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  • 1
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    Middle Eocene giant slope failure (sedimentary mélanges) in the Ligurian accretionary wedge (NW Italy) and relationships with tectonics, global climate changes and gas hydrates dissociation (2019)
    Geological Society of London
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    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉In Northern Apennines, upper Lutetian-Bartonian sedimentary mélanges, corresponding to ancient mud-rich submarine mass transport deposits, are widely distributed along the exhumed outer part of the External Ligurian accretionary wedge (ELAW), over an area of ∼300 km long and tens of kilometres wide. The occurrence of CH〈sub〉4〈/sub〉-derived carbonate concretions (septarians) in a specific tectono-stratigraphic position below sedimentary mélanges, allows us to document the relationships between a significant period of regional-scale slope failure, climate change (Early and Middle Eocene Optimum stages; EECO and MECO), gas hydrates dissociation, and accretionary tectonics during the Ligurian Tectonic Phase (early-middle Lutetian). The distribution of septarians at the core of thrust-related anticlines documents that gas hydrates dissociation was triggered by accretionary tectonics rather than climate changes. The different ages of slope failure emplacement and septarians formation support that gas hydrates dissociation was not the most important triggering for slope failure. The latter occurred during a tectonic quiescence stage associated with a depositional regressive trend, and probably minor residual tectonic pulses, which followed the Ligurian Tectonic Phase, favoring the dynamic re-equilibrium of the ELAW. Our findings provide useful information for better understanding factors controlling giant slope failure events in modern accretionary settings, where they may cause tsunamis.〈/span〉
    Print ISSN: 0370-291X
    Topics: Geosciences
    Published by Geological Society of London
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  • 2
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    Geoscience and decarbonization: current status and future directions (2019)
    Geological Society of London
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    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉At the 2015 United Nations International Climate Change Conference in Paris (COP21), 197 national parties committed to limit global warming to well below 2°C. But current plans and pace of progress are still far from sufficient to achieve this objective. Here we review the role that geoscience and the subsurface could play in decarbonizing electricity production, industry, transport and heating to meet UK and international climate change targets, based on contributions to the 2019 Bryan Lovell meeting held at the Geological Society of London. Technologies discussed at the meeting involved decarbonization of electricity production via renewable sources of power generation, substitution of domestic heating using geothermal energy, use of carbon capture and storage (CCS), and more ambitious technologies such as bioenergy and carbon capture and storage (BECCS) that target negative emissions. It was noted also that growth in renewable energy supply will lead to increased demand for geological materials to sustain the electrification of the vehicle fleet and other low-carbon technologies. The overall conclusion reached at the 2019 Bryan Lovell meeting was that geoscience is critical to decarbonization, but that the geoscience community must influence decision-makers so that the value of the subsurface to decarbonization is understood.〈/span〉
    Print ISSN: 1354-0793
    Electronic ISSN: 2041-496X
    Topics: Geosciences
    Published by Geological Society of London
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  • 3
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    A large paleo-landslide reactivated by high-speed railway construction works (N Spain) (2019)
    Geological Society of London
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    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉The presence of large paleo-landslides can hinder the construction of railway lines if they cause an alteration of the natural balance of the slope, significantly increasing the cost of the project. During the construction works in a section of the Madrid-Asturias high-speed railway line (Spain), a large-scale hillside instability affected 460 m of the section. The ground movement began ten months after the start of the excavations and remained active throughout the observation period (2008-2010). Data provided by fieldwork, boreholes and instrumental monitoring has allowed the investigation of the geological units involved, together with the geometry and the kinematics of the mass movement. This landslide involves a Paleozoic basement with an estimated volume of 4,400,000 m〈sup〉3〈/sup〉. It shows low displacement rates (〈45 mm/year) and was accommodated on a single surface of rupture, that reaches more than 60 m in depth. The kinematics is favoured by structural and lithological conditions, there being a strong rheological contrast in the lower part of the mobilized ground. This movement is linked to a large paleo-landslide that was partially reactivated when excavations undermined the lower slopes of the hillside. Technical solutions for the stabilization have already caused an additional cost of 17% over the initial budget.〈/span〉
    Print ISSN: 1470-9236
    Electronic ISSN: 2041-4803
    Topics: Geosciences
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  • 4
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    Comparison of stresses in 3D v. 2D geomechanical modelling of salt structures in the Tarfaya Basin, West African coast (2019)
    Geological Society of London
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    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉We predict stresses and strains in the Tarfaya salt basin on the West African coast using a 3D static geomechanical model and compare the results against a simplified 2D plane-strain model. Both models are based on present-day basin geometries, are drained, and use a poroelastic description for the sediments and visco-plastic description for salt. We focus on a salt diapir, where an exploratory well has been drilled crossing a major fault. The 3D model shows a significant horizontal stress reduction in sediments at the top of the diapir, validated with measured data later obtained from the well. The 2D model predicts comparable stress reduction in sediments at the crest of the diapir. However, it shows a broader area affected by the stress reduction, overestimating its magnitude by as much as 1.5 MPa. Both models predict a similar pattern of differential displacement in sediments along both sides of the major fault, above the diapir. These displacements are the main cause of horizontal stress reduction detected at the crest of the diapir. Sensitivity analysis in both models shows that the elastic parameters of the sediments have a minimal effect on the stress–strain behaviour. In addition, the 2D sensitivity analysis concludes that the main factors controlling stress and strain changes are the geometry of the salt and the difference in rock properties between encasing sediments and salt. Overall, our study demonstrates that carefully built 2D models at the exploration stage can provide stress information and useful insights comparable to those from more complex 3D geometries.〈/span〉
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    Electronic ISSN: 2041-496X
    Topics: Geosciences
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  • 5
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    Transpression and the build-up of the cordillera: the example of the Bucaramanga fault (Eastern Cordillera, Colombia) (2019)
    Geological Society of London
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    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉Widespread wrench tectonics has been described along the Northern Andes. The Bucaramanga fault, described as sinistral strike-slip, bounds the high Santander Massif. We combine structural and thermochronologic data at the central-southern portion of the fault, in order to investigate the vertical displacement.Structural survey data shows: 1) old phases of activity preserved in the host rocks along the fault trace, with superimposition of different slickenlines generations; and 2) both strike- and dip-slip kinematics indicators. New and previous thermochronologic data show that differential exhumation of the fault walls has been ongoing from 50 Ma. The hangingwall, the Santander Massif, records: 1) in the central portion, decreasing exhumation rates from the early Miocene to the middle-late Miocene; and 2) in the southern portion, constant rates through the Late Oligocene to the Pliocene.Combining such observations, the thermochronologic offset resulting from the relative motion of the two fault walls is comparable with the observed elevation drop across the fault, suggesting that the present topography of the Santander Massif is related to the vertical movement along the Bucaramanga fault. We infer that the fault has a significant Neogene reverse component, consistent with present-day horizontal GPS vector data, long-term exhumation rates and the structural assemblage.〈strong〉Supplementary material:〈/strong〉〈a href="https://doi.org/10.6084/m9.figshare.c.4620140"〉https://doi.org/10.6084/m9.figshare.c.4620140〈/a〉〈/span〉
    Print ISSN: 0370-291X
    Topics: Geosciences
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  • 6
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    Structurally controlled growth of fibrous amphibole in tectonised metagabbro: constraints on asbestos concentration in non-serpentinised rocks (2019)
    Geological Society of London
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    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉Asbestos nucleation and concentration in rocks are mostly associated with mechanisms of fibre formation, combined with the water-dependent mineralogical alteration produced during serpentinisation of ultramafic masses. Very little is known about the structural settings and tectonic histories that influence and control asbestos occurrence in non-serpentinised rocks, which are diffusely embedded within tectonised ophiolitic suites. Focussing on a case history provided by a tectonised metagabbro from the Ligurian Alps (northern Italy), a multiscale structural-petrographical approach is used to investigate the relationships between rock fabric and fibrous amphibole growth within the metagabbro. Meso- to micro-structural observations are used to document the role of structurally controlled fluid-rock interactions in localising the fibrous amphibole growth during ductile-to-brittle shearing (mylonitic foliation to shear veins). A qualitative structural scenario is here provided for illustrating the growth of asbestos amphiboles in shear veins during the progression of shear deformation towards semi-brittle rheological conditions. The mechanisms of structurally controlled growth of fibrous amphibole in non-serpentinised rocks imply an examination of the tectonic boundary conditions that are at the origin of the asbestos concentration in ophiolitic rocks involved in orogenic belt construction.〈/span〉
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    Topics: Geosciences
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  • 7
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    Prediction of tunnelling impact on flow rates of adjacent extraction water wells (2019)
    Geological Society of London
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    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉The decline or drying up of groundwater sources near a tunnel route is damaging to groundwater users. Therefore, forecasting the impact of a tunnel on nearby groundwater sources is a challenging task in tunnel design. In this study, numerical and analytical approaches were applied to the Qomroud water conveyance tunnel (located in Lorestan province, Iran) to assess the impact of tunnelling on the nearby extraction water wells. Using simulation of groundwater-level fluctuation owing to tunnelling, the drawdown at the well locations was determined. From the drawdowns and using Dupuit's equation, the depletion of well flow rates after tunnelling was estimated. To evaluate the results, observed well flow rates before and after tunnelling were compared with the predicted flow rates. The observed and estimated water well flows (before and after tunnelling) showed a regression factor of 0.64, pointing to satisfactory results〈/span〉
    Print ISSN: 1470-9236
    Electronic ISSN: 2041-4803
    Topics: Geosciences
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  • 8
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    Identification of structural domains considering the combined effect of multiple joint characteristics (2019)
    Geological Society of London
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    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉A structural domain represents a volume of rock masses with similar mechanical and hydrological properties. This paper presents a new multivariate method, built upon the classical statistical method, for identifying structural domains by considering a combined effect of multiple joint characteristics. First, joints are placed into corresponding cells according to a comprehensive categorization of joint characteristics. Second, based on the frequencies of joints in each cell, a contingency table analysis and appropriate χ〈sup〉2〈/sup〉 test are used to identify structural domains. In this method, the joint frequency in each cell is determined not only by joint orientation but also by joint trace length and aperture. A group of simulated joint populations is used to check the validity of the proposed method. Seven joint populations with a total of 731 joints collected in Southeast Dalian Port, China are evaluated using the proposed method. Calculations show that the differences in both distribution forms and sequences of joint characteristics produce apparently different identification results. A combined effect of multiple joint characteristics is found to play an important role in the identification of structural domains. Reliable results for the multivariate method are obtained, given the objective of analysis and practical application.〈/span〉
    Print ISSN: 1470-9236
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    Topics: Geosciences
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  • 9
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    Assessment of the engineering geological characteristics of the Bazoft dam site, SW Iran (2019)
    Geological Society of London
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    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉The geotechnical parameters and permeability of the Bazoft dam site were investigated. The bedrock of the Bazoft dam site belongs to the Asmari and Jahrum (Eocene, Oligocene and Miocene) formations. Rock mass rating (RMR) and geological strength index (GSI) classification systems were used to evaluate the dam site. Physical, mechanical and dynamic tests were performed on samples in a rock mechanics laboratory. Shear strength parameters and geotechnical parameters of the rock mass were determined. The results of Lugeon tests for determining rock mass permeability were in the range of 10–30. Based on the RMR, the dam site is located in the ‘good’ category. Finally, the relationship between Lugeon, the number of joints and rock quality designation 〈strong〉(〈/strong〉RQD) of the rock mass was evaluated using statistical analysis for 24 exploratory boreholes with a total length of 3400 m. The values of these parameters were determined and analysed using equations, tables and reports in sections of 5 m along the borehole. The results showed that the relationship between Lugeon with RQD and the joint number is an exponential equation with a good correlation coefficient. Multiple linear analysis also showed high accuracy of the estimated Lugeon based on RQD and joint number.〈/span〉
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    Electronic ISSN: 2041-4803
    Topics: Geosciences
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  • 10
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    Speciation, Risks, and Isotope-based Source Apportionment of Trace Elements in Soils of the Northeastern Qinghai-Tibet Plateau (2019)
    Geological Society of London
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    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉Trace elements in soils might cause contamination and ecological risks to the environment with increasing anthropogenic disturbance. This study investigated the distribution, speciation, risks, and possible sources of 28 target trace elements in soils of the northeastern Qinghai-Tibet Plateau. The average concentrations of trace elements in soils of the study area ranged from 0.25 (Hg) to 697.38 (Cr) mg/kg. The residual fraction was the dominant host of V, Cr, Cu, Sn, Sb, Hg and REEs while Co, Ni, Zn, Mo, Cd and Pb had large proportions in the non-residual fractions. Risk assessment code analysis showed that Cd should be recognized as a priority pollutant in the study area. Correlation analysis indicated that Pb, Cu, Zn, Cd and Sn might originate from the same or similar source. The 〈sup〉206〈/sup〉Pb/〈sup〉207〈/sup〉Pb and 〈sup〉208〈/sup〉Pb/〈sup〉206〈/sup〉Pb ratios of the soils were in the range of 1.166-1.224 and 2.031-2.122, respectively. The anthropogenic Pb contribution proportion was in the range of 0-53.92% for the study area. The anthropogenic Pb contribution was higher in the areas with more intensive anthropogenic activities. Heavy metals and excessive anthropogenic disturbance should be effectively controlled in the northeastern Qinghai-Tibet Plateau to maintain the ecological sustainability and human health of this fragile area.〈/span〉
    Print ISSN: 1467-7873
    Electronic ISSN: 1467-7873
    Topics: Chemistry and Pharmacology , Geosciences
    Published by Geological Society of London
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