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Results of geological investigation of gas hydrate accumulation within the underwater sedimentary Blake Outer Ridge are presented. The study was based on both published and new data that we obtained by processing 164 and 172 ODP leg observations. The geological control over the distribution of gas hydrates is not quite clear despite the detailed seismic surveys and drilling within the study area. The geologic, tectonic, and hydro-geologic conditions in the Blake Outer Ridge area have been analyzed. A radically new technical approach was used: The gas hydrate accumulation was examined as a separate object with its specific characteristics. It has been proved that the investigated gas hydrates formed under the conditions of dissipated percolation of gas-containing fluids, which controlled the shape and the size of the accumulation. Based on geochemical, geophysical, and sedimentological data, the regularities of gas hydrate distribution within the Blake Outer Ridge have been established. The accumulation is controlled by tectonic factors, is of filtration origin, and occurs mainly in coarse-grained sediments.

The magnitude and spatial distribution of potential Black Sea methane hydrate reservoirs has been estimated on the basis of 6

There are massive quantities of gas hydrates in permafrost regions and deep-sea sediments. The current estimates show that the amount of energy in these gas hydrates is twice total fossil fuel reserves, indicating a huge source of energy, which can be exploited in the right economical conditions. Furthermore, these gas hydrates are a safety hazard to drilling operation, as they could become unstable under typical wellborn conditions and produce large quantities of gas. The decomposition of natural gas hydrates in porous media could also be responsible for subsea landslides and global weather changes. Recent studies show that they might provide an opportunity for CO₂ sequestering.
Hydrate phase boundary in porous media is known to be a function of many factors, such as pore size, fluid saturation, in situ stresses, and sediment mineralogy. Deviations, as great as 100 m, have been observed between the measured and predicted thickness of hydrate stability zones in marine sediments. Laboratory efforts in measuring gas hydrate stability zone in porous media have concentrated on the effect of pore size and fluid saturation. However, there are considerable deviations and inconsistencies in the reported data.
This paper presents an experimental setup, test procedures, and some of the results obtained on porous glass beads with 306 and 158 pore sizes with using methane and CO₂. The test procedure is based on stepwise heating as compared to continuous heating used by many laboratories. The results proved that stepwise heating technique could provide reliable and consistent data on measuring hydrate phase boundary in porous media, without compromising on the time and cost of experiments. The data showed that there could be a significant difference between the hydrate free zone of gas hydrates in porous media and that of bulk conditions. These results are important in estimating the hydrate stability zones in porous media, as indicated by BSR in seismic surveys.

We have experimentally studied the peculiarities of water-gas hydrate and water-ice phase transitions under gas pressure in dispersed methane-saturated grounds on cyclic cooling-heating. Data on the conditions of hydrate and ice formation in the ground pores have been obtained. It is shown that on cooling of dispersed rocks, only part of the pore water passes into hydrates; the rest (intimately bound with the particle surface) transforms into ice on further cooling. Hydrate formation in the studied grounds, compared with the system pure water-gas, occurs at higher pressures and lower temperatures. It is demonstrated that the ground dispersion and cooling-heating cycles affect the PT-conditions of formation and decomposition of gas hydrates. Petrography of frozen artificially hydrate-saturated rocks is studied.

Over 200 sites of exhalation (95-98% methane) have been discovered through the past 15 years in the northwestern Black Sea. Fields of exhalation are most often attributed to large fault zones. Many sites are associated with carbonates.

Most typical examples of gas saturation images in acoustic fields are presented based on data obtained using a MAK-1M acoustic complex (designed at 'Yuzhmorgeologiya' Science Center) during research trips in the Black Sea and north-western Pacific.

We have characterized complexes of the guide faunal groups (small-shelled fauna, archaeocyathids, trilobites, and brachiopods) and followed their stratigraphic and lateral distribution in the Cambrian deposits of the northern Siberian platform. Eleven boundaries, where these complexes undergo major biotic transformations, have been established. The boundaries are compared with those characterized in other studies, as well as with the carbon isotope dating from different sections of the Siberian Platform. Some of the boundaries established in this study correlate well with global biotic events and with the extrema of carbon isotope ratio curves. The examples include Boundary 1, the lower boundary of the Tommotian stage; Boundary 3, the lower boundary of the Atdabanian stage; Boundary 5, the lower boundary of the Botomian stage; and Boundaries 7 and 8 marking the transition from the Lower to Middle Cambrian in the Siberian Platform. Additionally, Boundary 9 is an almost universally present lower boundary of the Triplagnostus gibbus Zone of the Amgan stage.

Data on the stratigraphy of siliceous-basalt deposits of Ordovician age from Central Kazakhstan have been summarized. The age, succession, and correlation between these deposits are refined. Geological dating and correlation are based chiefly on conodonts and, to a lesser extent, graptolites. It is established that the age of these formations in the west and east of Central Kazakhstan is constrained by the Early to Middle Ordovician and in the interior structures (Zhungaria-Balkhash zone) it spans the entire Ordovician and, possibly, early Silurian. The siliceous and siliceous-terrigene deposits of Ordovician age are the water-deepest hemipelagic and pelagic sediments, and their accumulation corresponds to the maximum of Arenigian-to-Llanvirnian transgression. The reported paleo-geographic and paleotectonic data are in agreement with the existing paleotectonic reconstructions according to which Central Kazakhstan was a marginal basin of the West Pacific type during the Ordovician.

The paper addresses a comparative geochemical study of volcanic complexes that evolved in the Asia/Pacific transition zone from the Late Cenonian to Present.
Chemical compositions were analyzed in 111 representative samples of Cenozoic rocks from the eastern side of the Valaga Ridge (Eastern Kamchatka) on continuation of the Emperor's Ridge axis, in the region of hotspot volcanism; the dataset also includes 39 additional precise analyses published earlier by Puzankov et al. Trace elements were determined by INAA, XRF, AAS, LL methods and gamma spectrometry developed in UIGGM, Novosibirsk.
The magmatic complexes of Eastern Kamchatka and the surrounding regions were interpreted on the basis of rock chemistry as formed in spreading, island-arc, and transitional geodynamic environments. Broad occurrence of transitional igneous complexes brings together the Meso-Cenozoic volcanic system including magmatic chambers at different depths. Accretion postdates the magmatic evolution. According to paleontological and K-Ar age constraints, the Eastern Kamchatka hotspot has not moved much for 40 Ma (from the Eocene to the Pleistocene), though the total extent of alkaline and subalkaline rocks attains 200-300 km.

The paper presents results of Ar and He isotopic studies in rocks and sulphide ores of the Late Precambrian Dovyra dunite-troctolite layered intrusion (Northern Baikal region). The intrusion shows ³He/⁴He and ⁴⁰Ar/³⁶Ar ratios similar to other basic intrusions in the continental crust, and the gases in fluid inclusions contain a significant crystal component. The lowest ³He/⁴He and ⁴⁰Ar/³⁶Ar ratios, similar to those typical of fluids in the continental crust, were found in sulphide ores of the intrusion, which indicates involvement of crystal fluids in magmatic mineralization of the intrusion.