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| Registros recuperados: 11 | |
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| Wilf,Peter; Singer,S; Zamaloa,María del Carmen; Johnson,Kirk R; Cúneo,N. Rubén. |
| The Pampa de Jones fossil site, a stratigraphically isolated roadcut near the northeastern shore of Nahuel Huapi Lake in Neuquén Province, Argentina, holds a rich fossil biota including a macroflora, a microflora, insects, and most famously, an ontogenetic series of pipid frogs. The site exposes tuffaceous mudstone and sandstone beds of probable lacustrine origin, considered to belong to the volcanic Huitrera Formation. However, there have been no reliable age constraints for the fossil assemblage. We undertook laser fusion analyses of sanidine and biotite crystals occurring in a tuff layer found 4.4 m above the main fossil horizon. Twentyeight sanidine crystals yielded an 40Ar/39Ar age of 54.24 ± 0.45 Ma that is preferred over our biotite age of 53.64 ±... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Early Eocene; Huitrera Formation; Geochronology; Paleobotany; Patagonia; Neuquén; Argentina. |
| Ano: 2010 |
URL: http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0002-70142010000200006 |
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| VASCONCELOS,PAULO M.; ONOE,ARTUR T.; KAWASHITA,KOJI; SOARES,ADALBERTO J.; TEIXEIRA,WILSON. |
| Laser heating 40Ar/39Ar geochronology provides high analytical precision and accuracy, mum-scale spatial resolution, and statistically significant data sets for the study of geological and planetary processes. A newly commissioned 40Ar/39Ar laboratory at CPGeo/USP, São Paulo, Brazil, equips the Brazilian scientific community with a new powerful tool applicable to the study of geological and cosmochemical processes. Detailed information about laboratory layout, environmental conditions, and instrumentation provides the necessary parameters for the evaluation of the CPGeo/USP 40Ar/39Ar suitability to a diverse range of applications. Details about analytical procedures, including mineral separation, irradiation at the IPEN/CNEN reactor at USP, and mass... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Geochronology; 40Ar/39Ar method; Irradiation; Calibration. |
| Ano: 2002 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652002000200008 |
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| Bühn,Bernhard; Pimentel,Márcio M.; Matteini,Massimo; Dantas,Elton L.. |
| Age determinations using the 235U and 238U radioactive decay series to the daughter isotopes 207Pb and 206Pb, respectively, using the mineral zircon (ZrSiO4), are widely used to decipher geological processes. A new method developed in the last couple of years, the laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS), overcomes previous laborious sample preparation, and yields isotopic ratios and age data with a high spatial resolution of ten of microns. The present study describes the analytical set-up and data reduction process as presently applied at the Laboratory for Geochronology of the University of Brasília. It explores the precision and accuracy of the method by cross-analysing three international zircon... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Geochronology; U-Pb isotopes; LA-MC-ICP-MS; Zircon; Age dating. |
| Ano: 2009 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652009000100011 |
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| Harris, Pierre; Fichez, Renaud; Fernandez, Jean Michel; Golterman, Han; Badie, Christian. |
| During the past century, the sediment deposition rate has been assessed by measuring excess Pb-210 activity in a sediment core sampled in the harbour area of the Papeete Lagoon (Tahiti, French Polynesia). Dated sediment samples were analysed following a sequential extraction method to quantify five sedimentary phosphorus pools: loosely sorbed or exchangeable phosphorus, ferric iron-bound phosphorus, authigenic calcium carbonate associated phosphorus, detrital apatite and detritic inorganic phosphorus, acid organic phosphorus. Results from sediment dating showed the core to cover the period from 1865 to 1995, with a sharp change around 1957 corresponding to a doubling in sediment deposition rates. From the bottom to the top of the core, concentrations... |
| Tipo: Text |
Palavras-chave: Géochronologie; Phosphore; Sédiment; Lagons coralliens; Geochronology; Phosphorus; Sediment; Coral reef lagoon. |
| Ano: 2001 |
URL: http://archimer.ifremer.fr/doc/00322/43365/42850.pdf |
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| Heimbuerger, Lars-eric; Cossa, Daniel; Thibodeau, Benoit; Khripounoff, Alexis; Mas, Virginie; Chiffoleau, Jean-francois; Schmidt, Sabine; Migon, Christophe. |
| The magnitude and the chronology of anthropogenic impregnation by Hg and other trace metals of environmental concern (V, Cr, Ni, Cu, Zn, Ag, Cd and Pb, including its stable isotopes) in the sediments are determined at the DYFAMED station, a site in the Ligurian Sea (Northwestern Mediterranean) chosen for its supposed open-sea characteristics. The DYFAMED site (VD) is located on the right levee of the Var Canyon turbidite system, at the end of the Middle Valley. In order to trace the influence of the gravity current coming from the canyon on trace metal distribution in the sediment, we studied an additional sediment core (VA) from a terrace of the Var Canyon, and material collected in sediment traps at the both sites at 20 m above sea bottom. The patterns... |
| Tipo: Text |
Palavras-chave: Marine sediments; Sediment traps; Mercury; Trace metals; Lead isotopes; Geochronology. |
| Ano: 2012 |
URL: http://archimer.ifremer.fr/doc/00073/18435/16125.pdf |
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| Small, David; Clark, Chris D.; Chiverrell, Richard C.; Smedley, Rachel K.; Bateman, Mark D.; Duller, Geoff A. T.; Ely, Jeremy C.; Fabel, Derek; Medialdea, Alicia; Moreton, Steven G.. |
| This contribution documents the process of assessing the quality of data within a compilation of legacy geochronological data relating to the last British-Irish Ice Sheet, a task undertaken as part of a larger community-based project (BRITICE-CHRONO) that aims to improve understanding of the ice sheet's deglacial evolution. As accurate reconstructions depend on the quality of the available data, some form of assessment is needed of the reliability and suitability of each given age(s) in our dataset. We outline the background considerations that informed the quality assurance procedures devised given our specific research question. We describe criteria that have been used to make an objective assessment of the likelihood that an age is influenced by the... |
| Tipo: Text |
Palavras-chave: British-Irish Ice Sheet; Deglaciation; Geochronology; Data compilations; Quality assurance; Bayesian. |
| Ano: 2017 |
URL: https://archimer.ifremer.fr/doc/00504/61598/65865.pdf |
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| Zwaan, J.C.. |
| As one of the most valuable gemstones, emeralds are known to occur in several countries of the world, such as Colombia, Zambia, Brazil, Pakistan, Afghanistan, Russia, Madagascar and Zimbabwe. The emerald deposits at Sandawana, Zimbabwe, are described, the emeralds from this deposit characterised and a model of emerald formation presented; this is compared with existing models. The emeralds from Sandawana, Zimbabwe, show relatively constant physical properties, with high refractive indices and specific gravities. They are characterized by laths and fibres of amphibole, both actinolite and cummingtonite. Other common inclusions are albite and apatite. Rare, opaque and chromium-rich inclusions constitute a new variety of ilmenorutile. Compared to emeralds... |
| Tipo: Article / Letter to the editor |
Palavras-chave: Emerald; Sandawana; Zimbabwe; Gemmology; Petrology; Geothermometry; Geochronology; 38.30. |
| Ano: 2006 |
URL: http://www.repository.naturalis.nl/record/209632 |
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| Albert,James S.; Val,Pedro; Hoorn,Carina. |
| ABSTRACT We review geological evidence on the origin of the modern transcontinental Amazon River, and the paleogeographic history of riverine connections among the principal sedimentary basins of northern South America through the Neogene. Data are reviewed from new geochronological datasets using radiogenic and stable isotopes, and from traditional geochronological methods, including sedimentology, structural mapping, sonic and seismic logging, and biostratigraphy. The modern Amazon River and the continental-scale Amazon drainage basin were assembled during the late Miocene and Pliocene, via some of the largest purported river capture events in Earth history. Andean sediments are first recorded in the Amazon Fan at about 10.1-9.4 Ma, with a large increase... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Biostratigraphy; Geochronology; Landscape Evolution Model; River capture; Transcontinental Amazon. |
| Ano: 2018 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1679-62252018000300306 |
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| Registros recuperados: 11 | |
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