LONG-DISTANCE CORRELATIONS BY SEQUENCE STRATIGRAPHY AND CYCLOSTRATIGRAPHY - EXAMPLES AND IMPLICATIONS (OXFORDIAN FROM THE SWISS JURA, SPAIN, AND NORMANDY)

The Oxfordian sedimentary successions studied in the Swiss Jura, in No rmandy, and in the Soria and Cazorla regions of Spain display complex facies evolution and stacking patterns. Based on biostratigraphy and a bsolute age dating, it is suggested that the shallow-water depositiona l settings in the Jura, Normandy, and the Soria region as well as the deeper-water environments in the Cazorla region, recorded climatic and sea-level fluctuations in the Milankovitch frequency band. Beds and b edsets corresponding to 20-, 100-, and 400-ka cyclicities can be ident ified. Facies evolution inside such small-scale sequences and also in the larger sequences of million-year scale is interpreted in terms of sequence stratigraphy. Superposition of high-frequency cyclicity on a longer-term sea-level trend led to multiplication of diagnostic surfac es: sequence-boundary and maximum-flooding zones in the large-scale se quences can thus be defined. These zones are correlated between closel y spaced sections, but also from the Swiss Jura to Normandy and to Spa in. The narrow time lines given by Milankovitch cyclicity then allow c omparison of facies evolution in the different regions on a scale of 1 00 ka or less. By filtering out local effects of differential subsiden ce and sediment supply, a long-term sea-level curve valid for the nort hwestern margin of the Tethys ocean can be reconstructed for the Middl e to Late Oxfordian. Differential subsidence is implied from varying t hicknesses of the sequences as well as from the distribution of silici clastics which have been channelized through depressions. Tilted block s, reduced sedimentation, or increased input of siliciclastics appeari ng at the same time in all study areas point to a widespread regional tectonic event. Distribution through the sequences of climate-dependen t facies components such as corals, ooids, palynomorphs, and silicicla stics indicates that climate changes were dependent on atmospheric cir culation patterns and thus on paleolatitude. Rainy periods and related increase of siliciclastics in the Swiss Jura were more abundant durin g low sea-level stands, whereas in the Soria region they coincided wit h sea-level highs. Through the combination of high-resolution sequence stratigraphy and cyclostratigraphy, and supported by biostratigraphy and absolute dating, it becomes possible to analyze paleoenvironmental changes in a very narrow time framework.