Recent studies have demonstrated the potentially robust nature of U-Pb and Pb/Pb systematics within certain sedimentary and metamorphic carbonates (e.g. Moorbath et al., 1987; Jahn, 1988; Jahn et al., 1990; DeWolf and Halliday, 1991). During the course of this work, the Pb/Pb dating technique has been applied successfully to the direct dating of Proterozoic stromatolitic carbonates from Western Australia and India, Silurian stromatoporoidal carbonates from Sweden and Archaean marbles from India, permitting the direct age determination of depositional/early diagenetic, late diagenetic and metamorphic events. Results indicate that large variations in μ value (²³⁸U/²⁰⁴Pb) and virtually homogeneous initial Pb isotopic compositions are a recurrent feature of sedimentary and metamorphic carbonates. Authigenic marine carbonates may incorporate U and Pb through a variety of geochemical mechanisms; <ul> <li>organic complexing;</li> <li>crystal lattice substitution;</li> <li>adsorption onto particulate oxyhydroxides and</li> <li>early diagenetic reduction.</li> </ul> Since modern and ancient carbonates have U and Pb concentrations of the order of ppm, whereas dissolved U and Pb in the oceans occur at 3.2 ppb and 0.003 ppb, preconcentration within the water column must be an important factor in the establishment of appropriate geochemical conditions. The rapid scavenging of Pb, compared to rates of U fixation under suboxic conditions, means that depositional μ values seldom approach the sea water figure of c.80,000. Owing to the largely independent geochemical behaviour of U and Pb, early diagenetic, late diagenetic and metamorphic recrystallisation may either partially disturb Pb/Pb and U-Pb systematics or effect complete resetting of radiometric ages. Consequently, results from geochronological studies should be interpreted only after due consideration of all available geological information. The extensive distribution of metamorphic and sedimentary carbonates throughout the geological record, coupled with the apparent robustness of Pb/Pb systematics, means that this technique can offer an effective means of event dating, stratigraphic correlation and time scale calibration, particularly in the Precambrian where independent age constraints are limited. In addition, the identification of late diagenetic recrystallisation ages offers exciting potential for constraining the diagenetic histories of sedimentary basins.

Thesis (Ph. D.)--Ohio State University, 1975. / Includes bibliographical references (leaves 273-279). Available online via OhioLINK's ETD Center.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 223-240). Also available via the Internet.

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Supervisors: Steven L. Bryant and James W. Jennings Jr. Vita. Includes bibliographical references.

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In their comment on our publications on pervasive remagnetization of Jurassic-Paleogene carbonate rocks of the Tibetan Himalaya (Huang et al., 2017, Journal of Geophysical Research: Solid Earth, 122, doi: 10.1002/2016JB013662 and 122, doi: 10.1002/2017JB013987), Yi et al. (2017) questioned our fold tests applied to their published paleomagenetic results from the Paleogene Zongpu and latest Cretaceous Zongshan carbonate rocks (Patzelt et al., 1996, Tectonophysics, 259(4), 259-284; Yi et al., 2011, Earth and Planetary Science Letters, 309(1), 153-165). They argued that authigenic magnetite pseudomorphic after pyrite, which is the dominant magnetic carrier within these carbonate rocks as indicated by our thorough rock magnetic and petrographic investigations, was formed during early diagenesis and that the primary natural remanent magnetization (NRM) is retained by these carbonate rocks. However, their statement for the invalidity of our fold tests is based on unrealistic assumptions that these carbonate rocks carry primary NRM and that the upper Zongpu Formation was deposited on a 10 degrees primary dip. Their argument for immediate oxidization of pyrite to authigenic magnetite after carbonate deposition onto the continental passive margin ignores that sulfate-reducing conditions were prevailing during early diagenesis, it is also inconsistent with the timing of the secondary remanence acquisition in remagnetized carbonate rocks elsewhere. As previously demonstrated, and agreed upon by Yi et al. (2017), the Zongpu and Zongshan carbonate rocks in Gamba are remagnetized; here we argue that the timing of remagnetization cannot be demonstrated to shortly postdate sedimentation. These data should therefore not be used for tectonic reconstructions.

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Thesis (M.S.)--University of Missouri, School of Mines and Metallurgy, 1931. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed December 14, 2009) Includes bibliographical references (p. 75).