Lake Cheko and the Tunguska Event: impact or non‐impact?

Several lines of evidence were presented in Gasperini et al. [Terra Nova (2007), vol. 19 , pp. 245–251] suggesting that Lake Cheko, a small lake close to the alleged epicentre of the 1908 Tunguska Event, might be a secondary impact crater. Collins et al. [Terra Nova (2008), this volume] argue against this hypothesis. We reply here arguing in favour of an impact origin for Lake Cheko.     

Tectonic map of the Vendian–Lower Paleozoic structural stage of the Lena–Tunguska petroleum province,Siberian Platform

A new version of the tectonic map for the Vendian–Lower Paleozoic structural stage of the Lena–Tunguska petroleum province is presented. The map is based on the electronic structure map at a scale of 1:1,000,000, which was the first to be compiled for the uppermost Vendian within the study area. However, no tectonic zonation was made for the deep-buried Meso-Cenozoic Yenisei–Khatanga and Vilyui depressions. The principles and methodology of mapping are given. The study presents spatial, morphological, and quantitative characteristics of the major and large structures.     

Key section of the Preobrazhenka productive horizon in the Vendian–Lower Cambrian carbonate complex (Lena–Tunguska petroliferous province)

We present results of lithofacies, reservoir, geochemical, well logging, and petrophysical studies of the key section of the Vendian–Lower Cambrian Preobrazhenka productive horizon in the Lena–Tunguska province. We have considered the composition, structure, and formation conditions of the deposits as well as the intensity of postsedimentation processes and the rock geochemistry, petrophysics, and reservoir properties.     

Traces of the Tunguska Event (1908) in Sediments of Zapovednoe Lake Based on SR–XRF Data

Doklady Earth Sciences - An anomalous layer enriched with chemical elements indicating the presence of terrigenous matter was discovered in the sediment core of Zapovednoe Lake located 60 km from...     

Cambrian Archocyathina from the Gorge District of the Yangtze

Previous studies of Archocyathina from the Gorge District of the Yangtze and other parts ofChina are briefly reviewed. Ninc species of Arch?ocyathina, belonging to four different genera andtwo families are described and illustrated, of which only two species are new. The presence ofCambrocyathus (="Archaeocyathus"). Archaeocyathus (="Spirocyathus"), Retecyathus andProtopharetra known from Siberia Sardinia and Australia is reported for the first time. Stratigraphicalposition and distribution of the Archaeocyathina beds in Hupch, Szechuan and Kwcichow are discussed.Special consideration is given to the so-called "Ichang limestone" of Cambrian age. The age of theArchaeocyathina beds in central China is referable to the Lower Cambrian.     

Geodynamics of the Barents–Kara margin in the Mesozoic inferred from paleomagnetic data on rocks from the Franz Josef Land Archipelago

New data on paleomagnetism and isotope geochronology of Jurassic and Early Cretaceous basic igneous rocks on Franz Josef Land Archipelago (FJL) represented by flows and dikes are discussed. The first paleomagnetic data obtained for these rocks offer the opportunity to suggest a model of spatial changes in the FJL block position during the Jurassic?Cretaceous. In the Early Jurassic, the block occupied a different position relative to Europe from the modern one. It was displaced in the northeasterly direction by a distance of approximately 500 km and rotated clockwise by about 40° relative to its modern position. By the Early Cretaceous, the FJL block occupied a position close to the present-day one avoiding subsequent substantial relative displacements. The data obtained are of principal significance for reconstructing the geodynamic evolution of Arctic structures in the Mesozoic and contribute greatly to the base of paleomagnetic data for the Arctic region, development of which is now in progress.     

Two Neoarchean supercontinents? Evidence from the Paleoproterozoic

An unresolved question in Precambrian geology is the relationship between Archean crustal fragments that are now separated by younger orogens: were they once contiguous? Williams et al. (1991) proposed the name ‘Kenorland' for a speculative Neoarchean supercontinent comprising the Archean provinces in North America. Recently, a large number of ca. 2.5–2.0 Ga magmatic, metamorphic, detrital and xenocrystic ages have been reported from North America. We interpret that the wide geographic distribution and temporal spread of these ages may signify long-lived, regional-scale mantle upwelling, and anorogenic magmatic and metamorphic processes related to the protracted breakup of Kenorland. Breakup may have extended from ca. 2.5 to 2.1 Ga, culminating with dispersion of continental fragments at ca. 2.1–2.0 Ga. In North America, ca. 2.5–2.1 Ga intracratonic basin successions (e.g. Hurwitz Group) formed in the interior of Kenorland before dispersion, and passive margin sequences flanking the Superior Province (e.g. Huronian Supergroup) and the Wyoming Province (e.g. Snowy Pass Supergroup) defined the edges of Kenorland. Earliest Paleoproterozoic magmatic and sedimentary rocks, which include voluminous quartz arenites and glacigenic deposits, are consistent with a high-standing supercontinent and a mantle superplume. The Paleoproterozoic record from the Baltic and Siberian shields is similar to that of North America, suggesting inclusion in Kenorland. A slightly different record from the southern continents suggests a second, coexisting supercontinent that included the Zimbabwe, Kaapvaal, and Pilbara cratons, (‘Zimvaalbara' of I.G. Stanistreet), the São Francisco Craton, and possibly, cratonic blocks in India. Attenuation of this second supercontinent started earlier than in Kenorland (ca. 2.65 Ga) and was accompanied by high sea level and deposition of vast Lake Superior-type iron formations. Immediately thereafter, both supercontinents became emergent and were subject to global cooling and glaciation.     

Tantalo–Niobate from the Apollo-17 Regolith

Doklady Earth Sciences - Particles of tantalo–niobate of the ferrotantalite-manganotantalite series are discovered for the first time in two lunar regolith fragments delivered by the...     

Deep Tectonophysical Process of the Uplift of the Northern Qinghai--Tibet Plateau--Evidence from the Integrated Geological--Geophysical Profile from Golmud to the Tanggula Mountains, Qinghai Province, China

The tectonic activities occurring since the Cenozoic in the northern part of theQinghai-Tibet Plateau (the region from the East Kunlun Mountains to the Tanggula Mountains)were probably caused by the intense intraplate deformation propagation after the collision be-tween the Indian plate and the Eurasian plate. Their main expressions include the substantial up-lifting of the plateau, alternation of horizontal extension and compression under the verticalgreatest principal stress σ_1, occurrence of rift-type volcanic activity, formation of thebasin-range system, and successive eastward extrusion of blocks resulting from large-scalestrike-slip faulting. Geophysical exploration and experiments have revealed that there exist close-ly alternating horizontal high-velocity and low-velocity layers as well as lithospheric faults of aleft-lateral strike-slip sense in the lower part of the lithosphere (the lower crust and lithosphericmantle, 60-120 km deep). Based on an integrated study of the geological-geophysical data avail-able, the authors have proposed a model of deep-seated mantle diapir and the associatedtectonophysical process as the dynamic source for the uplift of the northern part of theQinghai-Tibet Plateau.     

Campanian-Maastrichtian radiolarians from the Malokuril’skaya Formation,the Shikotan Island

The results of radiolarian analysis confirm the Campanian-Maastrichtian age of the Malokuril’skaya Formation in the Shikotan Island. The Campanian-Maastrichtian age of the formation is implied simultaneously by radiolarians and inoceramids. The studied Campanian and Campanian-Maastrichtian radiolarian assemblages include abundant specimens representing genus Prunobrachium, characteristic of which was bipolar distribution in cold-water to temperate basins. The new occurrence site of prunobrachids is established at the latitude of 43°N, the Far East of Russia.     

Oil geochemistry derived from the Qinjiatun–Qikeshu oilfields: insight from light hydrocarbons

A suite of 27 oils from the Qinjiatun–Qikeshu oilfields in the Lishu Fault Depression of the Songliao Basin was analyzed using whole oil gas chromatography. In combination with the relative distribution of C₂₇, C₂₈, and C₂₉ regular steranes, detailed geochemical analyses of light hydrocarbons in oil samples revealed crude oils characterized by the dual input of lower aquatic organisms and higher terrestrial plants. Several light hydrocarbon indicators suggest that the liquid hydrocarbons have maturities equivalent to vitrinite reflectances of around 0.78%–0.93%. This is consistent with the maturity determination of steranes C₂₉ 20S/(20S + 20R) and C₂₉ ααβ/(ααα + αββ). Crude oils derived from the two distinct oilfields likely both have source rocks deposited in a lacustrine environment based on light hydrocarbon parameters and on higher molecular weight hydrocarbon parameters. The results show that light hydrocarbon data in crude oils can provide important information for understanding the geochemical characteristics of the Qinjiatun–Qikeshu oils during geologic evolution.     

Multi-Stage Mineralization of the Early Yanshanian Granites from the Central Nanling Region, South China: Implications from REE Geochemistry

Please refer to the attachment(s) for more details.     

Geochemical Characteristics and Genesis of the Granitic Gneisses from the Southeastern Dabie Mountains

The granitic gneisses from the ultrahigh-pressure (UHP) metamorphic terrain of the southeastern Dabie Mountains encompass two types: monzonitic granitic gneiss and alkali-feldspar granitic gneiss, which are characterized by rich alkalis, poor CaO, high FeO/MgO, particularly high Ba, Rb, Th, Ta, REE (except Eu), Ga, Nb and Zn, and low Sr, Eu, Cr, Co and Ni. The gneisses, particularly the alkali-feldspar granitic gneiss, have typical chemical characteristics of A-type granites. They resulted from partial melting of crustal materials existing in the rift zone along the northern margin of the South China block during the Neoproterozoic. These gneisses might not have undergone UHP metamorphism during the late Triassic, but were involved into UHP rocks by the tectonic mixing process and kept the exhumation message of the UHP rocks from the middle and upper crust.     

Volcanic ash from the 2010 Eyjafjallajökull eruption

The April 2010 eruption of Eyjafjallajökull volcano created major disruption to European air traffic. The main uncertainty in predicting the volcanic ash distribution in air space was the nature of the eruption plume including the grain size of the volcanic ash. The volcanic ash samples collected in the vicinity of the volcano on April 15th 2010, the first day of air traffic disruption in Europe, reveal that up to 70% of the mass was less than 60 μm in diameter. This fine grained ash could remain suspended in the atmosphere for days, posing threats to air traffic.     

Abrupt climate changes: from the past to the future – a review

 A review of climatic variability is given with a focus on abrupt changes during the last glacial. Evidence from palaeoclimatic archives suggests that these were most likley due to reorganisations of the atmosphere–ocean system. The mechanisms responsible for these changes are presented. Their implication for future climate changes is discussed in light of recent climate model simulations. Received: 24 June 1998 / Accepted: 27 November 1998     

A continuous tephrostratigraphic record from the Labrador Sea spanning the last 65 ka

Volcanic ash preserved in marine sediment sequences is key for independent synchronization of palaeoclimate records within and across different climate archives. Here we present a continuous tephrostratigraphic record from the Labrador Sea, spanning the last 65–5 ka, an area and time period that has not been investigated in detail within the established North Atlantic tephra framework. We investigated marine sediment core GS16-204-22CC for increased tephra occurrences and geochemically analysed the major element composition of tephra shards to identify their source volcano(es). In total we observed eight tephra zones, of which five concentration peaks show isochronous features that can be used as independent tie-points in future studies. The main transport mechanism of tephra shards to the site was near-instantaneous deposition by drifting of sea ice along the East Greenland Current. Our results show that the Icelandic Veidivötn volcanic system was the dominant source of tephra material, especially between late Marine Isotope Stage (MIS) 4 and early MIS 3. The Veidivötn system generated volcanic eruptions in cycles of ca. 3–5 ka. We speculate that the quantity of tephra delivered to the Labrador Sea was a result of variable Icelandic ice volume and/or changes in the transportation pathway towards the Labrador Sea.     

Typochemical features of the rare-earth component of monazites from the Ilmen’ reserve

By means of X-ray fluorescence with synchroton radiation (XRF-SR), the contents of all 14 rare-earth elements (REEs) and that of Y were determined in 12 monazite samples from different veins in the Ilmen’ Reserve (South Urals). It was found that, in anphibole-micaceous-carbonate mineralized zones within metabasites, monazites were pronouncedly depleted in middle and, especially, in heavy rare-earth elements (HREEs) (from 0.25% and below for Sm, 0.08% or below for Gd, 0.03% for Dy, 0.01% for Er and Tm, below 0.005% for Yb, trace amounts of other odd HREEs, at a Y content of 0.1% or below). Monazites from the veins of granitic pegmatites were characterized by vastly decreased La contents (4–8 compared to 11–13% for the group above), at high values for Pr (to 3%), Nd (to 8%), Sm (to 1.3%), Gd (to 1.1%), Dy (to 0.9%), Er (to 0.2%), Yb (to 0.05%), and Y (from 0.2 to 1.7%). Here, the values for odd REEs are also quite high compared to the group above (to 0.2% for Tb, to 0.08% for Ho, and to 0.1% for Tm).

     

Early Stages of the Evolution of Uralides as Evidenced from the U–Pb Systematics of Detrital Zircons from Rift Complexes

The U–Pb isotope data and corresponding ages of detrital zircons from rocks of the basal complexes of the Uralides of different segments of the Ural Fold Belt are considered. It was established that complexes of ancient domains of the East European Platform (Volga-Uralia, Sarmatia, Kola, etc.) seem to have been the main provenance areas of the clastic material for the Southern, Middle, and Northern Urals. This means that there were relatively remote and local (igneous formations of the pre-Uralides) provenance areas. Rift rock associations of the Uralides of the Subpolar and Polar Urals were formed mainly through erosion of local provenance areas (predominantly, Late Riphean–Vendian island-arc and orogenic magmatic complexes of the Proto-Uralides–Timanides). Detrital zircons of Riphean age dominate in rocks of the basal complexes of the Uralides. A source for them could have been rock complexes of Svecofennian-Norwegian Orogen and Cadomides of the Scythian-Turan Plate, intraplate magmatic formations, and metamorphic complexes, as well as blocks accreted to the margin of the East European Platform in the Late Precambrian–Cambrian and later detached and displaced during the Ordovician rifting and spreading. In general, the basal complexes of Uralides were formed owing to supply of clastic material from both remote and local sources. Despite the appearance of information of a totally new level (U–Pb isotope ages of detrital zircons, their Lu–Hf systematics, and the distribution features of rare earth and trace elements), the contribution of these sources to the formation of the Late Cambrian–Early Ordovician clastic strata is hardly possible at present to evaluate.