Triassic Transgressive-Regressive Cycles in the Bresse-Jura and Adjacent Basins, Eastern France

The Triassic units in the Bresse-Jura area have been extensively drilled for salt and hydrocarbon exploration. Subsurface correlations have recently been refined using current concepts and methods of genetic stratigraphy. The Triassic series in the Bresse-Jura area discloses a net superimposition of two-order Transgressive-Regressive cyclicities of a second-order type. The major Triassic depositional cycle developed from Scythian to Late Carnian times; it started with fluvial sandstones. The transgressive regime climaxed during the Ladinian with regionally extended deposition of marine carbonates. Sulfate-dolomitic depositional facies of the uppermost Muschelkalk, together with overlying Keuper salt­bearing lithologies, marked gentle regressive conditions. The regression was then forced, as evidenced by a clear basinward shift of siliciclastic deposition. Initiation in Late Carnian times of the next major depositional cycle was expressed by dolostones that rapidly spread over the former continental deposits. Transgressive conditions of this upper major cycle culminated much later during Liassic times. Four minor second-order cycles have been identified throughout the Triassic: Scythian, Scythian Anisian, Anisian-Carnian, and Carnian-Norian. Restored depositional geometries with superimposed depositional environments in the Bresse-Jura area plus interregional comparison with adjacent basins of eastern France have permitted the respective influence of tectonics and eustacy on second-order T-R cycles to be discriminated.