Laboratory testing of coupled hydro-mechanical processes during rock deformation

This paper gives an overview of the published literature on laboratory testing of the stress dependence of rock-permeability. Additionally results of personal research on the stress dependence of the permeability of a low-porosity sandstone are presented. Stress-dependent permeability is examined in the laboratory under different stress fields and stress paths, depending on the intended application of the research. The most commonly applied stress paths are hydrostatic compression, triaxial compression, uniaxial strain conditions, and testing under a constant stress path. The published results of several studies on different rock types under one or more of the mentioned stress conditions are described and compared. A general trend of permeability evolution under hydrostatic and triaxial conditions can be established for sandstones and some crystalline rocks such as granite or rocksalt. For uniaxial strain tests and stress path tests the published results are limited to a few rock types (mainly sandstones). Therefore, a general conclusion for the stress dependence of permeability under these conditions is not possible. Electronic Publication     

Inundation and isolation: dynamics of phytoplankton communities in seasonal inundated flood plain waters of the Lower Odra Valley National Park — Northeast Germany

The flood plains of the Lower Odra are inundated in winter and spring and are desiccated in summer and autumn. Phytoplankton composition as well as its seasonal succession in permanent oxbows and separate lakes were investigated between 1993 and 1996. Solitary centric diatoms were the characteristic phytoplankton taxa of these flood plain waters. They dominated the main channel non-seasonally, the flood plains during the entire inundation phase and long periods of the isolation phase. Only during long phases of low mixing (maximal 1.5-2 months in summer) separate water bodies were dominated by Cyano- and/or Dinophyceae. This special feature of the Lower Odra Valley is explained by the Inundation-Isolation-Model of phytoplankton development influenced by inundation. Out of a high diverse algal spectrum of 495 taxa, specialities such as 9 endangered taxa and 6 halophilous taxa were discussed. Additionally, taxon specific cell-volumes and maxima of biovolumes were given.     

The wind-induced shaping and migration of an isolated dune: A numerical experiment

Numerical experiments are carried out to simulate the development and migration of a barchan dune starting with a conical pile of sand. Such an experiment is done in three steps: (1) computation of the steady-state wind field over and around a barchan using the numerical meso-scale simulation model FITNAH, whereby the horizontal variation of the friction velocity is also calculated; (2) computation of the sand transport using the friction velocity in the transport formula by Lettau and Lettau (1978); (3) computation of the erosion and deposition rates as the divergence of the sand transport, where a special treatment is used for the slip-face of the barchan dune. Adding these rates to the height field leads to a different shape of the dune after a time step t _h . Then this procedure has to be repeated for the next time step t _h .The results are in good agreement with observations: the initial pile of sand develops wings (horns) and a slip-face between them. In addition, flow separation over the lee-side can be simulated. Finally, the tendency to form a barchan in equilibrium is considered.     

Effect of chlorine on near-liquidus phase equilibria of an Fe–Mg-rich tholeiitic basalt

The importance of Cl in basalt petrogenesis has been recognized, yet constraints on its effect on liquidus crystallization of basalts are scarce. In order to quantify the role of Cl in basaltic systems, we have experimentally determined near-liquidus phase relations of a synthetic Fe–Mg-rich basalt, doped with 0.0–2.5 wt% dissolved Cl, at 0.7, 1.1, and 1.5 GPa. Results have been parameterized and compared with previous data from literature. The effect of Cl on mineral chemistry and liquidus depression is dependent on the starting basaltic composition. The liquidus depression measured for a SiO₂-rich, Al₂O₃-poor basalt is smaller than that observed for a basaltic melt depleted in silica and enriched in FeO_T and Al₂O₃. The effect of Cl on depression of the olivine–orthopyroxene–liquid multiple saturation pressure does not seem to vary with the starting composition of the basaltic liquid. This suggests that Cl may significantly promote the generation of silica-poor, Fe–Al-rich magmas in the Earth, Mars, and the Moon.     

Significance of slope sediments layering on physical characteristics and interflow within the Critical Zone – Examples from the Colorado Front Range,USA

The subalpine to montane zones within the Critical Zone (CZ) of the Colorado Front Range, USA outside Pleistocene glaciation limits are characterized by the abundance of stratified and multilayered slope deposits exhibiting depths >1 m. Initial luminescence dating for the upper sediment layers in different profiles give last glacial ages ranging between 40 and 12 ka. A periglacial origin by solifluction is hypothesized for these slope deposits, which is corroborated by geomorphic and sedimentologic parameters. The stratified slope sediments have a strong influence on the physical and chemical properties as well as on soil forming processes in the CZ. Examples are provided for the sediment derived contribution of some elements and common clay minerals together and the great importance of slope sediments as barriers and pathways for the interflow that runs in sediment layers are shown.     

Insights into the formation of silica‐rich achondrites from impact melts in Rumuruti‐type chondrites

Ancient, SiO₂‐rich achondrites have previously been proposed to have formed by disequilibrium partial melting of chondrites. Here, we test the alternative hypothesis that these achondrites formed by fractional crystallization of impact melts of Rumuruti (R) chondrites. We identified two new melt clasts in R chondrites, one in Pecora Escarpment (PCA) 91241 and one in LaPaz Icefield (LAP) 031275. We analyzed major, minor, and trace element concentrations, as well as oxygen isotopes, of these two clasts and a third one that had been previously recognized (Bischoff et al. 2011) as an impact melt in Dar al Gani (DaG) 013. The melt clast in PCA 91241 is an R chondrite impact melt closely resembling the one previously recognized in DaG 013. The melt clast in LAP 031275 has an L chondrite provenance. We show that SiO₂‐rich melts could form from the mesostases of R chondrite impact melts. However, their CI‐normalized rare earth element patterns are flat, whereas those of ancient SiO₂‐rich achondrites (Day et al. 2012; Srinivasan et al. 2018) and those of disequilibrium partial melts of chondrites (Feldstein et al. 2001) have positive Eu anomalies from preferential melting of plagioclase. Thus, we conclude that ancient SiO₂‐rich achondrites were probably formed by disequilibrium partial melting (due to an internal heat source on their parent bodies), rather than from impact melts.     

Rotational evaluation of a long-period spherical harmonic ocean tide model

By exchanging angular momentum with the solid earth, tidal variations in ocean currents and sea level cause the rotation of the solid earth to change. Observations of earth rotation variations can therefore be used to evaluate ocean tide models. The rotational predictions of a spherical harmonic ocean tide model that is not constrained by any type of data are compared here to the predictions of numerical ocean tide models and to earth rotation observations from which atmospheric and non-tidal oceanic effects have been removed. The spherical harmonic ocean tide model is shown to account for the observed variations at the fortnightly tidal period in polar motion excitation but not in length-of-day. Overall, its long-period polar motion excitation predictions fit the observed tidal signals better than do the predictions of the numerical ocean tide models studied here. It may be possible to improve its agreement with length-of-day observations by tuning certain model parameters, as was done to obtain the close agreement reported here between the modeled and observed polar motion excitation; alternatively, the discrepancy in length-of-day may point to the need to revise current models of mantle anelasticity and/or models of the oceanic response to atmospheric pressure variations.