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Carbonate Platform Depositional Sequences in an Extensional-to-Compressional Continental Margin, Upper Cretaceous, South-Central Pyrenees, Spain

A. Simo

Upper Cretaceous stratigraphy in the south-central Pyrenees reflects the spreading of the European and Iberian plates and the later continental subduction of the Iberian plate underneath the European plate. Detailed field mapping has identified five major stratigraphic sequences, each bounded by global unconformities.

Lower Cenomanian, lower Turonian, and middle Coniacian unconformities record short and small sea level drops followed by big and rapid sea level rises. Lowstands caused sporadic subaerial exposure, local siliciclastic influx to the inner platform, and cessation of the sediment supply to the basin. Subsequent rapid sea level rises drowned the entire platform and preserved depositional relief. Highstands induced backstepping (average of 18 km) of shallow-water carbonate sedimentation. Backstepping superimposed on topographic relief resulted in a deepening of the basin, an increase in the length of the depositional slope, and a narrowing of the platform.

The middle Santonian unconformity represents the onset of regional compressional tectonism and rapid transgression. As a result, an unstable trough filled by siliciclastics was formed. Transgression allowed for continued platform backstepping and generated 160 km of coastal onlap of carbonate sediments.

The upper Campanian and upper Maastrichtian unconformities are related to thrusts induced by the collision of the two plates. Thrusting modified basin morphology, produced a generalized shallowing of the basin, and increased siliciclastic supply which subsequently filled the basin.

Results of this study indicated that relative sea level rises, inherited depositional profile, and tectonism controlled carbonate platform evolution and associated depositional facies.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.