A new estimate of global methane flux from onshore and shallow submarine mud volcanoes to the atmosphere

A new estimate of global methane emission into the atmosphere from mud volcanoes (MVs) on land and shallow seafloor is presented. The estimate, considered a lower limit, is based on 1) new direct measurements of flux, including both venting of methane and diffuse microseepage around craters and vents, and 2) a classification of MV sizes in terms of area (km²) based on a compilation of data from 120 MVs. The methane flux to the atmosphere is conservatively estimated between 6 and 9 Mt y^–1. This emission from MVs is 3–6% of the natural methane sources and is comparable with ocean and hydrate sources, officially considered in the atmospheric methane budget. The total geologic source, including MVs, seepage from seafloor, microseepage in hydrocarbon-prone areas and geothermal sources, would amount to 35–45 Mt y^–1. The authors believe it is time to add this parameter in the Intergovernmental Panel on Climate Change official tables of atmospheric methane sources.GEM     

A model for superoutbursts in SU UMa-type binaries

We suggest a new mechanism for the superoutbursts in SU UMa binaries, in which the increase in the accretion rate resulting in a superoutburst is associated with the formation of a spiral “precessional” wave in the inner parts of the disk, where gas-dynamical perturbations are negligible. The existence of such waves was suggested by us previously. The results of three-dimensional gas-dynamical simulations have shown that a considerable increase in the accretion rate (by up to an order of magnitude) is associated with the formation of the precessional wave. The features of the precessional spiral wave can explain both the energy release in the superoutburst and all its observational manifestations. One distinguishing feature of superoutbursts in SU UMa-type stars is the formation of a “superhump” in the light curve. Our model reproduces well both the formation of a superhump and its observational features, including its period, which is up to 3–7% longer than the orbital period, and the detectability of the superhump independent of the orbital inclination of the binary.     

Chemical and isotopic (C, O, Sr, Nd) characteristics of the Xiluvo carbonatite (central-western Mozambique)

Summary The Xiluvo complex of central Mozambique is made up of coarse- to fine-grained calciocarbonatites (sövites and alvikites), heavily altered lamprophyres and syenitic rocks that intruded the Precambrian basement ca. 120Ma ago. The carbonatites have fractionated rare earth element patterns (chondrite-normalized La/Yb=30–80) and markedly negative Rb, K, P, Zr and Ti anomalies in mantle-normalized incompatible element diagrams. The ¹⁸O (+7 to +8), ¹³C (–5), and the age-corrected ⁸⁷Sr/⁸⁶Sr (0.7032–0.7033) and ¹⁴³Nd/¹⁴⁴Nd (0.51263–0.51262) indicate an origin in the mantle. A few carbonatitic samples have higher ¹⁸O (+13), indicating interaction with high-¹⁸O crust or late-stage fluids. The chemical and isotopic compositions of the Xiluvo carbonatites and nearby carbonatites of similar age in Malawi indicate very similar sources, characterized by time-integrated depletion of Rb with respect to Sr and of Sm with respect to Nd. These characteristics point to a source similar in many respects to those of other East African carbonatites and to those of some ocean island basalts, with the additional influx of components possibly located in the African lithospheric mantle.     

The 1996 Eruption of Karymsky Volcano, Kamchatka: Historical Record of Basaltic Replenishment of an Andesite Reservoir

The simultaneous eruption in 1996 of andesite from Karymskyvolcano and of basalt from the Academy Nauk vent 6 km away appearsto provide a case of mafic recharge of an andesite reservoirfor which the time of recharge is exactly known and direct samplesof the recharging magma are available. The explosive phreato-magmaticeruption of basalt was terminated in less than 24 h, whereasandesite erupted continuously during the following 4 years.Detailed petrological study of volcanic ash, bombs and lavasof Karymsky andesite erupted during the period 1996–1999provides evidence for basaltic replenishment at the beginningof the eruptive cycle, as well as a record of compositionalvariations within the Karymsky magma reservoir induced by basalticrecharge. Shortly after the beginning of the eruption the compositionof the matrix glass of the Karymsky tephra became more maficand then, within 2 months, gradually returned to its originalstate and remained almost constant for the following 3 years.Further evidence for basaltic replenishment is provided by thepresence of xenocrysts of basaltic origin in the andesite ofKarymsky. A conspicuous portion of the plagioclase phenocrystsin the Karymsky andesite has calcic cores, with compositionsand textures resembling those of plagioclases in the AcademyNauk basalt. Similarly, the earlier portion of the andesiteof the eruption sequence contains rare olivines, which occuras resorbed cores in pyroxenes. The composition of the olivinematches that of olivines in the Academy Nauk basalt. The sequenceof events appears to be: (1) injection of basaltic magma intothe Karymsky chamber with immediate, compensating expulsionof pre-existing chamber magma from the Karymsky central vent;(2) direct mixing of basaltic and andesitic magmas with dispersalof phenocrysts associated with the basalt throughout the andesiteso that newly mixed magma appeared at the vent within 2 months;(3) re-establishment of thermal and chemical equilibrium withinthe reservoir involving crystallization in the new hybrid liquid,which returned the melt composition to ‘normal’,formed rims on inherited calcic plagioclase, and caused theresorption of dispersed olivine xenocrysts. Taken together,these findings indicate that the Karymsky magma reservoir wasrecharged by basalt at the onset of the 1996 eruptive cycle.The rapidity and thoroughness of mixing of the basalt with thepre-existing andesite probably reflects the modest contrastin temperature, viscosity, and density between the two magmas. KEY WORDS: Karymsky; Kamchatka; magma mixing; andesite; volcanic glass; plagioclase     

The Influence of Geodynamic Factors on the Postsedimentary Lithogenesis of Jurassic Terrigenous Complexes of the Caucasus (Southern Dagestan)

The influence of geodynamic factors on the postsedimentary lithogenesis of terrigenous sequences during the replacement of the passive continental-margin regime to the active regime is considered with the Toarcian–Aalenian complexes of southern Dagestan as an example. It has been established that clayey rocks were lithified under conditions of subsidence lithogenesis, whereas the orogenic catagenesis of sandy rocks was related to stress initiated by the initial (amagmatic) subduction phase. The Kübler index has been used to reveal the postsedimentary zonality that is consistent with the intensity of folding and cleavage. The metagenesis zone fits the cleavage zone. The Rb–Sr and K–Ar datings of clayey rocks from the metagenesis zone yielded 180–190 Ma that can be interpreted as the timing of the maximal manifestation of postsedimentary lithogenesis.     

Oil and Gas Potential of Deep- and Ultradeep-Water Zones of Continental Margins

Oil- and gas-bearing basins of the World Ocean spreading to the continental shelf and foothill are considered. Large hydrocarbon resources, including oil pools have been discovered in the deep-water basins. The basins are confined to passive continental margins and characterized by the common mechanism of formation. Oil and gas (hereafter, petroleum) generation and accumulation are dictated by the optimum specifics of source and reservoir rocks accumulated under favorable conditions of rifts and deep-sea fans. Halokinesis played an important role in the formation of traps and migration of hydrocarbons. The global experience shows that the northern, eastern, and southern shelves of the Russian seas, as well as their continental slopes and foothills, have a big petroleum potential.     

Influence of long-period oscillations on the development of droughts in Northern Eurasia

Doklady Earth Sciences - Estimates of the influence of the Atlantic long-period oscillation (ALO) on the formation of droughts in Northern Eurasia were obtained using the results of numerical...     

Electrochemical effects in rocks: petroleum exploration and engineering–geological applications

The use of electrochemical effects in petroleum exploration and engineering–geological applications is discussed with reference to the Zhirnovsky oil and gas field where mobile forms of metals are 1.5–2 times above the background. Electrochemical stiffening applied to Maastrichtian shales, which are sliding planes of landslides in the Lower Volga area, increased their stiffness by a factor of 2 or more.     

Palynofloral study of the intertrappean bed exposed at a new locality in Kutch district,Gujarat and its implications on palaeoenvironment and age

A palynofloral assemblage has been recorded from the intertrappean bed exposed at a new locality, near Naredi, on Naliya-Narayan Sarovar Road in western Kutch, Gujarat. This intertrappean bed (ca. 0.6 m thick) of grey laminated clay is underlain and overlain by the volcanic traps. The assemblage recovered from this bed includes algal and fungal remains, pteridophytic spores, angiospermous pollen as well as cuticles of terrestrial plants. Important palynotaxa recovered are Azolla sp., Lygodiumsporites lakiensis, Polypodiaceaesporites intrapunctatus, Compositoipollenites argutus, C. conicus, Graminidites media, Ladakhipollenites minutus, Lakiapollis ovatus, Matanomadhiasulcites sp., etc. Besides, a variety of fungal remains belonging to the genera Dictyosporites, Frasnacritetrus (Tetraploa), Kutchiathyrites, Palaeomycites (VAM fungi), Papulosporonites, Parmathyrites, Phragmothyrites, Polycellaesporonites (Alternaria), etc have been recorded. It has been deduced that this intertrappean bed was deposited in a shallow depression over the trap during short interval of quiescence in a tropical-subtropical climate. The age of the intertrappean bed is suggested as Early Palaeocene.     

Transport and Dispersion of a Conservative Tracer in Coastal Waters with Large Intertidal Areas

In late December 1991, an accidental release of 5,700 CI of tritiated water (HTO) from the Savannah River Site was transported via site streams into the Savannah River where it was carried downstream to the coastal zone. HTO released into a semitropical Georgia estuary was forced into the tidal marshes surrounding the estuary as well as discharged directly into the Atlantic Ocean. The spreading of HTO was studied with a 3D hydrodynamic model (ALGE) that includes flooding and draining of intertidal areas. Comparisons of model simulations to measured HTO concentration showed that ALGE simulated well the general increase and decrease of HTO as its plume passed a given area. The “sheet flow” approximation for marsh and small tidal creek flow largely compensated for lack of model resolution and accurate bathymetry in areas with numerous small to medium-sized tidal creeks. The water volume of the unresolved tidal creeks had to be accounted for in the simulations by increasing the initial water depth over the marshes. ALGE and a simple box model both reproduced the trapping of HTO in intertidal areas. The time scale over which intertidal areas import and export HTO back to the tidal channels varies between 10 and 30 days.