Geological structure of the Curonian Spit (of the Baltic Sea) and its evolution history (revised)

The origin and evolution history of the Curonian Spit in the Baltic Sea are discussed based on geological and geomorphologic data. Evidence of the correlation between the spit formation stages and the Holocene sea level oscillations is presented. The ledges of moraine basement and marine accumulative features formed a single barrier. Its subsequent transformation occurred under the influence of the wave-related lithodynamic and eolian processes.     

Paleomagnetism of certain constituents of the Bay St. George sub-basin,western Newfoundland

Paleomagnetic studies have been made of certain constituents of the Bay St. George sub-basin. Specifically, results are reported from the Spout Falls Formation (Tournaisian), the Jeffreys Village Member of the Robinsons River Formation (Visean), and the Searston Formation (Namurian-Westphalian). The following magnetizations have been isolated: Spout Falls A (Tournaisian) with D = 343.5°, I = ?22.7°, k = 61.2, α₉₅ = 7.1° and the corresponding pole at 28.6°N, 139.5°E (4.5°, 8.5°); Spout Falls B (Kiaman) with D = 166.7°, I = 12.2°, k = 51.7, α₉₅ = 10.7° and the corresponding pole at 34.5°S, 42.7°W (5.5°, 10.9°); Jeffreys Village A (Visean) with D = 351.2°, I = ?27.3°, k = 54.0, α₉₅ = 7.6° and the corresponding pole at 26.5°N, 130.7°E (4.5°, 8.3°); Searston A (Namurian) with D = 161.7°, I = 11.7°, k = 107, α₉₅ = 7.4° and the corresponding pole at 33.9°S, 37.2°W (3.8°, 7.5°); and Searston C with D = 111.6°, I = ?13.8°, k = 28.8, α₉₅ = 14.5° and the corresponding pole at 19.6°S, 19.0°E (7.6°, 14.8°). After comparison with paleopoles of similar ages derived from eastern and western Newfoundland rocks, from constituents of the east coast basin and for interior North America, it is concluded that: (1) it is unlikely that any large scale relative motion took place since the Early Carboniferous between eastern and western Newfoundland; (2) it is unlikely that any north-south relative motion took place between the east coast basin and the Bay St. George sub-basin; and (3) the Bay St. George sub-basin results do not support the earlier proposed displaced terrane hypothesis of the northern Appalachians in as much as the motions during the Carboniferous are not supported. There is evidence of the northward motion of the Appalachians and North America as a whole during the Carboniferous. The magnetostratigraphic horizon marker in the Carboniferous separating a dominant normal and reversed magnetization on the older side and an entirely reversed (Kiaman) magnetization on the younger side may be placed in the Bay St. George sub-basin at the base of the Searston Formation.     

Yegorovite,Na<Subscript>4</Subscript>[Si<Subscript>4</Subscript>O<Subscript>8</Subscript>(OH)<Subscript>4</Subscript>]·7H<Subscript>2</Subscript>O,a new mineral from the Lovozero alkaline pluton,Kola Peninsula

A new mineral, yegorovite, has been identified in the late hydrothermal, low-temperature assemblage of the Palitra hyperalkaline pegmatite at Mt. Kedykverpakhk, Lovozero alkaline pluton, Kola Peninsula, Russia. The mineral is intimately associated with revdite and megacyclite, earlier natrosilite, microcline, and villiaumite. Yegorovite occurs as coarse, usually split prismatic (up to 0.05 × 0.15 × 1 mm) or lamellar (up to 0.05 × 0.7 × 0.8 mm) crystals. Polysynthetic twins and parallel intergrowths are typical. Mineral individuals are combined in bunches or chaotic groups (up to 2 mm); radial-lamellar clusters are less frequent. Yegorovite is colorless, transparent with vitreous luster. Cleavage is perfect parallel to (010) and (001). Fracture is splintery; crystals are readily split into acicular fragments. The Mohs hardness is ～2. Density is 1.90(2) g/cm³ (meas) and 1.92 g/cm³ (calc). Yegorovite is biaxial (?), with α = 1.474(2), β = 1.479(2), and γ = 1.482(2), 2V _meas > 70°, 2V _calc = 75°. The optical orientation is X ∧ a ～ 15°, Y = c, Z = b. The IR spectrum is given. The chemical composition determined using an electron microprobe (H₂O determined from total deficiency) is (wt %): 23.28 Na₂O, 45.45 SiO₂, 31.27 H₂O_calc; the total is 100.00. The empirical formula is Na_3.98Si_4.01O_8.02(OH)_3.98 · 7.205H₂O. The idealized formula is Na₄[Si₄O₈(OH)₄] · 7H₂O. Yegorovite is monoclinic, space group P2₁/c. The unit-cell dimensions are a = 9.874, b= 12.398, c = 14.897 Å, β = 104.68°, V = 1764.3 ų, Z = 4. The strongest reflections in the X-ray powder pattern (d, Å (I, %)([hkl]) are 7.21(70)[002], 6.21(72)[012, 020], 4.696(44)[022], 4.003(49)[211], 3.734(46)[(bar 2) 13], 3.116(100)[024, 040], 2.463(38)[(bar 4)02, (bar 2)43]. The crystal structure was studied by single-crystal method, R _hkl = 0.0745. Yegorovite is a representative of a new structural type. Its structure consists of single chains of Si tetrahedrons [Si₄O₈(OH)₄]∞ and sixfold polyhedrons of two types: [NaO(OH)₂(H₂O)₃] and [NaO(OH)(H₂O)₄] centered by Na. The mineral was named in memory of Yu. K. Yegorov-Tismenko (1938–2007), outstanding Russian crystallographer and crystallochemist. The type material of yegorovite has been deposited at the Fersman Mineralogical Museum of Russian Academy of Sciences, Moscow.     

Formation of accretion disks in close-binary systems with magnetic fields

We have developed a three-dimensional numerical model and applied it to simulate plasma flows in semi-detached binary systems whose accretor possesses a strong intrinsic magnetic field. The model is based on the assumption that the plasma dynamics are determined by the slow mean flow, which forms a backdrop for the rapid propagation of MHD waves. The equations describing the slow motion of matter were obtained by averaging over rapidly propagating pulsations. The numerical model includes the diffusion of magnetic field by current dissipation in turbulent vortices, magnetic buoyancy, and wave MHD turbulence. A modified three-dimensional, parallel, numerical code was used to simulate the flow structure in close binary systems with various accretor magnetic fields, from 10⁵ to 10⁸ G. The conditions for the formation of the accretion disk and the criteria distinguishing the two types of flow corresponding to intermediate polars and polars are discussed.     

New data on the structure of the Vitoria-Trindade seamount chain (western Brazil basin,South Atlantic)

In 2008, during cruise 24 of the R/V Akademik Vavilov, much of our research work was focused on the central segment (Jaseur and Davis seamounts, Dogaressa Bank) of the Vitoria-Trindade seamount chain (west of the Brazil basin) extending along 20.5° S. Work was conducted to survey the upper part of the sedimentary cover and to perform subbottom profiling. The samples dredged on the seamount slopes are represented by volcanites and Fe-Mn crusts.     

Geochemistry of organic matter of bottom sediments in the rises of the central Arctic Ocean

Based on geomorphological, lithological, and facial characteristics of the East Arctic continental margin, we studied the main factors controlling the Late Cenozoic supply of organic matter (OM) to the bottom sediments of the Central Arctic rises of the Arctic Ocean. Complex analysis of dispersed OM in the samples taken during the expeditions of the R/V “Akademik Fedorov” in 2000 and 2005 showed a significant difference between the sediments of the Lomonosov Ridge and Mendeleev Rise. The bottom sediments of the latter are strongly transformed and lack terrigenous components, as evidenced results from the main geochemical characteristics (contents of C_org, C_carb, N_org, bitumens, and humic acids) and the composition and distribution of hydrocarbon molecular markers (alkanes, saturated and aromatic cyclanes). The obtained data evidence that ancient sedimentary rocks containing genetically uniform deeply transformed (up to mesocatagenesis) OM played a significant role in the formation of the Pleistocene–Holocene sediments of the axial part of the Mendeleev Rise.     

Fragmentation and hydration of tektites and microtektites

Abstract— An examination of data collected over the last 30 years indicates that the percent of glass fragments vs. whole splash forms in the Cenozoic microtektite strewn fields increases towards the source crater (or source region). We propose that this is due to thermal stress produced when tektites and larger microtektites fall into water near the source crater while still relatively hot (>1150 °C). We also find evidence (low major oxide totals, frothing when melted) for hydration of most of the North American tektite fragments and microtektites found in marine sediments. High-temperature mass spectrometry indicates that these tektite fragments and microtektites contain up to 3.8 wt% H₂O. The H₂O-release behavior during the high-temperature mass-spectrometric analysis, plus high CI abundances (0.05 wt%), indicate that the North American tektite fragments and microtektites were hydrated in the marine environment (i.e., the H₂O was not trapped solely on quenching from a melt). The younger Ivory Coast and Australasian microtektites do not exhibit much evidence of hydration (at least not in excess of 0.5 wt% H₂O); this suggests that the degree of hydration increases with age. In addition, we find that some glass spherules (with <65 wt% SiO₂) from the upper Eocene clinopyroxene-bearing spherule layer in the Indian Ocean have palagonitized rims. These spherules appear to have been altered in a similar fashion to the splash form K/T boundary spherules. Thus, our data indicate that tektites and microtektites that generally contain >65 wt% SiO₂ can undergo simple hydration in the marine environment, while impact glasses (with <65 wt% SiO₂) can also undergo palagonitization.