Tapes Transgression Research Articles

Morphodynamics and morpotectonics of the varzuga river mouth area (terskiy coast of the white sea) in the late glacial and holocene

The Late- and post-glacial history of the development of the White Sea coastal zone in the area of the Varzuga River mouth is considered as a result of the interaction of endogenous and exogenous factors of coastal morpholithogenesis. Based on geomorphological investigations, study of Holocene deposits by lithostratigraphic, diatom and radiocarbon analyses, as well as collection and analysis of published data, new results on the area’s relief development for ~13 cal ka BP have been obtained. The features of the regional hierarchical morphostructure and local post-glacial tectonics of the territory — the spatial relationships of blocks and the speed of vertical movements – were determined. The superimposed linear Nizhnevarzugskaya depression, which determined the configuration of the Varzuga River estuary in the late and postglacial time, was identified for the first time. The influence of the spatial ratio of blocks and differentiated postglacial uplift on the coastal morpholithogenesis was established. The course of changes in the relative sea level (RSL), development conditions and morphodynamics of the open coast and the estuary of the Varzuga River were reconstructed and new data on the rhythms of coastal morpholithogenesis processes (coastal, estuarine, and aeolian) obtained. Three stages of the coastal zone development were identified, corresponding to regional rhythms of changes in the relative sea level and climate: (I) Late Glacial transgression and Early Holocene regression (~12–9.8 cal ka BP), (II) Middle Holocene Tapes transgression (7.8–4.9 cal ka BP), (III) Late Holocene regression (after 4.9 cal ka BP). The upper marine boundary of the Late Glacial transgression is traced at the elevation of ~54–55 m a. s. l. to the west of the Nizhnevaruzgskaya depression, — ~39–40 m a. s. l. to the east of it, and — 22–25 m a. s. l. in the depression. The shores of lower morphostructural blocks were probably blocked by dead ice up until ~10.2–9.8 cal ka BP. During the Tapes transgression, the RSL reached a maximum (~7.8–7.6 cal ka BP; ~20 m a. s. l.), and by 4.9 cal ka BP fall to ~15 m a. s. l. The prevailing directions of sediment fluxes, winds and wave approach became similar to those of today. However, the main source of the coastal zone sedimentary supply was the erosion of glaciofluvial sediments and the input of sands from the seabed. In the interval of ~4.9–1.7 cal ka BP, the RSL decreased to ~5 m a. s. l. The sediment runoff of the Varzuga River became the main source of feeding the coastal zone.

RELATIVE SEA-LEVEL CHANGE OF THE WHITE SEA IN THE LATE GLACIAL AND HOLOCENE: CASE STUDY OF THE SREDNYAYA TRET’ LAKE, EASTERN COAST OF THE GORLO STRAIT<a href="#FN4"><sup>4</sup></a>

The relative sea-level changes for the time interval of ~12.1–9.1 ka cal BP were reconstructed on the eastern coast of the Gorlo Strait using the results of paleolimnological, GPR and geomorphological analyses conducted in the basin of the Srednyaya Tret’ Lake (7.3 m a.s.l., 66.014009° N, 41.086294° E), as well as UAV surveying of the lake surroundings. Bottom sediments of the lake were studied from the four core sections and correlated with each other according to the results of GPR data interpretation. Lithostratigraphic descriptions of bottom sediment cores, grain-size and diatom analyses, radiocarbon dating (AMS), determination of LOI, Corg content and Corg /Norg ratio were performed. We present the reconstruction of the coastlines at heights of 4–5 and 12–15 m formed by currents and/or wave processes within the lower Ruch’i River valley and Srednyaya Tret’ Lake according to field observations and interpretation of space images. As a result, the position of the relative sea-level and the chronology of the Late Glacial (Younger Dryas) transgression and the early stages of the Holocene (Tapes) transgression were refined. Late glacial transgression finished earlier than ~12.1 ka cal BP, and its relative level was probably no higher than 15 m a.s.l. After a deep regression, the relative sea-level approached the modern again ~9.5 ka cal BP, and at the Tapes transgression maximum (~9.1 ka cal BP) it was near the lake runoff threshold (∼5 m). Though the coastline was near the lake basin, sea waters never entered the lake. Sands, carried by the wind, accumulated in the part of the basin facing the coast. The the Srednyaya Tret’ Lake basin was gradually filled by fresh water according to the results of diatom analysis.

Позднеледниково-голоценовая стратиграфия донных отложений из котловин малых изолированных озер баренцевоморского побережья (Кольский регион)

Lithological study and diatom analysis of the bottom sediments from small lakes belonging to the category of isolated basins located on the Barents Sea coast of the Kola region was carried out. Stratigraphic subdivision of depositional sequences was performed based on the new data obtained from the Settlement Teriberka area, as well as on the published data from other areas; lithostratigraphic units (LSU), which are stratogens, were identified in them. We found out that the proglacial reservoir was marine during deglaciation on the Barents Sea coast, freshwater (LSU 1) sediments of the ice-marginal basins were not found here (LSU 1). In the lake basins isolated from the sea, the depositional sequences in deep parts of isolated basins is represented by: brackishwater sediments of the proglacial basin (LSU 2), Lateglacial brackishwater sediments (LSU 3), marine sediments (LSU 4), sediments of an isolating lagoon (LSU 5), sediments accumulated in a meromictic lake (LSU 6), sediments of an onshore freshwater lake (LSU 7), sediments of a freshwater lake with slightly increased water mineralization deposited during Early-Mid Holocene Tapes transgression (LSU 8) and lacustrine sediments (LSU 9) are represent in the sedimentary sequences from small isolated lakes in the Barents Sea coast.

Postglacial relative sea level change in Norway

We present the first comprehensive postglacial relative sea-level (RSL) database for the Norwegian coast from Oslo to the Kola Peninsula. The database spans the last 20 kyrs and is composed of 413 index points and 610 limiting data points derived from raised beaches, archeological data, glaciomarine terraces, and sedimentary indicators from isolation basins, salt marshes, and peat bogs. The data are quality controlled, assigned standardized indicative meanings, and recalibrated to current standards. We use an ensemble of Bayesian statistical models, trained on sea-level index points and weighted by their fit to both index and sea-level limiting points, to assess the spatiotemporal patterns of Norwegian RSL change. Continuous RSL fall driven by isostatic rebound in response to Eurasian ice sheet collapse dominates the RSL signal at every inland location in Norway. A first transgression (episode of RSL rise), which occurred in southwest Norway during the Younger Dryas (14–11.7 ka), increased RSL by as much as 15 m in some locations. A second transgression, named the Tapes transgression, occurred during the early-mid Holocene between 10 and 5.5 ka. The spatiotemporal model ensemble constrains the timing, amplitude, and spatial distribution of the Younger Dryas and Tapes transgressions. Based on our modeling results, we speculate that the Tapes Transgression was the result of global mean sea level rise temporarily outpacing isostasy-driven RSL fall, while the Younger Dryas Transgression was likely the result of local ice sheet readvance combined with low viscosity asthenosphere and weak lithosphere in the region. We also describe the effects of peripheral bulge migration on Norwegian RSL, which caused increased RSL in the early Holocene and a delayed Tapes transgression. We show that postglacial RSL data in Norway contain complex spatiotemporal patterns of nearfield RSL change that can best be estimated by combining a high-quality data compilation with glacial isostatic adjustment modeling via a robust statistical model.

Reconstruction of the coastline of the Barents sea (the Kola Peninsula) during the Late Glacial and Holocene

Abstract. Comprehensive studies (lithological and micropaleontological) of bottom sedi ments from nine lakes at the Teriberka Village (the Kola Peninsula, Northwestern Russia) were carried out. The sediments formed after an isolation from the sea was dated. Based on these new data, a preliminary sea-level curve for the study area was constructed. The sea-level curve indicates several phases evolution of the Kola coast during the Late Glacial and Holocene. Rapid drop (~40 mm per year) of a sea-level was occurred ca. 11,500 cal. years BP. The sea level gradually elevated between ca. 11,000 and 7,600 cal. years BP (the Tapes transgression). Science ca. 7,300 cal years BP, the sea level slowly decreases by 2 3 mm per year.

Evolution and temporal constraints of a multiphase postglacial rock slope failure

Large rock slope failures are temporal processes which act to modify the landscape after glacial retreat. The slope failure process often shows a lag time of thousands of years after deglaciation, with multiple failure events possible. While global datasets constrain this lag time from extensive mapping and dating of paraglacial rock avalanches, the timeline is poorly refined in northern Norway. We present a case study of multiphase failure at Skredkallen on Vanna, one of a group of coastal islands in Troms, northern Norway. The site contains an actively deforming rock slope above a large rock avalanche deposit. The rock slope deformation (RSD) is a system of fractured and dislocated blocks up to 3 Mm3, and is moving slowly ~5 mm/yr downslope to the north-east. The metasedimentary rock mass contains four pervasive joint sets and a foliation, contributing to a compound structure failure mechanism. The rock mass is further weakened by foliation-parallel sheared mylonite, and the presence of a brittle fault in the immediate area, with evidence of hydrothermal fluid flow though the RSD.The rock avalanche deposit below the slope deformation is calculated to be 3 Mm3, and extends >1 km from the source area, displaying typical mobility for north Norwegian rock avalanches onto undrained sediments. The deposits showcase exceptional lobate morphology with elongated ridge-and-furrow features. Raised shorelines predating and postdating the deposit provide temporal constraints on the deposit and an opportunity to reconstruct a relative timeline for the slope evolution. The postglacial marine limit (>14 cal. ka BP) is obscured by the deposit, while shorelines corresponding to the early Younger Dryas (12.2 cal. ka BP) and the subsequent Tapes transgression maximum (7.6–7.2 cal. ka BP) are prominent across the deposits, implying that the avalanche was emplaced between 15 and 12.2 cal. ka BP. Failure occurred during a time of immense climate instability at the boundary to the early Holocene, consistent with global reports of mountain slope failure following glacial retreat. The avalanche was emplaced into what would have been the marine environment. The anomaly between the rock avalanche source area volume (35 Mm3), and the rock avalanche deposit implies previous failure events, the deposits of which were either removed due to failure of the underlying marine sediments into the fjord, by retreating glacial ice or scour. The initiation of movement at the RSD may be attributed to periods of local climate changes, such as the Holocene Thermal Maximum. Cosmogenic nuclide dating is suggested as the next step to fill gaps in the slope evolution story through the mid to late Holocene.

From a large basin to a small lake: Siliceous microfossils stratigraphy of the isolation basins on Big Solovetskiy Island (the White Sea, NW Russia) and its implication for paleoreconstructions

This paper discusses the results of siliceous microfossils studies performed in a “staircase” of four isolation basins (33.7 m–2.9 m a.s.l.) on Big Solovetskiy Island (Solovki Archipelago, the White Sea). Diatoms were used as a primary group for paleoinferences, while chrysophyte cysts and sponge spicules also demonstrated high indicative potential. In all study lakes, the siliceous microfossils stratigraphy revealed three main stages of their evolution, i.e. large-basin, transitional and small-lake stages, each characterized by certain composition of the diatom assemblages and floristic diversity, relative abundances of chrysophyte cysts and sponge spicules, and siliceous microfossils concentrations. In the uppermost lake, glaciolacustrine environments unfavorable for aquatic biota existed during the large-basin stage. The proglacial lake stage terminated prior to ca. 10.4 cal ka BP, followed by a (semi)terrestrial episode before the transition to small-lake environments. In the other three lakes, marine environments were inferred at the earlier stage, characterized by the predominance of marine and brackish-marine diatoms, increased proportions of sponge spicules and low “cysts to diatoms” ratio. At the transitional marine-freshwater stage, mass growth of small fragilarioid diatoms and decreased abundances of spicules indicated unstable environments, while increased proportions of cysts pointed to progressive freshening of the basins. The duration of the marine-freshwater transition expectedly prolonged from ca. 200 yr in the upper basin (16.6 m a.s.l) to ca. 500 yr in the lowermost lake (2.9 m a.s.l.). The isolation from the sea took place between ca. 6.3 and 1.4 cal ka BP. At the small-lake stage, siliceous microfossils stratigraphies reflected local specifics of the basins and their catchments. We argue that besides traditionally used diatom data, relative and absolute abundances of siliceous microfossils also possess high indicative value for isolation basin studies. Our study demonstrated that marine waters on Big Solovetskiy Island never reached ca. 34 m a.s.l. during the Holocene, unlike the western coast of the Onega Bay where the Preboreal marine intrusion was recorded even at higher elevated localities. Different rates and amplitudes of shoreline displacement are thus suggested for the inner and outer parts of the Onega Bay. During the mid-Holocene Tapes transgression, before ca. 6.3 cal ka BP, the relative sea level on Big Solovetskiy Island exceeded 17 m a.s.l. The average estimated rates of the shoreline retreat during the second half of the Holocene gradually decreased from 0.28 cm year−1 to 0.2 cm year−1, indicating slowed isostatic uplift.

Северо-западные берега Онежского полуострова Белого моря в голоцене: условия развития, динамика, хронология

According to detailed geomorphological studies, radiocarbon dating and Stolbovoe Lake sediments and terrace sedimentary cover diatom analysis three different stages of coastal zone development in the northwest of the Onega Peninsula had been identified and dated. The abrasion coastlines at elevations of 18.5–30 m were formed earlier ~9.5–8.5 cal kyr BP, during the Late Glacial transgression and the glacio-isostatic regression of the Early Holocene. A well-defined predominantly abrasion coastline at elevations of 14–18.5 m was formed ~8.2–5.8 cal kyr BP during the mid-Holocene Tapes transgression with insignificant fluctuations of the sea level with hydrodynamic activity greater than present. A short-term episode (~6.0–5.8 cal kyr BP) of the relative sea level rise on the shore of the Dvina Bay has been identified, probably associated with storm surges. Abrasion-accumulative coastlines at elevations up to 14–15 m were formed after ~5.8 cal kyr BP in the conditions close to modern. At all stages of development, the shores were dynamically young. The leading role of the postglacial uplift in the extension of the coast contour, and of the structure of the glacial relief–in the morpho- and lithodynamics of the coastal zone is shown. During the Tapes transgression, the rates of uplift of adjacent morphostructural blocks differed (~0.5 and 2.1–2.2 mm/year); then the uplift became uniform (~2.8–2.9 mm/year). The structure of the coastal forms indicates the constant prevailing directions of the waves and sediment transport, starting from the middle Holocene.

Between winter storm surges – Human occupation on a growing Mid-Holocene transgression maximum (Tapes) beach ridge at Longva, Western Norway

Substantial amounts of archaeological material have been found intermixed with beach pebbles and cobbles on the Tapes beach ridge at Longva on the island Flemsøya/Skuløya in Western Norway. The artefacts show that the beach ridge was settled in the Late Mesolithic. The most significant remains are fireplaces, birch bark from the floor of a tent/hut, fish sinkers and middens containing numerous waste flakes and lithic tools. Radiocarbon dating, mainly of burnt hazelnut shells, shows two periods of occupation. The older and longer period is dated to between 7600 and 6800 cal yr BP, and the younger phase to between 6200 and 5900 cal yr BP. Pollen analysis revealed open vegetation at the beach ridge during the occupation periods. Based on the beach ridge deposits and radiocarbon dates, we reconstructed the Tapes transgression maximum high tide sea level to 8.2–9.0 m between 7600 and 5600 cal yr BP. We conclude that the late Mesolithic inhabitants at Longva occupied the beach ridge while it was growing. During the largest storm surges – most likely to have been in the winter months – the sea would have washed over their settlements and deposited pebbles and cobbles on top of their remains. We suggest that the inhabitants abandoned the settlement before each stormy season, but returned and restored the site the following spring or summer.

PUTATIVE RECORDS OF THE HOLOCENE TSUNAMI IN LACUSTRINE BOTTOM SEDIMENTS NEAR THE TERIBERKA SETTLEMENT (KOLA PENINSULA, RUSSIA)

The results of lithological analysis, diatom analysis and radiocarbon dating of bottom sediments from the basin of a lake located at an elevation of 17 m above sea level near the Teriberka settlement (Barents Sea coast, Kola Peninsula) are presented. The stages of the lake evolution were revealed based on a comprehensive investigation of its bottom sediments. The lake basin was covered by sea at the end of the Pleistocene. The lake became isolated from the sea approximately 11500 cal. yrs BP, but was re-filled with sea water after 10400 cal. yrs BP due to the Tapes transgression. In lower part of the Tapes sediments, there is a disturbance of the sediment sequence, represented by a mixture of sand, gyttja and plant residues. According to radiocarbon dates, this disturbed hori­zon was deposited between 10400 and 8200 cal. yrs BP. An abrupt increase in the con­tent of marine diatoms was found in this horizon. The disturbed sediments have possibly formed as a result of the Storegga tsunami. When the horizon of tsunamigenic sediments was forming, the sea level was slightly above the threshold for discharge from the lake (ca. 18 m above modern sea level). The second local event (tsunami?) occurred after 8220 cal. yrs BP, when the coastline was already below the lake threshold. As a result of this event, an interlayer of sandy sediments formed in the bottom sediments within gyttja.

In the wake of the wake. An investigation of the impact of the Storegga tsunami on the human settlement of inner Varangerfjord, northern Norway

The Storegga tsunami (8175-8120 cal. BP, Bondevik et al., 2012) has often been described as a catastrophe spelling major disaster and demographic decline for the people in the danger zone. More nuance is needed if we are to understand the effects. Most studies have had a supra-regional or regional character; less effort seems to have put into studies at the sub-regional level. The Norwegian coast, for example, is a topographic, bathymetric and environmental mosaic and the sub-regional and local effects must surely have been different. This paper discusses the possible effects of the Storegga tsunami on the human settlement of inner Varangerfjord in northern Norway some 2000 km from the point of origin. Central to the discussion are the questions of: a) actual presence of people at the time of the event, b) safe altitudes above sea-level for settlement, c) the geological record and the compounding effects of the Tapes transgression, d) the archaeological record, and e) the combined effects of the Storegga tsunami and the 8200 cal. BP cold event and hunter-fisher-gatherer resilience. It is concluded that 1) the vertical run-up of the Storegga tsunami in inner Varangerfjord probably was 2 m or less, 2) the impact of the 8200 cal. BP cold event on the ecology of Finnmark was relatively weak, and 3) the combined effect of both on human life probably was minor given a high degree of resilience among the population.

COASTAL MORPHO- DYNAMICS OF THE NORTH-WESTERN ONEZHSKY PENINSULA, WHITE SEA IN THE HOLOCENE. KONYUKHOV BAY

Data from geomorphological surveys of the Konyukhov Bay coast (north-western part of Onezhsky Peninsula), radiocarbon dating of organogenic sediments, echo sounding of water areas of the bay and lakes (water lines at 15.8-26.1 m a. s. l.) performed during the voyage of the research vessel Ecolog in July 2014 were used to reconstruct the history of the landform development in the Holocene. The morphodynamics of the coast is considered as a result of interactions between coastal processes and the underlying litho- genic structure against the background of postglacial movements and climate change. Two geomorphological levels were distinguished and dated, which differ in the scope of transformation of ice-marginal formations of the Neva stage of the last glaciation by the sea and correspond to the main stages of post-glacial development of the relief: 1) paleo- straits and bays in depressions between moraine ridges at altitudes of 17.5-30 m a. s. l., filled in during the post-glacial transgression; the basinal stage of their development ended no later than 8540 ± 50 - 7610 ± 70 14 C (~9500-8400 cal.) BP; 2) marine terraces at altitudes below 15-17 m a. s. l., formed in the middle-late Holocene in the environments similar to modern ones. The abrasion coastline (14-17.5 m) formed during the sea level stabilization stage with its high wave activity, which took place during the Tapes transgression, was revealed. Bays at the upper level, with a threshold runoff below ~ 17.5 m a. s. l., were at that time re-filled with sea water. The relative uplift rate of the Konyukhov Bay coast was estimated according to the ages of the lower horizon of lacustrine and palus- trine sediments at 2-2.2 mm/year.

Mid- to late Holocene aeolian activity recorded in a coastal dunefield and lacustrine sediments on Andøya, northern Norway

In an effort to reconstruct past aeolian activity, a foredune stratigraphy and a continuous lake sediment record from the largest dunefield on Andøya, northern Norway, have been investigated. The dunefield extends landwards in a north-eastward direction and consists of several parabolic dunes, foredunes and blowouts. The sediment record (169 cm) from the nearby lake Latjønna and the foredune stratigraphy (10 m) covers the last 6200 and 3700 cal. yr BP, respectively. Both sites possess sediments deposited after the Tapes transgression maximum (~6800 cal. yr BP), which reached a level of ~7–8 m a.s.l. at the study site. The lake sediment record consists of several units dominated by sand grains interspersed by more organic-rich beds. The core has been examined by x-ray fluorescence (XRF), magnetic susceptibility (MS) and loss-on-ignition (LOI). Mineral grains were detected by wet sieving of the ignition residue (IR), and the influx of sand grains to Latjønna was calculated based on the weight of sand grains >250 µm/cm divided by the accumulation rate determined from a radiocarbon (14C)-based age–depth model. Phases with high influx of sand to Latjønna are recorded around 4800, 4250, 3000–2000, 1850–1750, 1600–600, 450, 300 and 150 cal. yr BP, which coincides with periods of increased storminess recorded in other studies around the North-Eastern Atlantic region. The two study sites show, however, quite contrasting results; high sedimentation rates in the lake record associated with greater aeolian influx correspond to stability in the foredune stratigraphy reflected by the presence of several palaeosols. Because of this out-of-phase behaviour, it is suggested that the foredune is mainly influenced by summer climate and relative sea level (RSL) change, whereas the lake record is more influenced by niveo-aeolian processes transporting sand grains farther inland during winter.

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.

A multi-proxy approach to assessing isolation basin stratigraphy from the Lofoten Islands, Norway

This study takes a comprehensive approach to characterizing the isolation sequence of Heimerdalsvatnet, a coastal lake in the Lofoten Islands, northern Norway. We use established methods and explore new techniques to assess changes in marine influence. Bathymetric and sub-bottom profiles were acquired to examine basin-wide sedimentation and a 5.8 m sediment core spanning the last 7800 cal yr BP was analyzed. We measured magnetic susceptibility, bulk organic matter properties, molecular biomarkers, diatom assemblages, and elemental profiles acquired by scanning X-ray fluorescence. These characteristics of the sediment reflect detailed changes in salinity and water column conditions as the lake was progressively isolated. Three distinct litho/chemo-stratigraphic units represent a restricted marine phase (7800–6500 cal yr BP), a transitional phase characterized by intermittent marine influence (6500–4900 cal yr BP), and complete isolation and freshwater sedimentation (4900 cal yr BP to present). Although there are uncertainties in the estimate of the threshold elevation of the lake, the timing of these phases generally corresponds with previous interpretations of the local relative sea-level history. This record captures sea-level regression following the Tapes transgression and supports the interpretation of a subsequent sea-level stillstand, dated in Heimerdalsvatnet from 6500 to 4900 cal yr BP.

Storegga tsunami sand in peat below the Tapes beach ridge at Harøy, western Norway, and its possible relation to an early Stone Age settlement

One of the early problems with the Storegga tsunami deposit was how to distinguish it from deposits of the midHolocene (Tapes) transgression. An excavation on Harøy, an island on the outermost western coast of Norway, shows a distinct, clean sand bed embedded in peat and clearly separated from the overlying Tapes beach deposits. This sand bed continues in the peat landwards of the beach ridge for at least 60 m. Radiocarbon dates of the peat show that the sand was deposited some time between 6900 and 7700 yr BP. The sedimentary structures of the bed, the 14C dates, and the fact that this is the only sand bed in the peat, suggest that the sand bed was deposited by a short‐lived event, the Storegga tsunami. On the neighbouring island, Fjørtoft, a Stone Age settlement, dated to 7500 yr BP, was discovered in the early 1970s. The settlement was found underneath a sand bed that later had been covered by the Tapes beach ridge deposits. When discovered, the sand covering the settlement was inferred as eolian sand. However, this investigation shows that the Storegga tsunami deposited a widespread sand bed on the land surface around this time with a similar grain size distribution to eolian sand. It is therefore suggested that the sand bed covering this settlement was deposited from the Storegga tsunami. Both the stratigraphy and 14C dates demonstrate that the Tapes transgression maximum was reached well after the Storegga tsunami on Harøy, between 6500 and 6100 yr BP.

Postglacial relative sea-level change and stratigraphy of raised coastal basins on Kola Peninsula, northwest Russia

A relative sea-level curve for the Holocene is constructed for Polyarny on the Kola Peninsula, northwest Russia. The curve is based on 18 radiocarbon dates of isolation contacts, identified from lithological and diatomological criteria, in nine lake basins situated between 12 and 57 m a.s.l. Most of the lakes show a conformable, regressive I–II–III (marine–transitional–freshwater) facies succession, indicating a postglacial history comprising an early (10,000–9000 radiocarbon years BP) phase of rapid, glacio-isostatically induced emergence (∼5 cm year −1) and a later phase (after 7000 years BP,) having a moderate rate of emergence (<0.5 cm year −1). Three lakes together record a phase of very low rate of emergence or slight sea-level rise at a level of ∼27 m a.s.l., between 8500 and 7000 years BP, which correlates with the regional Tapes transgression. Pollen stratigraphy in the highest lake shows that the area was deglaciated before the Younger Dryas and that previously reconstructed Younger Dryas glacier margins along the north Kola coast lie too far north.

Isolation basin stratigraphy and Holocene relative sea‐level change at the Norwegian—Russian border north of Nikel, northwest Russia

The marine‐lacustrine transition (isolation contact) in sediment cores from eight lake basins situated 13.5–72 m a.s.l., in the Norwegian‐Russian border area north of Nikel, northwest Russia, was identified based on lithological and diatom analysis, radiocarbon dated, and used to construct a relative sea‐level (RSL) curve for the Holocene. All the lakes except one (interpreted as having an unconformable slumped transition) show a regressive I‐II‐III (marine‐transitional‐lacustrine) facies succession, indicating a postglacial history of continuous emergence. The RSL curve shows rapid emergence between 10 000 and 8000 BP, very slow emergence between 7000 and 5000 BP, increased rate of emergence between 4500 and 4000 BP, and a moderate rate of emergence after 3500 BP. The low rate of emergence around 6000 BP correlates with the Tapes transgression of more coastal regions, but corresponding sea level, at 25–26 ma. present s.l., lies 5–10 m lower than the elevation predicted based on existing isobase maps for the region. The discrepancy suggests a need for further work in order to more rigorously define and map the Tapes transgression and associated shoreline complex in the northern Fennoscandian‐Kola region.

Distinction between the Storegga tsunami and the holocene marine transgression in coastal basin deposits of western Norway

Many coastal lakes were inundated by both the Storegga tsunami (7000 14 Cy r BP) and the mid-Holocene sea-level rise (the Tapes transgression) in western Norway. The tsunami eroded lake bottoms and deposited graded and/or massive beds of sand, rip-up clasts, and coarse plant material. By contrast, when the rising sea entered the lakes, it deposited only gyttja, silt and fine sand, without causing much erosion of the underlying lake sediments. Storegga tsunami deposits in some coastal lakes were interpreted previously as ordinary marine sediments from the Tapes transgression. Our reinterpretation of these deposits shows that the transgression maximum phase was reached after 6500 yr BP, more than 1000 yr later than previously inferred for the coast of Sunnmore. The new data cannot be combined in a shoreline diagram without showing the 6000 yr BP and 7000 yr BP shorelines as slightly warped. © 1998 John Wiley & Sons, Ltd.

Postglacial emergence and the Tapes transgression, north‐central Kola Peninsula, Russia

The history of postglacial emergence on the Murman coast, Kola Peninsula, is reconstructed based on twelve new radiocarbon ages from three marine sections and regional shoreline observations. Two pronounced shore levels are recognized below the Late Weichselian marine limit. The lower shoreline (11 ‐16 m a.s.l.) is associated with a transgression dated to 6200–6600 BP, correlative to the Tapes transgression on the Norwegian coastline. The upper shoreline (36–47 m a.s.l.) is not yet dated directly but probably correlates to the Main (Younger Dryas) shoreline. Strandline elevations descend eastward along the Murman coast. Observed emergence trends suggest the greatest regional Late Weichselian glacier load over the west‐central Kola Peninsula rather than in the southern Barents Sea.