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Accueil du site → Doctorat → États-Unis → 2011 → SPATIAL DISTRIBUTION AND GEOMORPHIC EVOLUTION OF PLAYA-LUNETTE SYSTEMS ON THE CENTRAL HIGH PLAINS OF KANSAS

University of Kansas (2011)

SPATIAL DISTRIBUTION AND GEOMORPHIC EVOLUTION OF PLAYA-LUNETTE SYSTEMS ON THE CENTRAL HIGH PLAINS OF KANSAS

Bowen, Mark William

Titre : SPATIAL DISTRIBUTION AND GEOMORPHIC EVOLUTION OF PLAYA-LUNETTE SYSTEMS ON THE CENTRAL HIGH PLAINS OF KANSAS

Auteur : Bowen, Mark William

Université de soutenance : University of Kansas

Grade : Doctor of Philosophy 2011

Résumé
Geographically and hydrologically isolated, ephemeral playa wetlands are ubiquitous features of the High Plains. Lunettes are dune-like features that form downwind of some larger playas. Although playas are important landscape elements, few systematic inventories have been conducted, and little is known about their evolutionary history. A comprehensive Geographic Information Systems database was created for Kansas utilizing several geospatial data sources, including aerial imagery, digital raster graphics, and SSURGO soils data. In addition, stratigraphic data collected from two representative playa-lunette systems (PLSs) were used to reconstruct paleoenvironment and geomorphic processes occurring within these systems throughout their formation and evolution. Mapping results indicate there are more than 22,000 playas in Kansas, ranging in size from 0.03 ha to 188 ha, with a mean area of 1.65 ha. More than 80% of all playas are smaller than 2 ha and only about 400 are larger than 10 ha. Results indicate that previous High Plains playa inventories failed to identify most playas smaller than 2 ha because data sources were not of sufficient resolution. Additionally, playa identification criteria have not been consistent for all inventories, making it difficult to compare results and establish trends for various playa attributes across the entire High Plains. Stratigraphic investigations of the two PLSs indicate they are composed of sediment spanning more than 40 kyrs, which began accumulating during at least Marine Isotope Stage (MIS) 3. Climate during MIS 3 was similar to modern : warm temperatures, low effective moisture, and playa floors exposed long enough to allow pedogenesis. During MIS 2, climate was relatively cool with higher effective moisture, and playas were inundated for longer periods. During the Pleistocene-Holocene transition, climate warmed, yet moisture availability remained relatively high. Several distinct shifts in δ13C identify rapid climate changes associated with the Bølling-Allerød/Younger Dryas climate sequence. Warming continued into the Holocene, though moisture availability was highly variable ; Holocene soils are common. Thus, PLSs represents a continuum of the uplands High Plains loess sequence, though deposits are altered by playa hydrology. Geomorphic processes alternated between fluvial- and eolian-driven as climate changed, and detailed records of environmental change throughout their evolution are preserved.

Mots Clés : Physical Geography – Geomorphology — Paleoclimate Science — High Plains – Kansas – lunette – mapping – playas — stratigraphy

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Page publiée le 3 novembre 2012, mise à jour le 25 septembre 2017