High-frequency cycles in the upper Aptian carbonates of the Organyà basin,NE spain

High-frequency cycles in Upper Aptian carbonates have been studied on the carbonate ramp of Organyà (southeastern Pyrenees). The depositional area comprises a shallow marine to deeper marine transect. A detailed facies model is developed subdividing the transect into an inner ramp area (above fairweather wave base), a mid-ramp area (between fairweather wave base and storm wave base) and an outer ramp area (below storm wave base). Based on microfacies analysis a cyclostratigraphic and sequence stratigraphic interpretation is established. Variations of the sedimentary patterns within different sections of the homoclinal ramp are due mainly to sea level changes. Sea level changes of third and fourth order are reflected by the shifting of the shallow subtidal facies belts up and down the ramp. The study of fifth-order sea level changes is based on statistical methods (quantitative facies analysis and principal component analysis). The ratio of the fourth- and fifth-order cycles is very similar to the well-known ratio of the eccentricity (100 ka) and the precession (18.6/22.5 ka). The absolute age values derived from the cyclostratigraphy fit into the biostratigraphic framework. Thus, a global eustatic control is assumed to be responsible for the cycles of higher frequency. The lower frequency third-order sequences, however, were considerably influenced by local tectonic processes.