Akademik Veri Yönetim Sistemi
20th Congress of the International Union for Quaternary Research (INQUA), Dublin, İrlanda, 25 - 31 Temmuz 2019, ss.2128-2129
Ice sheet growth and decay profoundly impact global eustatic sea-level and, regionally, isostatic depression and uplift. Raised shorelines, beaches, deltas and wave cut rock platforms are all landforms typically bearing witness of higher relative sea-level stands following a deglaciation, along previously glaciated coasts where the ice sheet have glacio-isostatically depressed Earth’s crust. In Scandinavia, the relative sea level history is commonly well studied in areas suitable for application of the isolation basin method. However, large uncertainties remain in many areas, e.g. along most of the arctic coastline of Finnmark, where Norway faces the Barents Sea. Here, we have employed a novel approach to reconstruct the chronology of postglacial shoreline displacement. We use terrestrial in-situ cosmogenic nuclide (TCN) dating directly on boulders and cobble found on the raised landforms (deltas and beach ridges).
We have targeted and dated deglaciation moraines, juxtaposed to raised shorelines, beaches and deltas and sampled for; i) n=25 rock samples from erratic boulders on top of moraines, ii) n=16 sediment samples from depth profiles in delta deposits, and iii) n=46 flat (<5 cm thick) cobbles from raised beaches, and measured the concentration of 36Cl and 10Be in these samples. Overall, initial results show that the northern coast of Finnmark was deglaciated at 14-15 ka, and that the ice sheet withdrew to the inner fjord areas where prominent moraines were built during the Younger Dryas chronozone. The ages obtained on raised beaches and deltas representing marine limit generally reflect the deglaciation ages, Some ages were obtained from levels below marine limit; these represent later relative sea levels and our goal is to use the data collectively to reconstruct rates of relative sea level change through different periods, especially during the Lateglacial for which other chronological data (e.g. from isolation basins) do not exist. Our first results are promising, especially for flat cobbles on raised beach ridges, which yielded the most consistent results so far. Some of the TCN dates are, however, ambiguous, reflecting limitations with TCN field sampling and dating precision.