Reef geometries and facies in Bajocian limestones of the Burgundy High (France): Environmental and sequence stratigraphy interpretations

In the southeastern Paris Basin. several wide Bajocian outcrops (natural cl iffs and quarries) show coral reefs rimmed by paleoslopes up to 50m high. F acies, geometries and diagenetic studies clarify the palaeoenvironmental an d sequential setting of the Bajocian carbonate platform and reveal cyclic r elative sea-level changes during reef development. Two basic types of reef architecture are distinguished. Type 1 architecture corresponds to large pinnacles aggrading 30 to 50 m over underlying Aaleni an and lowermost Bajocian limestones. Type 2 architecture corresponds to el ongate reef structures growing above and along normal synsedimentary faults . Large pinnacles include either coral framework facies and coral debris an d sometimes prograde thousand meters into various directions, but mainly to wards W and SW, suggesting an hydrodynamic control by waves coming from the east (from the Tethys). In the best exposed reef complexes, the cyclic aggradational-progradational geometry of reefal and peri-reefal deposits points out 3 depositional sequ ences during the Propinquans and Humphriesianum Lower Bajocian ammonite zon es. These sequences end with a sea level fall which does not exceed 10 mete rs in amplitude, leading to temporary emergence of some of the reef crests.