Glaciofluvial facies of hyperconcentrated flow (the Pleistocene of Denmark and Western Pomerania)

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

Which features of deposits should be included in a code and which not?

Since the classical publications on lithofacies and architectural element codes (Miall, 1977, 1985), sedimentologists have made several attempts to optimize those codes. The authors present and discuss the codes of lithology and the origin of clastic rocks which have been proposed in the last thirty five years. It appears that the codes hitherto proposed are unsatisfactory because they fail to reflect several important features of deposits. It is postulated that most of Miall’s original rules should be used as a starting point but some additional rules should also be followed: (1) lithofacies symbols should not be used to describe interpretations but lithologic features only; (2) code of texture should contain two capital letters at the most; (3) structure should be described by three lower-case letters at the most; (4) genetic code should indicate depositional process or parent depositional form by capital letters; (5) coding is best applicable in practice if both the lithofacies and genetic codes are used jointly. The present authors propose a modified combination of lithofacies and lithogenetic symbols, shown to make sedimentological analyses more effective and unambigous

Petrographical differentiation of Pleistocene deposits of Myoelibórz Lakeland (Western Pomerania) based on gravels from Chełm Górny and Cedynia

Petrographical content of Pleistocene gravels (4–10 mm) derived from till and glaciofluvial deposits of Western Pomerania was studied. The coarse-grained gravels (20–60 mm) have been additionally investigated for indicator erratics. There are three dominant petrographical groups within the gravels regardless of genetic type of sediments: crystalline rocks, Lower Paleozoic limestones and sandstones. Indicator erratics indicate the most effective glacial erosion in south-eastern Sweden. Theoretical stone center is located at 57.7°N and 16°E, that is in Smĺland. Other regions where the ice sheet could have been nourished were located in Dalarna and Ĺland Islands. The most numerous erratics found in the glacial sediments are: Smĺland granites and quartz porphyries, Ĺland rapakivi granites and quartz porphyries, Bredvad porphyries, Venjan and Grönklitt porphyrites

Orientation of gravels and soft-sediment clasts in subaqueous debrites – implications for palaeodirection reconstruction: case study from Puck Bay, northern Poland

Subaqueous debrites on a fan were recognized at Rzucewo (N Poland). Analysis of debrite fabric enabled debris-flow palaeodirections to be traced on the fan. The long axis azimuth and dip direction of lithic clasts (gravels) as well as soft-sediment clasts (SSC) were measured in the debrites. The results obtained indicate a palaeotransport direction to NNW, similar to the palaeocurrents interpreted from the asymmetrical ripples. However, detailed measurements of both gravels and SSC orientation show variability of palaeoflow directions between NW and NE sectors. In the proximal part of the fan, gravels indicate variable dip directions and dip angles, and a mostly scattered distribution of a-axis orientation. In the medial and distal parts of the fan, clasts are better ordered and usually their a-axes are oriented upslope or transverse to the palaeoslope inclination direction. Probably during the decelerating and halting of debris flows, the compression processes induced clast rotation and a change of inclination. In the distal part of the fan, debrites reveal a distinct variability of palaeoflow directions caused by flattened topography in which debris-flow lobes split and spread freely in different directions. Finally, we conclude that the individual sets of clast fabric usually indicate only local debris-flow directions

Glaciotectonically deformed glaciofluvial sediments with ruptured pebbles (the Koczery study site, E Poland)

Significant quantities of ruptured pebbles are found in glaciotectonically deformed glaciofluvial sediments of the Saalian glaciation (MIS 6) at the Koczery site (E Poland). To identify the responsible mechanisms for the pebble-rupture activity, structural, petrographic, roundness and shape analyses were done. Additionally, till fabric of overlying glacial diamicton was analysed and compared to the other outcomes. The origin of fractures in ruptured pebbles of glaciofluvial sediments is directly linked to compressive stress caused by glaciotectonic processes because of 1) ruptured pebbles occur mainly in glaciotectonically deformed sediments (a quarter of all pebbles is fractured); 2) ruptured pebbles almost always occur one-by-one primarily in gravelly lithofacies; 3) fractures occur in pebbles derived from all petrographic groups; 4) fracture occurrence is independent of pebbles size, shape and roundness; 5) fractures mostly occur parallel to each other (along long ‘a’ or short ‘c’ axis of pebbles) and parallel to the bedding of lithofacies; and 6) in most cases broken fragments of ruptured pebbles survived in the host sediment indicating that the observed damage occurred in situ. This novel study of ruptured pebbles found in glacigenic environments sheds new light on the dynamics of glaciotectonic processes, and may be useful in the characterization of palaeostresses that occur during glaciotectonic deformations

The relation between optical bleaching and sedimentological features of fluvial deposits in the Toruń Basin (Poland)

Distributions of equivalent doses (DE) obtained by the Single Aliquot Regenerative-dose (SAR) OSL method applied for large aliquots of coarse quartz grains extracted from fluvial sediments are presented and analysed with respect to a fluvial palaeoenvironment. The Nowe Dąbie and Łochowo fluvial succession from the western part of Toruń Basin (eastern part of Noteć–Warta streamway, Toruń-Eberswalde ice-marginal valley) was analysed. The fluvial depositional conditions controlling the extent of daylight bleaching are reconstructed by sedimentological studies. The relation between the amount of bleaching and sedimentological properties of fluvial deposits indicate that ripple cross-laminated sands that accumulated on the floodplain and horizontally-bedded sands deposited in shallow channels are more appropriate for OSL dating than sands derived from the deep channel. Along with luminescence results obtained for the river deposits, data measured from an ancient pottery sample, ensuring complete reset of the OSL signal, are presented, compared to and discussed. On this base the poorly bleached sediment samples are identified and an adjustment factor is introduced for correcting their OSL dating results in order to avoid age inversion. The application of the adjustment factor is found to minimize overestimation of OSL ages of sediments

Dumpstones as records of overturning ice rafts in a Weichselian proglacial lake (Rügen Island, NE Germany)

Dumpstones and dropstones up to 0.8 m in size occur in a silty/sandy Weichselian glaciolacustrine succession near Dwasieden on Rügen Island in the SW Baltic Sea (NE Germany). The deposits are exceptional because two levels of dumpstones and dropstones are present, suggesting two dumping phases interrupting characteristic fine-grained glaciolacustrine sedimentation. Plastic downwarping of sediments below the dumpstones and dropstones result in soft-sediment deformation structures. The distribution and orientation of the long axes of the clasts are useful tools for the reconstruction of the state of the lake bottom, as well as for the water depth. The horizontal position of the gravels and boulders (parallel to the bedding) suggests deposition in relatively shallow-water. The dumping events are linked to iceberg rafting in a glacial lake during the Weichselian Glaciation (MIS 2)

New developments in onshore paleoseismic methods, and their impact on Quaternary tectonic studies

Since the publication of Paleoseismology (2nd Edition) in 2009, there has been no comprehensive survey of new trends in Quaternary tectonics. This paper seeks to remedy that situation, by describing the new technologies and interpretations that arose over the past decade. The major technological advances have been in remote sending, e.g., unpiloted aerial vehicles (drones); airborne laser scanning (lidar); terrestrial laser scanning; 3D topographic surveys from Structure-from-Motion; and satellite geodesy such as D-InSAR. Advances have also been made in dating Quaternary deposits, including single-grain luminescence dating (in the laboratory), and portable optically-stimulated luminescence dating (in the field). Geophysical surveys are now a common component of neotectonic investigations, permitting a more formal, 3D integration of subsurface data with surface data. These techniques have lowered the threshold of recognition to smaller and smaller earthquakes, and allowed detection of off-fault deformation such as distributed faulting and folding. We are now collecting so much data that quality control of coseismic field measurements has become an issue, especially when assembling data sets made of old and new data. Soon this data problem will force a reassessment of our time-honored interpretive paradigms, most of which originated in the 1970s and 80s in the early days of neotectonics