Because of large eustatic variations, quaternary sedimentary record, on low subsidence passive continental margins, is reduced to incised valley fills and provide opportunities to study single stratigraphic sequences emplaced during the last sea level cycle (125-0 Ky). Those relatively thin deposits (tens of meters) allow to use Very High Resolution seismic profiling. Such data give very accurate images of the 3D architecture of those sediment deposits and then are useful analogues for deep reservoirs. We have recorded an extensive seismic survey of an incised valley (Charente river, French Atlantic coast) from its present-day estuary to its outer segment. The comparison of this outer incised valley infill with the Gironde one, show that small differences are interpretable as the consequence of their respective drainage basin and sediment supply. One particularity of the Charente drowned valley is the occurrence of a valley segment without any sediments at the transition between the outer segment and the present-day estuary. We compare those two disconnected valley fills which record the last Holocene transgression in two environments : wave an tide dominated (outer segment) and tide dominated (middle segment). Unlike the relatively simple stratigraphic pattern of the outer valley segment (high energy environment deposits at bottom and top with an intervening low energy unit), the middle segment fill displays large stratigraphic differences depending mainly of the present-day hydrodynamic setting. Within high velocity current areas, we observe an increasing energy environment record, as within low velocity current areas, the internal stratigraphic architecture indicate decreasing energy environments.
SEPM Research Symposium: Processes and Images of Incised Valley and Lowstand Deposits I