Home – Home – Jornals – Russian Geology and Geophysics 2014 number 12

The clay fractions of saprolites from granites, basalt, and schists in Egypt were subjected to mineralogical and geochemical investigations to examine the effect of source rock on the composition of the saprolites and the possibilities of these saprolites as a source of the nearby sedimentary kaolin deposits. The clay fractions of the studied saprolites show mineralogical and geochemical variations. Saprolites from the granites consist of kaolinite, while saprolites from the basalts are composed entirely of smectite. Schist-derived saprolites are composed of kaolinite in some cases and of a mixture of kaolinite, illite, and chlorite in the other. Saprolite from the basalts is characterized by relatively higher contents of TiO ₂ and Ni compared to saprolites from the granites. Saprolites from the granites have higher contents of Ba, Li, Pb, Sr, Th, Y, and Zr compared with those of the saprolites from the basalts and schists. Saprolites from different schists show variations in the distributions of many constituents, such as TiO ₂, Cr, Ni Ba, Y, and Zr. Although chondrite-normalized rare-earth element (REE) patterns are characterized by relative enrichments in light rare-earth elements (LREE) compared to heavy rare-earth elements (HREE) in all saprolites, granitic saprolites show negative Eu anomalies, while saprolites from the basalt have no Eu anomaly. The REE patterns of saprolites from the schists exhibit slight positive Ce anomalies and slight to moderate negative Eu anomalies. Weathering of saprolites from the basalt and metasediments is classified as bisiallitization type, while weathering of saprolites from the granite is allirization type. Saprolites from the schists vary from bisiallitization (Aswan and Abu Natash) to allirization (Khaboba) type. Saprolites from the Khaboba schist can be considered the possible source of the Carboniferous kaolin deposits in the Hasber and Khboba areas of Sinai, based on the similarity in the mineralogy and geochemistry of major, trace, and rare-earth elements between the saprolites and the deposits. On the other hand, Carboniferous sedimentary kaolin deposits in the Abu Natash area, as well as the Cretaceous kaolin deposits in all areas of Sinai, might have been derived from the nearby schist saprolites, based on the similarity in the mineralogy and geochemistry between the saprolites and the kaolin deposits. Granites from the Arabian-Nubian Shield (ANS) and East Sahara Craton (ESC) are the possible sources of the pisolitic and plastic kaolin deposits in the Kalabsha area (Aswan), as indicated from the similarity in the mineralogy and geochemistry of the granitic saprolites and the kaolin deposits.

In the autumn of 2010, contrasting dispersion aureoles of atomic mercury were revealed in the northern Sea of Japan, in the vicinity of the Vityaz’ and Alpatov Rises. Based on the elimination method, the assumption is made that the aureoles resulted from the supply of mercury from hydrothermal or water-gas bottom sources through the sea water column, either in gas bubbles or as a result of diffusion and turbulent mixing. It is inferred that gas-mercury measurements can be used in geological research in sea water areas.

We present results of a two-year research experiment on the processes involving iron-manganese bacteria at different biogeochemical barriers. Analysis of experimental samples was carried out on a scanning electron microscope (EVO-40HV, Carl Zeiss) and an X-ray diffractometer (Rigaku MiniFlexII). It is shown that goethite can form in vitro in the presence of iron-containing groundwater and iron-manganese bacteria.

A suite of mantle peridotites sampled in the Kamchatsky Mys includes spinel lherzolite, clinopyroxene-bearing harzburgite, and harzburgite. Mineral chemistry of olivine, chromian spinel, and clinopyroxene show strongly correlated element patterns typical of peridotite formed by 8% to more than 22% partial melting. Clinopyroxene in the Kamchatka peridotites is compositionally different from that of both abyssal and suprasubduction varieties: Clinopyroxene in lherzolite is depleted in LREE relative to abyssal peridotite and that in harzburgite has very low LREE and Sr unlike the subduction-related counterpart. These composition features indicate that the rocks ultra-depleted in basaltic components originated in the vicinity of a hotspot, possibly, proto-Hawaiian plume, which provided high temperature and melting degree of the MORB source mantle at mid-ocean ridge.

The contents of biogenic components in 1511 samples of the Baltic Sea sediments (depth range 0-5 cm) are studied, and maps of their distribution are compiled. The sediments contain ≤13.03 % Corg, ≤1.33 % N, ≤ 9.0 % SiO2 am, ≤5.0 % CaCO3, and ≤1.45 % P. The maximum and elevated contents of components are found in the mud of the sea deeps. The more fraction <0.01 mm the sediments contain, the higher are the contents of components. Four facies types of carbonaceous mud, precursors of shales, have been recognized: (1) shallow-water (lagoon) lime sapropel, (2) carbonaceous mud of the shallow-water Gulf of Finland, (3) carbonaceous mud of the middle-depth Baltic Sea, and (4) laminated carbonaceous metal-bearing mud. The latter type of mud is strongly enriched in manganese and ore-forming trace elements, which points to its formation in the stagnant environment. In composition the Baltic Sea mud is similar to petroliferous mudstones of the Bazhenov Formation in West Siberia and to ancient black shales.

The paper describes Lower Jurassic (horizons J ₁₆ and J ₁₅) and Achimovka (Neocomian clinoforms) reservoirs in the area of the Nyurol’ka megadepression and its framing (42,000 km ²). The total thicknesses of seven Achimovka sedimentary cycles are mapped. The thermal history of the Togur and Bazhenov parental sediments in the sections of 39 deep wells is reconstructed by paleotemperature modeling. The geotemperature criterion is used to identify paleosources of oil generation, starting from the Jurassic. The distribution of the relative density of the resources of the generated Togur and Bazhenov oils is estimated and shown on sketch maps. The Lower Jurassic reservoir is divided into zones depending on the distribution of the relative density of the Togur oil resources, and the Achimovka reservoir, of the Bazhenov oil resources. The top-priority oil search zones are proposed.

We present new data on the structure of deep horizons of the sedimentary cover of the South Kara syneclise, based on an integrated interpretation of data from modern seismic prospecting and data on the geologic structure of the adjacent folded areas. A network of seismic base profiles reprocessed with up-to-date programs is used to determine the structure of the wave fields of the pre-Jurassic sediments of the South Kara syneclise. The interpretation of the wave fields with the use of the network of seismic base profiles shows that the wave fields of the Pai-Khoi-Novaya Zemlya monoclise and the Novaya Zemlya-Taimyr terrace are fundamentally different from those of the South Kara central area of basins and uplifts. We substantiate a new structural and tectonic zonation of the northern West Siberian Plate, with areas of Hercynian and Early Cimmerian consolidation. The geologic evolution of the South Kara syneclise and adjacent areas in the Late Paleozoic-Early Jurassic is considered. The studies show that the Hercynides of the northern Taimyr Peninsula occupy the deepest central part of the South Kara syneclise, including the North Siberian step. They are separated from the coeval sediments of the surface part of the northern West Siberian Plate by the Early Cimmerian folding of the Yamal-Pai-Khoi saddle, which joins the Early Cimmerian West Taimyr folded area to the Early Cimmerides of Pai-Khoi and Novaya Zemlya. The Permo-Triassic rifts distinguished in central West Siberia have no shelf extension. Areal structural studies along the surface of the acoustic basement and analysis of wave fields showed that the structures of the South Kara syneclise were semiconcentric and concentric intermontane basins and troughs in the Permian and Lower-Middle Triassic. They formed at the orogenic stage of evolution of the Hercynides. In the Devonian-Carboniferous, the South Kara syneclise was an intracontinental block structure. It is presumed that elevated blocks consist of carbonate sediments, whereas the separating troughs consist of bathyal terrigenous sediments. The Hercynian folding, which affected mainly deep-water sediments, was followed by an inversion of the troughs, their uplifting and disintegration. The intermontane basins which formed instead of carbonate shelf in the Permian were filled with sediments from the uplifts which formed instead of the troughs. A well-grounded conclusion is made about the hydrocarbon potential of the pre-Jurassic basement of the South Kara syneclise. The layered seismic record of the pre-Jurassic sediments suggests their heterogeneous composition, i.e., the presence of sand and clay series (reservoirs and caps). The pools might be of the arch-bedded and lithologic (traps which formed in the case of the toplap of beds onto the eroded surface) types or be localized along the line of pinching-out of the Triassic sediments. The largest number of Paleozoic structures is concentrated on the Rogozinskii and Vilkitsky arches, in the Monskaya and Matusevich saddles, and in the northern Rusanov-Skuratov arch.

According to GPS monitoring, recent tectonic process between Tarim and West Siberia in the band within 80-95ºE is generated by the northward movement of the Tarim block. During the accompanying horizontal compression of the area, orogeny takes place within linear mobile zones when blocks are squeezed into the upper half-space. When the orientation of the mobile zones is transverse to the compression direction, the leading orogenic process is the formation of reverse faults. When these directions intersect at an acute angle, the principal features of the mountain relief are formed by oblique-slip and strike-slip faults. The spatial distribution of seismic activity A ₁₀ over a 40-year period of instrumental observations within the mobile zones of the study area is extremely nonuniform. Seismic activity increases to the south, toward the source of deformations - the Indo-Eurasian collision. The maximum activity is observed at the reverse-fault boundaries of the eastern Tien Shan (~40). The seismic activity of the strike-slip fault boundaries of the Great Altai is considerably lower (~0.11-0.16).

Lenses of water-saturated unfrozen rocks (taliks) in permafrost are important sources of freshwater in high-latitude regions. Taliks stand out against the host frozen rocks in much lower resistivity and thus are detectable by resistivity surveys. TEM soundings are especially efficient in this application as they can go without galvanic grounding, have small offsets, and are sensitive to buried conductors. Early-time TEM data in the Taz area of the Yamal-Nenets district bear strong effects of fast-decaying inductively induced polarization (IIP), which rules out the use of nonpolarizable earth assumption for their interpretation. The TEM responses are inverted by means of the TEM-IP software using the model of a polarizable earth with Cole-Cole complex frequency-dependent conductivity. The resulting earth model mainly includes three layers, with a 100 to 250 m thick highly resistive polarizable upper layer. The polarization parameters of the layer (chargeability, time constant and exponent) are typical of frozen sedimentary rocks, while the presence of a talik reduces notably the effective resistivity and chargeability. This feature can be used as a guide to taliks, as it was confirmed by TEM surveys and subsequent drilling.

The composition, structure, and properties of different genetic types of serpentinites developed after ultrabasic rocks are studied. The rocks were sampled from massifs located along the Main Ural Fault, in a Paleozoic subduction zone. We consider specific features of serpentinites developed after chromite-bearing ultrabasic rocks, in metamorphic zones of carbonate rocks, and within the zone of weathering of ultrabasic rocks. A comparative study of the microstructure and chemical and phase compositions of serpentinites is carried out by IR spectroscopy, scanning electron microscopy, and thermal, X-ray diffraction, and microprobe analyses. The petrophysical properties and acoustic emission of the rocks are examined. Several genetic and structural groups of serpentinites developed after different protoliths (mantle and crustal) in different geologic conditions are recognized.

Based on analysis of geothermal data from the Ural superdeep borehole (SG-4) and Onega parametric borehole, the first reconstructions of the ground surface heat flux changes for the last 40 kyr have been made. The increase in heat flux during the Pleistocene-Holocene warming (20-10 ka) proceeded ~2 kyr earlier than the growth in the surface temperature; reaching the maximum value of 0.08-0.13 W/m2 at ~13 ka, the heat flux was reduced. The coordinated changes in heat flux and average annual insolation at 60º N at 5-24 ka indicate that the orbital factors were the main cause of climatic changes in this period. The correlations between the changes in heat flux and CO2 content in the Antarctic ice cores with temperature changes are analyzed.