The Distinction Between Carbonate Cement and Internal Sediment in Quaternary Gravels: A Combined Field, Petrographic, and Stable Isotope Study from Northern Switzerland

  •  Dominik Letsch    


Quaternary glacial gravels are often partly cemented by carbonates, and comparable cements are also known from pre-Quaternary glacigenic rock sections. These cemented zones are of importance e.g. for applied geology or paleoclimate studies but have hitherto not been studied systematically. This article reports examples from the Alpine foreland of Northern Switzerland. It is based on geotechnical reports, field observations, petrographic and stable isotope analyses. It will be shown that carbonate cements in glacial gravel are of heterogeneous origin and that many of them should rather be considered as cemented internal sediment (i.e., sediment which infiltrated the gravel skeleton after deposition) the source of which is assumed to be the fine suspended fraction of glacier meltwater. This paper presents descriptive, petrographic, and geochemical criteria to distinguish between such cemented internal sediment and true cements, and develops genetic models to account for both the development of internal sediment and of true cements. It is suggested that the use of these models will help to better predict the spatial geometry of cemented zones in glacial gravel. Finally, we will discuss some consequences for the study of pre-Quaternary glacigenic deposits.

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