Thesis (doctoral)--Friedrich-Wilhelms-Universität zu Berlin, 1905. / Vita. Includes bibliographical references.

This study presents a petrographic description and a classification of ordinary chondrite NWA 6514 and aims to establish the first high-precision Pb-Pb age of a single ordinary chondrite chondrule. Furthermore, the distribution of different isotopic Pb signatures among chondritic components will be investigated by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). This study shows that NWA 6514 can be classified as a highly unequilibrated (subtype 3.10) L or LL chondrite that has experienced moderate terrestrial weathering (W2) and a low degree of shock (S2). The LA-ICP-MS measurements suggest that radiogenic Pb signatures have been locally preserved in chondrules. However, the Pb isotopic compositions of leaches from a large chondrule obtained by thermal ionization mass spectrometry show an anomalous distribution that indicates the presence of an exotic Pb component. The best estimate for the chondrule formation age is a model age of the last leach (4566.8 ± 2.6 Myr).

This study presents a petrographic description and a classification of ordinary chondrite NWA 6514 and aims to establish the first high-precision Pb-Pb age of a single ordinary chondrite chondrule. Furthermore, the distribution of different isotopic Pb signatures among chondritic components will be investigated by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). This study shows that NWA 6514 can be classified as a highly unequilibrated (subtype 3.10) L or LL chondrite that has experienced moderate terrestrial weathering (W2) and a low degree of shock (S2). The LA-ICP-MS measurements suggest that radiogenic Pb signatures have been locally preserved in chondrules. However, the Pb isotopic compositions of leaches from a large chondrule obtained by thermal ionization mass spectrometry show an anomalous distribution that indicates the presence of an exotic Pb component. The best estimate for the chondrule formation age is a model age of the last leach (4566.8 ± 2.6 Myr).

Thesis (doctoral)--University of Chicago, 1952. Presented under title: "A linguistic study of the 'Liber regum' of the 'Cronicón Villarense'" / Text of the Liber Regum: p. 17-39. Includes bibliographical references (p. 159-160).

Thesis (doctoral)--University of Chicago, 1952. Presented under title: "A linguistic study of the 'Liber regum' of the 'Cronicón Villarense'" / Text of the Liber Regum: p. 17-39. Includes bibliographical references (p. 159-160).

abstract: Historically, uranium has received intense study of its chemical and isotopic properties for use in the nuclear industry, but has been largely ignored by geoscientists despite properties that make it an intriguing target for geochemists and cosmochemists alike. Uranium was long thought to have an invariant 238U/235U ratio in natural samples, making it uninteresting for isotopic work. However, recent advances in mass spectrometry have made it possible to detect slight differences in the 238U/235U ratio, creating many exciting new opportunities for U isotopic research. Using uranium ore samples from diverse depositional settings from around the world, it is shown that the low-temperature redox transition of uranium (U6+ to U4+) causes measurable fractionation of the 238U/235U ratio. Moreover, it is shown experimentally that a coordination change of U can also cause measurable fractionation in the 238U/235U ratio. This improved understanding of the fractionation mechanisms of U allows for the use of the 238U/235U ratio as a paleoredox proxy. The 238U/235U ratios of carbonates deposited spanning the end-Permian extinction horizon provide evidence of pronounced and persistent widespread ocean anoxia at, or immediately preceding, the extinction boundary. Variable 238U/235U ratios correlated with proxies for initial Cm/U in the Solar System's earliest objects demonstrates the existence of 247Cm in the early Solar System. Proof of variable 238U/235U ratios in meteoritic material forces a substantive change in the previously established procedures of Pb-Pb dating, which assumed an invariant 238U/235U ratio. This advancement improves the accuracy of not only the Pb-Pb chronometer that directly utilizes the 238U/235U ratio, but also for short-lived radiometric dating techniques that indirectly use the 238U/235U ratio to calculate ages of Solar System material. / Dissertation/Thesis / Ph.D. Geological Sciences 2011

The source of potassium and argon in ordinary chondrites is determined by comparing the argon activation energies of feldspar, pyroxene, and olivine with that of the L chondrites Chico and North West Africa (NWA) 091. In addition, shock pressures of 29 to 55.8 GPa are shown to lower the activation energy of feldspar. Comparable shock pressures lowers the activation energy of pyroxene outside of error, but the variability of this value, even among unshocked samples, makes a clear distinction difficult. The effect of shock on olivine has not been investigated, by myself or others. Like many ordinary chondrites, Chico and NWA 091 have two major releases of argon, one at low temperature, and the other at high temperature. The low temperature release of Chico contains two releases, which match the activation energies of shocked and unshocked feldspar. The low temperature release of NWA 091 only contains a single release, which matches shocked feldspar. The high temperature release of both Chico and NWA 091 has an activation energy that is similar to pyroxene, but not olivine. A potassium mass balance of Chico shows that all the potassium in the meteorite is contained in feldspar, and Raman spectroscopy shows this feldspar has not been converted into a high pressure phase, indicating the high temperature release is inclusions in a high temperature mineral. This mineral is probably pyroxene based upon the activation energy, though thin sections provide evidence that feldspar is more closely associated with olivine. NWA 091 exhibits multiple isochrons, showing the presence of two nonprimordial and (probably) non-terrestrial trapped components of argon. The removal of these trapped components reveals a thermal event produced by a collisional impact on the L chondrite parent body at 475 ± 6 Ma (which supports a link between L chondrites and Ordovician fossil meteorites), as well as a similar event at ~800 Ma (which, combined with similar ages on other Solar System objects, suggests an increased impact flux at that time). Chico did not exhibit an isochron, and the age data for Chico is not reported.

Thesis (M. Ed.)--Kutztown University of Pennsylvania, 1991. / Source: Masters Abstracts International, Volume: 45-06, page: 2772. Abstract precedes thesis as [1] preliminary leaf. Typescript. Includes bibliographical references (leaves [41-46]).

Thesis (doctoral)--Aristoteleio Panepistēmio Thessalonikēs, 1981. / Romanized record. Includes bibliographical references (p. [7]-28).

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