A Holocene sea‐level curve and revised isobase map based on isolation basins from near the southern tip of Norway

Abstract

2015 (April): A Holocene sea-level curve and revised isobase map based on isolation basins from near the southern tip of Norway.We report a new Holocene relative sea-level curve based on the stratigraphy in five closely located isolation basins near Lista in southernmost Norway. The results detail the progress and timing of the mid-Holocene Tapes transgression, the peak of which in this region represents the highest postglacial sea level, as well as the rate of land emergence since then. One additional cored basin is situated above the marine limit. All the basins have bedrock sills that were levelled using a differential GPS. Isolation and ingression boundaries were identified by macrofossil analysis and radiocarbon dated on terrestrial plant remains. In most cases several dates were obtained from each transition. Relative sea level rose with a mean rate of 7 mm a −1 during the last part of the Tapes transgression 8600−8200 cal. a BP and then gradually slowed to a mean rate of 1 mm a −1 from 8200−7000 cal. a BP. Mean sea level reached ∼5 m higher than the present level when the transgression culminated. Land emergence took place after this, first slowly at a mean rate of 0.4 mm a −1 until ∼3900 cal. a BP before it increased to 2.6 mm between 3900 and 3400 cal. a BP. Since then it has slowly decreased until today and has been ∼0.2 mm a −1 for the last 2000 years. Based on the new curve we present updated Tapes isobases for the region that are displaced by ∼20 km in relation to the existing model. From one basin we also report a 5-10 cm thick layer of sorted, sandy gravel, embedded in a more than 5-m-thick deposit of homogeneous shallow-marine mud. The gravel was deposited ∼5500 cal. a BP, which is the same age as a tsunami deposit previously mapped in Shetland. As several typical characteristics of tsunami facies deposits are lacking, the origin of the gravel layer remains inconclusive. The age of boundaries between marine and lacustrine segments of the basin stratigraphy signify times when the sea level fell below or rose above the elevation of the bs_bs_banner

Evidence of early deglaciation (18 000 cal a bp) and a postglacial relative sea‐level curve from southern Karmøy, south‐west Norway

“…This approach is based on coring basins at different altitudes, before identifying and dating the transition between marine and lacustrine sediments (isolation contacts) or vice versa (ingression contacts). According to Romundset et al (2015) the method was probably first applied by Sundelin (1917), after which it has been widely used in Scandinavia (e.g. Hafsten, 1960;Svendsen and Mangerud, 1987;Lohne et al, 2004Lohne et al, , 2007 and other parts of the world (e.g.…”

“…Shennan et al, 1996;Long et al, 2011;Letham et al, 2016). Isolation-and ingression contacts are usually recognizable in the sediment as lithostratigraphic boundaries; however, biostratigraphic indicators, such as diatoms (Kjemperud, 1986;Lohne et al, 2007;Letham et al, 2016) or macrofossils (Romundset et al, 2015(Romundset et al, , 2018, are usually required for a more precise identification of the transitions. Here, we use a combination of lithostratigraphic evidence, macrofossils, geochemistry and microscopic phytoplankton (Kaland, 1984;Vasskog et al, 2013) to identify isolation contacts in two isolation basins called Grødheimsvatnet (vatnet = lake) and Kringlemyr (myr = bog).…”

Mistet på sjøen? En nyoppdaget fiskekrok fra steinalderen i Søgne, Vest-Agder.

“…Slike lag kan best beskrives som submarin organisk gytje, og kalles i noen tilfeller også submarin torv (se f.eks. Sollesnes og Faegri 1951;Romundset et al 2014). Det eneste prøvestikket hvor et slikt gytjelag ikke kunne sikkert dokumenteres i profil var i det østligste, der fiskekroken ble funnet.…”

“…Forekomster av torvlignende gytjelag på sjøbunnen ble påvist ved Sigersvoll på Lista alt i 1928, noe som indikerte at det må ha vaert tørt land under dagens havnivå på et tidspunkt etter siste istid (Sollesnes og Faegri 1951). De fleste av de senere strandlinjestudiene i Sør-Norge baserer seg imidlertid på landbassenger som har blitt påvirket av stigningen i havnivået under tapestransgresjonen etter istiden (Prøsch-Danielsen 1997:86;Bondevik et al 1998;Midtbø et al 2000;Romundset et al 2014). Strandlinjekurvene i regionen har derfor et kunnskapshull når det gjelder havets regresjonsminimum og forflytningen av strandlinjene under dagens havnivå.…”

Phylogeography of the temperate marine bivalveCerastoderma edule(Linnaeus, 1758) (Bivalvia: Cardiidae) in the Subarctic: Unique diversity and strong population structuring at different spatial scales

“…C. edule is characterized by high fecundity, external fertilization, broadcast spawning, and high dispersal potential due to the pelagic larval stage in the life cycle. Postglacial fossil records of cockles from Scandinavia are from the raised beaches and generally attributed to the Tapes transgression, 6 ka ago (Donner, Eronen, & Jungner, 1977;Møller, 1989;Romundset, Fredin, & Høgaas, 2015), while no post Last Glacial Maximum (LGM) fossilized cockle shells were recorded at shores of Kola Peninsula at all (Snyder, Korsun, & Forman, 1996). Earlier postglacial fossils from Northern Europe are lacking, because coastlines of that time are currently submerged (Bjerck, 2009).…”