Subcommission on geochronology: Convention on the use of decay constants in geo- and cosmochronology

Steiger, R.; Jäger, E.

doi:10.1016/0012-821x(77)90060-7

Cited by 9,012 publications

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“…At the northern end of the Napudet Hills, sedimentary strata comprise four sequences, the lowest of which is a volcaniclastic interval informally termed the Emunyan beds here (Extended Data Fig. 2a and Supplementary Table 2 we plotted the incremental release spectra of the plateau steps identified for sample 15-NPD-03 on an isochron plot, it was possible to observe that the 40 Ar- 36 Ar intercept was not purely atmospheric. Thus, we corrected the data using these trapped 40 Ar- 36 Ar components.…”

Section: Stratigraphy and Agementioning

confidence: 99%

“…2a and Supplementary Table 2 we plotted the incremental release spectra of the plateau steps identified for sample 15-NPD-03 on an isochron plot, it was possible to observe that the 40 Ar- 36 Ar intercept was not purely atmospheric. Thus, we corrected the data using these trapped 40 Ar- 36 Ar components. The corrected plateau 40 Ar- 39 Ar age obtained, 13.31 ± 0.04 Myr, is considered to be the most representative for this sample (Extended Data Fig.…”

Section: Stratigraphy and Agementioning

confidence: 99%

“…Thus, we corrected the data using these trapped 40 Ar- 36 Ar components. The corrected plateau 40 Ar- 39 Ar age obtained, 13.31 ± 0.04 Myr, is considered to be the most representative for this sample (Extended Data Fig. 2b).…”

Section: Stratigraphy and Agementioning

confidence: 99%

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New infant cranium from the African Miocene sheds light on ape evolution

Nengo

Tafforeau

Gilbert

et al. 2017

Nature

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and dental development, it possesses no definitive hylobatid synapomorphies. The combined evidence suggests that nyanzapithecines were stem hominoids close to the origin of extant apes, and that hylobatid-like facial features evolved multiple times during catarrhine evolution.Hominoids underwent a major evolutionary radiation during the Miocene epoch, with over 40 widely recognized species in at least 30 genera 1 . Despite this multitude of taxa, only about one-third are known from any cranial remains, and no more than half a dozen preserve any significant portion beyond the face and palate 2 . Thus, much about hominoid cranial evolution remains poorly understood, especially with respect to the ancestral morphology that gave rise to the clade containing extant apes and humans. Importantly, the African fossil record lacks any reasonably complete hominoid crania between 17 and 7 million years (Myr) ago, and no cranial specimens are known at all from between 14 and 10 Myr (refs 3-6), greatly hampering the analysis of hominoid evolution. The KNM-NP 59050 cranium reported here was recovered from Napudet (South Turkana, Kenya) and dated to 13 Myr; it thus falls within this critical yet poorly represented period. The infant specimen is nearly complete, but is missing the deciduous dental crowns (Fig. 1a-d and Extended Data Fig. 1a-f). The unerupted adult dentition, brain endocast, and bony labyrinths were visualized using propagation phase-contrast X-ray synchrotron microtomography (PPC-SR-CT; Fig. 1e-h Locality and horizon. Napudet (2° 57′ N, 35° 52′ E), Turkana Basin, Kenya, Emunyan Beds, Brown Bedded Tuffs (Extended Data Fig. 2a).Geological age. 13 Myr. Diagnosis.A large species of Nyanzapithecus, with M 1 significantly larger than in N. pickfordi (P < 0.05), N. harrisoni (P < 0.01), and probably N. vancouveringorum ( Fig. 3a and Extended Data Table 1a; Cranial morphologyKNM-NP 59050 is a nearly complete but somewhat distorted cranium of an infant primate (Fig. 1). The cranium is slightly crushed bilaterally and the posterior portion of the basicranium is both broken and distorted. All the deciduous tooth crowns are broken off, but their roots are preserved. The permanent teeth are unerupted, with the right I 1 being visible in its crypt.The overall dimensions of KNM-NP 59050 are similar to those of Symphalangus crania of equivalent dental age, except for the maxillo-alveolar size, which is similar to Hoolock (Extended Data Table 1b). Relative to overall cranial size, the snout is small as in juvenile hylobatids, and smaller than in extant juvenile hominids . This difference between hylobatids and hominids persists into adulthood (Extended Data Fig. 4b, d), and assuming that N. alesi followed the same pattern, its snout would have been relatively small as an adult, unlike that of Afropithecus and Saadanius.The orbits appear large, but are well within the expected range for an extant juvenile hominoid of its size (Extended Data Fig. 4e). The orbits are slightly taller than wide, which may reflect the bilateral dist...

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Section: Stratigraphy and Agementioning

confidence: 99%

Section: Stratigraphy and Agementioning

confidence: 99%

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New infant cranium from the African Miocene sheds light on ape evolution

Nengo

Tafforeau

Gilbert

et al. 2017

Nature

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“…3a. On such a plot, natural U should plot on the x-axis ( 236 U/ 238 U = 0) at a value of 238 U/ 235 U = 137.88±0.04 (18). The U isotopic compositions representing the plume in E33-45 form a tight cluster, while the perched water zone sample and the two shallow samples fall closer to the 238 U/ 235 U axis.…”

Section: Resultsmentioning

confidence: 98%

Identifying the Sources of Subsurface Contamination at the Hanford Site in Washington using High-Precision Uranium Isotopic Measurements

Christensen

Dresel

Conrad

et al. 2004

Environ. Sci. Technol.

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2In the mid-1990s, a groundwater plume of uranium (U) was detected in monitoring wells in the B-BX-BY Waste Management Area (WMA) at the Hanford Site in Washington. This area has been used since the late 1940s to store high-level radioactive waste and other products of U fuel-rod processing. Using multiple collector ICP source magnetic sector mass spectrometry (MC ICPMS) high precision uranium isotopic analyses were conducted of samples of vadose zone contamination and of groundwater. The ratios 236 U/ 238 U, 234 U/ 238 U and 238 U/ 235 U are used to distinguish contaminant sources. Based on the isotopic data, the source of the groundwater contamination appears to be related to a 1951 overflow event at tank BX-102 that spilled high level U waste into the vadose zone. The U isotopic variation of the groundwater plume is a result of mixing between contaminant U from this spill and natural background U. Vadose zone U contamination at tank B-110 likely predates the recorded tank leak and can be ruled out as a source of groundwater contamination, based on the U isotopic composition. The locus of vadose zone contamination is displaced from the initial locus of groundwater contamination, indicating that lateral migration in the vadose zone was at least 8 times greater than vertical migration. The time evolution of the groundwater plume suggests an average U migration rate of ~0.7-0.8 m/day showing slight retardation relative to a ground water flow of ~1 m/day. IntroductionGroundwater contamination at the Hanford Site, in south-central Washington, resulted from decades of nuclear fuel production and processing. Understanding the fate and transport of contamination is hindered by the presence of multiple potential contamination sources within relatively small areas, and the extended 50-year duration of activity. Natural sources of uranium have a uniform 238 U/ 235 U ratio (with the rare exception of the Oklo natural fission reactor (1)), but can have variable 234 U/ 238 U depending on natural processes that can disturb the secular equilibrium of the 238 U decay chain. In contrast, anthropogenic U can have altered 238 U/ 235 U due either to 235 U enrichment for nuclear applications or to changes resulting from the burn up of natural or enriched uranium in nuclear reactors. In addition, the consumption of uranium fuel rods in reactors produces 236 U (half-life = 23 million years) through neutron capture by 235 U. 236 U does not occur naturally to any significant degree. These contrasts in the isotopic compositions of natural and anthropogenic uranium, as well as the wide variation in the isotopic composition 3 of different anthropogenic uranium sources, promotes the measurement of uranium isotopic composition as a tracer of uranium contamination in the environment (e.g., refs 2-4).Multiple collector ICP magnetic sector mass spectrometry (MC-ICPMS) provides high precision isotopic analyses of a wide range of elements (5, 6, also see overview 7). MC-ICPMS has been used for high precision 234 U/ 238 U measurements (8) and for...

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“…J-val ues were cal cu lated with a preci sion of <0.25% and are re ported for each sam ple in the data ta bles. De cay con stants uti lized were those given in Steiger and Jäger (1977). The 40 Ar-39 Ar geo chron ol ogy lab o ra tory at the Uni ver sity of Lund uses a Micromass 5400 mass spec trom e ter with a Far a day and an elec tron mul ti plier.…”

Section: Methodsmentioning

confidence: 99%

New 40Ar-39Ar age constrains for magmatic and hydrothermal activity in the Holy Cross Mts. (southern Poland)

Nawrocki

Salwa

Pańczyk

2013

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New 40 Ar iso tope ages of diabase in tru sions from the Holy Cross Moun tains (Po land) con firm the pres ence of at least two events of Pa leo zoic mag matic ac tiv ity in the study area. The old est, lat est Si lu rian/ear li est De vo nian (ca. 424-416 Ma) ep i sode is re corded by a diabase from the Bardo Syncline (Zarobiny PIG-1 bore hole) in the Kielce Re gion. A youn ger, Serpukhovian (ca. 331-323 Ma) event is doc u mented by a diabase from the Milejowice-1 bore hole drilled in the £ysogóry Re gion. The diabase in tru sion pen e trated by the Wzorki-1 bore hole, also lo cated in the £ysogóry Re gion, is most prob a bly of the same age. It pro vided, how ever, con sis tent mid-Tri as sic (243 Ma) 40 Ar-39 Ar iso to pic age re flect ing its per va sive hy drother mal al ter ation. The first stage of the post-Cal edo nian hy dro ther mal ac tiv ity in the Holy Cross Mts. which pro duced polymetallic cop per and iron-bear ing min er ali sa tion may be linked with the youn ger mag matic phase de fined here. The second stage of post-Cal edo nian hy dro ther mal ac tiv ity in the Holy Cross Mts., as so ci ated with the lead-zinc min er ali sa tion, may be cor re lated with the Mid dle Tri as sic hy dro ther mal event re corded in the Wzorki diabase. Sug ges tions of tem po ral re la tionships be tween mag matic/hy dro ther mal ac tiv i ties and min er ali sa tion events should, how ever, be con strained by fur ther detailed geo chem i cal and min er al og i cal stud ies.

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Subcommission on geochronology: Convention on the use of decay constants in geo- and cosmochronology

Cited by 9,012 publications

References 11 publications

New infant cranium from the African Miocene sheds light on ape evolution

New infant cranium from the African Miocene sheds light on ape evolution

Identifying the Sources of Subsurface Contamination at the Hanford Site in Washington using High-Precision Uranium Isotopic Measurements

New 40Ar-39Ar age constrains for magmatic and hydrothermal activity in the Holy Cross Mts. (southern Poland)

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