Depositional architecture of a rimmed carbonate platform (Albian, Gorbea, western Pyrenees)

Abstract

A Lower Cretaceous carbonate platform depositional system with a rimmed margin and an adjacent oversteepened slope was analysed in order to determine its depositional architecture and major depositional controls. The platform is made up of coral, rudist, orbitolinid and algal limestones and, in a 12‐km dip transect, there is a gradation from lagoon to platform margin, slope and basin environments, each characterized by distinctive sedimentological features and facies associations. The rimmed platform is an aggradational system developed during approximately 4·2 million years of fluctuating relative sea‐level rise, and it is bounded by unconformities at its base and top. Internal cyclicity in the construction of the system is evident, mainly in platform interior and slope settings. The seven recognized sequences average 0·6 million years in duration and are related to minor relative sea‐level changes. Carbonate deposition occurred in shallow‐ and deep‐water settings during periods of high relative sea level. Reduced rates of sea‐level rise led to the development of shallowing upward sequences and, eventually, to the exposure of the shallowest parts of the platform during relative sea‐level falls. During low relative sea level, erosion surfaces developed on the slope, and gravitational resedimentation occurred at the toe of slope. Basinwards, resedimented units pinch out over distances of a few hundred metres. Active faults controlled sedimentation at the platform margin, promoting the development of steep slopes (up to 35°) and preventing progradation of the shallow‐water platform, despite high sediment production rates. The development of sequences is interpreted to be related to tectonic activity.