The Terres Noires of south-eastern France (Middle and Upper Jurassic) sequence stratigraphy interpretation

The Sub-alpine domain in south-eastern France was located on the proximal part of the South-European Tethys margin. it includes the Dauphinois basin which is characterised by relatively high rates of subsidence during Jurassic and Early Cretaceous times. Monotonous black shares - the so-called Terres Noires - were deposited under considerable thicknesses from Late Bathonian to Early Oxfordian limes. The subsiding part was bordered by carbonate platforms which were limited by a net of extensional or strike-slip faults. The western border of the basin on the Massif central side was determined by steep fault scarps. On the other hand, the eastern side was a long and gentle submarine slope that separated the Digne basin from the Provence platform in the Nice area. The time span studied here extends on the duration of two second-order transgressive/regressive cycles sensu Vail. dated as early Late Bathonian to early Late Oxfordian. This corresponds to the deposition of the Terres Noires and of alternating calcareous mudstones and shales known as "Argovian Formation". These two second-order cycle can be subdivided into 16 third-order depositional sequences. The maximum regression at the base of the earliest second-order cycle coincides with the Tethyan break-vp unconformity and is dated as earliermost Late Bathonian. The first transgressive half-cycle (T8a) can be divided into an aggradational phase dated as Late Bathonian and is followed by a backstepping phase dated as lower part of the Early Callovian. The corresponding peak-transgression coincides with the lower part of the Gracilis Zone. The following regressive half-cycle (R8a) begins with the infilling phase dated as upper part of the Lower Callovian which concerns both the basin and its borders. The subsequent forestepping phase is dated as Middle Callovian and is marked by sedimentary gaps on the platforms that surround the subsiding area. The maximum regression that bounds the two second-order cycle is dated as upper part of the Lower Callovian. It records an extensional episode with block- tilting that concerned wide areas ct the European Craton. The trangressive part (T8b) on the second half-cycle is dated as Late Callovian and Lowermost Oxfordian, it is characterised by a rapid transgression that extended widely on the European Craton and culminated in the Scarburgense Subzone of the Mariae Zone. Therefore an aggradational phase can hardly be recognised that could predate this main backstepping phase. The next regressive half-cycle (R8b) is dated mainly as Oxfordian. Then platforms were characterised by superimposed erosional surfaces that resulted probably from the sedimentary transit towards the basin. The regressive hall-cycle (R8b) can be divided into two parts. The infilling phase is dated as Early Oxfordian and is characterised by high sedimentation rates in the basin. Then, during the subsequent phase of progradation dated as Middle Oxfordian, the deposition of shales graded progressively to limestones on both the basin and the adjacent platforms. This records the approach of the Late Oxfordian maximum regression. The Terres Noires of the Dauphinois basin together with its surrounding carbonate platforms can be considered an appropriate area to study the influence of the structural evolution onto the variation of the accommodation space and the distribution of sediment during a phase of crustal extension and relatively rapid subsidence.