Present-day estuaries are progressively filled by sediments since the last Holocene transgressive phase. They provide an opportunity to evidence how analogues of deep reservoirs, like sandbanks, area preserved.
We present very high resolution (VHR) seismic data, recorded within mixed tide and wave dominated estuaries of the French atlantic coast. Those estuaries are characterized by small fluvial input due to reduced river drainage areas.
Seismic data interpretations are constrained by vibracore sampling and repetitive bathymetric surveys recorded since the begining of the 19th century.
We focus on sand banks capped below a mud dominated sheet drape. Three examples are presented, each one illustrating sandbank preservation at various present-day water depth. From shallow water to relatively deep water, we describe : (1) the nearshore prolongation of a present-day prograding coast; (2) remnants of old prograding coasts recording a lower sea level, located at the foot of a present-day sand spit; (3) Preserved sand waves made of reworked transgressive marine sands.
The three preserved sandbanks display similarities concerning their sedimentary facies succession with sands at base and mud at top of cores. Such sedimentary evolution may indicate strong and recent (< 2 ky) sedimentary environnement changes that we propose to link with : (1) rapid seaward coastal migration and/or (2) climate change. Despite similarities, sand to mud transition do not include the same period of time for the different sand banks.
SEPM Research Symposium -- Processes and Images of Incised Valley and Lowstand Deposits