A palaeomagnetic study of the Waterberg Group (Jones and McElhinny, 1967) did not find a consistent direction. However, a pattern was identified and interpreted in terms of apparent polar wander during the deposition and consolidation of the Waterberg sediments. These pole positions indicated that the Waterberg Group sedimentation commenced during emplacement of the Bushveld Complex, and intermittently continued through numerous tectonic events in the pre-existing Transvaal Basin to just before the Umkondo thermal event. The Swaershoek Formation as the basal unit of the Waterberg Group in the Nylstroom Protobasin has been tentatively correlated with the Wilge River Formation in the Middelburg Basin. A palaeomagnetic study has been conducted on the Swaershoek and Wilge River Formations in an attempt to redetermine the palaeomagnetic pole positions for these two Formations and to confirm the said geological correlation. A total of 49 sites across both basins were sampled, both within the sediments as well as in the associated diabase intrusions. Despite generally weak results, the calculated pole positions for the Swaershoek Formation (37.1° S, 335.9° E and A95:17.4°) and the Wilge River Formation (31.9° S, 332.7° E and A95: 20.5°) correlate very well, thereby confirming the association made between these two formations. The intrusive diabase in both basins was sampled to test for thermal overprinting of the calculated pole positions of the sediments. Although the calculated pole position for the diabase intrusion in the Nylstroom Protobasin (63.3° S, 233.2° E and A95: 14.2°). These two poles correlate very well with previous studies on post-Waterberg diabase (Jones and McElhinny, 1966) as well as on the Umkondo diabase (McElhinny and Opdyke, 1964). The pole positions from the Waterberg sediments and associated diabase are sufficiently displaced from each other to rule out any overprinting by these intrusions. Recent results from the Blouberg area (Bumby et al., 2001) indicate the Soutpansberg Group to be younger than the Waterberg Group. In an attempt to refine the Apparent Polar Wander Path (APWP) for the middle Proterozoic, another 6 sites from the Mogalakwena Formation (Waterberg Group) were sampled. Bumby et al. (2001) suggested that the Mogalakwena Formation pre-date the Wyllies Poort Formation (Soutpansberg Group). The calculated pole position for the Mogalakwena Formation was very weak, but correlated fairly well with a pole position (Group 2, McElhinny, 1968) from the Wyllies Poort Formation in the Soutpansberg Group. The location of the Mogalakwena Formation pole (36.1° S, 207.3° E and A95: 27.6°) on the APWP for Southern African confirms the Waterberg Group to be older than the Soutpansberg Group. / Dissertation (MSc)--University of Pretoria, 2006. / Geology / unrestricted

No description available.

published_or_final_version / abstract / Earth Sciences / Doctoral / Doctor of Philosophy

Ninety-five oriented samples were obtained from nine Recent Cascade lava flows in Oregon. Directions and intensities of remanent magnetization were measured on a spinner magnetometer which measures directions of magnetization to within 1.2° s.d. Angle measurements were plotted graphically using an equal area projection. Mean directions and statistics were calculated by digital computer. Samples were demagnetized in alternating magnetic fields while being rotated in a two axis tumbling device. All flow means, except one, calculated from the original magnetization vectors are distinct from the present geomagnetic field direction. A correspondence is found between scatter observed in a flow and the type of outcrop sampled (whether natural or man-made). This is believed to be a consequence of excessive blockiness and aa characteristics of the lavas. Results of demagnetization tests indicate low secondary magnetizations. Stability is indicated by lack of anisotropy, lack of isothermal and chemical remanent magnetizations, low viscous magnetization, and divergence of flow means from the present field direction. Flow mean directions for five dated flows are used to trace the secular variation of the paleomagnetic field back to 3000 B.P. This secular variation curve agrees with data taken in southwestern United States for the same period of time. It has generally been found that Recent mean pole positions are coincident with the geographical pole within the limits of error of the data. This study yielded a mean direction distinct from an axial dipole direction. However, the age span is limited as eight of the nine flows have ages between 300 and 3850 years. / Graduation date: 1968

In this thesis anomalous downcore shallowing of paleomagnetic inclinations is interpreted to be caused by sediment compaction. Thus, compaction-induced inclination shallowing may influence tectonic reconstructions that are based on inclinations from deep-sea sediment cores. Progressive downcore shallowing of the remanent inclination was observed in a 120-m section of Plio- Pleistocene sediments at Deep Sea Drilling Project (DSDP) site 578 in the northwest Pacific. Near the top of the section the average inclination corresponds to the expected geocentric axial dipole value of 53° but shallows downcore by about 6° to 8°. In sediments spanning the same time interval of neighboring site 576, no inclination shallowing was observed. This second site has considerably lower sedimentation rates, and the Plio- Pleistocene is represented by a 26-m sedimentary section. The inclination shallowing at site 578 was correlated to a downhole decrease in porosity, and these results are interpreted to suggest that both the downhole inclination shallowing and decrease of porosity in site 578 were caused by sediment compaction. Microscopic models demonstrate that sediment compaction may lead to inclination shallowing of the magnetic remanence. Furthermore, it is shown that inherent initial within-sample dispersion of the magnetic moments will transform any form of microscopic mechanism to an equation of a standardized form: tan (I-ΔI) = (1-a ΔV) tan I, where I is the inclination of the ambient field, ΔI is the inclination shallowing, a is a constant and ΔV the compaction. Paleomagnetic inclinations of Cretaceous DSDP sediments from the Pacific plate are known to be systematically shallower than predicted from paleolatitudes of hot spot reconstructions. Published paleomagnetic data were reexamined and the shallow Cretaceous inclinations explained as a result of sediment compaction. The Cretaceous data are used to estimate the parameter a. The resulting a values are comparable to those of previous studies of compaction-induced inclination shallowing, both from laboratory experiments and the considerably younger deep-sea sediments at site 578. Values of the parameter a suggest that it might be controlled by sediment lithology with greater shallowing for clayey than calcareous sediments. / Graduation date: 1991

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (p. 84-94).

published_or_final_version / Earth Sciences / Master / Master of Philosophy

Thesis (M.Sc.)--Memorial University of Newfoundland. / Typescript. Bibliography: leaves 83-86. Also available online.

Thesis (M.Sc.)-- Memorial University of Newfoundland, 1992. / Restricted until May 1993. Typescript. Bibliography: leaves [93]-99. Also available online.

Thesis (M. Sc.), Memorial University of Newfoundland, 1998. / Bibliography: leaves 63-73. Also available online.