Upper Precambrian sandstones in the Volga-Ural region: Mineralogy, petrography, lithogeochemistry, and formation conditions

The paper presents data on the mineralogy, petrography, and lithogeochemistry of Riphean and Vendian sandstones in the Volga-Ural region. The studied rocks generally differ in several parameters. The Zr/Sc and Th/Sc values typical of psammites suggest that the rocks are dominated by the petrogenic clastic material. This conclusion is supported by median K₂O/Al₂O₃ values (from 0.39 to 0.45). The fine-grained clastic rocks associated with sandstones are also characterized by sufficiently high K₂O/Al₂O₃ values, indicating the prevalence of the first cycle material therein. It is shown that the Prikamsk and Tukaevo sandstones include, in addition to the petrogenic quartz, a significant amount of lithogenic (multifold redeposited) quartz, whereas ratio of these rock types is approximately equal in the Leonidovo and Baikibashevo sandstones. Sandstones of the Kairovo and Shkapovo groups are dominated by the petrogenic quartz. Analysis of the ln(Q/L + CE)-ln(Q/F) diagram shows that the Vendian psammites are dominated by disintegration products of plutonic rocks, whereas the Riphean psammites contain a significant portion of clastic material (related to the erosion of metamorphic rocks) along with felsic and intermediate-felsic igneous rocks. Relationships of feldspars, rock clasts, polycrystalline quartz, and quartz, in general, reflected in the Q_t/(F + R)-Q_p/(F + R) diagram indicate that the Riphean psammites were deposited in a humid setting; the Vendian psammites, in a semihumid/semiarid setting.     

Shear strength characterization of municipal solid waste at the Suzhou landfill, China

The current practice of slope stability analysis for a municipal solid waste (MSW) landfill usually overlooks the dependence of waste properties on the fill age or embedment depth. Changes in shear strength of MSW as a function of fill age were investigated by performing field and laboratory studies on the Suzhou landfill in China. The field study included sampling from five boreholes advanced to the bottom of the landfill, cone penetration tests and monitoring of pore fluid pressures. Twenty-six borehole samples representative of different fill ages (0 to 13 years) were used to perform drained triaxial compression tests. The field and laboratory study showed that the waste body in the landfill can be sub-divided into several strata corresponding to different ranges of fill age. Each of the waste strata has individual composition and shear strength characteristics. The triaxial test results showed that the MSW samples exhibited a strain-hardening and contractive behavior. As the fill age of the waste increased from 1.7 years to 11 years, the cohesion mobilized at a strain level of 10% was found to decrease from 23.3 kPa to 0 kPa, and the mobilized friction angle at the same strain level increasing from 9.9° to 26°. For a confinement stress level greater than 50 kPa, the shear strength of the recently-placed MSW seemed to be lower than that of the older MSW. This behavior was consistent with the cone penetration test results. The field measurement of pore pressures revealed a perched leachate mound above an intermediate cover of soils and a substantial leachate mound near the bottom of the landfill. The measurements of shear strength properties and pore pressures were utilized to assess the slope stability of the Suzhou landfill.     

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.     

The response of nematodes to deep-sea CO2 sequestration: A quantile regression approach

One proposed approach to ameliorate the effects of global warming is sequestration of the greenhouse gas CO₂ in the deep sea. To evaluate the environmental impact of this approach, we exposed the sediment-dwelling fauna at the mouth of the Monterey Submarine Canyon (3262 m) and a site on the nearby continental rise (3607 m) to CO₂-rich water. We measured meiobenthic nematode population and community metrics after ～30-day exposures along a distance gradient from the CO₂ source and with sediment depth to infer the patterns of mortality. We also compared the nematode response with that of harpacticoid copepods. Nematode abundance, average sediment depth, tail-group composition, and length: width ratio did not vary with distance from the CO₂ source. However, quantile regression showed that nematode length and diameter increased in close proximity to the CO₂ source in both experiments. Further, the effects of CO₂ exposure and sediment depth (nematodes became more slender at one site, but larger at the other, with increasing depth in the sediment) varied with body size. For example, the response of the longest nematodes differed from those of average length. We propose that nematode body length and diameter increases were induced by lethal exposure to CO₂-rich water and that nematodes experienced a high rate of mortality in both experiments. In contrast, copepods experienced high mortality rates in only one experiment suggesting that CO₂ sequestration effects are taxon specific.     

Assessment of Pollution of the Kerch Strait and Adjacent Black Sea Area Based on Field Measurements of 2019–2020

Oceanology - The paper presents the results of an analysis of the main pollutants (heavy metals, pesticides, detergents, hydrocarbons) in water, suspended particulate matter, and bottom sediments,...     

Laboratory Simulations of the Radial Distribution of the Toroidal Magnetic Field in an Axial Jet from a Young Stellar Object

Results from experiments on the radial distribution of the magnetic fields in axial plasma flows formed during the compression of a plasma–current sheath carried out at the KPF-4-PHOENIX plasmafocus installation are presented. The plasma flows were generated in a discharge with stationary filling of the chamber with a working gas of argon or hydrogen, and also with a pulsed injection of argon. Analysis of the radial profiles of the magnetic field distribution and their time variations are used to localize regions of trappedmagnetic field, as well as regions where a return current flows at the periphery of the plasma flow. It is shown that the transverse (radial) size of the plasma flow depends on the density of the ambient medium (background gas) through which it propagates. These experiments were carried out in the framework of a project on laboratory simulations of non-relativistic jets from young stars.

     

Time-dependent stress change during failure of rocks

The energy balance of a solid subject to fracture has been explored using heat and mass transfer equations with regard to the volumetric and superficial components. In the suggested model, brittle fracture of a cracked solid considered as a heterogeneous two-phase medium is described by an equation analogous to the Griffith’s criterion for propagation of a single crack. The derived equation is used, together with estimates of relative change in specific interface area, to study the respective change of free strain energy and pressure in rocks associated with failure.