian (late Cretaceous) Sant Corneli Formation, south-central Pyrenees (Spain), is a spectacularly exposed example of a carbonate platform system that is controlled by accommodation change related to relative sea level, tectonics, paleoecology, climate and external sediment input patterns. The platform system formed on the southern margin of the Pyrenean rift basin, and records the interaction of two sediment sources: (1) a regional quartz-rich skeletal grainstone source prograding to the north (Aramunt Vell Mb), and (2) an isolated westward prograding rudist-coral-sponge ramp localized on top of the growing Sant Corneli / Boixols anticline (Collades de Basturs Mb).

Outcrops on the southern limb of the Sant Corneli anticline record three orders of cyclicity between deeper marl and shallower rudist biostrome and skeletal grainstone-rudstone facies, interpreted to be primarily driven by changes in relative base-level. Meter-scale cycles of in situ rudist biostromes and reworked skeletal debris stack into decameter-scale platform units that prograde and retrograde in response to eustasy and tectonically controlled changes in accommodation. The northern flank of the anticline records deposition in a higher energy ramp environment and preserves cycles of steeply (up to 12°) prograding quartz-rich grainstone shoals interbedded with rudist-coral-sponge biostrome facies. On both flanks of the anticline, the rudist facies decrease to the west (away from the anticline crest) as quartz-rich grainstone facies increases.

Syndepositional growth of the eastern part of the Sant Corneli / Boixols anticline provided suitable conditions to nucleate a rudist carbonate platform that was isolated from the regional, land-attached grainstone system. Critically, carbonates on the crest of the anticline lack clastic input, and so developed extensive low-angle rudist-coral-sponge biostromes. At the same time, the quartz-rich grainstone system prograded northward over the western end of the current Sant Corneli / Boixols anticline, indicating it had yet to form a topographic barrier. Ultimately, understanding the carbonate growth history and facies distribution of the Sant Corneli carbonate platforms help to unravel the complex and episodic growth of the Sant Corneli / Boixols anticline.