Postglacial relative sea-level history: sediment and diatom records of emerged coastal lakes, north-central Kola Peninsula, Russia

Sediment cores recovered from four emerged lakes (54, 41, 22, and 7 m a.s.l.) provide new data on the deglaciation and relative sea-level history of the Murman coast, Kola Peninsula. The transition from marine to lacustrine sediment is identified in the cores by analysis of sediment physical properties and diatom assemblages. Fourteen AMS-radiocarbon ages on organic macrofossils isolated from core sediment provide chronology for the records. Basal ages from two of the cores indicate deglaciation of the area prior to 11000 BP. Radiocarbon ages associated with the marine-lacustrine sediment transition in the cores further constrain the emergence history of the area. The prominent late-glacial shoreline on the Murman coast (48 m a.s.l.) is dated to c . 10500–10300 BP, the emergence ages of lake basins 54 and 41 m a.s.l. Glaciofluvial terraces graded to this shore level indicate remnant glaciers on the north-central Kola Peninsula during the Younger Dryas.     

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.     

Postglacial climate and vegetation history, north-central Kola Peninsula, Russia: pollen and diatom records from Lake Yarnyshnoe-3

A sediment core from Lake Yarnyshnoe-3 (69°04'N; 36°04'E), an emerged coastal lake from the tundra of the north-central Kola Peninsula, has been analyzed for fossil pollen and diatoms. The pollen record shows the Younger Dryas event marked by increasing Artemisia coupled with decreases in Poaceae, Cyperaceae and Salix at c. 10 700 to 10 000 BP. This core provides the first well-defined palynological record of the Younger Dryas event on the Kola Peninsula. Stomates from Pinus were recovered from the core interval between 8000 and 6000 BP. The stomates, coupled with elevated values of pine pollen, indicate that Pinus sylvestris grew near the arctic coastline of the central Kola Peninsula in the middle Holocene. However, the small number of stomates suggests that pines were not plentiful. The diatom record from the core reflects basin isolation from the sea and indicates additional limnological changes during the climate transition between c. 5000 and 4000 BP. The broadly similar climate and vegetation history on the north-central Kola Peninsula and in Fennoscandia demonstrates the propagation of late glacial and Holocene climate events from the North Atlantic region into the Eurasian Arctic.     

Neoproterozoic metamorphism and deformation at the southeastern margin of the East European Craton,Uralides, Russia

The eastern margin of the East European Craton (EEC) has a long lasting geological record of Precambrian age. Archaean and Proterozoic strata are exposed in the western fold-and-thrust belt of the Uralides and are known from drill cores and geophysical data below the Palaeozoic cover in the Uralides and its western foredeep. In the southern Uralides, sedimentary, metamorphic and magmatic rocks of Riphean and Vendian age occur in the Bashkirian Mega-anticlinorium (BMA) and the Beloretzk Terrane. In the eastern part of the BMA (Yamantau anticlinorium) and the Beloretzk Terrane, K-Ar ages of the <2-µm-size fraction of phyllites (potassic white mica) and slates (illite) give evidence for a complex pre-Uralian metamorphic and deformational history of the Precambrian basement at the southeastern margin of the EEC. Interpretation of the K-Ar ages considered the variation of secondary foliation and the diagenetic to metamorphic grade. In the Yamantau anticlinorium, the greenschist-facies metamorphism of the Mesoproterozoic siliciclastic rocks is of Early Neoproterozoic origin (about 970 Ma) and the S1 cleavage formation of Late Neoproterozoic (about 550 Ma). The second wide-spaced cleavage is of Uralian origin. In the central and western part of the BMA, the diagenetic to incipient metamorphic grade developed in Late Neoproterozoic time. In post-Uralian time, Proterozoic siliciclastic rocks with a cleavage of Uralian age have not been exhumed to the surface of the BMA. Late Neoproterozoic thrusts and faults within the eastern margin of the EEC are reactivated during the Uralian deformation.     

Postglacial vegetation history of Mitkof Island, Alexander Archipelago, southeastern Alaska

An AMS radiocarbon-dated pollen record from a peat deposit on Mitkof Island, southeastern Alaska provides a vegetation history spanning ∼12,900 cal yr BP to the present. Late Wisconsin glaciers covered the entire island; deglaciation occurred > 15,400 cal yr BP. The earliest known vegetation to develop on the island (∼12,900 cal yr BP) was pine woodland (Pinus contorta) with alder (Alnus), sedges (Cyperaceae) and ferns (Polypodiaceae type). By ∼12,240 cal yr BP, Sitka spruce (Picea sitchensis) began to colonize the island while pine woodland declined. By ∼11,200 cal yr BP, mountain hemlock (Tsuga mertensiana) began to spread across the island. Sitka spruce-mountain hemlock forests dominated the lowland landscapes of the island until ∼10,180 cal yr BP, when western hemlock (Tsuga heterophylla) began to colonize, and soon became the dominant tree species. Rising percentages of pine, sedge, and sphagnum after ∼7100 cal yr BP may reflect an expansion of peat bog habitats as regional climate began to shift to cooler, wetter conditions. A decline in alders at that time suggests that coastal forests had spread into the island's uplands, replacing large areas of alder thickets. Cedars (Chamaecyparis nootkatensis, Thuja plicata) appeared on Mitkof Island during the late Holocene.     

Carbon budget of boreal forests in Middle Siberia

Doklady Earth Sciences -     

Postglacial fire, vegetation, and climate history in the Clearwater Range, Northern Idaho, USA

The environmental history of the Northern Rocky Mountains was reconstructed using lake sediments from Burnt Knob Lake, Idaho, and comparing the results with those from other previously published sites in the region to understand how vegetation and fire regimes responded to large-scale climate changes during the Holocene. Vegetation reconstructions indicate parkland or alpine meadow at the end of the glacial period indicating cold-dry conditions. From 14,000 to 12,000 cal yr B.P., abundant Pinus pollen suggests warmer, moister conditions than the previous period. Most sites record the development of a forest with Pseudotsuga ca. 9500 cal yr B.P. indicating warm dry climate coincident with the summer insolation maximum. As the amplification of the seasonal cycle of insolation waned during the middle Holocene, Pseudotsuga was replaced by Pinus and Abies suggesting cool, moist conditions. The fire reconstructions show less synchroneity. In general, the sites west of the continental divide display a fire-frequency maximum around 12,000–8000 cal yr B.P., which coincides with the interval of high summer insolation and stronger-than-present subtropical high. The sites on the east side of the continental divide have the highest fire frequency ca. 6000–3500 cal yr B.P. and may be responding to a decrease in summer precipitation as monsoonal circulation weakened in the middle and late Holocene. This study demonstrated that the fire frequency of the last two decades does not exceed the historical range of variability in that periods of even higher-than-present fire frequency occurred in the past.     

Postglacial vegetation, fire, and climate history of the Siskiyou Mountains, Oregon, USA

The forests of the Siskiyou Mountains are among the most diverse in North America, yet the long-term relationship among climate, diversity, and natural disturbance is not well known. Pollen, plant macrofossils, and high-resolution charcoal data from Bolan Lake, Oregon, were analyzed to reconstruct a 17,000-yr-long environmental history of high-elevation forests in the region. In the late-glacial period, the presence of a subalpine parkland of Artemisia, Poaceae, Pinus, and Tsuga with infrequent fires suggests cool dry conditions. After 14,500 cal yr B.P., a closed forest of Abies, Pseudotsuga, Tsuga, and Alnus rubra with more frequent fires developed which indicates more mesic conditions than before. An open woodland of Pinus, Quercus, and Cupressaceae, with higher fire activity than before, characterized the early Holocene and implies warmer and drier conditions than at present. In the late Holocene, Abies and Picea were more prevalent in the forest, suggesting a return to cool wet conditions, although fire-episode frequency remained relatively high. The modern forest of Abies and Pseudotsuga and the present-day fire regime developed ca. 2100 cal yr B.P. and indicates that conditions had become slightly drier than before. Sub-millennial-scale fluctuations in vegetation and fire activity suggest climatic variations during the Younger Dryas interval and within the early Holocene period. The timing of vegetation changes in the Bolan Lake record is similar to that of other sites in the Pacific Northwest and Klamath region, and indicates that local vegetation communities were responding to regional-scale climate changes. The record implies that climate-driven millennial- to centennial-scale vegetation and fire change should be considered when explaining the high floristic diversity observed at present in the Siskiyou Mountains.     

Postglacial emergence and Late Quaternary glaciation on northern Novaya Zemlya, Arctic Russia

Recent observations on postglacial emergence and past glacier extent for one of the least accessible areas in the Arctic, northern Novaya Zemlya are here united. The postglacial marine limit formed 5 to 6 ka is registered on the east and west coasts of the north island at 10 ± 1 and 18 ± 2 m aht, respectively. This modest and late isostatic response along with deglacial ages of >9.2 ka on adjacent marine cores from the northern Barents Sea indicate either early (>13 ka) deglaciation or modest ice sheet loading (<1500 m thick ice sheet) of Novaya Zemlya. Older and higher (up to 50 m aht) raised beaches were identified beneath a discontinuous glacial drift. Shells from the drift and underlying sublittoral sediments yield minimum limiting ¹⁴C ages of 26 to 30 ka on an earlier deglacial event(s). The only moraines identified are within 4 km of present glacier margins and reflect at least three neoglacial advances in the past 2.4 ka.     

Source selectivity: An assessment of volcanic glass sources in the southern primorye region,far East Russia

Artifacts made from volcanic glass have been found in archaeological contexts dating from the Late Palaeolithic (ca. 20,000 yr B.P.) through to the end of the Bronze Age (ca. 2700 yr B.P.) in the southern Primorye region of Far East Russia. A geoarchaeological survey of volcanic glass outcrops assessed the various potential sources to determine their potential for sustained exploitation. A characterization study of source samples and artifacts from 27 spatially and temporally dispersed sites using a combination of PIXE‐PIGME and relative density identified which sources had actually been exploited and a technological analysis of the assemblages described patterns of use. The combination of these three approaches shows the impact of a relatively stable geological environment on patterns of procurement and exchange. © 2008 Wiley Periodicals, Inc.     

Plate boundaries in the Far East region of Russia (from GPS measurement,seismic-prospecting,and seismological data)

The recent geodynamics of the Far East region of Russia is considered, where three large tectonic plates converge—Eurasian, North American, and Pacific, as well as several microplates—Okhotsk, Bering, and Amurian—have been hypothesized to exist. The available data on the position of the plate boundaries, the relative plate rotation poles, and the regional seismicity were analyzed, and parameters of plate motion models for northeastern Russia were determined in this study. The regional deep structure was investigated, using data obtained by different geophysical methods. The results of observations of the Magadan–Vrangel Island profile by deep seismic sounding (DSS), common-depth point (CDP) method, and correlation refraction method (CRM) are presented.     

Petroleum Habitat of East Siberia,Russia

East Siberia comprises three petroleum provinces—Lena-Tunguska, Lena-Vilyuy, and Yenisey-Anabar—that occupy the area of the Siberian craton. Petroleum has been generated and has accumulated in Precambrian rifts beneath the sedimentary basins and, more importantly, within the section of the basin itself. The platformal deposits of the basins extend beneath overthrusts on the east and south and are covered by sedimentary rocks of the West Siberian overthrusts on the east and south and are covered by sedimentary rocks of the West Siberian province on the west. Permafrost and gas hydrate deposits are present throughout most of East Siberia.

In the Lena-Tunguska province, rifts that developed during Riphean time are filled by thick sedimentary rocks, in which petroleum deposits have formed. In Early Cambrian time a barrier reef extended across the East Siberian craton from southeast to northwest. A lagoon to the west of this reef was the site of thick rhythmic salt deposits, which are the main seal for petroleum in the province. The sedimentary section of the platform cover ranges in age from Late Proterozoic to Permian. More than 25 oil and gas fields have been discovered in the province, all in Riphean through Lower Cambrian rocks.

The Lena-Vilyuy province includes the Vilyuy basin and the Cis-Verkhoyansk foredeep. During Middle Devonian time, a rift formed along the axis of what was to become the Vilyuy basin. This rift is filled by Upper Devonian and Lower Carboniferous basalt, elastics, carbonates, and evaporites. During this rift stage the region that was to become the Cis-Verkhoyansk foredeep was an open geosynclinal sea. The sedimentary cover consists of Permian, coal-bearing sedimentary rocks as well as elastics from the Lower Triassic, Lower Jurassic, Lower Cretaceous, and Upper Cretaceous, the latter only in the Vilyuy basin. In the Lena-Vilyuy petroleum province as many as nine gas and gas-condensate fields have been discovered.

The Yenisey-Anabar province is largely an extension of the West Siberian petroleum province. Permian sedimentary rocks are present only in the east, where they consist of elastics and some salt. The Triassic, Jurassic, and Cretaceous each are represented by thick clastic deposits. Total thickness of the sedimentary cover is up to 15 km on the west and 8 km on the east. Twelve gas and gas-condensate fields have been discovered in the western part of the province.     

Postglacial relative sea‐level rise in the Limfjord region,northern Jutland,Denmark

A new core drilled at Nørrekær Enge, Løgstør, Denmark, shows terrestrial lake and bog sediments lying beneath 10 m of marine sediments. Pollen analysis, ¹⁴C dating and sedimentary observations show that these sediments relate to an ancient lake basin that was flooded when the rising sea levels reached 8.0 m b.s.l. This new study has allowed a review of previous data relating to shoreline displacement from the Limfjord region of northern Jutland, Denmark. Here we present a new shoreline displacement curve spanning the period between c. 11 700 and 7700 cal. a BP and built upon the Nørrekær Enge data and data from seven other boreholes and excavations from the Limfjord region. A previous shoreline displacement curve for this region suggested a very rapid relative sea‐level rise of 3 to 5 m 100 a^?1 whereas this new curve suggests a much slower rise of around 1 m 100 a^?1, similar to global rates.     

Postglacial growth history of a French Polynesian barrier reef tract, Tahiti, central Pacific

The internal structure and growth pattern of Tahiti reefs over the last 14 ka is reconstructed using sedimentological, morphological and palaeobiological data coupled with radiometric dates in drill cores through the modern barrier reef. Flooding of the volcaniclastic deposits or the karst surface of a Pleistocene reef started at ≈ 14 ka BP, and coral growth began shortly after inundation. The sequence in the Tahiti barrier-reef edge has formed predominantly through long-term keep-up growth controlled by stable environmental conditions, while the adjacent backreef deposits did not start to accumulate before sea-level stabilization, around 6 ka. The dominance of Porites communities and the coeval occurrence of branching gracile Lithophyllum in the lowermost part of the postglacial reef sequence (14–11 ka) suggest the prevalence of uniformly moderate- to low-energy conditions and/or growth in slightly deeper waters all over the drilled area during the early reef stages. During the last 11 ka, the reef frameworks developed in a high-energy environment, at maximum water depths of 5–6 m, and were dominated by an Acropora robusta/danai–Hydrolithon onkodes association; the local interlayering of other coralgal assemblages (dominated by tabular Acropora or domal Porites ) reflects distinct diversification stages, resulting either from the palaeotopographic control of the substrate or from slight and episodic environmental changes.     

Tectonics of the junction region between the East European craton and West Arctic platform

The region of the junction and interaction between the East European Craton (EEC) and the West Arctic Craton (WAC) is regarded as a complexly built zone or assembly of both the volumetric and dividing linear tectonic elements: the Trollfjord–Rybachi–Kanin (TRK) Lineament, the pericratonic subsidence zone of the EEC, the Karpinskii Lineament, the Murmansk Block of the Fennoscandian (Baltic) Shield, and the Kolmozero–Voronya Zone, which are briefly characterized in this paper. Evidences of thrusting have been established not only in the TRK Suture Zone and on the Rybachi Peninsula, which represent a fragment of the Timanides fold–thrust belt, but also to the southwest, in the Upper Riphean and Vendian terrigenous sequences making up the Sredni Peninsula and related to the pericratonic trough of the VEC. Two phases of fold–thrust deformations with elements of left-lateral strike-slip offset pertaining to the activity and evolution of the lineament suture dividing the Sredni and Rybachi peninsulas have been recorded. The variously oriented fault–fold systems within this fault zone are evidence for multistage deformation and can be explained by an at least twostage change in the kinematics that control displacement along the fault. The disintegrated granitic massifs of the Archean crystalline basement tectonically squeezed out in the upper crust as protrusions are localized within TRK Fault Zone. Plagiogranitic bodies, which underwent superposed fault-fold deformations of both kinematic stages, are an evidence of the vigorous tectonic event that predated folding and two-stage strike-slip displacement along the TRK Fault—by thrusting of Riphean sequences from north to south toward the Archean craton. The nappe–thrust regional structure was formed at this stage; elements of it have been recognized in the Sredni, Rybachi, and Kanin peninsulas. The main stages of tectonic evolution in the junction zone between the EEC and the WAP have been revealed and substantiated.     

Late Weichselian (Valdaian) and Holocene vegetation and environmental history of the northern Timan Ridge, European Arctic Russia

Lake and peat deposits from the Timan Ridge, Arctic Russia, were pollen analysed, reconstructing the vegetation history and paleoenvironment since the Last Glacial Maximum (LGM) 20–18,000 years ago. The sites studied are located inside the margins of a large paleolake of about 20 km², by us named Lake Timan. This lake developed in the Late Weichselian, more than 30,000 years after the deglaciation of this region, and was formed due to increased precipitation and warmer summers that accelerated the melting of stagnant ice within its catchment. The lake was drained during the early Holocene when the outlet rivers eroded the spillways. A new generation of much smaller lakes formed during the Holocene when the last remnants of buried glacier ice melted away causing the exposed floor of Lake Timan to subside. Since deglaciation, the following regional vegetation development has been recorded: (1) During the initial stage of Lake Timan, the dominant vegetation was discontinuous steppe/tundra, with patches of snow bed vegetation. (2) A dwarf-shrub tundra established during the Late Weichselian interstadial (Allerød), probably reflecting warmer and moister conditions. (3) The Younger Dryas cooling is recognised by a reversal to steppe/tundra and snowbeds on unstable mineral-soils, and higher palynological richness. (4) Soon after the transition into the Holocene, a birch-forest established on the Timan Ridge. (5) A cooling starting around 8200 cal.years BP initiated the deforestation of the exposed hills. In the most protected sites, birch trees persisted until later than 4000 years ago, reflecting a gradual development into the present treeless dwarf-shrub tundra.     

Sources of fluids and material for gold and antimony mineralization in the Adychanskii ore region (East Yakutia,Russia)

The peculiarities of fluid inclusions; the O and C isotope composition of host rocks, vein minerals, and inclusions; and the S and Pb isotope composition of sulfides allowed us to distinguish two groups of fluids with a similar temperature, salinity, and source of the aqueous part produced upon metagenesis and mobilized during collisional events. Quartz-A precipitates from the CO₂–H₂O hydrocarbonate–Na fluid with a salinity of 7–10 wt % eq. NaCl at a depth of ～6 km (290–340°C, 1550 bar). Regeneration of quartz (quartz-C), precipitation of quartz-B, and quartz-AB with carbonate and chlorite occurred at a depth from 3.5 to 1.5 km (250–380°C, 1250–900–350 bar) from CO₂–CH₄–N hydrous sulfate–hydrocarbonate Na–Mg fluids with Cl^–, Ca, and K and a salinity of 5–10 wt % eq. NaCl, and a wide variety of impurities. The localization of veins in sinistral shear dislocations and strong heterogeneity in the P–T conditions allow us to explain the formation of fluid-2 by the postcollisional events.     

Postglacial land uplift patterns of south Sweden and the Baltic Sea region

Comparison of the land uplift pattern for the last 10,300 years, shown by studies of raised shorelines of the Baltic Ice Lake, with the pattern of present-day land uplift of Fennoscandia, shows that significant regional changes of uplift pattern have taken place. Some of these changes seem to be related to a halt in ice retreat during the Younger Dryas cold stage. It is also probable that some observed anomalies in the present uplift are not of glacio-isostatic origin, but are possibly related to structures in the lower lithosphere and upper mantle or large scale tectonics.