Moränen versus Till: Empfehlungen für die Beschreibung, Interpretation und Klassifikation glazialer Landformen und Sedimente
95 - 112
E&G : Quaternary Science Journal
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Internationally, the description and interpretation of glacial sediments and landforms largely follow a set of uniform guidelines and terminology. Sediments are normally described according to their lithofacies characteristics (e.g. diamicton, sorted sands), and only after closer inspection and investigation are genetic terms applied (e.g. till, glaciofluvial outwash). Mixing of sedimentological and geomorphological terminology does not occur. In German-speaking countries, however, the term moraine is used for glaciogenic sediments and landforms such as end moraines and also adopted for till plains (“ground moraine landscapes”, “old/young morainic landscapes” etc.). Similar traditions of the latter kind are sometimes found as a relict in Scandinavian texts, and an equally profound mixing of terms is found in much of the French literature. The authors argue here that this mixture not only leads to unnecessary confusion for students but also makes international communication more difficult, especially when the terminological inconsistencies are as extensive and non-systematic as in the German community at present. The present paper presents a systematic overview of the state-of-the-art of till terminology, thereby providing the necessary background information for a useful description and interpretation of field evidence for communicating results in German and hopefully aiding more efficient communication of German Quaternary geologists and geomorphologists internationally. The aim is to provide a sedimentological terminology that is in agreement with international standards and can readily be distinguished from geomorphological vocabulary. The authors recommend that usage of the term ground moraine, for example, is restricted to certain landform associations encountered in NW Central Europe, and excluded from use when discussing sediments. For primary glaciogenic sediments sensu stricto the term till should be used only where appropriate sedimentological evidence exists. A process-based subdivision of till types (e.g. deformation, lodgement till) is not useful in most cases, because as a community we do not have the tools to reliably distinguish such processes at a macro-scale. This recognition has led to the creation of the highly useful umbrella term subglacial traction till and its distinction from overridden primary sediments that are termed glaciotectonite. The present contribution translates the older terminology to the internationally-accepted terminology that follows the scientifically-robust approach of splitting descriptive terminology – based on a lithofacies approach (e.g. diamicton)– from the latter interpretative stage (e.g. subglacial traction till, debris flow deposit). The authors present translations of the different till schemes that have existed through time and link these to the current state of the art, citing several examples and clear diagnostic criteria to distinguish various types of diamictic sediments. This contribution stresses that the majority of diamictons encountered in glacial environments, especially in ice-marginal settings, are not usually and certainly not automatically subglacial traction tills.