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

Abstract

Designing carbonate facies models requires the integration, correlation and conceptual interpretation of multiple geological data sets. Potential significant errors are sourced from uncertain stratigraphic correlations, speculative palaeoecological interpretations and poorly recorded palaeotopographic profiles. The present study explores a methodological workflow to define a well-supported facies model. An exhaustive literature review is presented on sedimentary facies and depositional profiles of Urgonian carbonate platform from SE France and Switzerland (Barremian–Aptian interval). The historical evolution of Urgonian facies models and related sedimentological concepts is investigated to contextualise published models. The presented conceptual model and table of depositional facies shows a consistent, process-based organization of specific elementary facies, facies associations and carbonate system. Within the chronostratigraphic framework, the study of synchronous strata correlations provides quantitative analyses of facies-belt extents and palaeobathymetric estimations. The resulting depositional profile is based on general palaeoecological and sedimentological concepts, facies distribution on palaeogeographic maps and stacking trends. In rare locations in the field, direct lateral facies belt transitions are recorded. Proximal (i.e. emersive and peloidal-foraminiferal) 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.