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Glaciation or not? An analytic review of features of glaciation and sediment gravity flows: introducing a methodology for field research
  • Mats O. Molén
Mats O. Molén
Umeå FoU AB

Corresponding Author:mats.dino@gmail.com

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For more than 150 years, geological features claimed to be evidence for pre-Pleistocene glaciations have been debated. Advancements in recent decades, in understanding features generated by glacial and mass flow processes, are here reviewed. It is timely to make renewed comparisons and to re-visit the interpretations of data used to support pre-Pleistocene glaciations. Similarities and differences of Quaternary glaciogenic and sediment gravity flow features, which are most often referred to as proxies and evidence of ancient glaciations, are documented, discussed and closely examined, in order to uncover the origin of more ancient deposits. It is necessary to use multiple proxies to develop a correct interpretation of ancient strata. Analyses and evaluation of data are from a) Quaternary glaciations and glaciers, b) formations which have been assigned to pre-Pleistocene glaciations, and c) formations with comparable features associated with mass-flow deposition (and occasionally tectonics). The aim is not to reinterpret specific formations and past climate changes, but to enable data to be evaluated using a broader and more inclusive conceptual framework. To achieve this goal, detailed descriptions of field evidences are documented from papers that may suggest different interpretations of these data. This is not in an intention to present revised interpretations of these papers, but to collect data and develop a foundation for enhanced analysis of geologic processes and features. Regularly occurring features interpreted to be glaciogenic and are contemporaneous with pre-Pleistocene diamictites which have been interpreted to be tillites, have often been shown to have few or no Quaternary glaciogenic equivalents. These same features commonly form by sediment gravity flows or other non-glacial processes, which may have led to misinterpretations of ancient deposits. These features include, for example, appearances and documented data from the extent and thickness of diamictite deposits, environmental and depositional affinity of fossils in close connection to diamictites, grading and bedding of diamictites, fabrics, size of erratics, polished and striated clasts and surfaces (“pavements”), boulder pavements, lineations, valleys, glaciofluvial deposits, dropstones, laminated sediments, glaciomarine sediments, periglacial structures, soft sediment tectonics, and surface microtextures. The analysis of these features provide detailed documentation that may be used to help identify the origin for many pre-Pleistocene diamictites. Recent decades of progress in research relating to glacial and sediment gravity flow processes has resulted in proposals by geologists, based on more detailed field data, more often of an origin by mass movements and tectonism than glaciation. The most coherent data of this review, i.e. appearances of features produced by glaciation, sediment gravity flows and a few other geological processes, are summarized in a Diamict Origin