Sedimentary environment dynamics and the formation of coal in the Pennsylvanian Variscan foreland in the Ruhr Basin (Germany, Western Europe)

During the Pennsylvanian, formation of coal was a phenomenon that was spread over many continents. It is the aim of this paper to illustrate factors that led to the formation of coal seams in paralic clastic sedimentary environments in the Ruhr Basin (German Variscan foreland) during the Pennsylvanian in terms of sequence stratigraphy and the structural evolution of the basin. Lithostratigraphic sections from exploration wells in the currently explored zone of the coal basin allowed the generation of volumetric lithofacies models, using geostastical methods. These models support the analysis of sedimentary facies and a sequence stratigraphic interpretation of the successions that are widely correlated throughout the basin. We then evaluate the relation of the sequence stratigraphic elements derived from the facies models with the abundance of coal seams.     

Geo- and cosmochemistry of the twin elements yttrium and holmium

We have analyzed the Y/Ho-ratios in bulk chondrites, chondrules and four Ca- and Al-rich inclusions (CAIs) from carbonaceous and unequilibrated ordinary and enstatite chondrites (EC) by laser ablation inductively coupled mass spectrometry (LA-ICPMS). We demonstrate that bulk rock sample preparation by containerless melting is a suitable method for preparation of bulk rock samples for high-precision LA-ICPMS. Bulk chondrites have variable Y/Ho-ratios. Carbonaceous chondrites (CI1, CM2, CV3, and CK4) have a common Y/Ho-ratio (25.94 ± 0.08, 2σ) that is regarded as the solar system Y/Ho-ratio. The Y/Ho-ratio increases from carbonaceous, through ordinary (LL, L, H) to enstatite chondrites (EL6), which show the highest Y/Ho-ratio of 27.25. We discuss the result with respect to the origin of fractionation of Re and Os between chondrite groups. Within analytical error, Y and Ho show a good correlation in OC and CV3 chondrules and define an Y/Ho-ratio of 26.22 ± 0.40 (2σ). Y/Ho-fractionation in Ca- and Al-rich inclusions is related to differences in volatility. The bulk silicate Earth is suggested to have a solar Y/Ho-ratio and links the Earth with carbonaceous chondrites. Y/Ho variations in primitive and differentiated terrestrial igneous rocks are discussed in framework of incompatibility of Y and Ho during partial melting. Applicability of Y/Ho as tracer for or against a sedimentary origin of the putative host rock of the Earth’s oldest traces of life from the island of Akilia is briefly discussed.     

On the turbulent Prandtl number in the stable atmospheric boundary layer

This study focuses on the behaviour of the turbulent Prandtl number, Pr _t , in the stable atmospheric boundary layer (SBL) based on measurements made during the Surface Heat Budget of the Arctic Ocean experiment (SHEBA). It is found that Pr _t increases with increasing stability if Pr _t is plotted vs. gradient Richardson number, Ri; but at the same time, Pr _t decreases with increasing stability if Pr _t is plotted vs. flux Richardson number, Rf, or vs. ζ = z/L. This paradoxical behaviour of the turbulent Prandtl number in the SBL derives from the fact that plots of Pr _t vs. Ri (as well as vs. Rf and ζ) for individual 1-h observations and conventional bin-averaged values of the individual quantities have built-in correlation (or self-correlation) because of the shared variables. For independent estimates of how Pr _t behaves in very stable stratification, Pr _t is plotted against the bulk Richardson number; such plots have no built-in correlation. These plots based on the SHEBA data show that, on the average, Pr _t decreases with increasing stability and Pr _t < 1 in the very stable case. For specific heights and stabilities, though, the turbulent Prandtl number has more complicated behaviour in the SBL.     

Intercomparison of Two Hydroxyl Radical Measurement Techniques at the Atmosphere Simulation Chamber SAPHIR

At the atmosphere simulation chamber SAPHIR in Jülich both Laser-Induced Fluorescence Spectroscopy (LIF) and Long-Path Differential Optical Laser Absorption Spectroscopy (DOAS) are operational for the detection of OH radicals at tropospheric levels. The two different spectroscopic techniques were compared within the controlled environment of SAPHIR based on all simultaneous measurements acquired in 2003 (13 days). Hydroxyl radicals were scavenged by added CO during four of these days in order to experimentally check the calculated precisions at the detection limit. LIF measurements have a higher precision (σ= 0.88×10⁶ cm^–3) and better time resolution (Δt = 60 s), but the DOAS method (σ= 1.24×10⁶ cm^–3, Δt = 135 s) is regarded as primary standard for comparisons because of its good accuracy. A high correlation coefficient of r = 0.95 was found for the whole data set highlighting the advantage of using a simulation chamber. The data set consists of two groups. The first one includes 3 days, where the LIF measurements yield (1 – 2) ×10⁶ cm^–3 higher OH concentrations than observed by the DOAS instrument. The experimental conditions during these days are characterized by increased NO_x concentration and a small dynamic range in OH. Excellent agreement is found within the other group of 6 days. The regression to the combined data of this large group yields unity slope without a significant offset.     

Phytoplankton response to climate changes in Lake Baikal during the Holocene and Kazantsevo Interglacials assessed from sedimentary pigments

Lake Baikal, an ancient pristine lake in Siberia, has accumulated sediment deposits that span 25 million years. These deposits have the potential to provide a long-term record of climate changes and their interaction with the ecology of the lake. In order to investigate whether sedimentary phytoplankton pigments could be used to reconstruct past changes in total phytoplankton abundance and productivity, we compared the spatial variability in sedimentary pigment distributions in Holocene cores from three separate regions of the lake; Vidrino in the south, Posolski on Selenga Delta and Continent Ridge in the north. Furthermore, we present the first continuous sedimentary pigment and organic carbon sequence of the Kazantsevo interglacial (roughly a time equivalent to the European Eemian, and Marine Isotopic Stage MIS5e) at a resolution of approximately 150 years. Results of the spatial study showed marked differences in the sediment pigment deposition. Lowest chlorophyll a plus its degradation products versus organic carbon ratios (Chlas/TOC) indicating lowest production, but highest variability with time (indicating strongest climatic oscillations) were found at Continent Ridge. The study of sedimentary pigments deposited during the last two interglacial periods at Continent Ridge showed Chlas/TOC ratios 50–1000 times higher during the Kazantsevo Interglacial compared to the glacial periods, whereas the TOC content was only five times higher, thus indicating the significance of the Chlas/TOC ratio for the reconstruction of the phytoplankton abundance and productivity. Strong oscillations occurred during the Kazantsevo Interglacial within centennial time scales. Chlorophyllb plus its degradation products provided additional information on the past development of Chlorophyceae. Highest Chlas/TOC ratios were found during the early Holocene at approximately 9 kyr BP. Indications of short phytoplankton production maxima were also found during the late Atlantic (6 kyr BP) and at the Subboreal/Subatlantic transition (3 kyr BP). From this we conclude that sedimentary chlorophyll a is a reliable indicator of phytoplanktonic response to climate changes and may serve for␣validation of future climate scenarios in continental regions.     

Long cores from small lakes—recovering up to 100 m-long lake sediment sequences with a high-precision rod-operated piston corer (Usinger-corer)

We present a unique, versatile piston corer for recovering continuous lake and bog sediment sequences with superior accuracy and quality. The main components of the system and their function are described, with special focus on measures for obtaining long, continuous lake sediment sections up to a current maximum length of 95 m. Examples of lake sediment profiles obtained with this system from different climatic zones are presented.     

Methane and carbon dioxide adsorption–diffusion experiments on coal: upscaling and modeling

Numerical modelling of the processes of CO₂ storage in coal and enhanced coalbed methane (ECBM) production requires information on the kinetics of adsorption and desorption processes. In order to address this issue, the sorption kinetics of CO₂ and CH₄ were studied on a high volatile bituminous Pennsylvanian (Upper Carboniferous) coal (VR_r=0.68%) from the Upper Silesian Basin of Poland in the dry and moisture-equilibrated states. The experiments were conducted on six different grain size fractions, ranging from <0.063 to 3 mm at temperatures of 45 and 32 °C, using a volumetric experimental setup. CO₂ sorption was consistently faster than CH₄ sorption under all experimental conditions. For moist coals, sorption rates of both gases were reduced by a factor of more than 2 with respect to dry coals and the sorption rate was found to be positively correlated with temperature. Generally, adsorption rates decreased with increasing grain size for all experimental conditions.Based on the experimental results, simple bidisperse modelling approaches are proposed for the sorption kinetics of CO₂ and CH₄ that may be readily implemented into reservoir simulators. These approaches consider the combination of two first-order reactions and provide, in contrast to the unipore model, a perfect fit of the experimental pressure decay curves. The results of this modeling approach show that the experimental data can be interpreted in terms of a fast and a slow sorption process. Half-life sorption times as well as the percentage of sorption capacity attributed to each of the two individual steps have been calculated.Further, it was shown that an upscaling of the experimental and modelling results for CO₂ and CH₄ can be achieved by performing experiments on different grain size fractions under the same experimental conditions.In addition to the sorption kinetics, sorption isotherms of the samples with different grain size fractions have been related to the variations in ash and maceral composition of the different grain size fractions.     

Determination of bioavailable Fe(III) content in column experiments with the reactive tracer phosphate

Different methods were compared to evaluate the oxidation capacity of ferric iron in column studies. The specific adsorption of the reactive tracer phosphate on the Fe(III) oxide surface was used as an alternative approach to determine the oxidation capacity utilizing the linear correlation between the long-term extent of Fe(III) reduction and the specific surface area of the oxide. Although a low crystalline form of ferric iron (two-line ferrihydrite) was used as electron acceptor and toluene as a carbon source, only 31 and 24% respectively of the total iron was reduced by Geobacter metallireducens in parallel experiments. The results of the phosphate tracer tests were in good agreement with the Fe(III) that was actually reduced and the microbially oxidized toluene. The oxidation capacity of ferric iron is therefore overestimated by the chemical extraction methods, which completely dissolve the ferrihydrite and neglect surface-dependent limitations.