Article

The isotopic composition of leachable osmium from river sediments

December 1994
Earth and Planetary Science Letters 128(3-4):591-599

December 1994
128(3-4):591-599

DOI:10.1016/0012-821X(94)90172-4

License
CC BY-NC-ND 4.0

Authors:

Bradley K. Esser

Lawrence Livermore National Laboratory

The ratios of acidic hydrogen peroxide leaches of river sediments are inferred to be representative of the isotopic composition of Os delivered to sea water from the continents. The values for river sediment leaches from the eastern and central U.S., the Ganges River, and the Rio Maipo range from 10.1 to 21.5. These results suggest that the of the soluble river load delivered from the major continental areas to the oceans is, on average, more radiogenic than average currently eroding continental crust (10.5). Sediment leaches from three rivers from the western U.S. that drain ophiolitic peridotites have distinctly lower values, 1.4–7.1; such rivers may be significant contributors to sea water of the relatively unradiogenic osmium required to yield the contemporary oceanic of 8.6.

Osmium in seawater : analysis and geochemistry

Thesis

Jan 1998

Oliver Brian Woodhouse

p>A method for the direct analysis of seawater osmium has been developed and is described in this thesis. Low and constant blanks are obtained (0.12 pg osmium with 187Os/186Os=2.6) and spike-sample equilibration is achieved using this method. A 191Os radiotracer was used to develop the method. The storage of samples and the distillation and microdistillation used for the isolation of the osmium were examined. It was demonstrated that seawater should be stored in either glass or Teflon bottles and acidified to pH2 using hydrochloric acid. Seawater was collected from the eastern Pacific Ocean and osmium concentrations (6.6 to 9.8 pg/L) and isotopic ratios (187Os/186Os = 8.7 to 9.2) were measured using the method. The vertical profile shows that osmium concentration is not constant through the water column in this ocean region. A minimum at around 500 m, coinciding with a minimum of both dissolved oxygen and light transmission, can be explained by two processes: the horizontal advection of a water mass low in osmium from the continental slope and the in-situ adsorption of osmium onto sinking particles. Whilst the concentration and isotopic composition values are similar to those measured in the Indian Ocean, the data from the Pacific Ocean shows reduced concentrations under anoxic conditions and presents an exception to the conservative behaviour of osmium. The seawater samples that were collected from close to the hydrothermal vents at 9°N of the East Pacific Rise, were not concentrated in osmium compared to deep seawater. Comparisons between filtered and unfiltered samples show that the majority of seawater osmium is in the dissolved phase. The results suggest that osmium exists in several oxidation states and chemical speciations in seawater, and that anoxic conditions may reduce the osmium to a particle-reactive species. A new calculation of the osmium oceanic residence time (34,800 years) indicates that osmium should be uniformly distributed throughout the oceans.</p

New Re-Os isotopic constrains on the formation of the metalliferous deposits of the Lower Cambrian Niutitang formation

Article

Apr 2016

The Terreneuvian Epoch (541–521 Ma)is also an important period for metallogenesis in South China, as was represented by the widespread occurrences of Ni-Mo polymetallic layers on the antecedent shallow platform margin and the V-enriched black shales in deeper slope-basin settings. In this study, we have measured Re-Os isochron ages of Ni-Mo polymetallic layers (Songlin, Niuchang, Sancha, Chuanpengwan), V-rich black shales (Bahuang), and non-metalliferous black shales (Shuidong) in the basal Niutitang Formation in Guizhou and Hunan province, South China. The Ni-Mo polymetallic layers and V-enriched black shales have similar Re-Os isochron ages, suggesting concurrent deposition of these two types of metalliferous ores. This suggestion is consistent with the traditional stratigraphic correlation by using the nodular phosphorite bed directly underlying these metalliferous layers as a stratigraphic marker. Furthermore, the metalliferous ores and non-metalliferous black shales have similar initial 187Os/188Os ratios of 0.8–0.9, arguing for a dominant seawater origin with minor contribution of hydrothermal activity. Furthermore, Re-Os isotopic data also imply that Ni-Mo and V ore might have derived from the same source. We suggest that the spatial distribution of metalliferous ores can be explained by the development of non-sulfidic anoxic-suboxic wedge (NSASW) in the slope-basin and sulfidic wedge in the previous platform margin. Upwelling of deep water first transects the mildly reduced, organic rich NSASW, in which V (V) is reduced to V (IV), and is preferentially removed from seawater by organometallic complex formation. As a result, V-rich black shale deposits in the slope-basin of Yangtze Platform. Further movement of deep water into the sulfidic platform margin results in Ni-Mo polymetallic layer formation. © 2016, China University of Geosciences and Springer-Verlag Berlin Heidelberg.

Himalayan uplift and osmium isotopes in oceans and rivers - Its relation to global tectonics and climate

Article

Jan 1999
GEOCHIM COSMOCHIM AC

Previous studies have shown that 187Os/188Os in seawater has become increasingly radiogenic over the last 40 Ma in a manner analogous to strontium. This rapid rise in the marine 187Os/188Os over the last 17 Ma has been attributed to an increase in the bulk silicate weathering rates resulting from the rise of the Himalayas and/or selective weathering and erosion of highly radiogenic organic rich ancient sediments. The key test of this hypothesis is the 187Os/188Os and the total osmium concentration of the Himalayan rivers. We report the concentration and isotopic composition of osmium in the Ganges, the Brahmaputra, and the Indus rivers. The 187Os/188Os of the Ganges close to its source (at Kaudiyal, 30°05′N, 78°50′E) is 2.65 and [Os] = 45 fM/kg. A second sample of the lower reaches of the Ganges at Patna (25°30′N, 85°10′E) gives 187Os/188Os =1.59 and [Os] = 171 fM/kg. The 187Os/188Os of the Brahmaputra at Guwahati (26°10′N, 91°58′E) is 1.07 and [Os] = 52 fM/kg. A sample of the Indus (Besham, 34°55′N, 72°51′E) has a 187Os/188Os of 1.2 and [Os] = 59 fM/kg. We infer that the Himalayas do not provide either a high flow of osmium or a highly radiogenic osmium component to the oceans. The overall trend for osmium and strontium could be explained by a regularly increasing input of global continental weathering sources but the Himalayas themselves appear not to be the dominant source.

Atmospheric supply of osmium to the oceans

Article

Nov 2002
GEOCHIM COSMOCHIM AC

Supply of Os to the oceans via atmospheric transport is assessed by means of aerosol analyses and tracking with 210Pb. Although the inferred continental Os flux at a coastal site (New Haven, Connecticut) was found to be large, this flux is not representative of the global atmospheric flux to the oceans. This conclusion is based on the observed 210Pb atmospheric flux pattern across the Pacific Ocean and the constancy of the 187Os/188Os in the oceans. The 210Pb-based flux of Os to Pacific islands based on a measure of the leachable Os in stream sediments and the measured Al flux to these islands is assessed. By means of this approach, 0.8 mol of Os per year of atmospherically transported Os to the world oceans is obtained. This value is considerably smaller than the value of ∼1500 mol of Os per year assigned to delivery by streams. However, there may be an additional flux of Os to the oceans from the release from coastal aerosols, although the amount is uncertain.

The Os isotopic composition of Himalayan river bedloads and bedrocks: Importance of black shales

Article

Mar 2000
EARTH PLANET SC LETT

Re-Os data are presented for bedrocks and bedloads of selected rivers from the Himalayan range, in Central Nepal and Bangladesh. These data demonstrate that the Os isotopic composition of most of the bedrocks is similar to that of the: average continental crust. Notable exceptions to this are the black:shales from the Lesser Himalaya (LH), which contain large quantities of radiogenic osmium. In the black shales, the Os is not concentrated in the sulfides, and may instead;be associated with organic matter. Bedloads collected from rivers which include LH black shales in their catchment basins have notably high Os ratios ((187)Os/(188)Os approximate to 3). This radiogenic signature persists into the Ganga river. In contrast, the Brahmaputra river is less radiogenic, suggesting an ophiolite input in the headwater region. Simple physical mixtures of LH black shales with eroded products from the high range require unreasonably high proportions of black shale to explain the high Os ratios observed at the outflow of the range. Assuming that our bedrock and bedload samples are representative of the source region and the eroded mixture, respectively, this observation suggests that erosion may not be occurring at steady-state. In addition, mass:balance calculations indicate that about 20% of the Os and 60% of the Re are carried in dissolved form, implying that chemical erosion plays an important role in the osmium budget. Finally, the contrast in Os isotope ratio between Ganga bedloads and bulk sediments in the Bengal Fan suggests that radiogenic Os carried by particulate matter and later remobilized may significantly influence the Os composition of seawater.

Sources of osmium to the modern oceans: New evidence from the Pt-190-(OS)-O-186 system

Article

Mar 2004
GEOCHIM COSMOCHIM AC

High precision Os isotope analysis of young marine manganese nodules indicate that whereas the composition of modern seawater is radiogenic with respect to 187Os/188Os, it has 186Os/188Os that is within uncertainty of the chondritic value. Marine Mn nodule compositions thus indicate that the average continental source of Os to modern seawater had long-term high Re/Os compared to Pt/Os. Analyses of loess and freshwater Mn nodules support existing evidence that average upper continental crust (UCC) has resolvably suprachondritic 186Os/188Os, as well as radiogenic 187Os/188Os. Modeling the composition of seawater as a two-component mixture of oceanic/cosmic Os with chondritic Os compositions and continentally-derived Os demonstrates that, insofar as estimates for the composition of average UCC are accurate, congruently weathered average UCC cannot be the sole continental source of Os to seawater. Our analysis of four Cambrian black shales confirm that organic-rich sediments can have 187Os/188Os ratios that are much higher than average UCC, but 186Os/188Os compositions that are generally between those of chondrites and average-UCC. Preferential weathering of black shales can result in dissolved Os discharged to the ocean basins that has a much lower 186Os/188Os than does average upper crust. Modeling the available data demonstrates that augmentation of estimated average UCC compositions with less than 0.1% additional black shale and 1.4% additional ultramafic rock can produce a continental end-member Os isotopic composition that satisfies the requirements imposed by the marine Mn nodule data. The interplay of these two sources provides a mechanism by which the 187Os/188Os of seawater can change as sources and weathering conditions change, yet seawater 186Os/188Os varies only minimally.

Black Shale Weathering and the Mobility of Osmium Isotopes, Rhenium, and Platinum Group Elements

Article

May 2000

Chemical signals for oxidative weathering predict Re–Os isochroneity in black shales, East Greenland

Article

Sep 2012
CHEM GEOL

Re and Os isotopes in shales are increasingly used for precise and accurate geochronology and for tracking rates of continental weathering in the geologic past. Moreover, trace element compositions of organic-rich shales reveal paleoredox conditions and properties of shale organic matter (OM) useful for lithostratigraphic correlations. Chemical weathering alters the original shale composition and hence may compromise geologic interpretations based on geochemical data. Here we compare Re–Os isotopes, trace elements and OM properties in correlative shales from outcrops and nearby drillcore to quantify the effects of weathering. We define chemical parameters that distinguish weathered from pristine shale in samples that are macroscopically identical.

Behavior of osmium at the freshwater–saltwater interface based on Ganga derived sediments from the estuarine zone

Article

Full-text available

Dec 2011
GEOCHEM GEOPHY GEOSY

1] Leaching experiments performed on several sediments of the Ganga river suggest that between 10 and 20% of the osmium is in an easily exchangeable position. Analyses of sediments from two estuarine rivers (the Pussur and the lower Meghna) reveal no enrichment of Os in the saltwater–freshwater mixing zone relative to Ganga sediments of similar Al 2 O 3 /SiO 2 ratio, suggesting that osmium is not signif-icantly trapped in this estuary. However, a significant decrease of the 187 Os/ 188 Os ratio is observed in the Pussur sediments relative to the Ganga composition. These latter are derived entirely from the Ganga or from erosion of the Ganga paleodelta, and thus would be expected to have similar Os isotopic composi-tions. Nd isotopic results from the Pussur are indistinguishable from those of the Ganga, while the Sr isotopic results are at the lower end of the Ganga range, confirming the absence of a major source dif-ference between Ganga and Pussur sediments. It thus seems unlikely that the difference in Os isotopic signature can be entirely explained by a change in provenance, suggesting instead that the Os compo-sitions have been modified. Our results show that the less radiogenic Os compositions of the Pussur sedi-ments cannot result simply from desorption of radiogenic Os or from scavenging of river or seawater Os. Instead, the decrease of the 187 Os/ 188 Os ratio could imply a complex exchange between dissolved Os, derived partly from seawater, and Os in the leachable fraction of sediments. This mechanism could there-fore constitute both a source and a sink for seawater osmium and may significantly influence the osmium marine budget. Components: 8200 words, 6 figures, 2 tables. Index Terms: 0442 Biogeosciences: Estuarine and nearshore processes (4235); 1040 Geochemistry: Radiogenic isotope geochemistry; 1051 Geochemistry: Sedimentary geochemistry.

Dissolved rhenium in the Yamuna River System and the Ganga in the Himalaya: Role of black shale weathering on the budgets of Re, Os, and U in rivers and CO2 in the atmosphere

Article

Jan 2002
GEOCHIM COSMOCHIM AC

Extensive measurements of dissolved Re and major ion abundances in the Yamuna River System (YRS), a major tributary of the Ganga, have been performed along its entire stretch in the Himalaya, from its source near the Yamunotri Glacier to its outflow at the foothills of the Himalaya at Saharanpur. In addition, Re analysis has been made in granites and Precambrian carbonates, some of the major lithologies of the drainage basin. These data, coupled with those available for black shales in the Lesser Himalaya, allow an assessment of these lithologies’ contributions to the Re budget of the YRS.

The marine osmium isotope record

Article

Oct 2000
TERRA NOVA

Over the past decade the marine osmium isotope record has been developed into a new tracer in palaeoceanographic research. Several analytical developments, particularly in the past few years, have significantly increased our ability to study the behaviour of osmium in the surficial environment. The ¹⁸⁷Os/¹⁸⁸Os and osmium concentration of seawater, river water, rain, and hydrothermal vent fluids have been measured directly. Recently, the behaviour of osmium in estuaries–critical for estimating the marine residence time of osmium–has been studied. Our knowledge of the surficial osmium cycle has thus significantly improved. In addition, reconstructions of past variations in the marine ¹⁸⁷Os/¹⁸⁸Os recently have been extended back into the Mesozoic. This review attempts to summarize our current understanding of the marine osmium system–present and past.

The Osmium Isotope Signature of Phanerozoic Large Igneous Provinces

Chapter

Full-text available

Dec 2020

The emplacement of Large Igneous Provinces (LIPs) throughout the Phanerozoic Eon introduced vast quantities of mafic rocks to the Earth's surface, which were subsequently weathered into the oceans. Osmium isotope data can be used to track these LIP‐related weathering fluxes, providing a global fingerprint of the timing and magnitude of LIP emplacement, and guiding assessments of the impact of these events on ocean biogeochemistry and the regulation of the global climate system. Sedimentary Os isotope records spanning late Phanerozoic LIP events are reviewed herein and new observations from Eocene hyperthermal event ETM‐2 are presented. While Os isotope stratigraphy can provide major constraints on LIP activity in the geological record, it cannot always distinguish whether the extrusive activity was subaerial or submarine. The utility of osmium isotopes as a global tracer of past volcanism may be enhanced when used alongside proxies such as mercury concentrations, which may be more diagnostic of the style of individual episodes of LIP emplacement. Hitherto, only a few high‐resolution Os‐isotope records across Phanerozoic LIPs have effectively exploited the short oceanic residence time of Os. Future high‐resolution studies across suitable, well‐preserved stratigraphic records will significantly improve our understanding of the nature, progression, and consequences of LIP emplacement.

Miocene seawater 187 Os/ 188 Os ratios inferred from metalliferous carbonates

Article

Jul 1998
EARTH PLANET SC LETT

Seawater 187 Os/ 188 Os ratios for the Middle Miocene were reconstructed by measuring the 187 Os/ 188 Os ratios of metalliferous carbonates from the Pacific (DSDP 598) and Atlantic (DSDP 521) oceans. Atlantic and Pacific 187 Os/ 188 Os measurements are nearly indistinguishable and are consistent with previously published Os isotope records from Pacific cores. The Atlantic data reported here provide the first direct evidence that the long-term sedimentary 187 Os/ 188 Os record reflects whole-ocean changes in the Os isotopic composition of seawater. The Pacific and the Atlantic Os measurements confirm a long-term 0.01/Myr increase in marine 187 Os/ 188 Os ratios that began no later than 16 Ma. The beginning of the Os isotopic increase coincided with a decrease in the rate of increase of marine 87 Sr/ 86 Sr ratios at 16 Ma. A large increase of 1 in benthic foraminiferal 18 O values, interpreted to reflect global cooling and ice sheet growth, began approximately 1 million years later at 14.8 Ma, and the long-term shift toward lower bulk carbonate 13 C values began more than 2 Myr later around 13.6 Ma. The post-16 Ma increase in marine 187 Os/ 188 Os ratios was most likely forced by weathering of radiogenic materials, either old sediments or sialic crust with a sedimentary protolith. We consider two possible Miocene-specific geologic events that can account for both this increase in marine 187 Os/ 188 Os ratios and also nearly constant 87 Sr/ 86 Sr ratios: (1) the first glacial erosion of sediment-covered cratons in the Northern Hemisphere; (2) the exhumation of the Australian passive margin-New Guinea arc system. The latter event offers a mechanism, via enhanced availability of soluble Ca and Mg silicates in the arc terrane, for the maintenance of assumed low CO 2 levels after 15 Ma. The temporal resolution (three samples/Myr) of the 187 Os/ 188 Os record from Site 598, for which a stable isotope stratigraphy was also constructed, is significantly higher than that of previously published records. These high resolution data suggest oscillations with amplitudes of 0.01 to 0.02 and periods of around 1 Myr. Although variations in the 187 Os/ 188 Os record of this magnitude can be easily resolved analytically, this higher frequency signal must be verified at other sites before it can be safely interpreted as global in extent. However, the short-term 187 Os/ 188 Os variations may correlate inversely with short-term benthic foraminiferal 18 O and bulk carbonate 13 C variations that reflect glacioeustatic events.

Os isotopic record of Japan Sea sediments over last glacial maximum

Article

Sep 2003

The effect of weathering regime on uranium decay series and osmium in two soil profiles

Article

Full-text available

Jan 2004

Two soil profiles from the United States with radically different emplacement and climatic histories were analyzed for U, Th and members of the 238U decay series (234U, 230Th, 226Ra, 210Pb), 137Cs and osmium isotopes. The arid New Mexico profile is developed on an approximately 250,000 years old colluvium while the temperate New Hampshire profile is formed on till after the last glaciation at about 10,000 years ago. Both the profiles show significant 234U/238U, 230Th/234U and 226Ra/ 230Th disequilibria, however, in the New Hampshire profile, the disequilibria are far more pronounced in mid-depths (20-50 cm). High Os concentration with highly radiogenic 187Os/ 188Os is another characteristic of the mid-depths of the New Hampshire profile. This layer, particularly at about 30-40 cm depth has the characteristics of a soil developed on black shale, as evidenced from both the high U and Os concentrations and the large excess of 230Th over 238U. This profile clearly shows that the regolith on which the contemporary soil is developing was not homogeneous. The presence of measurable excess 226Ra activity over 230Th activity in both profiles suggests the need for a source of 226Ra external to the regolith in both cases. Atmospheric deposition of 226Ra is a possible source for this 226Ra excess and brings to light the important role of atmospheric deposition of nuclides and their transport in the soil profile in pedogenic processes. It also shows that regolith developed by glacial processes need not be homogeneous, thereby confounding the understanding of vertically modified soil profiles.

Osmium isotope geochemistry in the Mackenzie River basin

Article

May 2004
EARTH PLANET SC LETT

The Cenozoic marine osmium isotope record is largely driven by changes in the continental input. We aid its interpretation by supplying direct measurements of present day riverine Os in known geological and environmental settings. We analyzed Os concentrations and isotopic ratios in the dissolved, suspended, and bed materials of the Mackenzie River in Canada and smaller rivers draining the Western Cordillera into the Pacific Ocean. Rhenium content was measured for suspended and bed materials to provide further constraint. Dissolved 187Os/188Os ratios range from 0.74 to 4.5 and are controlled to first order by age and lithology of the bedrock. The rivers draining Jurassic volcanic rocks are unradiogenic, as low as 0.74, and those draining the Precambrian Canadian Shield are radiogenic, as high as 3.5. The headwaters of the Mackenzie left bank tributaries draining metamorphic carbonates in the Eastern Cordillera and Paleozoic black and gray shales in the Transition zone and the Interior Platform are especially radiogenic (3.0–4.5) with relatively high concentrations of Os. These latter rivers are responsible for the Mackenzie being above world average in Os concentration and yield (mol Os/km2/year) as well as in 187Os/188Os. The dissolved load is more radiogenic than the suspended or bed loads and constitutes a significant fraction of total fluvial Os.

Deposition of Osmium and other Platinum-Group Elements beneath the ultramafic-hosted Rainbow hydrothermal plume.

Article

Full-text available

May 2003
EARTH PLANET SC LETT

Osmium and other platinum-group elements (PGEs) have been measured in sediments accumulating directly under the Rainbow hydrothermal plume at 36°N on the Mid-Atlantic Ridge. 187Os/188Os and PGE concentrations in the sediments of four cores taken 2-25 km from the active vent site reveal evidence of both radiogenic Os scavenged from seawater and, importantly, unradiogenic Os released by hydrothermal venting. The majority of analyses (n=16) yield 187Os/188Os ratios that fall in a narrow range (0.99-1.06) close to that of modern seawater. In these samples, Os concentrations correlate linearly with hydrothermal V enrichments, which are also derived from seawater scavenging. A smaller subset of samples, characterized by unusually high concentrations of Ni and Cr derived from ultramafic rock fragments, exhibit distinctly lower 187Os/188Os ratios. Their Ir content is also higher, and their PGE ratios are more similar to mantle material than the PGE patterns of the larger set of samples dominated by seawater-scavenged Os. Although the two most proximal cores lack evidence for any similar ultramafic `detritus' in their surficial sediments, 187Os/188Os ratios in these samples are also lower than that of ambient seawater, suggesting they are likely to have been influenced by unradiogenic Os from vent fluid incorporated into the plume. Samples from the most distal core, by contrast, exhibit 187Os/188Os ratios indistinguishable from that of seawater. Compared with `background' NE Atlantic sediments, Os is enriched four-fold in the seawater-dominated samples, while Pd, Pt and Ir are twice the background value. Burial fluxes of Os scavenged by hydrothermal Fe in these sediments are 200-400 pg cm-2 kyr-1, up to twice that found on the EPR, and several times the background (bg) of 50 pg cm-2 kyr-1. For Pt, burial fluxes are 1800-3000 pg cm-2 kyr-1 (bg ca. 1000 pg cm-2 kyr-1) and for Pd 2700-4600 pg.cm-2 kyr-1 (bg ca. 800 pg cm-2 kyr-1).

A new method for analysis of osmium isotopes and concentrations in surface and subsurface water samples

Article

Sep 2009
CHEM GEOL

We describe a new method for the determination of osmium (Os) content and 187 Os/ 188 Os isotopic ratio in water samples, particularly adapted to analysis of reducing waters such as groundwaters. The critical feature of the method is the improved oxidation step. We use a high pressure asher (HPA-S) to achieve oxidation of all Os species at high pressure (~ 130 bars) and high temperature (250 °C). A series of tests was performed on two groundwater samples in order to study the general behavior of Os during oxidation and to optimize the various parameters of the method. At high temperature (≥250 °C), using hydrogen peroxide as an oxidant, complete spike-sample equilibration and oxidation of Os species to the highest oxidation state (OsO 4) are obtained in less than 10 h. A strong contrast in oxidation behavior was observed between tests performed at high (250 °C) and low temperature (100 °C). The results for both samples indicate a difference in the oxidation kinetics between spike and sample. They also demonstrate that a non-negligible proportion of each sample is easily oxidized at low temperature whereas high temperatures are required to oxidize the rest of the sample. This last observation could provide evidence for the existence of several species of osmium in groundwater samples. Our results underscore the need for high temperatures to assure spike-sample equilibration and complete oxidation of all Os species potentially present in water. The method presented here, which is adapted to various matrices, opens the possibility of analyzing Os concentrations and isotopic compositions in groundwater and thus to better constrain the potential sources of osmium delivered to the ocean.

Rapid determination of Os isotopic composition by sparging OsO4 into a magnetic-sector ICP-MS

Article

May 2000
CHEM GEOL

We present a method for the rapid determination of Os isotopic compositions and platinum group element (PGE) concentrations using ICP-MS on the same sample split. The method makes use of transfer of volatile OsO4 by an Ar gas stream into the torch of a magnetic sector ICP-MS for analysis. A variety of partial or complete sample dissolution methods can be used, namely (1) microwave oven digestion of samples in pressurized Teflon vessels under oxidizing acidic conditions, (2) NiS fire assay for complete sample dissolution and PGE preconcentration, (3) acid leaching techniques to extract labile PGE fractions, and (4) Carius tube digestion. Microwave oven sample digestion with HF–HNO3–HCl in an all-Teflon system as well as Carius tube digestion also allows the determination of Os isotopic composition and Os and Re concentrations on the same sample split. Spike–sample equilibration can be monitored on-line during sparging into the ICP-MS. The elimination of a nebulizer for Os isotope ratio measurements minimizes memory problems that are often associated with the determination of Os isotope ratios in liquid samples by ICP-MS. The external reproducibility of measurements of an in-house Os standard solution using a single-collector, magnetic sector ICP-MS (Finnigan ELEMENT) is 0.78% (1 S.D., n=13) for analyte amounts ranging from 81 pg to 1.22 ng total Os. The ion yield for 7-min data acquisitions is ∼5×10−5. Compared to negative thermal ionization mass spectrometry (N-TIMS), sample throughput is about on an order of magnitude higher. If NiS fire assay is used for PGE preconcentration, complementary PGE can be determined in the liquid residue by ICP-MS using a microconcentric nebulizer after the extraction of OsO4.

Re-Os isotope systematics of sediments of the Brahmaputra River system

Article

Nov 2003
GEOCHIM COSMOCHIM AC

Re-Os analyses were performed on suspended loads and coarser grained bank sediments of the Brahmaputra River system. Re and Os concentrations of these sediments vary from 7 to 1154 ppt and from 3 to 173 ppt, respectively. ¹⁸⁷Os/¹⁸⁸Os ratios range from 0.178 to 6.8, and thus vary from nearly mantle to very radiogenic crustal values. Nevertheless, most of the sediments have ¹⁸⁷Os/¹⁸⁸Os ratios less than 1.5, and nearly all of the samples of the Brahmaputra main channel have ratios less than 1.2. Thus, as previously suggested, the Brahmaputra is much less radiogenic than the Ganga. The Siang River, the northern extension of the Brahmaputra, is quite radiogenic in Os despite receiving sediments from the Tsangpo River, which flows along a suture zone with ultramafic outcrops. The Brahmaputra main channel has a fairly constant ¹⁸⁷Os/¹⁸⁸Os ratio even though its tributaries contribute sediments with very heterogeneous Os isotopic compositions. These data, along with the corresponding Nd isotopic compositions, suggest that about 60–90% of the sediment in the Brahmaputra system is derived from Himalayan formations (Higher Himalaya and Lesser Himalaya) whereas 10–40% comes from ophiolite-bearing sequences, perhaps eastern equivalents of those of the Transhimalayan Plutonic Belt. Os data also confirm previously published Sr and Nd results, indicating that about half of the sediments delivered to the Brahmaputra are supplied by the Siang River, while the Himalayan and the eastern tributaries account for 40 and 10%, respectively.

Variations in seawater osmium isotope composition since the last glacial maximum: A case study from the Japan Sea

Article

Aug 2005
CHEM GEOL

Concentrations of Re and Os, and the isotopic composition of Os have been measured in the Japan Sea sediments to assess the response of the Japan Sea to glacial–interglacial climate change and associated weathering fluxes. The osmium concentrations in the sediment samples analyzed vary from 59 to 371 pg/g, and 187Os/188Os from 0.935 to 1.042. Only 187Os/188Os of sediment samples from dark laminations deposited under suboxic to anoxic conditions and having elevated concentrations of Re and Os, and with ≥ 80% hydrogenous Os are explained in terms of seawater composition. Lower 187Os/188Os were observed for sediments deposited during the last glacial maximum (LGM) when planktonic foraminifera from the Japan Sea recorded lighter oxygen isotopic composition. Decrease in dissolved Os fluxes from continents and/or change in the composition of the dissolved load to the Japan Sea are suggested as the driving mechanisms for the observed lower LGM 187Os/188Os. The results of this study, coupled with lower 187Os/188Os during the last glacial observed at other sites from ocean basins with different lithology and contrasting sediment accumulation rates, suggest that this trend is characteristic of the global oceans.Data from this study show that the Japan Sea recorded higher 187Os/188Os during the current interglacial coinciding with excursions of oxygen isotopic compositions of planktonic foraminifera to heavier values. This is explained in terms of preferential release of 187Os during deglacial weathering and/or higher continental Os flux driven by warm and wet climate. This study demonstrates that Os isotopic composition of reducing margin sediments has immense potential to track variations in the seawater composition. In addition, 187Os/188Os of reducing sediments may be used to draw inferences about local paleoceanographic processes in semi-enclosed basins such as the Japan Sea.

Re-Os isotope system in organic-rich samples for dating and tracing: Methodology, principle, and application

Article

Mar 2023
EARTH-SCI REV

Étude des isotopes de l'osmium dans les eaux souterraines du Bangladesh et les sédiments himalayens : implications et rôle de l'érosion himalayenne sur le budget océanique de l'osmium

Thesis

Jul 2008

Maxence Paul

A travers l'exemple himalayen, nous étudions les mécanismes influençant la composition en osmium des sédiments durant l'érosion, le transport sédimentaire et le dépôt dans les zones estuariennes. Au niveau du bassin himalayen de la Kali Gandaki, les relations observées entre les concentrations en osmium et les quantités de carbone organique confirment le rôle important des schistes noirs appartenant aux TSS (non radiogéniques) et au LH (radiogénique) malgré leurs faibles répartitions géographiques. Cependant, la composition fortement radiogénique mesurée dans les sédiments du Gange n'est pas couplée a un enrichissement en 187Os dont la quantité moyenne est comparable à celle mesurée dans la croûte continentale. La signature isotopique du Gange résulterait d'un appauvrissement en Os non-radiogénique, témoignant d'une forte dilution par des sédiments dérivés de l'érosion des roches cristallines de l'HHC. Nous montrons à travers l'étude de sédiments estuariens que le comportement de l'osmium en contact avec l'eau de mer est complexe et des échanges sont possibles à l'interface. Le développement analytique réalisé en parallèle des études sur les sédiments a permis de documenter pour la première fois la composition en osmium des eaux souterraines. L'étude des aquifères de la plaine du Bengale montre que les eaux souterraines possèdent des concentrations en osmium significativement plus élevées que les eaux de rivière ou l'eau de mer. Si ce résultat est généralisable aux aquifères mondiaux, un flux global de l'ordre de 170 kg d'osmium par an pourrait être apporté à l'océan. Cet apport est significatif et impliquerait la réévaluation du bilan océanique mondial et une diminution significative du temps de résidence de l'osmium dans les océans. Ce résultat n'est pas anodin puisqu'il pourrait en partie réconcilier le temps de résidence estimé par bilan de masse océanique et les variations glaciaires-interglaciaires observées par le rapport 187Os/188Os dans de nombreux enregistrements marins

Le cycle de l'osmium et du rhénium pendant l'érosion himalayenne

Thesis

Full-text available

Jul 2000

Anne-Catherine Pierson-Wickmann

Cette étude a permis de déterminer la composition isotopique d'Os des trois principales formations himalayennes (TSS, HHC et LH) à partir de roches sources, ainsi que celle de sédiments de rivières qui représentent le produit d'érosion de la chaîne. Les formations du Haut Himalaya ont un rapport 187 0s/188 0s comparable à celui de la croûte continentale moyenne. Par contre, le LH se distingue par des rapports radio géniques rencontrés dans deux lithologies distinctes: les schistes noirs et les marbres impurs du LH. Un mélange de trois pôles (silicates du Haut Himalaya + schistes noirs du LH + carbonates impurs du LH) permet d'expliquer les signatures des sédiments de rivières à la sortie de la chaîne ou dans le Gange. Les sédiments du Brahmapoutre montrent un rapport moins radio génique que ceux du Gange, expliqué d'une part par la présence d'affleurement d'ophiolites dans le bassin versant du Brahmapoutre et d'autre part par l'absence de carbonates résiduels. L'origine des carbonates radiogéniques dans le LH est à relier au métamorphisme himalayen qui a permis la mobilisation d'Os et de Re à partir des schistes noirs radio géniques du LH. L'altération à basse température étudiée à partir de sols a montré que les compositions isotopiques et les concentrations d'Os et de Re ne varient pas avec la profondeur. Cependant une perte importante d'Os et de Re a probablement lieu dans les premiers stades de l'altération, lors du passage de la roche saine au saprolite. Les sédiments récents du Cône du Bengale montrent que l'érosion de la chaîne himalayenne est la source majeure des sédiments, surtout dans le cône actif. Cependant, dans le reste de la Baie du Bengale, cette source himalayenne peut être masquée par des sources secondaires, comme l'érosion de la chaîne indo-birmane ou l'érosion du Sri Lanka. Il n'y a aucune preuve qu'une perte significative d'Os lors du transport ou après le dépôt dans le Cône se produise. Ceci implique que la contribution de l'érosion himalayenne au budget de l'Os marin est limitée à la phase dissoute, et donc insuffisante pour expliquer l'augmentation du rapport 187 0s/188 0s marin durant les 16 derniers Ma.

Advances in the study of the surficial geochemistry of platinum group elements

Article

Oct 2004

Platinum Group Elements (PGE) have been considered as being inert in surficial condition for a long time. However, the study of mobility of PGE during weathering of ultramafic-mafic complex and black shale indicates that PGE, released from the primary rocks due to weathering, are abnormally concentrated in soil, plant and water. The secondary enrichment of PGE, especially of Pt and Pd, in surficial media around complex could be used as a potential tool for exploring PGE deposits. And osmium in black shale, transferring during weathering, could contribute main importance to the increase of seawater 187 Os/188 Os since Cenozoic. While PGE emitted from automobile catalysis converters would have a negative effect on ecological environment and human health by their mobility.

Re-Os system of black schist from the Mesoproterozoic Bayan Obo Group, Central Inner Mongolia, China and its geological implications

Article

Dec 2015
LITHOS

The Mesoproterozoic Bayan Obo Group in central Inner Mongolia, China, represents a sedimentary sequence deposited in the Bayan Obo Rift Basin. New Re-Os dates are reported here for the black shale (schist) from the group. Re-Os geochronology of the black schist provides an age of 1447±42Ma, which is consistent with the previous work from the literature and provides a direct and new constraint for the age of the group. The dating indicates that the Re-Os isotopes for the black schist have remained undisturbed during lower amphibolite facies metamorphism. The ca. 250Ma age for gold-bearing sulfides also indicates that the Re-Os isotopes for the schist have not been affected by hydrothermal overprinting of reduced fluid. The initial 187Os/188Os value of 0.93±0.14 for the schist is interpreted to represent the Os isotopic composition of the seawater during deposition of the group, which indicates that the Os composition of Mesoprotozoic seawater fluctuated during the Mesoproterozoic, and was temporary very radiogenic similar to present day seawater. The Re-Os data suggests that rifting of the Bayan Obo Basin peaked during ca. 1447Ma, and the Bilute Formation in the Bayan Obo Group may have been deposited in the Bayan Obo Sea in a restricted or semi-restricted depositional environment.

Os Isotope Record in a Cenozoic Deep-Sea Core: Its Relation to Global Tectonics and Climate

Chapter

Jan 1997

The oceanic variation of 87Sr/86Sr over at least the last 100 million years has been established through the study of calcareous biogenic deposits found principally in deep-sea sediments. The large picture is that in sediments from about 100 million years ago until about 38 million years ago 87Sr/86Sr shows only small variations but from that time forward there has been an increase. This variation has been ascribed to the changing relative importance with time of two mixing components: Sr with relatively low 87Sr/86Sr derived primarily by the weathering of ridge basalts and added to the oceans at hydrothermal vents and more radiogenic Sr derived from the weathering of continental crust. The approximately 4-million-year residence time of Sr is about a thousand times the mixing time of the oceans, so a marine 87Sr/86Sr record anywhere in the deep ocean basins speaks to global changes. The fine details of the sources and types of the actual continental rocks undergoing weathering continue to be the subject of active discussion.

Evidence for arc related magmatism associated to the Ross Orogeny at the Walker Rock Nunatak, North Victoria Land, Antarctica

Article

Full-text available

Jan 1996

Osmium in the rivers

Article

Dec 1997
GEOCHIM COSMOCHIM AC

There is a large uncertainty in our understanding of the behavior of osmium during weathering and transport into deep oceans and the osmium budget of the oceans. The problem stems chiefly from the lack of osmium data on the dissolved load in the rivers and in the estuaries. In this study, the concentration and isotopic composition of osmium have been determined in three North American rivers (the Mississippi, the Columbia, and the Connecticut) and one river draining central Europe and flowing into the Baltic Sea (the Vistula). Osmium concentration in the Mississippi and the Vistula is about 45 femto mol kg^(−1); it is about 14 and 15 femto mol kg^(−1) for the Connecticut and the Columbia, respectively. The ^(187)Os/^(186)Os ratios estimated for the Mississippi and the Vistula are 10.4 and 10.7, respectively. For the Connecticut and the Columbia ^(187)Os/^(186)Os = 8.8 and 14.4, respectively. Of all the rivers examined, the Mississippi is by far the largest, supplying ∼1.6% of the total annual world river flow. Its osmium isotopic composition is identical to the upper Mississippi valley loesses (Esser and Turekian, 1993a) indicating (1) congruent dissolution of the bedrock and (2) little or no impact of anthropogenic sources on the osmium isotopic composition of the dissolved load. The latter observation indicates that the upper limit of the anthropogenic input in the dissolved osmium load of the Mississippi outflow is about 250 g yr^(−1). While the osmium concentration of the Vistula is high the isotopic composition does not appear to have been affected by substantial pollution. The river data can be used to put limits on the mean residence time of osmium in the oceans (T_(Os) and on the osmium budget of the oceans. If the bulk river influx of dissolved osmium into the oceans is similar to that of the Mississippi, we get a value for the net riverine inflow of osmium of 1680 mol yr^(−1). If there were no sequestering of osmium in the estuaries, this would give a value of T_(Os) of = 1.3 × 10^4 years. As the estuaries may trap a significant amount of river osmium, this is a lower limit so that T_(Os) » 1.3 x 10^4 years. Using the iridium data by Anbar et al. (1996), the Os/Ir ratio for the Vistula is 2.8. We infer that there is no large fractionation between osmium and iridium during the transport of these elements from the continents into the oceans. It follows that the high Os/Ir ratio (∼22) observed in seawater must be related to the different rain out mechanisms of these elements in the estuaries or in the oceans.

Isotope/element fractionation during surface adsorption

Article

Jan 2004

The adsorption of ions onto mineral surfaces accompanies isotope/element fractionation in planets and asteroids. A model based on simple classical physics is presented to predict these fractionations. The agreement between the experimentally observed isotope/element ratios and their predicted values is found to be excellent. This fractionation can be demonstrated experimentally in advanced physics laboratories using macroscopic particles. The success of the model shows students that even a very complex naturally occurring process can be explained quantitatively with simple physics.

Sources and sinks of unradiogenic osmium runoff from Papua New Guinea

Article

Nov 2000
EARTH PLANET SC LETT

The Fly and Sepik are two of the largest rivers draining the island of New Guinea and among the world's large rivers in discharge and sediment yield. Sediment from the upper Fly River and its delta have low 187Os/188Os of 0.511-0.560, and sediments from the upper and lower Sepik River have even lower ratios of 0.294-0.418. Filtered waters (1.2). Burial of Os of both seawater and riverine derivation occurs in conjunction with organic carbon burial in the Gulf of Papua. There is a negative correlation between the Os isotopic composition of the bulk sediment and the fraction of organic matter of terrestrial origin based on C isotopes. The systematic relationship between C and Os isotopic compositions in these samples indicates that organic matter is the major host of Os in tropical estuarine sediments. The Os/Corg of Gulf of Papua surface sediments is intermediate between that of other modern and ancient sediments. Approximately 1011 mol/yr of Corg and 20-57 mol/yr of Os are buried in the inner shelf (

Effects of black shale weathering on the mobility of rhenium and platinum group elements

Article

May 2000
GEOLOGY

Radiogenic Os from the continents dominates the late Cenozoic marine Os budget. A variety of proposed radiogenic sources includes organic-rich sediments, Precambrian shields, and Re-rich sulfides. Identifying the dominant sources of radiogenic Os to the oceans has a strong impact on past climate models because weathering of silicates acts as a net sink of CO2, whereas weathering of organic matter acts as a source. Here we investigate the effects of black shale weathering on the integrity of the Re-Os isotope system and release of Re and platinum group elements. Time-correlative pairs of fresh (drill core) and weathered (outcrop) black shales of Late Ordovician age (Utica Shale magnafacies, Québec) were analyzed for Re, Os, Ir, Pt, and Pd, as well as total S, N, and C (as Ccarb and Corg). The results indicate that 25% 64% of the initial Re budget, 45% 90% of the Os budget, 14% 65% of the Ir budget, 60% 77% of the Pt budget, 69% 86% of the Pd budget, and 44% 96% of the Corg budget are lost during weathering. We use positive correlations of Os, Pt, and Pd with Corg and N to calculate the respective platinum group element concentrations in the unweathered organic matter end member as ˜3 ng/g Os, ˜9 ng/g Pt, and 11 24 ng/g Pd. Although black shales make up

Residence time of osmium in the oceans

Article

Jun 2001
GEOCHEM GEOPHY GEOSY

Rachel Oxburgh

Estimates of osmium residence time in the oceans that are based on oceanic mass balance calculations (35-50 kyr) appear irreconcilable with those inferred from the recent evolution of the osmium isotope composition of seawater (3-4 kyr). It is argued that the osmium budget of the oceans is currently close to steady state and thus that the estimates made by the two methods should agree. As the inventory of osmium in the oceans is relatively well constrained, these disparate residence time estimates imply wildly different osmium input fluxes to the oceans. An osmium residence time of 8-10 kyr is proposed by evaluating the uncertainties and limitations of both methods, and it is argued that osmium inputs to the ocean are currently underestimated by a factor of ˜3. This reflects in part the underestimation of the river input of osmium to the oceans owing to a bias within the existing data set and in part the probable existence of sources of osmium to the oceans that have not yet been identified. The very short residence time of 3-4 kyr inferred from the postglacial change in seawater composition (assuming a single step change in input flux) is rejected as it implies unreasonably high osmium input fluxes to the oceans. It is concluded that a postglacial spike in osmium flux, associated with a meltwater event, must have driven part of the change in seawater composition. However, it is also shown that such a spike cannot be the dominant cause of the most recent shift in seawater 187Os/188Os.

The osmium isotopic composition change of Cenozoic sea water as inferred from a deep-sea core corrected for meteoritic contributions

Article

Dec 1999
GEOCHIM COSMOCHIM AC

A detailed study was made of the oceanic 187Os/186Os variation through the Cenozoic by using a hydrogen peroxide leaching procedure on a pelagic clay core from the North Pacific (Long Lines-44 GPC3). A 6% H2O2 solution was used. The range of 187Os/186Os obtained by this procedure was between 2 and 8.2. A milder leach (0.15% H2O2) in three out of four samples yielded a slightly higher 187Os/186Os value than the stronger leach implying that the stronger leach released some meteoritic Os with 187Os/186Os of 1. Using published 3He concentrations in GPC3 and cosmic dust 3He and Os fluxes to deep-sea sediments, the extraterrestrial Os concentration was estimated for each core segment and subtracted to yield “corrected” values of 187Os/186Os. The results based on the milder leaching protocol and the 3He correction protocol yield similar values. The “corrected” ocean water 187Os/186Os pattern for the past 25 million years is similar to that obtained by other workers and is compatible with other results for the entire Cenozoic. The variation with time in GPC3, uniquely, provides a statigraphic signature for the Paleogene.

The glacial–interglacial variation of seawater osmium isotopes as recorded in Santa Barbara Basin

Article

Dec 2004
EARTH PLANET SC LETT

The Pleistocene deposits of Santa Barbara Basin (SBB) show laminations during interglacial periods typical of an anoxic or suboxic depositional environment and more sporadically laminated deposits during glacial times, indicating a more oxic environment of deposition. The 187Os/188Os value of sediment leaches varies as a function of climate, consistent with a more radiogenic Os signal during interglacial times and less radiogenic Os values more typical of glacial times. The signal is confounded by contributions from a high Os detrital component with a variable 187Os/188Os value, but generally agrees with prior result from deposits from other marine environments.

The concentration and isotopic composition of Os in the oceans

Article

Aug 1997
GEOCHIM COSMOCHIM AC

Osmium is one of the rarer elements in seawater. Analytical difficulties have previously prevented the direct measurement of the osmium concentration and isotopic composition in seawater. We report a chemical separation procedure that yields quantitative extraction of osmium standard and of osmium tracer by iron hydroxide precipitation from seawater doped with osmium standard, osmium tracer, and FeCl3. The iron hydroxide precipitate is processed to extract osmium, using techniques developed for iron meteorites. Utilizing this procedure, water samples from the Pacific and Atlantic oceans were analyzed for osmium concentration and isotopic composition. Direct determination of the osmium concentration of seawater gives between 15 and 19 fM kg−1. Detailed experiments on different aliquots of one seawater sample from the North Atlantic Ocean, keeping the amounts of reagents constant, yield concentrations from 16 to 19 fM kg−1. The variability in concentration is outside the uncertainty introduced because of blanks and indicates a lack of full equilibration between the osmium tracer and seawater osmium. The most reliable osmium concentration of the North Atlantic deep ocean water is 19 fM kg−1 with the 187Os186Os ratio being 8.7 ± 0.2 (2σ). Detailed experiments on one seawater sample from the Central Pacific Ocean indicate that the most reliable osmium concentration of the deep ocean water from the Central Pacific is 19 fM kg−1 with the 187Os186Os ratio being 8.7 ± 0.3 (2σ). The directly measured osmium isotopic composition of the oceans is in good agreement with that obtained from the analysis of some rapidly accumulating organic rich sediments (Ravizza and Turekian, 1992). A sample of ambient seawater around the Juan de Fuca Ridge gave 187Os186Os= 6.9 ± 0.4. This is distinctly lower than the deep-sea water value and may reflect local hydrothermal activity or some analytical difficulty with this sample. The osmium isotopic composition of the deep oceans indicates that ∼80% of the osmium is derived from the continents and the rest from extraterrestrial and hydrothermal sources. Using the iridium data of Anbar et al. (1996, 1997) we find that the Os/Ir ratio is ∼22 for seawater. The mean residence time of osmium (τOs) cannot be derived directly from these data. However, using the Os/Ir ratio of seawater and the Os/Ir ratio of continental rocks, a lower limit can be established of τOs ≥ 4.4 × 104 years. The Os/Ir in modern deep sea sediments should be relatively constant and is distinctly less radiogenic than seawater osmium due to limited evaporation (26%) of osmium from infalling cosmic dust. Relative to the cosmic dust infall the hydrothermal sources may, however, play a smaller but significant role in the bulk economy of dissolved osmium and other Platinum Group Elements in the oceans.

The osmium riverine flux and the oceanic mass balance of osmium

Article

Dec 1999
EARTH PLANET SC LETT

The osmium concentration ([Os]) and isotopic composition were determined in a set of 17 of the largest rivers of the world. [Os] varies between 4.6 and 52.1 pg/kg and the 187Os/188Os ratio varies between 0.64 and 2.94. Measurement of rainwater samples shows that there is no input of oceanic Os to the continent through rain. Assuming a negligible anthropogenic Os input in the dissolved load, the natural average river water has an Os concentration of 7.9 pg/kg and a mean 187Os/188Os ratio of 1.54. The total riverine flux of Os to the ocean is estimated to be 295 kg/yr. The dissolved Os flux from island arcs and oceanic islands represents less than 5% of the total riverine flux and is not further considered. The continental Os flux to the ocean is then represented by the riverine flux, as dissolved Os from eolian dust and glacial sediments is negligible. Assuming steady state, it is possible to estimate a maximum unradiogenic flux to the ocean of 126 kg/yr (cosmic dust or mantle-derived) and an oceanic residence time between 2.5×104 and 5.4×104 with a mean of 3.5×104 year. The estimation of the flux of dissolved cosmic particles shows that their contribution to the seawater Os would be ∼14% of the contribution of the unradiogenic component, which means that the mantle-derived flux should contribute a major part. The first results on water from high temperature axial hydrothermal systems indicate that their input is probably negligible, which would necessitate that dominant contribution from the low temperature alteration of the oceanic crust and/or of the ultramafic exposures contributes dominantly to the input of unradiogenic Os to the seawater. We show that it would be necessary to leach 1.3% of the Os contained in the volume of ultramafic exposures accessible to seawater to account for all of the unradiogenic component contribution. Another simpler but less likely possibility is that the dissolved cosmic dust represents the only source of dissolved unradiogenic Os to the ocean in which case the riverine input represents 94% of the total dissolved flux to the ocean instead of 70%. The modern global dissolved Os flux to the ocean would then have a 187Os/188Os ratio of 1.44 instead of 1.06 and the system would be far from steady state.

The behavior of natural and anthropogenic osmium in Long Island Sound, an urban estuary in the eastern US

Article

Apr 1997
EARTH PLANET SC LETT

The Os concentration and187Os/186Os distributions in surface sediments of Long Island Sound (eastern U.S.) provide a way of determining the sources and estuarine transport of Os. The contribution of anthropogenic Os from sewer outfalls from the New York City region supplies a tracer with a characteristic187Os/186Os of about 1. The Os concentration of the bulk surface sediment increases steeply moving toward New York City in the westernmost Sound and generally follows the concentration of organic carbon. The187Os/186Os ratio of bulk surface sediment increases from west to east in the westernmost part of the Sound and is effectively constant in the central Sound. We interpret these results as indicating that the surface bulk sediments of the Sound contain a low187Os/186Os component, perhaps as a reduced coating associated with organic remains from sewer outfalls. The acid hydrogen peroxide leach fraction has an average187Os/186Os of 9.5 in the central Sound, significantly higher than both the bulk sediment value and the probable sea water value of about 8. The leach fraction in the westernmost part of the traverse is less radiogenic than the central Sound and follows the Os wsotope trend of the bulk sediment. Liquid effluent from a New York City sewer outfall contains 30 pg l−1 of dissolved Os with a187Os/186Os of about 2.5, consistent with its being an end-member of the west-east sediment pattern recorded in the leach fractions of the westernmost cores. The leachable Os from the central Sound predominantly reflects Os in ferromanganese oxyhydroxide coatings from continentally derived sediments with187Os/186Os ratios more radiogenic than seawater. The distribution patterns of anthropogenic and natural Os, with their characteristic isotopic signatures in the Sound, and the insights gained from the behavior of other particle-reactive species, indicates that very little Os in solution may pass through the estuarine gauntlet.

Os isotopic systematics of the MORB mantle: Results from altered abyssal peridotites (vol 133, pg 411, 1995)

Article

Jul 1995
EARTH PLANET SC LETT

Abyssal peridotites are fragments of the oceanic upper mantle. Previous studies have indicated that their Os isotopic compositions span a wide range, including values more radiogenic than most estimates of the average bulk Earth 187Os188Os ratio. This is difficult to reconcile with their derivation as residues of MORB partial melting. We present results that suggest that some of this variation, particularly the higher values, may be of secondary origin. Comparison of altered rims and unaltered cores of two mylonitic peridotites reveal that submarine weathering can increase 187Os188Os ratios by more than 5%. Leaching experiments demonstrate the presence of a radiogenic, easily leachable phase that is most easily explained as a seawater-derived component. Thus, Os isotopic results from abyssal peridotites must be interpreted with some caution unless it can be shown that the effects of seawater alteration were minor. We develop criteria based on Sr and Nd isotopic measurements, as well as major element compositional changes, that allow strongly altered samples to be identified. Applying these criteria, we find 10 samples, including literature data as well as new analyses, that have apparently suffered only minimal alteration. These samples range in 187Os188Os from 0.1221 to 0.1270, with a mean of 0.1246 and a standard deviation of 0.0014. Thus, we see no evidence for depleted mantle rocks more enriched in 187Os188Os than the preferred value of ∼ 0.127. Finally, if Os is lost from peridotites during weathering, it may provide a significant source of mantle Os to the world's oceans.

The marine 187Os/ 186Os record of the past 80 million years

Article

Feb 1995
EARTH PLANET SC LETT

We report new187Os/186Os data and Re and Os concentrations in metalliferous sediments from the Pacific to construct a composite Os isotope seawater evolution curve over the past 80 m.y. Analyses of four samples of upper Cretaceous age yield187Os/186Os values of between 3 and 6.5 and187Re/186Os values below 55. Mass balance calculations indicate that the pronounced minimum of about 2 in the Os isotope ratio of seawater at the K-T boundary probably reflects the enormous input of cosmogenic material into the oceans by the K-T impactor(s). Following a rapid recovery to187Os/186Os of 3.5 at 63 Ma, data for the early and middle part of the Cenozoic show an increase in187Os/186Os to about 6 at 15 Ma. Variations in the isotopic composition of leachable Os from slowly accumulating metalliferous sediments show large fluctuations over short time spans. In contrast, analyses of rapidly accumulating metalliferous carbonates do not exhibit the large oscillations observed in the pelagic clay leach data. These results together with sediment leaching experiments indicate that dissolution of non-hydrogenous Os can occur during the hydrogen peroxide leach and demonstrate that Os data from pelagic clay leachates do not always reflect the Os isotopic composition of seawater.

Dissolved osmium in Bengal plain groundwater: Implications for the marine Os budget

Article

Jun 2010
GEOCHIM COSMOCHIM AC

We report osmium concentrations and isotopic compositions of 40 groundwater samples from the Bengal plain. Groundwaters have Os concentrations (16.9–191.5 pg/kg), about 5–10 times higher than those published for most rivers or seawater. 187Os/188Os varies widely (from 0.96 to 2.79) and is related to the isotopic signatures of the sediments constituting local aquifers. Os contents are correlated with those of soluble elements such as Sr, Mg, and Ca, suggesting that differing extents of solid-solution interaction explain most of the variation in measured Os concentrations. The covariation between Os and Sr allows us to estimate the mean Os content of Bengal groundwater (∼70 pg/kg). This concentration is too low to allow Bengal groundwater to significantly influence the marine Os isotopic composition, if likely fresh groundwater discharge rates to the Bay of Bengal are assumed. However, if Bengal groundwater Os concentrations are typical, the global Os groundwater flux would be expected to be around 180 kg/year, making it the second largest input of Os to the ocean after the river flux. Including this flux in the current Os marine budget, and assuming that this and other fluxes have remained constant with time, would decrease the calculated residence time of Os in the ocean by about 30%.

Radiogenic Isotopes in Weathering and Hydrology

Article

Nov 2003

There are a small group of elements that display variations in their isotopic composition, resulting from radioactive decay within minerals over geological timescales. These isotopic variations provide natural fingerprints of rock-water interactions and have been widely utilized in studies of weathering and hydrology. The isotopic systems that have been applied in such studies are dictated by the limited number of radioactive parent-daughter nuclide pairs with half-lives and isotopic abundances that result in measurable differences in daughter isotope ratios among common rocks and minerals. Prior to their application to studies of weathering and hydrology, each of these isotopic systems was utilized in geochronology and petrology. As in the case of their original introduction into geochronology and petrology, isotopic systems with the highest concentrations of daughter isotopes in common rocks and minerals and systems with the largest observed isotopic variations were introduced first and have made the largest impact on our understanding of weathering and hydrologic processes. Although radiogenic isotopes have helped elucidate many important aspects of weathering and hydrology, it is important to note that in almost every case that will be discussed in this chapter, our fundamental understanding of these topics came from studies of variations in the concentrations of major cations and anions. This chapter is a "tools chapter" and thus it will highlight applications of radiogenic isotopes that have added additional insight into a wide spectrum of research areas that are summarized in almost all of the other chapters of this volume.The first applications of radiogenic isotopes to weathering processes were based on studies that sought to understand the effects of chemical weathering on the geochronology of whole-rock samples and geochronologically important minerals (Goldich and Gast, 1966; Dasch, 1969; Blaxland, 1974; Clauer, 1979, 1981; Clauer et al., 1982); as well as on the observation that radiogenic isotopes are sometimes preferentially released compared to nonradiogenic isotopes of the same element during acid leaching of rocks ( Hart and Tilton, 1966; Silver et al., 1984; Erel et al., 1991). A major finding of these investigations was that weathering often results in anomalously young Rb-Sr isochron ages, and discordant Pb-Pb ages. Rubidium is generally retained relative to strontium in whole-rock samples, and in some cases radiogenic strontium and lead are lost preferentially to common strontium and lead from weathered minerals.The most widely utilized of these isotopic systems is Rb-Sr, followed by U-Pb. The K-Ar system is not directly applicable to most studies of rock-water interaction, because argon is a noble gas, and upon release during mineral weathering mixes with atmospheric argon, limiting its usefulness as a tracer in most weathering applications. Argon and other noble gas isotopes have, however, found important applications in hydrology (see Chapter 5.15). Three other isotopic systems commonly used in geochronology and petrology include Sm-Nd, Lu-Hf, and Re-Os. These parent and daughter elements are in very low abundance and concentrated in trace mineral phases. Sm-Nd, Lu-Hf, and Re-Os have been used in a few weathering studies but have not been utilized extensively in investigations of weathering and hydrology.The decay of 87Rb to 87Sr has a half-life of 48.8 Gyr, and this radioactive decay results in natural variability in the 87Sr/86Sr ratio in rubidium-bearing minerals (e.g., Blum, 1995). The trace elements rubidium and strontium are geochemically similar to the major elements potassium and calcium, respectively. Therefore, minerals with high K/Ca ratios develop high 87Sr/86Sr ratios over geologic timescales. Once released into the hydrosphere, strontium retains its isotopic composition without significant fractionation by geochemical or biological processes, and is therefore a good tracer for sources and cycling of calcium. The decay of 235U to 207Pb, 238U to 206Pb, and 232Th to 208Pb have half-lives of 0.704 Gyr, 4.47 Gyr, and 14.0 Gyr, respectively, and result in variations in the 207Pb/204Pb, 206Pb/204Pb, and 208Pb/204Pb ratios (e.g., Blum, 1995). Uranium-234 has a half-life of 0.25 Myr and the ratio 234U/238U approaches a constant secular equilibrium value in rocks and minerals if undisturbed for ˜1 Myr. Differences in this ratio are often observed in solutions following rock-water interaction and have been used in studies of weathering and hydrology. Uranium and thorium tend to be highly concentrated in the trace accessory minerals such as zircon, monazite, apatite, and sphene, which therefore develop high 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios. Once released into the hydrosphere, lead retains its isotopic composition without significant geochemical or biological fractionation and tends to generally follow the chemistry of iron in soils and aqueous systems (Erel and Morgan, 1992). The use of the U-Th disequilibrium series as a dating tool falls outside the scope of this chapter and is reviewed in Chapters 6.14 and 6.17 as well as Chapter 3.15. The decay of 147Sm to 143Nd, 176Lu to 176Hf, and 187Re to 187Os have half-lives of 106 Gyr, 35.7 Gyr, and 42.3 Gyr, respectively, and result in natural variability in the 144Nd/143Nd, 176Hf/177Hf, and 187Os/188Os ratios (e.g., Blum, 1995). Neodymium is a rare earth element (REE), hafnium is a transition metal with chemical similarities to zirconium, and osmium is a platinum group element. The geochemical behaviors of these elements in the hydrosphere are largely determined by these chemical affinities.

Threads: A life in geochemistry

Article

Apr 2006

Karl K. Turekian

I returned and saw under the sun, that the race is not to the swift, nor the battle to the strong, neither yet bread to the wise, nor yet riches to men of understanding, nor yet favour to men of skill; but time and chance happeneth to them all. Ecclesiastes 9:11 (King James version)

Os isotopic composition of leachates and bulk sediments from the Bengal Fan

Article

Jul 1997
EARTH PLANET SC LETT

Os isotopic compositions and Os and Re concentrations were measured in H2O2—H2SO4 leachates and bulk sediment samples from Holes 717C and 718C of ODP Leg 116 in the Bengal Fan. Os isotopic results indicate that, at the sediment surface, the leachable Os fraction is derived from seawater. In contrast, leachable Os from Ganges River sediments has 187Os/188Os ratios [1] much higher than the marine value. This difference suggests that the leachable radiogenic Os carried by the river sediments is completely released to the oceans prior to sediment deposition in the Fan. A simple calculation, assuming these sediments to be typical of those delivered by the Ganges-Brahmaputra river system, suggests that this process can account for a substantial part of the rise in the seawater Os isotopic ratio observed over the past 16 m.y.

Os-Sr-Nd results from sediments in the Bay of Bengal: Implications for sediment transport and the marine Os record

Article

Full-text available

Aug 2001

Sr, Nd, and Os isotopic data are presented for sediments from diverse locations in the Bay of Bengal. These data allow the samples to be divided into three groups, related to their sedimentary contexts. The first group, mainly composed of sediments from the shelf off Bangladesh and the currently active fan, has Sr and Nd characteristics consistent with a dominantly Himalayan source. Their (187)Os/(188)Os ratios (similar to1.2-1.5) show that the average detrital material delivered by the Ganga-Brahmaputra (G-B) river system is not unusually radiogenic. A large difference in (187)Os/(188)Os ratio exists between these Bengal Fan sediments and Ganga bedloads ((187)Os/(188)Os similar to2.5, Pierson-Wickmann et al. [2000]). This difference mainly reflects addition of a less radiogenic Brahmaputra component, though mineralogical sorting and loss of radiogenic Os during transport may also play some role. The second sample group contains sediments from elsewhere in the Bay, particularly those located on the continental slope. They display Os isotopic compositions (0.99-1.11) similar to that of present seawater and higher Os and Re concentrations. These characteristics suggest the presence of a large hydrogenous contribution, consistent with the lower sedimentation rate of these samples. Sr and Nd ratios indicate that a significant fraction of these sediments is derived from erosion of non-Himalayan sources, such as the Indo-Burman range. These observations could be explained by the deflection of sediments from the G-B river system by westward currents in the head of the Bay. The third group contains only one sample, but shows that in addition to a Himalayan source, sediment discharge from Sri Lanka may influence the detrital component in the distal part of the fan. The similarity between the isotopic compositions of the group I RN Sonne samples and those of Ocean Drilling Program Leg 116 [France-Lanord et al., 1993, Reisberg et al., 1997] suggests that the material eroding in the Himalayas has been roughly constant since the Miocene. The high Os isotopic ratios of leachates of both Sonne group I and Miocene Leg 116 sediments imply that much of the leachable highly radiogenic Os component was conserved during transport through the estuary or interaction with seawater. In constrast, samples with lower, but still relatively high, sedimentation rates (Sonne groups II and III and Pliocene Leg 116) seem to have significantly adsorbed or exchanged Os and Re with seawater. This suggests that in some cases the Os isotopic ratios of leachates of detrital sediments can be used to constrain the ancient marine Os record, or conversely, to date unfossiliferous sediments.

Impure marbles of the Lesser Himalaya: Another source of continental radiogenic osmium

Article

Nov 2002
EARTH PLANET SC LETT

The marked rise of the (187)Os/(188)Os ratio of seawater over the Cenozoic Era is generally attributed to increased continental input, and particularly to increased erosion of black shales. Thus Os isotopes are thought to trace the weathering of organic carbon. Here we present evidence that impure marbles, lacking organic carbon, provide an important source of radiogenic Os to the bedload of Himalayan rivers. These marbles provide a critical component necessary for balancing the Os isotopic budget of the bedloads. The analyzed marbles have (187)Os/(188)Os ratios as high as 194 and often contain as much (187)Os as typical black shales. Most of this radiogenic Os is not contained in the carbonate itself, but rather in associated phases. These phases are often of hydrothermal origin, and their Os may ultimately be provided by fluids circulating through black shales. While these results complicate the relationship between the Os isotopic ratio of seawater and erosion of organic-rich rocks, they also provide new information necessary for understanding the marine Os isotopic record.

Osmium Isotopes Demonstrate Distal Transport of Contaminated Sediments in Chesapeake Bay

Article

Jun 2000

Because the isotopic composition of anthropogenic Os is normally distinctive in comparison to continental crust and is precisely measurable, this platinum-group element is attractive as a tracer of transport pathways for contaminated sediments in estuaries. Evidence herein and elsewhere suggest that biomedical research institutions are the chief source of anthropogenic Os. in the Chesapeake Bay region, uncontaminated sediments bear a crustal Os-187/ Os-188 signature of 0.73 +/- 0.10. Slightly higher Os-187/Os-188 ratios occur in Re-rich Coastal Plain deposits due to post-Miocene Re-187 decay. The upper Susquehanna Basin yields sediments also with higher Os-187/Os-188. Beginning in the late 1970s, this signal was overprinted by a low Os-187/ Os-188 (anthropogenic) source in the lower Susquehanna Basin. In the vicinity of Baltimore, which is a major center of heavy industry as well as biomedical research, anthropogenic Os has been found only in sediments impacted by the principal wastewater treatment plant. Surprisingly, a mid-Bay site distant from anthropogenic sources contains the strongest anthropogenic Os signal in the data set, having received anthropogenic Os sporadically since the mid-20th Century. Transport of particles to this site overrode the northward flowing bottom currents. Finding anthropogenic Os at this site cautions that other particle-borne substances, including hazardous ones, could be dispersed broadly in this estuary.

Re-Os isotope systematics in black shales from the Lesser Himalaya: Their chronology and role in the Os-187/Os-188 evolution of seawater

Article

Aug 1999
GEOCHIM COSMOCHIM AC

Re and Os abundances and Os isotope systematics have been measured in a number of black shales sampled from outcrops and two underground phosphorite mines, Maldeota and Durmala, in the Lesser Himalaya. The Re and Os concentrations in these samples exhibit wide range, 0.2 to 264 ng/g and 0.02 to 13.5 ng/g, respectively, with a mean Re/Os of ∼25. The 187Os/188Os of these samples also show a broad range 1.02 to 11.6, with many of them far more radiogenic than the currently eroding continental crust. The black shales from the Maldeota and Durmala mines, collected a few meters above the Krol-Tal (Pc-C) boundary and occurring in the same stratigraphic horizon, yield 187Re–187Os isochron ages of 554 ± 16 and 552 ± 22 Ma, respectively, consistent with fossil evidences and those assigned for the Pc-C boundary at various other locations. These results indicate closed system behaviour of Re and Os in these mine samples and reaffirm the validity of 187Re–187Os pair to date organic-rich sediments. The age of these mine samples from the outer belt seems to be a few hundred millions of years younger than the preliminary Re-Os age of 839 ± 138 Ma for black shales from Theog, collected from the inner belt. These initial results lean toward the hypothesis that the inner belt sediments were deposited earlier than the outer belt; however, more analyses of black shales are needed to confirm this. The role of weathering black shales from the Himalaya in contributing to the Os isotope evolution of seawater over the past ∼25 Ma was assessed using a simple budget model for seawater Os and assuming values for Os fluxes and 187Os/188Os based on the available limited data on Os concentration and its 187Os/188Os in rivers and oceans. These calculations indicate that the required contributions from black shale weathering to account for the entire increase in oceanic 187Os/188Os over the past ∼16 Ma is difficult to satisfy by varying only the Os flux from HTP rivers (187Os/188Os kept constant at 1.324) or their 187Os/188Os (188Os flux constant at today’s value, ∼131 moles/yr). The requirements to balance Os isotope budget in ocean through weathering of black shales, however, is easier to accommodate if both the Os flux from HTP (Himalayan-Tibetan Plateau) rivers and their 187Os/188Os are allowed to vary. Measurements of Os abundance in HTP rivers and its isotopic composition are needed to test the validity of the model results.

Osmium behavior in estuaries: The Lena River example

Article

Apr 2000
EARTH PLANET SC LETT

The behavior of dissolved osmium at the river/ocean interface was studied in the Lena River estuary. Dissolved osmium removal is observed at very low salinities. The loss is estimated to be 28% of the dissolved concentration of the river. The removal cannot be related to the flocculation of iron oxide–organic matter colloids, but occurs simultaneously with the loss of aluminum. The proposed mechanism is the adsorption of dissolved osmium on suspended particles in the maximum turbidity zone. If this is correct, then the removal of osmium in estuaries is probably a common phenomenon. No contribution of osmium from the sediments is detected but neither the samples nor the stratified nature of the estuary are favorable to the study of a flux from sediments. If this finding can be generalized, the estimated global riverine flux of osmium to the ocean has to be recalculated and the osmium residence time in the ocean would change from 3.3×104 yr to 4.6×104 yr.

Re-Os isotope systematics and weathering of Precambrian crustal rocks: Implications for the marine osmium isotope record

Article

Oct 1998
GEOCHIM COSMOCHIM AC

The effects of weathering of freshly exposed Precambrian rocks on the mobility of osmium were studied on soils developed on a chronosequence of glacial moraines from the western Wind River Range in Wyoming. The Os budget of the Precambrian granitoid source rocks is dominated by Os-rich trace phases, such as magnetite. Amongst the major silicates, biotite, or a trace phase in biotite, carries most of the Os and Re and is also the most radiogenic mineral with 187Os/186Os of ∼113 and 187Re/186Os of ∼2,000. Re-Os isotope systematics of source rocks and soils indicate that rapid oxidation of magnetite mobilizes Os with an isotopic composition similar to the isotopic composition of the bulk soils. A very radiogenic fraction of Os is mobilized through preferential weathering of biotite. Radiogenic runoff from Precambrian shields, inferred from osmium isotope analyses of freshwater Fe-Mn-nodules suggests that high-latitude Precambrian shields are important source areas of radiogenic Os in seawater. We propose that glacial scouring and weathering of glacial tills exposed after deglaciation of Precambrian shields surrounding the North Atlantic provides a mechanism for the slightly more radiogenic nature of North Atlantic seawater compared to other seawater masses. Glacial-interglacial variations in the osmium isotopic composition of seawater seem plausible and may be triggered by changes in weathering regimes on glacial-interglacial time scales in high-latitude shield areas surrounding the North Atlantic.

Evolution of the Ratio of Strontium87 to Strontium86 in Seawater from Cretaceous to Present

Article

Full-text available

Feb 1986

A detailed record of the strontium-87 to strontium-86 ratio in seawater during the last 100 million years was determined by measuring this ratio in 137 well-preserved and well-dated fossil foraminifera samples. Sample preservation was evaluated from scanning electron microscopy studies, measured strontium-calcium ratios, and pore water strontium isotope ratios. The evolution of the strontium isotopic ratio in seawater offers a means to evaluate long-term changes in the global strontium isotope mass balance. Results show that the marine strontium isotope composition can be used for correlating and dating well-preserved authigenic marine sediments throughout much of the Cenozoic to a precision of ±1 million years. The strontium-87 to strontium-86 ratio in seawater increased sharply across the Cretaceous/Tertiary boundary, but this feature is not readily explained as strontium input from a bolide impact on land.

Strontium isotopes in the Ganga-Brahmaputra River System : Weathering in the Himalaya fluxes to the Bay of Bengal and contribution to the evolution of the oceanic 87Sr/86Sr.

Article

Full-text available

Mar 1992
EARTH PLANET SC LETT

The concentrations of Rb and Sr and87Sr/86Sr isotopic ratios have been measured in the dissolved load of the Ganga-Brahmaputra (G-B) river system. The Ganga was sampled extensively from its source at Gangotri (in the Higher Himalaya) to Patna (on the alluvial plains). The Brahmaputra was sampled in its stretch in Assam, in India. The average Sr concentration in the Ganga (at Patna) is 1.2 μmol/l and that in the Brahmaputra (at Goalpara) is 0.73 μmol/l; the mean87Sr/86Sr ratios are 0.7239 and 0.7192, respectively. The87Sr/86Sr in the Ganga source waters (the Alaknanda, the Bhagirathi and their tributaries) range between 0.7300 and 0.7986, considerably higher than the global average runoff value of 0.7119. The high87Sr/86Sr in the Ganga source waters result from the intense weathering of Precambrian granites and gneisses enriched in radiogenic Sr. The Sr isotope systematics of the Ganga waters is dominated by silicate weathering, whereas carbonate weathering plays a significant role in their major ion chemistry.The G-B system transports about 910 million moles of dissolved Sr annually to the Bay of Bengal, with an average87Sr/86Sr of 0.7213. The Sr transported by the G-B system is about 2.7% of the global dissolved Sr flux to the oceans via rivers. Model calculations reveal that the G-B system has contributed significantly to the Sr isotope evolution of seawater during the past ∼ 20 Ma.The flux of Rb through the G-B system is ∼ 24 million moles per year. This is about 5% of the global river supply of Rb to the oceans, nearly twice the contribution of water via the G-B system to the oceans. Our study suggests that the marine geochemistries of Sr and Rb (and possibly U) may have been influenced considerably by the Himalayan orogeny.

The osmium isotope composition of the continental crust

Article

Full-text available

Jul 1993
GEOCHIM COSMOCHIM AC

Osmium isotopic compositions and concentrations have been determined for deltaic and continental shelf sediments from three major rivers (the Amazon, Changjiang, and Mississippi) and for two loesses from the upper Mississippi River Valley. The loesses have heavy mineral and clay compositions characteristic of Mississippi river and delta sediment. Concentrations range from 15 to 120 pg Os/g, and ¹⁸⁷Os/¹⁸⁶Os ratios range from 8.2 to 10.9. Sediments which are polluted (surface sediment from the Changjiang Estuary) or which have scavenged metals from seawater (Gulf of Mexico slope surface sediment and distal Amazon Shelf sediment) have high osmium concentrations and less radiogenic isotopic compositions. Purely terrigenous sediments have 15–90 pg Os/g, and ¹⁸⁷Os/¹⁸⁶Os= 10.0–10.9. North American loess and Mississippi Delta sediment osmium isotopic compositions are indistinguishable. We believe that ¹⁸⁷Os/¹⁸⁶Os= 10–11 is a good average for currently eroding upper continental crust—these sediments have neodymium isotopic compositions close to the global mean for river sediment. Terrigenous ¹⁸⁷Os/¹⁸⁶Os is significantly more radiogenic than seawater ¹⁸⁷Os/¹⁸⁶Os(8.6), requiring a nonriverine source of osmium to seawater. Terrigenous osmium is also significantly more radiogenic than bulk pelagic clay osmium. We use the improved estimate of terrigenous ¹⁸⁷Os/¹⁸⁶Os to recalculate the flux of extraterrestrial osmium to Pacific marine sediment.

Rhenium-Osmium Evidence for Regional Mineralization in Southwestern North America

Article

Full-text available

Oct 1993

More than 40 base metal porphyry ore deposits in southwestern North America are associated with the Laramide orogeny (about 90 million to 50 million years ago). Rhenium-osmium dates on molybdenite, a rhenium-enriched sulfide common in many of the deposits, reveal that in individual deposits mineralization occurs near the final stages of magmatic activity irrespective of the time of inception, magnitude, or duration of magmatism. Deposits that differ widely in location and in the extent and timing of magmatism have nearly identical ages for mineralization. Rhenium-osmium-ages suggest that mineralization occurred during two distinct intervals from about 74 million to 70 million years ago and from 60 million to 55 million years ago. Most deposits that formed in the oldest interval are within the older Precambrian basement of northwestern Arizona, whereas the younger deposits are restricted to the younger Precambrian basement in southern Arizona and northern Mexico. Synchronous, widespread mineralization indicates that similar crust-mantle interaction occurred on a regional scale for ore deposits once thought to be the product of localized processes.

The Oceans, Streams, and Atmosphere

Article

Jan 1969

Karl K. Turekian

The variation of the marine 87Sr 86Sr ratio during Phanerozonic time: interpretation using a flux model

Article

Jul 1976
GEOCHIM COSMOCHIM AC

Garrett W. Brass

The 87 Sr / 86 Sr ratio in sea water has varied over geologic time due to the addition of strontium to the sea from rocks with a variety of 87 Sr / 86 Sr ratios. The measurements by et al. (Geochim. Cosmochim. Acta 34 , 105-120, 1970) of the value of the marine 87 Sr / 86 Sr ratio have been confirmed by several other workers and by some new measurements on JOIDES samples. They form the basis of a model calculation of the relative proportions of `basaltic' ( 87 Sr / 86 Sr = 0.704) and `granitic' ( 87 Sr / 86 Sr = 0.718) strontium being supplied to the sea. For the last 200 million years, the proportions of these two sources appear to reflect the history of global tectonics; `basaltic' during rifting and increasingly `granitic' during the present episodes of uplift and continental collision

The Study of Molybdenites through the 187Re-187Os Chronometer

Article

Dec 1982
EARTH PLANET SC LETT

We determined the Re and Os concentrations in 11 molybdenites of various ages (30-2700 m.y.) and from various areas. No ``common'' osmium has been detected and Os was found to be purely radiogenic. Therefore, by comparing the concentrations, we were able to determine 187Re-187Os ages. For most samples these ages are in good agreement with those measured in surrounding rocks and probably correspond to the age of mineralization. However, two or three Re-Os ages seem unreliable being probably related to some rhenium leaching through later metamorphic and/or hydrothermal events: this shows that the petrographic characteristics of ores and the type of crystallization of MoS2 are important in choosing samples suitable for dating. Re and Os determinations combined with careful petrographic investigations may give important clues on the genesis and evolution of molybdenum ores.

Variations of the 187Os/186Os ratio of seawater over the past 28 million years as inferred from metalliferous carbonates

Article

Jul 1993
EARTH PLANET SC LETT

Greg Ravizza

The Os concentration and isotopic composition of metalliferous carbonates deposited on the East Pacific Rise over the past 28 Ma are reported with complimentary Sr isotope data. Variations in the Os isotopic composition of these samples are interpreted as a record of past changes in the Os isotopic composition of seawater. These results are consistent with isotopic analyses of leachable Os in pelagic clays which have also been interpreted as a record of the 187Os/186Os ratio of seawater through time [1]. The metalliferous carbonate record clearly shows that seawater Os and Sr isotope systems are partially decoupled from one another over the past 28 Ma. Accelerated weathering of ancient organic-rich sediments is suggested as a possible mechanism to account for this decoupling and the rapid increase in the 187Os/186Os ratio of seawater over the past 15 Ma. This rapid increase suggests that the seawater Os record can potentially be used as a stratigraphic tool in some Neogene marine deposits.

Radiogenic Osmium fromRhenium-Containing Molybdenite

Article

Sep 1954

DOI:https://doi.org/10.1103/PhysRev.95.1690

Re–Os isotope systematics of HIMU and EMII oceanic island basalts from the South Pacific Ocean

Article

Jan 1993
EARTH PLANET SC LETT

The Re-Os and complementary Sr, Nd and Pb systematics of 24 oceanic island basalts from the islands of Savaii, Tahaa, Rarotonga, Rurutu, Tubuai and Mangaia are investigated. Re concentrations range from 100 to 1621 ppt (parts per trillion), while Os concentrations vary from 26 to 750 ppt. The Re and Os concentration variations suggest that fractionation and accumulation of olivine, or a low Re/Os phase in conjunction with olivine, is important in determining the Os concentration and the Re/Os ratio of the erupted basalt. 187Os/186Os in EMII basalts from Samoa and Tahaa varies from 1.0261 to 1.1275. These ratios are mostly within estimates for depleted upper mantle, and do not constrain the involvement of recycled continental crust in the origin of the EMII signature. 187Os/186Os ratios in HIMU basalts from Rurutu, Tubuai and Mangaia range from 1.1159 to 1.2473, and provide strong evidence for the role of subducted oceanic crust in the HIMU source. The Pb-Pb systematics constrain the range of possible ages and 238U/204Pb and Th/U ratios of the subducted crust; this crust is estimated to pass through the subduction zone with Rb/Sr, Sm/Nd, Lu/Hf and Th/U ratios similar to fresh MORB. The homogeneity of the Os isotopic compositions in the Tubuai and Mangaia basalts indicates that interaction of these basalts with low 187Os/186Os mantle had an insignificant effect on the Os isotopic composition of the erupted magmas. This requires a network of channels, veins or cracks capable of delivering melt from the source region (plume) to the surface fast enough to avoid interaction with the depleted upper mantle and the oceanic lithosphere. The possible identification of the HIMU signature (high 206Pb/204Pb, low 87Sr/86Sr) with recycled oceanic crust suggests the possible presence of segments of recycled crust, with independent histories, in other oceanic mantle sources, including that of some mid-ocean ridge basalts.

Estimation of continental 187Os/186Os values by using 187Os/186Os and 143Nd/144Nd ratios in marine manganese nodules

Article

Dec 1984
P NATL ACAD SCI USA

The relationship between 187Os/186Os and 143Nd/144Nd in different manganese nodule fields is used to determine the 187Os/186Os ratio of the continental terrains bounding the major ocean basins. The Atlantic Ocean drainages yield 187Os/186Os of about 11; the Pacific Ocean, between 25 and 36; and the western Indian Ocean, 20. By assuming a two-component continental crust composed of “ultramafic rocks” (high Os concentration, low 187Os/186Os) and “granite” with only radiogenic 187Os produced in accessory Re-bearing molybdenite, the ultramafic contribution to weathering is about 0.2%. Some or most of this may come from the alteration of oceanic ultramafics.

187Os/186Os in marine manganese nodules and the constraints on the crustal geochemistries of rhenium and osmium

Article

Jan 1986

During their formation, marine manganese (or more properly ferromanganese oxide) nodules include and commonly concentrate elements dissolved in seawater. This attribute makes them especially valuable recorders of the isotopic composition of elements supplied to the oceans having radiogenic isotopes, for these can be used in exploring crustal composition and evolution1–5. From measurements of 187Os/186Os ratios in marine manganese nodules and comparison with the 143Nd/144Nd ratios of the same nodules, we have calculated the Os isotopic composition and the osmium and rhenium concentrations of the weatherable portion of the continental crust, together with the proportions of ‘ultra-mafic’ and ‘granitic’ rock that constitute this crustal mass.

Anthropogenic osmium in coastal deposits

Article

Dec 1993

We have determined the isotopic composition and concentration of Os, a platinum group metal, in estuarine sediments from New Haven Harbor and adjacent Long Island Sound. Anthropogenic Os is present in recent sediments and is isotopically distinct from natural Os. Preindustrial sediment from the Long Island Sound FOAM core has approximately 40 pg of Os/g and Os-187/Os-186 = 8.8. Surface sediments from the same site and from New Haven Harbor have 64-774 pg of Os/g and Os-187/Os-186 = 1.8-5.0. The Os-187/Os-186 ratio is inversely correlated with Os concentration (ng of Os/g of dry sediment), suggesting simple mixing between more radiogenic natural Os and less radiogenic anthropogenic Os. A possible carrier of anthropogenic Os is sewage sludge-a sample of New Haven Harbor sewage outfall had the lowest Os-187/Os-186 ratio measured in this study. The primary source of anthropogenic Os may be fixative solutions used to stain tissue for electron microscopy in medical laboratories. If the medical industry is the predominant source of Os to the coastal environment, the Os isotopic composition of coastal sediments may be used to track medical waste transport and burial.

Sr isotope composition of sea water over the past 75 Myr

Article

Apr 1985
NATURE

The 87Sr/86Sr ratio of ancient seawater, as recorded in marine carbonates, is an important tracer of long-term variations in ocean chemistry1-5. However, the Sr isotope balance of the oceans has been difficult to constrain; consequently, attempts to evaluate the temporal 87Sr/86Sr changes have been largely qualitative. To constrain the causes of these variations we have measured 87Sr/86Sr ratios in carefully cleaned unrecrystallized foraminifera from DSDP sites 21 and 357. The data presented here have been quantitatively modelled taking advantage of recent advances in understanding of the Sr geochemical cycle. They suggest that whereas hydrothermal fluxes and carbonate recycling are of major importance in defining the marine 87Sr/86Sr ratio, the major control over its variations through the Cenozoic has been changes in the isotope composition of Sr derived from the weathering of silicate rocks.

The variation of the marine 87Sr/86Sr ratio during Phanerozoic time: Interpretation using a flux model

Article

Jan 1976
GEOCHIM COSMOCHIM AC

G W Brass

Application of the Re-187-Os-187 System to Black Shale Geochronometry

Article

Dec 1989
GEOCHIM COSMOCHIM AC

The decay of 187Re to 187Os provides a tool for determining depositional ages of black shales. Re and Os concentrations and Os isotopic compositions of whole rock samples of the Bakken Shale, a Mississippian/Devonian boundary black shale, yield a whole rock isochron with an age of 354 ± 49 Ma. This age is in agreement with the accepted age of the Bakken Shale (≈360 Ma). The initial ratio of the isochron is 6.2 ± 3.3. This value is indistinguishable from the ratios observed in modern Black Sea sediments. The concentration of common Os in Bakken Shale samples is strongly correlated with total nitrogen, indicating that a large fraction of the Os in these samples is associated with a hydrogenous component, which overwhelms any Os supplied to the sediment in association with detrital material or cosmic dust. The dominance of the hydrogenous component imparts a relatively homogeneous initial ratio to the sediment at the time of deposition. The degree of scatter about the isochron exceeds the degree of scatter expected from either analytical error or from the estimated degree of initial isotopic heterogeneity. The pattern of scatter is consistent with postdepositional mobilization of Re and/ or Os on a small spatial scale. We suggest that this mobilization may be a consequence of petroleum formation and migration in the Bakken Shale.

Accretion rate of extraterrestrial particles determined from osmium isotope systematics of Pacific Pelagic clay and manganese nodules

Article

Jun 1988
GEOCHIM COSMOCHIM AC

Pelagic clay and Mn nodules from DOMES sites in the North Pacific and a varved glacial lake deposit from Connecticut were analysed for Os concentration and isotopic composition by isotope-dilution secondary ion mass spectrometry after treatment by NiS fusion or oxalic acid leaching. Bulk pelagic clay from DOMES site C has and Os = 0.14 ng/g. Oxalic acid leaches of this same sediment and of Mn nodules from DOMES sites A and C have more radiogenic ratios which average 8.3. Bulk glacial Lake Hitchcock sediment has and Os = 0.06 ng/g. The total Os flux to North Pacific pelagic clay is 7 to 10 ng Os/cm2/106 y.Lake Hitchcock sediment provides an integrated value for the local crustal ratio. The oxalic acid leaches are assumed to attack hydrogenous phases selectively. A simple model in which the only sources of Os to the ocean are continental crust with the isotopic composition of Lake Hitchcock () and extraterrestrial particles with results in a cosmic flux of osmium to the sediment of 4.9 ngOs/cm2/106 y of which 20% is hydrogenous. A model in which the sources of Os to the ocean are continental crust with an 187Os/186Os ratio of 30 (from the model of Palmer and Turekian, 1986), oceanic mantle or crust with and extraterrestrial particles with results in a cosmic flux of Os to the sediment of 5.7 ngOs/cm2/106 y of which none is hydrogenous. These extraterrestrial Os fluxes correspond to maximum C-1 chondrite accretion rates of between 4.9 × 104 and 5.6 × 104 tonnes/y.

Sr isotope evolution of seawater: The role of tectonics

Article

Mar 1992
EARTH PLANET SC LETT

We use a high-resolution seawater Sr isotopic evolution curve for the last 100 m.y. in conjunction with modern riverine Sr flux measurements, and also geologic, tectonic and geochronological data, to make the case for a close relationship between seawater Sr isotopic composition and the India-Asia continental collision. Using a simple seawater Sr budget model we begin by showing that the Sr flux associated with alteration of seafloor basalts is too small and does not have the right time evolution to account for much of the seawater Sr isotopic curve of the last 100 m.y. The flux of dissolved Sr carried by rivers originating in the Himalaya-Tibet region on the other hand is presently a significant fraction of the global Sr budget. We calculate how this riverine flux would have had to change with time in order to match the observed seawater Sr isotopic curve and find that the riverine flux remains relatively constant prior to the collision of India with Asia but then increases very significantly after collision. We note that the period of most rapid change in seawater Sr isotopic ratio, from 20 Ma to 15 Ma, is also a period of exceptionally high erosion in parts of the Himalayas and the Tibetan Plateau. As further evidence that Sr derived from the collision of India with Asia plays a major role in the Sr isotopic evolution of seawater we show that the total amount erosion of the Himalaya-Tibetan Plateau since collision, which we calculate separately, represents a total amount of Sr that is very nearly the same as the cumulative amount required by the Sr isotopic change of seawater since collision. The relationship between erosion and riverine Sr flux allows us to use the Sr isotopic evolution of seawater to reconstruct a history of erosion since collision, and we find that the erosion rate accelerates with time since collision, with the present having the largest rate.

Simple models for the geochemical response of the ocean to climatic and tectonic forcing

Article

Aug 1993
EARTH PLANET SC LETT

Simple models for the geochemical response of the ocean to periodic forcing are used as a framework to discuss the shortest periods of change resolvable by present analytical precision of elemental or isotopic ratio measurements of the chemical evolution of seawater. For chemical properties whose budget is dominated by fluxes into and out of the ocean, we show that the geochemical response to changing fluxes is strongly attenuated at periods shorter than the residence time, and that the response at these periods is also phase shifted so as to lag the forcing by one quarter cycle. The amplitude response as a function of period is used to estimate the periods of forcing resolvable by present analytical precision in measuring the 87Sr/86Sr and 234U/238U evolution of seawater, and we find that the shortest periods resolvable are of the order of 1 myr. If variations at periods shorter than this are found, we would argue that these are very likely of local, as opposed to global, origin. We illustrate the importance of phase shifts as a function of forcing period by discussing some recently published data that show a high degree of correlation (over the last 300 kyr) between changes in 87Sr/86Sr and δ18O measured in the same sediment core. At first sight this correlation might be taken as good evidence that both 87Sr/86Sr and δ18O are responding to some common climatic forcing, but given the long residence time of Sr in the ocean, Sr and O should in fact have different phase shifts relative to any proposed common forcing. Thus the apparent correlation between 87Sr/86Sr and δ18O over the past several 100 Ma is not necessarily an indication that they are responding to a common cause. Amplitude response curves are also used to place limits on permissible global seawater 234U/238U variations, and these are then compared with published data to identify local (diagenetic) effects. Application to 187Os/186Os and U records in seawater detectors is proposed.

The osmium isotopic composition of organic-rich marine sediments

Article

May 1992
EARTH PLANET SC LETT

The osmium (Os) concentration and187Os/186Os ratio of several recent, marine, organic-rich sediment samples from three widely separated sites have been measured. Os concentrations range from 0.095 to 0.212 ppb and187Os/186Os ratios range from 8.2 to 8.9. The calculated fraction of hydrogenous Os exceeds 78% in all samples. Thus, the187Os/186Os ratio of these samples reflects Os isotopic composition of seawater. The small range in measured187Os/186Os ratio indicates that the Os isotopic composition at these sites is fairly homogeneous. The large magnitude of the Os burial flux at these sites indicates the Os burial in association with organic-rich sediments is an important sink in the marine cycle of Os. These data also suggest that ancient organic-rich sediments may provide a record of past variations in the Os isotopic composition of seawater.

The geochemistry of rhenium and osmium in recent sediments from the Black Sea

Article

Dec 1991
GEOCHIM COSMOCHIM AC

The Os isotopic composition of recent sediments from the Black Sea are reported with the concentrations of Re, Os, and major and minor elements. Osmium concentrations range from 0.23 to 0.69 ppb and Re concentrations range from 21 to 85 ppb. Concentrations of both elements are large relative to average crustal material and are positively correlated with organic carbon. ratios range from 5.7 to 7.1; all of these values are less radiogenic than the estimated ratio of seawater and average continental crust material. Variations in the Os isotopic composition of these sediments are attributed to mixing of a hydrogenous component ( ratio between 7 and 9) and a less radiogenic detrital component ( ratio between 1 and 4). A mixing model is used to determine the fraction of Os in the sediment associated with each component, and the burial fluxes of Re and Os in the Black Sea are calculated. In addition the data are used to estimate the magnitude of systematic error which such initial Os isotopic heterogeneity may introduce into Re-Os age determinations of ancient organic-rich sediments.

Sources of osmium isotopes in manganese nodules

Article

May 1988
GEOCHIM COSMOCHIM AC

We have measured the and Os concentrations of ferromanganese crusts forming on serpentinized peridotites from the Atlantic Ocean and also report major element data for these samples and six manganese nodules previously analyzed for Os. Variations in the ratios of manganese nodules are the result of two processes operating on different spatial scales. The large scale variations result from the impression of intense local Os inputs from continental and oceanic sources on a generally homogeneous oceanic ratio. Fine scale variations may be understood as the result of the mixing of a constant fine-grained debris flux of meteoritic Os imposed on varying amounts of Os precipitated from seawater.

The record of sea water 187Os/186Os variation through the Cenozoic

Article

Nov 1992
EARTH PLANET SC LETT

The variation of sea water 187Os/186Os during the Cenozoic has been determined by analyzing the hydrogenous Os released by acidic hydrogen peroxide leaching of layers in an abyssal North Pacific pelagic clay core. Overall, sea water 187Os/186Os has increased from 3.2 at 58 Ma to the present-day value of ∼ 8.6. This pattern is similar to the well-known 87Sr/86Sr evolution of sea water. The increase in the proportion of continental Os (187Os/186Os⩾ 10) could be due to enhanced weathering rates of black shales associated with the uplift of the Himalayas. Other elements associated with black shale weathering, such as U and P, should show effects in the sedimentary record.

Negative thermal ion mass spectrometry of osmium, rhenium, and iridium

Article

Jan 1991
GEOCHIM COSMOCHIM AC

We report on a technique for obtaining intense ion beams of negatively charged oxides of Os, Re and Ir by thermal ionization, in a conventional surface ionization mass spectrometer. It was found that the principal ion species of Os, Re and Ir produced are OsO3−, ReO4− and IrO2−. The sharp distinction in the masses of the dominant molecular species produced by this technique permits the measurement of isotopic compositions of each element from mixtures of platinum-group elements without significant isobaric interferences. For 187Re-187Os isotope studies, this technique offers the advantage of isotopic analyses without prior chemical separation of Re from Os, as no isobaric interference between the oxides of 187Os and 187Re exists under these conditions. For 4 ng Os, stable ion currents of 3 × 10−12 A can be maintained for over one hour, which allows determination of isotopic ratios with a Faraday collector to a precision of better than . For 70 pg Os, isotopic ratios can be measured with a precision of better than ±5‰ using a secondary electron multiplier. The detection limit for Os is estimated to be below 10−14 g. Osmium isotopic ratios have also been determined by direct loading of natural iridosmine with a precision of ±0.5‰ or better. We have obtained ionization efficiencies of 2–6% for Os and >20% for Re; these are superior to those reported for other techniques available to date and demonstrate that negative thermal ion mass spectrometry will have widespread application to 187Re-187Os chronometry and to studies of the geochemistry and environmental chemistry of the platinum-group elements.

Concentrations of chromium, silver, molybdenum, nickel, cobalt, and manganese in suspended material in streams

Article

Nov 1967

Estimation of continental Os/Os values by using Os/Os and Nd/Nd ratios in marine manganese nodules

Article

Jan 1985

The relationship between (187)Os/(186)Os and (143)Nd/(144)Nd in different manganese nodule fields is used to determine the (187)Os/(186)Os ratio of the continental terrains bounding the major ocean basins. The Atlantic Ocean drainages yield (187)Os/(186)Os of about 11; the Pacific Ocean, between 25 and 36; and the western Indian Ocean, 20. By assuming a two-component continental crust composed of "ultramafic rocks" (high Os concentration, low (187)Os/(186)Os) and "granite" with only radiogenic (187)Os produced in accessory Re-bearing molybdenite, the ultramafic contribution to weathering is about 0.2%. Some or most of this may come from the alteration of oceanic ultramafics.

A Direct Measurement of the Terrestrial Mass Accretion Rate of Cosmic Dust

Article

Nov 1993

The mass of extraterrestrial material accreted by the Earth as submillimeter particles has not previously been measured with a single direct and precise technique that samples the particle sizes representing most of that mass. The flux of meteoroids in the mass range 10(-9) to 10(-4) grams has now been determined from an examination of hypervelocity impact craters on the space-facing end of the Long Duration Exposure Facility satellite. The meteoroid mass distribution peaks near 1.5 x 10(-5) grams (200 micrometers in diameter), and the small particle mass accretion rate is (40 +/- 20) x 106 kilograms per year, higher than previous estimates but in good agreement with total terrestrial mass accretion rates found by geochemical methods. This mass input is comparable with or greater than the average contribution from extraterrestrial bodies in the 1-centimeter to 10-kilometer size range.

Osmium-187/Osmium-186 in Manganese Nodules and the Cretaceous-Tertiary Boundary

Article

Dec 1983

As a result of the radioactive decay of rhenium-187 (4.6 x 1010 years) the osmium-187/osmium-186 ratio changes in planetary systems as a function of time and the rhenium-187/osmium-186 ratio. For a value of the rhenium-187/osmium-186 ratio of about 3.2, typical of meteorites and the earth's mantle, the present-day osmium-187/osmium-186 ratio is about 1. The earth's continental crust has an estimated rhenium-187/osmium-186 ratio of about 400, so that for a mean age of the continent of 2 x 109 years, a present-day osmium-187/osmium-186 ratio of about 10 is expected. Marine manganese nodules show values (6 to 8.4) compatible with this expectation if allowance for a 25 percent mantle osmium supply to the oceans is allowed. The Cretaceous-Tertiary boundary iridium-rich layer in the marine section at Stevns Klint, Denmark, yields an osmium-187/osmium-186 ratio of 1.65, and the one in a continental section in the Raton Basin, Colorado, is 1.29. The simplest explanation is that these represent osmium imprints of predominantly meteoritic origin.

Concentrations of Cr, Ag, Mo, Ni, Co, and Mn in suspended material in streams

Jan 1967
940

Turekian

K.K. Turekian and M.R. Scott, Concentrations of Cr, Ag, Mo, Ni, Co, and Mn in suspended material in streams, Environ. Sci. Technol. 1,940-942, 1967.

Seawater SVSr/S6Sr evolution from Cretaceous to present

Jan 1986
979-984

J Hess
M Bender
J.-G Schilling

J. Hess, M. Bender and J.-G. Schilling, Seawater SVSr/S6Sr evolution from Cretaceous to present, Science 231, 979-984, 1986.

Seawater 87Sr86Sr evolution from Cretaceous to present

Jan 1986
979

Hess

The isotopic composition of leachable osmium from river sediments

Abstract

No full-text available

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