Aalenian and Bajocian depositional sequences on the Burgundy High (France)

Sedimentologic, biostratigraphic and diagenetic studies made on Middle Aale nian to Lowermost Bathonian deposits in 25 outcrops of the Burgundy High (s outheastern Paris basin) lead to a sequence stratigraphy subdivision of the early Dogger record into 7 third order depositional sequences. These seque nces make up a second-order transgressive phase whose lower limit is a tect onically enhanced unconformity (the Mid-Cimmerian unconformity), associated with a large scale uplift during the Upper Toarcian and the Lower Aalenian . In the largest outcrops, where the geometry of sedimentary bodies is obse rvable at the hectometre to kilometre scale, the combination of diagenetic, biostratigraphical, spatial and sedimentologic studies is useful to unders tand the evolution of sediment distribution in the sequences. This approach also allows the measurement of sea level falls at the origin of the sequen ce boundaries. For example, we show that Lower Bajocian sequences end with decreases of accomodation space < 10 m in amplitude, leading to temporary e mergences of some reef complexes. Without interrupting the sedimentation on submarine peri-reef pediments during lowstands, these decreases of a few m etres of accomodation space can be related to either tectono-eustatic event s or thermo-eustatic events.