Über die Berechnung sämtlicher Feldgrössen aus der Vertikalintensität und deren Anwendung auf die Auswertung von Schwerebildern

Zusammenfassung In nachstehender Untersuchung wird in umfassender Weise gezeigt, wie sich aus der Karte der Vertikalintensität einer lokalen, für sich allein betrachteten Schwerestörung sämtliche anderen Feldgrössen und Ableitungen berechnen lassen. Es ergibt sich dadurch die Möglichkeit, den Verlauf des störenden Kraftfeldes auch unter der Erdoberfläche zu berechnen und aus einem Kraftlinienbild unmittelbar den Aufbau der Inhomogenitäten im Untergrund zu erkennen.

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Summary It is shown that the picture of a local anomaly in gravity (U _z ) may give the basement of structural calculations to an extend that was not known till now. FromU _z all other terms and derivations of the field of gravity are obtainable such asU, U _x ,U _y ,U _zz ,U _zzz , etc. The knowledge of these terms enables us to pursue the lines of gravity under the surface and thus to recognise immediately the characterising features of the structure itself.

     

Klima und Artbildung

International Journal of Earth Sciences - Der kurze Vortrag bezweckt lediglich, durch einige generelle Betrachtungen dem Paläontologen Anregungen bei Diskussionen über das Thema...     

Understanding the Interactions between Climate Change, Landscape Evolution, Surface Processes and Tectonics in the Earth System: What Can the Studies of Chinese Deserts Contribute?

Due to large deserts on Earth surface a thorough understanding of climate change, landscape evolution and geomorphological processes having occurred in deserts is crucial for Earth System Science. The landscapes in deserts are, however, diverse and different over the globe with regard to their geomorphological nature, human activities and geological histories. In the last decades a great number of efforts have been put to the investigation of the initial timing of the occurrence of arid climate, e. g. in northwestern China. Silty sediments in the downwind directions have been used to deduce the histories of deserts. In general, there is a lack of knowledge about processes and landscapes in Chinese drylands between the initial Miocene silt sedimentation at desert margins and the late Quaternary multiple occurrences of wetter climate with assumed large lakes in many of the deserts in northern China. The geomorphological concept of three primary triggering factors, i.e., the sediment supply, sediment availability and transport capacity of wind, and additionally the underground geology need to be fully considered for a better understanding of the environmental histories of sand seas which should not be viewed as equivalent for deserts because sand seas cover between < 1% and ca. 45% of the desert areas in various continents dependent on a complex interaction between various processes of both exogenous and endogenous origins.     

An Automated Iridium-Strip Heater for LA-ICP-MS Bulk Analysis of Geological Samples

In this paper we describe a flux‐free fusion technique for the highly precise LA‐ICP‐MS bulk analysis of geological samples. For this purpose we have developed an automated iridium‐strip heater with temperature and melt time control. To optimise the homogeneity of the fused glasses and to reduce possible depletion of volatile elements during melting, we undertook experiments with basaltic rock and glass powders using different melting temperatures (1300–1700 °C) and melting times (5‐80 s). Major and trace element microanalysis was performed using EPMA and LA‐ICP‐MS. Homogeneous glasses were obtained for temperatures ≥ 1500 °C and melting times ≥ 10 s. High loss (20‐90%) of highly volatile elements (e.g., Cs, Ge, Sn, Pb) was observed for high melting temperatures (≥ 1600 °C) and long melting times (80 s). Standard melting conditions (1600 °C, 10 s) represent a compromise, as the glasses were homogeneous with respect to major and trace elements and, at the same time, were not depleted in elements with condensation temperatures (at a pressure of 10^?4 bar) higher than about 900 K (e.g., Zr, Hf, Ba, Sr, REE, U, Mo, Ni, Rb, Ga). Several international geological reference materials with SiO₂ ranging between 47% m/m and 59% m/m were prepared using our standard melting conditions (1600 °C, 10 s) and subsequently analysed by LA‐ICP‐MS. These samples also include the new Brazilian basaltic reference material BRP‐1. Matrix‐matched calibration of the LA‐ICP‐MS data was performed using the basaltic reference glasses KL2‐G, ML3B‐G, BCR‐2G and BHVO‐2G. Most analytical data agreed within uncertainty at the 95% confidence level with the GeoReM preferred values published in the GeoReM database for reference materials of geological and environmental interest. To demonstrate routine bulk LA‐ICP‐MS analyses of geochemical and cosmochemical samples using the whole rock fusion technique, we also present trace element data for ocean island basalts from Lanai (Hawaii) and of Martian meteorites.     

Mesozoic to Quaternary continental margin dynamics in South-Central Chile (36–42°S): the apatite and zircon fission track perspective

Zircon and apatite fission track data provide constraints on the exhumation history, fault activity, and thermal evolution of the South-Central Chilean active continental margin (36°S–42°S), which we use to assess the tectonic and geomorphic response of the margin to the Andean subduction regime. Several domains with different exhumation histories are identified. The Coastal Cordillera is characterized by uniform and coherent exhumation between Late Triassic (～200 Ma) and late Miocene times, with surprisingly slow average rates of 0.03–0.04 mm/a. Thermal anomalies, related to Late Cretaceous and early Miocene magmatism, have regionally modified fission track age patterns. The Upper Cretaceous thermal overprint is of previously unrecognized significance and extent in the Coastal Cordillera south of 39°S. With the exception of a local but distinct Pliocene to Recent exhumation period in the high-relief Cordillera Nahuelbuta segment between 37°S and 38°S, Cenozoic overall exhumation in the Coastal Cordillera was very slow. The sedimentary record shows that uplift and subsidence here was episodic, with low amplitudes and durations. This rules out large-scale, long-term, Cenozoic accretion, trench-parallel tilting, and tectonic erosion processes in the forearc. The Main Andean Cordillera shows markedly greater long-term exhumation rates than the Coastal Cordillera and, at ～39°S, a steep exhumation gradient. To the south, long-term average Pliocene to Recent exhumation rates of ～1 to ～2 mm/a in the Liquiñe area (39°45′S) are almost an order of magnitude more rapid than average Paleogene to Recent exhumation near Lonquimay (38°30′S) and farther north. While no imprint of the intra-arc Liquiñe-Ofqui Fault Zone on the exhumation pattern is evident, long-term exhumation rates decrease from the crest of the Andes toward the western foothills. Exhumation gradients correlate with climatic gradients, suggesting a causal link to the variable intensity of late Miocene to Pleistocene glacial erosion.     

From micron-sized needle-shaped hydrates to meter-sized shotcrete tunnel shells: micromechanical upscaling of stiffness and strength of hydrating shotcrete

Knowledge on the stresses in shotcrete tunnel shells is of great importance, as to assess their safety against severe cracking or failure. Estimation of these stresses from 3D optical displacement measurements requires shotcrete material models, which may preferentially consider variations in the water–cement and aggregate–cement ratios. Therefore, we employ two representative volume elements within a continuum micromechanics framework: the first one relates to cement paste (with a spherical material phase representing cement clinker grains, needle-shaped hydrate phases with isotropically distributed spatial orientations, a spherical water phase, and a spherical air phase; all being in mutual contact), and the second one relates to shotcrete (with phases representing cement paste and aggregates, whereby aggregate inclusions are embedded into a matrix made up by cement paste). Elasticity homogenization follows self-consistent schemes (at the cement paste level) and Mori–Tanaka estimates (at the shotcrete level), and stress peaks in the hydrates related to quasi-brittle material failure are estimated by second-order phase averages derived from the RVE-related elastic energy. The latter permits upscaling from the hydrate strength to the shotcrete strength. Experimental data from resonant frequency tests, ultrasonics tests, adiabatic tests, uniaxial compression tests, and nanoindentation tests suggest that shotcrete elasticity and strength can be reasonably predicted from mixture- and hydration-independent elastic properties of aggregates, clinker, hydrates, water, and air, and from strength properties of hydrates. At the structural level, the micromechanics model, when combined with 3D displacement measurements, predicts that a decrease of the water–cement ratio increases the safety of the shotcrete tunnel shell.     

Effect of Secondary Circulations on the Surface–Atmosphere Exchange of Energy at an Isolated Semi-arid Forest

Afforestation in semi-arid regions can potentially enhance the global carbon sink by increasing the terrestrial biomass. However, the survival of planted forests under such extreme environmental conditions is not guaranteed a priori, and critically depends on the surface–atmosphere exchange of energy. We investigate the pine forest Yatir in Israel, an example of a man-made semi-arid ecosystem, by means of large-eddy simulations. We focus on the interaction between surface–atmosphere exchange and secondary circulations that couple the isolated forest to the surrounding shrubland. The large-eddy simulations feature a grid resolution that resolves the forest canopy in several layers, and are initialized by satellite data and Doppler lidar, eddy-covariance and radiosonde measurements. We perform three large-eddy simulations with different geostrophic wind speeds to investigate the influence of those wind speeds on the surface–atmosphere exchange. We reproduce the measured mean updrafts above the forest and mean downdrafts above the shrubland, which increase in strength with decreasing geostrophic wind speed. The largest updrafts emerge above the older, denser part of the forest, triggering secondary circulations. The spatial extent of these circulations does not cover the entire forest area, although we observe a reduced aerodynamic resistance in the regions of updraft. Our simulations indicate that the enhanced surface–atmosphere exchange of the Yatir forest is not sufficient to compensate for the increased net radiation, due to the lower albedo of the forest with respect to the surroundings, resulting in higher air temperatures inside the forest. However, the difference between the forest and shrubland temperatures decreases with increasing geostrophic wind speed due to reduction in the aerodynamic resistance.     

Where have all the people gone? The limits of resilience in coastal communities

The concept of resilience has been used to assess community development and its prospects in natural resource-based localities. The objectives of the article are to evaluate the resilience of two Icelandic coastal communities, and to reflect on the possible shortcomings of the resilience concept for providing policy guidance. Mixed qualitative methods were used, with several weeks of fieldwork in each location. The results showed that the two case communities have had to adjust to a radical change in the fisheries management, with the loss of resource entitlements. Additionally, substantial differences were found in their level of resilience. One community was undergoing a transition towards a non-fisheries-based existence through several innovative new initiatives, while the other was struggling to adjust and seemed to have reached its limits of resilience, as witnessed by continuing outmigration and declining services. A state-sponsored programme to rekindle the local economy has had limited success so far. The authors conclude by identifying some of the limitations of the focus on endogenous strategies in much of the resilience literature, which does not pay much attention to the broader political economy.