Bewegung und Textur in magmatischen Schmelzflüssen

Ohne Zusammenfassung     

Coal taxes as supply-side climate policy: a rationale for major exporters?

The shift away from coal is at the heart of the global low-carbon transition. Can governments of coal-producing countries help facilitate this transition and benefit from it? This paper analyses the case for coal taxes as supply-side climate policy implemented by large coal exporting countries. Coal taxes can reduce global carbon dioxide emissions and benefit coal-rich countries through improved terms-of-trade and tax revenue. We employ a multi-period equilibrium model of the international steam coal market to study a tax on steam coal levied by Australia alone, by a coalition of major exporting countries, by all exporters, and by all producers. A unilateral export tax has little impact on global emissions and global coal prices as other countries compensate for reduced export volumes from the taxing country. By contrast, a tax jointly levied by a coalition of major coal exporters would significantly reduce global emissions from steam coal and leave them with a net sector level welfare gain, approximated by the sum of producer surplus, consumer surplus, and tax revenue. Production taxes consistently yield higher tax revenues and have greater effects on global coal consumption with smaller rates of carbon leakages. Questions remain whether coal taxes by major suppliers would be politically feasible, even if they could yield economic benefits.     

Paleoclimatic implications of late quaternary lacustrine sediments in Western Nubia, Sudan

Owing to the hypercontinental location of Western Nubia, secular fluctuations of climate have been filtered and wet phases can be considered as representative of conditions throughout the southeastern Sahara. The study area is crossed by the 20-mm isohyet; between 9300 and about 4000 yr B.P., however, there were widespread lake and swamp environments with freshwater molluscs, ostracods, and diatoms, and a species-rich savanna mammal fauna. The center of the West Nubian Basin (approx. 18°N), an area of about 20,000 km², was occupied by a semiaquatic landscape which was situated at the same latitude as Paleolake Chad. From extensive lake carbonates up to about 4 m thick, a long-term rise of the groudwater table is inferred. Environments developed that now exist at about latitude 13°N. Radiocarbon dates from lake sediment sequences cluster between 30,000 and 21,000 yr B.P., indicating a Pleistocene wet phase. A gap in radiocarbon dates between 21,000 and 11,000 yr B.P. signals a phase of hyperaridity, similar to the present hyperarid phase, with eolian deflation and deposits of sand being the dominant forms of erosion and accumulation.     

Lower Miocene structural evolution of the central Vienna Basin (Austria)

The tectonic evolution of the Vienna Basin overlying the Alpine-Carpathian fold and thrust belt includes two stages of distinct basin subsidence and deformation. The earlier phase contemporaneous with thrusting of the Alpine-Carpathian floor thrust is related to the formation of a wedge-top basin (“piggy-back”), which was connected to the evolving foreland basin (Lower Miocene; c. 18.5–16 Ma). This stage is followed by the formation of a pull-apart basin (Middle to Upper Miocene; c. 16–8 Ma). Sediments of the latter unconformably overly wedge-top basin strata and protected them against erosion.     

Tectono‐sedimentary evolution of the northern Iranian Plateau: insights from middle–late Miocene foreland‐basin deposits

Sedimentary basins in the interior of orogenic plateaus can provide unique insights into the early history of plateau evolution and related geodynamic processes. The northern sectors of the Iranian Plateau of the Arabia–Eurasia collision zone offer the unique possibility to study middle–late Miocene terrestrial clastic and volcaniclastic sediments that allow assessing the nascent stages of collisional plateau formation. In particular, these sedimentary archives allow investigating several debated and poorly understood issues associated with the long‐term evolution of the Iranian Plateau, including the regional spatio‐temporal characteristics of sedimentation and deformation and the mechanisms of plateau growth. We document that middle–late Miocene crustal shortening and thickening processes led to the growth of a basement‐cored range (Takab Range Complex) in the interior of the plateau. This triggered the development of a foreland‐basin (Great Pari Basin) to the east between 16.5 and 10.7 Ma. By 10.7 Ma, a fast progradation of conglomerates over the foreland strata occurred, most likely during a decrease in flexural subsidence triggered by rock uplift along an intraforeland basement‐cored range (Mahneshan Range Complex). This was in turn followed by the final incorporation of the foreland deposits into the orogenic system and ensuing compartmentalization of the formerly contiguous foreland into several intermontane basins. Overall, our data suggest that shortening and thickening processes led to the outward and vertical growth of the northern sectors of the Iranian Plateau starting from the middle Miocene. This implies that mantle‐flow processes may have had a limited contribution toward building the Iranian Plateau in NW Iran.     

Late Quaternary (24–10 ka BP) environmental history of the Neotropical lowlands inferred from ostracodes in sediments of Lago Petén Itzá, Guatemala

We inferred late Pleistocene and early Holocene (24–10 ka BP) environmental conditions in and around Lago Petén Itzá, Guatemala from ostracode remains in the lake sediments. Multivariate statistics were run on autecological information for 29 extant ostracode species collected in 63 aquatic ecosystems on the Yucatán Peninsula along a steep, increasing NW–S precipitation gradient and across a large altitudinal range. Conductivity and water depth are the most important factors that shape ostracode communities. Transfer functions were developed and applied to fossil ostracode assemblages in a ~76-m sediment core (PI-6, ~85 ka) taken in 71 m of water from Lago Petén Itzá, to infer past shifts in conductivity and water level. Results suggest climate was cold and wet during the Last Glacial Maximum (LGM). Alternating dry and wet conditions characterized the deglacial. Early Holocene climate was warmer and wetter. The LGM was characterized by low ostracode species richness (4 spp.) and abundance (<940 valves g⁻¹), dominance of benthic over nektobenthic taxa, abundant Physocypria globula, conductivity as low as 190 μS cm⁻¹, and clay-rich sediments with relatively high total organic carbon and low C/N ratios (<14), suggesting relatively deeper water at the core site associated with abundant precipitation. Greatest water depth at the core site during the LGM occurred late in the period and was ~50 m. The deglacial was characterized by drier conditions, higher ostracode species richness (6 spp.) and abundances up to 18,115 valves g⁻¹, dominance of nektobenthic species, and presence of shallow-water and littoral-zone indicators such as Heterocypris punctata and Strandesia intrepida, conductivity up to 550 μS cm⁻¹, C/N ratios as high as 37, and gypsum deposition. Lowest inferred lake depth at the core site during the deglacial was ~20 m. The early Holocene was characterized by high numbers of ostracode remains, up to 25,500 valves g⁻¹, and the presence of L. opesta and P. globula. Cytheridella ilosvayi was absent from late Pleistocene sediments, suggesting it colonized northern Central America during the Holocene.     

The use of maximum entropy to increase the informational content of hydrological networks by additional gauges

ABSTRACT

The optimization and extension of existing gauging networks are a challenging task, which can be done under consideration of many different aspects. One possibility is to maximize the obtained information on regional hydrological characteristics by new gauges compared to existing ones. For this, information theory approaches are most suitable. Here, the principle of maximum entropy is applied to calculate the probability of non-similarity of catchments to determine locations of new gauges according to the catchment characteristics that are most relevant for the hydrological conditions. The realization in an interactive application, provided online, makes use easy for practitioners and scientists. Goodness-of-fit measures are applied to investigate the explanatory power of the model and the contribution of each characteristic to the model, which gives information on the most influential properties of the catchment. The relevance of the proposed approach is proven by comparing hydrological signatures between similar and non-similar catchment.     

Shake table testing of a miniature steel building with ductile-anchor,uplifting-column base connections for improved seismic performance

Previous research has demonstrated that uplifting-column or rocking building systems may exhibit improved seismic performance, including reductions in total base shear and decreased residual drift, when compared with systems rigidly connected to the foundation. These beneficial effects may be due to lengthened periods, activation of rocking modes, and energy dissipation of base fuse elements. In the current work, several configurations of a miniature steel building with different combinations of base connection and traditional superstructure fuse strength and stiffness were subjected to identical earthquake motions to evaluate differences in demands and performance. The uplifting base connections incorporate highly ductile concrete anchors with long stretch lengths, allowing robust connection performance and easy replacement of damaged connection elements following the seismic event, an advantage over previously tested systems. Testing and dynamic numerical analysis indicates that ductile anchor uplifting systems may reduce total base shear by over 20%, as well as reducing residual structural drift by more than 80%.     

Unusual sources of fossil micrometeorites deduced from relict chromite in the small size fraction in ~467 Ma old limestone

Extraterrestrial chrome spinel and chromite extracted from the sedimentary rock record are relicts from coarse micrometeorites and rarely meteorites. They are studied to reconstruct the paleoflux of meteorites to the Earth and the collisional history of the asteroid belt. Minor element concentrations of Ti and V, and oxygen isotopic compositions of these relict minerals were used to classify the meteorite type they stem from, and thus to determine the relative meteorite group abundances through time. While coarse sediment-dispersed extraterrestrial chrome-spinel (SEC) grains from ordinary chondrites dominate through the studied time windows in the Phanerozoic, there are exceptions: We have shown that ~467 Ma ago, 1 Ma before the breakup of the L chondrite parent body (LCPB), more than half of the largest (>63 μm diameter) grains were achondritic and originated from differentiated asteroids in contrast to ordinary chondrites which dominated the meteorite flux throughout most of the past 500 Ma. Here, we present a new data set of oxygen isotopic compositions and elemental compositions of 136 grains of a smaller size fraction (32–63 μm) in ~467 Ma old pre-LCPB limestone from the Lynna River section in western Russia, that was previously studied by elemental analysis. Our study constitutes the most comprehensive oxygen isotopic data set of sediment-dispersed extraterrestrial chrome spinel to date. We also introduce a Raman spectroscopy-based method to identify SEC grains and distinguish them from terrestrial chrome spinel with ~97% reliability. We calibrated the Raman method with the established approach using titanium and vanadium concentrations and oxygen isotopic compositions. We find that ordinary chondrites are approximately three times more abundant in the 32–63 μm fraction than achondrites. While abundances of achondrites compared to ordinary chondrites are lower in the 32–63 μm size fraction than in the >63 μm one, achondrites are approximately three times more abundant in the 32–62 μm fraction than they are in the present flux. We find that the sources of SEC grains vary for different grain sizes, mainly as a result of parent body thermal metamorphism. We conclude that the meteorite flux composition ~467 Ma ago ~1 Ma before the breakup of the LCPB was fundamentally different from today and from other time windows studied in the Phanerozoic, but that in contrast to the large size fraction ordinary chondrites dominated the flux in the small size fraction. The high abundance of ordinary chondrites in the studied samples is consistent with the findings based on coarse extraterrestrial chrome-spinel from other time windows.