Die Porositäten toniger Keuper- und Jura-Sedimente Südwestdeutschlands

After a short review of the basic principles governing compaction of clayey sediments, investigations of the porosities of Mesozoic shales from southwestern Germany are reported. The results reveal the influence of grain size, mineral content, temperature, and organic matter on the porosity of shales. All these and other factors have to be considered when evaluating primary porosities of shales at the time of deposition.     

Sedimentologische Untersuchungen an Grimmelfinger Graupensanden

Zusammenfassung Die Untersuchung von Korngrößenverteilung und Rundungsgrad der Grimmelfinger Graupensande an zwei durch 150 km Transportweg unterschiedenen Aufschlüssen gibt Hinweise auf die Einwirkungen auf das verfrachtete Sedimentmaterial unter gleichförmigen, fluviatilen Bedingungen.Am Anfang des untersuchten Rinnenabschnittes besteht das Sediment überwiegend aus je einer Modalfraktion im Mittelsandbereich, Grobsandbereich und Feinkiesbereich¹.Auf dem Transport wird die Mittelsandfraktion — vermutlich infolge der Schlagwirkung des Feinkieses — aufgerieben und fortgeführt. In den beiden gröberen Fraktionen wird am Ende des untersuchten Abschnittes keine Korngrößenabnahme und damit verbunden auch keine Rundungsgraderhöhung beobachtet. Dieses Ergebnis wird verglichen mit den in der Literatur mitgeteilten Untersuchungen in Abriebmühlen und Feldbeobachtungen. Danach dürfte der Rundungsgrad in der Feinkiesfraktion seinem unter den gegebenen Umständen erreichbaren Grenzwert sehr nahe sein und sich auch bei weiter fortgesetztem Transport kaum noch ändern. In der Grobsandfraktion wird der Anteil, dessen Rundung verbessert wird, infolge der damit verbundenen höheren Kugeligkeit bevorzugt fortgeführt.Die Untersuchungen bestätigen, daß die Abrundungseffekte an Sedimentmaterial in strömendem Wasser in Abhängigkeit von der Korngröße betrachtet werden müssen.

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The mechanical effects of fluvial transport over a distance of 150 km were studied by means of size frequency distributions and analysis of roundness in a Tertiary flow channel in Southern Germany filled by sand mixed with fine gravel.When entering the-channel the deposited material shows characteristic trimodal size frequency distributions. During transport the finer modal fraction (0.2...0.63 mm) is destroyed — probably through breakage by the gravel — and removed, while the sizes of the two coarser fractions remain unaffected. The roundness of the coarser fractions also remains unchanged by transport. This suggests that the roundness of the gravel material has approached its limiting roundness which is the optimum that can be achieved under the prevailing conditions. That part of the coarse sand fraction which becomes better rounded by transport may be removed preferably, because the grains getting higher sphericity by being rounded are transported more easily.Grain sizes have to be considered when abrasion effects are studied.

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Herrn Professor Dr. H. Aldinger danke ich für die Möglichkeit, die vorliegende Arbeit im Geologisch-Paläontologischen Institut der Technischen Hochschule Stuttgart anzufertigen, Herrn Dr. D. Elwert, Kiel, für die Überlassung von Probenmaterial.     

Efficient generation of conditional simulations by chebyshev matrix polynomial approximations to the symmetric square root of the covariance matrix

Consider the problem of generating a realization y₁ of a Gaussian random field on a dense grid of points ₁ conditioned on field observations y₂ collected on a sparse grid of points ₂. An approach to this is to generate first an unconditional realization y over the grid =_{1 2}, and then to produce y₁ by conditioning y on the data y₂. As standard methods for generating y, such as the turning bands, spectral or Cholesky approaches can have various limitations, it has been proposed by M. W. Davis to generate realizations from a matrix polynomial approximations to the square root of the covariance matrix. In this paper we describe how to generate a direct approximation to the conditional realization y₁, on ₁ using a variant of Davis' approach based on approximation by Chebyshev polynomials. The resulting algorithm is simple to implement, numerically stable, and bounds on the approximation error are readily available. Furthermore we show that the conditional realization y₁ can be generated directly with a lower order polynomial than the unconditional realization y, and that further reductions can be achieved by exploiting a nugget effect if one is present. A pseudocode version of the algorithm is provided that can be implemented using the fast Fourier transform if the field is stationary and the grid ₁ is rectangular. Finally, numerical illustrations are given of the algorithm's performance in generating various 2-D realizations of conditional processes on large sampling grids.     

Ground deformation of Nisyros Volcano (Greece) for the period 1995–2002: Results from DInSAR and DGPS observations

Differential GPS (DGPS) and Differential Interferometric Synthetic Aperture Radar (DInSAR) analyses were applied to the Kos-Yali-Nisyros Volcanic Field (SE Hellenic Volcanic Arc) to quantify the ground deformation of Nisyros Volcano. After intense seismic activity in 1996, a GPS network was installed in June 1997 and re-occupied annually up to 2002. A general uplift ranging from 14 to 140 mm was determined at all stations of the network. The corresponding horizontal displacements ranged from 13 to 53 mm. The displacement vectors indicate that the island is undergoing extension towards the East, West and South. A two-source “Mogi” model combined with assumed motion along the Mandraki Fault was constructed to fit the observed deformation. The best-fit model assumes sources at a depth of 5500 m NW of the centre of the island and at 6500 m offshore ESE of Yali Island. DInSAR analysis using four pairs of images taken between May 1995 and September 2000 suggests that deformation was occurring during 1995 before the start of the seismic crisis. An amplitude of at least 56 mm along the slant range appeared for the period 1996 through 1999. This deformation is consistent with the two-source model invoked in DGPS modelling. Surface evidence of ground deformation is expressed in the contemporaneous reactivation of the Mandraki Fault. In addition, a 600 m long N-S trending irregular rupture in the caldera floor was formed between 2001 and 2002. This rupture is interpreted as the release of surface stress in the consolidated epiclastic and hydrothermal sediments of the caldera floor.     

Assessment of small-diameter shallow wells for managed aquifer recharge at a site in southern Styria,Austria

An approach to establish the recharge component of managed aquifer recharge (MAR) has recently been proposed that uses small-diameter shallow wells installed using relatively inexpensive drilling methods such as direct push. As part of further development of that approach, a generalized procedure is presented for a technical and economic assessment of the approach’s potential in comparison to other systems. Following this procedure, the use of small-diameter wells was evaluated both experimentally and numerically for a site located in southern Styria, Austria. MAR is currently done at the site using a horizontal pipe infiltration system, and system expansion has been proposed with a target rate of 12 l/s using small-diameter wells as one possible option. A short-duration single-well field recharge experiment (recharge rate 1.3–3.5 l/s) was performed (recharge by gravity only). Numerical modeling of the injection test was used to estimate hydraulic conductivity (K). Quasi-steady-state, single-well recharge simulations for different locations, as well as a long-term transient simulation, were performed using the K value calibrated from the field injection test. Results indicate that a recharge capacity of 4.1 l/s was achievable with a maximum head rise of 0.2 m at the injection well. Finally, simulations were performed for three different well fields (4, 6 and 8 wells, respectively) designed to infiltrate a target rate of 12 l/s. The experimental and numerical assessments, supported by a cost analysis of the small-diameter wells, indicate that the small-diameter wells are a viable, cost-effective recharge approach at this and other similar sites.     

2D probabilistic prediction of sparsely measured earth properties constrained by geophysical imaging fully accounting for tomographic reconstruction ambiguity

Many hydrological, environmental, or engineering exploration tasks require predicting spatially continuous scenarios of sparsely measured borehole logging data. We present a methodology to probabilistically predict such scenarios constrained by ill-posed geophysical tomography. Our approach allows for transducing tomographic reconstruction ambiguity into the probabilistic prediction of spatially continuous target parameter scenarios. It is even applicable to data sets where petrophysical relations in the survey area are non-unique, i.e., different facies related petrophysical relations may be present. We employ static two-layer artificial neural networks (ANNs) for prediction and additionally evaluate, whether the training performance of the ANNs can be used to rank geophysical tomograms, which are mathematically equal reconstructions of physical parameter distributions in the ground. We illustrate our methodology using a realistic synthetic database for maximal control about the prediction performance and ranking potential of the approach. For doing so, we try to link geophysical radar and seismic tomography as input parameters to porosity of the ground as target parameter of ANN. However, the approach is flexible and can cope with any combination of geophysical tomograms and hydrologic, environmental or engineering target parameters. Ranking of equivalent geophysical tomograms based on additional borehole logging data is found to be generally possible, but risks remain that the ranking based on the ANN training performance does not fully coincide with the closeness of geophysical tomograms to ground truth. Since geophysical field data sets do usually not offer control options similar to those used in our synthetic database, we do not recommend the utilization of recurrent ANNs to learn weights for the individual geophysical tomograms used in the prediction procedure.     

Trends,drivers and impacts of changes in swidden cultivation in tropical forest-agriculture frontiers: A global assessment

This meta-analysis of land-cover transformations of the past 10–15 years in tropical forest-agriculture frontiers world-wide shows that swidden agriculture decreases in landscapes with access to local, national and international markets that encourage cattle production and cash cropping, including biofuels. Conservation policies and practices also accelerate changes in swidden by restricting forest clearing and encouraging commercial agriculture. However, swidden remains important in many frontier areas where farmers have unequal or insecure access to investment and market opportunities, or where multi-functionality of land uses has been preserved as a strategy to adapt to current ecological, economic and political circumstances. In some areas swidden remains important simply because intensification is not a viable choice, for example when population densities and/or food market demands are low. The transformation of swidden landscapes into more intensive land uses has generally increased household incomes, but has also led to negative effects on the social and human capital of local communities to varying degrees. From an environmental perspective, the transition from swidden to other land uses often contributes to permanent deforestation, loss of biodiversity, increased weed pressure, declines in soil fertility, and accelerated soil erosion. Our prognosis is that, despite the global trend towards land use intensification, in many areas swidden will remain part of rural landscapes as the safety component of diversified systems, particularly in response to risks and uncertainties associated with more intensive land use systems.