Piotr Weckwerth

Age and sedimentological features of fluvial series in the Toruń Basin and the Drwęca Valley (Poland)

The deposits of the Toruń Basin are dominated by a few-metre thick sand series which fill up buried valley-like depressions. In many cases they underlie the Weichselian till which builds up the ice marginal streamway (pradolina) terraces or they are exposed at the basin slopes. As the results of the geological and sedimentological studies, as well as of the dating of the deposits at the sites in the Toruń Basin indicate, the deposits include two fluvial series accumulated before the advancement of the Leszno Phase ice sheet, i.e. in Middle Weichselian and at the beginning of Late Weichselian. The oldest fluvial series connected with the Saalian Glaciation was found at the mouth section of the Drwęca Valley. The fluvial system of the Toruń Basin during Middle Weichselian and at the beginning of Late Weichselian developed in two phases of the sand-bed braided river. During the first one the river channel were dominated by large mid-riverbed sandbars, while during the second phase the water flow was smaller and, as a result, low transverse sandbars and two-dimensional dunes developed. Other active river channel also showed low-energy flows, more intensive meandering than in the case of the braided rivers, as well as sandy side-bars. Analysis of the rounding and frosting of the quartz grains indicate that the studied series of the Weichselian sandy deposits represent alluvia of a river which were fed from two diverse sources. The first one might have represented the alluvia of a warm river which transformed its load, while the other one might have mainly carried the underlying Quaternary deposits.

Heavy minerals as a tool to reconstruct river activity during the Weichselian glaciation (Toruń Basin, Poland)

Abstract The heavy-mineral composition of the Weichselian fluvial successions deposited by an ephemeral meandering river and by a sand-bed braided river in the Toruń Basin (central Poland) was analysed. On the basis of a lithofacies analysis, in combination with the composition of the heavy-mineral assemblages, the fluvial processes and river-channel morphology were reconstructed. This allows determining the provenance of the fluvial deposits and the rivers’ discharge regimes. A model is proposed which can explain the changes in the amount of individual minerals in the fluvial sediments of different ages under the conditions of the oscillating Scandinavian ice sheet. The model assumes that, during the ice-sheet advances, the proglacial streams supplied large amounts of heavy minerals that were less resistant to mechanical abrasion. During the main phase of the ice-sheet retreat, the distance between the ice sheet and the Toruń Basin increased, and the amount of non-resistant minerals diminished as a result of sediment reworking in proglacial rivers. Due to the unique location of the Toruń Basin at the front of the Scandinavian ice sheet during the Weichselian glaciation, the heavy-mineral assemblages in the fluvial deposits form a valuable tool for the recognition of the ice-sheet extent.

Periglacial and Fluvial Factors Controlling the Sedimentation of Pleistocene Breccia in NW Poland

Abstract Breccias were investigated on the terrace of the Toruń‐Eberswalde ice‐marginal valley at Rozwarzyn (NW Poland). Breccia layers include soft‐sediment clasts with diameters between 2 and 256 mm and soft‐sediment megaclasts with diameters from 256 mm to 7 m. The shape of the soft‐sediment clasts and megaclasts (derived from frozen sediments) in the breccia is diverse: from angular and irregular in the case of debris‐flow breccias to slightly rounded and tabular in fluvial breccias. These two types of breccias were developed during the Late Weichselian when the periglacial climate favored extensive lateral erosion by currents of frozen braided channels in the ice‐marginal valley. The dual presence of breccias of fluvial and debris‐flow origin in channel deposits is unique for Quaternary sediments. Zones of breccias existed in the channels where scours and obstacle marks related to megaclasts developed. The study of breccias shed new light on the fluvial processes in ice‐marginal valleys during the Pleistocene and can be considered as diagnostic for fluvio‐periglacial conditions.

Palaeoslopes of Weichselian sand-bed braided rivers in the Toruń Basin (Poland): results of a palaeohydraulic analysis

Palaeoslopes of Weichselian sand-bed braided rivers in the Toruń Basin (Poland): results of a palaeohydraulic analysis Palaeoslopes of Weichselian sand-bed braided rivers have been reconstructed for two stages of fluvial development in the Toruń Basin. (1) The palaeoslope of the ‘fossil’ fluvial succession (buried under Weichselian tills) was calculated on the basis of the median grain size and the Shields parameter. The hydraulic gradient thus found is comparable with the hydraulic gradient of the present-day river. (2) The second developmental stage of the Toruń Basin (as a apart of the Noteć-Warta ice-marginal valley) took place after deglaciation. The slopes of river terraces are a few times lower than those calculated on the basis of the Shields parameter. The palaeoslope of the then river was estimated on the basis of a constant interdependency between the braidplain width, the channel geometry and the grain size. The river gradient that was thus calculated is similar to the measured terrace slope. Palaeoslope estimates in valleys similar to those in the Toruń Basin should consider the width of the braidplain.

Short-term changes in thermal conditions and active layer thickness in the tundra of the Kaffiøyra region, NW Spitsbergen

This article describes and discusses the results of observations concerning short-term changes in the thermal conditions and the thickness of the active layer in a test field located in the tundra of the Kaffioyra (NW Spitsbergen) during the summer season of 2015. One of the objectives was to find a correlation between the dynamic of the changes and the local topography. In recent years, thawing of the active layer in the Kaffioyra region has been considerably varied in individual summer seasons. The test field area was 100 square meters, comprised 36 measurement points and was situated at approximately 3 m a.s.l. in the tundra. The measurements of the thickness and temperature of the active layer were carried out in July, August and early September of 2015. The greatest thickness of the active layer in the tundra was found near the moraine, in the area with the sharpest slope (156 cm to 212 cm). Ground temperatures were observed to follow the prevailing weather conditions with a delay, which amounted to about 24 h at a depth of 25 cm, and as much as 48 h at a depth of 75 cm. A greater thickness of the active layer was found in the western part of the test field, in the vicinity of a tidal channel, and in the eastern part of the field, bordering on the foot of the Aavatsmarkbreen’s moraine. A considerable sloping of the land, combined with increased surface runoff and infiltration at the time of precipitation, makes the water penetrating into the active layer increase its temperature. This demonstrates that the local land forms (tidal channels and terminal moraines) have a substantial influence on the extent and rate of changes which occur in the active layer.

Morphology and surficial sediments of the Waldemar River confined outwash fan (Kaffiøyra, Svalbard)

The development and evolution of confined outwash fans in high Arctic regions depend on the rate of meltwater discharge which is directly related to the glacier ablation rate associated with climate conditions. Another factor controlling outwash fan morphology (e.g. distributive channels depth and width) are processes of fluvial erosion, transport and sediments deposition. All these factors have not previously been considered in relation to the evolution of confined outwash fans incised into the top of permafrost which commonly occur in the forefield of a subpolar glacier and mountains in the high Arctic regions. Morphology and surficial sediments of a confined outwash fan of the Waldemar River (NW Spitsbergen, Svalbard) were analysed on the basis of geomorphological and sedimentological researches. Results of our investigations show multiple relations between the depth and width of distributary channels, fan slope and textural features of glaciofluvial surficial sediments supplied into the fluvial system from glacier and as a result of lateral fluvial erosion of permafrost.