EVIDENCE FOR SYNTECTONIC GROWTH OF A SANTONIAN CARBONATE PLATFORM ON THE SANT CORNELI ANTICLINE, SOUTH-CENTRAL PYRENEES, SPAIN

Upper Cretaceous carbonate strata of the South Central Pyrenees, Spain, preserve backstepping geometries that record the transition from regional extensional to compressional tectonics in response to the formation of the Pyrenees Mountains. In particular, Santonian-aged platform facies occur on the flanks of the syndepositional Sant Corneli anticline and provide some of the earliest evidence of compression in the region, making them useful for refining the early tectonic history of the Pyrenees. The Sant Corneli anticline is a south-verging thrust propagation fold related to the Boixols fault, the oldest thrust in the eastern region of the South Central Pyrenean thrust sheet system.

Santonian rudist/coral build-ups and skeletal grainstones interpreted to be shallow platform facies are well documented on both the northern and southern flanks of the Sant Corneli anticline. Recently, margin strata interpreted to be of Santonian age have been recognized on the crest of the anticline as well. In a regional sense, Santonian margin facies are restricted to the Sant Corneli anticline, and are surrounded on all sides by deeper water facies that lack evidence of shoaling. Based on the affinity of carbonates for growth in shallow water, it is plausible that the anticline localized shallow carbonate production by providing an elevated sea floor. Regionally, the Upper Cretaceous platforms propagate from the south to the north. However, Santonian carbonates on the Sant Corneli anticline show a more complex pattern, reflecting the response of the platform to the local influences of the growing anticline. In particular, continuous outcrops on the southern flank record simultaneous progradation of rudist/coral biostromes to the northwest, and sand-rich calcarenites to the northeast, into the same depocenter.

Compression in this transect of the South Central Pyrenees is conventionally interpreted to have begun in the Campanian, after deposition of the Santonian platforms. However, syntectonic carbonate growth along the crest of the Sant Corneli anticline suggests Santonian compression. A Santonian age for initial compression would match the onset of unconformable siliciclastic turbidite deposition towards the western region of the South Central Pyrenean thrust system.