Wyniki wyszukiwania - Biblioteka Nauki

Nowa wersja platformy, zawierająca wyłącznie zasoby pełnotekstowe, jest już dostępna.
Przejdź na https://bibliotekanauki.pl

Ograniczanie wyników

Znaleziono wyników: 4

Liczba wyników na stronie

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych: Weichselian

Sortuj według:

Ogranicz wyniki do:

Middle and Upper Weichselian Pleniglacial fluvial erosion and sedimenta- tion phases in Southwestern Poland, and their relationship to Scandinavian ice sheet build-up and retreat

100%

Krzyszkowski D. , Kuszell T.

tom Vol. 77, No 1

17-38

The sequence of Weichselian sediments and processes in SW Poland is almost identical to that of central Poland. Generally, three fluvial units occur, comprising silts and sands coarsening upwards to silts, sands and gravels, with aeolian deposits on top. This suggests very uniform processes throughout the palaeogeographic zone. To the south of this zone, there was extensive loess deposition and glacial deposition to the north. Climatic conditions during the Middle and Upper Weichselian Pleniglacial in SW Poland were similar to those in central Poland and northwestern Europe, though the period of 47-43 kyrs BP was slightly milder in SW Poland (shrub tundra, forest-tundra). Climatic conditions during the periods 38-27 kyrs BP and 23-18 kyrs BP were very uniform throughout central Europe, including SW Poland, though there may have been a strong north-south climatic gradient during the former period, as data from the loessic zone indicate at least patches of boreal forest or forest-tundra conditions in SW Poland at that time. It is also possible that there was a Middle Weichselian Pleniglacial interstadial with a lower age boundary at 25,900 ą 700 years BP, characterised by Pinus-Picea forest with no heliophytes. This interstadial represents the last mild period before the advance of the late Weichselian ice sheet into SW Poland. The Weichselian fluvial deposition of SW and central Poland may have been punctuated by at least three major erosional phases, characterised by similar incision depths during the cold stages. Erosion took place, with certainty, at around 75-60 kyrs BP (Lower Pleniglacial) and 27 kyrs BP, very probably at around 23/22 kyrs and possibly at around 40 kyrs BP, and valley aggradation occurred during the milder stages. The Upper Pleniglacial was characterised by valley aggradation, associated with southward ice sheet advance and restricted fluvial outflow. However, the frequent Middle Pleniglacial Weichselian climatic oscillations did not initiate sedimentation and erosion, they controlled only river discharge and type of fluvial sedimentation and aeolian activity. The occurrence of the erosional and aggradational phases were controlled by the changes in ice volume in Scandinavia, ice sheet build-up and retreat, respectively.

Optical dating of a late quaternary sediment sequence from Sokli, Northern Finland

94%

Alexanderson H. , Eskola K. O. , Helmens K. F.

tom Vol. 32

51-59

Interstadial and non-glacial stadial sediments collected in boreholes from Sokli in northeastern Finland have been dated by optically stimulated luminescence on quartz and feldspar grains. The quartz OSL ages follow stratigraphic order, with one exception, and support the litho- and biostratigraphical correlation with the NW European mainland climate-stratigraphy and the marine oxygen-isotope stages. Feldspar IRSL dates generally overestimate the age, probably due to incomplete bleaching. The data show that during the last glacial cycle north-eastern Finland was not glaciated until MIS 5b, around 90 ka. Interstadial conditions occurred around ∼94 ka (MIS 5c), ∼74-80 ka (MIS 5a) and 42-54 ka (MIS 3). The OSL ages have large standard errors mainly due to small sample sizes, relatively poor luminescence characteristics and uncertainties in dose-rate determinations.

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

84%

Weckwerth P. , Chabowski M.

2013

tom Vol. 19, No. 1-2

25--46

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.

Weichselian and Holocene bird remains from Komarowa Cave, Central Poland

67%

Tomek T. , Bochenski Z.

tom 48A

nr 1-2