Thesis (MS)--Montana State University--Bozeman, 2008. / Typescript. Chairperson, Graduate Committee: Cathy Whitlock. Includes bibliographical references (leaves 50-54).

Thesis (MS)--Montana State University--Bozeman, 2009. / Typescript. Chairperson, Graduate Committee: Cathy Whitlock. Includes bibliographical references (leaves 57-63).

Proefschrift--Groningen. / Summary in English. "Stellingen": [2] leaves inserted. Bibliography: p. 147-153.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1969. / eContent provider-neutral record in process. Description based on print version record.

Thesis (M.S.)--University of Wisconsin--Madison, 1967. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin, 1966. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2003. / Bibliography: leaves 102-109.

Made available in DSpace on 2014-06-11T19:32:21Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-08-16Bitstream added on 2014-06-13T21:04:03Z : No. of bitstreams: 1 capretz_rl_dr_rcla.pdf: 3353928 bytes, checksum: 7e9219802799c05db6d9550923870f72 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / No presente estudo é descrita uma floresta do Eopermiano do Norte do Gondwana, dominada por pteridófitas arborescentes, gimnospermas, licófitas e esfenófitas. Esta rica assembléia fossilífera localiza-se no Monumento Natural das Árvores Fossilizadas do Tocantins (MNAFTO), na Bacia do Parnaíba, Norte do Brasil. Dois aspectos se destacam: a abundância dos fitofósseis e seu excepcional nível de preservação. Os vegetais fósseis guardam semelhanças com aqueles do mesmo período em Chemnitz (Alemanha), na Província Euroamericana, e com a Flora Gondvânica, na Bacia do Paraná (Brasil), entre outros. A análise dos padrões de orientação de 178 caules, junto com observações geológicas, sugere paleocorrentes no sentido Oeste-Leste predominantemente, originadas durante tempestades de monções, com área-fonte muito distante a Oeste, talvez em um contexto de leque aluvial distal. A vegetação das margens dos principais canais fluviais e suas planícies de inundação era dominada por pteridófitas arborescentes no estrato superior da floresta (dossel), com licófitas, esfenófitas e outras pteridófitas menores ocupando o estrato inferior (sub-bosque). Gimnospermas ocupavam regiões mais distantes das margens dos canais. A comparação entre pteridófitas arborescentes permianas (do MNAFTO) com pteridófitas arborescentes atuais (em remanescentes de Floresta Ombrófila Densa Submontana) permitiu discutir nichos ecológicos ocupados por estas plantas, a estrutura da floresta em ambos os casos, e a inferência da altura verdadeira dos fitofósseis, em uma aplicação inédita de técnicas alométricas a estudos paleontológicos / This present study describes a Lower Permian forest in Northern Gondwana, composed by tree ferns, gymnosperms, lycophytes and sphenopsids. This fossil assemblage is located at Tocantins Fossil Trees Natural Monument (MNAFTO) at Parnaíba Basin, Northern Brazil. There are two remarkable aspects: the abundance of fossils and their exceptional level or preservation. The vegetation is similar to the plant fossils found at Chemnitz (Germany), to Euroamerican Flora sites, and to Gondwanian Flora at Paraná Basin (Brazil), among others. Orientation pattern analyses of 178 stems with geological observations suggest paleocurrents in West-East direction, in monsoon storms. The source area should be at West, several quilometers away, probably in a distal alluvial fan context. The forest in the margins of main fluvial channels was occupied by tree ferns at canopy, and lycophytes, sphenopsids and other small ferns at understory. Gymnosperms probably lived in more distant areas from the fluvial channels. The comparison between fossil tree ferns (from MNAFTO) and modern tree ferns (in Submontane Tropical Rain Forest remnants at the present) allowed discussions about ecological niche, forest structure and estimations of real height of fossil tree ferns, in a new way to apply allometric techniques to paleontological studies

Algal mats comprised primarily of Phormidium frigidum Fritsch, Lyngbya martensiana Menegh., and several species of pennate diatoms are found in the below-ice benthic regions of Lakes Bonney, Chad, Hoare, Fryxell, and Vanda, southern Victoria Land, Antarctica. Mats are also found in the littoral moats and ice-covers of several lakes, and in cryoconite holes on Canada Glacier. Variations in temperature, light, oxygen, salinity, and nutrient levels between lakes and different habitats in the same lake result in differences in species composition, morphology, biomass, and photosynthetic pigment content of the mats. Algal mats are trapping and binding sediment, and precipitating minerals, particularly calcite. Mats are removing organic and inorganic matter from the arheic lakes via transfer through the icecovers or by incorporation into the sediments. Some of the algal mats are laminated, organosedimentary structures and can be considered stromatolitic. Depending upon ambient and subsequent environmental conditions non-columnar, columnar, and pinnacle-shaped stromatolites are forming, some of which are partially lithified. If environmental variables (i.e. low light intensity, lack of burrowers or browsers, and relative lack of turbulence) associated with these stromatolites do not vary significantly, it is probable that they may result in a lacustrine carbonate sedimentary deposit. / Ph. D.

The southwest monsoon is responsible for a summer precipitation maximum for much of the southwest U.S. Biostratigraphies of pollen, plant macrofossils, and aquatic fossils in lakes from near modern monsoon boundaries in conjunction with climate modelling suggests variations in strength of the monsoon system during the late Quaternary. At Montezuma Well, Arizona, high percentages of Pinus and Juniperus pollen as well as maximum influxes of Quercus and Gramineae pollen suggest a shift from dominantly winter to summer precipitation between ca. 12,000 and 9000 yr BP. Maximum aridity occurred 7000-4000 yr BP, coincident with lowest lake levels. In the High Plateaus region of the Colorado Plateau, high Artemisia to Chenopodiaceae-Amaranthus pollen ratios suggests precipitation maxima until ca. 6000 yr BP at Fryingpan Lake and 5000 yr BP at Posy Lake. Pollen records suggest that Pinus edulis, P. ponderosa, and Quercus gambelii, were present on the western Colorado Plateau throughout the Holocene. Expansion of shadscale steppe vegetation at low elevations and upslope movement of ecotones for Pinus edulis, P. ponderosa, and Q. gambelii after ca. 6000 yr BP and low lake levels ca. 5000-3700 yr BP, suggest a period of maximum aridity from decreased summer precipitation. In the San Luis Valley, Colorado, pollen records from Head Lake on the basin floor suggest an expansion of oaks and junipers at the Pleistocene/Holocene boundary that may indicate increased summer precipitation. Lake levels of Head Lake fell sharply after ca. 9500 yr BP. Pollen records from Como Lake in the Sangre de Cristo Mountains suggest that Pinus ponderosa was established in the area by ca. 12,000 yr BP and Pinus edulis by ca. 9500 yr BP. Highland regions such as the High Plateaus (until ca. 6000-5000 yr BP) and central Colorado (until ca. 4000 yr BP) may have experienced Holocene summer precipitation maxima later into the Holocene than sites in lower elevation regions. Regional orographic uplift as a catalyst for convective summer precipitation may be responsible for the duration of summer precipitation maxima in these regions. On a longitudinal gradient, sites to the west such as in the southern Great Basin and Mohave Desert may have recorded enhanced summer precipitation earlier, reflecting different histories of the low-level jets in the southwest. The paleoecologic record generally confirm predictions of general circulation models (GCMs) that southwest monsoon circulation was enhanced from 12,000-6000 yr BP in response to peaks in annual (11,500-11,000 yr BP) and summer insolation (10,000-9000 yr BP) during the late Quaternary.