Uranium series dating of marine and lacustrine carbonates
Uranium-series and radiocarbon geochronology of deep-sea corals: The systematics of uranium-thorium-protactinium dating. Implications for Quaternary Climate Change G.
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Edwards , Cheng , Murrell , Goldstein. Direct U—Th dating of marine sediments from the two most recent interglacial periods Niall C. Slowey , Gideon M. Henderson , William B.
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Taken together, this suggests a strong teleconnection between the two regions. Finally, for the first time, the stability of Near East climate in the early Holocene is robustly demonstrated, suggesting that this could have been a key enabler of the development of agriculture at this time. Uranium-Series Dating of Ocean Formations. Precision and Accuracy in Geochronology. Geochronology in Earth and Solar System science is increasingly in demand, and this demand is not only for more results, but for more precise, more accurate, and more easily interpreted temporal constraints. Because modern research often requires multiple dating methods, scrupulous inter- and intramethod calibration in absolute time is required.
However, improved precision has highlighted systematic analytical biases and uncovered geologic complexity that affects mineral dates. At the same time, both enhanced spatial resolution through microbeam geochronology and creative uses of disparate data sets to inform age interpretations have helped explain complexities in age data.
Quantifying random and systematic sources of instrumental and geological uncertainty is vital, and requires transparency in methodology, data reduction, and reporting. Community efforts toward inter- and intracalibration of chronometers will continue to help achieve the highest possible resolving power for integrative geochronology. Detailed mapping of the seismic data and fault linkages with the onland geology demonstrate that the middle strand of the North Anatolian Fault Zone exits into the Aegean Sea near the town of Behramkale and that it extends into the Bababurnu pull-apart basin in the northeastern Aegean Sea as a right-releasing step-over active during the Quaternary.
Quaternary International , , 65— Thermochronological investigation of fault zones. The timing of faulting episodes can be constrained by radiometric dating of fault-zone rocks. The thermal regime of fault zones consists primarily of the following three factors: The thermal sensitivities of individual thermochronological systems are then reviewed, which critically control the response of each method against the thermal processes. Based on the knowledge above, representative examples as well as key issues are highlighted to date fault gouges, pseudotachylytes, mylonites and carbonate veins, placing new constraints upon geological, geomorphological and seismological frames.
Finally, the Nojima Fault is presented as an example for multiple applications of thermochronological methods in a complex fault zone. To facilitate the measurement of U—Th isotopic compositions suitable for high-precision and high-resolution Th dating of coral and speleothem carbonates, secondary electron multiplier SEM protocol techniques for multicollector inductively coupled plasma mass spectrometry MC-ICP-MS have been developed. This method features chemistry refinements, improvements to procedural and instrumental blanks, spectral inference reductions, and careful consideration of non-linear SEM behavior.
For fossil corals, a routine U—Th isotopic determination at permil-level precision requires only 10—50 mg of carbonate. Requirement of small sample size, 10—s mg carbonate, can permit high temporal resolution to date speleothems with slow growth rates, i. This high-precision Th chronology is critical to accurately establish age models, date events and splice geochemical proxy time series records from multiple samples in the fields of paleoclimatology and paleoceanography.
The U—Th isotopic determination techniques described here can also be applied to different environmental samples, such as waters, rocks, and sediments. The effect of curvature on weathering rind formation: Evidence from Uranium-series isotopes in basaltic andesite weathering clasts in Guadeloupe. To quantify rates of rind formation on weathering clasts under tropical and humid climate and to determine factors that control weathering reactions, we analyzed Uranium series isotope compositions and trace element concentrations in a basaltic andesite weathering clast collected from Basse-Terre Island in Guadeloupe.
U, Th, and Ti elemental profiles reveal that Th and Ti behave conservatively during rind formation, but that U is added from an external source to the rind. In the rind, weathering reactions include dissolution of primary minerals such as pyroxene, plagioclase, and glass matrix, as well as formation of Fe oxyhydroxides, gibbsite and minor kaolinite.
Rare earth element REE profiles reveal a significant Eu negative anomaly formed during clast weathering, consistent with plagioclase dissolution. Significant porosity forms in the rind mostly due to plagioclase dissolution. The new porosity is inferred to allow influx of soil water carrying externally derived, dissolved U. Due to this influx, U precipitates along with newly formed clay minerals and oxyhydroxides in the rind.
U-series geochronometry thus provides the first direct evidence that the curvature of the interface controls the rate of regolith formation at the clast scale. The weathering rates determined at the clast scale can be reconciled with the weathering rates determined at the watershed or soil profile scale if surface roughness equals values of approximately — Evaluation of boron isotope ratio as a pH proxy in the deep sea coral Desmophyllum dianthus: Evidence of physiological pH adjustment.
To test the veracity and practicality of this potential paleo-pH proxy in deep sea corals, samples of skeletal material from twelve archived modern Desmophyllum dianthus D. This mechanism partially compensates for the range of ocean pH and aragonite saturation at which this species grows, enhancing aragonite precipitation and suggesting an adaptation mechanism to low pH environments in intermediate and deep waters.
Consistent with the findings of Trotter et al. High-precision U-series measurements of more than , year old fossil corals. Robust, independent age constraints on the absolute timing of climate events based on the U-series dating of fossil coral are sparse before the last glacial cycle. The open-system model of Villemant and Feuillet [Villemant B. Earth and Planetary Science Letters 1 2 , However, the open-system model developed by Thompson et al. Thus the data provide evidence that the systematic addition of Th and U through alpha-recoil is a dominant open-system process occurring in the Henderson Island fossil reef system.
Several coral samples yield significantly older Thompson et al. The reliability of these ages is currently unclear. It is shown that separate aliquots of the same coral can yield different Thompson model ages. Therefore, there appear to be additional diagenetic mechanisms that create further anomalous excursions in the U-series systematics, limiting the reliability of the Thompson et al.
Directly dating geologic events: UPb dating of carbonates. Carbonates are ubiquitous, forming in a variety of settings including caves, soils, the oceans, during burial from hydrothermal fluids, and along faults. Here we review studies of U-Pb dating of carbonates from a range of depositional and diagenetic environments and consider published results with regard to stratigraphie associations and the behavior of U and Pb in various fluids. We detail the steps required to select suitable samples, summarize current laboratory techniques, and provide directions for improvement of analytical protocols.
The U-Pb dating of carbonates has tremendous potential for dating events of geologic interest and is virtually untapped. Assessing a novel paleoredox proxy. Our sample set consists of a variety of primary precipitates that represent a range of carbonate producing organisms and components that were important in the past scleractinian corals, calcareous green and red algae, ooids, and mollusks.
In addition, four short push cores were taken in different depositional environments to assess the impact of early diagenesis and pore water chemistry on the U isotopic composition of bulk carbonates. We find that U concentrations are much higher in bulk carbonate sediments avg. In almost all cases, the lowest bulk sediment U concentrations were as high as or higher than the highest concentrations found in primary precipitates. This is consistent with authigenic accumulation of reduced U IV during early diagenesis.
The extent of this process appears sensitive to pore water H2S, and thus indirectly to organic matter content.
To cope with such effects, proxies for syndepositional pore water redox conditions e. Luminescence Dating of Shell-Rich Deposits. Any stratum composed primarily of shells which consist of either aragonite or calcite biomineral. The remaining materials maybe a complex composition of siliciclastic or carbonate grains with or without carbonate cement.here
9. Uranium-series Dating of Marine and Lacustrine Carbonates | Request PDF
These shell-rich deposits can be either of marine or lacustrine origin, or artificial concentrations created by humans. This allows OSL to be used to answer chronologic questions pertaining to geologic processes and features and well as anthropological sites and events. Jul Environ Archaeol. The coloured stones used in buildings and monuments were an indicator of power and wealth during the ancient times.