Auto-correlation analysis in search of short-term patterns in varve data from sediments of Lake Gościā, Poland

The annually laminated, or varved, sediments of Lake Gościź, Poland, cover the last c. 12900 years, from Late Allerød up to the present. We have analysed the thickness of 1912 varves in this time-series by means of auto-correlation analysis, in the hope of obtaining information on patterns in past climate, for example patterns of 11 years, which might indicate a relation with solar activity. We analysed the total varve thickness and the thickness of the summer and the winter layer. Two single-bootstrap experiments confirmed the validity of the methods in general, but they indicated that the moving-window technique with overlapping windows hampered the assessment of statistical significance. Three global significance assessment procedures, taking into account the total number of auto-correlation coefficients (ACs) that is tested, showed significance of the ACs only at a lag of one year and only for the winter layer and the total varve. This auto-correlation with the preceding year may be explained by a factor internal to the lake, for instance some depositional mechanism. We found no indication of a relation between varve formation and the sun-spot cycle.     

Palaeoenvironmental interpretation of a Pleistocene alluvial succession in central Poland: sedimentary facies analysis as a tool for palaeoclimatic inferences

A Pleistocene valley-fill alluvial succession deposited in the Kleszczów Graben, central Poland, has been studied in the Belchatów openpit mine. The succession, palynologically documented to represent the Drenthe/Warthe interstadial, consists of three alluvial complexes whose component lithofacies associations indicate a fluvial system evolving from temperate-climate meandering river to transitional-type shallow braided network, to periglacial well-developed braided river influenced by aeolian sand supply. The study suggests that the abundance of fine-grained overbank deposits, occurrence of peats/palaeosols and fining-upward cyclothems are diagnostic attributes of perennial meandering river alluvium, which may indicate temperate climatic conditions. Periglacial braided river alluvium is recognizable by an admixture of wind-derived sand grains with aeolian surface textures and by the occurrence of ice-wedge features, indicative of cold climatic conditions. The distinction between the two basic types of alluvium is aided by the analysis of architectural elements and palaeocurrent directional data. The study demonstrates that sedimentological facies analysis can be a useful tool for the recognition of palaeoclimatic changes in Pleistocene alluvial successions.     

Pleistocene sandur deposits represent braidplains, not alluvial fans

Weichselian sandar in NE Poland show characteristics that are inconsistent with the commonly accepted alluvial-fan-like model for outwash deposition and sandur formation. Analysis of the lithofacies and their vertical and lateral transitions indicates that the Polish sandar developed as braidplains, not as alluvial fans. Analysis of the geomorphic conditions under which modern sandar form, indicates that these conditions (which are characterized by deposition in a narrow belt between ice-covered mountain ranges and the sea) cannot be considered representative of those that prevailed in the geological past when sandar developed as braidplains in confined valleys, to end up in a lowland area where the deposits could spread out further in lateral directions. The latter conditions have been found consistently for all Polish Weichselian sandar that were investigated in much sedimentological detail. This raises the question whether sandar are alluvial fans or not. Because the development of the sandar in NE Poland seems to be much more representative for outwash deposition than the present-day sandar in Iceland and elsewhere, the current alluvial-fan-like sandur model - based on the fairly exceptional present-day situation with deposition in a narrow belt - should therefore be replaced by the braidplain-like sandur model - based on deposition in a valley and in a wider lowland area in front - that has been established for the Polish examples.     

Origin of Pleistocene outwash plains in various topographic settings, southern Poland

The style of Pleistocene outwash sedimentation in the foreland of the central European Mountains (the Carpathians and Sudetes) was controlled to a large extent by the topography. The deposits of three outwash plains formed in various morphological situations in front of the Upper Odra Lobe during the Odranian glaciation (older Saalian) are described here to show the conditions of their development and to reveal the relation between outwash plain sedimentology and proglacial topography. One outwash plain was formed between the mountain front and the ice-sheet margin, which advanced into the zone of fore-mountain alluvial fans. This outwash, deposited parallel to the ice margin, was under the considerable influence of extraglacial rivers flowing from the mountains. The second outwash was deposited in a small valley dipping away from the ice sheet and successively buried by glaciofluvial sediments. It evolved from a narrow valley sandur to an unconfined outwash plain. The third one was formed in a relatively broad, dammed valley dipping towards the ice sheet, where proglacial lake base level controlled the pattern of outwash channels as well as the character of the sedimentation. The studied outwash plains have different sedimentary successions. Their sedimentary profiles differ from each other even in the neighbouring valleys, indicating that distinct depositional conditions existed at the same time in closely spaced areas. It is suggested that the glaciomarginal deposition was controlled mostly by the orientation of the valleys and the inter-valley areas relative to the ice-sheet front. Size and morphology of valleys and interfluves were also important. Depending on their orientation, the outwash plains were fed by meltwaters in various ways; the dip of their surfaces was markedly different and the dynamics of the proglacial river systems were diverse.     

SPECIFIC EROSIONAL AND DEPOSITIONAL PROCESSES IN A PLEISTOCENE SUBGLACIAL TUNNEL IN THE WIELKOPOLSKA REGION,POLAND

The Pleistocene Cie?le succession accumulated in a subglacial tunnel and shows three sedimentological units: (1) trough cross‐stratified sand with granules deposited in deep channels up to 5.4 m, (2) trough stratified and massive gravels deposited in a very deep channel up to 6.2 m eroded by a catastrophic hyperconcentrated flow, and (3) a massive diamicton, interpreted as a basal till of melt‐out type. We focus on angular and deformed sandy clasts that occur in the second unit. It appears that thermal erosion, short transport in a sediment‐laden current and sudden sedimentation were responsible for the oversized sandy clasts that occur in the gravel glaciofluvial deposits. The deposits are characterized by large‐scale erosional scours, massive structure, and fluid‐escape deformations. This combination of features can be used as a key tool for the interpretation of hyperconcentrated‐flow conditions beneath Pleistocene ice sheets.