Glacifluwialne facje strumieni przeciążonych zawiesiną na przykładzie plejstoceńskich osadów wschodniej Jutlandii i Pomorza Zachodniego

Abstract

Glaciofluvial facies of hyperconcentrated flow (the Pleistocene of Denmark andWestern Pomerania).S u m m a r y. Beverage & Culbertson (1964) defined hyperconcentrated flow as a flow of water-sediment mixture with a behaviour intermediate between that of a debris flow (mudflow) and that of a stream flow. However, the essence of this definition has largely been misunderstood and lost in the subsequent literature. It would appear that almost any deposit can possibly be attributed to a hyperconcentrated flow, because this genetic label has been attached to: non-stratified deposits with normal or inverse-to-normal grading, as well as deposits that were stratified; some of these deposits had polymodal and only other bimodal grain-size distribution, occasionally bearing outsized cobble gravels and boulders. Arguably, the Beverage and Culbertson original definition implies a turbulent, non-Newtonian fluidal flow with pseudoplastic rheological behaviour, intermediate between that of a mudflow (plastic) and a stream flow (Newtonian fluid), which may suggest sediment deposition by rapid dumping from suspension (Lowe, 1988; Vrolijk & Southard, 1997), rather than tractional emplacement. The study areas in Western Pomerania and east Jutland are located in transition fan and glaciofluvial fans (Weichselian glaciation). Three assemblages of deposits derived from hyperconcentrated flow are exposed: massive cobble gravel (monofacial association GCm), massive sand (monofacial association Sm) and massive sand and planar-cross bedded sand (lithofacies association Sm, Sp). The reason for significant grain-size distribution diversity of sediments derived from the same depositional process was difference in competence flow which came out from discharge flow changes. Despite different grain framework grain-size distribution, grains within hyperconcentrated flows were mostly moved by turbulences and dispersive grain pressure.