Kim Cohen, Utrecht University (Netherlands)
Marc P. Hijma, Utrecht University (Netherlands)
Esther Stouthamer, Utrecht University (Netherlands)
Ad J.F. Van der Spek, Deltares (Netherlands)
Sytze Van Heteren, Deltares (Netherlands)
The Early Holocene landscape of Rotterdam was a wide Rhine river plain flanked by slightly higher terrain of last glacial age. It is now buried below 15-20 m of Holocene sediment. 12000 years ago sea-level stood over 50 m lower than today and the shoreline was at distance downstream. By 9000 years ago, the area started to experience post-glacial transgression and coastal prism aggradation set on. By 6000 years ago, sea level had risen to within 5 m of the present level, and great volumes of early-middle Holocene Rhine sediment had been accommodated below it. The landscape had evolved from a low land alluvial valley into a barrier-lagoon system, with several river outlets that functioned as estuaries. Upstream in the back-barrier lagoon the Rhine-Meuse delta developed coevally.
Especially for the episode of rapid sea-level rise and rapid drowning (9500 - 6000 years ago) interlinked reconstruction of developments at the Rhine mouth is a challenge. We collected archived data from various sources, obtained new material from cores and underground railway construction pits. >100,000 corings/cone penetration tests, detailed offshore seismics, >200 relevant 14C and OSL datings, and numerous pollen/diatom counts were made available (efforts of Utrecht University; TNO B&O Netherlands Geological Survey; BOOR Rotterdam City/Harbour; others).
The material so far allowed to:
(1) Reconstruct early Holocene ground water level rise during valley, initial transgression and lagoonal stages by dating laterally-extensive basal peats that overly Early Holocene floodplains and flanks of inland dunes. This extends the window of sea-level rise reconstructions in the Rotterdam area back in time by ∼1000 years to ∼9000 cal BP at ∼22 m-MSL.
(2) Reconstruct the sedimentary architecture of the Early-Middle Holocene base of the Holocene coastal prism in detail. This includes avulsive backstepping and termination of fluvial sand bodies into the rapidly drowning area, the nature of tidal inlet channels and associated floodbasins during eustatic transgression, and initial coastal barrier formation when eustatic high stand was approximated ∼6000 years ago.
We present the interlinked coastal and fluvial development of the lower Rhine-Meuse delta, based on the accumulated data set and our mapping approach.