SEA LEVEL AND TECTONIC CONTROLS ON THE DEVELOPMENT OF THE SANTONIAN COLLADES DE BASTURS CARBONATE PLATFORM, SOUTH-CENTRAL PYRENEES, SPAIN

The Upper Cretaceous (Santonian) les Collades de Basturs carbonate platform in the south-central Pyrenees, Spain, was influenced by both tectonic and climatic controls. The platform lies on the south limb of the east-west trending Sant Corneli Anticline, where beds dip 70-90° to the south and provide a cross-section through the platform. The Basturs platform developed on the southern margin of the Pyrenean Basin that formed between Spain and France, during a phase of extensional tectonics in the Upper Cretaceous. Four main facies are recognized. Hippuritid biostromes with in situ rudists and a matrix of skeletal wackestone to grainstone record deposition on a shallow carbonate shelf. This facies is interbedded with a reworked hippuritid biostrome facies consisting of rudist floatstone to rudstone and skeletal grainstone created through wave activity. A deeper water reef facies composed of coral-rudist-sponge floatstone occurs down-dip on the slope of the platform. The deepest facies consists of marl and nodular skeletal wackestone with coral layers common throughout. These facies grade down dip from hippuritid biostromes and reworked hippuritid biostromes to coral-rudist-sponge reefs to deeper marls and nodular wackestone.

Les Collades de Basturs facies distributions reflect changes in sea level, tectonics, and sediment supply. Variations in sea level controlled the distribution of shelf facies. When sea level was low, shallow facies such as hippuritid biostromes and reworked hippuritid biostromes (rudist floatstone to rudstone and skeletal grainstone) were deposited on the shelf, while coral-rudist-sponge floatstone occurred on the slope. When sea level was high, deeper facies such as nodular limestone and marls were deposited across the entire platform. Facies distribution was also effected by tectonics through syndepositional faults, which localized the platform margin and resulted in a down-dip change from a shallow (hippuritid biostromes) to deeper (coral-rudist-sponge floatstone) reefs. High sedimentation rates during periods of shallow carbonate production resulted in progradation of shallow facies through time.