Behaviour of REE during weathering of granite in a tropical climate

Weathering is essentially a leaching process and thus, one way of determining the extent of weathering is to monitor the mobility of different elements. Rate of loss of elements in a weathering profile can be determined by comparing the concentrations of …     

Carbonate weathering rates in the Jura Mountains, France—The influence of vegetation

In order to better understand what controls carbonate weathering rates, we report results from the Jura Mountains (East France), an area exclusively composed of carbonate rocks. This region presents an altitude gradient increasing from 250 m to 1300 m. Ov…     

The large-wavelength deformations of the lithosphere： materials for a history of the evolution of thought from the earliest times to plate tectonics

The notable authority on tectonics and the history of geosciences, Professor Celal Sengor from Istanbul, has produced another remarkable book-which, as he tells the reader, grew rapidly from an initial paper into a massive tome. Just as Georges Cuvier liked the idea of ‘bursting the limits of time‘, so Professor Sengor has again ‘burst the limits of a paper‘!     

Performance of alkaline reactive materials in the remediation of acidic groundwater

Acidic groundwater and surface water are common problems in coastal Australia causing massive fish kills, attack of concrete and steel structures, and clogging of waterways. The best solution is the construction of a permeable reactive barrier （PRB） to neutralise the acidic groundwater before entering nearby waterways. A PRB consists of a trench filled with reactive material that intersects the flow-path of a contaminant plume and ameliorates the contaminated groundwater. A PRB is being designed in a pilot scale study in ASS in southeastern Australia. The groundwater is acidic （pH 3） with high A1 （40 mg/L） and Fe （530 mg/L） levels. When the acidic groundwater comes into contact with this PRB, the acid will be neutralized by the alkaline reactive materials and the aluminum and iron will be removed from the groundwater. Twenty-five alkaline materials were tested for use in the PRB, with an emphasis on waste materials, including oyster shells and recycled concrete. Batch tests were used to select the best two reactive materials for use in the column tests. The pH achieved by each material was controlled by the reaction kinetics of the dominant alkaline component.     

Significance of molecular-level behaviour incorporation in the constitutive models of expansive clays – a review

Expansive clays are widely prevalent all over the world as one of the most problematic soils. These soils undergo significant volume change with a change in the moisture regime, thereby posing problems to the stability of the structures founded on such strata. Efforts have been made to model the erratic behaviour of these soils at the macro, micro, and, to a lesser extent, nano levels. Micro and nano level fabrics, believed to have a central role in the overall behaviour of expansive clays, are only partially considered in the modelling concepts; natural clay fabrics with multiple clay minerals, silt and sand inclusions, micro fissures, cementation, overconsolidation, induration and other such features have never been considered. This paper covers a review of deficiencies in the existing constitutive models for the expansive characteristics of the natural clayey soils at macro, micro and nano levels. These shortcomings are discussed in the light of the understanding of the fundamentals including fabric and structure controlling the swelling mechanism of the expansive clayey soils at the molecular level. Finally, a framework based on authors’ work to incorporate molecular level behaviour in the constitutive modelling of expansive clays is presented.     

Carbonate weathering rates in the Jura Mountains, France-The influence of vegetation

In order to better understand what controls carbonate weathering rates, we report results from the Jura Mountains （East France）, an area exclusively composed of carbonate rocks. This region presents an altitude gradient increasing from 250 m to 1300 m. Over the basin, this gradient generates climatic contrasts of 5℃ and a runoff three times higher in altitude. This place offers a good opportunity for understanding the controlling factors of carbonate weathering. Contrary to thermodynamic calculations that predict the highest concentrations at low temperature, we observe that carbonate dissolution is two times higher at low elevation than in the mountains. This observation can only be explained by a variation in soil pCO2. In order to better constrain the observed variation in cation contents （principally Ca and Mg） of rivers, we used the ASPECTS ecological model （Rasse et al., 2001）. Based on both hourly climatic data, vegetation type and soil type, ASPECTS may reconstruct pCO2 in soil.     

Biomass burning — a review of organic tracers for smoke from incomplete combustion

Biomass combustion is an important primary source of particles with adsorbed biomarker compounds in the global atmosphere. The introduction of natural product organic compounds into smoke occurs primarily by direct volatilization/steam stripping and by thermal alteration based on combustion temperature. Although the molecular compositions of organic matter in smoke particles are highly variable, the molecular tracers are generally still source specific. Dehydroabietic acid is typically the major tracer for conifer smoke in the atmosphere. Degradation products from biopolymers (e.g. levoglucosan from cellulose, methoxyphenols from lignin) are also excellent tracers. Additional markers of thermally-altered and directly-emitted natural products in smoke have been defined which aids the assessment of the organic matter types and input from biomass combustion to aerosols. The precursor to product approach of compound characterization by organic geochemistry has also been applied successfully to provide source specific tracers for studying the chemistry and dispersion of ambient aerosols and the intermingling of natural with anthropogenic emissions and with smoke plumes. A brief review of the organic matter composition in aerosols derived from the major sources is also given, with emphasis on the detection of biomass burning components. These major sources are the natural background from biogenic detritus (e.g. plant wax, microbes, etc.) and anthropogenic particle emissions (e.g. oils, soot, synthetics, compounds, etc.). The emissions of organic constituents in coal smoke particulate matter are also reviewed and depend on combustion temperature, ventilation, burn time, and coal rank (geologic maturity). The components of peat and brown coal and to a lesser degree semi-bituminous coal consist mainly of hydrocarbons, biomarkers, and aromatic components, quite similar to burning of contemporary biomass. Dispersion from the source and long range transport of smoke particulate matter with the associated organic compounds is also discussed.     

The role of weathering in the initiation and mobility of a rare complex avalanche at the Nigeria–Cameroon border,West Africa

A catastrophic rock debris avalanche on one of the highlands demarcating Cameroon and Nigeria, 3 days after a transient period of heavy rainfall in November 2010, killed two people and damaged economic trees, plants and farmlands. Detailed field investigation and sampling were undertaken by a team from the International Programme on Landslide to analyse the slope movement. The investigation was in two phases—5 days and then 7 months after the event to study the effect of alternating dry and rainy seasons on the geotechnical properties of the materials associated with the slope failures. It was also aimed at assessing the effect of time on the morphology of the slip plane as a new approach to understanding the development of potential failure planes and reactivated landslides. Available evidence showed that present failure planes form mini-deposition axes which may become future slip zones as they are still steep enough to accelerate instability. The research also traced the pattern of rock weathering and joints evolution in the area and found that the systematic weathering of feldspar in the basement aggravated slope instability by creating zones of weakness characterized by structures that aid fragmentation. Soils were thin (<1 m) in some slopes and deep (>2 m) in others and may represent the differential effect of weathering and erosion on the mountains which are important in analyzing the mechanism and mobility of the failed masses. Samples collected were subjected to various geotechnical laboratory tests such as unconsolidated undrained triaxial, consistency, particle size and permeability tests.     

Optimum cross section index (OCI): a new approach for identification of an optimum channel—a case study of the Ichamati River,India

The Ichamati River drains the east and south side of the North 24 Parganas district which belongs to the Ganga-Brahmaputra Delta (GBD), covered by deep Quaternary sediments produced under tropical monsoon climate in India. The district is densely populated. The river has huge impact on its population. In this paper, particular attention has been paid to a new method, named optimum cross section index (OCI), which is a numerical representation of a river cross section with respect to its optimum condition. To establish the validity and reliability of OCI, as circumstantial evidences, we have measured and analyzed the geometric parameters, such as width, depth, hydraulic radius, wetted perimeter, and bank profile at 22 points, and applied the areal difference asymmetric index (ADAI). The paper considers that the changing characters of the geometric form of the cross sections and ADAI stand for the OCI. All the techniques reveal that (1) the area of channel decreases abruptly upstream downward, (2) the upstream channel is more symmetrical than the lower reach, and (3) the area of optimum channel gradually increases upstream downward. Results of the study show that the river is going to be deteriorating from upstream downward. OCI has been constructed based on width and depth, which are relatively easily available data. So, this model may be well assessable to identify the optimum channel for a river management.     

Mineral systems and the thermodynamics of selenites and selenates in the oxidation zone of sulfide ores – a review

Mineralogy and Petrology - Contemporary mineralogy and geochemistry are concerned with understanding and deciphering processes that occur near the surface of the Earth. These processes are...     

A review of the pressure–temperature–time evolution of the Limpopo Belt: Constraints for a tectonic model

Published literature argues that the Limpopo Belt can be subdivided into three zones, each with a distinctive geological character and tectono-metamorphic fingerprint. There are currently two contrasting schools of thought regarding the tectono-metamorphic evolution of the CZ. One camp argues that geochronological, structural and prograde pressure–temperature (P–T) evidence collectively indicate that the CZ underwent tectono-metamorphism at ca. 2.0 Ga which followed a clockwise P–T evolution during a transpressive orogeny that was initiated by the collision of the Kaapvaal and Zimbabwe cratons. Deformation and metamorphism consistent with this scenario are observed in the southern part of the NMZ but are curiously absent from the whole of the SMZ. The opposing view argues that the peak metamorphism associated with the collision of the Kaapvaal and Zimbabwe cratons occurred at ca. 2.6 Ga and the later metamorphic event is an overprint associated with reactivation along Archean shear zones. Post-peak-metamorphic conditions, which at present cannot be convincingly related to either a ca. 2.6 or 2.0 Ga event in the CZ reveal contrasting retrograde paths implying either near-isothermal decompression and isobaric cooling associated with a ‘pop-up’ style of exhumation or steady decompression–cooling linked to exhumation controlled by erosion. Recent data argue that the prograde evolution of the ca. 2.0 Ga event is characterised by isobaric heating prior to decompression–cooling. Contrasting P–T paths indicate that either different units exist within the CZ that underwent different P–T evolutions or that some P–T work is erroneous due to the application of equilibrium thermobarometry to mineral assemblages that are not in equilibrium. The morphology of the P–T path(s) for the ca. 2.6–2.52 Ga event are also a matter of dispute. Some workers have postulated an anticlockwise P–T evolution during this period whilst others regard this metamorphic event as following a clockwise evolution. Granitoid magmatism is broadly contemporaneous in all three zones at ca. 2.7–2.5 suggesting a possible causal geodynamic link. P–T contrasts between and within the respective zones prevent, at present, the construction of a coherent and inter-related tectonic model that can account for all of the available evidence. Detailed and fully-integrated petrological and geochronological studies are required to produce reliable P–T–t paths that may resolve some of these pertinent issues.     

Quantitative risk assessment of slope hazards along a section of railway in the Canadian Cordillera—a methodology considering the uncertainty in the results

Railway alignments through the Canadian Cordillera are constantly exposed to slope instabilities. Proactive mitigation strategies have been in place for a few decades now, and instability record keeping has been recognized as an important aspect of them. Such a proactive strategy has enhanced the industry’s capacity to manage slope risks, and some sections have been recognized as critical due to the frequency of instabilities. At these locations, quantification of the risks becomes necessary. Risk analysis requires knowledge of some variables for which statistical data are scarce or not available, and elicitation of subjective probabilities is needed. A limitation of such approaches lies in the uncertainty associated to those elicited probabilities. In this paper, a quantitative risk analysis is presented for a section of railway across the Canadian Cordillera. The analysis focused on the risk to life of the freight train crews working along this section. Upper and lower bounds were elicited to cope with the uncertainties associated with this approach. A Monte Carlo simulation technique was then applied to obtain the probability distribution of the estimated risks. The risk probability distribution suggests that the risk to life of the crews is below previously published evaluation criteria and within acceptable levels. The risk assessment approach proposed focuses on providing a measure of the uncertainty associated with the estimated risk and is capable of handling distributions that cover more than two orders of magnitude.     

The Depositional Environment of the Cretaceous Kizilsu Group in Xinjiang——With a Discussion of the Lowermost Marine Horizon of the Cretaceous in the Western Tarim Basin

In this paper. it is demonstrated that there exist marine horizons in the upper part of the lower subcycleand the upper subeycle of the Kizilsu Group in Xinjiang. based on new evidence of authigenic glauconite.boron content. carbon and oxygen stablc isotopic analyses. and lithological and sedimentary features. The up-per part of the lower subeycle is the lowermost marine horizon of the Cretaceous in the western Tarim Basin,which is inferred to be of Barremian age.     

Ion microprobe UPb ages on detrital zircon grains from the Ghanzi Group: implications for the identification of a Kibaran-age crust in northwest Botswana

Ion microprobe UPb ages of 1104 ± 16 Ma, 1363 ± 11 Ma and 1748 ± 13 Ma have been obtained on detrital zircons from the siliciclastic rocks of the Ghanzi Group intersected in borehole CKP4 in northern Botswana. Available data show that the time of deposition of the Ghanzi Group is bracketed between 1106 ± 2 and 627 ± 6 Ma. These ages permit constraints to be placed on the source of the sediments. It is shown that the main component of the sediments is sourced locally, from the Kibaran-age Kgwebe igneous rocks. These data are taken to indicate that the Kibaran orogenic event affected northwest Botswana. The Kibaran-age lithological units of northern Botswana represent a link between the Kibaran-age belts of central-eastern Africa and southern Africa. The other two populations of zircons are probably exotic. One is linked to the ca. 1400-1300 Ma rocks known within the Kibaran orogenic system in central and southwest Africa, possibly the Choma-Kalomo Block in Zambia, whereas the ca. 1750 Ma detrital zircons were probably sourced from Palæproterozoic granitoids exposed in northern Namibia and southern Angola.     

Sediment geochemistry of Dahu Swamp in the Nanling Mountains,South China: implication for catchment weathering during the last 16,000 years

This study emphasizes to testify the potential of geochemical proxies of lacustrine sediments as indicative of past climatic changes since the last deglaciation over the catchment of a small closed lake in South China. Based on the study on the core K02 from Dahu Swamp, a small lake in the eastern Nanling Mountains, we inferred that chemical features of clastic materials, which were mainly derived from the granite weathering crust and transported by surface runoff into this lake, possibly had played an important role in affecting chemical characteristics of the sediments. Wetter climatic conditions would lead to stronger chemical weathering intensity (CWI), resulting in more soluble and mobile elements being easily leached downward in granite weathering crusts and the insoluble ones being enriched in the top materials of the weathering crusts. In contrast, dry conditions would exert a converse influence. Although this study presents a different climatic implication of geochemistry from lacustrine sediments in South China from that in north-central China, the results demonstrate that chemical elements of sediments in the small lake in South China can be utilized to reflect the CWI, which was closely in association with variations in temperature and precipitation in the lake catchment.     

Effects of decomposition on the compressibility of fibrous peat — A review

Peat deposits are comprised of high organic content substances primarily derived from dead plant vegetation. Peat itself is not inert but undergoes continuous biological decomposition that causes progressive destruction of the peat fabric, reductions in fibre and organic contents and biogas generation. Depending on the degree of decomposition, the organic solids can exist as fresh (intact) fibres, slightly decomposed or ultimately completely decomposed (amorphous) material. From a geotechnical perspective, an understanding of the relationship between degree of decomposition and engineering properties, including the level of compressibility, is important in dealing with such problematic deposits. However a review of the literature indicates that such relationships have not been sufficiently investigated. Moreover, potential impacts of uncontrolled or unexpected decomposition in-situ are regularly discounted in geotechnical practice. This paper reviews decomposition effects in peat and potentially significant knock-on effects in terms of the material’s physical properties and compressibility. Progressive reduction in solids volume and deterioration in the integrity of the organic structure due to on-going decomposition may cause significant additional settlement to occur over time. More decomposed peat generally undergoes lower primary consolidation and creep strains and is also less prone to future decomposition, compared with lesser decomposed peat.     

Landslide management in the UK—the problem of managing hazards in a ‘low-risk’ environment

The UK is a country with limited direct experience of natural disasters. Whilst landslide losses are not negligible and fatalities are rare, accounts are under-reported. Financial losses from landslides are poorly understood but likely to be considerably in excess of £10 million per year. As a result, a strategic management framework has evolved based upon small, low-impact events punctuated by occasional larger events or larger landslides affecting urban areas. We present an overview of the different landslide management mechanisms in the UK and discuss them in context of cases studies to explore their effectiveness. We conclude with three issues that may have implications for landslide management in the UK and other ‘low-risk’ countries. Firstly, the evidence base by which landslide hazards and risks are measured is insufficient and limitations in existing information need to be better understood. Secondly, existing guidance on strategic and responsive management needs to be assessed for its fitness for purpose. Thirdly, we encourage debate about the importance of near misses.     

Samovar: a thermomechanical code for modeling of geodynamic processes in the lithosphere—application to basin evolution

We present a new 2D finite difference code, Samovar, for high-resolution numerical modeling of complex geodynamic processes. Examples are collision of lithospheric plates (including mountain building and subduction) and lithosphere extension (including formation of sedimentary basins, regions of extended crust, and rift zones). The code models deformation of the lithosphere with viscoelastoplastic rheology, including erosion/sedimentation processes and formation of shear zones in areas of high stresses. It also models steady-state and transient conductive and advective thermal processes including partial melting and magma transport in the lithosphere. The thermal and mechanical parts of the code are tested for a series of physical problems with analytical solutions. We apply the code to geodynamic modeling by examining numerically the processes of lithosphere extension and basin formation. The results are directly applicable to the Basin and Range province, western USA, and demonstrate the roles of crust–mantle coupling, preexisting weakness zones, and erosion rate on the evolutionary trends of extending continental regions. Modeling of basin evolution indicates a critical role of syn-rift sedimentation on the basin depth and a governing role of Peierls deformation in cold lithospheric mantle. While the former may increase basin depth by 50%, the latter limits the depth of rift basins by preventing faulting in the subcrustal lithosphere.