Wyniki wyszukiwania - BazTech

1

Origin, weathering and paleoclimatic significance of Middle-Late Pleistocene slope covers, Mt. Kenya, Kenya

Mahaney William C., Hancock Ronald G. V.

Studia Quaternaria

|

2022

|

Vol. 39, Nr 2

51--81

EN

Stacks of the Pleistocene tills and associated airfall/slopewash/colluvial sediment abound on East African Mountains but few localities exist where thick deposits of middle to Late Pleistocene age can be studied to bedrock with topography the main soil-forming agent over <0.8 Ma. Two tills form the main structure of the catena, the oldest buried in the crest, backslope and footslope of the deposit, the youngest forming the crest and upper backslope, with massive colluvial infill forming a still younger sediment mass superposed on older sediment in the lower backslope, footslope and toeslope, the latter all radiocarbon dated to within the last glaciation (Liki on Mt. Kenya; Weichselian in Europe, Wisconsin in North America). The moraine stack, first identified by J.W. Gregory in the late 19th century, as belonging to the 'Older Glaciation' (Illinoian in North America; Teleki on Mt. Kenya), is much older than originally thought with tills and other paraglacial sediment extending to saprolitic bedrock, paleomagnetic assessment and relative weathering indices placing the mass in the Brunhes Chron. These results demonstrate that despite erosion and weathering, paleosols in toposequences near the margins of successive glaciations retain properties allowing reconstruction of environmental changes over long periods of time.

2

Intra-individual variability of dental enamel δ13C and δ18O values in Late Pleistocene cave hyena and cave bear from Perspektywiczna Cave (southern Poland)

Czernielewski Michał, Krajcarz Magdalena, Krajcarz Maciej T.

Studia Quaternaria

|

2020

|

Vol. 37, Nr 2

121--128

EN

An important source of palaeoecological and palaeoenvironmental information is intra-specimen variability of isotopic composition of mammal tooth enamel. It reflects seasonal or behavioral changes in diet and climate occurring during a life of the animal. While well-known in ungulates, in carnivorans this variability is poorly recognized. However, carnivoran remains are amongst the most numerous in the Pleistocene fossil record of terrestrial mammals, so their isotopic signature should be of particular interest. The aim of the study was to verify if enamel of a fossil cave hyena (Crocuta crocuta spelaea) and a cave bear (Ursus ingressus) records any regular inter- or intra-tooth isotopic variability. We examined intra-individual variability of δ13C and δ18O values in permanent cheek teeth enamel of fossil cave hyena and cave bear from the site of the Perspektywiczna Cave (southern Poland). We conclude that the isotopic variability of the cave hyena is low, possibly because enamel mineralization took place when the animals still relied on a uniform milk diet. Only the lowermost parts of P3 and P4 enamel record a shift toward an adult diet. In the case of the cave bear, the sequence of enamel formation records periodic isotopic changes, possibly correlating with the first seasons of the animal life.

3

Fluvial response to environmental conditions during MIS 4-3 : a sedimentary record at the Brześnica site, central-western Poland

Moskalewicz Damian, Tylmann Karol, Woźniak Piotr Paweł, Kopyść Natalia, Moska Piotr

Geological Quarterly

|

2020

|

Vol. 64, No. 4

915--930

EN

Fluvial deposits subjected to this study are exposed at the Brześnica site, in the south-western part of the Wielkopolska region in Poland, which was close to the ice-sheet limit during the Last Glacial Maximum (LGM). Sedimentological analyses, including lithofacies descriptions, palaeocurrent measurements, grain size and rounding analyses and heavy mineral compositions indicate that the fluvial deposits at Brześnica were deposited in braided river environment. The following fluvial sedimentary processes were inferred: (1) shallow, rapid flow alternating with waning flow, (2) infilling of erosional channels with fluvial sediments during flood events, (3) changes from supercritical to subcritical flows, and (4) shallow sheet floods. The results of OSL dating indicated sediment deposition ~65.2 ±1.5 ka, i.e. in MIS 4, that was here characterized by cold environmental conditions and a general shift from meandering to braided fluvial sedimentation style. This finding contrasts with accumulation/erosion phases interpreted previously in this region for that time interval; however, it is consistent with recent studies of fluvial systems functioning during MIS 5-2 and of factors responsible for sedimentation style.

4

Middle Weichselian Pleniglacial sedimentation in the Krasówka river palaeovalley, central Poland

Wachecka-Kotkowska L., Krzyszkowski D., Klaczak K., Król E.

Annales Societatis Geologorum Poloniae

|

2014

|

Vol. 84, No. 4

323--340

EN

This study from the Szczerców field of the Bełchatów open-cast mining complex, central Poland, reveals the local geomorphic and stratigraphic history of the Krasówka river palaeovalley – a major western tributary of the river Widawka. The data are from the western flank of the N-trending palaeovalley and the study combines detailed lithofacies analysis of outcrop sections, sediment petrology, AMS measurements and palynological evidence. Radiocarbon dates are of crucial importance for the reconstruction of the palaeovalley history. The study contributes to a better understanding of the response of the Central European river systems to the Vistulian Pleniglacial conditions. The Vistulian Pleniglacial sedimentation in the study area commenced with the accumulation of the latest Eemian to earliest Weichselian (≥45 ka) deposits by sheetwash processes in a local karstic topographic depression. The Krasówka river then formed to the east and shifted farther eastwards, but later approached twice the study area with a net aggradation prior to 43 ka BP – flooding it with overbank deposits. The river subsequently incised by nearly 20 m around 40 ka BP and began to fill in its valley by aggradation around 35 ka BP, while migrating eastwards and markedly decreasing its flooding capacity from 33 to 24 ka BP. The fluvial system was rejuvenated around 21 ka BP, with some initial erosion, and kept filling its valley by aggradation while flooding the valley flank. The river after filling its valley continued to aggrade, but gradually ran out of vertical accommodation and migrated westwards. The fluvial activity at this stage was increasingly accompanied by aeolian sedimentation. Once the Mid-Weichselian Pleniglacial came to an end around 14.5 ka BP, the Krasówka river had re-incised by nearly 5 m and assumed its present-day altitude in response to the post-glacial regional isostatic rebound of crustal basement.