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Дисертації з теми "Late Precambrian"

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Автор: Grafiati
Опубліковано: 10 грудня 2022
Оновлено: 28 січня 2023

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1

Cardenas, S. Fidel A. "The geochemistry of a late Precambrian weathering profile, northwest Scotland." Thesis, University of Strathclyde, 1986. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=21485.

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Анотація:
In an attempt to understand the environment of the Precambrian weathering at Rispond, and compare it with weathering processes taking place at the present time, samples weathered to different degrees have been taken at various distances immediately below the Cambrian Unconformity. These samples have been subjected to chemical analysis by X-ray fluorescence spectometry and wet analysis, and to mineralogical analysis by X-ray diffraction and polarised light microscopy. Interpretation of these results indicate that the samples represent a weathering profile (although not necessarily an unchanged one as these rocks have been subjected to a maximum temperature of 250°C during burial subsequent to the deposition of the Cambrian strata). This is inferred from the minerals present in the soil, the nature of the chemical changes observed, the similarities of the data on the Kronberg weathering diagram to those of present-day weathering, and the position of the profile immediately below the unconformity. Further interpretation of the results in terms of the thermodynamic properties of the minerals present in the profile, the chemical reactions believed to have taken place, the geological evidence and a survey of the chemical composition of present-day surface waters leads to the conclusion that the rocks below the Cambrian Unconformity at Rispond represent a fossil soil profile. These rocks contain pyrophyllite, considered to have been formed by low-grade metamorphism rather than by weathering. Three possible modes of origin have been considered, and that involving the weathering of potassium feldspar to kaolinite alone in an acid environment rejected. The two mechanisms involving the weathering of the feldspar to illite in an arid alkaline environment with restricted drainage are considered to be more likely. The illite produced in these mechanisms was further weathered to produce, in the one case, kaolinite, and in the other one, potassium beidellite as a mixed layer mineral with illite. These two mechanisms can be mixed in any proportion, the exact amount of potasium beidellite present depending upon the relative thermodynamic stabilities of kaolinite and beidellite. As the latter is unknown, further accuracy cannot be achieved at present. The presence of abundant potassium feldspar in the Fucoid Beds, and the existence of trace fossil planolites in such rocks as well as the temperature to which they have been heated (about 250°C) suggested the possible existence of an ammonium feldspar in the area. Therefore, a method to measure the amount of ammonia content in these rocks has been designed. The results of twenty-two samples from the Cambro-Ordovician succession of N.W. Scotland analysed by this method show that the ammonia content is very low. If all the ammonia is present as an ammonium feldspar (buddingtonite), it represents about 0.3% of the mineral in the shales and even less in other rock types.
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2

Sun, Weiguo. "Contributions to palaeontology and stratigraphic correlation of the late precambrian in China and Australia /." Title page, contents and summary only, 1985. http://web4.library.adelaide.edu.au/theses/09PH/09phs957.pdf.

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3

Al, Rajaibi Ibrahim Mohamed amur. "Origin and variability of the late Precambrian-Cambrian Athel Silicilyte, South Oman Salt Basin." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/origin-and-variability-of-the-late-precambriancambrian-athel-silicilyte-south-oman-salt-basin(4117c367-a1fa-4937-877e-d1391f95c406).html.

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The Precambrian-Cambrian Athel Silicilyte is an enigmatic chert unit of up to 390 m thick found as slabs (each slab typically 2 × 6 km across) entrapped within salt domes at a depth of 4-5 km in the South Oman Salt Basin. This formation is a prolific self-charged reservoir with high porosity (up to 34 %) and high oil saturation (80 %). Despite its economic value, the origin and the variability of this formation are not fully understood. This study therefore aims to investigate the variability and the origin (silica source and precipitation mechanism) of the Athel Silicilyte. Data obtained from core, wireline log and petrographical analysis were employed to establish the vertical and the lateral variability and, with the assistance of geochemical data, the likely source and precipitation mechanism of silica was determined.The Athel Silicilyte is only present in the deepest parts of the South Oman Salt Basin within the fault-bounded Athel Basin, bounded by two silt-rich mudstone units. Six lithofacies were recognised in the Athel Silicilyte that reflect variability in detrital material contents (three silica-rich facies), sediment remobilisation (slumped and brecciated lithofacies) and diagenetic modification (carbonate-bearing lithofacies), with the silica-rich facies being the most abundant (> 97 % of the total thickness). The Athel Silicilyte exhibits wavy discontinuous lamination and it is predominately (silica-rich facies average = 80 wt. %) composed of connected-networks of microcrystalline quartz (1-5 µm). Other constituent components are detrital quartz (3 wt. %), illite (10 wt. %), pyrite (4 wt. %) and organic carbon (TOC = 3 wt. %). The detrital contents increase towards the Upper Athel Silicilyte and towards the basin margins (ranging from 3 to 30 wt. %). The wavy laminations are interpreted to have a microbial origin. The homogeneity, loose packing of detrital grains and preservation of 390 m thick laminated fabric suggest that the Athel Silicilyte precipitated syndepositionally in microbial layers during low detrital input. The intense detrital input during bounding mudstones sedimentation inhibited Athel Silicilyte precipitation as a result of the rapid burial of microbial layers. The Athel Silicilyte shows strong enrichments of redox-sensitive elements (U, V and Mo), Mn-depletion, positive Ce anomalies, and small framboidal pyrites (3.6-4.0 µm), suggesting that the water column was euxinic during precipitation.Based on the petrographical evidence for the Athel Silicilyte forming as a syndepositional precipitate alongside seawater-like rare earth element (REE) characteristics, silica is interpreted to have been sourced directly from seawater. Mass balance calculations support this interpretation, indicating that silica-rich Precambrian seawater provided the significant silica mass in the Athel Silicilyte. The ability of dissolved silica to form hydrogen bonds with the functional groups (e.g. carboxyl and hydroxyl) in microbial layers was the key for Athel Silicilyte precipitation. The formation of hydrogen bonds was made possible under euxinic conditions, where the pH values were probably lower (< 7) than for the normal seawater as a result of HS- and H+ production by sulphate reducing bacteria and HS- oxidation at the redox boundary by sulphur oxidising bacteria. Consequently, dissolved silica was concentrated in microbial layer microenvironemnts, resulting in silica nucleation and polymerisation.
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4

Horak, Jana M. "The late Precambrian Coedana and Sarn complexes, Northwest Wales : a geochemical and petrochemical study." Thesis, Cardiff University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.580636.

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5

Wang, Ping. "Geology and Tectonic Significance of the Late Precambrian Eastern Blue Ridge Cover Sequence in Central Virginia." Diss., This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-06062008-142355/.

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6

Tribe, Ian Roger. "Deformation of granitoid rocks, Channel Islands, UK : Implications for the structural evolution of a late Precambrian arc." Thesis, Oxford Brookes University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262069.

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7

Herrington, Paul M. "Stratography, sedimentology and diagenesis of late Precambrian carbonates from the Upper Limestone-Dolomite 'series', central east Greenland." Thesis, University of Birmingham, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.694379.

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8

Killick, M. F. "Sedimentological and geochemical studies on late Precambrian sequences of the Eastern block of the Massif Ancien, High Atlas, Morocco." Thesis, University of Reading, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383479.

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9

Restrepo, Pedro Alonso. "Late Precambrian to Early Mesozoic tectonic evolution of the Colombian Andes, based on new geochronological geochemical and isotopic data." Diss., The University of Arizona, 1995. http://hdl.handle.net/10150/187450.

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Анотація:
⁴⁰Ar/³⁹Ar and U/Pb geochronology of the basement rocks in the Colombian Andes confirm the presence of the Grenvillian age high metamorphic grade belt . The Grenvillian, or locally known as Nickerie-Orinoquiense orogenic belt, is exposed within basements uplifts along the Eastern Cordillera of Colombia and the Sierra Nevada of Santa Marta in the Caribbean coast. Rare Earth element geochemistry and petrology indicate that the Nickerie-Orinoquiense basement rock's protoliths are dominantly of continental affinity, now consisting mainly of metapsammites, metavolcanics and metaplutonic rocks metamorphosed to granulite facies PT conditions. Nd crustal residence ages and U/Pb zircon data indicate variable involvement of 'older' Late Archean - Early Proterozoic components and 'younger' ~ 1.1 Ga additions, which were tectonically mixed during the Nickerie-Orinoquian collisional metamorphic episode. Low metamorphic grade rocks that overlie the Nickerie-Orinoquian basement are exposed along the Eastern Cordillera of Colombia at the Quetame-Floresta-Santander massifs, Périja Range and Merida Andes. A U/Pb zircon age obtained from a synkinematic pluton structurally concordant with the low metamorphic grade belt from the Santander Massif, yielded a 477 ± 16 Ma, indicating a Mid-Ordovician regional greenschist to amphibolite facies metamorphic event for these rocks. The latter is referred-to as the 'Caparonensis Orogeny' in the Venezuelan Andes. Rare Earth Element geochemistry and petrologic data indicate that the low metamorphic grade belt consists of a thick supracrustal sequence i.e. metapelitic-metapsammitic sequence with minor crosscutting mafic dikes. Additional trace element discrimination plots indicate that the Caparonensis synkinematic plutons are of continental arc affinity. ⁴⁰Ar/ ³⁹Ar geochronology, petrology and field observations in Santander Massif, indicate a widespread regional metamorphic overprint took place in Late Triassic-Early Jurassic time. This event was the result of a thermal welt associated with back-arc extension and concomitant intrusion of a high volume of calk-alkalic plutons. Deposition of a thick molassic sequence (2000-4000 m) followed, flanking the uplifted region. The lower Paleozoic metamorphic rocks were elevated from greenschist to sillimanite (locally kyanite) PT metamorphic conditions and the Mid-Upper Paleozoic sedimentary cover was locally metamorphosed from greenschist to lower PT metamorphic conditions, as a function of relative distance to the plutonic centers at time of metamorphism.
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10

Larkin, Emma A. "FIELD, GEOCHRONOLOGIC, AND GEOCHEMICAL CONSTRAINTS ON LATE PRECAMBRIAN TO EARLY PALEOZOIC TERRANE ACCRETION IN THE SOUTHERN APPALACHIAN BLUE RIDGE PROVINCE." UKnowledge, 2016. http://uknowledge.uky.edu/ees_etds/39.

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Xenolith-bearing orthogneiss of Amazonian affinity discovered in the Dellwood quadrangle in the Blue Ridge basement complex represents the oldest crustal component of the southern Appalachians (1.33 – 1.37 Ga: Quinn, 2012). New U-Pb zircon ages for migmatitic paragneiss of the Cartoogechaye terrane exposed in the Dellwood quadrangle reveal two unique detrital zircon age signatures that indicate either a local eastern Laurentian margin source or an exotic source. Detailed mapping, whole rock geochemistry, and U-Pb zircon geochronology were conducted to determine whether this exotic crustal component extends farther south into the Hazelwood 7.5” quadrangle. Lithological similarities exist between paragneisses in the Dellwood quadrangle and those in the Hazelwood quadrangle. However, the increase in proportion of leucosome and polyphase folding prevent direct correlation of lithologies between the areas. Whole rock major element compositions overlap the composition of basement orthogneisses. Zircon ages of six paragneiss samples reveal multiple detrital zircon age modes that are dominated by two Grenville modes at ~1050 and 1150 Ma. Minor zircon populations exist at ~450 – 480, 700 – 900, and 1300 – 1500 Ma. Age distributions and compositional trends are evidence that the protolith of the paragneiss in the Hazelwood quadrangle was Neoproterozoic rift sediments with a dominant Laurentian margin source.
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11

Singh, Updesh. "Late Precambrian and Cambrian carbonates of the Adelaidean in the Flinders Ranges, South Australia : a petrographic, electron microprobe and stable isotope study /." Title page, abstract and contents only, 1986. http://web4.library.adelaide.edu.au/theses/09PH/09phs1792.pdf.

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12

Temperley, Stephen. "The late Proterozoic to early Palaeozoic geological development of the Glen Banchor area in the Monadhliath Mountains of Scotland : with particular reference to deformation in late-Precambrian shear zones and in the Central Highland steep belt." Thesis, University of Hull, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293171.

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13

Haines, Peter W. "Carbonate shelf and basin sedimentation, late Proterozoic Wonoka Formation, South Australia /." Title page, contents and summary only, 1987. http://web4.library.adelaide.edu.au/theses/09PH/09phh152.pdf.

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14

Walsh, Kevin B. Jr. "GEOCHRONOLOGICAL AND GEOCHEMICAL CONSTRAINTS ON THE ORIGIN OF THE CARTOOGECHAYE TERRANE, WESTERN NORTH CAROLINA: IMPLICATIONS FOR THE LATE PRECAMBRIAN TO EARLY PALEOZOIC EVOLUTION OF THE EASTERN LAURENTIAN MARGIN." UKnowledge, 2018. https://uknowledge.uky.edu/ees_etds/57.

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The Cartoogechaye terrane (CT) is an enigmatic migmatite terrane within the Central Blue Ridge province of the southern Appalachians. Previous work identified exotic Pb isotope compositions within the CT (Quinn, 2012). More recent studies that mapped the extent of potentially exotic metaigneous lithologies yield U-Pb zircon ages consistent with a native Laurentian margin metasedimentary origin (Larkin, 2016). This study focused on the possible extent of similar lithologies in the Clyde quadrangle and provides further constraints on the crustal affinity of the CT. The Clyde quadrangle consists of four distinct lithologic packages: the CT, Ashe metamorphic suite, Great Smoky Group, and Grenville basement. Five samples within the Clyde quadrangle and one sample from Wayah Bald quadrangle were collected for detrital zircon (DZ) U-Pb geochronology and whole rock geochemistry for comparison similar anlayses from other bedrock units in the region. Dominant DZ age modes consist of the Grenville doublet (1050 Ma and 1150 Ma) or a modified version of it. Minor age modes exist at ~450 Ma, 600-750 Ma, and 1300-1550 Ma. Zircons for all but one sample display heterogeneous external and internal cathodoluminescence morphologies, consistent with a sedimentary protolith for the paragneisses. Whole rock compositions are consistent with weathering of and derivation from a local basement source. U-Pb age data are most consistent with an eastern Laurentian sedimentary provenance for five samples. The presence of 450-460 Ma grains is most consistent with high-grade Taconian regional metamorphism. The lack of a major Shawinigan age mode and zircon morphology for ca. 980-1050 Ma metamorphic zircons indicate that sample CLY16-1 is a syn-orogenic metasediment within the Grenville basement underlying the CT.
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15

Simmons-Ferguson, Heather Elizabeth. "Total and organic mercury in periphyton from a Precambrian shield lake." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/mq21700.pdf.

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16

Davis, Chris. "Habitat, distribution and abundance of juvenile lake trout, sculpin and burbot in four small, precambrian shield lakes in Ontario." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ27344.pdf.

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17

Allan, Craig James. "Lake ice cover development and meltwater mixing in the spring acidification of small Canadian Precambrian Shield lakes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1987. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq21669.pdf.

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18

Halter, Ghislaine. "Zonalite des alterations dans l'environnement des gisements d'uranium associes a la discordance du proterozoique moyen (saskatchewan, canada)." Université Louis Pasteur (Strasbourg) (1971-2008), 1988. http://www.theses.fr/1988STR13078.

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Cette etude porte sur les conditions des gisements d'uranium du saskatchewan de la region de waterbury lake, qui sont associes a la discordance entre le socle archeen/aphebien et la couverture sedimentaire helikienne. Deux episodes tardi-hudsoniens gouvernent la remobilisation in situ de l'uranium: une retromorphose (facies schiste vert) et une alteration hydrothermale affectant les zones tectonisees du socle. Les donnees isotopiques des phyllites revelent que la diagenese des gres est realisee en presence d'une saumure qui est egalement a l'origine du fluide mineralisateur
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19

Sun, Weiguo. "Contributions to palaeontology and stratigraphic correlation of the late precambrian in China and Australia / by Sun Weiguo (W.G. Sun)." Thesis, 1985. http://hdl.handle.net/2440/20400.

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20

Myrow, Paul Michael. "Sedimentology and depositional history of the Chapel Island Formation (late Precambrian to early Cambrian) southeast Newfoundland /." 1987. http://collections.mun.ca/u?/theses,97100.

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21

Haines, Peter W. "Carbonate shelf and basin sedimentation, late Proterozoic Wonoka Formation, South Australia." Thesis, 1987. http://hdl.handle.net/2440/21574.

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Five folded ill. in pocket; Bibliography: leaves 141-152; ix, 152, 12 leaves, [17] leaves of plates : ill. (some col.) ; 31 cm.
Thesis (Ph.D.) -- University of Adelaide, Dept. of Geology and Geophysics, 1987
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22

Theron, Salomon Johannes. "The North Break Zone of the late Precambrian Otavi carbonate platform sequence in Namibia: stratigraphic setting, petrography and relationship with Tsumeb Cu-Pb-Zn deposit." Thesis, 2014. http://hdl.handle.net/10210/10360.

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M.Sc. (Geology)
The main objective of this study was to characterize the North Break Zone of the Otavi Mountain Land, Namibia in terms of stratigraphy and petrography and to investigate its relationship with the Tsumeb ore body and other mineralized prospects in the immediate vicinity of Tsumeb. The Late Proterozoic Otavi carbonate platform sequence is famous for its base metal deposits. The North Break Zone is a stratabound zone of sporadic mineralization, brecciation and silicification occurring in the lower part of Iithozone T6 of the Hoffenberg Formation (Tsumeb Subgroup). It intersects the pipe-like Tsumeb Cu-Pb-Zn-Ag ore body at a depth of about 900m below surface. Where the North Break Zone intersects the Tsumeb ore body large massive ore associated with calcitized dolomite, dolomite breccia as well as feldspathic sandstone lenses occur. These features extend along strike and dip outside the normal dimensions of the Tsumeb ore body. The genesis of the Tsumeb ore body is poorly understood. The conventional model is that meteoric fluids circulated through the so-called North Break Zone paleo-aquifer, dissolving carbonate and giving rise to solution collapse and eventually the creation of the Tsumeb karst pipe. However, no direct evidence is available to support this model. This study was devised to critically evaluate the relationship between the North Break Zone and formation of the Tsumeb ore body. The study entailed field mapping, detailed sampling of the stratigraphic sequence and ore bodies, white light, reflected light, UV/blue light and cathodoluminescence petrography. Cathodoluminescence proved to be the most effective petrographic tool for differentiating various carbonate phases. The North Break Zone is defined as a 10 to 14m thick chert free oolitic to intraclastic dolomitic grainstone, stromatolite and mudstone unit, in which discontinuous lenses of mineralized secondary quartz are present. It is interbedded with dark grey cherty micritic dolomite of Lithozone T6 of the HOffenberg Formation. Minor calcification, Cu-Pb-Zn mineralization and manganese and iron enrichment are associated with the quartz-rich bodies. The mineralized quartz bodies are only present up to 2.5km to the west and 2.6km to the east of the Tsumeb ore body. The petrographic study indicated that 1) the epigenetic sequence of carbonate alteration, precipitation of new carbonate phases and mineralization is virtually identical in all Cu-Pb-Zn occurrences and 2) that the mineralization is closely associated with Mn-bearing brightly luminescent (CL) carbonates. Earlier Cu-Pb-Zn sulphide mineralization is associated with Mn-bearing bright red luminescent sparry dolomite (dolomite IIIB). Late stage Cu-arsenate, oxide and silicate mineralization is associated with an episode of Mn-bearing bright yellow luminescent calcite (calcite II) which also causes dolomitization of the associated dolomites. A very simple paragenetic model of mineralization is proposed. The earliest is defined by pre-mineralization calcite (calcite I) vein formation with associated dolomitization. This phase is followed by deposition of kerogen luminescent Mn-bearing dolomite IIIB - quartz and Cu-Pb-Zn sulphides representing the main mineralization event. It is followed by a late mineralization event composed of Mn-bearing calcite (calcite II) with associated Cu-arsenates, oxides and silicates. Supergene alteration is represented by the precipitation of very late stage non-luminescent Mn and Fe-poor calcite (calcite III) and quartz without any associated Cu-Pb-Zn mineralization. The sequence of mineralization is explained by the evolution of a single hydrothermal fluid, from relatively cold to hot and then back to cold, during a major period of fluid migration through the carbonate platform sequence. The North Break Zone probably never acted as a paleo-aquifer for fluids that formed the Tsumeb ore body. Rather hydrothermal fluids moved from the Tsumeb ore body into the North Break Zone. Hydrothermal fluids may have been derived from the Damara orogen to the south of Tsumeb during a period of tectonic loading and thrust deformation.
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