The Nordkalott Project: studies of Quaternary geology in northern Fennoscandia

The Quaternary geology of the Nordkalott area in northern Fennoscandia is depicted in five maps. The themes of the maps are: Quaternary deposits, glacial geomorphology and paleohydrography, ice-flow indicators, Quaternary stratigraphy and ice-flow directions. The maps are briefly presented and an outline of the glacial history of the Nordkalott area is given.     

Ancient and Modern Subduction Zone Contributions to the Mantle Sources of Lavas from the Lassen Region of California Inferred from Lu-Hf Isotopic Systematics

Hafnium isotopic compositions have been determined on a suiteof calc-alkaline and high-alumina-olivine tholeiitic lavas fromthe Lassen region of California and are used, in conjunctionwith previously published mineralogical, geochemical, and isotopicdata, to constrain their petrogenesis. Positive correlationbetween     

A Late Pleistocene coarse-grained spit-platform sequence in northern Jylland, Denmark

Several well-preserved Late Pleistocene spit systems occur uplifted in northern Jylland, Denmark. Their present-day morphological expression allows detailed study of spit growth patterns while the internal sedimentological organisation can be examined in a series of pits distributed along the length of the spits. Two characteristic vertical sequences are recognized in the systems. The first (Sequence I) consists of a giant-scale cross-bedded foreset unit, overlain by topset and beach units, while the second (Sequence II) consists of the foreset unit overlain by bar-trough and beach units. The two sequence types pass laterally into each other with a short overlap zone. They can be interpreted in terms of Meistrell's (1966, 1972) model for spit-platform growth based on scaled wave tank experiments. The giant-scale cross-bedded unit corresponds to prograding of a coarse-grained subaqueous spit-platform while the topset, bar-trough and beach units reflect the growth of the subaerial spit. The alternation between sequence I and II reflects the inversely related growth of the spit and platform structures: when the rate of subaqueous platform progradation declines, the subaerial spit grows uniformly, and when the platform progrades uniformly spit growth declines. The model is probably only valid for relatively coarse-grained systems because only these deposits would have a relatively steep front. The water depth in which the spit system progrades and thus bottom topography, determines the thickness of the giant-scale cross-bedded foreset unit because the water depth over the top of the platform is relatively constant. If the water is less than a few metres deep the spit-platform is not developed as seen where the Late Pleistocene spit systems prograded over elevations of the sea bottom. Conversely, the correct recognition of spit-platform sequences allows precise determination of sea-level and water depth at the time of formation. Finally, the model adds one further mode of formation of giant-scale cross-bedding to those already known from fluvial transverse, lateral and point bars, subtidal sand waves and Gilbert deltas.     

Postglacial sea-level history of Edgeøya and Barentsøya, eastern Svalbard

Four relative sea-level curves from Edgeøya and Barentsøya are constructed based on 81 radiocarbon age determinations on carefully selected and levelled samples in raised beaches, mostly driftwood embedded in beach gravel. All the dates, covering the period from the deglaciation to the present, are calibrated to calendar years, and the sea-level curves are defined by fitting the data with a least square regression curve. The dates are internally very consistent, and the results are some of the most precise sea-level curves from the Arctic.
The four curves are quite similar, and from the marine limit at 85-90 m a.s.l. they show a rapid emergence (ca 40 mm/year), formed about 11,000 cal yrs BP (∼10,000¹⁴C yrs BP). A minimum rate of emergence close to 8000 cal years ago is explained by a decreased rate in isostatic uplift parallel with a sustained rate of eustatic sea-level rise. During the last 7000 cal years, the emergence rate has decreased linearly. The uplift rates have been slightly higher on southern Edgeøya than further north during the last 7000 years. By comparing the sea-level curves from Storøya (ca 270 km to the north) and Hopen (ca 150 km to the south), we suggest that a memory of an earlier and larger glacio-isostatic downwarping in the southern Barents Sea is detected in the sea-level curves from Hopen and southern Edgeøya.     

Varve chronology based upon glacial sediments in the area between Karlskrona and Kalmar, southeastern Sweden

Varve series of fine-grained glacial sediments have been studied in an area of the Baltic Ice Lake near the border between the provinces of Blckinge and Smalånd, southeastern Sweden. The main purpose of the investigation was to establish a more reliable connection than earlier between the varve chronologies of the Karlskrona area (Ringberg 1971 and 1979) and the Kalmar area (Rudmark 1975). The varve series have been linked to the local chronology of Antevs (1915) as the most recent revision of the Swedish time scale has not yet been completed. The investigation has led to two alternative connections. There are no differences between the alternatives in the southern part of the study area. In the middle of the area there is a difference of 17 years and in the northern part of the area there is a difference of 85 years between the two alternatives. Continued investigations will show which is the most reliable alternative. At present, the uncertainty of the ice recession chronology is at most 85 years in the investigation area.     

Occurrence of larch (Larix) in Fennoscandia during the Eemian interglacial and the Brørup interstadial according to pollen analytical data

The occurrence of pollen and macrofossils of larch in Eemian deposits in northern Finland indicates that this species must have grown in the area during the last interglacial. Lark spread to Finland from the east, its date of arrival being deducible from the general vegetational succession. It probably did not grow in central or southern Finland during the interglacial, but is thought to have extended fairly far south in Sweden and Noway along the Fennoscandian mountain range. The Lark pollen found at the upper boundary of the interglacial deposits at Margreteberg and Stenberget in southern Sweden may suggest that it did reach southern Sweden by the very end of the Eemian, but it cannot be said for certain whethcr this pollen represents an influx of Larix from the north or from Central Europe.     

A method for determining total clast roundness in sediments

This method for determining total roundness of clast fractions takes into account both the abrasion and the crushing processes. It is developed from a slightly modified visual estimation method and a newly defined parameter - crushing processes. Based on visual estimation, the method is most useful as a tool for the Quternary field geologist.     

Dynamics of the last glaciation in eastern Svalbard as inferred from glacier-movement indicators

Glacial striae and other ice movement indicators such as roche moutonées, glacial erratics, till fabric and glaciotectonic deformation have been used to reconstruct the Late Weichselian ice movements in the region of eastern Svalbard and the northern Barents Sea. The ice movement pattern may be divided into three main phases: (1) a maximum phase when ice flowed out of a centre east or southeast of Kong Karls Land. At this time the southern part of Spitsbergen was overrun by glacial ice from the Barents Sea; (2) the phase of deglaciation of the Barents Sea Ice Sheet, when an ice cap was centred between Kong Karls Land and Nordaustlandet. At the same time ice flowed southwards along Storfjorden; and (3) the last phase of the Late Weichselian glaciation in eastern Svalbard is represented by local ice caps on Spitsbergen, Nordaustlandet, Barentsoya and Edgeøya.
The reconstructed ice flow pattern during maximum glaciation is compatible with a centre of uplift in the northern Barents Sea as shown by isobase reconstructions and suggested by isostatic modelling.     

Radiocarbon dating of the Goti-Finiglacial boundary of the Swedish Time Scale

While working with the revision of the Swedish Time Scale, based on clay-varve chronology, mollusc shells of Portlandia (Yoldia) arctica were found in the clay at Ekensberg, Stockholm, Sweden, deposited at the beginning of the Finiglacial epoch. The clay-varves have been connected with the revised Swedish Time Scale and the time for deposition is 10,370 clay-varve years cal BP. Shells of bivalves, shell fragments and periostracum have been AMS radiocarbon-dated at the The Svedberg Laboratory in Uppsala. The 11 radiometric datings are grouped in two assemblages, one between 10,500 and 11,600 BP (shell carbonate) and one between 8200 and 9100 BP (periostracum). These results are compared with the radiocarbon age obtained for a fish skeleton ( Salmo alpinus ) found in varved clay close to Ekensberg during the geological mapping of the area. The age of the fish is 8600 BP, which is in agreement with the periostracum datings. Reservoir effects and calibration of the radiocarbon ages (BP) to sidereal years (cal BP) are discussed.