Exploring the impact of diagenesis on (isotope) geochemical and microstructural alteration features in biogenic aragonite

For the Quaternary and Neogene, aragonitic biogenic and abiogenic carbonates are frequently exploited as archives of their environment. Conversely, pre‐Neogene aragonite is often diagenetically altered and calcite archives are studied instead. Nevertheless, the exact sequence of diagenetic processes and products is difficult to disclose from naturally altered material. Here, experiments were performed to understand biogenic aragonite alteration processes and products. Shell subsamples of the bivalve Arctica islandica were exposed to hydrothermal alteration. Thermal boundary conditions were set at 100°C, 175°C and 200°C. These comparably high temperatures were chosen to shorten experimental durations. Subsamples were exposed to different ¹⁸O‐depleted fluids for durations between two and twenty weeks. Alteration was documented using X‐ray diffraction, cathodoluminescence, fluorescence and scanning electron microscopy, as well as conventional and clumped isotope analyses. Experiments performed at 100°C show redistribution and darkening of organic matter, but lack evidence for diagenetic alteration, except in Δ₄₇ which show the effects of annealing processes. At 175°C, valves undergo significant aragonite to calcite transformation and neomorphism. The δ¹⁸O signature supports transformation via dissolution and reprecipitation, but isotopic exchange is limited by fluid migration through the subsamples. Individual growth increments in these subsamples exhibit bright orange luminescence. At 200°C, valves are fully transformed to calcite and exhibit purple‐blue luminescence with orange bands. The δ¹⁸O and Δ₄₇ signatures reveal exchange with the aqueous fluid, whereas δ¹³C remains unaltered in all experiments, indicating a carbonate‐buffered system. Clumped isotope temperatures in high‐temperature experiments show compositions in broad agreement with the measured temperature. Experimentally induced alteration patterns are comparable with individual features present in Pleistocene shells. This study represents a significant step towards sequential analysis of diagenetic features in biogenic aragonites and sheds light on reaction times and threshold limits. The limitations of a study restricted to a single test organism are acknowledged and call for refined follow‐up experiments.     

沉水植物氧化塘对污水厂尾水深度净化效果与机制的小试研究

室外采用玻璃缸装置研究了抚仙湖常见的9种沉水植物氧化塘对澄江县污水厂尾水营养盐的去除效果及机制.结果表明:氧化塘中沉水植物的光合作用导致水体较高的DO和pH值,从而提高氧化塘总氮和总磷的去除率,但沉水植物叶片的腐烂分解则提高了水体氮磷的含量.沉水植物氧化塘对总氮和总磷的去除率分别介于19.44%-64.71%和28.13%-98.33%.沉水植物的直接吸收对总氮和总磷量去除的贡献比较低,占氧化塘总氮和总磷量的0.26%-1.54%和0.47%-1.77%.沉水植物氧化塘内DO、pH变化,促进了氮的降解及氧化还原分解,使其对氮的去除占氧化塘总氮量的30.71%-65.25%,而磷的去除则主要通过化学沉淀及基质吸附,占氧化塘总磷量的73.37%-93.34%.最终,选出蓖齿眼子菜、苦草、黑藻、金鱼藻和光叶眼子菜对氧化塘中氮磷具有较高的去除率.     

Report of centimeter-sized tektites in Pima County,Arizona, cannot be verified

Abstract— Glassy objects reportedly found in Pima County, Arizona, have been identified as tektites. A field survey of the area where they were said to occur, however, did not produce any other tektites, nor did it reveal any other geologic features that might indicate a nearby impact crater. The major-, minor-, and trace-element composition of one specimen is similar to those measured in indochinites, which suggests the objects reportedly from Pima County were instead transported to southern Arizona from Indochina by people.     

Sediment related impacts of climate change and reservoir development in the Lower Mekong River Basin: a case study of the Nam Ou Basin,Lao PDR

This study applies the soil and water assessment tool (SWAT), with climate (precipitation and temperature) outputs from four general circulation models (GCMs) and a regional circulation model (PRECIS), to evaluate (1) the impacts of climate change on reservoir sedimentation and (2) the impacts of climate change and reservoir development on sediment outflow in the Nam Ou River Basin located in northern Laos. Three reservoir–density scenarios, namely one reservoir (1R), three reservoirs in series (3R), and five reservoirs in series (5R), were evaluated for both no climate change and climate change conditions. The results show that under no climate change conditions, by 2070, around 17, 14, and 15% of the existing reservoir storage volume in the basin will be lost for 1R, 3R, and 5R scenarios, respectively. Notably, under climate change scenario with highest changes in erosion and sediment outflux from the basin, the additional reduction in reservoir storage capacity due to sedimentation is estimated to be nearly 26% for 1R, 21% for 3R, and 23% for 5R. Climate change alone is projected to change annual sediment outflux from the basin by ?20 to 151%. In contrast, the development of reservoirs in the basin will reduce the annual sediment outflux from the basin varying from 44 to 80% for 1R, 44–81% for 3R, and 66–89% for 5R, considering climate change. In conclusion, climate change is expected to increase the sediment yield of the Nam Ou Basin, resulting in faster reduction of the reservoir’s storage capacity. Sediment yield from the Nam Ou River Basin is likely to decrease significantly due to the trapping of sediment by planned reservoirs. The impact of reservoirs is much more significant than the impact of climate change on the sediment outflow of the basin. Hence, it is necessary to investigate appropriate reservoir sediment management strategies.     

Applicability of Kinetic Models for In Situ Combustion Processes with Different Oil Types

The in situ combustion (ISC) process is of interest as an enhanced oil recovery method because it is an alternative to traditional steam-based processes for heavy oil and bitumen recovery. ISC is a technique applicable outside the window of reservoir conditions deemed appropriate for steam injection (such as deeper and thinner reservoirs). The process involves complex chemical reactions and physical recovery mechanisms, and predicting the likelihood of successful ISC in field applications remains challenging. This paper describes a numerical investigation of the capability of different ISC kinetic models to predict the combustion behaviors of different types of oils (light oil, heavy oil, and bitumen). Three kinetic models (of Coats, Crookston, and Belgrave) were selected from literature and compared using data from four published combustion-tube experiments. The comparison procedure is as follows: (1) validate the numerical modeling of each kinetic model by matching the selected experimental results or duplicating the numerical results found in published literature; (2) adjust fluid viscosities and densities to match the fluid properties of each experiment;and (3) use each validated kinetic model to predict the performance of the other experiments without further tuning the kinetic parameters. The knowledge derived from the experiments provides guidance for choosing the appropriate kinetic model when no other data are available and for the preliminary design and screening study of a potential ISC project.     

(Re)constructing rural–urban spaces: gendered livelihoods,migration, and natural resources in South Africa

Critical approaches to development theory and practice provide alternative perspectives that focus on counterhegemonic and discursive dimensions of the development process. Feminist development is one such approach that opens up new spaces and opportunities to promote socially progressive and sustainable economic strategies. This paper uses feminist development geography as a framework to highlight the intersection of diverse spaces and economic strategies at the household and community levels. The analysis focuses on gendered livelihoods that are linked to circular migration and use of natural resources as a way to understand the integration of rural and urban spaces of development. The empirical section of this paper examines demographic patterns and socio-economic trends in Limpopo Province, South Africa as a context for the case study of two community-based women’s producer groups. These examples illustrate how economic strategies and social identities are embedded in and integrate both rural and urban spaces. This analysis contributes to feminist and post-structural development theory and practice by highlighting the potential for progressive forms of economic and social empowerment.     

Modelling in-situ upgrading of heavy oil using operator splitting method

The in-situ upgrading (ISU) of bitumen and oil shale is a very challenging process to model numerically because of the large number of components that need to be modelled using a system of equations that are both highly non-linear and strongly coupled. Operator splitting methods are one way of potentially improving computational performance. Each numerical operator in a process is modelled separately, allowing the best solution method to be used for the given numerical operator. A significant drawback to the approach is that decoupling the governing equations introduces an additional source of numerical error, known as the splitting error. The best splitting method for modelling a given process minimises the splitting error whilst improving computational performance compared to a fully implicit approach. Although operator splitting has been widely used for the modelling of reactive-transport problems, it has not yet been applied to the modelling of ISU. One reason is that it is not clear which operator splitting technique to use. Numerous such techniques are described in the literature and each leads to a different splitting error. While this error has been extensively analysed for linear operators for a wide range of methods, the results cannot be extended to general non-linear systems. It is therefore not clear which of these techniques is most appropriate for the modelling of ISU. In this paper, we investigate the application of various operator splitting techniques to the modelling of the ISU of bitumen and oil shale. The techniques were tested on a simplified model of the physical system in which a solid or heavy liquid component is decomposed by pyrolysis into lighter liquid and gas components. The operator splitting techniques examined include the sequential split operator (SSO), the Strang-Marchuk split operator (SMSO) and the iterative split operator (ISO). They were evaluated on various test cases by considering the evolution of the discretization error as a function of the time-step size compared with the results obtained from a fully implicit simulation. We observed that the error was least for a splitting scheme where the thermal conduction was performed first, followed by the chemical reaction step and finally the heat and mass convection operator (SSO-CKA). This method was then applied to a more realistic model of the ISU of bitumen with multiple components, and we were able to obtain a speed-up of between 3 and 5.