The Barremian–Aptian Urgonian platforms from southeast France: towards a regional chronostratigraphic model?
Résumé
Since the 19th century, southeast France is recognized as a key area for the study of Early Cretaceous geological systems, particularly those of the Barremian–Aptian period. Reference unit-stratotypical sections of this time interval has been defined in the Vocontian Basin and surrounding carbonate platforms, the so-called “Urgonian limestones”. In addition, standard eustatic curves and biostratigraphic charts of both shallow-water and basinal index species for the Barremian–Aptian transition mostly derive from the Vocontian domain and its margins.
Urgonian platforms are considered as valid outcrop analogues of Middle East oilproducing carbonate reservoirs. Uncertainties in predicting subsurface sedimentary and petrophysical heterogeneities can, therefore, be reduced from their analyses. However, geologists from different “schools of thought” developed contrasting models regarding the chronostratigraphy, the sedimentary model and the overall architecture of the peri-Vocontian Urgonian platforms. As a result, the geological characterisation of Urgonian carbonate bodies remains a matter for debate that hampers the harmonisation of a regional platform model.
Based on a thorough historical review, our study explores some of the major debates by providing a complete synthesis of the literature and a re-examination of current concepts. Integration of available data together with the acquisition of new material bring extra evidences and constraints for addressing past controversies. First results document a comparable regional stratigraphic evolution despite a significant syndepositional tectonic activity. Global changes in sedimentary system and possible links to oceanographic changing conditions across the Barremian–Aptian boundary are also examined.