Seismic stratigraphy and Quaternary sedimentation in the Skagerrak (northeastern North Sea)

Abstract

Ice movement, sea-level fluctuations and currents are the controlling factors of the Late Pleistocene and Holocene sedimentation processes in the Skagerrak. The erosional truncation at the top of a Mesozoic depositional sequence defines the extent of the Norwegian Channel and functions as the initial depositional surface for Quaternary sedimentation. On this surface in shallow waters off the Danish coast, Weichselian glacial sediments are deposited. An end-morain ridge marks a temporary stillstand of the retreating ice front. At the beginning of ice-free conditions some 15,000 yrs ago when the sea was about 70 m below the present level, the Skagerrak was a fjord-like forebasin of the Northern Atlantic, and constituted a favorable outlet for rivers draining the subaerial glacial deposits of the southern Skagerrak and the present southern North Sea. Fluvial erosion released large amounts of detrital material which was laid down in the form of a progradational delta-prodelta complex. Slumping and mass-flow processes led to high sedimentation rates and a rapid infilling of the Norwegian Channel in front of the delta complex. With the rapid transgression of the southern North Sea at the beginning of the Holocene, a dramatic change in the depoenvironment of the Skagerrak took place. The modern current pattern became established, whereby sediment transport and redeposition became the rule along the Danish coast. Sandwaves and megaripples with an apparent northeasterly migration direction were formed as a result of the wind-forced Jutland Current. Fine suspended particles bypass the coastal zones to settle out in the deep Norwegian Channel.