Questioning carbonate facies model definition with reference to the Lower Cretaceous Urgonian platform (SE France Basin)

A facies model, which is generally used to fill data gap, is based on multiple data integration and correlation, interpretation and concepts. Main uncertainties of model build up reside in chronostratigraphic interpretations, synchronous strata correlations, palaeoecology of extinct ecosystems, poorly recorded palaeotopographic profiles and contemporaneous palaeoecological successions. The precise recording and tracking of data and concepts that were used to support model interpretation and definition represents a great challenge for the geologists who build a facies model and is close to impossible for the user of a facies model. The present study explores a methodological workflow to define a well-supported facies model. An exhaustive literature review is presented on sedimentary facies and profiles of Urgonian carbonate platforms from SE France and Switzerland (Barremian–Aptian interval). The study provides a thorough analysis of available data to propose a harmonised and integrated facies model. The conceptual evolution of the Urgonian model through time is investigated to help comparing published models. The structure of the conceptual model and table of depositional facies shows a consistent organisation of specific elementary facies, facies associations and carbonate system; the model promotes the study and understanding of sedimentary processes. Quantitative analyses of facies belt extent and palaeobathymetric estimation are provided. The resulting sedimentary profile is based on general palaeoecological and sedimentological concepts, facies distribution on palaeogeographic maps and consistent stacking trends. In very rare locations, direct lateral facies belt transitions are recorded. Proximal depositional facies are rarely observed; most outcrops record the (i) rudist facies association, which corresponds to distal parts of the inner platform, (ii) coral, ooidal and bioclastic facies associations, which are interpreted to occur on the outer platform, and (iii) calcisiltite, slope and basinal deposits. Key data and concepts allow for the building up of a robust, harmonised facies model that can be used to properly interpret palaeoenvironmental changes, stacking trends and stratigraphic sequence evolution, the resolution of which depends on the available chronostratigraphic framework.