Quantitative stratigraphy of rudist limestones and its bearing on spatial organisation of rudist communities: the Late Barremian, Urgonian, sequences of Provence (S.E. France)

Rudist beds in platform carbonates of Late Barremian age (Early Cretaceous) cropping out in the Marseille region (Provence, SE France) possess a substantial lateral continuity (>40 km) whereas associated rudist bodies tend to be less continuous. Transition probabilities (Markov chain analysis) are used at a regional scale to test the lateral continuity of rudist bodies and their four associated rudist assemblages. Each rudist assemblage has a specific probability to be adjacent to itself or to any one. At a local scale, analysing the variations of transition probabilities as a function of distance, using various proxies, shows a periodic spatial trend, the style of which depends on the type of rudist assemblage, i.e., community type. The foregoing documents two groups with different properties. Group 1 includes two communities characterised by small forms restricted to very shallow and muddy settings, organised spatially into small patches (c. 1000-1500 m) with moderate spacing (c. 1500-2000 m). Group 2 includes two communities characterised by mixed size or large forms, typical of deeper water and more sandy settings, organised spatially into large patches (c. 3000 m) with a larger spacing (c. 3000-4000 m). The internal architecture and the dimensions of these rudist bodies argue against a reefal nature. Quantitative estimates of lateral continuity and spatial variations of rudist bodies have a significant potential for reservoir modelling of hydrocarbon-bearing rudist-rich platform carbonates.