Dissertations / Theses: 'Isotope geology'

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Morante, Richard. "Permian-Triassic stable isotope stratigraphy of Australia." Phd thesis, Australia : Macquarie University, 1996. http://hdl.handle.net/1959.14/47568.

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"September, 1995"
Thesis (Ph.D.) -- Macquarie University, School of Earth Sciences, 1996.
Bibliography: leaves 171-183.
Introduction -- Australian ð¹³Corg-isotope profiles about the Permian-Triassic (P/TR) boundary -- Strontium isotope seawater curve in the late Permian of Australia -- ð¹³Cco₃ AND ð¹⁸Oco₃ seawater profiles through the Permian-Triassic of Australasia -- Paleomagnetic stratigraphy about the Permian/Triassic boundary in Australia -- Synthesis.
The Permian-Triassic boundary mass extinction is the largest in the Phanerozoic and therefore is the major event in the Phanerozoic. The mass extinction cause is problematical but studying global geochemical and geophysical signatures about the Permian-Triassic boundary can provide insights into the cause of the mass extinction. Global events about the Permian-Triassic boundary are marked by changes in: ð¹³C values of carbon ; ⁸⁷Sr/⁸⁶Sr in unaltered marine calcite ; magnetic polarity. -- This study aims to identify these features in the sedimentary record and to test the ca libration of the Australian biostratigraphical schemes to the global geological timescale. The following features are found in the Permian-Triassic sediments of Australia: a ð¹³Corg in Total Organic Carbon excursion in 12 marine and nonmarine sections from Northwest to Eastern Australia ; a ⁸⁷Sr/⁸⁶Sr minimum in a composite section mainly from the Bowen Basin ; a magnetic polarity reversal in the Cooper Basin, central Australia. The Australian sections are thus time correlated, as follows: The negative ð¹³Corg excursion indicates the Permian-Triassic boundary and occurs: 1) in Eastern and Central Australia at the change from coal measures to barren measures with red beds at the beginning of the Early Triassic coal gap; 2) in Northwest Australia about the boundary between the Hyland Bay Formation and the Mount Goodwin Formation in the Bonaparte Basin and at the boundary between the Hardman Formation and the Blina Shale in the Canning Basin. The base of the negative ð¹³Corg excursion lies at or near the base of the Protohaploxypinus microcorpuspalynological zone. The ⁸⁷Sr/⁸⁶Sr minimum determined about the Guadalupian/Ochoan stage boundary in North America is found in the Bowen Basin about the boundary between the Ingelara and Peawaddy Formations. The ð¹³Corg excursion in the Cooper Basin is near a magnetic reversal within the Permo-Triassic mixed superchron. The implications of these findings include: confirmation of the traditional placement of the Permian-Triassic boundary at the coal measures/barren measures with redbeds boundary in Eastern Australia ; the linking of the the Permian-Triassic boundary to a mass extinction of plant species on land and the beginning of the Triassic coal gap indicated by the Falcisporites Superzone base that is coincident with the negative ð¹³Corg excursion ; a mass extinction causal model that links the ⁸⁷Sr/⁸⁶Sr minimum determined about the Guadalupian/Ochoan stage boundary to a fall in sealevel that led to changing global environmental conditions. The model invokes greenhouse warming as a contributing cause of the mass extinction.
Mode of access: World Wide Web.
xii, 183 leaves ill., maps

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Nicholas, Christopher John. "Strontium isotope stratigraphy in the Cambrian system." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321030.

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Diamond, Roger Edward. "Stable isotope hydrology of the Table Mountain group." Doctoral thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/21190.

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Rain was collected from 2010 to 2012 at 15 locations around the Cape Fold Belt, at the same time as samples from rivers, springs, seeps and boreholes, totalling 435 samples. Precipitation ranged from -75 ‰ to +40 ‰ for δD and -12 ‰ to +8 ‰ for δ¹⁸O , showing seasonal patterns, with lower δ values in winter and higher in summer. Certain anomalous δ values can be attributed to individual weather events, such as thunderstorms. Using weighted data, the meteoric water line is δD = 6.15 δ¹⁸O + 8.21, which is similar to previous equations. The best fit line for groundwater δ values is δD = 7.09 δ¹⁸O + 10.08, the steeper gradient and higher intercept reflecting the predominance of heavy rainfall events with lower δ values in recharge, known as selection. The range of -47 ‰ to 0 ‰ for δD and -8 ‰ to -1 ‰ for δ¹⁸O values for all groundwater data is about half that of the rain values, due to the averaging effect from mixing during groundwater flow. Rainfall isotope composition is negatively correlated with continentality, as defined by the product of distance to the Atlantic and the closest coast. Isotope composition of rainfall is also strongly negatively correlated with altitude. Sites that are elevated within the landscape have a reduced altitude effect, such as tall peaks, whereas mountain valleys display enhanced altitude effects. Temporal and spatial variations in the strength of the amount effect reveal meteorological variability and emphasise the need for long term monitoring.

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Yu, Chunjiang. "Lead isotope compositions of subducting sediments around the Pacific." Online access for everyone, 2005. http://www.dissertations.wsu.edu/Thesis/Fall2005/c%5Fyu%5F101705.pdf.

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Petach, Tanya N. "The Strontium Isotope Record of Zavkhan Terrane Carbonates: Strontium Isotope Stability Through the Ediacaran-Cambrian Transition." Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:14398540.

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First order trends in the strontium isotopic (87Sr/86Sr) composition of seawater are controlled by radiogenic inputs from the continent and non-radiogenic inputs from exchange at mid-ocean ridges. Carbonates precipitated in seawater preserve trace amounts of strontium that record this isotope ratio and therefore record the relative importance of mid-ocean ridge and weathering chemical inputs to sea water composition. It has been proposed that environmental changes during the Ediacaran-Cambrian transition may have enabled the rapid diversification of life commonly named the “Cambrian explosion.” Proposed environmental changes include 2.5x increase in mid-ocean ridge spreading at the Ediacaran-Cambrian boundary and large continental fluxes sediment into oceans. These hypotheses rely on a poorly resolved strontium isotope curve to interpret Ediacran-Cambrian seawater chemistry. A refined strontium isotope curve through this time period may offer insight into the environmental conditions of the early Cambrian. New age models and detailed mapping in the Zavkhan terrane in west-central Mongolia provide the context necessary for robust geochemical analysis. This study aims to better resolve the coarse strontium isotope curve for the early Cambrian period by analyzing carbonate sequences in the Zavkhan basin. These carbonate sections are rapidly deposited, have undergone little diagenesis, and are likely to preserve a primary seawater signal. Strontium isotope analysis of these sequences was carried out to determine changes in hydrothermal activity and weathering fluxes during this time period. Recompiling these data with a global dataset of strontium isotopes through this time period indicates a stable strontium isotope signal through much of the early Cambrian. These data do not support previous hypotheses attributing the driving mechanism for the early Cambrian transition from Mg-dominated to Ca-dominated seas to increased sea floor spreading rates.

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Phillips, Robert John. "Isotope hydrogeology and aqueous geochemistry of selected British Columbia hotsprings." Thesis, University of Ottawa (Canada), 1994. http://hdl.handle.net/10393/10156.

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Hydrogeochemical analyses of the thermal waters at Hotsprings Cove, west coast Vancouver Island, reveal the presence of a stable geothermal reservoir. Temperature (50.5$\sp\circ$C), and aqueous geochemical data are nearly identical to those dating back to 1898. $\delta\sp $O-D plots indicate local recharge for these thermal waters, whereas radiocarbon isotopes suggest mean residence times of several thousand years and modification by sulphate-reducing bacteria. Bromide/chloride ratios, when considered with tritium and $\sp{34}$S data, are indicative of minor seawater mixing near the discharge zone. Binary mixing models, with local recharge waters and local seawater as end-member components, point to maximum local seawater contributions of about 1% and 4% for Hotsprings Cove and associated Mate Island thermal waters, respectively. Most chemical and isotopic geothermometer estimates are 90$\sp\circ$C. The Ahouset hotspring, located 12 km south of Hotsprings Cove has low total dissolved solids, a pH of 10.05, and a different geochemistry. Data from the Selkirk Range show a consistent sodium-sulphate geochemistry among the three hotsprings sampled in the Kuskanax Batholith. All waters have low bicarbonate content. $\sp $C values in excess of 100 pmc at the Nakusp hotspring imply incorporation of $\sp $C-active DIC from soil zone organics entrained during recharge, with possible additional $\sp $C contributions occurring due to sulphate reduction and incorporation of soil zone organics during mixing with non-thermal groundwaters near discharge. $\sp $C-derived mean residence times for the sulphide-rich waters of Halcyon hotspring are also short; possibly ${\sim}$1000 years. Geothermometer estimates for all three springs are consistent and fall into two groups, one group near ${\sim}$90$\sp\circ$C and the other between 115$\sp\circ$C and 155$\sp\circ$C. (Abstract shortened by UMI.)

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Beck, Kimberly D. "Investigation of the Lead Isotope Signatures of Marine Sediments in Relation to the Lead Isotope Signatures of Northern Andean Ores." FIU Digital Commons, 2015. http://digitalcommons.fiu.edu/etd/2201.

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Lead isotope ratios of ores and igneous rocks in the Central and Southern Andes show a large-scale geographic pattern related to magmatic source processes. This pattern changes in the Northern Andes for reasons that are not well understood; this study is an investigation of potential causes of this change. Deep ocean sediment samples from the Nazca Plate were analyzed for 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb, and the data were compared with published data on central Andean ores and ores and igneous rocks from Ecuador. Lead isotopic compositions of the Nazca Plate sediments are quite homogenous and are a close match with Andean ore lead in the coastal arc from central Perú through south-central Chile. However, the lead isotope ratios of the sediment samples are much lower than northern Perú and Ecuador ores. Variations in sediment composition are probably not the source of the northern Andean ore lead isotope pattern.

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Jones, Charles Edward. "Strontium isotopes in Jurassic and Early Cretaceous seawater." Thesis, University of Oxford, 1992. http://ora.ox.ac.uk/objects/uuid:fe3733bd-8e31-4bba-a78b-6d8275a0075f.

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The collection and analysis of a large number of belemnites and oysters with excellent biostratigraphic and diagenetic control has resulted in a highly detailed determination of the seawater Sr-isotope curve through the Jurassic and Early Cretaceous. The new data confirm the broad trends established by previous work, but the much sharper resolution of the new data allows the application of Sr-isotope stratigraphy with an optimal stratigraphic resolution of ± 1 to 4 ammonite subzones (± 0.5 to 2 Ma). The data show a general decline from the Hettangian (Early Jurassic) to a minimum in the Callovian and Oxfordian (Middle/Late Jurassic). This is followed by an increase through the Kimmeridgian (Late Jurassic) to a plateau reached in the Barremian (Early Cretaceous). In addition, there are major negative excursions in the Pliensbachian/Toarcian (Early Jurassic) and Aptian/Albian (Early Cretaceous). Stable isotope data collected from belemnites and oysters have resulted in the most extensive Jurassic δ¹³C and δ¹⁸O database to date. While both the carbon and oxygen data appear to give reasonable marine signals, the scatter in the data suggests that future research must document possible biological fractionation effects and develop better indicators for the diagenetic alteration of 613C and 6i 8O. The final chapter documents an unexpected correlation between sudden shifts in the Sr-isotope curve, the occurrence of positive 513C excursions, and the eruption of flood basalts. In the Jurassic and Cretaceous there is a correlation in time between sudden downward shifts in the Sr-isotope curve (Pliensbachian, Aptian, Cenomanian/Turonian), the occurance of positive 613C excursions, and the eruption of flood basalts. Each of these major downward shifts in the Sr-isotope curve is followed by a sudden upward shift, which although associated with a positive 613C excursion is not associated with an episode of flood basalt volcanism. In the Cenozoic the Sr-isotope curve no longer displays downward shifts, but the correlation continues between the occurrence of flood basalts and positive 513C excursions. Several lines of evidence suggest that the eruption of flood basalts is associated with pulses of hydrothermal activity, and that this hydrothermal activity brings about the conditions necessary for the genesis of carbon-burial events.

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Elders, Christopher Frank. "Caledonian tectonics from stratigraphy and isotope geochemistry of lower palaeozoic successions." Thesis, University of Oxford, 1987. http://ora.ox.ac.uk/objects/uuid:bf48a950-7ffb-4b58-bae3-915a2f7b5a94.

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The Southern Uplands of Scotland is interpreted as a Lower Palaeozoic accretionary complex which formed on the northern margin of the Iapetus Ocean. Seven conglomerates which contain detritus derived from the north-west, from sources on the Laurentian continental margin, were studied. Granite clasts in five of the conglomerates have distinct petrographic and geochemical characteristics which indicate that separate source areas supplied detritus to the Southern Uplands at different times. The Llandeilo Corsewall Point and Caradoc Glen Afton conglomerates, which occur in Tracts 1 and 2 of the Northern Belt, contain granite clasts that yield similar Rb-Sr whole-rock isochron ages (c. 1,200 Ma, 600-660 Ma and c. 475 Ma) and similar Sm-Nd model ages. This suggests that the clasts in the two conglomerates were derived from related sources. Some of the granite clasts in the early Ashgill Shinnel Formation conglomerate, which occurs in Tract 3 of the Northern Belt, resemble those in the Corsewall Point conglomerate, but most are petrographically and geochemically distinct, and yield younger Sm-Nd model ages. The lower Llandovery Pinstane Hill conglomerate occurs in Tract 4 of the Central Belt, and contains granitic detritus which yields a Rb-Sr whole-rock isochron age of 458 ± 26 Ma and has similar characteristics to the clasts in the Shinnel Formation conglomerate. The granite clasts in the Corsewall Point and Glen Afton conglomerates are of a different age to the granite intrusions of northern Scotland, and are unlikely to have been derived from this region. Conglomerates in the Midland Valley contain granite clasts with different petrographic and isotopic characteristics to those supplied to the Southern Uplands during the Llandeilo and Caradoc. However, north-west Newfoundland has a similar igneous history to that recorded by the Southern Uplands clasts, which could be derived from this region. The clasts supplied to the Shinnel Formation and Pinstane Hill conglomerates during the Ashgill and Llandovery have more in common with the granitic detritus in the Midland Valley. Thus, the Southern Uplands form a distinct Caledonian terrane which was south-east of Newfoundland in the Llandeilo, and was affected by sinistral strike-slip displacements during and after accretion.

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Wartho, Jo-Anne. "Argon isotope systematics and mineralogy of metamorphic hornblendes from the Karakoram." Thesis, University of Leeds, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304839.

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Bates, Steven Matthew. "Conodont oxygen isotope records of late carboniferous paleoenvironmental variability /." free to MU campus, to others for purchase, 2004. http://wwwlib.umi.com/cr/mo/fullcit?p1426047.

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Dove, Melissa B. "The geology, petrology, geochemistry and isotope geology of the eastern St Peter Suite western Gawler Graton, South Australia /." Title page, contents and abstract only, 1997. http://web4.library.adelaide.edu.au/theses/09SB/09sbd743.pdf.

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Thesis (B. Sc.(Hons))--University of Adelaide, Dept. of Geology and Geophysics, 1998.
National Grid Reference 1:250 000 Geological Series Sheet SI 53-2 and Sheet SI 53-6. Includes bibliographical references (6 leaves ).

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Bajjali, William Tawfiq. "Recharge and regional circulation of thermal groundwater in northern Jordan using isotope geochemistry." Thesis, University of Ottawa (Canada), 1994. http://hdl.handle.net/10393/6671.

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The scarcity of water resources in Jordan poses difficulties for the development of the country and its relationship with its neighbours. Thermal groundwaters recently identified in the northern part of the country represent a 40 MCM/y resources for exploitation to meet the increasing demand for water. These thermal groundwaters are found in three well fields (Mukhebeh, JRV and Ramtha) and were investigated to determine their recharge origin, mean subsurface residence times, and the source of heat. They discharge in the northern part of Jordan Rift Valley and the rifted Yarmouk Valley, which are low elevation (50 to 150 m below sea level) zones of recent tectonism and volcanic activity. The range of temperatures is 30 and 56$\sp\circ$C and salinities vary between 500 and 2500 mg/l. Non-thermal groundwaters within the study area have also been studied. In particular shallow groundwater in adjacent highlands region (Ajloun Mountains) are examined to determine their role in recharge to those regional flow systems. The principal aquifer is the Upper Cretaceous B2/A7 group, a package of carbonate formations with high kerogen content at depth. This aquifer outcrops in the Ajloun Mountains and flanking regions and is confined by overlying marls in the down gradient regions. A deeper sandstone aquifer underlies the study area and hosts thermal groundwater which was sampled in the Ramtha area. The major geochemical processes in the subsurface have generated various geochemical facies in the thermal waters. These include carbonate dissolution to calcite saturation in the recharge areas. The thermal groundwater in Mukhebeh and JRV well fields are found to be chemically similar to the carbonate groundwater from Ajloun mountains recharge area. All thermal waters are characterized by sulphate reduction, driven by oxidation of kerogen. Sulphate is of marine evaporite origin dissolved from within the aquifer with a component of volcanogenic sulphur. Some thermal waters have also Na-Cl salinity component related to evaporite dissolution. The thermal waters are of meteoric provenance, originating as rain falling over the carbonate highlands in Jordan and Syria. The $\delta\sp $O and $\delta$D isotopic data show that all thermal groundwaters are largely associated with Eastern Mediterranean Meteoric Water Line, signifying recharge under the climate regime which dominates today in Jordan. The exception is groundwater from the deep sandstone aquifer which is associated with Global Meteoric Water Line, signifying recharge during Pleistocene time. The isotopic composition of groundwater suggests two distinct recharge areas for the Mukhebeh well field: Ajloun Mountains (Jordan) and Mount Hermon (Syria). (Abstract shortened by UMI.)

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Bradbury, Harold John. "Calcium isotope insight into the global carbon cycle." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/273425.

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Over the course of my PhD, I developed the analytical capability to measure calcium isotopes at the University of Cambridge and analyzed calcium isotopes in a range of fluids and minerals in modern and past environments. After discussing my methodological development, I report my work in the glacial precursor to the Dead Sea. Here, the calcium isotope composition of aragonite varies synchronously with lake level fluctuations over the last 70,000 years. My numerically reconstructed lake calcium budget led me to conclude that 20,000 years ago, the Dead Sea was wetter than modern conditions, rather than colder and drier, as had previously been proposed. The primary focus of my PhD research was understanding the sedimentary sink for carbon. The formation of authigenic carbonate in marine sediments is caused by the microbial degradation of organic matter. I used pore fluid measurements and a numerical model to identify zones of authigenic carbonate precipitation. This knowledge was then combined with an understanding of the microbial processes that occur beneath the seafloor to determine the link between microbial activity and authigenic carbonate formation. Two processes, sulfate reduction and the anaerobic oxidation of methane were determined to be the main drivers of authigenic carbonate precipitation. In order to assess the importance of the carbon isotope signal imparted by each of the two identified processes, I created Artificial Neural Networks to predict the areal extent of authigenic carbonate precipitation and the dominant microbial process driving the precipitation. My ANNs identified that 37% of the modern seafloor is precipitating authigenic carbonate, which leads to a flux of 1.2*10^12 moles of carbon per year, of which 88% is due to the anaerobic oxidation of methane, and 12% is due to sulfate reduction. This represents 2-3% of the modern global carbon deposition, however I was able to show that this would be significantly higher in the geological past when ocean conditions were vastly different to how they are today. Finally, I conclude by proposing that some variations in the global carbon cycle in the past can be explored by linking marine calcium concentrations to authigenic carbonate formation and the flux of alkalinity from the seafloor.

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Graham, David W. "Helium and lead isotope geochemistry of oceanic volcanic rocks from the East Pacific and South Atlantic." Woods Hole, Mass. : Woods Hole Oceanographic Institution, 1987. http://catalog.hathitrust.org/api/volumes/oclc/17021004.html.

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Thesis (Ph. D.)--Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution, 1987.
Funding was provided by the National Science Foundation under grants OCE 15270 and OCE 16082.

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Burgess, Jamie M. "Carbon isotope stratigraphy of the interglacial Umberatana Group, Adelaide, Fold Belt, South Australia /." Title page, contents and abstract only, 1999. http://web4.library.adelaide.edu.au/theses/09PH/09phb9552.pdf.

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Heerden, Leon Andre van. "A nitrogen and carbon stable isotope study of some Western Australian diamonds." Thesis, Open University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262015.

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MacDonald, Joanne. "Microstructure, crystallography and stable isotope composition of Crassostrea gigas." Thesis, University of Glasgow, 2011. http://theses.gla.ac.uk/2939/.

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Many marine molluscs produce complex shells of calcium carbonate. These shells are formed under strict biological control to provide a range of functions to ensure the survival of the living organism. These inspiring biomineral structures can also provide an archive of environmental change via proxies such as δ18O and δ13C within the shell carbonate. However, the intimate relationship between the biological and environmental controls influencing biomineral production can often obscure the environmental signal, making it difficult to interpret environmental information from shell proxies. Understanding the design of biomineral structures will further our knowledge of biomineralisation as a whole, while understanding the controls that influence shell production will ensure that shell proxies applied to palaeoenvironmental studies are accurate. Oysters are sessile bivalve molluscs that have evolved since the Triassic and expanded to occupy a range of habitats with almost global distribution, providing an example of a highly successful biomineral system. This study investigates the ultrastructure, crystallography and stable isotope composition of the Pacific oyster, Crassostrea gigas from estuarine and marine environments. The method by which oysters adhere to hard substrates is also investigated. Both valves of the oyster shell are composed predominantly of low Mg calcite in three forms; an outer prismatic region, an inner foliated structure and chalk lenses which appear sporadically throughout the valves. Aragonite is restricted to the myostracum and parts of the hinge structure. Crystallographic analysis shows that, despite variations in structural morphology, the superimposed layers of the oyster shell maintain a single crystallographic orientation with the crystallographic c-axis orientated perpendicular to the outer shell surface. Varying crystal morphology, while maintaining crystallographic unity, may be a deliberate design to provide the oyster shell with both strength and flexibility. In general, there is no difference in the overall ultrastructure or microstructural arrangement of estuarine and marine oysters. Estuarine oysters contain significantly more chalk than marine equivalents suggesting that the appearance of chalk lenses is, to some degree, triggered by an external environmental stimulus. Stable carbon and oxygen isotope analysis of folia and chalk provides further insights into the appearance of chalk in the oyster shell structure. There is no significant difference in the isotope composition of folia or chalky layers, although patterns of δ13C and δ18O of folia and chalk reveal key differences between the two structures. Folia display a narrower range of δ18O values compared with chalk and exhibit significant interspecimen variation with respect to δ13C. Interspecimen variation, with respect to either δ18O or δ13C is absent in chalk samples. These patterns suggest that secretion of folia requires a more specific environmental stimulus and a greater input of metabolic carbon than chalk. Chalk is apparently secreted across a greater range of environmental conditions, with less metabolic regulation. Deviation from optimal environmental conditions, for example during periods of reduced salinity and/or cold or warm temperatures, may reduce metabolism causing the oyster to deliberately default from folia to chalk secretion. In general, folia and chalk in both estuarine and marine oysters is secreted in oxygen isotope equilibrium with the ambient environment. Another aspect of the oyster biomineral system is their ability to adhere tightly, and usually permanently, to a range of hard substrates by cementation of the left valve. Investigation of the contact zone between oyster shells and biological (other oyster shells) and inorganic (rock) substrates reveals the influence of both biogenic and non-biogenic processes in oyster cementation. Original adhesion is brought about by secretion of an organic adhesive which acts as a nucleating surface onto which crystals precipitate which have random orientation and are composed of high Mg calcite. The lack of orientation and elevated Mg content suggests that these crystals are nucleating outwith the biological control experienced by the shell biomineralisation process and are formed from inorganic precipitation from seawater. It is proposed that oysters do not control, or secrete, the crystalline cement but instead they secrete an organic film onto which crystals precipitate from seawater. Oysters thus provide excellent examples of both biologically induced and biologically controlled mineralisation.

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Whitehead, Benjamin. "The oxygen isotope composition of the country rock of the Koegel Fontein igneous complex." Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29636.

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The Koegel Fontein Complex is a Cretaceous anorogenic complex located in southern Namaqualand, west of Bitterfontein, South Africa. The complex comprises a large granite intrusion (the Rietpoort Granite), a series of NW-striking quartz porphyry dykes, and numerous other minor igneous bodies. A breccia plug, and the quartz porphyry dykes have δ18O values as low as -4.1‰, and these are believed to be the result of selective dehydration and melting of previously 18O-depleted rock (Curtis et al., 2013; Olianti and Harris, 2018). This thesis investigates the oxygen isotope composition of the country rock of the Koegel Fontein Complex, which consists of Namaqua-Natal Belt granulite facies rock and minor remnants of overlying Gariep Supergroup metasedimentary rock. The Brak Fontein Shear Zone (BFSZ) is investigated as a protolith for low δ18O (<6 ‰) units of the Koegel Fontein Complex. Geological mapping combined with oxygen isotope data of the country rock confirms that 18Odepletion occurred prior to the emplacement of the Koegel Fontein Complex and is localised in the ~545 Ma BFSZ. Generation of rock with δ18O values as low as -4 ‰ requires a combination of high temperature water-rock interaction, a high water-rock ratio and very low δ18O values in the alteration fluid. Deformation in the BFSZ coincides with the Pan-African Orogeny and a 549-545 Ma global glaciation, and it is reasonable to assume that ambient meteoric water had a very low δ18O value, perhaps as low as -30 ‰. Assuming a possible Δrock-water range from 0.5 to 2.8, a δ18O value of 8‰ for the rock before alteration, a δ18O value of -2‰ for the rock after alteration, a δ18O value of -30‰ for the fluid before fluid-rock exchange and exchange at a temperature range of 400°C to 700°C, a waterrock ratio of ~0.31 to ~0.40 is required to create the observed 18O-depletion in the BFSZ. The calculated water-rock ratio suggests that a significant amount of meteoric water passed through the BFSZ, into the brittle-ductile transition zone. A cold climate only coincides with a suitable tectonic setting during the Pan-African Orogeny, suggesting that the 18O-depletion is syn-tectonic. Furthermore, strong recrystalisation and annealing after deformation and a lack of brittle overprint or cross-cutting fractures and/or veins suggest a low permeability in the BFSZ after the Pan-African deformation. Therefore 18O-depletion in the BFSZ must have occurred during the Pan-African Orogeny and may be evidence for the infiltration of meteoric water into the ductile crust, possibly requiring variable strain rates or seismic pumping.

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Bishop, Peter Mark Edward. "Isotope systematics and microstructures of slates from South-West England and North Wales." Thesis, University of Leeds, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278216.

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Morisset, Natalie Carleton University Dissertation Geology. "Stableisotope and radioisotope geochemistry of the Panda Hill carbonatite, Tanzania." Ottawa, 1992.

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Telus, Rose Guensly. "Identification of Heavy Rainfall Events Using High-Resolution Carbon Isotope Measurements Across Tree Rings." Thesis, University of Louisiana at Lafayette, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10682793.

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Models suggest that global warming will cause an intensification of the hydrologic cycle, but they are poor at predicting changes in the frequency of short, intense precipitation events at the regional to local scale. High-resolution stable isotope measurements across tree rings have shown potential for resolving precipitation at sub-annual resolution, but identification of single intense precipitation events across multiple tree rings has proven elusive. In this work, I report 218 high-resolution carbon isotope (δ¹³C) measurements made across eight growth rings of two Pinus trees cored in southern Louisiana. Tree rings were targeted for the presence and absence of extreme rainfall associated with land-falling tropical cyclones within 100 km of the study site. Comparison of the δ¹³C record to meteorological data yields a significant correlation (r = -0.576, p = 0.0004) with monthly precipitation and δ¹³C value measured across the rings. Significant, intra-ring declines of >1‰ are associated with monthly precipitation > 200 mm that cannot be resolved by low-resolution sampling. Comparing the effects of sample resolution on δ¹³C patterns suggests that wide-ringed samples are preferred for identifying precipitation events at sub-seasonal resolution. Recent technical and methodological advancements allow for more rapid preparation and analysis of intra-ring δ¹³C data and provide opportunity for quantifying sub-seasonal environmental information within high-resolution tree-ring datasets. This work indicates the potential for quantifying changes in the magnitude and frequency of extreme precipitation events at individual sites from long-term intra-ring δ¹³C records.

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Wickson, Steven. "High-Resolution Carbon Isotope Stratigraphy of the Ordovician-Silurian Boundary on Anticosti Island, Quebec: Regional and Global Implications." Thesis, University of Ottawa (Canada), 2011. http://hdl.handle.net/10393/28928.

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The end-Ordovician was a critical time in Earth history and marked the occurrence of a mass extinction and a period of continental glaciation. The Ellis Bay Formation on Anticosti Island in Quebec represents up to 100 meters of relatively undisturbed, continuous, low latitude, shallow water carbonate ramp deposits that span the Hirnantian Stage and terminate close to the Ordovician-Silurian (O-S) boundary. In this study, approximately 400 samples of micritic limestones were collected from six Ellis Bay sections ranging from the basin margin to more distal basin center of the Anticosti Basin. delta13C and delta18O isotopic ratios were measured from these samples and integrated within a recently proposed framework of sequence stratigraphy and biostratigraphy for the Ellis Bay Formation. The measured delta13C values in most sections show a positive excursion (∼2‰) in the lower Ellis Bay Formation followed by a larger excursion (∼4‰) in the upper Ellis Bay Formation. The delta 13C profile of the Ellis Bay Formation on Anticosti Island exhibits a pattern similar to those of other profiles in graptolite-rich Hirnantian basinal successions from the rest of the world. The delta13C record on Anticosti Island is not consistent with predictions and observations based on current models that describe the state and evolution of the global carbon cycle during the Late Ordovician.

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24

Owen, Robert. "Development and application of speleothem-based proxies for past climate change." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:0a44a913-7c28-40ac-9a5e-76811a393a8e.

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This thesis develops and applies new techniques for reconstructing past environments from the speleothem archive. Chapter 3 introduces Ca isotopes as a novel palaeo-aridity proxy. Recent dripwater, farmed calcite and bedrock data show that, in the modern environment, 36% of initial dripwater Ca is removed by prior calcite precipitation at the HS4 dripsite (Heshang Cave, Central China). A speleothem record spanning the 8.2kyr event suggests this value increased to 60% during the event, in response to a decrease in effective rainfall of approximately a third. Modern Ca isotope systematics, and the cycling of other Group II metals, are studied further in Chapter 4. Data from Heshang Cave monitoring samples explore the temporal and spatial controls on these proxy systems. Results highlight the importance of secondary calcite as a potential source of dripwater metals, as well as the significant contribution of particulate calcite to bulk dripwater chemistry. At the HS4 dripsite, over a third of bulk dripwater Ca is present as particulate calcite. This influences bulk dripwater Ca concentrations and isotopes, as well as potentially impacting speleothem growth and chemistry. Chapters 5 introduces CaveCalc, a new numerical model for dripwater and speleothem chemistry and isotopes based on PHREEQC. Key strengths of CaveCalc include its ability to model multiple proxy systems in a single framework, the ability to quantify the extent of open-system dissolution, and the extensible nature of its design. Chapter 6 applies CaveCalc to disentangling the controls on dripwater and speleothem δ¹³C values. Model results are compared with speleothem data. At Heshang Cave, anomalously high δ¹³C is quantitatively explained as the result of CO₂ degassing and prior calcite precipitation, an interpretation made possible by the availability of coupled δ¹³C, a¹⁴C and Ca isotope data. This approach provides a powerful tool to help researchers better interpret dripwater and speleothem δ¹³C data.

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25

Leslie, Karen Ann. "Oxygen isotope study of migmatites and associated rocks from Nanga Parbat-Harmosh Massif, Pakistan Himalaya." Thesis, Royal Holloway, University of London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287481.

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Collision of the Indian and Eurasian plates (-65Ma) caused the formation of the Himalayan chain. The Nanga Parbat-Haramosh Massif within the western Himalaya, Pakistan, is experiencing the fastest uplift anywhere in the world (-10mmyr-1). The massif contains amphibolite facies pelitic and semipelitic migmatites with subordinate calc-silicates and amphibolites. Intruded into these migmatites are very young tourmaline leucogranites (2- l OMa). Only in the central portion of the massif is the granulite facies sillimanite-K-feldspar-cordierite assemblage found. The migmatites themselves contain lit-par-lit quartzo-feldspathic leucosomes (cros) and cross-cutting cordierite-bearing seams (cros). Tourmaline leucogranites have been derived from muscovite vapour-absent melting of this basement, while cordierite seams have been derived from biotite-dehydration melting of these migmatites. The rapid uplift experienced by the massif reduced the effects of post migmatisation mineral-mineral oxygen isotope diffusional exchange. Thus, primary fractionation values are more likely to be preserved. To study the effects of migmatisation on the fractionation of oxygen isotopes, mineral separates from mesosomes, leucosomes and seams were analysed by laser-fluorination mass spectrometry. The use of a Nd: YAG laser required the establishment of a method to analyse quartz and alumino-silicates. Proxy heating with a standard ferromagnesian mineral is followed by a mass balance calculation to obtain 818Oquartz/feldspafr om the mixture. Precision for non-ferromagnesian minerals is ±0.4%o (2sd) for a standard quartz, NBS-28, using this method. Results indicate that Mgtrmelt-mesosomaen d Ofeldmelt-mesosomaer e positive. It is considered unlikely that there was substantial fluid infiltration during migmatisation because quartz shows large infra- and inter-sample variability, indicating that 8180 values have not been homogenised by fluids. Any fluids that were present are likely to have been metamorphic rather than meteoric in origin, because the latter have particularly low 8180 values (-15%o to -16%o). Reequilibration between mesosome and leucosome produced diffusion profiles within quartz. Within quartz, an array of fluid inclusion types (H2O and CO2), salinities and homogenisation temperatures, suggest that fluids have been present within the massif over much of its history. Mineral-mineral fractionations suggest fast cooling in a fluid undersaturated environment.

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26

De, Baun Derik K. "Silica Replacement in the Southern White Pine Range, East Central Nevada| A Stable Isotope Study." Thesis, California State University, Long Beach, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10841608.

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In the southern White Pine Range (SWPR) silica is found to have been deposited from hydrothermal solution within the Currant Gap Detachment fault (CGD). Silica has been observed to occur in three modes of deposition: (1) narrow veins within the lower plate Pole Canyon limestone, (2) bulk silicification of carbonates and (3) breccia matrix found in proximity to the CGD.

Through stable isotope analysis of oxygen from quartz samples and hydrogen from fluid inclusions we see that there is a history of meteoric waters penetrating into the Lower Pole Canyon Formation, in the lower plate of the CGD. This study reveals that silica in the SWPR formed from aqueous fluids at temperatures between 260 °C and 315 °C within lower plate quartz veins and 150 °C to 300 °C within the upper plate of the CGD. These temperature ranges are in line with what would be expected in a brittle regime (T < 350 °C).

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27

McEwan, C. J. A. "Geology, geochemistry and stable isotope studies of an epithermal hydrothermal system, Rosita Hills, Colorado." Thesis, University of Aberdeen, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383565.

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The Rosita Hills volcanic centre is an alkali-calcic mid-Tertiary caldera complex overlying ortho- and paragneissic basement on the eastern margin of the Wet Mountains graben in southcentral Colorado. There were two mineralising events at the Rosita centre. Au, Ag and base metal mineralisation occurred in a phreatomagmatic breccia pipe at the northern margin of the complex. Later, Ag and base metal mineralisation occurred in veins in the centre of the complex. Mapping, petrological and XRD studies outline 4 alteration facies related to hydrothermal activity at the centre. Propylitic/argillic, K-feldspar-sericitic, advanced argillic and silicic alteration assemblages are recognised. The areas of most intense alteration are controlled by the dominant structural trends within the caldera. Sub-volcanic magma movement is postulated as the dominant cause of the fracture patterns. A lithogeochemical grid survey for Au, Ag, Sr, Rb, Cu, Pb, Zn and Mn across areas of hydrothermal alteration reveal complex patterns indicative of multi-stage hydrothermal activity. District-wide Sr, Zn and Mn depletions are related to the propylitic/argillic alteration. Au, Ag, Rb and Cu enhancements are related to the K-feldspar-sericite alteration. Late stage advanced argillic alteration modified the trace element dispersion patterns by leaching previously formed enhancements. Stable isotope studies (O and H) of whole rock and mineral separate (quartz and sericite) samples from veins and hydrothermal eruption breccias show that the hydrothermal fluid had both meteoric and magmatic components. δD values from whole rock samples show a crudely concentric pattern centring on areas of sericitic and advanced argillic alteration in the middle of the lithogeochemical grid. Fluid inclusion data from vein gangue minerals (quartz, baryte and sphalerite) and from silicified rock in the advanced argillic alteration zone again show that the hydrothermal fluid had more than one component fluid. A highly saline, high temperature fluid occurs in quartz associated with base metal mineralisation. Less saline inclusions occur in the upper parts of the system in the silicic alteration. The data indicate that mixing of these two end-member fluids precipitated the vein mineralisation. The source of metals in the Bassick breccia pipe orebody was a highly differentiated magma body underlying the breccia pipe. Incipient ring faulting probably controlled the emplacement of the magma. Other similar breccia pipes in Colorado are postulated as overlying Cu-Mo porphyry mineralisation. The source of the metals in the Rosita vein orebodies was the volcanic host rocks (and the Precambrian basement?). The Rosita Hills vein mineralisation shows features typical of adularia-sericite systems in the western United States. The Au:Ag ratio in these deposits can be related to the origins of the crust underlying the deposits.

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28

Watanabe, Shizuko. "The Evolution of a Chemically Zoned Magma Chamber: the 1707 Eruption of Fuji Volcano, Japan." Oxford, Ohio : Miami University, 2003. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=miami1070588662.

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Thesis (M.S.)--Miami University, Dept. of Geology, 2003.
Title from first page of PDF document. Document formatted into pages; contains viii, 105 p. : ill. Includes bibliographical references (p. 83-91).

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29

Farrell, Sean Bradley. "The sulphur isotope geochemistry of carbonatites and associated silicate rocks from the Superior Province of the Canadian Shield." Thesis, University of Ottawa (Canada), 2005. http://hdl.handle.net/10393/26901.

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Thirty-five sulphur isotopic analyses have been obtained from six carbonatite-alkalic rock complexes ranging in age from 1906 Ma to 1008 Ma located within the Ontario portion of the Superior Province. Pyrrhotite, chalcopyrite and pyrite mineral separates were used. The overall range of delta 34SCDT values are from +3.4 to -4.5‰. Each complex shows its own distinct range and mean sulphur isotopic composition. The overall range in the sulphur isotopic composition in conjunction with carbon and oxygen isotopic data suggests that these carbonatites and associated silicate rocks were derived from a relatively primitive mantle source. This is consistent with previously published Sr and Nd isotopic data that suggest that the mantle source underlying the Superior Province has remained essentially a closed system from about 2700 Ma to at least 1008 Ma. The sulphur isotopic data reported here is the first ever for carbonatites from the Superior Province. (Abstract shortened by UMI.)

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30

Fletcher, Timothy Andrew. "The geology, mineralisation (Ni-Cu-PGE) and isotope systematics of Caledonian mafic intrusions near Huntly, NE Scotland." Thesis, University of Aberdeen, 1989. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=88127.

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The Caledonian mafic and ultramafic intrusions of the Grampian region of N.E. Scotland are a suite of synorogenic tholeiitic plutons of mid-Ordovician Age. They include layered cumulates, granular gabbronorites, quartz biotite norites and xenolithic contact facies lithologies. They postdate two regional deformation events in the enclosing Late Precambrian Dalradian metasediments, but are themselves locally deformed by a major regional ductile shear zone system. A detailed study of the Huntly-Knock area was undertaken combining geological mapping, petrological, geochemical and stable isotope techniques. In the study area, layered peridotitic to gabbroic cumulates, transitional cumulate types, granular gabbronorites quartz biotite norites and complex xenolithic contact facies rock types are present as a series of disrupted bodies formed by multiple intrusive events and subsequent deformation of a laccolithic and sheeted intrusive complex. Progressive cryptic fractionation trends are observed from basal peridotites to quartz biotite norites in the 'roof' of the intrusion. The chemistry and mineralogy of the rocks places them in the Lower and Middle Zone of the regional Younger Basic 'stratigraphy', although isolated pockets of Upper Zone may occur. Fine grained disseminated Fe-Ni-Cu sulphides are widespread throughout the mafic and ultramafic rock types. Richer sulphide concentrations locally occur as: gabbronorite hosted disseminated to massive bodies in the structurally complex, Littlemill-Auchencrieve contact zone; disseminated horizons within cumulates; disseminated to submassive graphite-rich pods in pyroxenitic pegmatites. The sulphide assemblage is dominated by pyrrhotite with minor pentlandite and chalcopyrite. Sulphide textures are attributed to magmatic processes with local modification by ductile deformation and hydrothermal reworking. Field, textural and Cu/Cu+Ni relations of certain submassive-massive sulphides is consistent with their derivation from an ultramafic parent. Maximum Ni and Cu levels are 3.02% and 6.46% respectively. The highest combined Pt+Pd+Au values occur in remobilised net sulphide (574ppb) and graphitic pyroxenite (700ppb). These metal values are generally low and comparable to other orogenic Caledonian intrusions. Sulphide immiscibility occurred many times during cooling of the tholeiitic parent magma(s), however early sulphide melts are generally of most economic importance. While there is abundant evidence for magma/country rock interaction, only locally is there evidence for involvement of metasediment sulphur, the system being dominated by a magmatic signature. In the Littlemill-Auchencrieve contact zone, crustal involvement may have been the principal factor controlling sulphide immiscibility. Subsequent hydrothermal reworking within ductile shear zones under amphibolite facies metamorphic conditions modified metal values. Depletion, especially of Au, Pt and Pd was mainly observed but local significant zones of enrichment may also be present.

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31

Carrigan, William J. "Stable isotope ratios of carbonate and sulfide minerals from the Gunflint Formation: Evidence for the origin of iron formations." Thesis, University of Ottawa (Canada), 1990. http://hdl.handle.net/10393/5785.

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The $\sim$1.9 Ga Gunflint Formation is a Lake Superior type iron-formation, located in the Thunder Bay district of northwestern Ontario, that was deposited on a shallow shelf analogous to modern carbonate environments. Carbonate minerals in the iron-rich lithofacies of the Gunflint Formation include siderite, ankerite, and calcite. Petrographic evidence indicates that siderite precipitation initiated either within the water column or at the sediment/water interface and continued during very early diagenesis. Ankerite and calcite formed during early to late diagenesis as pore-filling cements and as replacements of other minerals. The iron-poor limestone facies contains very early diagenetic dolomite and early to late diagenetic calcite. $\delta\sp $C values of carbonate minerals from unmetamorphosed rocks range between 0 and $-6\perthous$ (PDB). The values near 0$\perthous,$ which are considered to be representative of the basin water composition, indicate that the primary source of carbon was marine bicarbonate. The lighter values indicate that a minor component of oxidized organic carbon was added during early diagenesis. The heaviest $\delta\sp $O values for unmetamorphosed carbonate minerals range between $-$5 and $-7\perthous$ (PDB), which is the same range of values observed for many early Proterozoic marine carbonates. $\delta\sp $O values of carbonate minerals are the result of isotopic exchange with pore waters, originally of marine composition, at increasing temperatures and/or are the result of isotopic exchange with $\sp $O-depleted meteoric water during early diagenesis. Disseminated fine-grained, very early diagenetic pyrite is widespread throughout the formation, usually in amounts less than about 2%. However, pyrite is locally observed as laminae or thin layers, suggesting that some pyrite may have formed at or above the sediment/water interface. Low S/C ratios indicate that dissolved sulphate was the limiting factor in pyrite formation. $\delta\sp{34}$S values between +5 and +12$\perthous$ (CDT) imply that sulfide formed by bacterial sulphate reduction under closed system conditions. In the lower part of the Gunflint Formation coarse-grained pyrite and pyrite concretions are associated with syndepositional faults. High S/C ratios and highly variable $\delta\sp{34}$S values ($-$33 to +35$\perthous)$ suggest an external source of sulphate was introduced by fluids moving upward along these faults. The Gunflint basin is best characterized by a stratified water column with high concentrations of dissolved ferrous iron below the redox boundary. Volcanic activity or rifting within this basin contributed a high flux of reducing hydrothermal solutions to the seawater. Hydrothermal activity was probably the dominant source of iron, although reduction of detrital ferric iron may have contributed significant amounts of dissolved iron. During periods of increased tectonic activity, the expansion of the redox boundary to shallower water allowed the transport of iron to the shallow shelf. Ferric iron-bearing minerals would have been precipitated on the shelf by oxidation in surface waters whereas ferrous iron-bearing minerals would have been precipitated under more reducing conditions either in deeper water or in sheltered environments. The transition to the iron-poor limestone member resulted from a lowering of the redox boundary. (Abstract shortened by UMI.)

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32

Moore, Collin. "Seasonal Temperature Reconstruction for Northeastern Siberia during the Late Pleistocene from High-Resolution Oxygen Isotope Measurements Across Fossil Wood." Thesis, University of Louisiana at Lafayette, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10683887.

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Cellulose is resistant to degradation on geologic timescales and provides a reliable record of the oxygen isotope composition of meteoric water (δ¹⁸O_MW). A strong empirical relationship between the δ¹⁸O_MW value and temperature has been observed in modern settings, allowing researchers to reconstruct mean annual temperature via measurements of the δ18O value of cellulose (δ18Ocell). I present high-resolution intra-annual δ18Ocell measurements across fossil growth rings in mummified wood collected from late Pleistocene sediments (∼50,000 to 44,000 14C BP) within the Yedoma Silt Ice Complex at Duvanny Yar in far northeastern Siberia. These data are used to quantify year-to-year changes in seasonal temperatures at the site, including warm and cold month mean temperatures (T_max and T_min, respectively). Results suggest T_max = 6.4 ± 3.0 °C (average ± 1σ) and T_min = -37.7 ± 2.9 °C during the late Pleistocene, which is significantly (T_max p = 0.0005, T_min p = 0.05) colder than today’s values (modern: T_max = 13.2 ± 2.1 °C, T_min = -34.8 ± 2.6 °C). Assuming a normal distribution for monthly temperatures similar to modern continental climates, I calculate that above-freezing mean monthly temperatures occurred in ~1.6 fewer months during the late Pleistocene than today. These cold conditions allowed for the Arctic to act as a significant carbon sink during the late Pleistocene, despite shorter growing seasons as compared to today. Extrapolation to current Arctic warming suggests that increased temperatures will allow for longer periods of net carbon release from Arctic soils each summer, despite increased photosynthesis.

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33

Xia, Xiaoping. "Spot U-Pband Hf isotope analyses of detrital zircons from the khondalites in the western block of the North China craton." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B35773698.

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34

Potter, Elyn. "Changes in stable carbon isotopes of methane along a salinity gradient in a hypersaline microbial mat system." Diss., Columbia, Mo. : University of Missouri-Columbia, 2007. http://hdl.handle.net/10355/5089.

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Thesis (M.S.)--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 November 1, 2007) Includes bibliographical references.

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35

Reeves, Jessica Marie. "The use of ostracoda in the palaeoenvironmental reconstruction of the Gulf of Carpentaria, Australia, from the last interglacial to present." Access electronically, 2004. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20050111.153534/index.html.

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36

Almasi, Peter Ferenc. "Dating the paleobeaches of Pampa Mejillones, northern Chile, by cosmogenic chlorine-36." Thesis, The University of Arizona, 2001. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu_etd_hy0182_sip1_w.pdf&type=application/pdf.

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37

Vennemann, Torsten Walter. "A geochemical and stable isotope study of some rocks from the Bandelierkop formation, southern marginal zone of the Limpopo Belt, South Africa( vol.1 Text)." Doctoral thesis, University of Cape Town, 1989. http://hdl.handle.net/11427/23476.

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The Bandelierkop Formation of the Southern Marginal Zone (SMZ) of the Limpopo Belt consists of metamorphosed ultramafic, mafic and sedimentary rocks. Metamorphic conditions indicated by the petrography of these different rock groups are consistent with upper amphibolite to granulite facies. The ultramafic and mafic rocks are geochemically akin to peridotitic-pyroxenitic intrusive rocks and high-Mg basalts respectively. Metamorphism of these two rock groups in the SMZ was an essentially closed system process, except for the highly volatile phases such as H₂O and CO₂. The metasediments appear to represent a sequence of high (Mg+Fe)-greywackes and/or deep-water shales with minor amounts of iron formation material. The unusually mafic character of the metasediments can be ascribed to a high ultramafic + mafic source component to the original sediment. Some modification of the major and trace element compositions of the pelitic rocks has been caused by the removal of partial melts and the metamorphism of the pelitic rocks is not therefore considered to have occurred under closed system conditions. Variable extraction of partial melts is implied by the chemical variations shown by the pelitic rocks and is also suggested by the presence of large pegmatitic felsic bodies which are commonly found close to the pelitic rocks. Detailed petrographic study of the Bandelierkop Formation rocks suggests an increase in metamorphic grade, and/or a decrease in water activity, from south to north within the Southern Marginal Zone. Peak metamorphic conditions of 730°C + 65°C at pressures of 6.1 ± 1.5 kbars may be deduced from a careful application of several cation thermometers and barometers on selected mineral analyses. A rigorous application of garnet-biotite thermometry to the pelitic rocks indicates that the transition from orthoamphibole gneisses in the south to orthopyroxene-bearing rocks in the north of the SMZ terrane, is a function of changing biotite composition and/or decreasing water activities rather than an increase in metamorphic temperatures. In contrast to the major and trace element data, the stable isotope data for the ultramafic and mafic rocks in the SMZ indicate open system behaviour for some of these rocks, but closed system behaviour for the pelites. Extraction of SO to 70% partial melts from the pelitic rocks, should not, however, have affected the δ¹⁸O value of the restite. Petrological and stable isotope data in the SMZ rocks are consistent with retrogression in all these rocks and open system behaviour for oxygen in some ultramafic and mafic rocks, being caused by the crystallization and accompanying fluid release of melts produced during prograde metamorphism of the pelitic rocks. Small scale (-5 to 30m's) heterogeneity is implied by both oxygen and carbon stable isotope compositions of closely spaced rock samples, even for those collected from within large "shear zones", suggesting small fluid/rock ratios for most of the samples in the high-grade terrane or heterogeneous stable isotopic compositions of the fluids. Furthermore, a similarity in mineral-mineral stable isotope fractionation factors is observed for all the pelitic rocks, including the orthoamphibole gneisses found immediately south of the orthopyroxene isograd. These features preclude the presence of pervasive fluid infiltration after peak metamorphism. Two implications are, that granulite facies metamorphism in the SMZ terrane was not caused by an influx of mantle derived CO₂-rich fluid and, that the orthoamphibole gneisses are not retrogressed equivalents of the granulites found to the north of the orthopyroxene isograd. It is suggested that this isograd represents a change in the water activities of the rocks during metamorphism. Apparent disequilibria in mineral - mineral stable isotope fractionations observed amongst different minerals within any one pelitic rock, may be explained by a combination of the crystallization of residual melt within these rocks and oxygen diffusion amongst minerals which have not reached their oxygen-closure. The concordant quartz-plagioclase, quartz-biotite and plagioclase-biotite oxygen isotope equilibration temperatures are taken to represent minimum crystallization temperatures for the melts (-560°C), while successively higher quartz-orthopyroxene, quartz-amphibole and quartz-garnet oxygen isotope equilibration temperatures are a function of increasing closure temperatures for the orthopyroxene, amphibole and garnet respectively. The minimum estimate to peak metamorphic temperatures is given by the quartz-garnet oxygen isotope temperature averaging 736 + 52°C. If oxygen diffusion experiments performed in hydrothermal systems are appropriate for the SMZ rocks, then cooling rates for the SMZ terrane could have been as low as 12 to 25°C/My over a temperature range of 480 to 600°C. Stable isotope modeling of hypothetical fluids that may have been in equilibrium with the high-grade rocks, suggests that a mixture of CO₂ and H₂O, with CO₂/H₂O mole ratios > 0.1 can precipitate both quartz and carbonate of stable isotope composition similar to those determined for quartz and carbonate from the mineralized Archaean lode gold deposits of the Murchison and Pietersburg greenstone belts. A model involving granulite facies metamorphism, partial melt extraction and subsequent release of fluids, Au, K and S upon crystallization of such melts, appears to be viable for gold mineralization occuring in the adjacent lower grade greenstone belts and in the high-grade terrane of the Southern Marginal Zone.

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38

Wade, Stephen James Rochfort. "Radiogenic isotope studies of crust-forming processes in the Lofoten-Vesterålen province of north Norway." Thesis, University of Oxford, 1985. http://ora.ox.ac.uk/objects/uuid:d57ed241-b1c8-4502-8ee5-8de8be20d80e.

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The Lofoten-Vesterålen province of North Norway consists almost exclusively of Precambrian granulite-facies rocks. The oldest rocks in the province are monzonitic and dioritic migmatitic gneisses, the protoliths of which were formed at 2.7 Ga. The migmatites are overlain by a series of supracrustal gneisses, from 2.1 Ga, largely volcanogenic in origin, but with interbedded marbles and banded ironstones. The first occurrence of marble in western Lofoten is reported. Deposition in a subsiding back-arc basin or in an Andean- type environment on a thin continental margin is inferred. Both gneiss sequences were intruded by basic rocks at 1.8 Ga. The basic rocks could not have been formed simply by extraction from the mantle at 1.8 Ga. The required contribution from 2.7 Ga migmatites could be as much as 37%, but less if contamination took place via anatectic melts. The first report of eclogitic rocks from the Lofoten-Vesterålen province is made in this study; their formation is associated with shear deformation Both gneiss sequences and the basic rocks were intruded by mangeritic rocks at 1.8 - 1.7 Ga. Their chemical compositions can be explained by fractional crystallization from magmas formed from 2.7 Ga and 2.1 Ga gneisses and 1.8 Ga mantle-derived magmas. Parameters derived from Rb-Sr, Sm-Nd and U-Pb systems to express the relative proportions of crust and mantle contributions to the mangerites mutually correlate, supporting the crust-mantle source model for the mangerites. Mixing calculations suggest that the late Archaean contributes in excess of 50% by mass for almost all mangerites. Anatectic veins present, especially in the Moskenesøy supracrustal gneisses, are inferred to represent partial melts which coalesced to form the mangerites at higher structural levels. Anatexis was caused by basaltic underplating associated with limited crustal extension. Later rock-forming events were the emplacement of dolerite dykes; the 1.65 Ga Lødingen Granite; the Leknes Group metasediments and the Caledonian granite pegmatites.

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Cramer, Bradley Douglas. "Glaciation CO2, and organic carbon burial during the early Silurian: carbon isotope stratigraphy from the mid-continent of North America." The Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=osu1406711650.

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40

Heri, Alexandra Regina. "Geochemistry, geochronology and isotope geochemistry of eocene dykes intruding the Ladakh batholith." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B50899624.

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Eocene dykes intruding the Ladakh batholith were sampled along the southern margin of the Trans-himalayan plutonic arc in Ladakh, NW-India. Approximately 30 dykes were encountered in the 40 km trail between Leh and Hemis Shugpachan. The dykes in the east of the field are trending E to NE and those in the west trending N to NW, exhibiting sub-parallel orientations within each area. Eighteen dykes were sampled (two of them multiple times) and subjected to petrographic, geochemical and isotopic analyses. They exhibit various degrees of differentiation from basaltic to rhyolitic compositions and are mainly composed of plagioclase, quartz, hornblende (s.l.) and/or biotite and magnetite. Furthermore, dykes in the eastern part of the field area contain quartz xenocrysts resulting from crustal assimilation, while no relict quartz was found in the west. The dykes exhibit alteration phases and features suggesting that they underwent autometamorphism, i.e. hydration reactions due to igneous cooling. Whereas the dykes in the east of the field area record low-T alteration, the mineral parageneses in the west are typical for alteration at elevated temperatures typical for greenschist metamorphic facies. Al-in-hornblende barometry performed on Magnesio-hornblende and Tschermakitic-hornblende phenocrysts of the least altered dyke indicates formation in upper-amphibolite metamorphic facies conditions and pressures of about 6 kbar corresponding to an intrusion depth of approximately 20 km. Major and trace element analyses and Rb-Sr and Sm-Nd isotope analyses revealed a stunning variability in geochemistry and isotopic composition amongst the coeval dykes. All dykes exhibit LREE enrichment and HREE depletion as well as negative Tb and Nb anomalies characteristic for subduction-related intrusives and extrusives. Their REE patterns support a clear subdivision into chemically distinct groups. The group hypothesis was further tested and found valid using statistical tools designed to assess similarity/dissimilarity amongst individuals of a group with a common ancestor, such as hierarchical cluster analysis and multidimensional scaling. The dykes are cogenetic, but clearly not consanguineous, i.e. have not formed from one, progressively differentiating magma chamber. The variability observed in Sr-Nd isotopes can be explained by the dykes having undergone differing degrees of crustal assimilation. In particular the dykes in the east containing quartz xenocrysts show negative iiNd) and positive N(Sr) values caused by crustal assimilation, whereas the dykes in the west with no quartz xenocrysts exhibit positive qqNd) and N(Sr) near zero. 39Ar-40Ar dating by incremental heating of several hornblende-bearing dykes revealed crystallization ages between 50 and 54 Ma, whereas two biotite-bearing dykes gave ages of 45 and 37 Ma, likely to be cooling or recrystallisation ages. The combination of structural field evidence with petrographic, petrologic, geochemical, isotopic and geochronological analyses demonstrates that the dykes, although sharing a common origin, i.e. having formed in the same tectonic setting at roughly the same time, have undergone further geological processes leading to an unexpected diversification of the dykes. These findings provide ample scope for further in-depth and breadth investigations on “late-magmatic dykes” in the future.
published_or_final_version
Earth Sciences
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Doctor of Philosophy

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41

Barovich, Karin Marie. "Behavior of lutetium-hafnium, samarium-neodymium and rubidium-strontium isotopic systems during processes affecting continental crust." Diss., The University of Arizona, 1991. http://hdl.handle.net/10150/185602.

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Combined Lu-Hf, Sm-Nd and Rb-Sr isotopic studies of continental crustal rocks were undertaken to assess the relative effects of secondary crustal processes on isotopic systematics of whole-rock systems. The processes studied include ductile deformation, and three cases of hydrothermal alteration, involving fluids of varying composition. The Rb-Sr system proved to be easily disturbed during all secondary processes, while Sm-Nd and Lu-Hf systems were, for the most part, resilient. These results show that Nd or Hf isotopic information obtained from old rocks that have undergone typical crustal deformational and alteration events can be counted on to be equally reliable. Nd and Hf isotopic analyses were performed on four suites of Early Archean felsic gneiss complexes from Greenland, Labrador, Swaziland, and Michigan to explore questions associated with Early Archean crustal growth. The Sm-Nd isotopic data yield initial ∊(Nd) values that are mostly consistent with published age data for the suites. Calculations show limited scatter may be attributed to subtle changes in the Sm/Nd ratio or Nd isotopic composition. The Hf isotopic results are more variable and complex than the Nd results. The relevance of the studies on isotopic mobility in the first part of this work is that they have demonstrated that Nd and Hf isotopes are equally resilient during a range of secondary crustal processes. Given the robustness of the Nd isotopic data from the Archean samples, however, it seems unreasonable to attribute the much wider variation in Hf isotopic data to post-Archean isotopic disturbances. Differences in initial Hf isotopic ratios from differing magma sources seem called for. Nd and Hf whole-rock analyses of a Late Archean pristine garnet-bearing granitoid complex from northern Canada point out the importance of garnet in fractionating Lu/Hf ratios, and in developing anomalous ∊(Hf) signatures in potential source regions. Calculations show that even short-lived upper mantle/lower crustal heterogeneities, products of previous partial melting events involving garnet fractionation, can develop the range of positive and negative ∊(Hf) values seen in the Early Archean samples.

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42

Calkins, Brad Thomas 1953. "Petrographic, geochemical, X-ray, and stable isotope studies at the Morenci porphyry copper deposit, Greenlee County, Arizona." Thesis, The University of Arizona, 1997. http://hdl.handle.net/10150/278615.

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Morenci is located in southeast Arizona. Copper grade hypogene mineralization averages 0.15%; one or more generations of supergene enrichment have increased mineralization to 0.96%. Intense supergene alteration has made it difficult to determine phyllosilicate paragenesis. The purpose of this study is to differentiate hypogene from supergene phyllosilicates. Forty-nine samples from five drill holes were obtained for petrographic, geochemical, mineralogical, and stable isotope data. Petrographic examination, X-ray diffraction and X-ray powder camera techniques established alteration of feldspars to kaolinite, montmorillonite, and sericite. Whole rock analyses using XRF determined cationic gains and losses that correspond with kaolinite and sericite. Stable isotopes of oxygen and hydrogen using kaolinite and sericite from 14 samples were tested to determine provenance of water. Stable isotope data show a trimodal distribution of phyllosilicates consistent with early hypogene alteration of magmatic origin, and two generations of supergene enrichment due to meteoric waters.

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43

Watkins, Richard Charles. "Foraminiferal biostratigraphy, palaeocology and stable isotope geochemistry of the Santonian to Lower Campanian chalks of the Anglo-Paris Basin." Thesis, University of Liverpool, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.295837.

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44

Bullard, Reuben G. Jr. "Estimation of Slope Erosion Rates from ¹⁰Be Nuclide Accumulation: A Northern Kentucky Example." University of Cincinnati / OhioLINK, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=ucin990706816.

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45

Cyr, Andrew J. "GEOCHEMICAL AND STABLE ISOTOPIC EVALUATION OF FENGHUOSHAN GROUP LACUSTRINE CARBONATES, NORTH-CENTRAL TIBET: IMPLICATIONS FOR THE PALEOALTIMETRY OF THE MID-TERTIARY TIBETAN PLATEAU." Connect to this document online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=miami1080329128.

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Thesis (Master of Science)--Miami University, Dept. of Geology, 2004.
Title from first page of PDF document. Document formatted into pages; contains [1], v, 76 p. : ill. Includes bibliographical references (p. 42-50).

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46

Yang, Chao. "Geology, geochronology, stable isotope, and sulfides of the Tiegelongnan porphyry-epithermal Cu (Au) deposit, Tibet, China." Doctoral thesis, Université Laval, 2020. http://hdl.handle.net/20.500.11794/67954.

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47

Basapuram, Laxmi Gayatri Devi. "Lake Victoria - Carbon, Nitrogen, Phosphorus and Stable Isotope (δ13C) comparison between lake and catchment sediments." Thesis, Linköpings universitet, Tema Miljöförändring, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-149283.

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Lake Victoria situated in East Africa faces an acute problem with eutrophication. Many reasons like agricultural production, industrialization, anthropogenic processes, the introduction of species, and economic activities have caused a stress to the overall well-being of the lake. Excess carbon, nitrogen, and phosphorus drive an increase in productivity which affects eutrophication. Previous studies on sediments and nutrient concentrations in the lake have concluded that nutrient concentrations increase due to release from the catchment. This study focuses on catchment sediments collected from four different sites and compares the results with sediments from two additional sites in the lake. The sediment core from Siaya indicates the highest concentrations of TOC (180 g/kg), TN (13 g/kg) and TP (17000μg/L). It is a rural site and poor agricultural practices such as the burn and slash, use of too many fertilizers, clearance of land, atmospheric deposition and precipitation increase elemental concentrations in the sediments compared to the more urban sites. In the lake sediments, the BILL core had higher concentrations of TP (430g/kg) and TN (16 g/kg) compared to the other site (LV-95) which is located far away from the margins of the lake. This core, however, had high TOC levels (180g/kg). The increase of nutrient levels in lake sediments is thought to be due to non-point sources from the catchment. Analyses of stable carbon isotope were used to infer the different organic matter source in the sediments. Based on the range of values for δ13C vs. C/N it is inferred that aquatic algal production and C4 vascular plants are the dominant sources for the organic matter input. The chemical characterization of catchment and lake sediments provides a qualitative link to nutrient influx and eutrophication in the lake.

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48

Odri, Agnes. "Oxygen and radiogenic isotope constraints on the generation of coexisting silica-undersaturated and oversaturated felsic magmas of the Ditrau Alkaline Massif (Romania)." Doctoral thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29841.

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The Ditrău Alkaline Massif (DAM) is a Mesozoic igneous complex (~200-230 Ma) was generated in a continental rift environment. This study has investigated the relationship between the silica-undersaturated and oversaturated Ditrău rocks based on oxygen, Sr, Nd and Pb isotope data. Different models have been proposed previously to explain the coexisting silica-undersaturated and oversaturated rocks in general: (1) both silicaundersaturated and oversaturated magmas evolve from the same mantle-derived, undersaturated melt, with the oversaturated rocks being produced by crustal assimilation (Foland et al., 1993); (2) both are derived from the same mantle source, but do not evolve from the same parental melt (Giret and Lameyre, 1985); (3) the sources are heterogeneous on a scale that allows undersaturated and oversaturated melts to be produced (Harris, 1995). The previous petrogenetic model of the DAM emphasises the importance of fractional crystallisation of a silica-undersaturated, mantle-derived magma (e.g. Morogan et al., 2000). The Ditrău rocks show variable initial 87Sr/86Sr ratios up to 0.72372, whereas ɛNdi values are from +5.5 to +0.8. High-temperature equilibrium O-isotope fractionations between minerals are generally preserved, but there was some sub-solidus O-isotope re-equilibration during slow cooling. Quartz, zircon and amphibole were used as a proxy for the magma δ18O values. The estimated magma δ18O values for Ditrău rocks are from 5.7 to 11.7‰. Isotope data are consistent with the involvement of both mantle and crustal sources in the formation of the DAM. The Nd and O isotope values of quartz monzonite can be explained by the subequal contribution of mantle-derived camptonite and the lower crustal partial melts generated by the intrusion of hot, mantle magmas. Both O and Nd isotope values show the dominantly mantle origin of hornblendites, diorites and nepheline syenites. The Nd and O isotope variations imply the involvement of 20-65% upper crustal melts into the re-injected camptonite magma to generate the Ditrău syenites, quartz syenites and granites. The isotope results of the DAM require the combination of the previously proposed models to explain its evolution and the relationship of the silica-undersaturated and oversaturated rocks.

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49

Brown, Christine P. "A stable isotope study of fluid-rock interaction in serpentinites of the Franciscan Complex, San Rafael Mountains, California." Thesis, California State University, Long Beach, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1526895.

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The fluid history of serpentinites from three locations in the Franciscan Complex, San Rafael Mountains, California is evaluated with petrologic and stable isotope data that allow interpretation of the serpentinization history and tectonic origin of these rocks. Petrologic evidence shows that most samples were originally serpentinized in a relatively low temperature seafloor hydrothermal environment, but some rocks underwent subsequent recrystallization. Data obtained from serpentine-magnetite geothermometry indicate that the serpentinization temperatures ranged from 168°C to 306°C. Oxygen isotopic values suggest that the serpentinites may have originated in a forearc setting. Hydrogen isotopic values obtained do not reflect the original conditions of serpentinization, but indicate that the rocks subsequently underwent isotopic exchange with meteoric water once they were emplaced onto the continent.

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50

Fang, Yi. "A stable isotope study of fluid-rock interactions in the San Gabriel fault zone and its relationship to seismic process." Thesis, California State University, Long Beach, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1527313.

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Dissertations / Theses on the topic 'Isotope geology'

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