Abstract
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.
Highlights
Vast continental areas are covered with unlithified Quaternary sediments which were deposited by glaciers and glacier-fed streams during the Pleistocene
Quaternary glacial gravels are often partly cemented by carbonates, and comparable cements are known from pre-Quaternary glacigenic rock sections
As we know of no sedimentary process in a delta environment which deposits an extremely bimodal sediment as layer No 2 in one instance, we conclude that the fine grained putty is either a pure cement, or a later cemented, fine grained internal sediment which infiltrated the initially very porous gravel skeleton
Summary
Vast continental areas are covered with unlithified Quaternary sediments which were deposited by glaciers and glacier-fed streams during the Pleistocene (tills, gravel etc.). Despite its importance for applied geology (e.g., gravel exploitation, underground excavations, stability of natural cliffs etc.), almost no systematic studies on this topic exist so far (but see Elbracht, 2010). It would be desirable for the engineering geologist to be able to predict the spatial extension of cemented zones in otherwise loose sediment. In the sparse literature and among applied geologists, contradictory rules of thumb concerning this question are encountered (Aber, 1979; Paxton & Martin, 1980) As all of these studies were exclusively concerned with observations made in natural and artificial outcrops, the question of how deep cementation may reach could not be addressed sufficiently
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