Clay mineralogy, grain size distribution and their correlations with trace metals in the salt marsh sediments of the Skallingen barrier spit, Danish Wadden Sea

To understand the behavior of trace metals in the salt marsh at Skallingen, Danish Wadden Sea, we investigated a profile from surface to 25?cm depth of the salt marsh sediment, focusing primarily on clay mineralogy and grain size distribution of the sediments and their relationship with trace metals. The clay assembly of the sediment consists of illite, kaolinite and much less chlorite and smectite. The major clay minerals of illite, kaolinite as well as chlorite correlate very poorly with all the trace metals investigated, due probably to the weak competing strength of these clays compared with the other adsorbents and to low availability of the mobile trace metals in the system. Correlation between trace metals and clay minerals may therefore be used as an indicator in environmental assessment. Fine grain fractions of the sediment increased markedly after salt marsh invasion in about 1931 but decreased after 1964. This increase was contributed mainly by the grains finer than 20???m while the fraction of 40?C63???m actually decreased soon after the invasion. The relation between most of the trace metals and grain size distributions is close in general but far from linear. The drastic turning point is observed at about 30???m, around where the correlation coefficient r drops from 0.8 to 0.1. Adsorption is the controlling mechanism for the behavior of trace metals in the salt marsh. Fe/Mn (hydr)oxides and organic matter play the key role.     

Thermo-hydro-mechanical modeling of carbon dioxide injection for enhanced gas-recovery (CO2-EGR): a benchmarking study for code comparison

The objective of this paper was to investigate the THM-coupled responses of the storage formation and caprock, induced by gas production, CO₂-EGR (enhanced gas recovery), and CO₂-storage. A generic 3D planer model (20,000?×?3,000?×?100?m, consisting of 1,200?m overburden, 100?m caprock, 200?m gas reservoir, and 1,500?m base rock) is adopted for the simulation process using the integrated code TOUGH2/EOS7C-FLAC3D and the multi-purpose simulator OpenGeoSys. Both simulators agree that the CO₂-EGR phase under a balanced injection rate (31,500?tons/year) will cause almost no change in the reservoir pressure. The gas recovery rate increases 1.4?% in the 5-year CO₂-EGR phase, and a better EGR effect could be achieved by increasing the distance between injection and production wells (e.g., 5.83?% for 5?km distance, instead of 1.2?km in this study). Under the considered conditions there is no evidence of plastic deformation and both reservoir and caprock behave elastically at all operation stages. The stress path could be predicted analytically and the results show that the isotropic and extensional stress regime will switch to the compressional stress regime, when the pore pressure rises to a specific level. Both simulators agree regarding modification of the reservoir stress state. With further CO₂-injection tension failure in reservoir could occur, but shear failure will never happen under these conditions. Using TOUGH-FLAC, a scenario case is also analyzed with the assumption that the reservoir is naturally fractured. The specific analysis shows that the maximal storage pressure is 13.6?MPa which is determined by the penetration criterion of the caprock.     

Identification of a karst system’s intrinsic hydrodynamic parameters: upscaling from single springs to the whole aquifer

For water management purposes, information about an entire aquifer system is generally more important than information about a specific spring. Since a karstic aquifer system might drain to several outlets, conclusions derived from a single spring can be misleading for characterization and modeling. In this study we apply a conceptual model to an Alpine dolomite karst system in Austria. The particular challenge was that several small springs with strongly varying hydrological behavior and diffuse flow into surrounding streams drain this system. Instead of applying the model to a single spring, it was calibrated simultaneously to several observations within the system aiming to identify the karst system’s intrinsic hydrodynamic parameters. Parameter identification is supported by modeling the transport of water isotopes (δ¹⁸O). The parameters were transferred to the whole system with a simple upscaling procedure and a sensitivity analysis was performed to unfold influence of isotopic information on parameter sensitivity and simulation uncertainty. The results show that it is possible to identify system intrinsic parameters. But the sensitivity analysis revealed that some are hardly identifiable. Only by considering uncertainty reasonable predictions can be provided for the whole system. Including isotopic information increases the sensitivity of some intrinsic parameters, but it goes along with a sensitivity decrease for others. However, a possible reduction of prediction uncertainty by isotopic information is compensated by deficiencies in the transport modeling routines.     

The regional pressure impact of CO<Subscript>2</Subscript> storage: a showcase study from the North German Basin

A regional scale, showcase saline aquifer CO₂ storage model from the North German Basin is presented, predicting the regional pressure impact of a small industrial scale CO₂ storage operation on its surroundings. The intention of the model is to bridge the gap between generic and site-specific, studying the role of fluid flow boundary conditions and petrophysical parameters typically found in the North German Basin. The numerical simulation has been carried out using two different numerical simulators, whose results matched well. The most important system parameters proved to be the model’s hydrological boundary conditions, rock compressibility, and permeability. In open boundary aquifers, injection-induced overpressures dissipate back to hydrostatic level within a few years. If a geological flow barrier is present on at least one side of the aquifer, pressure dissipation is seriously retarded. In fully closed compartments, overpressures can never fully dissipate, but equilibrate to a compartment-wide remnant overpressure. At greater distances to the injection well, maximum fluid pressures are in the range of a few bar only, and reached several years to decades after the end of the actual injection period. This is important in terms of long-term safety and monitoring considerations. Regional pressure increase impacts the storage capacities of neighbouring sites within hydraulically connected units. It can be concluded that storage capacities may be seriously over- or underestimated when the focus is on a single individual storage site. It is thus necessary to assess the joint storage capacities and pressure limitations of potential sites within the same hydraulic unit.     

Economic evaluation of structural and non-structural flood risk management measures: examples from the Mulde River

The concept of flood risk management, promoted by the EU Floods Directive, tries to mitigate flood risks not only by structural, hydraulic engineering measures, but also by non-structural measures, like, e.g., land-use planning, warning and evacuation systems. However, few methods currently exist for the economic evaluation of such non-structural measures and, hence, their comparison with structural measures. The objective of this paper is to demonstrate the potential benefits of employing a wider range of economic appraisal methods for flood projects, in particular, it provides examples and applications of methodologies which may be employed to evaluate non-structural measures and their transaction costs. In two case studies at the Mulde River, Germany, two non-structural measures, a resettlement option and a warning system, are evaluated and compared with structural alternatives with regard to their effectiveness, cost-effectiveness and efficiency. Furthermore, a simple approach is tested in order to show the transaction costs of these measures. Case study results show that the choice of evaluation criteria can have a major impact on the assessment results. In this regard, efficiency as an evaluation criterion can be considered as superior to cost-effectiveness and effectiveness as it is also able to consider sufficiently the impacts of non-structural measures. Furthermore, case study results indicate that transaction costs could play an important role, especially with non-structural measures associated with land-use changes. This could explain why currently these kinds of measures are rarely selected by decision makers.     

Tracing contingencies: analyzing the political in assemblages of web 2.0 cartographies

Our paper presents a theoretical approach to critical research on web 2.0 cartographies. Within the geoweb, dynamic and collaborative web based maps have become a popular medium for collating and communicating geographic information. Web 2.0 cartographies are often promoted as facilitating public participation and democratizing geographic knowledge. Such claims demand a closer look at the processes through which people do engage in these cartographic projects and the multiple actors, institutions, norms and technologies at work. In the context of ‘theorizing the geoweb’, here we propose conceptual tools for analyzing these myriad interactions within web 2.0 cartographies. We understand web 2.0 cartographies as assemblages of subjects, materialities and practices, or ‘actor networks’. Yet explorations of actor‐networks describe existing relations and as a consequence tend to overlook what has been excluded or lies outside of such assemblages. In order to overcome this blindness we suggest bringing together actor‐network theory with the concepts of hegemonic discourses, contingency and the political from Chantal Mouffe and Ernesto Laclau. These two political theorists stress the idea that specific social realities become fixed, sedimented and perceived as natural while other possible social realities become marginalized. Using the example of the dynamic ‘Palestine Crisis Map’ (an Ushahidi Crowdmap) we demonstrate a methodology that emphasizes sensitivity towards moments of exclusion and struggle, where the political unfolds. Theorizing the political in this way extends the processual approach within Critical Cartography and offers a conceptual basis for critical research on the social dimensions of web 2.0 cartographies and geoweb practices.     

Example of Neogene tectonic indentation in the Eastern Betic Cordilleras: the Arc of Aguilas (Southeastern Spain)

Abstract

Neogene deformations have deeply disturbed the initial architecture of the pile of nappes within the Eastern Betic zone. The Arc of Aguilas, displaying a southeast-facing concavity, is a spectacular example of such a post-nappe structuration. Miocene deposits involved in the torsion of the Arc provide a chronology of the deformation. The Arc of Aguilas is one element within a system of rigid-plastic indentation including the following units, from the inner (SE) to the outer (NW) zones : — A rigid block, little deformed, located in the present day abyssal plain, play the part of the indenter.

— A structural pad corresponding to the Aguilas Arc itself. It was severely folded during Miocene times.

— A large peripheral zone mainly subjected to faulting during the Neogene (essentially strike-slip faults). These faults control the evolution of different types of sedimentary basins during the Late Neogene (Tortonian to Pliocene).

Two large shear zones: N020 sinistral (Palomares and Terreros faults), N100 dextral (Las Moreras faults) guided the deformation of the Aguilas Arc within a compressive stressfield of which major tensor axis oscillated between NW-SE and N-S.     

Quartz and calcite microfabric transitions in a pressure and temperature gradient,Sivrihisar, Turkey

Interlayered quartzite and marble in the southern Sivrihisar Massif, Turkey, record metamorphic conditions ranging from high-pressure/low-temperature through a Barrovian overprint from chlorite- to sillimanite-zone conditions. This sequence was exhumed under transtension, producing macroscopic constrictional fabrics (L-tectonites) during crustal thinning. Quartz microstructures consist of dynamically recrystallized aggregates in the dislocation creep regime dominated by grain boundary migration. Quartz microstructures are relatively constant across the high metamorphic gradient, and crystallographic fabric patterns transition from plane strain to constriction strain. Calcite fabrics are characterized by progressive overprinting of a columnar texture inherited from the high-pressure polymorph aragonite. In the low-temperature Barrovian domain (<400?°C), shearing of calcite rods produced a very strong c-axis point maximum. At moderate temperature, calcite rods were partially to totally recrystallized and the strong preferred orientation maintained. At temperature >500?°C and high constriction strain, marble has no crystallographic fabric, likely reflecting a transition from dislocation creep to diffusion creep. Phengite in high-pressure/low-temperature marble and quartzite yields relatively simple age spectra with Late Cretaceous (88–82 Ma) ⁴⁰Ar/³⁹Ar ages. Barrovian muscovite records significantly younger ages (63–55 Ma). The transtension system and associated metamorphism may have occurred above a subduction zone in Paleocene–Eocene time as a precursor to intrusion of Eocene (~53 Ma) arc plutons.     

La Mamora,charnière entre la Meseta et le Rif: son importance dans l'évolution géodynamique postpaléozoïque du Maroc / The Mamora Plain,a hinge between the Meseta and the Rif. Its importance in the post-Paleozoic geodynamic evolution of Morocco

Abstract

The Mamora area (Morocco) is located in the northern part of the Meseta and the southern part of Rharb. The recent formations (Mesozoic to Quaternary) lie unconformably on a Paleozoic basement. This study based on hydrogeological, sedimentological, drilling data and seismic reflection profiles interpretation, proposes new interpretations of geodynamical evolution of this area particularly in terms of tectonic patterns. The most ancient formations recognized in this region are Paleozoic schists and quartzites in the Tifíete sector. They represent the basement of the basin on which Triassic conglomerates and red mudstones associated with basalts lie unconformably. Jurassic and Cretaceous sediments are limestones and marls. The Mio-pliocene formations are open marine blue marls. Plio-quaternary sediments are limestones and sands containing gravel and pebbles. Miocene to Pliocene blue marls facies corresponds to deep marine marls (bathyal as indicated by planctonic foraminifers) with an attributed age from upper Miocene [9] to middle Pliocene [7]. A facies distribution map of the top of the blue marls has been realized where four main facies—conglomerate, shelly sandstone, limestone and marls—indicate a major regression in the Mamora basin. The datation of the formations was mostly realized by Wernli [22, 23, 24, 25], and Cirac [10], In the Mamora area, Hercynian faults show two main structural directions, N020°E-N040°E (Agadir-Rabat), N120°E (Rabat- Tiflète) [5], and a new major Hercynian fault (K2S). The seismic profiles have been studied between Sidi Slimane and Sidi Yahia area, to illustrate the structure of the Mamora, and to replace it, in the geodynamical evolution. The seismic reflection lines and drilling data show that the eastern Mamora was subdivided into two sectors: i) the southern sector is affected by Hercynian faults which create horsts and grabens in the Paleozoic. Mio-Pliocene formations infill these depressions and are covered by Quaternary sediments; ii) the northern sector is constituted by various formations: 1. Paleozoic formation as basement covered by autochthonous Mesozoic to Miocene, 2. Prerifain nappes (marls and evaporites), 3. Mio-Plio-Pleistocene formations as subautochthonous to autochthonous. These two sectors are separated by a major fault (K2S). On the other hand, in the occidental Mamora, the facies distribution and the Plio-Pleistocene thickening seem to be induced by faults with a NE-SW and NW-SE trends which affect the Paleozoic basement. Then, between the Meseta domain and the septentrional Rharb basin, two major Hercynian initially dextral shear zones, Rabat- Tiflete and K2S, have been recognised. During the Atlantic Ocean opening, they are probably senestral shear zones. At the same time the subsidence in Rharb basin is active, major action of these faults is normal. Therefore, Mamora represents a real hinge between stable Meseta and unstable septentrional Rharb basin. © 2001 Éditions scientifiques et médicales Elsevier SAS