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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.
41

Strontium and carbon isotope stratigraphy of the Llandovery (Early Silurian) implications for tectonics and weathering /

Gouldey, Jeremy C., January 2008 (has links)
Thesis (M.S.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 38-43).
42

40Ar/39Ar dating of young supergene Mn-Oxides : implication for late Cainozoic weathering history and landscape evolution, Mary Valley, Southeast Queensland, Australia /

Feng, Yuexing. January 2005 (has links) (PDF)
Thesis (Ph.D.) - University of Queensland, 2005. / Title reads superscript Ar/superscript Ar. Includes bibliography.
43

Kimberlite weathering mineralogy and mechanism /

Morkel, Jacqueline. January 2006 (has links)
Thesis (Ph.D.)(Metallurgical Engineering)--University of Pretoria, 2006. / Includes summary. Includes bibliographical references. Available on the Internet via the World Wide Web.
44

Pedogenesis, weathering processes, and elemental distribution along a soil climosequence in the southern Piedmont

Feldman, Steven B. 06 June 2008 (has links)
Lack of age control for deposits >40,000 yr makes it impossible to differentiate between the complex effects of climate and geomorphic age on weathering intensity, soil profile development, mineral stability, and elemental flux within the pedoenvironment. Upland soils formed in similar granitic parent materials along a climatic gradient in the nonglaciated Southern Piedmont Province were analyzed in order to investigate whether soil response to variations in the weathering environment follows predictable, systematic patterns related to climate, and to quantify the nature and magnitude of these relationships, particularly with regard to processes of secondary mineral neoformation and transformation. With few exceptions, all measures of weathering intensity increase dramatically from north to south on the Piedmont. The effective depth of pedogenesis in the Georgia and Alabama soils studied is nearly twice that of soils in Virginia and North Carolina, closely corresponding to calculated effective leaching indices developed for each site. Kaolinite and gibbsite are poor indicators of soil age, weathering intensity, or paleoenvironment because of complex mechanisms of formation. Kaolinite genesis is shown to result from i) desilication of 2: 1 phyllosilicates in surficial horizons ii) hydrolysis of K-feldspars, iii) resilication of gibbsite deep in the saprolite, and iv) recrystallization of halloysite in the soil/saprolite transition zone. Gibbsite forms from both desilication of kaolinite and by reprecipitation after N a-feldspar dissolution at depth. Halloysite is common to all soils as the product of both feldspar and biotite weathering, thus illustrating the overriding influence of microenvironment in secondary minerals formation. Clay content is linearly related to Fed in Virginia, North Carolina, and Georgia soils, with regression slopes decreasing from north to south. Clay content levels off at higher Fed values for Alabama soils, indicating that i) steady-state conditions are approached as pedogenic clay formation reaches some intrinsic, self-limiting threshold value, and ii) the limiting factor in clay production over time is leaching intensity, and not the concentration of Fe-bearing primary minerals, in contrast to the soils studied soils in Virginia, North Carolina, and Georgia, appear to have reached a steady-state with regard to clay production. These data suggest that soils farther south on the Piedmont have experienced conditions of greater geomorphic stability and longer weathering. Until we can obtain numetical dates for Piedmont soils, however, one can only speculate as to whether the observed differences in pedogenesis and weathering intensity are due to age effects, climatic effects - or both. / Ph. D.
45

Mineral Chemistry of Heavy Minerals in the Old Hickory Deposit, Sussex and Dinwiddie Counties, Virginia

Lener, Edward F. 23 December 1997 (has links)
The Old Hickory is the largest of a series of Pliocene (?) age heavy mineral sand deposits in Virginia and North Carolina. The high density of heavy minerals allows for selective concentration during transport and deposition. Under the right conditions, placers of considerable size can be formed. The elliptically shaped ore body of the Old Hickory Deposit extends in a North - South direction and is approximately 13 km (8 miles) long and up to 2.5 km (1.5 miles) wide, with an average thickness of 6.5 m (20 feet). The deposit lies along the Fall Zone, where a thin wedge of Cenozoic Coastal Plain sediments unconformably overlies the older rocks of the Piedmont. The principal minerals of economic interest found in the heavy mineral sands at the site are ilmenite (FeTiO₃), leucoxene (Fe<SUB>2-x</SUB>Ti<SUB>3+x</SUB>O<SUB>9+x/2</SUB>) where x is less than or equal to 2, rutile (TiO₂), and zircon (ZrSiO₄). An important focus of this study is the alteration of ilmenite by leaching away of iron, which results in enrichment in titanium. Titanium metal is highly valued for its light weight and high strength. In terms of total economic value, however, the use of titanium dioxide pigments for paint, coated paper, and other products is far more important. As the value of the ore is heavily dependent on the titanium content, the weathering process is a matter of considerable interest to the mineral industry. Analysis of ilmenite grains using reflected light microscopy revealed a wide range of alteration textures. Quantitative analysis and mapping of trace elements showed altered areas with enrichment in Ti and depletion in Fe, Mn, Mg, and Cr. It is believed that the weathering process took place in a reducing environment prior to final deposition according to the reaction: Fe²⁺TiO₃ + 2H⁺ --> Fe²⁺ (aq) + TiO₂ + H₂O Reducing environments are found in water-logged soils such as floodplains and other low-lying areas. Repeated cycles of burial and exhumation during transport would have created conditions ideal for the removal of iron from the ilmenite. / Master of Science
46

Taphonomy: What About the Small Bones, Long Bones, and Cranial Bones? A Study of the Representation and Weathering of Human Remains from the Battle of Stoney Creek during the War of 1812 / The Representation and Weathering of Human Remains

Casaca, Lia 11 1900 (has links)
Disarticulated, commingled, and fragmented assemblages occur over a range of geographic and temporal contexts, yet the relationship between the representation and weathering of bone in these collections is unclear. Previous studies have produced inconsistent results and there is little elaboration discussing why the representation of large bones differ from small bones in archaeological collections containing commingled remains. The purpose of this research was to determine which bones were better represented, and if the representation correlated to the weathering of bone in the collection of human remains from the Battle of Stoney Creek, a War of 1812 site. The soldiers from the battle were likely buried in a mass grave; however, almost 200 years of extensive taphonomic disturbances created an assemblage that was disarticulated, commingled, and fragmented. A database of the collection was used to gather information on bone fragment completeness recorded using the zonation method (Knüsel and Outram 2004), and weathering scores recorded using the scale by McKinley (2004). Results from the Z-statistic and Wilcoxon Rank-Sum statistic indicated that small bones (metacarpals, metatarsals, tali and calcanei) were better represented and less weathered than long upper and lower limb bones (femora, tibiae, fibulae, humeri, ulnae and radii) (p=0.05). The binomial distribution also determined that the crania were underrepresented in comparison to two cemetery sites; the West Tenter Street and Cross Bones burial ground (p=0.1). There are a number of possible reasons for this expression of representation and weathering including the size, morphology, and density of bones, taphonomic disturbances, the burial environment (e.g., soil characteristics, the feather edge effect), and clothing. This study highlights the importance of preservation analyses in commingled, disarticulated, and fragmented collections. The findings from this research suggest that small bones may be better represented than the larger limb bones at sites with extensive taphonomic disturbances. / Thesis / Master of Arts (MA)
47

A histological examination of bone weathering

Liggett, Isabella A. 10 March 2022 (has links)
This project histologically examined weathering on faunal bones. The sample consisted of a mixture of faunal remains, assessed and assigned to weathering stages (WS) 0-2 from Behrensmeyer’s (1978) scoring method. A total of 77 bones sections were observed for histological analysis. A portion were obtained, partially fleshed, commercially and were placed at the Outdoor Research Facility (ORF) in Holliston, MA. After deposition, bones were collected at specific time intervals allowing for 2, 4, 6, 8, 12, and 18-month exposure times. Bones were also collected from several outdoor locations in Ohio, having been exposed for an unknown period, and ranging from WS 0-2. Following histological preparation of the sample, the microstructure of each weathering stage was observed using the image analysis software Fiji from the National Institutes of Health (NIH). Data recorded included the number of cracks present per unit area and the depth of cracking. The number of cracks per unit area for each section of bone was calculated by dividing the number of cracks per section by the total section area resulting in number of cracks per mm2. Depth of cracking was analyzed through maximum crack length and average crack length. This data was compiled and one-way ANOVA tests were applied to determine where weathering stage and exposure time were statistically significant. This was followed by Bonferroni post-hoc analyses which were utilized to analyze the interactions within the WS and exposure time variables; to allow for analysis of statistical significance of WS to one another and exposure time intervals to one another. It was hypothesized that different weathering states would be statistically significant from one another, and microscopically identifiable through a histological examination, and that these would be able to be differentiated from other sources of microtaphonomic alteration including burial and thermal alteration. It was also hypothesized that exposure time would significantly impact the histological characteristics including the number of cracks per mm2 and the maximum and average crack depth. One-way ANOVA analysis indicated that WS has a significant impact on the number of cracks per mm2 and the maximum crack length. No significance was observed for analysis of WS and average crack length. Post-hoc analysis involving the number of cracks per mm2 revealed statistical significance between WS 0 and WS 1, WS 0 and WS 2. Analysis involving maximum crack length indicated significance only between WS 0 and WS 1. Post-hoc analysis involving average crack length did not indicate any statistically significant relationships between the WS. One-way ANOVA analysis of exposure time indicated that exposure time has a significant impact when on all three variables: number of cracks per mm2, average crack length, and maximum crack length. Post-hoc analysis involving the number of cracks per mm2 found that months 0, 2, 4, 6, and 8 were all statistically significant from 18 months. Analysis of average crack length revealed that months 0 and 2 were both statistically from 8 months of exposure. Post-hoc analysis involving maximum crack length reveals statistical significance between months 0 and 8, 0 and 12, and 2 and 8. Histological characteristics of weathered bone were found to include delamination and cracking. Delamination was observed on several bones in WS 2 and one in WS 1, while cracking was observed in bones of all stages. Positive relationships were observed between WS and number of cracks per mm2, and between exposure time and cracks per mm2 indicating that as one increased so did the other. No trend was observed for the relationship between exposure time and either of the crack length variables; the same was observed for the relationship between WS and the two crack length variables. Through comparison of the histological characteristics of weathered bone with other sources of microtaphonomic alterations, it was determined that weathering and its histological characteristics are different from other alteration sources, including burial and thermal alteration, to allow for determination of the microtaphonomic process affecting the bone.
48

Stratigraphy and palaecology of five late Cainozoic formations in the Kenya Rift Valley

Pickford, Martin Hubert Luke January 1974 (has links)
The geology of five sedimentary units outcropping west of Lake Barinjo in the Kenya Rift Valley is presented. The units range in age from mid-Miocene (about 13 million years) to late-Miocene (about 5 million years). Regional geological mapping has resulted in the determination of the stratigraphic relationships of the sediments, which have been calibrated by radiometric techniques Faunal studies confirm the mid-to late-Miocene ages of the sediments suggested by radiometric age determinations on intercalated lavae. A succession of vertebrate faunas over this time span is presented.
49

Mechanical characterization of granitic rocks of Hong Kong by improvedindex testing procedures with reference to weathering inducedmicrostructural changes

Basu, Arindam. January 2005 (has links)
published_or_final_version / abstract / Earth Sciences / Doctoral / Doctor of Philosophy
50

Pore water chemistry reveals gradients in mineral transformation across a model basaltic hillslope

Pohlmann, Michael, Dontsova, Katerina, Root, Robert, Ruiz, Joaquin, Troch, Peter, Chorover, Jon 06 1900 (has links)
The extent of weathering incongruency during soil formation from rock controls local carbon and nutrient cycling in ecosystems, as well as the evolution of hydrologic flow paths. Prior studies of basalt weathering, including those that have quantified the dynamics of well-mixed, bench-scale laboratory reactors or characterized the structure and integrated response of field systems, indicate a strong influence of system scale on weathering rate and trajectory. For example, integrated catchment response tends to produce lower weathering rates than do well mixed reactors, but the mechanisms underlying these disparities remain unclear. Here we present pore water geochemistry and physical sensor data gathered during two controlled rainfall-runoff events on a large-scale convergent model hillslope mantled with 1 m uniform depth of granular basaltic porous media. The dense sampler and sensor array (1488 samplers and sensors embedded in 330 m(3) of basalt) showed that rainfall-induced dissolution of basaltic glass produced supersaturation of pore waters with respect to multiple secondary solids including allophane, gibbsite, ferrihydrite, birnessite and calcite. The spatial distribution of saturation state was heterogeneous, suggesting an accumulation of solutes leading to precipitation of secondary solids along hydrologic flow paths. Rapid dissolution of primary silicates was widespread throughout the entire hillslope, irrespective of up-gradient flowpath length. However, coherent spatial variations in solution chemistry and saturation indices were observed in depth profiles and between distinct topographic regions of the hillslope. Colloids (110-2000 nm) enriched in iron (Fe), aluminum (Al), and phosphorus (P) were mobile in soil pore waters.

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