Geochemical evidence for the ophiolitic nature of the gabbros,gabbroanorthosites, and ultramafic rocks of the Gerbikan fragment of the Baladek Massif of the southeastern framing of the North Asian craton

The Baladek Massif represents a tectonic block located at the boundary between the SE framing of the North Asian craton and the fold structures of the Galam terrane of the Mongol-Okhotsk fold belt. According to the existing concepts, the rocks of this massif are regarded as Precambrian complexes of the aforementioned craton. This paper reports the results of studying the fragment of the Baladek Massif in the Gerbikan River basin. New geochemical data obtained on the gabbros, gabbroanorthosites, and ultramafic rocks testify to their similarity with typical ophiolite complexes. An underlying complex of metamorphic ultrabasic rocks, a layered complex of pyroxenites and “cumulate” gabbros, gabbroanorthosites, and a complex of isotropic gabbros were distinguished within this fragment. It is highly possible that the basic volcanic rocks and jaspers of the Silurian-Lower Devonian sequences of the Galam segment of the Mongol-Okhotsk fold belt also belong to the inferred ophiolite complex.     

Noble-metal mineralization in the Semenov-2 hydrothermal field (13°31′N), mid-atlantic ridge

The porous fine-grained to microcrystalline copper-zinc ore of the Semenov-2 hydrothermal field, a site in the Semenov hydrothermal cluster discovered in 2007 (13°31′N, MAR), is anomalously enriched in Au (22–188 ppm) and Ag (127–1787 ppm). Chalcopyrite, isocubanite, würtzite, and opal are major minerals; sphalerite, marcasite, pyrite, and covellite are auxiliary; and galena, pyrrhotite, native gold, silver telluride, barite, and aragonite are sporadic. Gold containing 0.31 to 23.07 wt % Ag occurs as up to 9-μm-sized subhedral, dendritelike, and elongated grains mostly hosted in opal and less frequently in sphalerite and in pores within isocubanite-chalcopyrite aggregate. An elongated grain (2 × 4 μm in size) of the Ag-Te phase was found in a pore. So far only basalts have been dredged from the Semenov-2 field, but anomalous gold and silver concentrations suggest the influence of ultramafic rocks; the latter were found 1.5 km westward, in the Semenov-1 hydrothermal field. Mineral assemblage and morphology of gold particles indicate its primary origin in contrast to the hydrothermal fields hosted in basalts, where gold is a product of remobilization. Zonal gold grains, found on oceanic floor for the first time, are characterized by low Ag content in the cores and high Ag content in the outer rims, reflecting variation in formation conditions.     

Comparative analysis of marine paleogene sections and biota from West Siberia and the Arctic Region

The analysis of the main biospheric events that took place in West Siberia and the Arctic region during the Early Paleogene revealed the paleogeographic and paleobiogeographic unity of marine sedimentation basins and close biogeographic relations between their separate parts. Most biotic and abiotic events of the first half of the Paleogene in the Arctic region and West Siberia were synchronous, unidirectional, and interrelated. Shelf settings, sedimentation breaks, and microfaunal assemblages characteristic of these basins during the Paleogene are compared. The comparative analysis primarily concerned events of the Paleocene-Eocene thermal maximum (PETM) and beds with Azolla (aquatic fern). The formation of the Eocene Azolla Beds in the Arctic region and West Siberia was asynchronous, although it proceeded in line with a common scenario related to the development of a system of estuarine-type currents in a sea basin partly isolated from the World Ocean.     

Influence of spatial variability of permeability property on steady state seepage flow and slope stability analysis

In recent years, spatial variability modeling of soil parameters using random field theory has gained distinct importance in geotechnical analysis. In the present study, commercially available finite difference numerical code FLAC 5.0 is used for modeling the permeability parameter as spatially correlated log-normally distributed random variable and its influence on the steady state seepage flow and on the slope stability analysis are studied. Considering the case of a 5.0 m high cohesive–frictional soil slope of 30°, a range of coefficients of variation (CoV%) from 60 to 90% in the permeability values, and taking different values of correlation distance in the range of 0.5–15 m, parametric studies, using Monte Carlo simulations, are performed to study the following three aspects, i.e., (i) effect of stochastic soil permeability on the statistics of seepage flow in comparison to the analytic (Dupuit′s) solution available for the uniformly constant permeability property; (ii) strain and deformation pattern, and (iii) stability of the given slope assessed in terms of factor of safety (FS). The results obtained in this study are useful to understand the role of permeability variations in slope stability analysis under different slope conditions and material properties.     

3d transition metal L-edge X-ray absorption studies of the dichalcogenides of Fe, Co and Ni

The X-ray absorption spectra of the transition metal L_3,2-edges of the dichalcogenides FeS₂ (pyrite), FeSe₂, FeTe₂, CoS₂, CoSe₂, CoTe₂, NiS₂, NiSe₂ and NiTe₂ have been studied. These spectra are compared with theoretical simulations make using the atomic multiplet approach assuming on octahedral site for the metal atoms. The Ni spectra can be closely simulated using this approach but the Fe and Co spectra show less good fits to the experimental data. The reasons for this and its implications for the use of L-edge spectra in the study of such minerals are discussed in terms of the covalency and the ground states of the compounds; these results indicate the mixing of the ground states increases in the order Ni<Co<Fe.     

Some applications of paleoecology to the management of tidal marshes

The shallow-water habitat is under increasing environmental pressures from accelerated sea-level rise and continual urban sprawl and will require well-informed management decisions to maintain its health into the future. One of the keys to the effective management of the shallow-water habitat is understanding the processes responsible for its development. Paleoecology has the potential to provide much insight into the development of the system, particularly when the impacts of accelerated sea-level rise on vegetation and sedimentation dynamics in tidal marshes is being considered. For example, a paleoecological comparison of tidal salt marshes to tidal freshwater marshes shows that rates of development will dictate the system's response to accelerated sea-level rise, with tidal freshwater marshes capable of transgressing landward more rapidly than their saline counterparts. Such information implies that management of the adjacent uplands is as important to the future of the system as management of the marsh itself. Therefore, it is important to consult paleoecological research when management strategies are being considered. *** DIRECT SUPPORT *** A01BY074 00010     

Mineral dissolution in the Cape Cod aquifer, Massachusetts, USA: I . Reaction stoichiometry and impact of accessory feldspar and glauconite on strontium isotopes, solute concentrations, and REY distribution

To compare relative reaction rates of mineral dissolution in a mineralogically simple groundwater aquifer, we studied the controls on solute concentrations, Sr isotopes, and rare earth element and yttrium (REY) systematics in the Cape Cod aquifer. This aquifer comprises mostly carbonate-free Pleistocene sediments that are about 90% quartz with minor K-feldspar, plagioclase, glauconite, and Fe-oxides. Silica concentrations and pH in the groundwater increase systematically with increasing depth, while Sr isotopic ratios decrease. No clear relationship between ⁸⁷Sr/⁸⁶Sr and Sr concentration is observed. At all depths, the ⁸⁷Sr/⁸⁶Sr ratio of the groundwater is considerably lower than the Sr isotopic ratio of the bulk sediment or its K-feldspar component, but similar to that of a plagioclase-rich accessory separate obtained from the sediment. The Si-⁸⁷Sr/⁸⁶Sr-depth relationships are consistent with dissolution of accessory plagioclase. In addition, solutes such as Sr, Ca, and particularly K show concentration spikes superimposed on their respective general trends. The K-Sr-⁸⁷Sr/⁸⁶Sr systematics suggests that accessory glauconite is another major solute source to Cape Cod groundwater. Although the authigenic glauconite in the Cape Cod sediment is rich in Rb, it is low in in-grown radiogenic ⁸⁷Sr because of its young Pleistocene age. The low ⁸⁷Sr/⁸⁶Sr ratios are consistent with equilibration of glauconite with seawater. The impact of glauconite is inferred to vary due to its variable abundance in the sediments. In the Cape Cod groundwater, the variation of REY concentrations with sampling depth resembles that of K and Rb, but differs from that of Ca and Sr. Shale-normalized REY patterns are light REY depleted, show negative Ce anomalies and super-chondritic Y/Ho ratios, but no Eu anomalies. REY input from feldspar, therefore, is insignificant compared to input from a K-Rb-bearing phase, inferred to be glauconite. These results emphasize that interpretation of groundwater chemistry, even in relatively simple aquifers, may be complicated by solute contributions from “exotic” accessory minerals such as glauconite. To detect such peculiarities, groundwater studies should combine the study of elemental concentration and isotopic composition of several solutes that show different geochemical behavior.     

Impact of quarrying gypsum in a semidesert karstic area (Sorbas,SE Spain)

The Messinian gypsum of Sorbas is intensively karstified, with hundreds of dolines and numerous, highly unusual exo- and endokarstic forms. Amongst these the tumuli are especially spectacular, as are the large caverns, adorned with numerous speleothems, some of which have not been described anywhere else in the World. The extraction of the gypsum has impacted practically all the elements of the environment (landscape, water, soil, subsoil, flora, fauna, etc.) and, in particular, all of the karstic forms. In addition to endangering the caves and the natural treasures that they contain, it affects the surface waters, markedly modifying the hydrographic network. Groundwaters, which now occur in the bottom of a quarry, are also affected.     

Recent landslide activity in Manaihan,East Belgium

Past landslides have been recognized in the Battice area in E-Belgium. In contrast to the other inactive landslides, the Manaihan landslide responded immediately to heavy rainfall events in the last two decades. This study aims to map its spatial extent and the dominant surface features; to measure surface displacement using GPS; to investigate subsurface structure with Cone penetration test (CPT) and corings; and to determine the depth of the shear surface by inclinometers. Results show a partial landslide reactivation. Surface velocities range between 20 and 40 cm/year and are strongly dependent on winter rainfall. CPT results give clear boundaries between the landslide mass and the undisturbed bedrock in the head scarp. Distinct shear surfaces have been determined with displacement rates up to 15.8 mm in 21 days. Further research should apply geophysical methods for two-dimensional information on the ground, investigate geotechnical properties of the landslide mass, model slope instability, and determine the influence of a sewage pipe crossing the central landslide mass as a potential cause for landslide activity.