Browsing by Author "Pleskot, Krzysztof"
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Item Holoceńskie zmiany środowiska okolic Poznania (środkowa Wielkopolska) w świetle badań paleolimnologicznych jezior: Strzeszyńskiego, Kierskiego i Glinnowieckiego(2019) Pleskot, Krzysztof; Szczuciński, Witold. PromotorNiniejsza praca przedstawia szczegółową analizę zapisu osadowego z trzech jezior: Strzeszyńskiego, Kierskiego i Glinnowieckiego, a główny problem jaki podejmuje to zmiany środowiska w Wielkopolsce w trakcie holocenu. Rekonstrukcja przedstawiona w pracy opiera się przede wszystkim na wynikach uzyskanych ze skanowania XRF i jest uzupełniona analizą podatności magnetycznej, gęstości objętościowej, azotu całkowitego, pierwiastków śladowych, izotopów stabilnych węgla i azotu, pyłku i okrzemek. Modele wieku analizowanych rdzeni zostały opracowane na podstawie 64 dat radiowęglowych. Wyniki pokazują, że osady Jeziora Strzeszyńskiego zawierają najbardziej szczegółowy zapis zmian środowiska, który sugeruje że po okresie dynamicznych przekształceń jezior i ich zlewni przed ~10,2 tys. lat BP nastąpiła faza długotrwałej stabilizacji. Faza ta zakończyła się ok. 1,7 tys. lat BP z powodu zaburzeń środowiska związanych z działalnością człowieka. Zapis XRF z osadów Jeziora Strzeszyńskiego ujawnia 9 krótkotrwałych zaburzeń sedymentacji (10,1; 9,3; 6,4–6,1; 5,5–5,1; 4,7–4,5; 2,7–2,4; 1,3–1,2; 0,8– 0,6; 0,4–0,2 tys. lat BP) wynikających pradwdopodobnie z wahań poziomu wody wywołanych zmianami klimatycznymi. W celu oszacowania skutków upadku Meteorytu w Morasku, który miał miejsce na terenie dzisiejszego Poznania ok. 5,5 tys. lat temu, osady rdzeni korespondujące ze środkowym holocenem zostały poddane wielowskaźnikowej analizie przeprowadzonej w wysokiej rozdzielczości. Brak wyraźnego zapisu tego zdarzenia w osadach wskazuje, że zdarzenie to miało niewielki wpływ na środowisko badanego obszaru.Item Late Holocene Vistula River floods recorded in grain size distributions and diatom assemblages of marine sediments of the Gulf of Gdańsk (Baltic Sea)(Elsevier, 2023-05-01) Szcześniak, Marta; Kokociński, Mikołaj; Jagodziński, Robert; Pleskot, Krzysztof; Zajączkowski, Marek; Szczuciński, WitoldDuring the large flood of the Vistula River in 2010, the riverine brackish water surface plume extended up to 70 km into the Gulf of Gdańsk (Baltic Sea), leaving a thin layer of medium-grained sand deposits. It inspired a search for palaeoflood records in marine sediments. Thus, we aimed to identify the most useful flood indicators and apply them to reveal palaeoflood records in sediment cores from the Gulf of Gdańsk. The study is based on analyses of surface samples, collected during and one year after the 2010 flood, and two long sediment cores, which were subjected to high-resolution grain size, diatom, and geochemical analyses, while chronology was based on the combined AMS 14C, 210Pb and 137Cs dating. It was found that, in a water depth of less than 30 m, modern large flood deposits were not preserved after a year. Sediment cores retrieved from greater water depths (over 60 m) were composed of sandy mud, and most of the 1 cm thick sediment samples were characterized by unimodal grain size distribution. However, some of the samples were bimodal, with the additional mode in fine-grained fractions, which is interpreted to be the result of direct deposition from riverine flood surface water plume. The diatom assemblages revealed a moderate downcore variability, except for the intervals characterized by bimodal grain size distributions. They contained elevated amounts of benthic oligohalobous (freshwater) and decreased euhalobous and mesohalobous taxa, supporting the likely interpretation of these layers as deposited during river flood events. During the last c. 4 ka, a dozen major flood events were identified. However, their application to flood climate reconstruction is challenging because of relatively frequent and partly unknown changes in major river mouth positions in the past. We suggest that thin deposits of major floods left on the seafloor and subjected to further mixing maybe still recognized using a combination of high-resolution grain size distribution and diatom analyses supplemented by a good understanding of the depositional system history.Item Refining the history of extreme coastal events in southern Newfoundland, NW Atlantic, with lake sediment archives(Elsevier, 2023-11) Pleskot, Krzysztof; Cwynar, Les C.; Kowalczyk, Cyprian; Kokociński, Mikołaj; Szczuciński, WItoldExtreme events, including tsunamis, storm surges and hurricanes, affect the western North Atlantic coast, threatening communities and impacting ecosystems. Although these extreme coastal events (ECEs) are currently thoroughly monitored in the area, older ECEs are known only from short historical evidence. Therefore, establishing a reliable ECE history that extends more than several decades into the past requires data from geological records. This study aims to refine the existing record of ECEs on the southern Burin Peninsula (Newfoundland, Canada) that extends back to the mid-18th century by providing the first lake-sediment-based reconstruction of the event history of the Canadian province of Newfoundland and Labrador. We investigated short sediment cores collected from four shallow coastal lakes. The identification of ECEs relied mainly on lithostratigraphic evidence and peak detection of sand grain counts. Diatoms, dry bulk density, and loss-on-ignition were also analyzed. The age-depth models of the cores were based on 210Pb and 137Cs dating. The correlation of our records with major historical events confirmed that statistically significant sand count peaks, sand layers, and redeposited peat clasts are indicative of major ECEs. We found that the type and characteristics of ECE records depended mainly on the availability of sediment, distance from the seashore, and magnitude of the event. Although some of our ECE markers are associated with marine inundations, only slight diatom community changes were observed, contrary to what is commonly expected from the disturbance of brackish and freshwater ecosystems by major saltwater intrusions. Combined, our records indicate that at least eight ECEs occurred since the late 17th century, three of which might correlate with historically documented events, namely the 1755 CE Lisbon tsunami, the 1775 CE Great Independence Hurricane, and the 1929 CE Newfoundland tsunami. Although further investigations are required to better constrain the type and magnitude of particular ECEs, our study confirms the suitability of geological archives for improving hazard assessment in coastal regions.Item Sedimentological characteristics of debris flow Deposits within ice−cored moraine of Ebbabreen, central Spitsbergen(De Gruyter / © Polish Academy of Sciences, 2016-06-25) Pleskot, KrzysztofThe Ebbabreen ice−cored moraine area is covered with a sediment layer of up to 2.5 m thick, which mostly consists of massive diamicton. Due to undercutting by lateral streams, debris flow processes have been induced in marginal parts of this moraine. It was recognized that the sedimentology of deposits within the deposition area of debris flows is the effect of: (1) the origin of the sediments, (2) the nature of the debris flow, and (3) post−debris flow reworking. Analysis of debris flow deposits in microscale (thin sections) suggests a common mixing during flow, even though a small amount of parent material kept its original structure. The mixing of sediments during flow leads to them having similar sedimentary characteristics across the deposition area regardless of local conditions (i.e. slope angle, water content, parent material lithology). After the deposition of sediments that were transported by the debris flow, they were then reworked by a further redeposition process, primarily related to meltwater stream action.