Early Holocene brackish and marine facies in the Fehmarn Belt, southwest Baltic Sea: depositional processes revealed by high-resolution seismic and core analysis

Abstract

Holocene stratigraphy is established from 3.5-kHz seismic reflection data and a number of vibro cores across the narrow Fehmarn Belt between Germany and Denmark. Using detailed line drawings, texture, seismic and lithofacies analyses in a selected part of the study area, a distinct depositional unit 5 was identified. The unit was subdivided into sub-units 5a to 5j due to a different seismic texture and facies pattern. The base of the unit 5 is generally smooth but with step-like parts which are interpreted to result from tectonism. In each sub-unit the seismic facies association includes mound, oblique seismic facies and within channel deposits sigmoid, shingled and parallel facies. The sub-unit represents offset stacked lagoonal and spit deposits deposited under conditions of progressive sea-level rise. Sub-units 5a to 5h show a change in depositional style from fluvial domination to gradually more wave-influenced. Thus, the dynamic evolution of the shallow marine sub-sea-floor environment and changes in depositional conditions are revealed by high-resolution seismic facies associations.