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Keywords:

  • Depositional energy;
  • diatoms;
  • heavy minerals;
  • inorganic geochemistry;
  • North Sea;
  • salt marsh;
  • tidal flat

Abstract

The barrier islands of the southern North Sea were formed during the Holocene sea-level rise. These islands form part of a highly dynamic environment whose evolution continues today. Subjected to sea-level changes, tides and storm events, the sedimentary record reflects processes occurring under varying energy conditions. This article presents geochemical, mineralogical and diatom investigations carried out in the salt marsh of the East Frisian barrier island of Langeoog, which is re-exposed to a rising sea-level due to de-embankment. The major aim of this study is to improve the knowledge of the sedimentological and geochemical development of these deposits under the influence of sea-level rise, with a special focus on the geochemistry and distribution of heavy mineral-associated elements. Correlation diagrams between FeO, TiO2 and MnO, as well as ternary plots (Al2O3–SiO2–Zr or TiO2), clearly indicate the variable appearance of heavy minerals in different lithological facies, comprising marsh soil, mixed and sand flat, and relocated beach sands. A dominating abundance of ilmenite followed by zircon, garnets and some other heavy minerals is evidenced by Scanning Electron Microscope-Energy Dispersive X-ray measurements. The data presented here suggests that these geochemical proxies are useful tools for characterizing depositional energy conditions. Increasing depositional energy is evident for the lithological units in the following order: marsh soil, mixed flat, sand flat and relocated beach sand. The energetic conditions during sediment deposition, as well as the sedimentary history, are confirmed by diatom analyses as an additional independent indicator. Depending on source rock composition, the geochemical parameters used in this study may also help to investigate depositional energy regimes of other siliciclastic sedimentary systems.