Discontinuity surfaces on a shallow-marine carbonate platform (Berriasian, Valanginian, France and Switzerland)

Discontinuities in sedimentation are commonly expressed as surfaces in outcrop sections and are due to rapid and substantial environmental changes. On shallow-marine carbonate platforms most such surfaces represent hiatuses below biostratigraphic resolution, and detailed analysis is necessary to identify and evaluate the environmental change involved. Surfaces in nine sections of the Lower Cretaceous of the French and Swiss Jura platform are characterized on the basis of eight universally applicable criteria (geometry, lateral extent, morphology, biological activity, mineralization, facies contrast, diagenetic contrast, and biostratigraphy). Nine different surface types are distinguished by their common features and environment of formation. All of them are related to environmental changes in the form of subaqueous erosion, subaerial exposure, subaqueous omission, or changes in texture and facies. The distribution of surface types in the studied sections shows that condensation and exposure-related surfaces tend to occur repetitively in certain intervals. Calibrated by biostratigraphy, these surface zones can be correlated across the platform from proximal to distal positions. In comparison with the global sequence-stratigraphic framework (Hardenbol et al. 1997) most exposure zones correlate with third-order sequence boundaries; condensation zones fall in between. In the studied sections, third-order eustatic sea-level drops appear to be represented rather by zones of small-scale discontinuities than by widespread and well-marked