Добірка наукової літератури з теми "Paleopedology – Oligocene"

Geology
M.S.
Understanding local and regional reactions to the global Eocene-Oligocene climate transition is a continuing challenge. The White River Group in the North American midcontinent preserves dynamic fluvial, volcaniclastic and lacustrine facies that yield to aeolianites. To test whether this shift in sedimentation style was driven by climate change, 20 paleosols from 8 profiles were analyzed from the fluvial-aeolian Orella Member through the aeolian-dominated Whitney Member of the earliest Oligocene Brule Formation at Toadstool Geologic Park, NE. Paleosol morphology and geochemistry were used to assess the balance of aeolian vs. alluvial sedimentation at key stratigraphic intervals and lithologic transitions. Significant loess deposition began at least as early as the lower Orella Member but is masked in most settings by concomitant fluvial deposition. As fluvial influence on landscapes waned across the Orella-Whitney Member boundary, loess deposits predominated and became more recognizable. Paleosols follow different pedogenic pathways in direct response to depositional setting. Whereas all paleosols formed through top-down pedogenesis in alluvial settings, paleosols in aeolian-dominated settings formed though pedogenic upbuilding during aggradational phases and through top-down pedogenesis during depositional hiatuses. The disparity between each style of pedogenic development creates fundamentally different pedogenic associations that must first be understood before climatic interpretations can be drawn from macroscopic paleosol morphology alone. Microscopic analysis of loessic and alluvial paleosols indicates that pedogenic features do not greatly change across the Orella-Whitney Member boundary. Furthermore, results of climofunction calculations from five paleosol Bw and Btk horizons show mean annual temperature (ca. 9.0-10.5 °C) and precipitation (ca. 650-800 mm/y) do not significantly vary across the Orella-Whitney Member transition. Clay mineralogy and the presence of pedogenic carbonate and translocated clay corroborate paleoclimate estimates. However, geochemical paleosol profiles are uniform and do not reflect observed vertical associations of pedogenic features. Constant additions of aeolian sediment, which replenishes base losses through leaching, explain this phenomenon. Interpretations of paleovegetation from root trace morphology and paleosol taxonomy indicate that predominantly open canopy to savanna habitats were in place in the lower Orella Member and continued into the Whitney Member. Evidence for riparian partitioning exists in the lower Orella Member but disappears as fluvial deposits wane in the Whitney Member. Lacking evidence of climate change from paleosol analysis, changes in sedimentation style and vegetative biomes are most likely a reaction to increased aeolian deposition.
Temple University--Theses

Sections in and around Badlands National Park, Custer County, South Dakota contain a wealth of faunal and floral data within the White River Group. The Chadronian and Orellan North American Land Mammal Ages define the Eocene-Oligocene boundary here. Faunal and floral changes associated with the Chadronian-Orellan interval have long been attributed to the global Greenhouse-Icehouse climatic transition. Stable isotopes were obtained from paleosol carbonates across the Chadronian-Orellan boundary at three locations in Badlands National Park. Results show wide fluctuations of oxygen isotopes in the uppermost Chadronian and lower Orellan, while carbon isotopes remain relatively stable. The records provide an opportunity to compare the continental response to global change with a near-shore marine system response (Gulf Coastal Plain, USA); and to the world at large. Results indicate a decoupling of the terrestrial response to the Oi-1 glacial event from the marine response. Local conditions appear to play an important role in controlling the record of stable isotopes in paleosol carbonates in the region.
Geologic history of the Eocene-Oligocene -- Climate records -- Causes of climate change -- Climate change across the Eocene-Oligocene -- Current findings -- Discussion.
Department of Geology