Subglacially precipitated carbonates record geochemical interactions and pollen preservation at the base of the Laurentide Ice Sheet on central Baffin Island,eastern Canadian Arctic

The mineralogy and isotopic compositions of subglacially precipitated carbonate crusts (SPCCs) provide information on conditions and processes beneath former glaciers and ice sheets. Here we describe SPCCs formed on gneissic bedrock at the bed of the Laurentide Ice Sheet (LIS) during the last glacial maximum on central Baffin Island. Geochemical data indicate that the Ca in the crusts was likely derived from the subglacial chemical weathering Ca-bearing minerals in the local bedrock. C and Sr isotopic analyses reveal that the C in the calcite was derived predominantly from older plant debris. The δ¹⁸O values of the SPCCs suggest that these crusts formed in isotopic equilibrium with basal ice LIS preserved in the Barnes Ice Cap (BIC). Columnar crystal fabric and the predominance of sparite over micrite in the SPCCs are indicative of carbonate precipitation under open-system conditions. However, the mean δ¹⁸O value of the calcite crusts is ~ 10‰ higher than those of primary LIS ice preserved in the BIC, demonstrating that SPCCs record the isotopic composition of only basal ice. Palynomorph assemblages preserved within the calcite and basal BIC ice include species last endemic to the Arctic in the early Tertiary. The source of these palynomorphs remains enigmatic.     

Robust optimisation of CO2 sequestration strategies under geological uncertainty using adaptive sparse grid surrogates

Geologic CO₂ sequestration in deep saline aquifers is a promising technique to mitigate the effect of greenhouse gas emissions. Designing optimal CO₂ injection strategy becomes a challenging problem in the presence of geological uncertainty. We propose a surrogate assisted optimisation technique for robust optimisation of CO₂ injection strategies. The surrogate is built using Adaptive Sparse Grid Interpolation (ASGI) to accelerate the optimisation of CO₂ injection rates. The surrogate model is adaptively built with different numbers of evaluation points (simulation runs) in different dimensions to allow automatic refinement in the dimension where added resolution is needed. This technique is referred to as dimensional adaptivity and provides a good balance between the accuracy of the surrogate model and the number of simulation runs to save computational costs. For a robust design, we propose a utility function which comprises the statistical moment of the objective function. Numerical testing of the proposed approach applied to benchmark functions and reservoir models shows the efficiency of the method for the robust optimisation of CO₂ injection strategies under geological uncertainty.     

Using Discriminant Analysis and Logistic Regression in Mapping Quaternary Sediments

Mapping the occurrence and thickness of layers within a soil profile is a prerequisite for soil characterization. The objective of this paper is to compare the applicability of two statistical methods—discriminant analysis (DA) and logistic regression (LR)—used to calculate the thickness of Quaternary sediments in a formal way and to identify parameters controlling the occurrence of these sediments. The investigations were carried out in southern Bavaria in an area of about 150 ha presenting a large variability in relief and parent material (Tertiary material, Pleistocene loess, colluvial/alluvial sediments). Comparisons between the two statistical methods were carried out with a training dataset and an evaluation dataset. The results show that DA was preferable under the assumptions of normality and equal variance/covariance matrices. The analyses produced models with 80 % and 79 % correctly reclassified assignments and a canonical correlation coefficient of approximately 0.60. From the simulations, it was found (i) that the determining predictors were altitude, slope, and upslope catchment area (partly expressed as topographical wetness index), SAGA wetness index and specific catchment area; and (ii) that a disadvantage of LR was that trial and error was frequently necessary to find the optimal composition of variables. In this study, a hierarchical combination of binary and ordinal LR was used and revealed (iii) that when the probabilities in LR between adjacent categories were similar, the possibility of incorrect calculations increased and (iv) that visual inspections as well as RMSE showed that DA with weighted depths (5 cm-stepwise DA) provided the best prediction accuracy. This information can help improve soil surveys and the predictability of the spatial heterogeneity in landscapes.     

Kaolin-Kohlentonsteine im flözführenden Oberkarbon des Niederrheinisch-Westfälischen Steinkohlenreviers

Starting from general considerations of the rocks existing in the Ruhr Carboniferous and the mineral layers in coal seams, an informative review is given about the definition of clay stones and kaolin coal tonsteins as well as about the stratigraphic distribution of key horizons with special regard to the kaolin coal tonsteins. Information follows about the first evidence of individual kaolin coal tonsteins, their existence in the normal geologic columns and more recent stratigraphic sections as well as about the concentration of repositories. Besides, the kaolin coal tonsteins are characterized according to their macroscopic and microscopic external form. The paper reports about their material constituents (mineral components, trace elements, anorganic chemical constituents and organic substances in form of coal hydrates and amino acids). The paper closes with some statements about the importance and utilization of kaolin coal tonsteins to solve local and regional duties in mining geology.     

西阿尔卑斯Zermatt-Saas洋壳深俯冲超高压变质带与我国新疆西南天山超高压变质带的比较

根据对西阿尔卑斯Zernatt-Saas带的野外地质考察及有关资料的总结,详细地介绍了西阿尔卑斯Zermatt-Saas洋壳深俯冲超高压变质带的地质概括、岩石组成和变质作用演化过程,并着重与我国新疆西南天山洋壳深俯冲超高压变质带进行了比较,探讨了这两个洋壳深俯冲超高压变质带在变质作用和地质演化方面的异同。在此基础上,总结了这两个目前世界上已知最典型的洋壳深俯冲超高压变质带的基本地质特征是都具有保存完好的洋壳岩石组合特征和较低的地热梯度。