Publication: Research - peer-review › Journal article – Annual report year: 2012
Tills dominate large parts of the superficial sediments on the Northern hemisphere. These glacial diamictons are extremely heterogeneous and riddled with fractures and lenses of sand or gravel. The frequency and geometry of sand lenses within tills are strongly linked to glaciodynamic processes occurring in various glacial environments. This study specifically focuses on the appearance and spatial distribution of sand lenses in tills. It introduces a methodology on how to measure and characterize sand lenses in the field with regard to size, shape and degree of deformation. A set of geometric parameters is defined to allow characterization of sand lenses. The proposed classification scheme uses a stringent terminology to distinguish several types of sand lenses based on the geometry. It includes sand layers, sand sheets, sand bodies, sand pockets and sand stringers. The methodology has been applied at the Kallerup field site in the Eastern part of Denmark. The site offers exposures in a number of till types that underwent different levels of glaciotectonic deformation. Sand lenses show high spatial variability and only weak uniformity in terms of extent and shape. Secondly, the genesis of the various types of sand lenses is discussed, primarily in relation to the depositional and glaciotectonic processes they underwent. Detailed characterization of sand lenses facilitates such interpretations. Finally, the observations are linked to a more general overview of the distribution of sand lenses in various glacial environments. Due to the complex and mutable appearance of sand lenses, geometric descriptions can reveal the deformation history and even give indications on the palaeo-glaciological conditions during the deposition of the surrounding tills. This information can support the understanding of till genesis and further inform till classifications. In this regard, structural heterogeneity such as sand lenses can supplement traditional directional element analysis to identify till types and may be used as a novel tool in till investigations.
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- Clayey till, Sand lenses, Sand stringers, Classification, Glacial diamictons, Subglacial deformation