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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.
941

A study of the eskridge shale

Wells, John David. January 1950 (has links)
Call number: LD2668 .T4 1950 W4 / Master of Science
942

Experimental constraints on crustal contamination in Proterozoic anorthosite petrogenesis

Hill, Catherine Mary January 2017 (has links)
A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. Johannesburg, 2017. / Massif-type anorthosites formed in the Proterozoic Eon are the most voluminous anorthosite occurrences on Earth, reaching tens of thousands of square kilometers in aerial extent. While they formed throughout the Proterozoic, most formed during a 700 Ma period between 1800 and 1100 Ma. The rocks are dominated by plagioclase (typically 70 – 95 volume %) of intermediate composition (An40-65). Olivine, orthopyroxene, clinopyroxene and Fe-Ti oxides make up the minor mafic proportion. While most researchers agree that the anorthosites formed from a high-alumina basaltic parental magma, there are disparate views on how that parental magma was generated. Whether the parental magma formed by partial melting of the lower crust, or by mantle melting, is a topic of much debate. The anorthosites commonly have crust-like isotopic signatures, but this could be produced by melting of the lower crust, or by crustal contamination of mantle-derived magmas. Many Proterozoic anorthosite complexes consist of both olivine-bearing and orthopyroxene-bearing anorthosites. This has been attributed to variable amounts of crustal contamination of mantle-derived magmas, based on evidence from isotopes and field relations. While geochemical and petrologic evidence for crustal contamination is plentiful, existing experimental work shows that a thermal divide exists for high-alumina basalts fractionating at lower crustal depths, casting doubts on whether fractionation of a mantle melt could produce anorthosite. Here I use high-pressure experiments to test whether the fractionation of high-alumina basalt can form anorthosites, and to what extent crustal contamination affects the fractionation sequence. The results are compared to new geochemical and petrologic data from the Kunene Anorthosite Complex (KAC), in Angola and Namibia. The KAC is one of the largest anorthosite complexes in the world, with an area of ~18 000 km2. The KAC (1438 – 1319 Ma) has an elongate shape and intruded into Palaeoproterozoic to Mesoproterozoic country rocks (~2200 to 1635 Ma) at the southern margin of the Congo craton. It is associated with a suite of granitoid rocks of variable composition, which are akin to the granitoids associated with nearly all Proterozoic anorthosites. The granitoids have been shown to be coeval with the anorthosites, but were from a chemically independent magma series. The most distinctive granitoids in the KAC are the Red Granites, which outcrop around the southern margins of the complex, and also cross-cut the complex in a NE-SW linear belt, dividing the complex roughly into northern and southern domains. The rocks of the KAC are highly variable in terms of mode, mineral chemistry, and texture, but there is a general trend of more olivine-bearing anorthosites north of the granite belt, and orthopyroxene-bearing anorthosites to the south. The olivine-bearing rocks (or leucotroctolites) typically contain plagioclase and cumulus and/or intercumulus olivine, with lesser interstitial orthopyroxene and/or clinopyroxene, Fe-Ti oxides, and biotite. The orthopyroxene-bearing anorthosites (or leuconorites) contain cumulus plagioclase ± cumulus orthopyroxene, and interstitial orthopyroxene, clinopyroxene, oxides and biotite. The leucotroctolites are characterized by more calcic plagioclase (An56-75), while the leuconorites contain more intermediate plagioclase (An48-56). The variability of the rocks across the complex suggests that the KAC consists of several coalesced plutons with different histories. The petrologic data and field observations in this study are consistent with the leuconorites of the complex being derived from a mantle-derived magma that experienced contamination by silica-rich rocks, crystallizing orthopyroxene rather than olivine, and less calcic plagioclase. The leucotroctolites experienced less or no contamination. To test whether the mineral dichotomy and the variations in plagioclase chemistry observed in Proterozoic anorthosites are due to variably contaminated mantle-derived magma, piston cylinder experiments were conducted on a synthetic high-alumina basalt (HAB) composition, as well as a mixture of this HAB with 30% of a Red Granite composition. Experiments were conducted at 10 kbar, to simulate the depth at which anorthosite differentiation most likely begins (based on Al-in-orthopyroxene geobarometry of highly aluminous orthopyroxene megacrysts that occur in many massifs). The uncontaminated experiments produced olivine as the first liquidus phase, followed by plagioclase (An65-68), and then by clinopyroxene, pigeonite and ilmenite at progressively lower temperatures. Residual liquids evolve towards more silica-rich compositions with decreasing temperature. The contamination experiments produced liquidus orthopyroxene, followed by plagioclase (An51-56), and then by pigeonite at lower temperatures. The experiments show that contamination of a primitive HAB magma by granitic material, most likely produced by partial melting of the lower crust during anorthosite formation, can shift the mineral assemblages of the crystallizing anorthosite from olivinebearing to orthopyroxene-bearing, and produce less calcic plagioclase than the uncontaminated HAB magma. This could explain the observation of olivine-bearing and orthopyroxene-bearing anorthosites in the KAC and many other Proterozoic anorthosites. Previous high-pressure experimental studies, using a slightly more evolved HAB composition, indicated the presence of a thermal divide, which causes liquids to evolve to more Si-poor compositions. The experimental results presented in this study however, do not show a thermal divide, indicating that small variations in experimental starting composition can cause large differences in the liquid line of descent. The results of this study indicate that partial melting of the mantle can produce anorthosite parental magmas, and that the range in mineral assemblages of the anorthosites can be accounted for by crustal contamination of a mantle-derived magma. Fractionation of the experimental starting compositions was also modeled using the MELTS algorithm. These calculations produce a close match to the experimental liquid trends. This allows for modeling of a variety of compositional and environmental variables. The MELTS modeling shows that as little as 10% contamination of HAB magma with a granitic composition may position the magma in the orthopyroxene stability field, forming orthopyroxene-bearing anorthosites. The modeling also shows that a variety of silica-rich contaminants, including granites, granodiorites and tonalities, produce similar results and liquid evolution trends, so a range of granitoid compositions may successfully produce the shift in mineral assemblages of the anorthosites. This suggests that crustal contamination of mantle-derived HAB could be a widespread process and the primary mechanism that produces the distinctive crust-like signatures in Proterozoic anorthosites. In summary, the mineralogical and chemical diversity observed in Proterozoic anorthosites can be produced by variable amounts of crustal contamination of mantle-derived, highalumina basaltic magma. The experimental results in this study combined with field observations, and geochemical and isotopic data, provide evidence for a model of massif-type anorthosite petrogenesis. Orthopyroxene-bearing rocks formed from an originally highalumina basaltic magma that experienced contamination by granitic partial melts of the lower crust, during ponding of the magma at the Moho. This process preconditioned the surrounding crust and possibly prevented further anatexis. Following emplacement of orthopyroxene-bearing anorthosites, subsequent magma pulses ponded at the Moho did not assimilate any/as much granitic material, as they were interacting with preconditioned crust, and formed olivine-bearing anorthosites. With better constraints on the parental magma composition, magma source, and crustal contamination processes, addressing aspects such as the tectonic setting and emplacement mechanisms of these massive intrusions should be prioritized. Understanding these enigmatic aspects of anorthosite petrogenesis is leading the anorthosite community towards answering the ultimate questions of why massif-type anorthosites are restricted to the Proterozoic. / XL2018
943

The geology of the lily syncline and portion of the eureka syncline between the consort mine and Joe's Lucic siding, Barberton mountain land.

Viljoen, Morris James January 1963 (has links)
Thesis submitted for the degree of Master of Science in the Faculty of Science, University of the Witwaiersrand, Johannesburg. / The following is an account of the stiatigiaphy, structure, metamorphism and mineralization in a complexly deformed area of the northwest part of the Barberton Mountain Land. It is situated at the eastern extremity of the Jamestown Hills and covets a region along the contact zone between the ancient layered rocks of the Archaean Complex and the Nelspruit Granite. In the first section is given a fairly comprehensive account of previous work done in the Barberton region- especially as it applies to the area under discussion. This is followed by a consideration of the petrology and stratigraphy of the area and a description of the various structures encountered. A more detailed statistical treatment of the minor structures is also included and from these results an attempt is made to unravel the tectonic history of the area and to fit it into the regional structural pattern of the Mountain Land as a whole. The area mapped consists of two basically Identical successions separated by a major high angled thrust fault. The northern succession, which has been quite strongly thermally metamorphosed, represents the fairly steeply south dipping northern limb of the Lily Syncline. That to the south has suffered very little metamorphism and forms part of the northern limb of the Eureka Syncline. A well developed and layered basic suite of rocks lying below the Fig-tree Series .and constituting the basal zone of the Lily Syncline, is classed in the Onverwacht Series, It lies in direct contact with the Nelspruit Granite and is considered to represent a metamorphosed succession of impure dolomites with arenaceous and minor shaly horizons, together probably with some basic and acid lavas. The Onverwacht rocks are overlain by metamorphosed Fig-tree shales and "lavas", and these in turn by metamorphosed conglomerates and quartzites of the Moodies System. At the base of the homfelses lies the Consort "Contact" or Consort "Bar", a siUcified, mineralized zone which is the main ore horizon of the Consort Mine. The homfelses grade into rocks which have been termed "lavas" but which are thought to be mote of the nature of crystalline tuffs. The succession to the south of the Main Fault Is on a broad scale Identical to the one just described above, differing mainly in metamorplilc state. Thus, whereas the Onverwacht rocks of the northern succession have been converted to hornblende and tremolite-actinollte schists, similar rocks to the south of the Main Fault have been changed to carbonate-bearing talc and chlorite phylUtes. The basic Intrusive rocks of the Jamestown are considered to be of a much smaller distribution than was previously thought,and are represented mainly by the massive bodies of pure serpentinite. There is a possibility however; that certain of the purer talc- carbonate schists along the Kaap Rivet,represent altered ultrabasic intmsives. The Nelspruit gneiss and migmatlte is considered to represent a completely granitized pre-Swaziland System sequence which at a much later date acted as the basement upon which the layered rocks of the Mountain Land were deposited, A re-moblllzed border phase of this migmatite was largely responsible for the contact metamorphism around the edge of the Mountain Land and late hydrothermal solutions from this same intrusive granite resulted in the mineralization of the area. The isolated patches of black amphibolites situated well within the granite outcrop area, are considered to be isolated downfolded remnants of a once mote extensive sheet of Onverwacht. Their high grade metamorphic state, as with the Onverwacht rocks along the immediate contact zone. Is due to the effects of the Intrusive granites plus the re-heaied migmatite. Three distinct facies of contact metamorphism (related to the Nelspruit Granite) ate recognised in the area. The area can be divided into three fairly distinct structural zones, each one characterized by the good development (as compared to the other zones) of one or mote particular types or styles of deformation. Thus in the Consort Mine area (Zone I), a northwest-trending fold system is the strongest and most apparent structural feature. In the southern part of the area (Zone U), minor ctenulation and conjugate folds are very well developed. In the rocks along the granite contact zone (Zone IH), a metamorphic fabric and well/developed lineations associated with strong shearing, are the most noteworthy structural features. ’ Special attention was devoted to the accurate observation and recording of minor structural features. As a result of this, 4 distinct phases of deformation, corresponding fairly closely to those described by Ramsay (1963), were recognised. The first resulted in strong folding about northeast-trending axes and caused the formation of the major synclines (Including the Eureka and Lily Synclines) and the major faults (Including the Lily, Main Southern and Woodstock Faults). The first period was followed by the widespread development of cleavage, associated with which is the marked flattening and elongation of conglomerate pebbles,and development of various types of lineations including the alignment of metamotphic minerals along the immediate contact belt. Certain of the lineations appear to have formed mainly after crystallization of the granite, and are closely connected with the mechanical deformation (in the form of strong differential shearing) which affected the rocks along the contact. At a late stage during the 2nd period, hydrothermal solutions from the granites entered zones of strong shearing and structural disturbance which had started to develop in the layered rocks. The initial development of the 3rd fold stmctures (especially in the northwest part of the Mountain Land) is considered to have played an important part In the localization of these ore fluids. Both the 1st. and 2nd formed stmctures have been strongly deformed by a northwest-trending fold system. These 3rd phase folds teach their best development in the Consort Mine area where they constitute by far the strongest stmctural feature. This period of folding,which during the very early stages probably played a part in the localisation of the ore fluids, outlasted the mineralizing episode and in the Consort Mine area, strongly deformed the mineralized "Contact”. The marked inflection in the northwest part of the Mountain Land, including the "bending" of the Eureka and Ulundi Synclines, occuned at this stage. Most of the major faults truncate the 3rd folds and are thought to have formed, or to have been rejuvenated,at a late stage during this period of deformation. The 4th and final phase of deformation is represented by the fairly widespread development of minor crenulation and conjugate folds. Their development is largely controlled by the rock types and they only occur in lithologically favourable varieties. The maximum deforming stress which caused these folds must have been nearly vertical. These 4th structures are completely separate and unrelated to the main northwest-trending fold system (3rd structures) with which they were classed by Ramsay (1963), From an economic point of view, three zones of potential mineralization, corresponding in all cases to zones of strong shearing and stmcmral disturbance, occur in the area. The most Important is the silicified and mineralized zone (within the northern limb of the Lily Syncline) between basic schists of the Onverwacht and the overlying Fig-tree homfelses, known as the Consort "Contact" or Consort "Bar". Another potential zone of mineralization is the westward extension of the so-called Lily Fault which occupies exactly the same stratigraphic position as the Consort "Contact", viz. between shales and basic rocks of the Flg-uee and Onverwacht Series respectively, but within the northern limb of the Eureka Syncline. Finally, certain shaly horizons within the "footwall" quartzitic layers of the Consort Mine area also show signs of weak mineralization. / AC 2018
944

High-pressure megacrysts and lower crustal contamination: probing a mantle source for Proterozoic massif-type anorthosites

Bybee, Grant Michael 05 March 2014 (has links)
Many aspects of Proterozoic massif-type anorthosite petrogenesis have been, and remain, controversial. Mafic lower crust and depleted mantle have both been proposed as mutually exclusive sources of these near-monomineralic, temporally restricted batholiths. The debate surrounding the magma source has also led to uncertainty regarding the tectonic setting of these massifs, with a range of possibilities including convergent, divergent and anorogenic settings. The dramatic geochemical effects of crustal contamination in these massifs are well known and strong crustal signatures are evident in most, if not all, Proterozoic anorthosite massifs. The source debate, in the simplest sense, reduces to whether the ubiquitous crustal signature is derived principally from melting of a lower crust or is an effect of crustal assimilation. The origin of this crustal signature, and whether it obscures the original isotopic composition of the magmas or not, has fuelled the debate surrounding the source of the anorthosites. Using major element, trace element and isotopic compositions, as well as energyconstrained assimilation-fractional-crystallisation (EC-AFC) modelling from samples representing various stages of the polybaric crystallisation history of the magmas, including high-pressure megacrysts, anorthosites and their internal mineral phases, I remove the obfuscating effects of possible crustal contamination and probe the source of the magmas. In order to assess the effects of crustal contamination, if any, anorthosites from three massifs – the Mealy Mountains Intrusive Suite, Nain Plutonic Suite (both in eastern Canada) and Rogaland Anorthosite Province (Norway), have been analysed – all of which intrude into crust of significantly different age and chemical character. Sm-Nd geochronology of high-Al, high-pressure orthopyroxene megacrysts, as well as the comagmatic, host anorthosites, indicate that the magmatic system is long-lived, with an age difference between the megacrysts and hosts of ~110-130 million years. Isotopic compositions of primitive megacrysts qualitatively show that the magmas were derived from melting of the depleted mantle. Strong links between the isotopic offset from depleted mantle evolution and the age and composition of the surrounding crust confirm that the geochemical nature of the crustal contaminant plays a significant role in the petrogenesis of the anorthositic rocks. The geochronological indications of a long-lived magmatic system point to Proterozoic anorthosite formation in a continental magmatic arc – one of the only environments capable of supplying geographically-localised magma and heat to the base of the crust for over 100 million years. Proposed divergent or ‘anorogenic’ settings could not plausibly supply magma to the base of the crust for over 100 m.y. without initiating ocean formation or continental break-up. Anorthosite emplacement at mid-crustal levels may coincide with late- to post-orogenic events in several terranes, but evidence presented for a long-lived magmatic system is incongruent with this proposed setting. In this thesis, I propose that the petrogenesis of these intrusives must span both orogenic and post-orogenic periods. An overlap in megacryst crystallisation age with the onset of calc-alkaline orogenic magmatism in the Sveconorwegian Orogen, both occuring ~100 m.y. before anorthosite emplacement, confirms that initial magma and megacryst formation coincides with the main phase of magmatic and orogenic activity in a convergent magmatic arc. These geochronological constraints have implications for regional geodynamics in the Sveconorwegian Orogen (and the Labrador region) with the evidence providing corroboratory support for a long-lived accretionary orogen, as opposed to the widely-held view that the Sveconorwegian orogeny was predominantly collisional. Compositions of high-pressure megacrysts, anorthosites and analysis of internal isotopic disequilibrium indicates that lower crustal contamination has a significant influence on the isotopic composition of the rocks, with relatively minor contributions from the mid- to upper crust. Energy-constrained AFC modelling confirms that significant lower crustal contamination occurs during ponding of magmas at the Moho and is able to reproduce the observed isochronous isotopic compositions of the megacrysts as well as the compositions of the host anorthosites. Evidence of varying degrees of internal isotopic disequilibrium reinforces the significant role that assimilation of crust of different age and chemical nature have on the compositions of Proterozoic anorthosites. Unexpected patterns of isotopic disequilibrium show that anorthosite petrogenesis is not a “simple” case of progressive crustal contamination during polybaric ascent of viscous, partially-molten 4 magma mushes, but is more likely to involve significant differentiation and solidification at lower crust depths, followed by ascent of high-crystallinity bodies (> 50 % crystallinity) to upper crustal levels. Although the composition of the bulk continental crust is different to plagioclase-rich Proterozoic anorthosites, both are missing a mafic component. It is unclear how this missing mafic component was generated in the continental crust, because most of the evidence for these crustal differentiation processes is sequestered below or near the Moho. However, Proterozoic anorthosites, formed by viscous, plagioclase-rich mushes, entrain rare cumulate megacrysts from these depths and consequently preserve evidence of magmatic differentiation processes at the Moho. The evidence for the formation and sequestration of dense ultramafic cumulates in ponding magmas at the Moho can not only explain the missing mafic component in Proterozoic anorthosites, but also suggests that cumulate formation in crust-forming, arc environments is a significant process and should be taken into account in models dealing with evolution and differentiation of the continental crust. Sampling and petrographic and geochemical analysis of five pegmatitic segregations, or “pods”, from anorthosites of the Mealy Mountains Intrusive Suite reveal a diverse range of compositions from mafic, Fe-rich and Si-poor, to Fe-poor and Sirich felsic compositions and from monzogranite through quartz-monzodiorite and monzodiorite to Fe-P-rich gabbronorite. Each pod shows a range of noteworthy graphic, myrmekitic and symplectic textures on a variety of scales, along with distinctive mineralogical assemblages and highly-enriched trace element compositions. Derivitive minerals (e.g. apatite and zircon), high concentrations of Fe, Ti, P (and in some cases SiO2) and 10-1000 times chondrite enrichment suggest that many of the pods are highly fractionated. U-Pb zircon geochronology reveals that all the pods are the same age as the anorthositic hosts and confirms that the Mealy Mountains Intrusive Suite was emplaced between 1654 and 1628 Ma. Using the aforementioned evidence, I show that the pods represent the fluid-bearing, late-stage crystallisation products of a residual liquid in the massif anorthosite system and provide a window into the final stages of crystallisation in the anorthosite system. A range of rock types (monzonites, monzonorites, ferrodiorites and jotunites) observed in similar pod-like structures, as well as dykes and plutons, have also been documented in other Proterozoic anorthosite massifs. These have, at one time or another, controversially been interpreted as the residual liquids of anorthosite crystallisation. The observation of in-situ pods with similar compositions to all of the aforementioned rock types and displaying textures indicative of late-stage crystallisation support the notion that these associated lithologic units are comagmatic with, but residual to, the anorthosites and are not residual liquids of other crustally-derived rocks, immiscible liquids, parental magmas or cumulates. Isotopic compositions of these highly-fractionated, late-stage pods also overlap with those of anorthosites, lending further evidence to the case that upper crustal contamination plays only a minor role in developing the chemical signature of the anorthosites. With these results I propose that the nature/composition of the residual liquids of Proterozoic anorthosite magmas can vary dramatically, depending on geochemical differences in the original magma pulses and by mixing of mobilised, independently-evolved segregations of residual liquids. This process could explain why so many varied rock types associated with Proterozoic anorthosites have been suggested as residual liquids: these rocks all represent residual liquids resulting from varying degrees of differentiation, subsequent mobilisation, mixing and final solidification as plutons or dykes. Proterozoic anorthosite petrogenesis is an inherently polybaric process and so by its very nature produces a range of complicated and contradictory features which have clouded interpretation of numerous aspects of the rocks formation. In analysing crystallisation products from numerous stages of the anorthosites polybaric history, I have been able to probe the magmatic processes operating at different stages of Proterozoic anorthosite petrogenesis. In doing so I show that the magmas are derived from melting of the depleted mantle in continental-arc-like settings – two controversial aspects of Proterozoic anorthosite petrogenesis. These constraints on the source and tectonic setting will allow renewed investigation into the ultimate question surrounding Proterozoic anorthosites: why are these rock types restricted to the Proterozoic and what clues does this temporal restriction offer about Earth’s geodynamic evolution during this period? The assertion in this thesis that 5 Proterozoic anorthosites formed in arc environments dictates that subduction processes or geodynamic conditions during the Proterozoic favoured the production of voluminous masses of plagioclase, because modern-day magmatic arc terranes show no evidence of anorthosites with similar compositions. However, calcic anorthositic inclusions and xenoliths are observed in modern-day volcanic and continental arcs suggesting that anorthosites may be forming in these environments, but that conditions such as water content or style of subduction are different to the Proterozoic, producing less and compositionally different plagioclase and anorthosite. The results of this thesis shed new light on and refine the petrogenesis of Proterozoic anorthosites, but the focus of research must now shift to explaining the temporal restriction of these intrusions and the implications of this restriction for the geodynamic evolution on Earth during the Proterozoic.
945

The postcranium of the carnivorous cynodont Chiniquodon from the Middle Triassic of Namibia and the palaeo-environment of the Upper Omingonde Formation

Mocke, Helke Brigitte 22 January 2016 (has links)
A Dissertation submitted to the Faculty of Science, University of the Witwatersrand, in fulfilment of the requirements for the Degree of Master of Science Johannesburg, 2015 / The Chiniquodontidae is a family of Triassic carnivorous cynodonts well represented in the Middle-Upper Triassic of Argentina and Brazil. Chiniquodontids were more recently discovered in Madagascar and central Namibia, representing the only record of the family outside South America. The Namibian specimen was discovered in the Upper Omingonde Formation and is represented by the skull and a partial skeleton. The new chiniquodontid was identified as Chiniquodon and is diagnosed by the postcranial characteristics identified; a strong bend in the proximal portion of thoracic ribs, reduced curvature of the clavicle, although this may be due to deformation, robustness of the neck of the ilium, differences in the angulation between the edge of the posterior lamina of the ilium and the margin of the neck, and a large ischium, which is more than twice the size of the pubic plate. The postcranial material of the chiniquodontid from Namibia is described and compared with that of South American chiniquodontids. Chiniquodontids lack costal plates on ribs, show a tall and slender scapular blade, a large acromion process positioned well above the scapular neck and absence of disc-like phalanges in the autopodium. The Namibian Chiniquodon provides the first evidence of elements from the pes in chiniquodontids, and one of the few for non-mammaliaform cynodonts. Sedimentological studies confirm that the Upper Omingonde Formation of Namibia represents fluvial deposits of braided and meandering rivers formed in a predominately arid climatic regime during the Middle Triassic.
946

The dietary behaviour of early pleistocene bovids from Cooper's Cave and Swartkrans, South Africa

Steininger, Christine Marrie 06 March 2012 (has links)
Ph.D., Faculty of Science, University of the Witwatersrand, 2011 / There is ongoing speculation about how an increasingly arid environment contributed to the extinction of Paranthropus robustus, given that a mosaic landscape with a major part of the area consisting of predominantly open grassland environment accompanied by an escalating cooler drier climate remains the persistent palaeoecological reconstruction for this species. It has been suggested that P. robustus, a dietary specialist, was not able to adapt to an increasingly xeric habitat. This notion has been challenged by recent multi-disciplinary research on P. robustus remains, including stable light isotope and dental microwear analyses, which portray a more complex diet. Paranthropus robustus is present in a number of key fossil assemblages spanning the period ca. 1.8 to 1.0 Ma. Analysis of the stable carbon isotope composition of bioapatites and dental microwear texture analysis of different bovid taxa, associated with P. robustus remains from five discrete deposits, were used to reconstruct dietary behaviour and by inference availability of local resources. The overall pattern emerging from the bovid data indicates a more mixed and varied diet than previously thought, suggesting a heterogeneous environment, and hence a less static ecological profile for Paranthropus. The significant occurrence of mixed diets and relatively few obligate C4 grazers suggest that although C4 grasses were available in a mosaic environment, a C4-dominated ecosystem was not present. Swartkrans Member 2 (ca. 1.6 Ma) contains substantially more C3 feeders than other P. robustus deposits, signifying a vegetation community structure that was more C3-dominated than the other deposits. There is an apparent indication of shifting vegetation structure between P. robustus deposits. Thus, despite its derived craniodental morphology, P. robustus seems to have thrived through a range of climatic and ecological shifts by selecting from a variety of available foods present on the landscape.
947

The geology of the lily syncline and portion of the eureka syncline between the consort mine and Joe's lucic siding, Barberton mountain land

VILJOEN, Morris, James January 1963 (has links)
Thesis submitted for the degree of Master of Science in the Faculty of Science, University of the Witwatersrand, Johannesburg. / The following is an account of the stiatigiaphy, structure, metamorphism and mineralization in a complexly deformed area of the northwest part of the Barberton Mountain Land. It is situated at the eastern extremity of the Jamestown Hills and covets a region along the contact zone between the ancient layered rocks of the Archaean Complex and the Nelspruit Granite. In the first section is given a fairly comprehensive account of previous work done in the Barberton region- especially as it applies to the area under discussion. This is followed by a consideration of the petrology and stratigraphy of the area and a description of the various structures encountered. A more detailed statistical treatment of the minor structures is also included and from these results an attempt is made to unravel the tectonic history of the area and to fit it into the regional structural pattern of the Mountain Land as a whole. The area mapped consists of two basically Identical successions separated by a major high angled thrust fault. The northern succession, which has been quite strongly thermally metamorphosed, represents the fairly steeply south dipping northern limb of the Lily Syncline. That to the south has suffered very little metamorphism and forms part of the northern limb of the Eureka Syncline. A well developed and layered basic suite of rocks lying below the Fig-tree Series .and constituting the basal zone of the Lily Syncline, is classed in the Onverwacht Series, It lies in direct contact with the Nelspruit Granite and is considered to represent a metamorphosed succession of impure dolomites with arenaceous and minor shaly horizons, together probably with some basic and acid lavas. The Onverwacht rocks are overlain by metamorphosed Fig-tree shales and "lavas", and these in turn by metamorphosed conglomerates and quartzites of the Moodies System. At the base of the homfelses lies the Consort "Contact" or Consort "Bar", a siUcified, mineralized zone which is the main ore horizon of the Consort Mine. The homfelses grade into rocks which have been termed "lavas" but which are thought to be mote of the nature of crystalline tuffs. The succession to the south of the Main Fault Is on a broad scale Identical to the one just described above, differing mainly in metamorplilc state. Thus, whereas the Onverwacht rocks of the northern succession have been converted to hornblende and tremolite-actinollte schists, similar rocks to the south of the Main Fault have been changed to carbonate-bearing talc and chlorite phylUtes. The basic Intrusive rocks of the Jamestown are considered to be of a much smaller distribution than was previously thought,and are represented mainly by the massive bodies of pure serpentinite. There is a possibility however; that certain of the purer talccarbonate schists along the Kaap Rivet,represent altered ultrabasic intmsives. The Nelspruit gneiss and migmatlte is considered to represent a completely granitized pre-Swaziland System sequence which at a much later date acted as the basement upon which the layered rocks of the Mountain Land were deposited, A re-moblllzed border phase of this migmatite was largely responsible for the contact metamorphism around the edge of the Mountain Land and late hydrothermal solutions from this same intrusive granite resulted in the mineralization of the area. The isolated patches of black amphibolites situated well within the granite outcrop area, are considered to be isolated downfolded remnants of a once mote extensive sheet of Onverwacht. Their high grade metamorphic state, as with the Onverwacht rocks along the immediate contact zone. Is due to the effects of the Intrusive granites plus the re-heaied migmatite. Three distinct facies of contact metamorphism (related to the Nelspruit Granite) ate recognised in the area. The area can be divided into three fairly distinct structural zones, each one characterized by the good development (as compared to the other zones) of one or mote particular types or styles of deformation. Thus in the Consort Mine area (Zone I), a northwest- trending fold system is the strongest and most apparent structural feature. In the southern part of the area (Zone U), minor ctenulation and conjugate folds are very well developed. In the rocks along the granite contact zone (Zone IH), a metamorphic fabric and well/developed lineations associated with strong shearing, are the most noteworthy structural features. ’ Special attention was devoted to the accurate observation and recording of minor structural features. As a result of this, 4 distinct phases of deformation, corresponding fairly closely to those described by Ramsay (1963), were recognised. The first resulted in strong folding about northeast-trending axes and caused the formation of the major synclines (Including the Eureka and Lily Synclines) and the major faults (Including the Lily, Main Southern and Woodstock Faults). The first period was followed by the widespread development of cleavage, associated with which is the marked flattening and elongation of conglomerate pebbles,and development of various types of lineations including the alignment of metamotphic minerals along the immediate contact belt. Certain of the lineations appear to have formed mainly after crystallization of the granite, and are closely connected with the mechanical deformation (in the form of strong differential shearing) which affected the rocks along the contact. At a late stage during the 2nd period, hydrothermal solutions from the granites entered zones of strong shearing and structural disturbance which had started to develop in the layered rocks. The initial development of the 3rd fold stmctures (especially in the northwest part of the Mountain Land) is considered to have played an important part In the localization of these ore fluids. Both the 1st. and 2nd formed stmctures have been strongly deformed by a northwest-trending fold system. These 3rd phase folds teach their best development in the Consort Mine area where they constitute by far the strongest stmctural feature. This period of folding,which during the very early stages probably played a part in the localisation of the ore fluids, outlasted the mineralizing episode and in the Consort Mine area, strongly deformed the mineralized "Contact”. The marked inflection in the northwest part of the Mountain Land, including the "bending" of the Eureka and Ulundi Synclines, occuned at this stage. Most of the major faults truncate the 3rd folds and are thought to have formed, or to have been rejuvenated,at a late stage during this period of deformation. The 4th and final phase of deformation is represented by the fairly widespread development of minor crenulation and conjugate folds. Their development is largely controlled by the rock types and they only occur in lithologically favourable varieties. The maximum deforming stress which caused these folds must have been nearly vertical. These 4th structures are completely separate and unrelated to the main northwest-trending fold system (3rd structures) with which they were classed by Ramsay (1963), From an economic point of view, three zones of potential mineralization, corresponding in all cases to zones of strong shearing and stuctural disturbance, occur in the area. The most Important is the silicified and mineralized zone (within the northern limb of the Lily Syncline) between basic schists of the Onverwacht and the overlying Fig-tree homfelses, known as the Consort "Contact" or Consort "Bar". Another potential zone of mineralization is the westward extension of the so-called Lily Fault which occupies exactly the same stratigraphic position as the Consort "Contact", viz. between shales and basic rocks of the Flg-uee and Onverwacht Series respectively, but within the northern limb of the Eureka Syncline. Finally, certain shaly horizons within the "footwall" quartzitic layers of the Consort Mine area also show signs of weak mineralization. / AC 2018
948

Sequence stratigraphy of the arcadia formation, Southeast Florida: an integrated approach

Unknown Date (has links)
The Arcadia Formation is a mixed carbonate-siliciclastic rock unit that existed as a shallow carbonate ramp to platform environment during the Late Oligocene to Early Miocene Epoch. It can be divided into two distinct, informal sections based on lithological properties: the upper Arcadia Formation and lower Arcadia Formation. The sections are part of a major, third-order sequence that can be further divided into four higher-frequency, lower magnitude sequences: ARS1, ARS2, ARS3, and ARS4. The sequence boundary separating ARS2 and ARS3 represents a drastic change in the depositional regime from a high-energy, inner ramp/platform to a lower-energy, deep outer ramp environment. ARS3 represents the period of maximum flooding and constitutes a major portion of the regressive system tract (RST) of the third order depositional sequence. In certain sections, the Arcadia Formation is heavily bioturbated including ichnotaxa from the glossifungites, cruziana, and scolithos inchofacies. Thalassinoides sp. burrows of the glossifungites ichnofacies were found to be commonly associated with firmground substrates and breaks in sedimentation. The lithofacies associations were grouped into paleodepositional environments that ranged from restricted marine to deep outer ramp with lithology ranging from grainstone to wackestone to mudstone with variable amounts of siliciclastic and phosphatic constituents. Each sequence boundary extends regionally south from Broward County to southern Miami-Dade County utilizing gamma-ray geophysical signatures unique to each sequence. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection
949

A preliminary analysis of the basement structure of the Cenozoic Niger Delta basin : insights from high-resolution potential field data

Onuba, Leonard Nnaemeka January 2016 (has links)
No description available.
950

Dynamic topography and drainage of Africa and Madagascar

Paul, Jonathan David January 2014 (has links)
No description available.

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