CORRELATION OF UPPER JURASSIC LOWER CRETACEOUS CONTINENTAL SEQUENCES FROM THE SOUTHERN BISCAY MARGIN, NORTHERN SPAIN

Biostratigraphical data indicate that fresh-water carbonate deposits from the southern part of the the Cantabrian Basin, northern Spain are of earliest Cretaceous (Berriasian) age. Charophyte assemblages enable correlation with fresh-water carbonate rocks of the western Cameros Basin to the south. The charophytes also support correlation with Berriasian marginal marine carbonate sequences in the Jura Mountains, southern England and northern Germany, indicating that these continental carbonate rocks represent fresh-water equivalents of the 'Purbeckian' facies. The biostratigraphical correlation is enhanced by the parallel facies evolution observed in the Upper Jurassic-Berriasian of the Cameros and Cantabrian basins. Interpretation of these successions as non-marine depositional sequences permits member-scale correlation between the two basins. Further strong facies similarities in the overlying alluvial clastic rocks of the two areas suggest a revised correlation of the overlying Valanginian-Albian deposits. The two basins were connected at least intermittently during the Late Jurassic-Early Cretaceous; only during periods of higher sea-level did facies differences develop as a result of greater marine influence in the north. At other times, vast alluvial, lake and marsh systems extended over the region, leading to the deposition of genetically-related alluvial and lacustrine or palustrine deposits in these linked half-graben Systems. In Cantabria and the Cameros Basin, strong lateral variations in facies, thickness and stratigraphy reflect erosion at the onset of Late Jurassic rifting, differential subsidence in the Early Cretaceous, and erosion beneath Aptian-Albian unconformities. Improved understanding of the successions described here may assist interpretation of similar Upper Jurassic-Lower Cretaceous sequences on the northern margin of the Biscay rift, such as those in the Wessex and North Celtic Sea basins.