Abstract: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.
This study investigated the surge dynamics of Aavatsmarkbreen, a glacier in Svalbard and its geomorphological impact based on remote sensing data and field observations. The main objective was to analyse and classify subglacial and supraglacial landforms in the context of glacial deformation and basal sliding over a thin layer of thawed, water‐saturated deposits. The study also focused on the geomorphological evidence of surge‐related sub‐ and supraglacial crevassing and glacier front fracturing. From 2006 to 2013, the average recession of Aavatsmarkbreen was 363 m (52 m a−1). A subsequent surge during 2013–2015 resulted in a substantial advance of the glacier front of over 1 km and an increase in its surface area of more than 2 km2. The surface of Aavatsmarkbreen was severely fractured. Significant ice‐flow acceleration was noted whereby the highest surface velocity reached 4.9 m day−1. The ephemeral water‐escape structures and mini‐flutings on the fine‐grained till surface that formed during the surge are indicative of high subglacial pore‐water pressure and enhanced basal sliding. Two genetic types of clast pavements occur in the marginal zone of Aavatsmarkbreen. The results of this study will help to constrain glaciological and geomorphological processes involved in surge phenomena. Understanding the scale and effects of these processes provides insight into the behaviour of fast‐flowing glaciers and ice streams and reveals their relationships with external factors.
Dis tri bu tions of equiv a lent doses (D E ) ob tained by the Sin gle Aliquot Re gen er a tive-dose (SAR) OSL method ap plied for large aliquots of coarse quartz grains ex tracted from flu vial sed i ments are pre sented and ana lysed with re spect to a flu vial palaeoenvironment. The Nowe D¹bie and £ochowo flu vial suc ces sion from the west ern part of Toruñ Ba sin (east ern part of Noteae-Warta streamway, Toruñ-Eberswalde ice-mar ginal val ley) was ana lysed. The flu vial depositional con di tions con trolling the ex tent of day light bleach ing are re con structed by sedimentological stud ies. The re la tion be tween the amount of bleach ing and sedimentological prop er ties of flu vial de pos its in di cate that rip ple cross-lam i nated sands that ac cu mu lated on the floodplain and hor i zon tally-bed ded sands de pos ited in shal low chan nels are more ap pro pri ate for OSL dat ing than sands de rived from the deep chan nel. Along with lu mi nes cence re sults ob tained for the river de pos its, data mea sured from an ancient pot tery sam ple, en sur ing com plete re set of the OSL sig nal, are pre sented, com pared to and dis cussed. On this base the poorly bleached sed i ment sam ples are iden ti fied and an ad just ment fac tor is in tro duced for cor rect ing their OSL dat ing re sults in or der to avoid age in ver sion. The ap pli ca tion of the ad just ment fac tor is found to min i mize over es ti ma tion of OSL ages of sed i ments.Key words: OSL age in ver sion, quartz, op ti cal bleach ing, sand-bed braided river, ice-mar ginal streamway/val ley.
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