Study of subsurface geology in locating arsenic-free groundwater in Bengal delta,West Bengal,India

Over a large area of the Bengal delta in West Bengal, India, arsenic distribution patterns in groundwater were studied. One hundred and ten boreholes at different target locations were made, subsurface sediments were logged and analysed, and arsenic values in sediments vis-à-vis groundwater were compared. The study elucidates the subsurface geology of the western part of Bengal delta and characterises the sediments that were intersected in different boreholes with contrasting values of arsenic in groundwater. It reveals an existence of multiple aquifers stacked over each other. Depending on the color and nature of aquifer-sands and their overlying clay beds six aquifer types (Type-1 to Type-6) are classified and described. Sediment-arsenic for all the varieties of aquifer sands are near similar but the groundwater-arsenic of these six aquifers varies widely. Type-2 and Type-5 aquifers host arsenic-contaminated groundwater whereas the other four aquifers are arsenic-free. Type-2 and Type-5 aquifers are capped by a grey to dark grey soft organic matter-rich clay unit which makes these aquifers semi-confined to leaky-confined. These contribute in releasing arsenic from the sediments. The results of this study are employed in a proposed georemedial measure against this hazardous toxic element.     

Composition and origin of the Çaldağ oxide nickel laterite,W. Turkey

The Çalda? nickel laterite deposit located in the Aegean region of W. Turkey contains a reserve of 33 million tons of Ni ore with an average grade of 1.14% Ni. The deposit is developed on an ophiolitic serpentinite body which was obducted onto Triassic dolomites in the Late Cretaceous. The deposit weathering profile is both laterally and vertically variable. A limonite zone, which is the main ore horizon, is located at the base of the profile. A hematite horizon is located above the limonite, which in the south of the deposit is capped by Eocene freshwater limestones and in the north by a siliceous horizon. The deposit is unusual in lacking a significant saprolite zone with little development of Ni-silicates. The boundary between the limonite zone and serpentinite below is sharp with a marked decrease in concentrations of MgO from 13 to 1 wt.% over a distance of 2 mm representing the ‘Mg discontinuity’. Ni concentrations within goethite, the main ore mineral, reach a maximum of ~3 wt.% near the base of the limonite zone. Silica concentrations are high throughout most of the laterite with up to 80 wt.% silica in the upper portion of some profiles. The combination of a serpentinite protolith and a high water table at Çalda?, in association with an aggressive weathering environment in a tropical climate, resulted in the formation of an oxide-dominated deposit. The precipitation of silica may coincide with a change in climate with silica precipitation linked to an increase in seasonality. Additional variations within profile morphology are attributed to transportation during and after laterite development as a result of faulting, pocket type laterite formation and slumping, each of which produces a contrasting set of textural and geochemical features.     

Flexible–inflexible: socio-demographic,spatial and temporal dimensions of flat sharing in Leipzig (Germany)

Flat sharers are one of the most distinct representatives of the ‘new’ household types, but have received only very limited attention from researchers. Back in the 1960s shared flats were usually founded with a strong ideological impetus, whereas flat sharing nowadays is just one household type among many others. Typically, this housing arrangement consists of at least two young adult individuals without children. Sharing the flat and the housing costs is the basis of their relationship but living with others is an additional motive. As a rule, flat sharing bridges two distinct events in the course of one’s life: the leaving of the parental home and the foundation of the first independent household. Thus for a restricted period in time, it is a flexible household type adapted to the situational needs of its members. Germany has one of the strongest and longest traditions of flat sharing in Europe, especially among university students. An explorative study was conducted in Leipzig to come to a deeper understanding of what flat sharing means in its ambivalence of being both an economic unit and a social arrangement. Based on qualitative and quantitative evidence from group discussions and Internet adverts, we shed light on the highly under-researched social practice of flat sharing. We will show that despite the structural flexibility of this household type, there is also evidence for its socio-demographic selectivity, spatial concentration and temporal limitation over the individual life courses.     

Analysis of seismic noise in the Romanian-Bulgarian cross-border region

We present the first detailed investigation of the background seismic noise recorded in the Romanian-Bulgarian cross-border region over 3 years (2012–2015). We used the power spectral densities probability density functions (PSD PDFs) to study the noise variations in the period domain (0.025–1 s) as well as in the secondary microseism band (2–10 s). Strong diurnal variations and an increase of the noise levels during working days were observed at high frequencies at all stations, thus confirming the anthropic origin of the noise at low periods. The noise variations observed at longer periods (>?1 s) are relatively small among the stations and are related to season changes. The dominant feature in the noise spectra between 2 and 10 s is the double-frequency peak (DFP) whose amplitude increases and changes during winter. For a specific interval, from 25th to 27th of January 2014, when a storm was reported in the Black Sea area, the maximum of the DFP shifted from larger periods (~?5.5 s) at stations far from the Black Sea towards smaller periods (~?1.8 s) at stations located on the coastline. The polarization analysis showed that the short period double-frequency microseisms originating from the Black Sea dominate during the winter month. Finally, we showed that site conditions vary due to noise variations related to weather conditions in the Black Sea or to changes in anthropogenic noise sources.     

Brine evolution in two inland evaporative environments: influence of microbial mats in mineral precipitation

This paper gives new insight into the precipitation sequences in six playa basins that host microbial mats. The study basins are distributed across two evaporitic endorheic drainage systems located in the Central part of Spain with markedly different hydrochemistry and mineralogy. One group, in the north, consists of highly alkaline, brackish to saline lakes containing a high concentration of chloride with dominant carbonate over sulphates. A second group of lakes are mesosaline to hypersaline, with sulphate the dominant anion over chloride. Mineral assemblages identified in both contain several phases that provide evidence for mixed carbonate-sulphate precipitation pathways, in the north, and sulphate-dominated pathways in the south. Regardless of their ionic composition, saline lakes support thin veneers of microbial mats which, by integrating several lines of evidence (hydrochemical and physical analyses, statistical analyses of ions, mineralogical assemblages, textural relationships among mineral phases and microbial mats) are shown to modify the chemical behavior of the evaporitic sediment and promote the formation of carbonates and sulphates from Ca-poor waters with high Mg/Ca ratios. Geochemical changes induced in the environment surrounding the microorganism favor the nucleation of hydrated Mg-carbonates (hydromagnesite and nesquehonite), calcite and dolomite. Simultaneously, the microbial mats provide nucleation sites for gypsum crystals, where they are subjected to episodic stages of growth and dissolution due to saturation indices close to zero. In addition, the bubbles produced by the metabolic activities of microorganisms are shown to promote the precipitation of hydrated Mg-sulphates, despite permanent subsaturation levels. Although common in the studied playa basins, this effect has not been previously reported and is key to understanding sulphate behavior and distribution. Modern and natural evaporitic microbial environments are important analogs for understanding brine evolution and mineral precipitation pathways in shallow water settings that have existed since the Archean on Earth and perhaps on Mars.     

Geo-scape,a granularity depended spatialization tool for visualizing multidimensional data sets

Recently,the expertise accumulated in the field of geovisualization has found application in the visualization of abstract multidimensional data,on the basis of methods called spatialization methods.Spatialization methods aim at visualizing multidimensional data into low-dimensional representational spaces by making use of spatial metaphors and applying dimension reduction techniques.Spatial metaphors are able to provide a metaphoric framework for the visualization of information at different levels of gran...     

Early Paleozoic tectonic evolution of the Chinese South Tianshan Orogen: constraints from SHRIMP zircon U–Pb geochronology and geochemistry of basaltic and dioritic rocks from Xiate,NW China

Traditionally the Chinese South Tianshan has been regarded as a late Paleozoic orogenic belt. However, little is known about the early Paleozoic tectonic architecture of the region. This paper presents the first evidence of Cambrian–Ordovician MORB-type basalts and adakitic diorites on the southern margin of the Yili plate in China. Basalts from Xiate in southwestern Tianshan show a typical transitional (T-) MORB and ferrobasalt composition, which indicate a formation at a propagating spreading ridge. The basalts give a weighted mean ²⁰⁶Pb/²³⁸U crystallization age of 516.3 ± 7.4 Ma by SHRIMP U–Pb zircon dating and have experienced contact metamorphism due to the intrusion of a dioritic pluton. The dioritic pluton has a weighted mean ²⁰⁶Pb/²³⁸U crystallization age of 470 ± 12 Ma and geochemical characteristics resembling that of adakitic rocks. The pluton is considered to have been formed by partial melting of garnet amphibolites from thickened lower crust in arc or continental collision settings. The basalts and diorites are considered to outline the eastern extension of the early Paleozoic suture zone, the Nikolaev Line, which stretches east–west for hundreds of kilometers between the Northern Tianshan and Central Tianshan terranes of Kyrgyzstan. Our findings substantiate that the Yili and Central Tianshan plates were separated by the early Paleozoic Terskey ocean. The Terskey ocean probably closed during the early stage of the late Ordovician (Lomize et al. in Geotectonics 31(6):463–482, 1997), resulting in the final amalgamation of the Yili and Central Tianshan plates. Consequently, an early Paleozoic suture zone is documented in the Chinese Tianshan region, which is most likely represented by the North Nalati fault.     

Hafnium isotopic variations in East Atlantic intraplate volcanism

The broad belt of intraplate volcanism in the East Atlantic between 25° and 37° N is proposed to have formed by two adjacent hotspot tracks (the Madeira and Canary tracks) that possess systematically different isotopic signatures reflecting different mantle source compositions. To test this model, Hf isotope ratios from volcanic rocks from all individual islands and all major seamounts are presented in this study. In comparison with published Nd isotope variations (6 εNd units), ¹⁷⁶Hf/¹⁷⁷Hf ratios span a much larger range (14 εHf units). Samples from the proposed Madeira hotspot track have the most radiogenic Hf isotopic compositions (¹⁷⁶Hf/¹⁷⁷Hf_m up to 0.283335), extending across the entire field for central Atlantic MORB. They form a relatively narrow, elongated trend on the Nd vs. Hf isotope diagram (stretching over > 10 εHf units) between a depleted N-MORB-like endmember and a moderately enriched composition located on, or slightly below, the Nd–Hf mantle array, which overlaps the proposed “C” mantle component of Hanan and Graham (1996). In contrast, all samples from the Canary hotspot track plot below the mantle array (¹⁷⁶Hf/¹⁷⁷Hf_m = 0.282943–0.283067) and form a much denser cluster with less compositional variation (~4 εHf units). The cluster falls between (1) a low Hf isotope HIMU-like endmember, (2) a more depleted composition, and (3) the moderately enriched end of the Madeira trend. The new Hf isotope data confirm the general geochemical distinction of the Canary and Madeira domains in the East Atlantic. Both domains, however, seem to share a common, moderately enriched endmember that has “C”-like isotope compositions and is believed to represent subducted, <1-Ga-old oceanic lithosphere (oceanic crust and possibly minor sediment addition). The lower ¹⁷⁶Hf/¹⁷⁷Hf ratio of the enriched, HIMU-like Canary domain endmember indicates the contribution of oceanic lithosphere with somewhat older recycling ages of ≥1 Ga.     

The relative importance of land use and climatic change in Alpine catchments

Carbon storage and catchment hydrology are influenced both by land use changes and climatic changes, but there are few studies addressing both responses under both driving forces. We investigated the relative importance of climate change vs. land use change for four Alpine catchments using the LPJ-GUESS model. Two scenarios of grassland management were calibrated based on the more detailed model PROGRASS. The simulations until 2100 show that only reforestation could lead to an increase of carbon storage under climatic change, whereby a cessation of carbon accumulation occurred in all catchments after 2050. The initial increase in carbon storage was attributable mainly to forest re-growth on abandoned land, whereas the stagnation and decline in the second half of the century was mainly driven by climate change. If land was used more intensively, i.e. as grassland, litter input to the soil decreased due to harvesting, resulting in a decline of soil carbon storage (1.2−2.9 kg C m^–2) that was larger than the climate-induced change (0.8–1.4 kg C m⁻²). Land use change influenced transpiration both directly and in interaction with climate change. The response of forested catchments diverged with climatic change (11–40 mm increase in AET), reflecting the differences in forest age, topography and water holding capacity within and between catchments. For grass-dominated catchments, however, transpiration responded in a similar manner to climate change (light management: 23–32 mm AET decrease, heavy management: 29–44 mm AET decrease), likely because grassroots are concentrated in the uppermost soil layers. Both the water and the carbon cycle were more strongly influenced by land use compared to climatic changes, as land use had not only a direct effect on carbon storage and transpiration, but also an indirect effect by modifying the climate change response of transpiration and carbon flux in the catchments. For the carbon cycle, climate change led to a cessation of the catchment response (sink/source strength is limited), whereas for the water cycle, the effect of land use change remains evident throughout the simulation period (changes in evapotranspiration do not attenuate). Thus we conclude that management will have a large potential to influence the carbon and water cycle, which needs to be considered in management planning as well as in climate and hydrological modelling.