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The recent interest in exploration for shale gas increases the demand for a reliable, compatible resource assessment. Many different assessment methods are used, commonly depending on types and quantity of data available, which may lead to significantly divergent results for the same shale-gas play. This study compares results obtained using performance-based and gas-in-place methodologies to assess a well-developed and active shale-gas play (Woodford Shale, Arkoma Basin, USA) and two untested, hypothetical shale-gas plays (Shublik and Brookian, Alaska North Slope, USA). Results show that the two assessment methods produce comparable results when assessment units are identically defined and similar geological constraints are used as input parameters. Inherent uncertainties are associated with both assessment methods, and these are related to aspects of shale-gas production that are not well understood. The performance-based method relies on decline trend analysis to generate distributions of estimated ultimate recovery (EUR), and uncertainty increases in cases of short production history. The gas-in-place method requires the application of a recovery factor to estimate technically recoverable resources, and both absolute values of recovery factors and their spatial variability are poorly documented, and therefore a source of uncertainty.

The Bashkirian anticlinorium of the southwestern Urals shows a much more complex structural architecture and tectonic evolution than previously known. Pre-Uralian Proterozoic extensional and compressional structures controlled significantly the Uralian tectonic convergence. A long-lasting Proterozoic rift process created extensional basement structures and a Riphean basin topography which influenced the formation of the western fold-and-thrust-belt with inversion structures during the Uralian deformation. A complete orogenic cycle during Cadomian times, including terrane accretion at the eastern margin of the East European platform, resulted in a high-level Cadomian basement complex, which controlled the onset of Uralian deformation, and resulted in intense imbrication and tectonic stacking in the subjacent footwall of the Main Uralian fault. The Uralian orogenic evolution can be subdivided into three deformation stages with differently oriented stress regimes. Tectonic convergence started in the Late Devonian with ophiolite obduction, tectonic accretion of basin and slope units and early flysch deposits (Zilair flysch). The accretionary complex prograded from the SE to the NW. Continuous NW/SE-directed convergence resulted finally in the formation of an early orogenic wedge thrusting the Cadomian basement complex onto the East European platform. The main tectonic shortening was connected with these two stages and, although not well constrained, appears to be of Late Devonian to Carboniferous age. In the Permian a final stage of E–W compression is observed throughout the SW Urals. In the west the fold-and-thrust-belt prograded to the west with reactivation of former extensional structures and minor shortening. In the east this phase was related to intense back thrusting. The East European platform was subducted beneath the Magnitogorsk magmatic arc during the Late Paleozoic collision. The thick and cold East European platform reacted as a stable rigid block which resulted in a narrow zone of intense crustal shortening, tectonic stacking and high strain at its eastern margin. Whereas the first orogenic wedge is of thick-skinned type with the involvement of crystalline basement, even the later west-directed wedge is not typically thin-skinned as the depth of the basal detachment appears below 15 km and the involvement of Archean basement can be assumed.

The selection process of Indian teams for the International Chemistry Olympiad (IChO) currently goes through three stages. Indian National Chemistry Olympiad (INChO) is the national level theoretical examination administered at the second stage of selection and around 300 students selected from initial screening examination qualify for INChO. The current paper reviews the INChO examinations for (i) the areas that are generally covered and the weightage allocated to them, (ii) its correlation with existing secondary school chemistry syllabi within India and with IChO theoretical syllabi, (iii) the prototypical performance of students on these examinations and (iv) its implications for teaching and learning of chemistry at senior secondary level.

J. Makris Institut fiir Geophysik der Universit~it, W-2000 Hamburg, Bundesrepublik Deutschland Back-arc spreading in the Okinawa Trough is evidenced from elongated local ridges in central graben structures. It is believed to be in a nascent stage, to have initiated in the southern trough, and to migrate north at present. The transition between arcand back-arc volcanism is probably represented in the middle Okinawa Trough [3]. During cruises SO 55 and SO 56, several target areas were investigated in the Okinawa Trough (Fig. 1). Methane concentrations in seawater samples were determined on board using a modification of the technique described in [4, 5]. The method is based on inert gas stripping followed by gas chromatography. Shore-based helium and neon measurements were realized on a Clarke-type double-collecting mass