Дисертації з теми "Isotope evolution"
Щоб переглянути інші типи публікацій з цієї теми, перейдіть за посиланням: Isotope evolution.
Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями
Ознайомтеся з топ-50 дисертацій для дослідження на тему "Isotope evolution".
Біля кожної праці в переліку літератури доступна кнопка «Додати до бібліографії». Скористайтеся нею – і ми автоматично оформимо бібліографічне посилання на обрану працю в потрібному вам стилі цитування: APA, MLA, «Гарвард», «Чикаго», «Ванкувер» тощо.
Також ви можете завантажити повний текст наукової публікації у форматі «.pdf» та прочитати онлайн анотацію до роботи, якщо відповідні параметри наявні в метаданих.
Переглядайте дисертації для різних дисциплін та оформлюйте правильно вашу бібліографію.
1
Via, Rachael Kathleen. "Evolution of Atlantic deep-water circulation: from the greenhouse to the icehouse." Texas A&M University, 2005. http://hdl.handle.net/1969.1/2609.
Повний текст джерелаАнотація:
To better understand how the evolution of Cenozoic deep-water circulation
related to changes in global climate and ocean basin configuration, we generated Nd
isotope records from Ocean Drilling Program sites in the southeastern Atlantic to track
deep water mass composition through time. We used fossil fish debris from ODP Sites
1262-1264 (Leg 208), spanning present-day water depths of 2500-4750 m, to reconstruct
the isotopic signature of deep waters over the past ~53 Ma. The data indicate an initial
transition from relatively non-radiogenic values (??Nd=~-10) at 53 Ma to more radiogenic
values (~-8.5) at ~32 Ma. From ~32 Ma to 3.85 Ma, the Nd signal becomes more nonradiogenic,
~-12.3 at the top of the record. Comparison of our data with Nd isotopic
records derived from a North Atlantic Fe-Mn crust show similar non-radiogenic values
(~-10.5) in the 53??32 Ma interval and a trend toward more non-radiogenic values
beginning at ~20 Ma.
The data likely reflect an overall shift from a Southern Ocean deep water source
to the ultimate incursion of deep waters from the North Atlantic. The non-radiogenic
values at the base of the record reflect a Southern Ocean source of deep water. The shift
toward more radiogenic values indicates an increased contribution of Pacific waters to
the Southern Ocean source as the tectonic gateways changed after ~35-33 Ma. The
subsequent trend toward more non-radiogenic Nd isotope values is approximately
concurrent with the increase of benthic foraminiferal ??18O values, based on comparison
with a compilation of global data. Thus, changes in oceanic gateway configuration in addition to overall cooling and the build-up of continental ice on Antarctica may have
altered the Nd isotope character of Southern Ocean deep waters during the early
Oligocene.
2
He, Chengfei. "Deciphering the deglacial evolution of water isotope and climate in the Northern Hemisphere." The Ohio State University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=osu1620739423120004.
Повний текст джерела
3
Davis, Steven Joseph. "Synorogenic evolution of large-scale drainage patterns : isotope paleohydrology of sequential Laramide basins /." May be available electronically:, 2008. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
Повний текст джерела
4
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.
Повний текст джерела
5
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.
Повний текст джерелаАнотація:
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).
6
Whittington, Alan Geoffrey. "The thermal, metamorphic and magmatic evolution of a rapidly exhuming terrane : the Nanga Parbat Massif, northern Pakistan." Thesis, Open University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363324.
Повний текст джерела
7
Thériault, Réginald J. "Evolution of the ca. 1.9 gallium Taltson magmatic zone, Northwest Territories: A neodymium isotope perspective." Thesis, University of Ottawa (Canada), 1990. http://hdl.handle.net/10393/5788.
Повний текст джерелаАнотація:
The Taltson magmatic zone is a north-trending belt of Early Proterozoic granitoids exposed over an area exceeding 18,000 km$\sp2$ in the Northwest Territories. Three petrologically and chronologically distinct intrusive suites comprise the Taltson zone. These are the 1986 Ma Deskenatlata suite, the 1955 to 1925 Ma Slave suite and the 1935 Ma Konth suite. The Deskenatlata suite is composed of a biotite-hornblende diorite to granite suite whose major and trace element chemistry supports derivation by arc magmatism. The Slave and Konth suites are leucocratic granitoids which contain numerous xenoliths of dominantly pelitic high grade paragneiss and display S-type granite mineralogy which commonly duplicates that of the pelitic gneisses. Bulk rock chemistry for the Konth suite is consistent with a homogeneous crustal magma source whereas the Slave suite is compositionally more heterogeneous. The Deskenatlata suite is considered as continental arc-derived granitoids resulting from eastward subduction of oceanic lithosphere beneath the Churchill Province. The Slave suite is regarded as the result of melting of various segments of heterogeneous Archean crust whereas the Konth may have evolved exclusively from melting of pelitic metasediments. (Abstract shortened by UMI.)
8
Henderson, Gideon Mark. "The uranium and strontium isotope evolution of seawater over the past four hundred thousand years." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338310.
Повний текст джерела
9
Cockburn, Hermione Anne Phoebe. "Landscape evolution in Namibia and Antarctica : quantifying denudation rates using in-situ cosmogenic isotope analysis." Thesis, University of Edinburgh, 1998. http://hdl.handle.net/1842/21151.
Повний текст джерелаАнотація:
In-situ cosmogenic 10Be, 26A1 and 21Ne concentrations from locations in central Namibia and the Transantarctic Mountains, Antarctica have been used to investigate rates of landscape change in passive margin settings and contrasting hot and cold arid conditions. Concentrations of cosmogenic 10Be and 26A1 in quartz separated from 14 samples from the Gamsberg in central Namibia have been measured using accelerator mass spectrometry. The Gamsberg is a flat-topped residual forming part of the Great Escarpment of central Namibia. Rates of summit denudation range from 0.2 to 0.8 m Ma-1 and rates of slope retreat have been 10 m Ma-1 over the past 0.04 to 1.5 Ma. The data indicate that backwearing is much more significant than downwearing but that summit denudation is occurring. Low rates of escarpment retreat of 10 m Ma-1 are incompatible with the idea that retreat from the coast has been at a uniform rate since rifting occurred 130 Ma BP. The data are consistent with geological evidence and data from apatite fission track thermochronology that suggest that the escarpment retreated rapidly soon after rifting but has not retreated significantly during the Tertiary. Measurements of cosmogenic 10Be and 26A1 from three granite borhardts on the coastal plain of Namibia seaward of the Great Escarpment in the arid/hyper-arid central Namib Desert indicate mean rates of summit lowing ranging from2.2 to 6.3 m Ma-1 over the pat 1-3 x 105 a. Low variability in estimated denudation rates between the sampling sites and the long term persistence of an arid climate implies that a rate of summit lowering of 5 m Ma-1 has characterised bedrock exposures in the central Namib for at least the past 10 Ma. It has been demonstrated that in-situ cosmogenic isotope analysis can provide unobtainable data on denudation rates over timescales intermediate between short-term process studied and long-term estimates from techniques such as thermochronology. Cosmogenic isotopes analysis has significant potential for evaluating controls on denudation rates in a range of geomorphic settings and constraining models of long-term landscape evolution.
10
Stevenson, Ross Kelley. "Implications for the evolution of continental crust from hafnium isotope systematics of detrital zircons in Archean sandstones." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184895.
Повний текст джерелаАнотація:
The fractionation of zircons by sedimentary processes into continental margin sandstone deposits results in a biased preservation of pre-existing continental crust in the form of zircon in those sequences. This provides a unique opportunity to distinguish between the contrasting theories of episodic growth versus constant volume of continental crust over geologic time through Hf isotope ratios of detrital zircons. ¹⁷⁶Hf/¹⁷⁷Hf ratios were determined for detrital zircon fractions from 2.6-3.0 Ga old sedimentary sequences from the Canadian Shield, North Atlantic, Wyoming, and Kaapvaal Cratons. Hf T(CHUR) ages are less than 3.0 Ga and ε(Hf) values are positive or slightly negative at the time of deposition for most of the Malene, Canadian Shield, Wyoming and upper portions of the Kaapvaal sediments. Notable exceptions are basal samples of the Pongola (3.32 Ga), Dominion (3.11 Ga) and Witwatersrand (3.13 Ga), an arkose from Michigan (3.20 Ga) and one Malene sample (2.97 Ga), all of which either unconformably overlie or are closely associated with pre-3.0 Ga crust. Nd data for shales from the same sequences in the Canadian Shield and Kaapvaal sequences mimic the Hf results. The late Archean sequences appear to be dominated by zircon populations of late Archean age. Hf model ages, from pre-3.0 Ga strata (Upernavik of Labrador and quartzites from Montana), range from 3.1 to 3.6 Ga and are broadly consistent with ages of coexisting volcanics or intrusives, suggesting little inheritance of significantly older material. 2.0-2.5 Ga old quartzites from the Canadian Shield, Wyoming and South Africa have 2.58 to 2.84 Ga model Hf ages indicative of a large expanse of late Archean crust exposed at the time of deposition. The data strongly suggest inheritance of pre-3.0 Ga zircons only in areas where pre-3.0 Ga old crust exists today, and imply that the quantity of continental crust prior to 3.0 Ga ago was not much greater in extent than the pre-3.0 Ga crust exposed today. Small amounts of continental crust prior to 3.0 Ga ago and rapid addition of continental crust between 2.5 and 3.0 Ga ago are consistent with the episodic growth theory of crustal evolution.
11
Georgiev, Svetoslav. "Sources and evolution of Late Cretaceous magmatism in Eastern Srednogorie, Bulgaria : constraints from petrology, isotope geochemistry and geochronology /." Zürich : ETH / Department of Earth Sciences Fluids and Mineral Deposits Group, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17778.
Повний текст джерела
12
Schmidt, Angelika. "Temporal and spatial evolution of the Izu Island Arc, Japan in terms of Sr-Nd-Pb isotope geochemistry." [S.l. : s.n.], 2001. http://e-diss.uni-kiel.de/diss/d465.pdf.
Повний текст джерела
13
Parks, Jane Elizabeth. "Crustal evolution of Grenville terranes in the central and southern Appalachians : the Pb isotope perspective for Grenville tectonics /." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-06162009-063235/.
Повний текст джерела
14
Stepner, Daniel. "Source and Magma Evolution of the Tuff of Elevenmile Canyon, Stillwater Range, Clan Alpine and Northern Desatoya Mountains, Western Nevada." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/36893.
Повний текст джерелаАнотація:
The tuff of Elevenmile Canyon (TEC) is a 25.1 Ma trachydacite to rhyolite intracaldera tuff produced by the largest of 6 Oligocene overlapping calderas that, along with related plutons, constitute the Stillwater Caldera Complex, one of the largest eruptions of the Western Nevada Volcanic Field during the mid-Tertiary ignimbrite flare-up. Typically crystal-rich with a mineral assemblage of plagioclase > quartz sanidine > biotite ± hornblende and clinopyroxene, there are two discernable pumice types throughout the tuff: a lighter crystal-rich pumice and a darker, commonly aphyric pumice type. Rb-Sr and Sm-Nd isotopic compositions of pumice fragments and whole rock samples indicate an enriched mantle component (87Sr/86Srin = 0.70495 – 0.70535, Nd[t=25.1Ma] = -1.13 to -0.39) similar to that of coeval Cenozoic mafic lavas. Pb isotopes (206Pb/204Pbin = 19.042 – 19.168, 207Pb/204Pbin = 15.557 – 15.664) fall along a tight trend between the Northern Hemisphere Reference Line (Hart 1984) and an endmember similar to local granitic units. Major and trace element modelling support a source for the TEC derived from the mixing of anatectic melts of crustal rocks with intruded mantle-derived magmas similar to a local basaltic-andesite.
15
Moertle, Jasmine A. "Stable isotope evidence for a complex fluid evolution of the Northwestern British Columbia Coast Mountains related to terrane accretion." Thesis, California State University, Long Beach, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10147322.
Повний текст джерелаАнотація:
Stable isotope analysis of thirty-five samples from the Northwestern Coast Mountains indicates a complex fluid history related to terrane accretion, metamorphism, and magmatism. The greenschist to amphibolite facies metasedimentary rocks from the Western Metamorphic Belt have variable δD and δ 18O values that appear to be in isotopic equilibrium with metamorphic fluids at low water-rock ratio conditions. Carbon isotope values indicate organic rich protoliths. Stable isotope values from the Coast Shear Zone indicate the involvement of both magmatic and meteoric-hydrothermal fluids during deformation, in contrast to meteoric-free fluid systems related to Au-mineralization along strike to the north (Goldfarb et al., 1988). The Coast Mountain Batholith and Central Gneiss Complex have homogeneous δD and δ 18O values that indicate magmatic fluids at low water-rock ratio (Magaritz and Taylor, 1976). Further to the east, large amounts of meteoric-hydrothermal fluids circulated through a network of ductile-to-brittle normal faults (Andronicos et al., 2003; Heah, 1990).
16
Scudeler, Carlotta, Luke Pangle, Damiano Pasetto, Guo-Yue Niu, Till Volkmann, Claudio Paniconi, Mario Putti, and Peter Troch. "Multiresponse modeling of variably saturated flow and isotope tracer transport for a hillslope experiment at the Landscape Evolution Observatory." COPERNICUS GESELLSCHAFT MBH, 2016. http://hdl.handle.net/10150/621948.
Повний текст джерелаАнотація:
This paper explores the challenges of model parameterization and process representation when simulating multiple hydrologic responses from a highly controlled unsaturated flow and transport experiment with a physically based model. The experiment, conducted at the Landscape Evolution Observatory (LEO), involved alternate injections of water and deuterium-enriched water into an initially very dry hillslope. The multivariate observations included point measures of water content and tracer concentration in the soil, total storage within the hillslope, and integrated fluxes of water and tracer through the seepage face. The simulations were performed with a three-dimensional finite element model that solves the Richards and advection–dispersion equations. Integrated flow, integrated transport, distributed flow, and distributed transport responses were successively analyzed, with parameterization choices at each step supported by standard model performance metrics. In the first steps of our analysis, where seepage face flow, water storage, and average concentration at the seepage face were the target responses, an adequate match between measured and simulated variables was obtained using a simple parameterization consistent with that from a prior flow-only experiment at LEO. When passing to the distributed responses, it was necessary to introduce complexity to additional soil hydraulic parameters to obtain an adequate match for the point-scale flow response. This also improved the match against point measures of tracer concentration, although model performance here was considerably poorer. This suggests that still greater complexity is needed in the model parameterization, or that there may be gaps in process representation for simulating solute transport phenomena in very dry soils.
17
Luo, Yan. "U-Pb age and Hf isotopic study of detrital zircons from the Liaohe Group constraints on the evolution of the Jiao-Liao-Ji Belt, North China craton /." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B36639242.
Повний текст джерела
18
Wasilewski, Benjamin. "Geochronology, Petrogenesis and Crustal Evolution of the Saglek-Hebron Complex (Northern Labrador): Over One Billion Years of Archean Geological History." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39617.
Повний текст джерелаАнотація:
The Saglek-Hebron Complex (SHC) in Northern Labrador represents one of the oldest terrains on Earth and it is closely related to the Archean Itsaq Gneiss Complex (IGC) in Greenland. The SHC is a typical granite-greenstone terrain that recorded over one billion years of magmatic history between ~3900 Ma and ~2700 Ma. Our geochronological and geochemical study shows that the SHC includes five generations of trondhjemite-tonalite-granodiorite suites (TTG): the ~3870 Ma Iqaluk gneiss, the ~3750 Ma Uivak I gneiss, the ~3600 Ma Uivak II gneiss, the newly described ~3300 Ma Iluilik gneiss, and the ~3220 Ma Lister gneiss. These granitoid units are mostly consist of trondhjemite and tonalite with only rare granodiorites that appear to define a distinct unit formed at ~3330 Ma and newly defined as the Iluilik gneiss. The Iluilik granodiorite appears to be derived from a Hadean mafic crust as supported by its combined whole-rock geochemical composition, its positive µ142Nd value of +6, and its low εHf= -6 and εNd= -3, at 3300 Ma. SHC granites were emplaced throughout the Archean, from 3800 to 2700 Ma, but are predominant in the Neoarchean. They appear to have been mainly formed from the reworking of the SHC TTG, as supported by their low εHf and εNd initial values of respectively -16 and -11 at 2700 Ma. The granitoids include numerous enclaves of supracrustal rocks from various size, up to a few kilometers in scale, consisting of metavolcanic metasedimentary rocks. Previous work has suggested that they were formed at two different ages, with the younger Upernavik supracrustal unit deposited around 3400 Ma and the older Nulliak supracrustal assemblage deposited at around 3750 Ma. We show that both units are comparatively geochemically homogeneous with no distinction between the mafic and ultramafic rocks from both supracrustal assemblages. They mainly consist of mafic metavolcanic amphibolites with tholeiitic affinities, consistent with more depleted mafic and more enriched compositions produced by magmatic differentiation. Their complementary Eu anomaly and whole-rock geochemistry suggest that they formed from fractional crystallization of gabbroic assemblage that derived from similar if not the same parental magma. The mafic metavolcanic rocks are also often associated with ultramafic rocks that we divided into two distinct units, respectively referred as the high-Fe and the low-Fe ultramafic rocks, characterized by different FeO contents and Al/Ti ratio. They both represent olivine-rich cumulative rocks derived from distinct parental komatiitic basalt magmas. Our interpretation contrasts with previous work suggesting that the SHC ultramafic rocks were komatiites and slivers of residual lithospheric mantle. Most SHC TTG exhibit a positive 142Nd anomaly, as high as µ142Nd = +15, suggesting a source formed by differentiation in the Hadean. This 142Nd isotopic composition is similar to the Nulliak supracrustal rocks that exhibit on average a µ142Nd of +10. TTG is generally considered to derive from a mafic precursor. This study therefore shows that mafic crustal source of the SHC Eoarchean TTG, potentially the Nulliak metabasalts, derives from an ancient highly depleted mantle, described as the Saglek mantle, sharing a similar early history as the mantle reservoir involved in the formation of the ancient Itsaq terrane of southwest Greenland. The Saglek depleted mantle is interpreted to have formed at ~4400 Ma, exhibit highly depleted signature with a 147Sm/144Nd ratio of 0.221-0.240.
19
Hannon, Jeffrey S. "Reconstructing the Generation, Evolution, and Migration of Arc Magmatism using the Whole-rock Geochemistry of Bentonites: A Case Study from the Cretaceous Idaho-Farallon Arc System." University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1613745220524224.
Повний текст джерела
20
Young, Elisa Joanna. "Mass-dependent and mass-independent sulfur isotope fractionation in precambrian sediments as a key to early atmospheric and oceanic evolution /." [St. Lucia, Qld.], 2005. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe19447.pdf.
Повний текст джерела
21
Starkey, Natalie. "Evolution of the Earth's mantle-crust-atmosphere system from the trace element and isotope geochemistry of the plume-mantle reservoir." Thesis, University of Edinburgh, 2009. http://hdl.handle.net/1842/5934.
Повний текст джерелаАнотація:
The 62 million year old lava flows of Baffin Island and West Greenland represent the earliest phase of magmatism in the North Atlantic Igneous Province (NAIP). These picritic lavas are characterised by high magnesium contents owing to their high proportion of olivine crystals. The parental magmas for the picrites are likely to have accumulated olivine crystals on their transit through the lithosphere and crust. Debate over the origin of accumulated crystals in the lavas results in uncertainty in the temperature and composition of the parental magmas for the early NAIP. The magnesium-rich olivine crystals (up to Fo93) in the picrites of this study are shown not to have a xenocrystic origin. The samples, therefore, support the inference of high potential temperatures for the Baffin Island-West Greenland magmas, ~200oC above ambient mantle. The picrites of Baffin Island and West Greenland display the highest terrestrial magmatic 3He/4He (up to 50 Ra, where Ra is the atmospheric value 1.39 x 10-6), values that are considerably higher than the highest 3He/4He in contemporary ocean island basalts, which reach a maximum of ~30 Ra. High 3He/4He in Baffin Island and West Greenland are associated with a wide range of incompatible trace element and lithophile radiogenic isotopic compositions, not dissimilar to the range of compositions displayed by lavas at mid-ocean ridges, and overlapping the range displayed by most northern hemisphere ocean island basalts. Crustal contamination modelling in which high-grade Proterozoic crustal basement rocks are mixed with depleted parents cannot account for the compositional trends displayed by the picrites. Major and trace element compositions were determined on melt inclusions in high- 3He/4He picrites that span a wide range of whole-rock incompatible trace element and radiogenic isotopic compositions. The melt inclusions support the findings from the whole-rock study since melt inclusion compositions reflect the composition of their associated whole-rock, with no anomalous compositions present. In addition, there is no evidence for a contribution of a proportion of depleted melts to the source of the relatively enriched whole-rock samples. Therefore, since all melt inclusions were contained within high-3He/4He samples, it is shown that high 3He/4He is a feature of both depleted and relatively enriched melt compositions. The wide range in whole-rock compositions of the Baffin Island and West Greenland picrites represents that of the sub-lithospheric mantle source region and is inconsistent with derivation of the picrites from residues of ancient mantle depletion. The apparent decoupling of helium from trace elements and radiogenic isotopes is hard to reconcile with simple mixing of a high-helium concentration, high-3He/4He reservoir with various depleted and enriched helium-poor mantle reservoirs. It is possible that primordial helium has diffused into a reservoir with a composition similar to that of the convecting upper mantle. However, this must have occurred after the development of existing mantle heterogeneity. The high-3He/4He picrites require the existence of a deep, primordial helium-rich reservoir. Whether this reservoir is present in the upper or deep mantle, or even the core, remains uncertain.
22
Bright, Jordon, and Jordon Bright. "Multi-Disciplinary Paleoenvironmental Context for the Integration of the Lower Colorado River Corridor, Bouse Formation, CA-AZ, USA, and Middle to Late Pleistocene Human Evolution, the Koora Plain, Southern Kenya." Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/625880.
Повний текст джерелаАнотація:
Since the seminal works of Wegener and Darwin the notion that things evolve, and the how and the why of it, has generated intense debate. The surface of the Earth, and the creatures that live on it, are not static entities. Landscapes evolve. Organisms evolve. Understanding the how and the why requires a firm understanding of a myriad of interdependent and complex variables such as (but not limited to) climate, ecology, and tectonics. Unravelling the complexities though which landscapes and ecosystems evolve requires a broad interdisciplinary approach, where multiple investigative tools are simultaneously brought to bear on a given question. The study of old lake sediments, or paleolimnology, is a marquee example of a powerful interdisciplinary methodology that has been used extensively in reconstructing the Earth's past.
This work showcases two examples where the discipline of paleolimnology advances our understanding of evolution on a landscape scale and on a human scale. In the southwestern United States, a record of the processes involved during the late Miocene and early Pliocene (~ 5 Ma) evolution of a major continental river drainage - the Colorado River – is partially preserved along the southern border of Arizona and California as the enigmatic Bouse Formation. And in southern Kenya, nearly 170 meters of lake and wetland sediments that have accumulated in the Koora Plain preserve a one-million-year long record of the environmental conditions against which our species, Homo sapiens, evolved.
My research allows me to conclude that the depositional environment of the Bouse Formation was lacustrine; a fully marine interpretation that has been previously proposed is untenable. I also demonstrate that over the past 1.0 Ma, Homo sapiens in southern Kenya evolved against a backdrop of increasing regional aridity.
23
Herbert, Gregory S. "Biotic evolution in Plio-Pleistocene marine environments of tropical America : systematic, phylogenetic, and stable isotope investigations of the Muricidae (Mollusca: Gastropoda) /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2005. http://uclibs.org/PID/11984.
Повний текст джерела
24
Li, Jiayue. "The preservation of protein dynamics from bacteria to human dihydrofolate reductase." Diss., University of Iowa, 2019. https://ir.uiowa.edu/etd/6984.
Повний текст джерелаАнотація:
Protein motions are complex, including occurring at different time scales, and their roles in enzyme-catalyzed reactions have always been of great interest among enzymologists. In order to characterize the potential factors that play a role on the chemical step of enzymatic reactions, variants of dihydrofolate reductase have been used as a benchmark system to study the motions of proteins correlated with the chemical step. A “global dynamic network” of coupled residues in Escherichia coli dihydrofolate reductase (ecDHFR), which assists in catalyzing the chemical step, has been demonstrated through quantum mechanical/molecular mechanical and molecular dynamic (QM/MM/MD) simulations, as well as bioinformatic analyses. A few specific residues — M42, G121, and I14 — were shown to function synergistically with measurements of single turnover rates and the temperature dependence of intrinsic kinetic isotope effects (KIEsint) of site-directed mutants. Although similar networks have been found in other enzymes, the general features of these networks are still unclear. This project focuses on exploring homologous residues of the proposed global network in human DHFR through computer simulations and measurements of the temperature dependence of KIEsint. The mutants M53W and S145V, both remote residues, showed significant decreases in catalytic efficiency. Non-additive isotope effects on activation energy were observed between M53 and S145, indicating their synergistic effect on hydride transfer in human DHFR.
Apart from the effects of the conserved residues, we also extend our studies to exploring three potential phylogenetic events that account for the discrepancies between E. coli and human DHFR. They are L28, PP insertion and PEKN insertions by phylogenetic sequence analysis. Two of them (N23PP and G51PEKN E. coli DHFR) have been proved to be important both by MD simulation and experimental probe of KIEs measurement. The experiments have found that PP insertion itself rigidified the M20 loop and motions coupled to hydride transfer were impaired, however, loop rigidification was improved after incorporating PEKN. Furthermore, deletion of PP and PEKN of the engineered human enzyme also show a similar outcome. However, the effect of the key residue of L28 is not clear. In this project, we have step-wise engineered the human DHFR to be like hagfish (F31M) and E. coli (F32L). And it is found out that there is an increase in the temperature dependence of KIEs when the enzyme was bacterilized into a more primitive variant. This indicates that not only is residue F32 important and correlated with the chemical step as indicated by bioinformatic studies, but it is possible to trace the evolutionary trajectory. A triple mutation F32L-PP26N-PEKN62G on the human DHFR was also conducted, and it is not surprising to find out that the temperature dependence of KIEs has retained its behavior like wild-type human DHFR. These results suggest that the three predicted phylogenetically coherent events coevolved together to maintain the evolutionary preservation of the protein dynamics to enable H-tunneling from well-reorganized active sites.
As has been indicated by the previous project, as the enzyme evolves, the active site of the enzyme will “reorganize” to form the optimal transition state for chemical step (from F32L-F32M-wild type DHFR). Here in this project, we aimed to systematically address this point of view through a series of cyclic permutation DHFR from directed evolutions. As this primitive enzyme is 7 orders of magnitude less efficient than the well-evolved human DHFR, together with four generations of evolved variants (cp, cp’ and cp”), this provides a good model system for explorations of the molecular basis of enzyme evolution. It is found that the organizations of transition state are improved before the catalytic efficiency is enhanced as the enzyme evolves.
25
McNeil, Mardi A. "Spatial and temporal evolution and internal sedimentary architecture of Holocene Halimeda bioherms; northern Great Barrier Reef." Thesis, Queensland University of Technology, 2021. https://eprints.qut.edu.au/209916/1/Mardi_McNeil_Thesis.pdf.
Повний текст джерелаАнотація:
This research investigates the initiation and growth of Holocene Halimeda algal limestone build-ups in the Great Barrier Reef. Legacy sediment samples and newly acquired analytical data were combined to explain inter-reef Halimeda bioherm origins, temporal growth and development, spatial distribution, geomorphology, carbonate volume, nutrient source, and habitat significance. Halimeda bioherms are much more complex than previously thought. The project contributes a significant new understanding of the Halimeda bioherm geological and ecological system in space and time, elevating the importance of Halimeda bioherms as Holocene sedimentary archives and modern inter-reef benthic habitats.
26
Luo, Yan, and 羅彥. "U-Pb age and Hf isotopic study of detrital zircons from the Liaohe Group: constraints on the evolution of theJiao-Liao-Ji Belt, North China craton." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B36639242.
Повний текст джерела
27
Cochrane, Dylan. "Stratigraphic and Carbon Isotope Evolution of an Ediacaran Mixed Siliciclastic Deep-Marine Base-of-Slope System, First Isaac Carbonate, Windermere Supergroup, Canadian Cordillera, British Columbia." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37363.
Повний текст джерелаАнотація:
The first Isaac carbonate (FIC) is a mixed siliciclastic-carbonate base-of-slope succession in the Neoproterozoic Windermere Supergroup (WSG). Outstanding outcrop exposure at three study areas provided an excellent opportunity to observe the stratigraphic and isotopic evolution of an ancient deepwater mixed turbidite system. Based on lithological and stratal dimensions, the FIC can be subdivided into lower and upper parts suggesting temporal changes in patterns of sediment transport and deposition. δ13Ccarb also changes from -5.2‰ at the base of the FIC to 2.5‰ in the middle and then decreases to -6.3‰ at the top. Notably, the δ13Ccarb of primary cement in FIC strata is substantially more positive than most other Neoproterozoic deep-marine sections, suggesting the retention of their original shallow-marine isotopic signature. Nevertheless, this trend potentially correlates with the EN2 excursion in China and therefore the Gaskiers glaciation (~580 Ma), although better age control of WSG is needed to corroborate this correlation.
28
Fries, Anthony Charles. "The effect of migratory activity of waterfowl on the evolution and ecology of influenza A viruses." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1439893550.
Повний текст джерела
29
Li, Shanying. "Petrological and stable isotopic study of lacustrine and paleosol carbonates: Implications for paleoelevation and tectonic evolution of the Tibetan Plateau." Miami University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=miami1461562459.
Повний текст джерела
30
Linde, G. M., J. H. Trexler, P. H. Cashman, G. Gehrels, and W. R. Dickinson. "Three-Dimensional Evolution of the Early Paleozoic Western Laurentian Margin: New Insights From Detrital Zircon U-Pb Geochronology and Hf Isotope Geochemistry of the Harmony Formation of Nevada." AMER GEOPHYSICAL UNION, 2017. http://hdl.handle.net/10150/626478.
Повний текст джерелаАнотація:
Uranium-lead (U-Pb) geochronology and Hafnium (Hf) isotope geochemistry of detrital zircons of the Harmony Formation of north central Nevada provide new insights into the tectonic evolution of the Late Paleozoic western Laurentian margin. Using laser-ablation inductively coupled plasma mass spectrometry, 10 arenite samples were analyzed for U-Pb ages, and 8 of these samples were further analyzed for Hf isotope ratios. Three of the sampled units have similar U-Pb age peaks and Hf isotope ratios, including a 1.0-1.4Ga peak with epsilon Hf values of +12 to -3 and a 2.5-2.7Ga peak with epsilon Hf values of +7 to -5. The remaining seven samples differ significantly from these three, but are similar to one another; having age peaks of 1.7-1.9Ga with epsilon Hf of +10 to -20 and age peaks of 2.3-2.7Ga with epsilon Hf of +6 to -8. The data confirm the subdivision of the Harmony Formation into two petrofacies: quartzose (Harmony A) and feldspathic (Harmony B). The three samples with 1.0-1.4 and 2.5-2.7Ga peaks are the Harmony A, which originated in the central Laurentian craton. The other seven samples are the Harmony B, which originated in eastern Alberta-western Saskatchewan, north of the Harmony A source. We propose that all Harmony Formation strata were deposited near eastern Alberta and subsequently tectonically interleaved with Roberts Mountains allochthon strata. We interpret that the entire package was tectonically transported south along the western Laurentian margin and then emplaced eastward onto the craton during the Late Devonian-Early Mississippian Antler orogeny.
31
Zeng, Wen. "The evolution of the metamorphic series in the NW Fujian Province, the NE Cathaysia Block, and the significance in the reconstruction of Precambrian Supercontinents." Thesis, Curtin University, 2010. http://hdl.handle.net/20.500.11937/1091.
Повний текст джерелаАнотація:
This thesis focuses on the Paleoproterozoic to Late Paleozoic basement evolution of the metamorphic rocks scattered in the NW Fujian Province, the NE Cathaysia Block the southeastern area of South China. Field observation, systematic sampling and petrographic investigation combined with of whole rock geochemistry, zircon U-Pb, Lu-Hf isotopes, trace elements, amphibole and biotite 40Ar/39Ar analyses and mineral chemistry study were applied in this project to determine the nature, ages and relations of the leucosomes, felsic paragneiss and mafic metamorphic rocks in study area and their implications to the reconstruction of the Precambrian Rodina Supercontinent.Following conclusions are made: 1. Based on this study, according to their metamorphism and deformation characteristics, the metamorphic rock series in the study area can be divided into two types, moderately to strongly metamorphosed rock series that experienced ductile deformation and moderately metamorphosed rock series that have experienced ductile deformations. New La-ICPMS U-Pb zircon ages presented here and in previous study suggest that the original lithostratigraphy should be abandoned and the terminology “Complex” should be used instead of “Group” and “Formation” for the high grade metamorphic rock series in northwestern Fujian, where the protoliths were strongly reworked by Early Paleozoic tectono-thermal events.2. Obvious zircon U-Pb age peaks of ~1800 Ma suggest that the protoliths ofthe Cathaysia Block be comparable to the basements of North America ratherthan those of Eastern India and East Antarctica. Although the peaks of ~1800Ma are also present in Western Australia, their 176Hf/177Hf ratios (0.280706 -0.281510) are apparently lower than those of zircons from SW Cathaysia (0.281515 - 0.282098) and from this study (0.281232 - 0.282213, NECathaysia). Besides, detrital zircons in Cathaysia and NW Yangtze indicatesignificant juvenile input during Paleo- to Mesoproterozoic according to thezircon Hf isotopes, which are distinctly different from Western Australia.These evidences suggest that the basement of the Cathaysia share similaritieswith that of North America, lending support for the Rodinia configurationproposed by Li et al. (2008), in which Cathaysia was next to western Laurentia before and during the late Mesoproterozoic assembly of Rodinia.2. Obvious zircon U-Pb age peaks of ~1800 Ma suggest that the protoliths of the Cathaysia Block be comparable to the basements of North America rather than those of Eastern India and East Antarctica. Although the peaks of ~1800 Ma are also present in Western Australia, their 176Hf/177Hf ratios (0.280706 - 0.281510) are apparently lower than those of zircons from SW Cathaysia (0.281515 - 0.282098) and from this study (0.281232 - 0.282213, NE Cathaysia). Besides, detrital zircons in Cathaysia and NW Yangtze indicate significant juvenile input during Paleo- to Mesoproterozoic according to the zircon Hf isotopes, which are distinctly different from Western Australia. These evidences suggest that the basement of the Cathaysia share similarities with that of North America, lending support for the Rodinia configuration proposed by Li et al. (2008), in which Cathaysia was next to western Laurentia before and during the late Mesoproterozoic assembly of Rodinia.3. The protoliths of the felsic paragneiss in the NW Fujian area are immaturesediments, consisting of greywacke, arkose and lithic arenite compositions.The significant input of the paragneiss protolith was dominantly formed byseveral magmatic events during Neoproterozoic (820 ± 6 Ma, 780 ± 6 Ma, 776± 6 Ma, 758 ± 3 Ma, 740 ± 8 Ma and 722 ± 9 Ma), probably deposited notearly than middle Neoproterozoic (~680 Ma). Many metamorphic rockscontain 0.99 - 0.72 Ga detrital magmatic zircons, which are interpreted asreflecting the tectono-thermal events related to the assembly and break-up of the Rodinia supercontinent during the Neoproterozoic.4. In this study, new La-ICPMS U-Pb anatectic zircon data from the NWFujian area suggest that the strong and widespread tectono-thermal eventswere related to the orogeny probably having started during the MiddleCambrian and lasted until the Middle Devonian, consisting of at least threemain episodes (~473 Ma, ~445 Ma, ~423 Ma), with major orogeny events(including syn- to post-orogenic melting) constrained between ~473 Ma and~407 Ma in the NE Cathaysia, and between ~468 Ma and ~415 Ma in the SWCathaysia. The age peaks in the Cathaysia Block (ca. 488, 471, 455, 440 and415 Ma) are within the age range of the Qinling-Tongbai-Dabie orogen during 512 - 406 Ma. This suggests a possible linkage or interaction of the two orogens.5. The duration of the “Caledonian” orogeny in the NW Fujian area was noshorter than ~50 Myr, starting at ~473 Ma (~Early Ordovician) or earlier, andterminating at ~423 Ma (~Middle Silurian) or later. The “Caledonian”orogenic event in the Cathaysia Block was likely due to an intracontinentalcollision rather than the subduction of oceanic crust or arc-continentalcollision. Considering the inhomogeneous cooling paths for the Tianjingping,the Jiaoxi and Mayuan complexes, and different time restraint of thewidespread anatectic and magmatic events occurred in different places, the“Caledonian” tectono-thermal events in the Cathaysia Block might vary between different segments of the orogen.
32
Sossi, Paolo. "Petrogenesis of ultramafic rocks and an experimental and natural investigation of non-traditional stable isotope fractionation at high temperatures : implications for the chemical evolution of the earth and planets." Phd thesis, Canberra, ACT : The Australian National University, 2015. http://hdl.handle.net/1885/124061.
Повний текст джерелаАнотація:
The fractionation of stable isotopes at high temperatures offers a unique insight into the sources and
processes operative during planetary accretion. Through analysis of meteorites and samples that are
representative of planetary reservoirs, a coherent picture is built of the isotopic variation present in
solar system materials. However, this objective is complicated by the selection of samples appropriate
to characterise the isotopic composition of the entire Earth. In minimising the uncertainty in this
assumption, ultramafic (olivine-rich) rocks are used, as these are most representative of the Earth's
mantle, which constitutes ~ 70% (by mass) of the Earth. Peridotites from the Balmuccia massif and a
global selection of komatiites, with care taken to select only the least chemically-modified examples,
were collected and characterised. Because it is known that stable isotopes fractionate during
magmatic processes, the best estimate of the composition in equilibrium with the primitive mantle is
computed by considering the petrogenetic processes that lead to the formation of these rocks.
Through the course of this exercise, a new model is posited to explain chemical depletion in
peridotites, which arises, not only from melt extraction, but from pressure-solution re-distribution of
pyroxenes, two complementary processes. It is proposed that, since the chemical trends observed in
peridotites are of global significance, this process is ubiquitous, occurring in-situ in zones of adiabatic
decompression mantle melting. Komatiites, as high degree partial melts of the mantle, require high
mantle temperatures that can only have been achieved early in Earth history. It is demonstrated that
the origin of the two distinct komatiite types, Aluminium-Depleted and Aluminium Undepleted,
reflects not only the pressure, but the degree of melting. Over time, their mantle sources incorporate
progressive amounts of depleted, upper mantle material, effectively tracking crustal growth.
Furthermore, because the magnitude of stable isotope fractionation is proportional to 1/T2, these high
temperature samples allow an assessment of mantle composition through time and space. Due to the
small variations in isotope composition at these high temperatures, optimised analytical procedures
for the measurement of Cu, Fe, Zn and V isotopes are detailed, and document improved precision with
respect to previously published methods. Using this technique, new values for the Fe and Zn isotope
compositions of the Bulk Silicate Earth are derived. Supplementary analyses of the isotopic
composition of Mars, together with already-published analyses of chondritic meteorites (the
supposed building-blocks of Earth) and the Moon, shows that the Earth-Moon system has a
fractionated isotopic composition. With this information, a new interpretation of the timescales and
composition of Earth's accretion is suggested. Briefly, the volatile element budget of the Earth was set early in its accretion, by material more volatile-depleted than any of the known chondrite groups.
Accretion then became progressively more oxidising, culminating in the Moon-forming impact, which
delivered % of the Earth's complement of iron, and, importantly, in an oxidised form, as observed in
the contemporary mantle. These interpretations are underpinned by experimental measurements of
expected iron isotope fractionation factors between common igneous phases - silicates, oxides and
metal. These determined partition coefficients are also applied to a series of igneous problems,
including the generation of basalt, crystallisation of the lunar magma ocean, and the formation of
granites.
33
Dia, Aline. "Sediments et evolution geochimique (evolution de la croute continentale et etude de la limite cretace-tertiaire) : contraintes apportees par l'analyse isotopique (neodyme et plomb) et les teneurs en elements traces." Paris 7, 1988. http://www.theses.fr/1988PA077050.
Повний текст джерелаАнотація:
L'utilisation d'analyses isotopiques (nd et pb) et des teneurs en elements-trace a permis d'aborder plusieurs aspects de la geochimie des roches sedimentaires. On s'interesse a l'aspect temporel enregistre par les sediments avec la caracterisation de la croissance de la croute continentale et l'etude de son evolution chimique au cours du temps (afrique du sud et canada). L'autre aspect etudie concerne l'individualisation des contributions respectives des sources de particules sedimentaires (etude isotopique de la limite cretace-tertiaire, evolution geochimique du bassin oceanique marocain), les concentrations secondaires ou les phenomenes de circulation
34
Li, Yuyu M. S. "Petrologic Insights into Basaltic Magma Genesis beneath East Antarctica." Bowling Green State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1593363487482443.
Повний текст джерела
35
Wraith, C. "The evolution of nuclear structure in odd-A zinc isotopes." Thesis, University of Liverpool, 2018. http://livrepository.liverpool.ac.uk/3029031/.
Повний текст джерела
36
Broadley, Michael Ward. "Tracing mantle structure and chemical evolution using noble gas isotopes." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/tracing-mantle-structure-and-chemical-evolution-using-noble-gas-isotopes(a231d757-1535-4edd-899c-b2ecff0accf9).html.
Повний текст джерелаАнотація:
The mantle is the largest reservoir of many of the Earth’s volatile species. Detailed isotopic studies of noble gases within the mantle volatiles have demonstrated that they are of a primordial origin, which have been trapped in the mantle since the Earth’s accretion. This original volatile signature has continually evolved over time, due to the production of in situ radiogenic isotopes and through the recycling of surface volatiles back into the mantle (Lupton and Craig, 1975; Holland and Ballentine, 2006). The study of noble gases within magmatic samples has enabled the composition and structure of the mantle to be determined and has distinguished the multiple volatile reservoirs (primordial, crustal, marine etc.) that have contributed to the mantle composition sampled. Together with the halogens (Cl, Br and I) they represent key tracers of volatile transport processes in the Earth. Therefore a combined analytical approach including the halogens and noble gases is not only be able to track the influx of surface volatile into the mantle, but also provide a greater understanding to the fundamental controls of transport, storage and partitioning of volatiles within the mantle. A combined noble gas and halogen study was undertaken on three different geological samples sets to determine how surface volatiles interact with the mantle on a variety of different scales. Firstly continental xenoliths from the Western Antarctic Rift were analysed to establish the role of subduction volatiles in the creation of the rifts volcanic products. The xenoliths have 3He/4He ratios of 7.5RA indicating that the rift is dominated by the rising asthenospheric mantle. However the Br/Cl and I/Cl ratio and heavy noble gases within the xenoliths indicate that marine derived volatiles have been incorporated into the mantle beneath the rift and may have provided and fundamental control on the formation of the rift itself. Secondly the role of surface contamination on mantle samples has been evaluated. A transect along a MOR pillow basalt has been analysed for its halogen concentrations in conjunction with the previously determined noble gases. The outer sections are enriched in Cl relative to Br and I due to the assimilation of a high salinity brine during eruption. In contrast the crystalline interior of the pillow has MORB like Br/Cl and I/Cl ratios but elevated 132Xe/36Ar ratios indicative of the incorporation of pelagic sediments. This small scale analytical approach has shown that submarine pillow basalts are prone to contamination from the surrounding marine environment and provides a method for the identification and quantification of marine contamination. Finally the halogens within olivine phenocrysts from three Emperor Seamounts have been analysed to determine the distribution of the halogens within the lower mantle. The I/Cl ratio of the samples evolves from a MORB-like ratio in the oldest seamount to elevated values similar to sedimentary pore fluids and chondrites in the younger seamounts. This indicates that the Hawaiian mantle plume contains isolated pockets of subducted or primordial material which have been isolated from whole mantle mixing and have therefore retained a halogen signature distinct from the average mantle values.
37
Albers, Michael [Verfasser]. "Evolution of nuclear deformation in neutron-rich Kr isotopes / Michael Albers." München : Verlag Dr. Hut, 2011. http://d-nb.info/1015606350/34.
Повний текст джерела
38
Dawelbeit, Mohammedahmed Eltahir Ahmed. "Evolution sédimentaire et climatique du Kordofan (Soudan) au quaternaire supérieur." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAU022/document.
Повний текст джерелаАнотація:
Cette étude concerne la région du Kordofan, au centre-Sud du Soudan. La région étudiée est comprise entre les méridiens 28° 00' et 31° 00' E, et les latitudes 11° 30' et 15°00' N, et couvre une surface d’environ 125 835 km2. Le Kordofan est situé en bordure Sud du Sahara actuel. Les dépôts du Pléistocène supérieur-Holocène du Kordofan, ont enregistré des discontinuités sédimentaires qui reflètent des fluctuations climatiques au cours du Quaternaire terminal. Des datations au 14C et des collectes archéologiques ont permis de dater la série étudiée. Quatre unités stratigraphiques ont été identifiées, qui comprennent huit faciès sédimentaires.La première unité est antérieure à ≈ 10 ka BP et est formée de grès ou siltstone marmorisés d’origine éolienne. La deuxième unité (≈ 10 à 6 ka BP) comprend des faciès palustres et lacustres au Nord et au centre, et des faciès fluviatiles au Sud. La troisième unité, d’âge ≈ 6 à 3 ka BP, n’est présente qu’au Sud; elle est faite de dépôts éoliens intercalés de faciès fluviatiles ou de plaine d’inondation. La quatrième unité est plus jeune que 1000 ans BP, et est dominée par des grès rouges éoliens au Nord, et par des dépôts de plaine d’inondation au Sud. Entre ≈ 6 et 1 ka BP au Nord et entre ≈ 3 et 1 ka BP au Sud, un hiatus est marqué par une surface de déflation au North, et est interprété comme une période de forte activité éolienne, qui a empêché le dépôt et a même érodé une partie des sédiments déposés entre 6 et 3 ka BP.Plusieurs proxys (sédimentologie, gastéropodes, pollens, isotopes stables, géochimie des majeurs, minéralogie des argiles et paléo-hydrologie) ont servi à reconstituer l’évolution climatique de la région depuis 13000 ans, qui est cohérente avec l’évolution paléo-climatique de l’Afrique nord-orientale à la même époque. Nos résultats montrent que la région a connu un climat aride avant 10 ka BP, matérialisé par d’épais dépôts éoliens. Entre 10 et 6 ka BP, un climat humide est démontré par le développement de nodules calcaires pédogénétiques, le dépôt local de calcaires palustres et lacustres, l’abondance de gastéropodes aquatiques et semi-aquatiques, le haut niveau de lacs, et les valeurs très négatives du δ18O des coquilles d’escargots et des nodules calcaires. Après ≈ 6 ka BP, le climat s’assèche dans le Nord de la région étudiée comme le suggèrent la forte activité éolienne enregistrée par un hiatus sédimentaire, des érosions et surfaces de déflation, alors que le Sud reste plus humide, comme le montrent des dépôts fluviatiles (chenaux et plaine d’inondation), et les pollens tropicaux et aquatiques. Après 1000 ans BP, et plus probablement après 3 ka BP, la région devient aride comme en témoignent les dépôts éoliens, la prédominance de pollens de milieu aride et l’enrichissement en 18O des coquilles d’escargots terrestresThis study is conducted in the Kordofan region, central-southern Sudan. The study area is bounded by longitudes 28° 00' and 31° 00' E, and latitudes 11° 30' and 15°00' N and covers an area of about 125835 km2. The Kordofan region is located at the southern end of the present-day Sahara. Late Pleistocene-Holocene deposits in Kordofan, recorded sedimentary discontinuities that probably reflect climatic fluctuations during the latest Quaternary. 14C dating and some archeological findings have been used to date the latest Pleistocene-Holocene succession. In the investigated sections, four stratigraphic units have been recognized, which exhibit eight sedimentological facies.The first unit is older that ≈ 10 ky BP and is formed of mottled sandstone or siltstone facies of aeolian origin. The second unit (≈ 10 to 6 ky BP) comprises palustrine and lacustrine facies in the central and northern parts, and fluviatile facies in the South. The third unit ranges from ≈ 6 to 3 ky BP and is restricted to the southern part; it is made of aoelian deposits intercalated with fluviatile or flood plain facies. The fourth unit is younger than 1000 y BP, and is dominated by aeolian red sandstone in the North, and by flood plain facies to the South. Between ≈ 6 and 1 ky BP in the North and between ≈ 3 and 1 ky BP in the South, no deposits are recorded. This hiatus is marked by deflation surfaces in the North, and is interpreted as a period of strong aeolian activity, which prevented deposition, or even eroded part of the sediments deposited between 6 and 3 ky BP.Several proxies (sedimentology, gastropod sub-fossil shells, pollens, stable isotopes, major element chemistry, clay mineralogy and paleohydrology) have been used to reconstruct the climatic evolution of the region for the past 13 ky, which can be correlated to the well-known evolution of Eastern Sahara during this time-span. Our results indicate that the region has been subjected to arid climate prior to 10 ky BP as evidenced by thick aeolian deposits. Between 10 and 6 ky BP, the region experienced a wet climate as evidenced by the development of pedogenetic calcareous nodules, local deposition of palustrine and lacustrine limestone, abundance of aquatic and semi-aquatic gastropods, high lake levels, and depleted δ18O values from gastropod shells and calcareous nodules. After ≈ 6 ky BP, climate evolved to dry conditions in the northern part of the region as indicated by an strong aeolian activity recorded by erosion features, sedimentary hiatus and deflation surfaces, while its southern part remained more humid, as shown by channel and flood plain deposits, and tropical and aquatic pollen taxa. From 1000 yr BP to Present, and probably after 3 ka BP, the region became arid as evidenced by aeolian deposits, the predominance of arid indicator pollens and the enrichment in 18O of land snail shells
39
Hards, Victoria L. "The evolution of the Snaefell Volcanic Centre, eastern Iceland." Thesis, Durham University, 1995. http://etheses.dur.ac.uk/1452/.
Повний текст джерела
40
Rinckenbach, Thierry. "Diagenese minerale des sediments petroliferes du delta fossile de la mahakam (indonesie) : evolution mineralogique et isotopique des composants argileux et histoire thermique." Université Louis Pasteur (Strasbourg) (1971-2008), 1988. http://www.theses.fr/1988STR13117.
Повний текст джерелаАнотація:
On etudie la diagenese des sediments deltaiques deposes sur plus de 4000m d'epaisseur du miocene inferieur a l'holocene a l'emplacement du delta actuel de la mahakam. On aborde les phenomenes de cimentation, de dissolution avec formation de porosite secondaire et de neoformations de kaolinite et illite a l'aide de la diffraction rx, de la microscopie electronique a balayage et a transmission, de la geochimie isotopique. On analyse les mecanismes d'illitisation ainsi que la formation de l'interstratifie illit nonesmectite en fonction de l'evolution thermique de la region
41
Dean, Matthew, Geoffrey Findlay, Michael Hoopmann, Christine Wu, Michael MacCoss, Willie Swanson, and Michael Nachman. "Identification of ejaculated proteins in the house mouse (Mus domesticus) via isotopic labeling." BioMed Central, 2011. http://hdl.handle.net/10150/610018.
Повний текст джерелаАнотація:
BACKGROUND:Seminal fluid plays an important role in successful fertilization, but knowledge of the full suite of proteins transferred from males to females during copulation is incomplete. The list of ejaculated proteins remains particularly scant in one of the best-studied mammalian systems, the house mouse (Mus domesticus), where artificial ejaculation techniques have proven inadequate. Here we investigate an alternative method for identifying ejaculated proteins, by isotopically labeling females with 15N and then mating them to unlabeled, vasectomized males. Proteins were then isolated from mated females and identified using mass spectrometry. In addition to gaining insights into possible functions and fates of ejaculated proteins, our study serves as proof of concept that isotopic labeling is a powerful means to study reproductive proteins.RESULTS:We identified 69 male-derived proteins from the female reproductive tract following copulation. More than a third of all spectra detected mapped to just seven genes known to be structurally important in the formation of the copulatory plug, a hard coagulum that forms shortly after mating. Seminal fluid is significantly enriched for proteins that function in protection from oxidative stress and endopeptidase inhibition. Females, on the other hand, produce endopeptidases in response to mating. The 69 ejaculated proteins evolve significantly more rapidly than other proteins that we previously identified directly from dissection of the male reproductive tract.CONCLUSION:Our study attempts to comprehensively identify the proteins transferred from males to females during mating, expanding the application of isotopic labeling to mammalian reproductive genomics. This technique opens the way to the targeted monitoring of the fate of ejaculated proteins as they incubate in the female reproductive tract.
42
Cooper, Mark. "The Sudbury igneous complex : insights into melt sheet evolution and ore genesis." Thesis, Open University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340675.
Повний текст джерела
43
Moiroud, Mathieu. "Evolution de la circulation oécanique profonde durant le Crétacé : apport des isotopes du néodyme." Thesis, Dijon, 2014. http://www.theses.fr/2014DIJOS030/document.
Повний текст джерелаАнотація:
Le Crétacé est décrit comme la période la plus chaude des derniers 300 millions d’années. La circulation océanique et l’origine des eaux profondes alimentant les bassins restent mal connues pour le Crétacé, alors qu’elles sont capitales dans la compréhension du rôle de l’océan dans l’évolution du climat à cette époque. Les isotopes du néodyme (Nd) permettent de tracer la circulation océanique et les échanges entre les masses d’eau, et ont été utilisés pour explorer la circulation océanique globale des océans actuels et dans le passé. La composition isotopique en Nd (εNd) des océans dérive de celle des continents qui les entourent. Les courants océaniques exportent cette signature, et les eaux profondes de chaque bassin océanique ont une composition en Nd qui leur est propre. L’interprétation du signal du Nd des eaux océaniques au Crétacé est rendue difficiles du fait de l'insuffisance de la couverture spatiale et temporelle des données existantes. L’objectif de cette thèse est l’acquisition la signature en Nd sur les marges continentales et dans les régions dépourvues de données pour le Crétacé, en se focalisant prioritairement sur les zones potentielles de production d’eau profonde. L’εNd est analysé à partir d’échantillons de dents de poissons, d’oxydes encroûtant les tests de foraminifères et de fraction détritique extraits des sédiments. Les résultats sont comparés aux données de la littérature afin d’identifier les sources des eaux profondes et leur évolution au cours du Crétacé. Les liens entre les changements océanographiques, paléogéographiques et climatiques sont explorés avec un modèle climatique couplé océan-atmosphèreThe Cretaceous is depicted as the warmest period of the last 300 Ma. The oceanic circulation and location of the source zones of deep-waters are essential to understand the role of oceans in the evolution of the climate during the Cretaceous, yet they remain unclear for this period. The neodymium (Nd) isotopes are used to track oceanic circulation and exchanges between water masses, in both past and modern oceans. The Nd isotope composition (εNd) in the ocean is related to the nature of the surrounding continental landmasses. The oceanic currents transport this isotopic signature, thus every oceanic basin acquires a singular εNd. Unequivocal interpretations of the Cretaceous seawater εNd values stem from the insufficient spatial and temporal cover of available data. This PhD thesis intents to collect the Nd signature of continental margins and in regions without data for the Cretaceous, with special attention given to the potential source zones of deep-water production. Fossil fish teeth, coatings on foraminifera tests and detrital fraction from Cretaceous sediments are analyzed for their εNd. The results are compared to published data sets, in order to identify deep-waters source zones and their evolution throughout the Cretaceous. The links connecting oceanographic, palaeogeographic and climatic changes are investigated with a coupled ocean-atmosphere circulation model
44
Ansari, Saba. "Shape evolution in neutron-rich Zr, Mo and Ru isotopes around mass A=100." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS384/document.
Повний текст джерелаАнотація:
La forme d’un noyau, ou la déviation de la distribution en masse par rapport à une forme sphérique, est une des propriétés fondamentales du noyau. Elle est gouvernée à la fois par des effets macroscopiques et microscopiques, tels que l'énergie de liaison donnée par le modèle de la goutte liquide ou la structure en couche du noyau, respectivement. L’étude de la forme des noyaux exotiques par spectrométrie gamma permet de tester finement différents modèles théoriques initialement développés pour les noyaux stables. L’objectif de cette thèse est l’étude de l’évolution de la forme des noyaux exotiques riches en neutrons dans les chaînes isotopiques allant du Zr (Z=40) au Pd (Z=46). Le plus souvent, la forme des noyaux évolue lentement de la forme sphérique, près des fermetures de couche ou des noyaux magiques (ou doublement magiques), à des formes allongées (prolate), pour des noyaux avec de nombreux nucléons de valence. Cependant, Les noyaux auxquels nous nous intéressons ont tendance à avoir des états excités qui évoluent rapidement en fonction du nombre de neutrons, ce qui peut être interprété comme des variations rapides de la forme du noyau. Ceci inclue dans de rares cas l'observation d'états de forme aplatie (oblate) et triaxiale. Jusqu'à présent, les propriétés connues de ces noyaux se limitent (principalement) aux énergies d'excitation. Les informations sur le degré de collectivité nucléaire (que l'on peut déduire de la durée de vie des états excités) sont rares, tandis que les informations directes de forme sont pratiquement inexistantes. L'estimation la plus simple de la déformation nucléaire dans les noyaux pairs peut être obtenue à partir de l'énergie du premier état 2⁺. Pour les isotopes du Sr (Z = 38) et du Zr (Z = 40), il a été observé que cette énergie diminue considérablement à N = 60, alors que son évolution est beaucoup plus progressive pour les isotopes du Mo (Z = 42). Des mesures précises de durée de vie constituent un élément clé de l'étude systématique de l'évolution de la déformation nucléaire et du degré de collectivité dans cette région. Des noyaux riches en neutrons dans la région de masse A = 100-120 ont été peuplés par la réaction de fusion-fission d'un faisceau de ²³⁸U à 6,2 MeV/u sur une cible ⁹Be. Le noyau composé ²⁴⁷Cm était produit à une énergie d'excitation de ∼45 MeV avant de fissionner. Le dispositif expérimental utilisé pour cette étude comprenait le spectromètre de masse de haute résolution VAMOS pour l'identification les noyaux en Z et A, le réseau de 35 détecteurs au germanium AGATA (Advanced γ-ray Tracking Array) AGATA, pour la spectroscopie de rayons γ, ainsi qu'un mécanisme de "plunger" pour mesurer la durée de vie jusqu'à quelques ps par la méthode RDDS (Recoil Distance Doppler Shift). De plus, la cible était entourée de 24 détecteurs LaBr₃ (Bromure de lanthane) pour mesurer des durées de vie plus de 100 ps avec la méthode du "fast-timing". La combinaison de spectromètres sophistiqués utilisée dans cette expérience a permis de mesurer des durées de vie d'états nucléaires allant de 100 picosecondes à quelques picosecondes. Dans cette thèse, nous exposerons de nouveaux résultats pour les états à courte durée de vie dans les noyaux riches en neutrons A∼100, en mettant l'accent sur les chaînes des Zr, Mo et Ru. Nous discuterons des techniques expérimentales utilisées pour évaluer les durées de vie ainsi que l'interprétation de celles-ci à l'aide de modèles de structures nucléaires récentsThe shape of an atomic nucleus, ie. the deviation of its mass distribution from sphericity, is a fundamental property and governed by a delicate interplay of macroscopic and microscopic effects, such as the liquid-drop like binding energy and the nuclear shell structure, respectively. Studying nuclear shape properties using gamma ray spectroscopic methods allows detailed tests of different nuclear models, which were originally developed for stable nuclei. We proposed a project to study the evolution of nuclear shapes in exotic nuclei, far from the valley of stability, specifically in neutron-rich nuclei in the isotopic chains from Zr (Z=40) to Pd (Z=46). Usually, nuclear shapes are slowly evolving from spherical shapes around closed-shell or (doubly-) magic nuclei to elongated (prolate) shapes in nuclei with many valence nucleons. The nuclei of interest, however, show rapidly evolving patterns of excited states, which can be interpreted as rapid variations of the nuclear shape, including the rare observation of oblate (disk-like) and triaxial shapes. So far the known properties for these nuclei are (mainly) limited to excitation energies. Information on the nuclear collectivity, which can be deduced from the lifetime of the excited states, are sparse, while direct information of the shape is practically non existing. The simplest estimate of nuclear deformation in even-even nuclei can be obtained from the energy of the first 2⁺ state. For Sr (Z = 38) and Zr (Z = 40) isotopes this energy is observed to decrease dramatically at N = 60, while its evolution is much more gradual in Mo nuclei (Z = 42). Precise lifetime measurements provide a key ingredient in the systematic study of the evolution of nuclear deformation and the degree of collectivity in this region. Neutron-rich nuclei in the mass region of A = 100-120 were populated through the fusion-fission reaction of a ²³⁸U beam at 6.2 MeV/u on a ⁹Be target. The compound nucleus ²⁴⁷Cm was produced at an excitation energy of around 45 MeV before undergoing fission. The setup used for this study comprised the high-resolution mass spectrometer VAMOS in order to identify the nuclei in Z and A, the Advanced gamma ray Tracking Array AGATA of 35 germanium detectors to perform gamma ray spectroscopy, as well as a plunger mechanism to measure lifetimes down to a few ps using the Recoil Distance Doppler Shift method (RDDS). In addition, the target was surrounded by 24 Lanthanum Bromide (LaBr₃) detectors for a fast-timing measurement of lifetimes longer than 100 ps. The sophisticated set of spectrometers used in this experiment allowed measurement of nuclear lifetimes in a range from 100’s of picoseconds down to a few picoseconds. In this thesis, we will report on new lifetime results for short-lived states in neutron-rich (A ~ 100) nuclei, with an emphasis on the Zr, Mo and Ru chains. We will discuss the experimental techniques used to evaluate the lifetimes as well as their interpretation in terms of state-of-the-art nuclear structure models
45
Fleming, Thomas Harold. "Isotopic and Chemical Evolution of The Ferrar Group, Beardmore Glacier Region, Antarctica /." The Ohio State University, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487929745335032.
Повний текст джерела
46
Macaulay, Calum Ian. "Clastic diagenesis and porefluid evolution : an isotopic study, Magnus oilfield, North Sea." Thesis, University of Strathclyde, 1990. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=27954.
Повний текст джерелаАнотація:
The Upper Jurassic Magnus Sandstone is a medium-grained feldspathic submarine fan sandstone, which was derived from the northwest and deposited in the East Shetland Basin as four stacked lobes. These formed a reservoir up to 200m thick within the Kimmeridge Clay oil source rocks. The oilfield was formed by uplift and subaerial erosion of a fault block from early to mid Cretaceous, followed by burial beneath Late Cretaceous mudstones and marls which form the seal. Major diagenetic events within the reservoir sands comprise dissolution of feldspar and garnet and resultant precipitation of quartz overgrowths and kaolinite, followed by growth of magnesian siderite, ankerite and illite. The cement sequence is very similar in each of three wells studied along a 4km traverse from the crest to the flank of the field. The present day reservoir is buried to 3200m and 120°C, with a formation fluid salinity half that of seawater and a 8180 +2%0. Calcite cement is virtually absent, probably due to a lack of detrital shell carbonate. Siderite is distributed throughout the sandstone but localised around degrading detrital biotite grains and mud clasts. Rhombic crystals show distinct compositional evolution through three growth zones, and have more magnesian compositions downdip. This suggests different porefluid compositions across the field. Ankerite is only found close to mudstones, from where Fe and Mg were released during burial. These carbonates have 813C values which suggest a supply from decarboxylation of organic material. Within each well, diagenetic mineral 8180 values consisent with increasing temperature follow the mineral diagenetic sequence. Geothermal gradients of 45°Ckm-1 are inferred during rapid burial. The 8180 values for each mineral are persistently 3-4%0 more negative for samples from the crest of the field than from the flank. This is interpreted to indicate persistently stratified porewaters during burial. The influence of isotopically negative meteoric-derived water in the crest contrasts with more marine-derived porewaters downdip. This surprising deduction suggests that diagenesis was dominated by local flow or diffusion and not by regional fluid movement. This oilfield perhaps represents an end member of the diagenetic spectrum.
47
Kelly, Jennifer Christine. "The fluid evolution of the Mount Mica and Irish Pit pegmatites, Maine| Evidence from stable isotopes." California State University, Long Beach, 2013.
Знайти повний текст джерела
48
Wynn, Jonathan Guy. "Paleosols, stable carbon isotopes, and paleoenvironments of hominid evolution in the Neogene Turkana Basin, Northern Kenya /." view abstract or download file of text, 2001. http://wwwlib.umi.com/cr/uoregon/fullcit?p3018403.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--University of Oregon, 2001.Typescript. Includes vita and abstract. Includes bibliographical references (leaves 145-170). Also available for download via the World Wide Web; free to University of Oregon users.
49
Schneider, Albrecht. "Eruptive processes, mineralization and isotopic evolution of the Los Frailes Karikari region, Bolivia." Thesis, Imperial College London, 1985. http://hdl.handle.net/10044/1/37847.
Повний текст джерела
50
Heureux, Ana Magali Carrera. "Carbon fixation in eukaryotic marine algae : evolution of photosynthetic machinery and isotopic footprints." Thesis, University of Oxford, 2016. http://ora.ox.ac.uk/objects/uuid:eb2b64e5-5740-424b-802e-702c6b88c937.
Повний текст джерелаАнотація:
Photosynthesis in the world's oceans by marine algae is responsible for approximately 50% of CO2 fixed into organic carbon. Aquatic primary producers are intricately linked to the climate system due to their reliance on CO2 as a substrate for photosynthesis and role in the removal and export of carbon from the surface ocean to marine sediments. The evolutionary history of marine algae was shaped by changes in the climate system. As a result, fossilized marine algae and modern representatives of ancient groups have the potential to unlock information about the Earth’s climatic past. To use this information and fully understand the role of marine algae in the carbon cycle, however, it is essential to develop an in-depth understanding of CO2 fixation in these organisms. In this thesis I look at carbon fixation in biomineralizing marine algae from a geological and a biological perspective. First I apply a carbon isotope proxy for CO2 to organic material preserved in marine diatom frustules from an extremely transformative period in geological history, the Eocene-Oligocene boundary. Subsequently, this thesis aims to address gaps in our understanding of carbon fixation in eukaryotic marine algae. I present a novel dataset of kinetics of the carbon fixing enzyme, Rubisco, in eukaryotic algae, investigate the role of a pyrenoid-based carbon concentrating mechanism, and identify plastic changes in carbon fixing machinery in response to changing CO2. The findings from this thesis refine our understanding of primary production in the oceans and how we apply algae-based CO2 proxies to understand ancient climates.