Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 40 for “"glaciations"”.
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Multiple Glaciations on Mars?
… so it is plausible that similar cycles control glaciations on Mars. However, one factor within these cycles, the obliquity shifts, is a major difference between Earth and Mars. The large obliquity shifts of Mars causes a redistribution of ice from the north and south poles to mid-latitude …
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Ozone chemistry during global glaciations : a possible climate feedback
… ozone chemistry during late Proterozoic global glaciations is developed. The possible significance of temperature, humidity, nitrogen oxides, reactive chlorine, lightning frequency, surface deposition and albedo as altered constraints on ozone processes is discussed. An elementary box model is …
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Weichselian glaciations in the middle Notec River region, northwest Poland
… ice movement mechanism during the Weichselian glaciations in the middle Notec River area, NW Poland. A new lithostratigraphy of the study area has been established, based on correlation of stratigraphical position, clast lithology, fabrics and grain size composition of till units. The …
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Triple oxygen isotope measurements in chert: insights into the Snowball Earth glaciations
… of questions about the dynamics of these global glaciations, especially regarding the relationship between the cryosphere and hydrosphere during this time. This study analyzes silica precipitates within a carbonate sequence immediately underlying a Cryogenian diamictite to better understand this …
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Chemostratigraphy of the Early Paleoproterozoic carbonate successions (Kaapvaal and Wyoming cratons)
Evidence of three glaciations in Paleoproterozoic successions of North America and at least one on three other continents, suggests that these glaciations were of global extent. In common with the Neoproterozoic record, carbonates cap the glacials. However, the relationship between biogeochemical …
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Organic geochemistry and stable isotope constraints on Precambrian biogeochemical processes
… The events of the Late Proterozoic onset to glaciations and what types of early life existed in the Archean are two of the many provoking topics within the Precambrian. We set out to improve the understanding of these geologic intervals by examining stable isotopic signatures and molecular …
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Morphometric Theory and Application to Evolution and Biogeography in Argopecten (Bivalvai: Pectinidae) From the Southeastern United States
… morphologies, likely associated with Pleistocene glaciations. That speciation mirrors macroevolution suggests self-similarity in evolution. Convergence on circular disk shape (a local maximum of swimming efficiency) seen in numerous pectinid lineages implies adaptative evolution and precludes …
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Weathering Pathways and Limitations in Biogeochemical Models: Application to Earth System Evolution
… matches the observed gaps between extreme glaciations at this time, suggesting that the late Neoproterozoic system was oscillating around a steady state temperature below the snowball threshold. In the model, the period of disequilibrium following snowball glaciations is characterised by …
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The Evolutionary History of the Antarctic Flora
… Maximum (LGM; ~22-18 kya) as well as previous glaciations, suggesting terrestrial life must have been extremely limited during these periods. In contrast, recent biogeographic and genetic studies support most extant groups of Antarctic terrestrial fauna having survived past glaciations in situ. …
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The Neoproterozoic São Francisco Basin, central Brazil: tectonic evolution, paleoclimate, and mineral systems
… of a complete Wilson Cycle, three Neoproterozoic glaciations, and global changes in the biogeochemical cycling of nutrient elements. The basal Macaúbas Group (ca. 950-650 Ma), composed of rift-related sediments, accumulated during breakup of the supercontinent Rodinia. Deposition was punctuated by …
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Four problems in nonlinear Earth system dynamics
… global warming events, “Snowball Earth” glaciations, and mass extinctions. Although the details are different, underpinning them all is the nonlinearity of the Earth system: small changes sometimes trigger much larger responses. This thesis addresses four related problems in this subject …
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Phylogeny and Biogeography of Ice Crawlers (Insecta: Grylloblattodea): Evidence from Six Molecular Loci
… and genera are not known. Late Pleistocene glaciations had a major effect on the current Grylloblatta distribution, because their specific habitat requirements restrict them to small geographical areas. Six genes were sampled in 37 individuals for 18S rRNA, 28S rRNA, histone 3, 12S rRNA, 16S …
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Geological constraints on Neoproterozoic glacial episodes
… glacial episodes are amongst the most intense glaciations that the Earth has experienced, and are associated with major changes in the Earth System, such as the breakup of a supercontinent, the evolution of complex multicellular life and extreme geochemical perturbations. A Neoproterozoic …
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Phylogeographic and morphometric studies on the Eurasian pygmy shrew Sorex minutus: insights into its evolutionary history and postglacial colonisation in Europe
… that would explain the effects of the Quaternary glaciations on the current distribution of the species. I also explore the genetic and morphological diversity and origin of pygmy shrew populations in the British Isles, particularly focusing on Ireland and the Orkney islands. Mitochondrial and …
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Phylogeography of eastern leatherwood (Dirca palustris L.) resolved by chloroplast sequencing and microsatellite genotyping
… migration, and admixture over Pleistocene glaciations. I used next-generation sequencing for de novo isolation of highly polymorphic microsatellite loci from D. palustris. Microsatellite genetic analyses provided further evidence for mid-latitudinal refugia. Results from both markers were …
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Colonisation and diversification in invertebrates: looking within species on islands to connect pattern and process
… that the UK was not completely defaunated during glaciations, then recolonised from external sources, but that a more complex pattern, involving persistence within small cryptic refugia, may have featured in the history of its invertebrate soil dwelling fauna. I reveal two instances of shared …
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Re-Os geochronology and geochemistry of Proterozoic sedimentary successions
… Formation may be correlative with Sturtian glaciations rather than middle Cryogenian events. Laboratory-based hydrous pyrolysis experiments were employed to evaluate the complexation of Re and Os in ORS and their transfer behaviour into petroleum. The findings from these experiments …
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The Pleistocene History of the Birmingham District
… sediments attributed to at least three lowland glaciations (Anglian, Wolstonian, and Devensian) as well as a variety of non-glacial sediments. Understanding the age of the Pleistocene glacial deposits is critical to reconstructing the palaeoenvironmental history of the district and its …
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Geochemical and Paleontological investigations of the Neoproterozoic-Cambrian Transition: Case Studies on geochemical clast provenance, emerging paleo redox proxies, and ambiguous dubiofossils
… changes in the environment, including global glaciations and rising atmospheric oxygen levels precipitated the conditions in which variety of complex life emerged, diversified, and proliferated. However, questions persist regarding the timing and duration of those environmental events, and …
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Tectonic-Climate Interactions And Glacial History Within The Chugach And Kenai Mountains, Alaska
… period was the beginning of a series of many glaciations which increased erosion in orogens experiencing fast rock uplift. We characterize the threshold for the onset of effective glacial erosion and record the increase in erosion rate during the late Cenozoic in the Chugach and Kenai …
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