Physical and biological influences on the formation of sedimentary fabric in an oxygen-restricted depositional environment: Eckernforde Bay, Southwestern Baltic Sea
Sedimentological and radiochemical investigations of sediments in Eckernforde Bay were coordinated with observations of benthic biology and benthic-boundary-layer dynamics to identify processes influencing the formation of preserved sedimentary fabric. The bay is a trap for fine sediments because of its fjord-like basin geometry and hydrodynamic regime. Sediments are derived from both local sources (transported by winter storms) and sources in adjacent Kiel Bight (fair-weather transport of suspended sediment by internal waves). In the central basin of the bay, strata consist of pelletized, clay-rich beds and silty laminations, and reflect the interaction of bioturbation with alternating fair-weather and storm-associated sediment transport and deposition. Sediment-accumulation rates in the central basin of the bay are ~0.39 cm/yr (from 210Pb geochronology). Results from a numerical model, as well as study of X-radiographs and accumulation rates, indicate that fair-weather processes contribute 0.15 cm/yr of time-averaged sediment accumulation, and the remaining 0.24 cm/yr is contributed by storm-generated deposition. Seasonal oxygen depletion restricts the benthic community to a pioneer assemblage of small-bodied, deposit-feeding polychaetes and bivalves. Excess 234Th analyses indicate that bioturbation is restricted to the upper 1 cm of the seabed. Macrofaunal feeding activity produces abundant ovoid fecal pellets and biogenic microfabric in beds deposited under fair-weather conditions. In contrast, primary depositional fabric is preserved as laminations when storm deposits thicker than the depth of bioturbation disrupt biological communities.
Publication Source (Journal or Book title)
Bentley, S., & Nittrouer, C. (1999). Physical and biological influences on the formation of sedimentary fabric in an oxygen-restricted depositional environment: Eckernforde Bay, Southwestern Baltic Sea. Palaios, 14 (6), 585-600. https://doi.org/10.2307/3515315