RECONSTRUCTION OF DEPOSITIONAL-ENVIRONMENTS OF DELTA PLAIN ORGANIC SEDIMENTS - APPLICATION TO THE SEDIMENTOLOGY OF THE BRENT-GROUP (NORTH-SEA)

The organic rich sediments (coals and coaly shales) record particular events in the delta plain sedimentation history. Reconstructing their depositional environment gives palaeoecological and sedimentological i nformation permitting the use of these coals and shales as regional is ochronous markers. There is a wide variety of diagrams used for recons tructing the depositional settings of coals and coaly shares. They all are based on two types of petrographic analysis, rarely used in combi nation: maceral and microlithotype analyses. This synthesis work is ba sed on a large number of combined analyses (575 samples) and takes int o account the sedimentologic and sequential context. We propose an upd ating of the most commonly used diagrams, as well as the guides to the ir interpretation and give the example of a regional study of the Bren t Group fluvial-deltaic series (Mid Jurassic, North Sea).