D. Phil. / A Mesoproterozoic basement and a Cambrian-Ordovician carbonate platform characterize the Precordillera terrane. These characteristics and its distinct geologic history mark a difference between this suspected exotic-to-Gondwana terrane and the Gondwanan autochthonous, leading to speculation that the Precordillera was derived from Laurentia. The surprising similarities of the carbonate sequences between the Precordillera and certain parts of southeast Laurentia suggest a common geological history. However, other models interpret the origin of the Precordillera terrane as being para-autochthonous with respect to Gondwana. All these models are still controversial. A combination of several methodologies including petrography and heavy minerals analysis, geochemistry, Sm-Nd and Pb-Pb isotopes and zircon dating were applied to several Ordovician and Ordovician to Silurian units of the Precordillera terrane. Geochemistry and petrography indicates that all the Formations studied have similar characteristics, with at least two sources providing detritus to the basin. The dominant source has an unrecycled upper continental crust composition whereas the other component is more depleted. The study of detrital chromian spinels suggests that mid-ocean ridge basalts, continental intraplate flood basalts and ocean island basaltrelated rocks were among the sources for the detrital record of the Precordillera terrane. Nevertheless, the mafic sources and their ages remain unknown. Nd isotopes account for negative εNd values and TDM ages in a range of variation found elsewhere within Gondwana and basement rocks of the Precordillera. The Sm/Nd ratios of certain samples indicate fractionation of LREE. Pb isotopes indicate that a source with high 207Pb/204Pb was important, and point to Gondwanan sources. Detrital zircon dating constrain the sources as being dominantly of Mesoproterozoic age (but with a main peak in the range 1.0 to 1.3 Ga), with less abundant populations of Neoproterozoic (with a main peak in the range 0.9 to 1.0 Ga), Palaeoproterozoic, Cambrian and Ordovician ages in order of abundance. i The uniformity shown by the provenance proxies indicate that there were no important changes in the provenance from the Lower Ordovician until the Early Silurian. Several areas are evaluated as sources for the Precordillera terrane. The rocks that fit best all the provenance constraints are found within the basement of the Precordillera terrane and the Western Pampeanas Ranges. Basement rocks from the Arequipa-Antofalla area (Central Andes) also match the isotopic characteristics, but a northern source is less probable, except for the Western tectofacies. On the other hand, areas such as Antarctica, Falklands/Malvinas Microplate, the Natal-Namaqua Metamorphic belt and the Grenville Province of Laurentia can be neglected as sources. The proposal of these areas as sources is in agreement with palaeocurrents and facies analyses and suggests proximity between them and the Precordillera since at least the Late Arenig to Early Llanvirn. This has important implications for the proposed models regarding the geotectonic evolution of the Precordillera terrane. The models would need to be adjusted to the here proposed youngest timing of collision.

M.Sc. / The sedimentary succession of the Paleoproterozoic Pretoria Group is very important for understanding Earth’s ancient history. It represents a time of extreme environmental changes on Earth, from global ice-ages to hot-houses. However, the genetic stratigraphy of the succession is poorly understood so that the stratigraphic relationships between the events remain uncertain. This dissertation provides a genetic stratigraphic model of the succession by utilising an integrated sedimentological and geochemical approach which culminates in a new sequence stratigraphic subdivision of the Pretoria Group. The study focuses on the Potchefstroom area in the western part of the Transvaal depository. The Pretoria Group commences with the Rooihoogte Formation which overlies the Chuniespoort Group with erosional contact. New stratigraphic data indicates that the Rooihoogte Formation is a correlative of the Duitschland Formation in the eastern Transvaal. The succession was deposited in a foreland basin. An important new finding is that a diamictite at the base of the formation contains striated and bull-nosed pebbles and is of glacial origin. The discordantly overlying Timeball Hill Formation is composed of a coarsening upward carbonaceous shale – hematite oolite-bearing quartzite unit overlain by a second carbonaceous shale, capped by a second glacial diamictite (the well known Rietfonteindam diamictite). The oolitic ironstones in the quartzites suggest that they formed in a warm oxidizing environment. The shales display mature chemical indices of alteration which supports this theory. ä13Corganic values increase from –35‰ to –24‰ from the bottom to the top of the Timeball Hill Formation indicating net carbon burial, which translate to a decrease in atmospheric CO2 and colder climates as deposition evolved. In turn this can be linked to the presence of the glacial Rietfonteindam diamictite in the upper part of the Timeball Hill Formation. The Rietfonteindam diamictite is overlain by conglomerate, quartzite and shale of the Boshoek Formation, which were deposited as an upwards fining transgressive sedimentary unit following on post-glacial eustatic sea-level rise. It is in turn overlain by the 2.22Ga. Hekpoort basalt. This basalt is metasomatically altered, but has remained virtually unaffected by regional metamorphism, as shown by detailed SEM petrographic analyses. Excellent examples of zeolite- filled amygdales are preserved in the lavas. The Hekpoort lavas are overlain by fluvial red beds of the Dwaalheuwel Formation. A lateritic paleosol (Hekpoort paleosol) is developed below the red bed succession. The red beds are overlain with sharp gradational contact by the carbonaceous shelf mudstone of the Strubenskop Formation which grades up into the shallow marine Daspoort quartzite. The Silverton Formation, mainly composed of carbonaceous shale, overlies the Daspoort Formation with sharp gradational contact and grades upwards into shallow marine Magaliesberg quartzite. ä13Corganic values decrease from –25‰ to –29‰, from middle to top of the Silverton Formation, most probably indicating carbon input into the atmosphere and therefore rising atmospheric temperature. The Machadodorp lava, which was previously thought to be restricted to the eastern part of the Transvaal basin, was found to be present in the Potchefstroom area as well. Five unconformity-bounded sequences are present in the succession. Estimates are that they were deposited in time intervals of 60m.y. each.

The Nsuta manganese deposit is located in the Western Region of Ghana, approximately five kilometers south of Tarkwa Goldfields. The deposit has been an important source of manganese ore since mining began in 1916. The purpose of this project was to produce a concise model of the stratigraphy, sedimentology and structural evolution of the deposit in support of future exploration projects. The manganese ores occur as an up to 45m thick carbonate bed in a thick turbidite-greenstone succession that is part of the ~2.2 Ga Birimian Supergroup. Calc-alkaline volcanics, volcaniclastics, turbidites, argillites and phyllites are thought to have been deposited in a backarc basin environment. The entire sedimentary succession, including the manganese orebody, is a thick turbidite package hosted between an upper and lower greenstone unit consisting predominantly of volcaniclastic material. The entire lithological succession at Nsuta is interpreted to have been deposited within the middle to lower reaches of a submarine fan environment. Field evidence suggests a simple stratigraphy, commencing with a lower greenstone unit composed largely of volcaniclastic material. This is followed by an upward-fining lower turbidite unit deposited in response to a marked transgression and sea level rise. Maximum rate of sea level rise provided ideal conditions for manganese precipitation and concentration, as detrital influx ceased. The central portion of the carbonate orebody that formed hosts the manganese orebody. An upward-coarsening turbidite unit follows above the carbonate unit. This upward-coarsening succession reflects a regression and a highstand systems tract in terms of sequence stratigraphic principles. It is capped by an unconformity that formed during a period of rapid relative sea level fall. It is overlain by a second upward-fining turbidite succession. This succession is not fully preserved as there is a sheared contact between it and the overlying upper greenstone unit. Post-depositional deformation and metamorphic alteration are largely attributed to the Paleoproterozoic Eburnean Orogeny. A first phase of compression was directed along a NW-SE axis and produced a series of isoclinal anticlines and synclines (F1) with NE-SW striking axial planes. This was followed by thrusting between the anticlines and synclines. The age of this deformation and closely associated greenschist metamorphism can be accurately constrained between 2.09 Ga and 2.07 Ga. E-W oriented oblique listric faulting has a prominent effect on the appearance of the Nsuta manganese deposit, as it produced a series of imbricate fault blocks dipping to the north. Associated with this period of deformation is small-scale cross folding with axes plunging to the east (F2). The faults post-date the Eburnean Orogeny and must be associated with a second major tectonic event. Finally, a NNE-SSW striking normal fault, locally known as the German Line, caused further block rotation, notably in the northern parts of the mining concession. Late Mesozoic deep lateritic weathering and incision of the lateritic peneplane by modern rivers have resulted in the complex dissected appearance of the Nsuta orebody. However, based on the detailed structural analysis provided in this study, a feasible target for future exploration of manganese ore buried beneath Late Mesozoic and Cenozoic sediments and soils, has been identified. This target is located to the west of Hills A and B. / Dr. J.M. Huizenga Prof. Nic Beukes Prof. J. Gutzmer

After the establishment of the N-S Andib-Ganamub trough, the ubiquitous Lower Nosib subarkose was succeeded in the west by the Upper Nosib greywacke which indicates that orthogeosynclinal subsidence was already active in pre-Damara times. A pulse of NNE folding (F₁N) concluded this sedinentary cycle and was accompanied by amphibolite-grade metamorphism (M₁), occasional migmatisation (A₁), and later feldspar blastesis. This episode was most intense in the west, so that the overlying Damara rocks paraconformable in the east, are unconformable there. Martin's (1965) separation of the succeeding Damara basin into a western eugeosyncline and an eastern miogeosyncline applies very well to this area, though the separating hinge-line appears to have been located farther to the west (±80 Km) of the Kamanjab inlier, along the western flank of a N-S geanticlinal belt. The Lower Bakos semipelite and lenticular carbonate, thinning out against the eastern flank of this positive element controlling the deposition, may, prior to deformation, have created a transition between the western eugeosynclinal greywacke and the eastern miogeosynclinal Lower Otari carbonates. The fractured hinge-zone provided channels for the ascent of syndepositional intrusions and volcanics. Regional erosion following upwarping in the east caused a large influx of detritus into the Khomas furrow prior to the disconformable deposition of the Tillite Substage, which is the only reliable chronostratigraphic link between the base of the Upper Otavi and that of the Upper Bakos Series, the latter partially intertongueing with the succeeding Khomas Series. Gravitational creeping of the miogeosynclinal carbonates down the western slope of the upwarped Kamanjab inlier towards the sinking basin, produced the first folding (F₂O) in the east. Almost contemporaneously, buoyant uplifting forces, related to anatexis (A₂) along the axis of the eugeosyncline, created slopes sufficient to convey nappes (F₂S) of scarcely metamorphosed Damara schists towards the eastern foreland, overriding the miogeosyncline along the N-S Sesfontein Thrust. Eastern foredeeps were rapidly filled by the Mulden molasse. Steep slip folding (F₂S and F₄) in the cores and roots, and the formation of scattered domes at depth, controlled the successive structural evolution of the nappes. Large-scale axial undulations were later produced by orthogonally superposed F₃ folds striking east. The Damaran metamorphism (M₂ ), which outlasted deformation, has a Barrovian character and grades in the Damara sediments from amphibolite (sillimanite) grade in the west to greenschist (sericite- chlorite) grade in the east. In the previously dehydrated, deformed and metamorphosed, polymetamorphic (M₁/M₂ ) Nosib terrains, retrograde parageneses and transition granulites developed to the east and to the west of the Damaran hornblende-oligoclase isograd respectively. The Damaran tectono-thermal episode culminated in advanced migmatisation of the Khomas greywacke (possibly equivalent to the Salem granite-gneiss) and final anatexis (A₂ ) in the late-kinematic Ganias -Uhima (possibly equivalent to the Donkerhoek) granite, followed by widespread feldspar blastesis. The drop in rheomorphism in the deformed mass at the margin of the migmatite zone induced intense shearing and produced belts of mylonite and cataclastic gneiss. At a later stage, the Sesfontein Thrust was buffered against the Otavi dolomite relief and its speed of advancement reduced to match that of the erosion of its frontal toe, which now separates two completely different structural-stratigraphic domains: i) an eastern miogeosynclinal, feebly metamorphosed and volcanic-free domain (Damara System, Outjo Facies) deformed into non-basement-involving tectonites, overridden by ii) a western domain of suprastructural nappes and metamorphosed eugeosynclinal sediments (Damara System, Swakop Facies) deformed in response to basementinvolving tectonic processes promoted by deeply seated anatexis along the axis of the former eugeosyncline. The present model involves many stratigraphic revisions, one of the most important being that no rocks older than the Nosib Formation outcrop in the area and possibly along most of the Damara mobile belt in the western Kaokoveld.

No description available.

Thesis (Ph. D.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on December 28, 2007) Includes bibliographical references.

Epithermal vein and carbonate replacement deposits in Cunningham Gulch are located within the western San Juan Tertiary volcanic field in southwestern Colorado. The Pride of the West epithermal vein system is hosted within the intracaldera facies of the Sapinero Mesa Tuff, a voluminous ash-flow tuff that erupted from and resulted in the formation of the San Juan Caldera at 28 mybp. The Pride of the West vein system is developed along a radial fracture formed during resurgence of the San Juan Caldera prior to eruption of the Crystal Lake Tuff (27.5 mybp). This eruption led to the concomitant collapse of the Silverton Caldera, nested within the larger San Juan Caldera. The Pride of the West, Osceola, and Little Fanny mines are positioned near the intersection of the Pride radial fracture system and the buried structural margin of the San Juan Caldera, suggesting that ore concentration was controlled by this structural setting. Large limestone blocks of the Mississippian Leadville Formation are incorporated into the intracaldera fill volcanics in the mine area. These blocks appear to have been engulfed within mudflow breccias of the Tertiary San Juan Formation (32.1 mybp). They were then emplaced in their present structural position within a caldera-collapse breccia which caved from the oversteepened margin of the San Juan Caldera. Regional propylitic alteration of the hosting volcanics to a chlorite-calcite-pyrite assemblage preceded vein-associated alteration and mineralization. The veins are enveloped by a narrow phyllic alteration assemblage of quartz, sericite, illite, kaolinite, and pyrite. The veins are comprised of sphalerite, galena, chalcopyrite, pyrite, hematite, magnetite, quartz, pyroxmangite, calcite, and minor barite. Substantial bodies of replacement ore are present where the vein structures intersect the limestone blocks; the mineral assemblages of the replacement deposits are identical to those of the feeding vein structures. Commonly, replacement textures are spectacular concentrations, especially the "zebra ore" which primarily consists of regularly spaced, alternating bands of sulfides and quartz. These "zebra" laminations are stratigraphically controlled and appear to represent replacement of a depositional or diagenetic fabric. Main ore-stage mineralization began with widespread deposition of quartz with or without pyrite, followed by sphalerite, chalcopyrite, and galena. Post ore-stage brecciation and silicification events are evident and were followed by deposition of calcite and minor barite during the waning stages of the hydrothermal system. The distributions of Fe, Mn, Pb, and Ca suggest a lateral component of fluid flow from northwest the southeast, away from the structural margin of the Silverton Caldera. Fluid inclusion data from both vein and replacement-type sphalerite and quartz indicate that mineral deposition occurred over a range of 200 to 312°C (mean 243°C) from solutions containing 1 to 5% total salts. The high base metal to precious metal content of the ore, the phyllic alteration assemblage, and the temperature and composition of the ore-forming fluid indicate that the mine workings are within the lower portion of a fossil geothermal system. / text

A detailed stratigraphic analysis of the Lower Lias of southern Britain using the technique of gamma-ray spectrometry is presented. Gamma-ray data were collected, at the maximum stratigraphic resolution possible, from the Rhaetian to Pliensbachian successions exposed in southern Britain in the Bristol Channel Basin, Wessex Basin and East Midland Shelf. The data, in the form of measured gamma-ray signatures and hence geochemical profiles, is placed within a biostratigraphic framework. The outcrop gamma-ray logs collected from the Somerset coast (Rhaetian - Lower Sinemurian) can be subdivided, on the basis of both total gamma-ray signature and elemental log-signature into 9 gamma-ray units. These units are at a higher level of resolution than the single LL 1 gamma-ray unit defined by Whittaker et al (1985) for the Blue Lias in the subsurface. Outcrop gamma-ray correlation is possible between Somerset and Glamorgan, in some cases at a resolution greater than that offered by ammonite subzonal biostratigraphy. This resolution of correlation suggests the presence of a stratigraphic gap in Somerset within the johnstoni Subzone of the planorbis Zone. The outcrop gamma-ray logs collected from the Dorset coast (Rhaetian - Pliensbachian) can be divided into 10 gamma-ray units. These gamma-ray units can be correlated with the subsurface succession in the Winterborne Kingston and the Burton Row boreholes. The ability to correlate across numerous fault blocks and between different basins suggests that the controls upon gamma-ray signature were probably regional. A model is presented in which the degree of detrital influence within a fine grained mud and pelagic carbonate depositional system can be qualitatively assessed. Proximal and distal mudrock facies can be identified from the Th concentration log with proximal facies characterised by a Th concentration 10 ppm and above and distal facies characterised by a Th concentration of 8 ppm and below. The Th concentration log can also be used to determine intervals of mudrock progradation (increasing Th concentration) and retrogradation (decreasing Th concentration). These signatures can be interpreted within a sequence stratigraphic framework, of which the genetic stratigraphic model of Galloway (1989) is most applicable to the Lower Lias of southern Britain. The succession can be divided into eight genetic stratigraphic sequences. Maximum flooding surfaces are inferred at condensed limestone horizons of low Th concentration. The distal expression of the sequence boundary (the correlative conformity) is inferred at horizons of highest Th concentration. The development of anoxia within the epeiric sea can only partly be explained in terms of sequence stratigraphy with anoxia developing during periods of relative sea-level fall and rise or not at all.

M.Sc. / Please refer to full text to view abstract

The study area is located in central Columbia County and encompasses approximately 373 square kilometers. The purpose of the study was to map lithofacies to a scale of 1:31250, study the petrography of the lithofacies, determine the stratigraphy, and develop a model for environment of deposition of the Scappoose Formation.