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Thilo Bechstädt (Info)
Rainer Zühlke (Info)
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+49 6221 54-8292
+49 6221 54-6055
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+49 6221 54-5503
Thilo Bechstädt (Info)
Rainer Zühlke (Info)
Phone
+49 6221 54-8292
+49 6221 54-6055
Fax
+49 6221 54-5503
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Diagenesis and Fluid Flow |
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| Focus Field-studies, sampling Thin section petrography Cathodoluminescence XRD, SEM Poroperm properties Major and minor element geochemistry Stable and radiogenic isotopes Fluid inclusion thermometry and Cryo-Raman spectroscopy Crush-leach analyses Field-studies, sampling An essential prerequisite for a diagenetic study is the careful sampling in the field or from cores and cuttings. If possible, this should be undertaken by the responsible scientist. In the field, the areal distribution of certain diagenetic phases (if observable macroscopically) and of macroscopically observable porosity as well as eventual leaching episodes has to be established. In the case of dolomitization, precursor rock samples have to be collected as close as possible to the sampled dolomites. Thin section petrography and fabric analyses Standard petrographic studies in transmitted and reflected light are a first step in outlining different diagenetic phases as well as macro-porosity. Also the areal distribution or in the stratigraphy can be outlined. Selective dissolution of specific components or of part of the rock is of special importance. Staining with different solutions, e.g. potassium ferricyanide, further helps in the analysis of the distribution of specific diagenetic phases. Cathodoluminescence Cathodoluminescence (CL) microscopy is a powerful tool for better outlining different diagenetic phases; it gives also the first hints to trace element contents of these phases. Cathodoluminescence can be applied to carbonate rocks as well as clastic sediments, but also to some ore types. XRD, SEM XRD analysis is crucial for the determination of different mineralogical phases; in the case of dolomitization, bulk mineralogy, stoichiometry and ordering of dolomites can be investigated, which are of importance to understand the type of dolomitization. SEM is of special importance for the distribution of minute mineralogical phases as well as of microporosity and obstructing mineral phases, e.g. kaolinite, illite. Poroperm properties The poroperm properties and their regional and stratigraphic distribution are of special importance for applied studies, especially when cross-checked with other analytical results, e.g. with the distribution of pores observable in thin sections. Major and minor element geochemistry Geochemistry is an essential tool for most applied studies, especially when very small and areawise strictly defined samples can be taken and analyzed. Sr, Na, Fe and Mn are important tracers. Diagenetic overprint can often be well established with these analyses. Stable and radiogenic isotopes Stable isotopes (C, O) are a standard tool in diagenetic and fluid flow studies. They allow, for instance, to decipher if a rock contains the original sea-water values or has been strongly modified and recrystallized. It is also important to compare the values of less diagenetically altered rocks with those of altered ones. Negative or positive excursions, especially of carbon isotopes, can often be used for isotope stratigraphy, even in dolomitized rocks. Sr isotopes are an important tracer for the amount of recrystallization and the rock-water interactions in a closed or open diagenetic system, but also for contact of more radiogenic fluids derived from specific lithologies. Fluid inclusion thermometry and Cryo-Raman spectroscopy Fluid inclusion studies provide information on the relative salinity of the fluids, from which the different diagenetic phases precipitated, as well as on their temperature, if pressure corrections are applied. Salinity calculated only from microthermometry may lead to an underestimation of true salinities, because not only Na ions may be present and complex mixtures are difficult to calculate. Cryo-Raman spectroscopy, i.e. a combination of Raman spectroscopy and low-temperature microthermometry reveals in much greater accuracy the salinity and the major types of dissolved cations and anions in single fluid inclusions. This improved analytical method of fluid inclusions analysis is a valuable contribution for the interpretation of fluid history and fluid flow. Crush-leach analyses In the crush-leach method, the single diagenetic phases are crushed and the fluids entrapped in fluid inclusions are washed out with deionized water and/or methanol. Often Cl, Br, Na, K, Ca, Mg and Li are analyzed and their ratios calculated. This allows, for instance, to draw conclusions on the relationship between a diagenetic fluid and sea-water. From the salinity determined by microthermometry and the Cl concentration in the crush-leach solution, the values can be recalculated to estimate their concentration in the fluid inclusions. Halogen ratios, specifically Cl/Br, are useful indicators of the source of salinity, especially if seawater is supposed to be involved. In contrast to Cl and Br, elements such as Na, K and Li are easily changed from their original concentration by fluid-rock interactions. Selected services are carried out in cooperation with other laboratories. |
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