Recently collected high-resolution seismic records offshore the westernrnNetherlands, in a km-sized grid, suggest the presence of a dense, previously unknownrnnetwork of tidal-channel fills in the shallow subsurface of the North Sea. We analyzed thernsix channel fills comprising this network in detail to infer relationships among the fills inrntime and space, and to identify factors governing channel and tidal-basin development. Thernmajority of the channels are oriented perpendicular to the coast, but parts of some have arnstrong coast-parallel component. Shell associations and sedimentological characteristics inrnmost channel fills are typical of back-barrier depositional environments. The channel fillsrnare part of an Atlantic-age tidal-channel system, draining a tidal basin protected by barrierrnislands. The barrier-island chain was positioned at least 12 km seaward of the presentrncoastline in the northern part of the study area, and at least 6 km seaward of the presentrncoastline in the southern part. The tidal channels grew and migrated actively beforernpartially filling in between 7300 14C-yr BP and 5500 14C-yr BP, reflecting an initial tidalprismrnincrease followed by a substantial decrease. The tidal-prism increase was governedrnby a doubling of the tidal amplitude between 8000 14C-yr BP and 7000 14C-yr BP; thernsubsequent decrease by a gradual decrease of the rate of sea-level rise. Rapidrnretrogradation of the coastline put a sudden end to the existence of the tidal basin. Thernensuing shoreface erosion removed all but the deepest parts of the channel fills, which dornnot show any evidence of systematic landward migration. This field observationrncorroborates recent modeling results suggesting that rapidly increasing back-barrierrnaccommodation may create the conditions necessary for overstepping of sandy barriers.
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