Glacial history, Holocene shoreline displacement and palaeoclimate based on radiocarbon ages in the area of Bockfjorden, north-western Spitsbergen, Svalbard

Age determinations of bivalve shells indicate that Bockfjorden, a fjord in north-western Spitsbergen, Svalbard, was deglaciated shortly before 10 Kya, and that the upper marine limit in this area, with an altitude of about 50 m a.s.l., has the same age. During most of the Holocene, the glaciers in Bockfjorden were less extensive than they are today. Their maximum Holocene extension occurred during the Little Ice Age. The initial shoreline emergence after the deglaciation was rapid, and former shorelines younger than 8.5 Ky are below the present sea level. A mid- Holocene transgression of the sea is traced as well as a transgression during the last thousand years

Spor etter Mjølnirnedslaget i Janusfjellprofilet på Svalbard

The 40 km diameter Mjølnir Crater was formed 142 ± 2.6 Ma (Volgian-Ryazanian boundary) by the impact of a 1.6 km diameter asteroid into the 350-400 m deep paleo-Barents Sea. The structure is buried and well preserved in sediments on the Bjarmeland Platform, which has been tectonically stable since late Paleozoic. The studied Janusfjellet Section (level 0-49.1 m) on Svalbard (450 km northwest of the crater) includes the upper part of the Agardhfjellet Formation, represented by the Slottsmøya Member (level 0-38 m), and lower part of the Rurikfjellet Formation, represented by the Myklegardfjellet Bed (level 38-39.5 m) and the Wimanfjellet Member (level 39.5-49.1 m). This study indicates that geological parameters may carry information indicating possible environmental impact influence. Redox-parameters (the geochemical ratios Cr/V, Th/U, Ni/(Ni+V), MnO/Fe2O3) in the Slottsmøya Member indicate dominating anoxic/hypoxic depositional conditions in level 0-32 m. In level 32-38 m, redox-parameters, degree of bioturbation and TOC-values show dominating oxic depositional conditions. This could be related to tsunami effects caused by the Mjølnir impact, especially in Ir-enrichment level (33.6-34.0 m). High TOC-values in the same level could be related to soot-concentration in sediments after impact. Phosphate-rich levels are found in 37.25 m and 37.60 m, and may be related to transgressive events. Redox-parameters (Cr/V, Th/U, Ni/(Ni+V), MnO/Fe2O3) in the Myklegardfjellet Bed indicate dominating anoxic/hypoxic depositional conditions. The Myklegardfjellet Bed is glauconite-rich, and contains some belemnites in its lower part, indicating oxic/dysoxic depositional conditions. Redox-parameters (Cr/V, Th/U, Ni/(Ni+V), MnO/Fe2O3) and degree of bioturbation in the Wimanfjellet Member, show dominating oxic depositional condition. Grain size-parameters ((quartz + feldspar)/(sum clay minerals) and SiO2/Al2O3) in the Slottsmøya Member indicate shallowing upwards developments in the 0-32 m interval,. There are large variations in grain-size-parameters in level 32-38 m, with several low values in level 33.3-34.0 m (Ir-enrichment level). This could be explained by shifting sedimentary provenances, caused by turbidite/density currents, avalanches and slides after the impact. Grain size-parameters ((quartz + feldspar/(sum clay minerals)) and SiO2/Al2O3) in the Myklegardfjellet Bed and the Wimanfjellet Member indicate coarsening upwards developments. The maturity-parameter (quartz/feldspar) variations are on average higher in the Slottsmøya Member than in both the Myklegardfjellet Bed and the Wimanfjellet Member. There are many high values in interval 33.3-38.0 m. The upper part of the Slottsmøya Member represents a regression followed by a transgression. The base of the Myklegardfjellet Bed represents a transgressive surfase. The Ir-anomaly in the Janusfjellet Section (2.1 ppb at level 33.7 m) occurs in carbonate sediments. Ir-enrichments with possible Mjølnir ejecta have also been discovered in The Barents Sea and in Siberia, 2500 km away fram the impact site. The ejecta distribution in the area was probably highly assymetrical. The geological, geochemical and paleontological signals in the sediments show that the environmental consequences of the impact (the results of impact generated waves, currents, changing redox-conditions) were more symmetrically distributed. Influences of the asteroid impact have been discovered in cores of marine sediments from 30 to 500 km away from the impact site

Scarboro Town Report - 1915

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Deglaciation of coastal south-western Spitsbergen dated with in situ cosmogenic 10Be and 14C measurements

The Svalbard-Barents ice sheet was predominantly a marine-based ice sheet and reconstructing the timing and rate of its decay during the last deglaciation can inform predictions of future decay of marine-based ice sheets (e.g. West Antarctica). Records of ice-sheet change are now routinely built with cosmogenic surface exposure ages, but in some regions, this method is complicated by the presence of isotopic inheritance yielding artificially old and erroneous exposure ages. Here, we present forty-six 1025 Be ages from bedrock (n = 38) and erratic boulders (n = 8) in southwestern Spitsbergen that, when paired with in situ 1427 C measurements (n = 5), constrain the timing of coastal deglaciation following the last glacial maximum. 10Be and 1428 C measurements from bedrock along a ~400 m elevation transect reveal inheritance-skewed 10Be ages, whereas 1429 C measurements constrain 400 m of ice-sheet thinning and coastal deglaciation at 17.4 ± 1.5 ka. Combined with three additional 10Be-dated coastal sites, we show that the southwestern margin of the Svalbard-Barents ice sheet retreated out of Norwegian Sea between ~18-16 ka. In situ 1432 C measurements can provide key chronological information on ice-sheet response to the last termination in cases where measurements of long-lived nuclides are compromised by isotopic inheritance

Two observations of pumice levels from the west coast of Spitsbergen

During the summer of 1983 pumice was observed on raised beaches in two localities on the west coast of Spitsbergen. This is an area where pumice has not been reported (Salvigsen 1984), and a preliminary note should therefore be of interest

Occurrence of pumice on raised beaches and Holocene shoreline displacement in the inner Isfjorden area, Svalbard

Finds of pumice on raised beaches in the inner Isfjorden area are reported. Pumice is abundant in two zones, and four levels can be distinguished in some areas. The highest lying level has the greatest concentration of pumice and is dated to a maximum of 6,500 years B.P. Tentative correlations with pumice levels from other places in Svalbard indicate approximate ages of 6,000, 4,100, and 3,100 years for the lower levels in inner Isfjorden. A shoreline displacement curve based on the pumice levels and on 10,OOO year old driftwood is presented