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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
81

Environmentální dynamika svrchního pleistocénu ve střední Evropě: multidisciplinární výzkum spraší, paleopůd a jezerních sedimentů / Upper Pleistocene environmental dynamics in central Europe: multidisciplinary research of loess/paleosols sequences and lacustrine sediments

Hošek, Jan January 2017 (has links)
The principal goal of this thesis was to provide relevant information on the spatiotemporal dynamics of erosion-sedimentation and weathering processes in the last climatic cycle and to interpret the obtained data in the context of European paleoenvironmental development. Representative sequences of loess, paleosols and lacustrine sediments from the area of the Bohemian Massif, the Carpathian Foredeep, the the Vienna Basin and the northern edge of the Panno-nian Basin were investigated using a wide range of instru-mental tools and paleontological methods. A uniform analytical approach applied to these sedimentary facies has provided ample new information about the paleoclimatolog-ical and paleoenvironmental development of East-Central Europe - an important region in the transition zone from oceanic to continental macro-climatic settings. The individu-al studies included in this PhD thesis cover the complete period of the Upper Pleistocene (MIS 5-2; ~130-12.7 ky BP) and are presented as separate chapters in the order of the superposition of strata. Chapters III/1-3 deal with the results of research into six loess/paleosol sequences (LPSs) situated in the Central Bohemian Massif, throughout the Moravian Valleys, and at the northwest and north edge of the Pannonian Basin. A detailed paleoenvironmental...
82

Loess as an Environmental Proxy for Reconstruction of Palaeoclimate in the High Arctic / Lössjord som miljöindikator för rekonstruktion av forntida klimat i Arktis

Rognås, Sara January 2023 (has links)
We are currently speeding towards significant changes in the climate of the earth which, if ignored, will lead to severely altered climatic conditions with serious consequences for several species and ecosystems. The polar regions especially are very sensitive to climate changes, and the changes these regions undergo affect the climate on a global scale. To slow the global warming, it is crucial that we understand earth’s climatic and environmental history, and how it responds to changes in the climate. Palaeoclimatic archives hold much information of past climate variations stored in proxies that can be analysed to understand past environments. This study focuses on loess as one such proxy to analyse grain sizes, carbon storage and organic matter in a sequence from Adventdalen, Svalbard. The study has been conducted using grain size analysis and loss on ignition (LOI) as main methods to reconstruct late Holocene climate changes in the region. The results have provided an overview of temperature oscillations, many of which coincide with main climatic events of the past, and have been used to estimate the depositional ages of the different layers of the sequence. / Dagens klimatförändringar går allt snabbare mot en framtid med svårt omkastade klimatförhållanden som medför allvarliga konsekvenser för flera arter och ekosystem. Polarområdena är särskilt känsliga för klimatförändringar, och de förändringar som sker här påverkar klimatet på global nivå. En avgörande faktor för att bromsa den globala uppvärmningen är att vi förstår jordens klimathistoria och hur jorden reagerar på förändringar i klimatet. Paleoklimatiska arkiv innehåller mycket information om klimatvariationer förr. Sådan information finns lagrad i material som kan analyseras för att vidare förstå miljöer från förr. Den här studien fokuserar på lössjord som ett sådant material för att analysera kornstorlekar och organiskt material i en lössekvens från Adventdalen i Svalbard. Studien har genomförts genom att använda en kornstorleksanalysator och loss on ignition (LOI) som huvudsakliga metoder för att rekonstruera klimatförändringar under yngre Holocen i området. Resultaten har givit en överblick av temperaturförändringar, av vilka flera sammanfaller med större förflutna klimathändelser, och har använts för att göra en uppskattning av åldrar på de olika lagren av sekvensen.
83

Last glacial loess dynamics in the Southern Caucasus (NE-Armenia) and the phenomenon of missing loess deposition during MIS-2

Wolf, Daniel, Lomax, Johanna, Sahakyan, Lilit, Hovakimyan, Hayk, Profe, Jörn, Schulte, Philipp, Suchodoletz, Hans von, Richter, Christiane, Hambach, Ulrich, Fuchs, Markus, Faust, Dominik 22 April 2024 (has links)
The Marine Isotope Stage (MIS) 2 is considered the coldest, driest and stormiest period during the last Glacial-Interglacial cycle in large parts of Eurasia. This resulted from strongly decreased northern hemisphere temperature and related maximum extension of northern ice sheets that strongly reinforced large-scale circulation modes such as westerlies and East Asian Winter Monsoon driven by the Siberian High. Normally, this intensified circulation is reflected by maximum loess deposition in numerous loess regions spanning Europe and Asia. However, here we present a new loess record from the Caucasus region in NE-Armenia providing evidence in support of heavily reduced or even lacking loess formation during the MIS-2. Owing to implementations of comprehensible luminescence dating work and a provenance survey using rock magnetic and geochemical data, we are able to define distinct loess formation phases and to retrace sediment transport pathways. By comparing our results to other Eurasian palaeo-records, we unveil general atmospheric circulation modes that are most likely responsible for loess formation in the Southern Caucasus. Moreover, we try to test different scenarios to explain lacking loess formation during MIS-2. In line with other archive information, we suggest that loess formation was hampered by higher regional moisture conditions caused by a southward-shift of westerlies and renewed moisture absorption over the Black Sea. Our results show that modifications of MIS-2 circulation modes induced a very heterogeneous moisture distribution, particularly in the lower mid-latitudes of Eurasia producing a juxtaposition of very dry (morphodynamically active) and moderately dry (morphodynamically stable) areas.
84

Soils and geomorphology of a lowland rimu forest managed for sustainable timber production

Almond, Peter C. January 1997 (has links)
Saltwater Forest is a Dacrydium cupressinum-dominated lowland forest covering 9000 ha in south Westland, South Island, New Zealand. Four thousand hectares is managed for sustainable production of indigenous timber. The aim of this study was to provide an integrated analysis of soils, soil-landform relationships, and soil-vegetation relationships at broad and detailed scales. The broad scale understandings provide a framework in which existing or future studies can be placed and the detailed studies elucidate sources of soil and forest variability. Glacial landforms dominate. They include late Pleistocene lateral, terminal and ablation moraines, and outwash aggradation and degradation terraces. Deposits and landforms from six glacial advances have been recognised ranging from latest Last (Otira) Glaciation to Penultimate (Waimea) Glaciation. The absolute ages of landforms were established by analysis of the thickness and soil stratigraphy of loess coverbeds, augmented with radiocarbon dating and phytolith and pollen analysis. In the prevailing high rainfall of Westland soil formation is rapid. The rate of loess accretion in Saltwater Forest (ca. 30 mm ka⁻¹) has been low enough that soil formation and loess accretion took place contemporaneously. Soils formed in this manner are known as upbuilding soils. The significant difference between upbuilding pedogenesis and pedogenesis in a topdown sense into an existing sediment body is that each subsoil increment of an upbuilding soil has experienced processes of all horizons above. In Saltwater Forest subsoils of upbuilding soils are strongly altered because they have experienced the extremely acid environment of the soil surface at some earlier time. Some soil chronosequence studies in Westland have included upbuilding soils formed in loess as the older members of the sequence. Rates and types of processes inferred from these soils should be reviewed because upbuilding is a different pedogenic pathway to topdown pedogenesis. Landform age and morphology were used as a primary stratification for a study of the soil pattern and nature of soil variability in the 4000 ha production area of Saltwater Forest. The age of landforms (> 14 ka) and rapid soil formation mean that soils are uniformly strongly weathered and leached. Soils include Humic Organic Soils, Perch-gley Podzols, Acid Gley Soils, Allophanic Brown Soils, and Orthic or Pan Podzols. The major influence on the nature of soils is site hydrology which is determined by macroscale features of landforms (slope, relief, drainage density), mesoscale effects related to position on landforms, and microscale influences determined by microtopography and individual tree effects. Much of the soil variability arises at microscales so that it is not possible to map areas of uniform soils at practical map scales. The distribution of soil variability across spatial scales, in relation to the intensity of forest management, dictates that it is most appropriate to map soil complexes with boundaries coinciding with landforms. Disturbance of canopy trees is an important agent in forest dynamics. The frequency of forest disturbance in the production area of Saltwater Forest varies in a systematic way among landforms in accord with changes in abundance of different soils. The frequency of forest turnover is highest on landforms with the greatest abundance of extremely poorly-drained Organic Soils. As the abundance of better-drained soils increases the frequency of forest turnover declines. Changes in turnover frequency are reflected in the mean size and density of canopy trees (Dacrydium cupressinum) among landforms. Terrace and ablation moraine landforms with the greatest abundance of extremely poorly-drained soils have on average the smallest trees growing most densely. The steep lateral moraines, characterised by well drained soils, have fewer, larger trees. The changes manifested at the landform scale are an integration of processes operating over much shorter range as a result of short-range soil variability. The systematic changes in forest structure and turnover frequency among landforms and soils have important implications for sustainable forest management.
85

Soils and geomorphology of a lowland rimu forest managed for sustainable timber production

Almond, Peter C. January 1997 (has links)
Saltwater Forest is a Dacrydium cupressinum-dominated lowland forest covering 9000 ha in south Westland, South Island, New Zealand. Four thousand hectares is managed for sustainable production of indigenous timber. The aim of this study was to provide an integrated analysis of soils, soil-landform relationships, and soil-vegetation relationships at broad and detailed scales. The broad scale understandings provide a framework in which existing or future studies can be placed and the detailed studies elucidate sources of soil and forest variability. Glacial landforms dominate. They include late Pleistocene lateral, terminal and ablation moraines, and outwash aggradation and degradation terraces. Deposits and landforms from six glacial advances have been recognised ranging from latest Last (Otira) Glaciation to Penultimate (Waimea) Glaciation. The absolute ages of landforms were established by analysis of the thickness and soil stratigraphy of loess coverbeds, augmented with radiocarbon dating and phytolith and pollen analysis. In the prevailing high rainfall of Westland soil formation is rapid. The rate of loess accretion in Saltwater Forest (ca. 30 mm ka⁻¹) has been low enough that soil formation and loess accretion took place contemporaneously. Soils formed in this manner are known as upbuilding soils. The significant difference between upbuilding pedogenesis and pedogenesis in a topdown sense into an existing sediment body is that each subsoil increment of an upbuilding soil has experienced processes of all horizons above. In Saltwater Forest subsoils of upbuilding soils are strongly altered because they have experienced the extremely acid environment of the soil surface at some earlier time. Some soil chronosequence studies in Westland have included upbuilding soils formed in loess as the older members of the sequence. Rates and types of processes inferred from these soils should be reviewed because upbuilding is a different pedogenic pathway to topdown pedogenesis. Landform age and morphology were used as a primary stratification for a study of the soil pattern and nature of soil variability in the 4000 ha production area of Saltwater Forest. The age of landforms (> 14 ka) and rapid soil formation mean that soils are uniformly strongly weathered and leached. Soils include Humic Organic Soils, Perch-gley Podzols, Acid Gley Soils, Allophanic Brown Soils, and Orthic or Pan Podzols. The major influence on the nature of soils is site hydrology which is determined by macroscale features of landforms (slope, relief, drainage density), mesoscale effects related to position on landforms, and microscale influences determined by microtopography and individual tree effects. Much of the soil variability arises at microscales so that it is not possible to map areas of uniform soils at practical map scales. The distribution of soil variability across spatial scales, in relation to the intensity of forest management, dictates that it is most appropriate to map soil complexes with boundaries coinciding with landforms. Disturbance of canopy trees is an important agent in forest dynamics. The frequency of forest disturbance in the production area of Saltwater Forest varies in a systematic way among landforms in accord with changes in abundance of different soils. The frequency of forest turnover is highest on landforms with the greatest abundance of extremely poorly-drained Organic Soils. As the abundance of better-drained soils increases the frequency of forest turnover declines. Changes in turnover frequency are reflected in the mean size and density of canopy trees (Dacrydium cupressinum) among landforms. Terrace and ablation moraine landforms with the greatest abundance of extremely poorly-drained soils have on average the smallest trees growing most densely. The steep lateral moraines, characterised by well drained soils, have fewer, larger trees. The changes manifested at the landform scale are an integration of processes operating over much shorter range as a result of short-range soil variability. The systematic changes in forest structure and turnover frequency among landforms and soils have important implications for sustainable forest management.
86

Loess from Saxony / Löss in Sachsen. Rekonstruktion der spätpleistozänen Landschaftsentwicklung und Paläoumwelt anhand von Löss-Paläobodensequenzen aus Sachsen (Deutschland)

Meszner, Sascha 19 September 2016 (has links) (PDF)
A number of studies have been published in the last few decades on Pleistocene palaeo-temperature reconstruction based on isotopic studies on deep sea cores and ice core records from Greenland. Such temporal high-resolution data represents northern hemispheric circulations and has to be reconfirmed through the study of terrestrial archives in order to recognise the character of such fluctuations in different regions. Loess-palaeosol sequences (LPSs) are suitable to interpret them as palaeoenvironmental archives, because loess is a widely distributed terrestrial deposit and is datable using luminescence techniques. The Saxon loess region (SLR) is characterised by a loess cover of ca. 8 m thickness, mainly representing deposits of the last glacial cycle. Over the past 35 years, Saxon loess remains under-researched wherefore a reactivation with the objective of contributing to the European loess research is important. There is a clear need to re-examine Saxon LPSs and close this gap of knowledge, because in recent years much work has been done on important and European-wide known loess sections as well as in adjacent loess areas. In this study, LPSs from Saxony were investigated and a regional palaeoenvironmental reconstruction of the last Glacial/Interglacial cycle was developed. The established stratigraphical scheme has to be advanced by results of optically stimulated luminescence (OSL) dating. The stratigraphical results should be compared with previous work from Saxony and with results from adjacent loess areas, to verify if our results have to be interpreted as singularities or if they are in accordance with known European conceptions. Therefore, 8 sections, mostly never investigated before, were described and correlated with each other to finally generate an independent standard stratigraphy for this area. Carbonate content, pH-value, soil organic matter, total and pedogenic iron, magnetic susceptibility and classical grain size analyses were obtained from every section. Furthermore, rare earth elements concentrations were measured from selected positions in order to prove if there are variations in the deposit composition during the glaciation. The OSL dating results were processed by Kreutzer (2012). As previously noted, the first step towards a regional palaeoenvironmental reconstruction was to establish a standard stratigraphic scheme where all found units are involved. Based on features regarding grain size distribution, the found palaeosols and the magnetic susceptibility Baumgart et al. (2013), 5 units could be defined. Unit V reflects the pre-Weichselian sediments modified by the Eemian soil formation. Unit IV contains deposits from the beginning of the Weichselian glaciation. Typically, this unit starts with the first Weichselian deposit, a bright-greyish Mn- and Fe-precipitates enriched layer which shows an aggregation of charcoal at its top. This layer is covered by a greyish, humus-enriched and reworked relict of a Chernozem-like soil. After a Gelic Gleysol and a reddish-brownish soil sediment, a loess package with an embedded interstadial Cambisol-like soil is preserved. The top of the unit is represented by another brownish soil sediment which forms the lower part of the Gleina complex. Typically, unit IV is characterised by stronger reworked layers and soil sediments but at the Rottewitz section an older loess package is preserved. Unit III represents the reactivation of aeolian sedimentation. The base of this unit is made up of a strong Gelic Gleysol (upper part of the Gleina complex). The deposits of this unit are mostly pedogenically overprinted and show features of at least two Gelic Gleysols. Unit II is dominated by unweathered loess. Its lower part (unit IIb) is built of a more stratified loess facies whereas the upper part (unit IIa) is built of a homogeneous loess facies. They are separated by a strong Gelic Gleysol. Unit I represent the upper part of the loess section, which is modified by the Holocene and Late Pleistocene soil development. Within this succession, a huge hiatus is found between unit III and IV of ca. 35 ka. It is labelled as the Gleina complex according to Lieberoth (1963). Furthermore, we demonstrate how combined analyses of high-resolution grain size distributions and microscopic analysis can be used to discriminate depositional and pedogenetic features of loess-palaeosol profiles from the SLR. Generally, it was observed that an increase of coarse material is linked with an increase of the mineralogical components which refers to slope processes. Rounded shapes of Mn- and Fe-precipitates, mostly found in Early Weichselian humus layers, indicate strong interstadial soil development modified by subsequent redeposition. Further observations suggest that the class of medium sand is dominated by secondary precipitates. The varying amount of very fine sand shows that sequences are cyclically built up of pure loess comparable to the Nussloch section. Studying coarse grain size fractions by microscopic analysis, a differentiation between loessic layers formed by periglacial slope processes and layers overprinted by pedogenetic processes is possible. Furthermore, an increase of fine material and secondary Mn- and Fe-precipitates can be attributed to soil forming processes (clay formation, redoximorphic processes, and illuviation). Additionally, a palaeoenvironmental reconstruction for the Late Pleistocene is proposed. As palaeo-temperature proxies ice wedges, pure loess sedimentation or the platy soil structure due to former ice lensing for cold periods and soil formations or vegetation remnants for warmer periods were used. A reconstruction of wind speed is directly deduced from the very fine sand content. The stability/instability of the landscape surface could be indicated by soil formation (stable) or through an increase of coarse sand (active). The type of soil development for the reconstruction is of major importance. For example, a humus enriched soil indicates warmer and dryer conditions than a Gelic Gleysol. The results of grain size analyses reveal a similar temporal and lithogenic pattern of Weichselian aeolian dynamics of the study area and other records from Europe. Furthermore, grain size results independently confirm the luminescence chronology of the studied sections. Reworked loess-like sediments show varying OSL age estimates; aeolian loess shows a systematic change of OSL ages. Generally, the findings of this study agree with observations from other loess areas. In most areas, a similar hiatus between Middle and Upper Weichselians is documented. Additionally, OSL dating suggests that we found an older loess package with an age between ca. 60 and 70 ka and a younger loess package with an age of ca. 15 and 30 ka. These periods of aeolian deposition are in accordance with MIS 4 and MIS 2 as well as with dust concentrations results derived from lake sediments and from ice cores. A major finding of this study is that we uncover the internal differences of loess-palaeosol sequences regarding their temporal resolution. In periods of loess sedimentation, a temporally high-resolution record is preserved. In contrast, in periods dominated by interstadial soil development or redeposition, a temporal low-resolution record is preserved and a reconstruction of palaeoenvironment is almost impossible. / In den vergangenen Jahrzehnten wurden viele Studien über die Rekonstruktion der pleistozänen Temperaturentwicklung veröffentlicht, welche anhand von Isotopenanalysen aus Tiefsee- und Eisbohrkernen des grönländischen Eises abgeleitet werden konnten. In solchen zeitlich hochaufgelösten Daten sind nordhemisphärische Klimaschwankungen repräsentiert und diese sollten durch Untersuchungen terrestrischer Archive validiert und deren regionale Ausprägung in verschiedenen Räumen abgeschätzt werden. Löss-Paläobodensequenzen eignen sich hervorragend als Paläoumweltarchiv, da der Löss ein weit verbreitetes Sediment und mittels Lumineszenzverfahren datierbar ist. Die Sächsische Lössregion ist durch eine ca. 8 m mächtige Lössdecke charakterisiert, welche vornehmlich aus Ablagerungen des letzten glazialen Zyklus besteht. In den vergangenen 35 Jahren wurde die Lössforschung in diesem Raum vernachlässigt, sodass eine Wiederbelebung wichtig ist, um einen Beitrag zur europäischen Lössforschung zu leisten. Da in den letzten Jahren an wichtigen europäischen Lössprofilen, wie auch in angrenzenden Lössregionen, intensiv geforscht wurde besteht der dringende Bedarf, die Forschungen an sächsischen Löss-Paläobodensequenzen wieder aufzunehmen und die entstandene Wissenslücke zu schließen. In dieser Studie werden sächsische Löss-Paläobodensequenzen untersucht und eine regionale Umweltrekonstruktion für den letzten glazialen Zyklus vorgestellt. Die Standardstratigraphie wird dabei durch optisch stimulierte Lumineszenz (OSL)-Alter erweitert. Die Ergebnisse werden mit älteren Arbeiten aus diesem Raum verglichen, um abzuschätzen, ob es sich hierbei um Einzelbefunde handelt oder ob sich die Ergebnisse in schon bekannte europäische Konzepte einordnen lassen. Es werden 8, meist noch nie bearbeitete Profile beschrieben und miteinander korreliert, um schließlich eine unabhängige Standardstratigraphie für diesen Raum zu erarbeiten. Von jedem Profil wurde der Kalkgehalt, der pH-Wert, der Anteil der organischen Substanz, das pedogene und Gesamteisen, die magnetische Suszeptibilität und die Korngrößenverteilung (klassisch) bestimmt. Zudem wurde die Konzentration der Seltene Erden Elemente an ausgewählten Positionen bestimmt, um zu prüfen, ob es Verschiebungen in der mineralogischen Zusammensetzungen über das letzte Glazial hinweg gab. Die OSL-Datierungen wurden dabei von Kreutzer (2012) realisiert. Wie schon erläutert wurde, bestand der erste Arbeitsschritt darin, eine Standardstratigraphie zu erarbeiten, worin alle Befunde integriert werden können. Auf Grundlage der Korngrößenverteilung, der gefundenen Paläoböden und der magnetischen Suszeptibilität Baumgart et al. (2013) konnten 5 Einheiten ausgewiesen werden. Die Einheit V stellt die prä-weichselzeitlichen Sedimente dar, welche von der eemzeitlichen Bodenbildung überprägt wurden. Einheit IV beinhaltet die Sedimente vom Beginn der Weichselkaltzeit. Typischerweise befindet sich an der Basis dieser Einheit eine hellgraue, an Mn- und Fe-Konkretionen angereicherte Schicht, welche eine Häufung von Holzkohlebruchstücken im oberen Bereich zeigt. Diese Schicht ist wiederum von einem Rest einer schwarzerdeähnlichen Bodenbildung überlagert und zeigt eine Anreicherung an organischer Substanz. Über einem Nassboden und einem rotbraunen Bodensediment ist ein Lösspaket, mit einem zwischengelagerten interstadialen braunerdeartigen Boden, erhalten. Der obere Bereich der Einheit IV ist durch ein weiteres rötlichbraunes Bodensediment geprägt, welches dem unteren Teil des Gleinaer Komplexes entspricht. Normalerweise ist die Einheit IV in Sachsen durch stark umgelagerte Schichten charakterisiert, jedoch ist im Profil Rottewitz in dieser Einheit ein älteres Lösspaket erhalten. Die Einheit III repräsentiert eine Reaktivierung der äolischen Sedimentation. Ihre Basis bildet ein kräftiger Nassboden (oberer Teil des Gleinaer Komplex). Die Sedimente dieser Einheit sind meist pedogen überprägt und es können mindestens zwei separate Nassböden ausgewiesen werden. Die Einheit II besteht vornehmlich aus unverwittertem kalkhaltigen Löss. Ihr unterer Abschnitt (Einheit IIb) wird durch eine streifige Löss-Fazies gebildet, wohingegen der obere Teil von einer homogenen Löss-Fazies dominiert wird. Diese sind durch einen kräftigen Nassboden voneinander getrennt. Die Einheit I bildet den oberen Teil des Lössprofiles und ist durch die pedogene Überprägung der spätpleistozänen und holozänen Bodenentwicklung geprägt. In dieser Abfolge ist ein Alterssprung von ca. 35 ka zwischen der Einheit IV und III nachgewiesen. Dieser Hiatus befindet sich im durch Lieberoth (1963) definierten Gleinaer Komplex. Weiterhin konnte gezeigt werden, dass mit Hilfe einer kombinierten Untersuchung aus Korngrößenanalyse und Mikroskopieren es möglich ist, eine durch Bodenbildung bedingte und eine durch Umlagerung hervorgerufenen Überformung von Lösssedimenten voneinander zu unterscheiden. Generell wurde festgestellt, dass ein Anstieg der groben Kornfraktionen oft mit einer Erhöhung der mineralischen Komponente einhergeht und dies auf laterale Umlagerungsprozesse hindeutet. Abgerundete Mn- und Fe-Konkretionen aus humosen frühweichselzeitlichen Schichten lassen eine kräftige interstadiale Bodenentwicklung mit anschließender Umlagerung vermuten. Es wurde zudem festgestellt, dass die Mittelsandfraktion durch sekundäre Fe- und Mn-Konkretionen dominiert wird. Der variierende Feinstsandanteil zeigt, dass die Sequenzen in verschiedenen Zyklen aus unverwittertem Löss aufgebaut wurden, wie es auch aus dem Profil Nussloch beschrieben wird. Bodenbildungsprozesse bedingen demgegenüber ein Anstieg der Feinkomponenten und der Mn- und Fe-Konkretionen in den Sandfraktionen. Weiterhin wird eine Paläoumweltrekonstruktion für das Spätpleistozän vorgeschlagen. Hierbei werden verschiedenste Indikatoren als Paläotemperaturzeiger herangezogen. Für kalte Phasen stehen zum Beispiel Eiskeilpseudomorphosen, Pakete aus unverwittertem Löss oder plattige Strukturen infolge von Schichteisbildung. Für wärmere Phasen sprechen Paläoböden oder Pflanzenreste. Eine Rekonstruktion der Paläowindgeschwindigkeiten wird direkt über die Feinstsandanteile abgeleitet. Die Stabilität einer Landschaftoberfläche wird durch Bodenbildungen (stabil) oder einem Anstieg der groben Sandkomponenten (aktiv) repräsentiert. Den Paläoböden kommt bei einer solchen Rekonstruktion eine Schlüsselstellung zugute. Zum Beispiel signalisiert ein Steppenboden wärmere und trockenere Bedingungen im Vergleich mit einem Nassboden. Die Ergebnisse der Korngrößenuntersuchungen zeigen, dass hinsichtlich ihres Aufbaues und ihrer chronologischen Einordnung die äolisch dominierten Phasen der sächsischen Lössprofile bekannten Mustern aus anderen Archiven in Europa folgen. Zudem zeigt sich, dass die Ergebnisse der Korngrößenverteilung die mittels OSL bestimmten Alter untermauern. Umgelagerte Sedimente zeigen größere Altersschwankungen, wohingegen äolische Sedimente eine kontinuierliche Altersentwicklung haben. Die Ergebnisse dieser Untersuchungen stimmen mit Beobachtungen aus anderen Lössgebieten überein. In den meisten Regionen wird ein ähnlicher Hiatus zwischen der mittleren und oberen Weichselkaltzeit beschrieben. Zudem deuten die OSL-Ergebnisse an, dass in Sachsen ein älteres Lösspaket mit einem Alter von ca. 60 bis 70 ka und ein jüngeres Lösspaket mit einem Alter von ca. 15 bis 30 ka existiert. Die beiden äolischen Phasen korrelieren mit der marinen Isotopenstufe 4 (MIS) beziehungsweise der MIS 2, sowie mit Ergebnissen pleistozäner Staubkonzentration der Atmosphäre, abgeleitet aus Seesedimenten oder Eisbohrkernen. Eine wichtige Erkenntnis dieser Untersuchungen ist, dass wir innerhalb eines Lössprofiles Pakete unterschiedlicher zeitlicher Auflösung identifizieren konnten. Aus Phasen kräftiger Lösssedimentation sind zeitlich hoch aufgelöste Sequenzen erhalten. Demgegenüber ist aus Phasen, dominiert durch Bodenbildungen oder Umlagerungen, ein zeitlich nur sehr schlecht aufgelöstes Archiv erhalten, weshalb anhand dieser Abschnitte eine Paläoumweltrekonstruktion nur bedingt möglich ist.
87

Posouzení bezpečnostního celíku u podzemní stavby / The face safety pillar assessment for underground construction

Zapletal, Adam January 2017 (has links)
The master thesis parametrically compares different methods to determine the required lengths of the safety pillar when building secondary urban collector in Brno. The analytical calculation by Šedivý is compared with mathematical modeling executed in the program Plaxis 2D 2015.02. version and also in the program Plaxis 3D Introductory 2013 version.
88

Analyses of Common Elements and Oxides in the Paleosols of the Bahamas and of the Northern Mariana Islands

Ersek, Vasile 07 August 2004 (has links)
Paleosols from the Bahamas and the Northern Mariana Islands (CNMI) are closely related to past atmospheric circulation and dust load. In the Bahamas the sources of insoluble residue (IR) must be allogenic because the islands consist of almost pure carbonates. The Al2O3:TiO2 ratio was used to establish the provenance of the IR of the paleosols. Comparisons of this ratio from Bahamian paleosols, North African dust, Lesser Antilles ash and North American loess reveal that the African dust is the major contributor to the IR, with a potential minor volcanic input from the Lesser Antilles. The contribution of the North American loess to the IR was not determined because of geochemical similarities with the North African dust. The study of two outcrops in Eleuthera indicate that paleosols can act as aquicludes. The Bahamian samples were collected on a roughly north-south transect in order to establish the climatic influence on paleosol properties. Even though there is a marked climatic gradient in the Bahamas, the paleosol geochemistry shows no trend that could be related to paleoclimate. While previous studies indicated that the source of insoluble residues in the soils of CNMI is carbonate dissolution, the present study shows that atmospheric deposition of ash from the Mariana arc and dust from the Asian continent may play a significant role in paleosol formation.
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Zakládání na objemově nestálých zeminách / Foundations in Volume Unstable Soils

Legut, Dana Unknown Date (has links)
This dissertation is concerned with the foundations in volume unstable soils and objects disorders which are related to this. The thesis was focused on the study of clay and loess soils which are abundant in the geological profile of the Czech Republic. First, the formation of the two groups of soils is introduced, then their properties are examined and finally the influence of vegetation on the former type and the influence of collapsibility in the latter type are investigated. The conclusion is, in fact, a recommendation on the design of structures so that the system of clay / structure is not damaged and that structures are not subject to renovations. Several instance of problems with structures are discussed which were subject to structural repairs employing both a civil and geotechnical engineers.
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Tunel Blanka: Inženýrskogeologické problémy a rizika ražby / The Blanka tunnel, geological hazadrs and problems during boring

Sedláček, Václav January 2016 (has links)
The Blanka tunnel has two boring sections: Brusnice tunnel and Královská obora tunnel. Both tunnels were boring in difficult geologycal conditions, but the geology conditions of these tunnels are not same. Also they had not the same hazards during boring. There was used a spectrum of different technical works with hazard reduction purpose and safety process of boring. There were three serious accidents, wnich everyone made a creater on the surface, but they have not the same causes. This text has a task to describe a geological survey before and during the boring of both tunnels. How other reasons affected the process of boring? How the tunnels were bored? What events preceded the everyone of three major failure? This text does not deal with economical things of boring and effects of specific personal influence on the process of boring. Key words Tunnel, excavation, Blanka, Brusnice, Letná, Stromovka park, Vltava river, underground water, geology, ordovik, New Austrian Tunnelling method, pilot tunnel, calotte, bench, bottom, arche, bolt, lining, grouting, collapse of ceiling, failure, tube, shale, quarzite, soil, loess, ballast, clay

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