Age and chemical composition of dredged igneous rocks from the Vityaz Ridge, Pacific slope of the Kuril Island Arc

Original results of igneous rock studies are presented. The rocks were dredged during a marine expedition (cruise 37 of R/V Akademik M.A. Lavrent'ev in August-September, 2005) in the region of the submarine Vityaz Ridge and the Kuril Arc outer slope. Several age complexes (Late Cretaceous, Eocene, Late Oligocene, Miocene, and Pliocene-Pleistocene) are recognizable on the Vityaz Ridge. These complexes are characterized by a number of common geochemical features since all of them represent formations of island arc calc-alkali series. At the same time, they also have individual features reflecting different geodynamic settings. The outer slope of the Kuril Arc demonstrates submarine volcanism. Pliocene-Pleistocene volcanic rocks dredged here are similar to volcanites of the Kuril-Kamchatka Arc frontal zone.

(Table 1) K-Ar age and inert-gas-isotopes at DSDP Holes 68-501, 69-504B and 69-505B

Conventional K-Ar ages have been determined and inert-gas abundances have been measured on representative samples of altered rocks from Deep Sea Drilling Project Holes 501, 504B, and 505B in an attempt to correlate their degree of alteration with inert-gas and K-Ar data. Samples taken from the first 60 meters below the sediment/basalt interface give significantly higher ages than would be expected from the magnetic stratigraphy, though at greater depths the calculated ages are in broad agreement with the expected age. The inert gas ratios 20Ne/36Ar, 36Ar/84Kr, and 84Kr/130Xe also show a marked discontinuity at the 60-meter depth, and all these effects are interpreted as being a consequence of low-temperature alteration produced by burial metamorphism and by interaction with sea water (halmyrolysis).

Age and isotopes in bottom sediments from Core VER-99-1-St2, Baikal Lake

A simple, reliable, and efficient method has been elaborated for direct determination of isotopic composition of authigenic uranium in siliceous lacustrine sediments. The method is based on studying kinetics of selective extraction of authigenic uranium from sediments by weak solutions of ammonium hydrocarbonate followed by ICP-MS analysis of nuclides. To estimate contamination of authigenic uranium by terrigenous one contents of 232Th and some other clastogenic elements in the extracts were measured simultaneously. Selectivity of extraction of authigenic uranium from the sediments treated with 1% NH4HCO3 solution appeared to be no worse than 99%. The method was applied to analysis of isotopic composition of authigenic uranium at several key horizons of the earlier dated core from the Baikal Lake. Measurements directly show that 234U/238U values in Baikal water varied depending on climate, which contradicts existing hypotheses. Measured 234U/238U ratios in water of the paleo-Baikal match corresponding values reconstructed from isotopic data for total uranium in the sediments on supposition that U/Th ratio is constant in terrigenous fraction of the sediments. Direct experimental determination of total and authigenic nuclides in sediments enhances potentiality of the method for 234U-230Th dating of non-carbonate lacustrine sediments including those from the Baikal Lake within intervals corresponding to periods of glaciation, when sediments were rich in terrigenous components. Portions of terrigenous and authigenic uranium are well separated and we can study variability of sources of terrigenous matter and refine the earlier model for reconstructing climate humidity in the East Siberia.

(Table 1) Magnetozone boundaries, age and sedimentation rate at DSDP Hole 93-605

Natural Remanent Magnetization (NRM) was measured for regularly spaced samples from the 620-m-thick, lower middle Eocene to upper Maestrichtian section of DSDP Site 605. The total NRM of the Eocene chalks was too low (5-50 µA/m) to establish a reliable magnetic polarity stratigraphy. However, the results from the somewhat more clayrich Paleocene-upper Maestrichtian section are useful. A fourfold quality classification of the results of progressive demagnetization studies aided in determining the polarity of the original remanence. Two types (1 and 2a) showed a Characteristic Remanent Magnetization (ChRM) direction with reversed and normal polarity, respectively; the third type (2b) can be interpreted as having a reversed ChRM, which could not be cleaned, whereas the fourth type (3) is considered to be unreliable. The Site 605 magnetic polarity stratigraphy compares well with published sections, adding important detail to the correlation with planktonic microfossil zones and, hence, to the resolution of this portion of the time scale (C24-C32 on the Berggren et al., 1985, scale). The Cretaceous/Tertiary boundary occurs in a reversed polarity zone that has been correlated with Subchron C29r. We suspect the presence of an unconformity at the boundary between lithostratigraphic Units Va and IV a location which is also the level of Reflection Horizon A*.

Age and chemical composition of volcaniclastic rocks from the Sea of Japan

Petrographic and geochemical studies showed that Oligocene - Early Miocene volcaniclastic rocks from the southern part of the Sea of Japan are ascribed to high-potassium aluminous rocks of sub-alkaline volcanic series from active continental margins. A comparative analysis revealed spatiotemporal relation of Oligocene - Early Miocene subaerial volcanism of the Sea of Japan with Late Cretaceous and Eocene - Early Miocene ignimbrite volcanism of the East Eurasian margin. This allows to refer the volcaniclastic rocks of the Sea of Japan to the stage of ignimbrite volcanism that occurred during relative quiescence against general extension in the continental margin setting.

Isotope age and relative abundance of planktonic foraminifera in Core Vulk-34-90, Sea of Okhotsk

Based on analyses of taxonomic composition of planktonic foraminifera and oxygen isotopic composition of their shells in the sediment core V34-90 from the eastern slope of the USSR Academy of Sciences Rise in the southeast Sea of Okhotsk the main climatic and hydrological variations over the past 20 Ka have been traced and dated by the radiocarbon method. The followed periods have been revealed: glacial (20-12.5 Ka), deglaciation (12.5-8.0 Ka) with a pronounced cooling event (Late Drias about 10.8 Ka) and post deglaciation (last 8.0 Ka).

Age and sedimentation rates of bottom sediments from the Baltic Sea

An automated system is described for collecting and processing information from radiometric devices used in determination of isotopic age and sedimentation rate by radiocarbon and lead-210 methods. The system is used in a day-and-night continuous measuring mode, with six radiocarbon liquid counters and two low-background beta-counters. Examples are given of use of the system to determine average sedimentation rates in the Baltic Sea.

Age and d18O analysis relating to Cenozoic greenhouse climatesXXX

Past episodes of greenhouse warming provide insight into the coupling of climate and the carbon cycle and thus may help to predict the consequences of unabated carbon emissions in the future.

Age and alkenone-derived Holocene sea-surface temperature records of sediment core M40-4-SL78

This Special Issue of The Holocene contains 16 research papers based on a symposium at the 11th International Meeting of the European Union of Geosciences held in Strasbourg in April 2001. The aim of the symposium was a state-of-the-art assessment of empirical studies of postglacial marine and terrestrial climatic archives and their integration with numerical climate models. This editorial places the individual papers in the broader context of natural climate variability and anthropogenic impacts on the global climate system, regional differences in climate between maritime and continental areas, and the need for an improved theoretical basis for understanding the underlying causes of environmental change. The focus of the Special Issue is the dynamic and relatively well-understood climate of the North Atlantic and the European realm, where, in relation to the steepest offshore temperature gradient on Earth, observational data are abundant and many recent advances have been made in climate reconstruction from proxy archives. The editorial also contains a summary and overview of the papers included in the four main sections of the Special Issue, which emphasize: (1) numerical modelling experiments; (2) models of glacier buildup and equilibrium-line altitude; (3) marine and terrestrial proxy records of climatic change; and (4) multiproxy palaeoenvironmental reconstruction of a Portuguese lagoonal system.

Age and growth, and reproductive data from two benthic (Trematomus bernacchii and Trematomus pennellii) and two pelagic (Pagothenia borchgrevinki and Trematomus newnesi) ice fishes from McMurdo Sound, Antarctica

Data on age, total length, total weight, gonad weight, gonadosomatic index (GSI), sex and reproductive stage for ice fish specimens collected along the sea ice gradient in McMurdo Sound, Antarctica. Species on which data are provided are; Trematomus bernacchii, Trematomus bernacchii, Pagothenia borchgrevinki and Trematomus newnesi. Location and year of collection is also included for each fish.