DEPOSITIONAL ENVIRONMENT OF THE VEJLE FJORD FORMATION OF THE UPPER OLIGOCENE LOWER MIOCENE OF DENMARK - A BARRIER-ISLAND BARRIER-PROTECTED DEPOSITIONAL COMPLEX

The Vejle Fjord Formation was deposited in the coastal area at the eas tern margin of the Upper Oligocene to Lower Miocene North Sea. Detaile d studies of lithology and depositional structures demonstrate that co arsening-upwards successions resulted from landwards migration of barr ier complexes as a response to relative sea-level rise. The formation of barriers, their migration and construction of new barriers was cont rolled 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 themsel ves are only sparsely represented in the studied exposures. Their infl uence on the depositional pattern is revealed by the formation of stor m wash-over deposits and tidal inlet/tidal delta deposits. The destruc tional pattern of the barriers (storm erosion or tidal inlet widening) was apparently controlled by the orientation of barrier sections rela tive to the prevailing storm direction. A back-barrier beach deposit w as developed with landwards-dipping heavy-mineral lamination. It forms part of a shallowing-upwards succession and represents a transgressiv e 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 bioturba ted. The tidal Rat 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 elastic material forced new barriers to form further seawards than older ones, resulting in an ove rall regressive trend. (C) 1998 Elsevier Science B.V. All rights reser ved.