Soft‐sediment deformation structures in a Pleistocene glaciolacustrine delta and their implications for the recognition of subenvironments in delta deposits

The development of soft‐sediment deformation structures in clastic sediments is now reasonably well‐understood but their development in various deltaic subenvironments is not. A sedimentological analysis of a Pleistocene (ca 13·1 to 15 ¹⁰Be ka) Gilbert‐type glaciolacustine delta with gravity‐induced slides and slumps in the Mosty‐Danowo tunnel valley (north‐western Poland) provides more insight, because the various soft‐sediment deformation structures in these deposits were considered in the context of their specific deltaic subenvironment. The sediments show three main groups of soft‐sediment deformation structures in layers between undeformed sediments. The first group consists of deformed cross‐bedding (inclined, overturned, recumbent, complex and sheath folds), large‐scale folds (recumbent and sheath folds) and pillows forming plastic deformations. The second group comprises pillar structures (isolated and stress), clastic dykes with sand volcanoes and clastic megadykes as examples of water‐escape structures. The third group consists of faults (normal and reverse) and extensional fissures (small fissures and neptunian dykes). Some of the deformations developed shortly after deposition of the deformed sediment, other structures developed later. This development must be ascribed to hydroplastic movement in a quasi‐solid state, and due to fluidization and liquefaction of the rapidly deposited, water‐saturated deltaic sediments. The various types of deformations were triggered by: (i) a high sedimentation rate; (ii) erosion (by wave action or meltwater currents); and (iii) ice‐sheet loading and seasonal changes in the ablation rate. Analysis of these triggers, in combination with the deformational mechanisms, have resulted – on the basis of the spatial distribution of the various types of soft‐sediment deformation structures in the delta under study – in a model for the development of soft‐sediment deformation structures in the topsets, foresets and bottomsets of deltas. This analysis not only increases the understanding of the deformation processes in both modern and ancient deltaic settings but also helps to distinguish between the various subenvironments in ancient deltaic deposits.     

CHANGES OF RIVER BED PATTERN OF A LOWLAND RIVER: EFFECT OF NATURAL PROCESSES OR ANTHROPOGENIC INTERVENTION?

GPR and aerial surveys were conducted to study changes of channel pattern in the lower course of the Obra River (western Poland). The river is an example of an intensive anthropogenic transformation, however, the origin of the river pattern changes in its lower course is not obvious. The GPR measurements were done using a georadar MALÅ ProEx equipped with a shielded 250 MHz antenna. A 3D analysis of the GPR data supported with lithologic information indicated traces of a multi‐channel pattern. A variable orientation of sediment layering within channel bars and differences in channels depth and width pointed to changes of direction of the river bed migration. Analysis of aerial photographs and a satellite image indicated that only a few of the channels inferred from GPR could be discerned. The reason could be the more than 1 m thick fine sands layer covering all the alluvial structures. Analysis of historical maps from the eighteenth and the nineteenth centuries showed that 250 years ago the Obra was a meandering river. The maps illustrate also several meander cutoffs and decreased wetlands surface. The following transformations of the river bed pattern were discerned: 1. From braided to meandering channel pattern which could be a natural process caused by climatic and sediment transport rate changes that was also observed in case of other lowland rivers. 2. From meandering to sinuous pattern with channel islands and then to sinuous with oxbow lakes. However, further research is needed to study reasons and timing of the observed changes.     

Rapid ground deformation corresponding to a mining-induced seismic event followed by a massive collapse

Natural Hazards - On 17 April 2015, the Wujek/?l?sk underground coal mine in Poland was struck by a strong induced tremor of magnitude M4.0. The event was followed by a massive rock burst...     

A mixing-length model for predicting vertical velocity distribution in flows through emergent vegetation

Abstract

The vertical profiles of streamwise velocities are computed on flood plains vegetated with trees. The calculations were made based on a newly developed one-dimensional model, taking into account the relevant forces acting on the volumetric element surrounding the considered vegetation elements. A modified mixing length concept was used in the model. An important by-product of the model is the method for evaluating the friction velocities, and consequently bed shear stresses, in a vegetated channel. The model results were compared with the relevant experimental results obtained in a laboratory flume in which flood plains were covered by simulated vegetation.     

A near‐annual palaeohydrological study based on testate amoebae from a sub‐alpine mire: surface wetness and the role of climate during the instrumental period

We present the first testate amoeba‐based palaeohydrological reconstruction from the Swiss Alps, and the first depth to the water table (DWT) calibration dataset for this region. Compared to existing models, our new calibration dataset performs well (RMSEP = 4.88), despite the length of the water table gradient covered (53 cm). The present‐day topography and vegetation of the study mire Mauntschas suggest that it is partly ombrotrophic (large Sphagnum fuscum hummocks, one of which was the coring site) but mostly under the minerotrophic influence of springs in the mire and runoff from the surrounding area. Ombrotrophic Sphagnum fuscum hummocks developed at the sampling site only during the last 50 years, when testate amoebae indicate a shift towards dry and/or acid conditions. Prior to AD 1950 the water table was much higher, suggesting that the influence of the mineral‐rich water prevented the development of ombrotrophic hummocks. The reconstructed DWT correlated with Pinus cembra pollen accumulation rates, suggesting that testate amoebae living on the mire and P. cembra growing outside of it partly respond to the same factor(s). Finally, temperature trends from the nearby meteorological station paralleled trends in reconstructed DWT. However, contrary to other studies made on raised bogs of northwestern Europe, the highest correlation was observed for winter temperature, despite the fact that testate amoebae would more logically respond to moisture conditions during the growing season. The observed correlation with winter temperature might reflect a control of winter severity on surface moisture during at least the first part of the growing season, through snow melt and soil frost phenomena influencing run‐off. More ecohydrological work on sub‐alpine mires is needed to understand the relationships between climate, testate amoebae and peatland development. Copyright © 2009 John Wiley & Sons, Ltd.     

A new discovery of parautochthonous moldavites in southwestern Poland,Central Europe

Moldavites represent tektites derived from the Ries impact structure (~24 km diameter, ~15 Myr old) in southern Germany. Two new localities with parautochthonous moldavites in southwestern Poland were found. In these localities, fluvial sediments of the so‐called Gozdnicka formation host the moldavites. Characteristic tektite features, especially bubbles and inclusions of lechatelierite, are reported. The moldavites' size distribution and their abraded shapes indicate that they were redeposited from the nearby Lusatia substrewn field.     

Discovery of the most distal Ries tektites found in Lower Silesia,southwestern Poland

We report the first occurrence of moldavites in Poland. This discovery confirms the hypothesis that moldavites could have been distributed up to 500 km from the Ries crater in Germany. The tektites were reworked from Middle Miocene sediments and redeposited in Late Miocene (Pannonian) fluvial deposits of the Gozdnicka Formation in Lower Silesia. The Polish moldavites are represented by nine (<8 mm) fragments with a total of 0.471 g. The lack of the autochthonous tektites indicates that tektites investigated here had to be redeposited in a fluvial environment, probably from the Lusatian area. The chemical composition of the Polish moldavites plots in the same area with those from other localities.     

Water Temperature Dynamics in a Complex of Reservoirs and Its Effect on the Temperature Patterns of a Mountain River

The article presents the spatial and temporal dynamics of water temperature in two reservoirs on the upper course of the Dunajec River in the Polish Carpathians. It aims at presenting how spatial patterns and time evolution of water temperature in the reservoirs affect the water temperature in the river. The analysis is based on the results of water temperature measurements in hydrometric verticals in two reservoirs as well as in the river upstream and downstream of the reservoirs. The measurements were carried out in 2012 and 2013, in hydrometeorological conditions typical for each season of the year. Based on the measurements, it has been demonstrated that the complex of reservoirs affects the water temperature in the river over the year and the existence of the smaller lower reservoir may attenuate the cooling or heating effect of the main reservoir on the river.