D–H evidence for the timing of kaolinization in Northeast Bavaria, Germany |
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Authors: | H Albert Gilg |
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Institution: | Lehrstuhl für Angewandte Mineralogie und Geochemie, Technische Universität München, Lichtenbergstr. 4, D-85747 Garching, Munich, Germany |
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Abstract: | The δDSMOW values of sedimentary kaolins from the western border of the Bohemian Massif, northeast Bavaria, that did not suffer a deep burial (less than 1000 m) nor a hydrothermal overprint, change systematically from Late Triassic (?50‰) to Mid-Jurassic and Late Cretaceous (?56‰ to ?66‰) to Upper Oligocene–Mid-Miocene (?77‰ to ?90‰). All analyzed clays are far from hydrogen isotope equilibrium with present-day meteoric waters. Combined oxygen and hydrogen isotope data of selected samples indicate low temperatures of formation (<30°C) and no evidence for preferential D/H exchange with younger waters. The hydrogen isotopic evolution of kaolins is interpreted as reflecting a systematic isotopic change of paleo-meteoric waters in that region. This can be related mainly to the northward drift of stable Europe after the break-up of Gondwana. Increasing continentality, surface uplift and global cooling are additional factors responsible for decreasing δDSMOW values since the Mid-Cretaceous. Kaolinite hydrogen isotope ratios of two large residual economic deposits (Tirschenreuth: δDSMOW=?80‰ to ?76‰; Hirschau–Schaittenbach: δDSMOW=?70‰ to ?63‰) can be used in combination with additional geological evidence to constrain the timing of weathering in these areas. A late Early Cretaceous kaolinization age is suggested for the Early Triassic sandstone-hosted deposits near Hirschau–Schnaittenbach, whereas a Late Oligocene to Mid-Miocene age is indicated for the Carboniferous granite-hosted Tirschenreuth deposits. |
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Keywords: | D/H ratio Northeast Bavaria Kaolins |
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