Molecular and structural-group characteristics of hydrocarbons in Late Devonian oils of the Timan–Pechora Province

The paper presents gaz chromatography–mass spectrometry and ¹H- and ¹³C-NMR data on the composition of hydrocarbon markers and structural-group composition of oils in the Timan–Pechora oil and gas province. The set of samples is subdivided into groups whose oils differ in composition and the distribution of their polycyclic biomarkers. All of the oils show closely similar geochemical characteristics, types of their source organic matter, and thermal maturity. Comparison of oil characteristics (composition of the polycyclic biomarkers) and parameters determined by chromatography–mass spectrometry makes it possible to reveal certain important (and calling for further investigation) relations between the composition of the structural groups of hydrocarbons in the oil fluid and its geochemical characteristics.     

Zircon geochronology of the Klyuchevskoi gabbro-ultramafic massif and the problem of the age of the Mohorovicic paleoboundary in the Central Urals

The Klyuveskoi gabbro-ultramafic massif is the most representative ophiolite complex on the eastern portion of the Uralian paleoisland arc part. The massif is composed of dunite-harzburgite (tectonized mantle peridotites) and dunite-wehrlite-clinopyroxenite-gabbro (layered part of the ophiolite section) rock associations. The U-Pb age was obtained for the accessory zircons from the latter association using a SHRIMP-II ion microprobe at the Center for Isotopic Research at the Karpinskii Russian Geological Research Institute. The euhedral zircon crystals with thin rhythmic zoning from dunites are 441.4 ± 5.0 Ma in age. Zircons from olivine clinopyroxenite show three age clusters with sharply prevalent grains 449.0 ± 6.8 Ma in age. Two points give 1.7 Ga, which is probably related to the age of the mantle generating the layered complex. One value corresponds to 280 Ma, which possibly reflects exhumation of ultramafic rocks in the upper crust during the collision of the Uralian foldbelt. Thus, dunites and olivine pyroxenites from the Klyuchevskoi massif are similar in age at 441–449 Ma. The bottom of the layered part of the ophiolite section corresponds to the M paleoboundary and, consequently, the age of the Mohorovicic discontinuity conforms with the Ordovician-Silurian boundary in this part of the Urals.     

Absolute geomagnetic paleointensity as recorded by ∼1.09 Ga Lake Shore Traps (Keweenaw Peninsula, Michigan)

Absolute geomagnetic paleointensity measurements were made on 255 samples from 38 lava flows of the ～1.09 Ga Lake Shore Traps exposed on the Keweenaw Peninsula (Michigan, USA). Samples from the lava flows yield a well-defined characteristic remanent magnetization (ChRM) component within a ～375°C–590°C unblocking temperature range. Detailed rock magnetic analyses indicate that the ChRM is carried by nearly stoichiometric pseudo-single-domain magnetite and/or low-Ti titanomagnetite. Scanning electron microscopy reveals that the (titano)magnetite is present in the form of fine intergrowths with ilmenite, formed by oxyexsolution during initial cooling. Paleointensity values were determined using the Thellier double-heating method supplemented by low-temperature demagnetization in order to reduce the effect of magnetic remanence carried by large pseudosingle-domain and multidomain grains. One hundred and two samples from twenty independent cooling units meet our paleointensity reliability criteria and yield consistent paleofield values with a mean value of 26.3 ± 4.7μT, which corresponds to a virtual dipole moment of 5.9 ± 1.1×10²² Am². The mean and range of paleofield values are similar to those of the recent Earth’s magnetic field and incompatible with a “Proterozoic dipole low”. These results are consistent with a stable compositionally-driven geodynamo operating by the end of Mesoproterozoic.     

Deep crustal structure of the kamchatkan volcanic regions

Crustal structure in a number of Kamchatka volcanic regions is deduced from geophysical data. Anomalous structure and physical properties of the crust are found beneath some volcanic groups. Beneath the Klyuchevskaya and Avachinskaya volcanic groups crustal layers have high elastic properties. There is a thick transition layer from the crust to the upper mantle which has lower clastic properties and electrical resistance. These data, supported by experimental investigations of elastic properties of xenoliths in volcanic rocks at high pressures and temperatures, enable the probable substance composition of the crustal layers to be defined. The feeding zones and magma chambers of individual volcanoes are deduced from anomalies in gravity, electrical conductivity and seismic wave propagation.     

LAND-USE MAPPING FROM REMOTE SENSING DATA: A WORLD SUMMARY

A brief history of land-use mapping sets the stage for a survey of contemporary land-use mapping across the world, and more specifically, the applications of remote sensing methods in such mapping. Other issues addressed include the need to refine the definition of land use to encompass the totality of geographic space, to formally recognize the difference between large-scale maps of agricultural land-use and smaller-scale general land-use maps, and to investigate more closely the wisdom and desirability of a standardized world land-use classification. Four types of land-use maps are identified: diagnostic/informational, historical, dynamic, and predictive. Translated from: Vestnik Leningradskogo Universiteta, 1983, No. 24, pp. 52-61.     

Empirical Estimates of the Contribution of Greenhouse Gases and Natural Climatic Variability to Surface Air Temperature Trends for Various Latitudes

Doklady Earth Sciences - Quantitative estimates of the contribution of anthropogenic forcing, characterized by changes in the radiative forcing of greenhouse gases in the atmosphere, and key modes...     

Laboratory Modeling of Aftershock Sequences: Stress Dependences of the Omori and Gutenberg–Richter Parameters

Izvestiya, Physics of the Solid Earth - Laboratory experiments on studying the aftershock regime are carried out on sandstone specimens at different levels of axial loading and uniform compression...     

The first Lu–Hf zircon isotope data for gabbro–diorite–tonalite associations of the Urals

Doklady Earth Sciences - The Lu–Hf isotope systematics of zircon from the gabbro–plagiogranite association (gabbro, diorite, tonalite, and plagiogranite), which is one of the most...