scholarly journals Magnetostratigraphic evidence for post-depositional distortion of osmium isotopic records in pelagic clay and its implications for mineral flux estimates

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Yoichi Usui ◽  
Toshitsugu Yamazaki
Keyword(s):  
Accumulation Rate ◽  
Late Eocene ◽  
Main Process ◽  
Isotopic Ratios ◽  
Mechanical Mixing ◽  
Redox Change ◽  
Pelagic Clay ◽  
Isotopic Records ◽  
The Stability ◽  
Age Constraints

AbstractChemical stratigraphy is useful for dating deep-sea sediments, which sometimes lack radiometric or biostratigraphic constraints. Oxic pelagic clay contains Fe–Mn oxyhydroxides that can retain seawater 187Os/188Os values, and its age can be estimated by fitting the isotopic ratios to the seawater 187Os/188Os curve. On the other hand, the stability of Fe–Mn oxyhydroxides is sensitive to redox change, and it is not clear whether the original 187Os/188Os values are always preserved in sediments. However, due to the lack of independent age constraints, the reliability of 187Os/188Os ages of pelagic clay has never been tested. Here we report inconsistency between magnetostratigraphic and 187Os/188Os ages in pelagic clay around Minamitorishima Island. In a ~ 5-m-thick interval, previous studies correlated 187Os/188Os data to a brief (< 1 million years) isotopic excursion in the late Eocene. Paleomagnetic measurements revealed at least 12 polarity zones in the interval, indicating a > 2.9–6.9 million years duration. Quartz and feldspars content showed that while the paleomagnetic chronology gives reasonable eolian flux estimates, the 187Os/188Os chronology leads to unrealistically high values. These results suggest that the low 187Os/188Os signal has diffused from an original thin layer to the current ~ 5-m interval, causing an underestimate of the deposition duration. The preservation of the polarity patterns indicates that a mechanical mixing such as bioturbation cannot be the main process for the diffusion, so diagenetic redistribution of Fe–Mn oxyhydroxides and associated Os may be responsible. The paleomagnetic chronology presented here also demands reconsiderations of the timing, accumulation rate, and origins of the high content of rare-earth elements and yttrium in pelagic clay around Minamitorishima Island.

scholarly journals Magnetostratigraphic Evidence for Post-Depositional Distortion of Osmium Isotopic Records in Pelagic Clay and Its Implications for Mineral Flux Estimates

2020 ◽  
Author(s):  
Yoichi Usui ◽  
Toshitsugu Yamazaki
Keyword(s):  
Accumulation Rate ◽  
Late Eocene ◽  
Main Process ◽  
Isotopic Ratios ◽  
Mechanical Mixing ◽  
Redox Change ◽  
Pelagic Clay ◽  
Isotopic Records ◽  
The Stability ◽  
Age Constraints

Abstract Chemical stratigraphy is useful for dating deep sea sediments which sometimes lack radiometric or biostratigraphic constraints. Oxic pelagic clay contains Fe-Mn oxyhydroxides that can retain seawater 187Os/188Os values, and its age can be estimated by fitting the isotopic ratios to the seawater 187Os/188Os curve. On the other hand, the stability of Fe-Mn oxyhydroxides is sensitive to redox change, and it is not clear whether the original 187Os/188Os values are always preserved in sediments. However, due to the lack of independent age constraints, the reliability of 187Os/188Os ages of pelagic clay have never been tested. Here we report inconsistency between magnetostratigraphic and 187Os/188Os ages in pelagic clay around Minamitorishima Island. In a ~ 5 m thick interval, previous studies correlated 187Os/188Os data to a brief (< 2 million years) isotopic excursion in the late Eocene. Paleomagnetic measurements revealed at least 12 polarity zones in the interval, indicating a > 3.3–7.4 million years duration. Quartz and feldspars content showed that while the paleomagnetic chronology gives reasonable eolian flux estimates, the 187Os/188Os chronology leads unrealistically high values. These results suggest that the low 187Os/188Os signal has diffused from an original thin layer to the current ~ 5 m interval, causing an underestimate of the deposition duration. The preservation of the polarity patterns indicates that a mechanical mixing such as bioturbation cannot be the main process for the diffusion, so diagenetic re-distribution of Fe-Mn oxyhydroxides and associated Os may be responsible. The paleomagnetic chronology presented here also demands reconsiderations of the timing, accumulation rate, and origins of the high content of rare-earth elements and yttrium in pelagic clay around Minamitorishima Island.

Magnetostratigraphic evidence for post-depositional distortion of osmium isotopic records in pelagic clay: implications for mineral flux estimates

2021 ◽  
Author(s):  
Yoichi Usui ◽  
Toshitsugu Yamazaki
Keyword(s):  
Accumulation Rate ◽  
Late Eocene ◽  
Main Process ◽  
Mechanical Mixing ◽  
Deep Sea Sediment ◽  
Age Model ◽  
Pelagic Clay ◽  
Isotopic Records ◽  
The Stability ◽  
Age Constraints

&lt;p&gt;Deep-sea sediment sometimes lacks biostratigraphic or radiometric age constraints. Chemical stratigraphy and magnetostratigraphy is useful for dating it. Oxic pelagic clay contains Fe-Mn oxyhydroxides that can retain seawater &lt;sup&gt;187&lt;/sup&gt;Os/&lt;sup&gt;188&lt;/sup&gt;Os values, and its age can be estimated by fitting the isotopic ratios to the seawater &lt;sup&gt;187&lt;/sup&gt;Os/&lt;sup&gt;188&lt;/sup&gt;Os curve. On the other hand, the stability of Fe-Mn oxyhydroxides is sensitive to redox change, and it is not clear whether the original &lt;sup&gt;187&lt;/sup&gt;Os/&lt;sup&gt;188&lt;/sup&gt;Os values are always preserved in sediments. However, due to the lack of independent age constraints, the reliability of &lt;sup&gt;187&lt;/sup&gt;Os/&lt;sup&gt;188&lt;/sup&gt;Os ages of pelagic clay have never been tested. Magnetostratigraphy is often unsuccessful for pelagic clay older than a few Ma, which has been attributed to diagenesis. Here we report multiple polarity reversals in ca. 35 Ma pelagic clay around Minamitorishima Island, which is inconsistent with a &lt;sup&gt;187&lt;/sup&gt;Os/&lt;sup&gt;188&lt;/sup&gt;Os age model. In a ~5 m thick interval, previous studies correlated &lt;sup&gt;187&lt;/sup&gt;Os/&lt;sup&gt;188&lt;/sup&gt;Os data to a brief (&lt;1 million years) isotopic excursion in the late Eocene. Paleomagnetic measurements revealed at least 12 polarity zones in the interval, indicating a &gt;2.9 &amp;#8211; 6.9 million years duration. Quartz and feldspars content showed that while the paleomagnetic chronology gives reasonable eolian flux estimates, the &lt;sup&gt;187&lt;/sup&gt;Os/&lt;sup&gt;188&lt;/sup&gt;Os chronology leads unrealistically high values. These results suggest that the low &lt;sup&gt;187&lt;/sup&gt;Os/&lt;sup&gt;188&lt;/sup&gt;Os signal has diffused from an original thin layer to the current ~5 m interval, causing an underestimate of the deposition duration. The preservation of the polarity patterns indicates that a mechanical mixing such as bioturbation cannot be the main process for the diffusion, so diagenetic re-distribution of Fe-Mn oxyhydroxides and associated Os may be responsible. The paleomagnetic chronology presented here also demands reconsiderations of the timing, accumulation rate, and origins of the high content of rare-earth elements and yttrium in pelagic clay around Minamitorishima Island. It is also indicated that old oxic pelagic clay can be a faithful paleomagnetic recorder, and success of magnetostratigraphy depends on sedimentation rate and polarity length rather than diagenesis.&lt;/p&gt;&lt;p&gt;Usui, Y., Yamazaki, T. &lt;em&gt;Earth Planets Space&lt;/em&gt;&amp;#160;&lt;strong&gt;73,&amp;#160;&lt;/strong&gt;2 (2021). https://doi.org/10.1186/s40623-020-01338-4&lt;/p&gt;

scholarly journals Influence of optimal conditions of ultrasonic dispersion on the stability of suspensions of finely ground slags

2019 ◽  
Vol 265 ◽  
pp. 01017 ◽  
Author(s):  
Svetlana Samchenko ◽  
Irina Kozlova ◽  
Оlga Zemskova ◽  
Ekaterina Baskakova
Keyword(s):  
Aqueous Dispersion ◽  
Cement Composite ◽  
Cement Stone ◽  
Mechanical Mixing ◽  
Dispersion Parameters ◽  
Ultrasonic Dispersion ◽  
Sedimentation Stability ◽  
Granulated Blast Furnace Slag ◽  
The Stability ◽  
Furnace Slag

The preparation in the jet mill of finely ground slag (FGS) from the waste of metallurgical production granulated blast-furnace slag, the obtaining of slag suspensions, and the behavior of FGS particles in an aqueous dispersion medium are considered in the paper. It was found that FGS particles in the suspension form micelles of two types with negative (micelle 1) and positive (micelle 2) charges of FGS surface. To increase the aggregative and sedimentation stability of FGS particles in suspensions, studies were carried out using ultrasonic dispersion. The results of investigations on the detection of optimal dispersion parameters for slag suspensions are presented. It was found that in the absence of temperature control, the process of coagulation of slag particles is accelerated and aggregative and sedimentation stability of suspensions of FGS is reduced. The slag particles in the suspension form aggregates that lead to a deterioration of the strength characteristics of the cement stone using suspensions of FGS. Optimal parameters of ultrasonic dispersion of slag suspensions are established: the frequency of ultrasonic vibrations is equal to 44 kHz; the dispersion temperature is 25 ± 2 °C; the dispersion time is 15 min. It was found that the application of ultrasonic dispersion to slag suspensions with the observance of dispersion conditions can increase the aggregative and sedimentation stability of FGS suspension by 2-3 times in comparison with the mechanical mixing of suspensions. The strength of samples with suspensions of FGS prepared using UST under the recommended dispersing conditions increased by 19 to 39% in the first day; for 28 days of hardening - by 19 - 36%, which allows using slag suspensions in the production of cement composite materials and concretes based on them.

scholarly journals Stratigraphy and petrophysical characteristics of Lower Paleocene cool-water carbonates, Faxe quarry, Denmark

2021 ◽  
Vol 69 ◽  
pp. 97-121
Author(s):  
Jens Martin Hvid ◽  
Frans van Buchem ◽  
Frank Andreasen ◽  
Emma Sheldon ◽  
Ida Lykke Fabricius
Keyword(s):  
Large Scale ◽  
Accumulation Rate ◽  
Carbonate System ◽  
Cool Water ◽  
Entry Pressure ◽  
Rapid Accumulation ◽  
Basement High ◽  
Capillary Entry Pressure ◽  
Ground Penetrating ◽  
Age Constraints

The Faxe limestone quarry in eastern Denmark exposes Danian (Lower Paleocene) cool-water carbonate deposits. They constitute remnants of an apparent build-up that covers about 12 km2 today. The Danian deposits at Faxe are conspicuous due to their pronounced thickness of coral limestone relative to the regional carbonate system. In the Faxe quarry, scleractinian corals are uniquely exposed in up to 30 m high mounds. The rapid accumulation of scleractinians combined with induration of the mounds may locally have protected the limestone from Quaternary glacial erosion and created a Danian thickness anomaly at Faxe. The position of Faxe above a local fault-bounded basement high and the extent of coral limestone has been better defined by new mapping. A mapped lithostratigraphic surface in the quarry reveals the large-scale organisation of nested bryozoan mounds on three elongated ridges striking NW–SE. The main scleractinian coral mounds are located above this horizon. Data for reservoir characterisation, mainly of the bryozoan mounds, were collected as photographs of the outcrop, petrophysical and petrographical data from cored boreholes, and as ground-penetrating radar sections. Old boreholes and measured sections were used to reconstruct the build-up, and new nannofossil data allow a discussion of stratigraphy and accumulation rate. The petrophysical data show that common mound-building bryozoan packstone has higher permeability and lower capillary entry pressure than chalk, whereas less commonly occurring grain-dominated packstone and grainstone deposits from local higher-energy sites of the mound complex were found to have reduced amounts of coccolith mud, significantly higher permeability and a higher degree of lithification. Based on biostratigraphic age constraints, correlation of flint – limestone couplets and recog-nised hierarchical patterns, we develop a cyclostratigraphy for the middle Danian and suggest that cyclicity in lithology and petrophysical characteristics of bryozoan limestone are controlled by precession and eccentricity of the orbit of the Earth.

scholarly journals The ferrocenium/ferrocene couple: a versatile redox switch

ChemTexts ◽  
2020 ◽  
Vol 6 (4) ◽  
Author(s):  
Luigi Fabbrizzi
Keyword(s):  
Electrochemical Sensors ◽  
Structural Features ◽  
Ferrocene Derivatives ◽  
Redox Switch ◽  
Redox Change ◽  
The Stability ◽  
The One ◽  
Redox Switches ◽  
Orange Solution ◽  
Molecular Framework

Abstract Woodward and co-workers in 1952 characterised the unique structural features of ferrocene (the first sandwich compound), demonstrated its aromatic nature and observed that on treatment with mild oxidising agents (aqueous Ag2SO4, p-benzoquinone in organic solvents) the orange solution of ferrocene (Fc) turned blue due to the formation of ferrocenium (Fc+). A few months later, the one-electron Fc/Fc+ redox change was characterised polarographically by Page and Wilkinson with E1/2 = 0.31 V vs SCE (0.56 V vs NHE) in ethanol/water 9:1. Since then ferrocene has become an icon of organometallic electrochemistry. Owing to the stability of its molecular framework, to the ease of functionalisation at the cyclopentadienyl rings and to the fast, reversible and kinetically uncomplicated Fc/Fc+ redox change, ferrocene has been used as a building block for the design of switchable functional systems. In this review, we will consider (1) electrochemical sensors for metal ions, anions and metal–anion pairs operating through the Fc/Fc+ redox change, (2) ferrocene-based redox switches of fluorescence and (3) cross-transport of electrons and anions through a liquid membrane mediated by lipophilic ferrocene derivatives. Graphic abstract

Monitoring and Stability Evaluation of the Damaged Landslide Based on Multiple Monitoring Technologies

2021 ◽  
Author(s):  
Wei Huang ◽  
Chang Zhou ◽  
Hong Xu ◽  
Lichuan Chen ◽  
Yunping Liao ◽  
...  
Keyword(s):  
Rock Mass ◽  
Accumulation Rate ◽  
Airborne Lidar ◽  
Stability Evaluation ◽  
Displacement Monitoring ◽  
Rescue Work ◽  
Weak Layer ◽  
Barrier Lake ◽  
Barrier Dam ◽  
The Stability

Abstract The stability evaluation of the damaged landslide is important for rescue work and emergency operation. This paper investigated a predisposing geological emergence, inducing the factors and deformation processes of the Zhongbao landslide, which happened on 25 July 2020. The stability of the damaged landslide was evaluated by an integrated monitoring system consisting of ground-based radar, unmanned aerial vehicles, airborne Lidar, thermal infrared temperature monitoring, GNSS displacement monitoring, deep displacement monitoring and rainfall monitoring. The strata and weak layer controlled the landslide failure, and topography defined the boundary of the failed rock mass. A continually intensive rainfall caused the deformation and accelerated failure of the landslide. The shallow and steep deposit (Part I) firstly slid at a high velocity, and then pushed the rear part of the landslide (Part II) to deform, forming numerous cracks, and the rainfall infiltrated into the rock mass. Finally, the rock and soil mass sliding along the weak layer, a barrier dam and a barrier lake were formed. The monitoring results showed that after the landslide failure, there were still local collapse and deformation occurrence which threatened rescue work and barrier lake excavation. Therefore, the barrier dam wasn’t excavated until the accumulation rate gradually stabilized on July 28. Moreover, most of the reactivated deposits still accumulated in the transportation and source areas. Thus, in August, the displacement of the damaged landslide gradually accelerated in a stepwise manner, and responded strongly to rainfall, especially in the accumulation area, so that it was inferred that the damaged landslide could slide again and caused a more threatening and severe failure. The analysis results of the study area can provide references for the failure mechanism of a rainfall-induced landslide and the stability evaluation of a damaged landslide.

Geochemical constraints on Eocene–Miocene geodynamic and magmatic evolution of the Varan-Naragh area, Urumieh-Dokhtar Magmatic Arc, Iran

2020 ◽  
Vol 57 (9) ◽  
pp. 1048-1065
Author(s):  
Ghosoun Zheira ◽  
Fariborz Masoudi ◽  
Bahman Rahimzadeh
Keyword(s):  
Rare Earth ◽  
Lithospheric Mantle ◽  
Active Continental Margin ◽  
Volcanic Rocks ◽  
Late Eocene ◽  
Early Miocene ◽  
Temporal Association ◽  
Second Phase ◽  
Isotopic Ratios ◽  
Magmatic Arc

Two different types of igneous rock formed during separate Cenozoic magmatic phases in the Varan-Naragh area in the central part of the Urumieh-Dokhtar Magmatic Arc (UDMA) of Iran as a part of the Alpine-Himalayan system. The first phase comprises late Eocene – early Oligocene Naragh gabbroic rocks (Ns), and the second phase is characterized by the emplacement of both volcanic and plutonic rocks of the early Miocene. Both phases display moderate enrichment of large rare earth elements and depletion of high field strength elements coupled with negative Nb, Ti, and P anomalies, indicative of subduction-related magmatic events within an active continental margin. Initial values of 87Sr/86Sr and εNdT are 0.70684 and +0.15 and 0.70560–0.70654 and +2.55 to +3.49 for Ns and early Miocene intrusive and volcanic rocks, respectively. Comparisons of rare earth element patterns and mantle-like isotopic ratios suggest that Ns mafic and early Miocene magmatic rocks were derived from partial melting of a common subcontinental lithospheric mantle. Geochemical and isotopic ratios of Ns gabbroic rocks, in combination with the data related to other coeval and proximal mafic-intermediate intrusions (such as Nashalj), suggest enrichment of the lithospheric mantle by slab-derived fluids with a minor subducted sediment melt. The low εNdT of Ns gabbroic rocks can reflect involvement of slab-derived components. The geochemical similarity and the close spatial and temporal association of Varan intrusive and volcanic rocks suggest a common petrogenetic relationship. Geochemical, isotopic, and geochronological evidence from the region indicate three major phases of igneous activity in the Kashan magmatic segment of the central UDMA during late Eocene to Miocene, resulting in complex tectonic regime transition from compressional subduction to extensional post-collisional settings. Integrated with published studies, the new results support a model suggesting that subduction-related magmatic activity was still influencing the central UDMA in the early Miocene time and are also consistent with the notion of oblique and diachronous collision along the northeast margin of the Arabia plate.

scholarly journals Isotopic diffusion in polar firn: implications for interpretation of seasonal climate parameters in ice-core records, with emphasis on central Greenland

1998 ◽  
Vol 44 (147) ◽  
pp. 273-284 ◽  
Author(s):  
Kurt M. Cuffey ◽  
Eric J. Steig
Keyword(s):  
Accumulation Rate ◽  
A Priori ◽  
Ice Core ◽  
Published Data ◽  
High Accumulation ◽  
Proxy Records ◽  
New Information ◽  
Isotopic Records ◽  
Diffusive Mixing ◽  
Ice Core Records

AbstractIf it were possible to properly extract seasonal information from ice-core isotopic records, paleoclimate researchers could retrieve a wealth of new information concerning the nature of climate changes and the meaning of trends observed in ice-core proxy records. It is widely recognized, however, that the diffusional smoothing of the seasonal record makes a “proper extraction" very difficult. In this paper, we examine the extent to which seasonal information (specifically the amplitude and shape of the seasonal cycle) is irrecoverably destroyed by diffusion in the firn. First, we show that isotopic diffusion firn is reasonably well understood. We do this by showing that a slightly modified version of the Whillans and Grootes (1985) theory makes a tenable a priori prediction of the decay of seasonal isotopic amplitudes with depth at the GISP2 site, though a small adjustment to one parameter significantly improves the prediction. Further, we calculate the amplitude decay at various other ice-core sites and show that these predictions compare favorably with published data from South Pole and locations in southern and central Greenland and the Antarctic Peninsula. We then present numerical experiments wherein synthetic ice-core records are created, diffused, sampled, reconstituted and compared to the original. These show that, alter diffusive mixing in the entire fini column, seasonal amplitudes can be reconstructed to within about 20% error in central Greenland but that all information about sub-annual signals is permanently lost there. Furthermore, most of the error in the amplitude reconstructions is due to the unknowable variations in the sub-annual signal. Finally, we explore how these results can be applied to other locations and suggest that Dye 3 has a high potential for meaningful seasonal reconstructions, while Siple Dome has no potential at all. An optimal ice-core site for seasonal reconstructions has a high accumulation rate and a low temperature.

scholarly journals Age constraints for the Trachilos footprints from Crete

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Uwe Kirscher ◽  
Haytham El Atfy ◽  
Andreas Gärtner ◽  
Edoardo Dallanave ◽  
Philipp Munz ◽  
...  
Keyword(s):  
Magnetic Susceptibility ◽  
Late Miocene ◽  
Accumulation Rate ◽  
Sediment Accumulation ◽  
Time Frame ◽  
Magnetic Polarity ◽  
Calcareous Nannoplankton ◽  
Calcareous Nannofossil ◽  
Normal Polarity ◽  
Age Constraints

AbstractWe present an updated time frame for the 30 m thick late Miocene sedimentary Trachilos section from the island of Crete that contains the potentially oldest hominin footprints. The section is characterized by normal magnetic polarity. New and published foraminifera biostratigraphy results suggest an age of the section within the Mediterranean biozone MMi13d, younger than ~ 6.4 Ma. Calcareous nannoplankton data from sediments exposed near Trachilos and belonging to the same sub-basin indicate deposition during calcareous nannofossil biozone CN9bB, between 6.023 and 6.727 Ma. By integrating the magneto- and biostratigraphic data we correlate the Trachilos section with normal polarity Chron C3An.1n, between 6.272 and 6.023 Ma. Using cyclostratigraphic data based on magnetic susceptibility, we constrain the Trachilos footprints age at ~ 6.05 Ma, roughly 0.35 Ma older than previously thought. Some uncertainty remains related to an inaccessible interval of ~ 8 m section and the possibility that the normal polarity might represent the slightly older Chron C3An.2n. Sediment accumulation rate and biostratigraphic arguments, however, stand against these points and favor a deposition during Chron C3An.1n.

scholarly journals Eocene Loranthaceae pollen pushes back divergence ages for major splits in the family

PeerJ ◽  
2017 ◽  
Vol 5 ◽  
pp. e3373 ◽  
Author(s):  
Friðgeir Grímsson ◽  
Paschalia Kapli ◽  
Christa-Charlotte Hofmann ◽  
Reinhard Zetter ◽  
Guido W. Grimm
Keyword(s):  
Fossil Record ◽  
Middle Miocene ◽  
Molecular Data ◽  
Late Eocene ◽  
Molecular Dating ◽  
The Family ◽  
Minimum Age ◽  
Age Constraints ◽  
Scanning Electron ◽  
Lineage Diversification

BackgroundWe revisit the palaeopalynological record of Loranthaceae, using pollen ornamentation to discriminate lineages and to test molecular dating estimates for the diversification of major lineages.MethodsFossil Loranthaceae pollen from the Eocene and Oligocene are analysed and documented using scanning-electron microscopy. These fossils were associated with molecular-defined clades and used as minimum age constraints for Bayesian node dating using different topological scenarios.ResultsThe fossil Loranthaceae pollen document the presence of at least one extant root-parasitic lineage (Nuytsieae) and two currently aerial parasitic lineages (Psittacanthinae and Loranthinae) by the end of the Eocene in the Northern Hemisphere. Phases of increased lineage diversification (late Eocene, middle Miocene) coincide with global warm phases.DiscussionWith the generation of molecular data becoming easier and less expensive every day, neontological research should re-focus on conserved morphologies that can be traced through the fossil record. The pollen, representing the male gametophytic generation of plants and often a taxonomic indicator, can be such a tracer. Analogously, palaeontological research should put more effort into diagnosing Cenozoic fossils with the aim of including them into modern systematic frameworks.

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