Depositional environment of the Vejle Fjord Formation of the Upper Oligocene-Lower Miocene of Denmark: a barrier island/barrier-protected depositional complex

Abstract

The Vejle Fjord Formation was deposited in the coastal area at the eastern margin of the Upper Oligocene to Lower Miocene North Sea. Detailed studies of lithology and depositional structures demonstrate that coarsening-upwards successions resulted from landwards migration of barrier complexes as a response to relative sea-level rise. The formation of barriers, their migration and construction of new barriers was controlled by a varying balance between sediment supply and sea-level rise. The exposed sediments are mainly back-barrier deposits and represent deposition on the lagoon-facing barrier beach, wash-over fans, tidal flood deltas, tidal flats and the lagoonal floor. The barriers themselves are only sparsely represented in the studied exposures. Their influence on the depositional pattern is revealed by the formation of storm wash-over deposits and tidal inlet/tidal delta deposits. The destructional pattern of the barriers (storm erosion or tidal inlet widening) was apparently controlled by the orientation of barrier sections relative to the prevailing storm direction. A back-barrier beach deposit was developed with landwards-dipping heavy-mineral lamination. It forms part of a shallowing-upwards succession and represents a transgressive phase. Wash-over sands are up to 50 cm thick massive sand beds which pinch out laterally and interdigitate with lagoonal mud. Tidal inlet/tidal delta deposits are sandy intercalations in the lagoonal mud. The thickness is highly variable and marginal parts are strongly bioturbated. The tidal flat facies is dominated by small-scale channel fills of heterolithic deposits with a distinctive tidal rhythmicity, both on a single-tide scale and a neap—spring scale. The Vejle Fjord Formation is constructed of transgressive coarsening-upwards successions, which represent the growth and migration of barriers over their fine-grained back-barrier deposits. A large supply of clastic material forced new barriers to form further seawards than older ones, resulting in an overall regressive trend.