Consulta: subjectFacets:"Geochronology"
Registros recuperados: 11
Data/hora: 12/06/2024 12:35:32

Using geochronology to reconstruct the evolution of particulate phosphorus inputs during the past century in the Papeete Lagoon (French Polynesia)
Provedor de dados: 5
Autores: 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

Natural and anthropogenic trace metals in sediments of the Ligurian Sea (Northwestern Mediterranean)
Provedor de dados: 5
Autores: 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

Etude du fonctionnement hydrosédimentaire d'un écosystème lagunaire sur des échelles de temps multiples. Application au complexe lagunaire "étangs Palavasiens - étang de l'Or - canal du Rhône à Sète"
Provedor de dados: 5
Autores: Castaings, Jerome.
The sedimentary evolution of coastal lagoons is a complex phenomenon involving both short term extreme processes (floods, storms) and long term processes (mean sea level variations, climate change). If general mechanisms of these phenomena are well known, their spatial and temporal variability makes them difficult to assess at the local scale. The diversity of lagoonal environments and human influence makes this even more risky. I have focussed this study on the case of a Mediterranean lagoon system : “Palavasian lagoons, Or lagoon, and Rhône-Sète waterway” which is located in the Gulf of Lion (South of France). A ultidisciplinary approach was used to assess sediment dynamics on multiple time scales. An average filling rate of 1.3 mm.year-1 over the two...
Tipo: Text
Palavras-chave: Dynamique sédimentaire; Géochronologie; Hydrodynamique; Échelles temporelles; Lagunes; Sediment dynamic; Geochronology; Hydrodynamic; Time scales; Lagoons.
Ano: 2012
URL: http://archimer.ifremer.fr/doc/00193/30436/28853.pdf

Devising quality assurance procedures for assessment of legacy geochronological data relating to deglaciation of the last British-Irish Ice Sheet
Provedor de dados: 5
Autores: 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

Gemmology, geology and origin of the Sandawana emerald deposits, Zimbabwe
Provedor de dados: 16
Autores: 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

The changing course of the Amazon River in the Neogene: center stage for Neotropical diversification
Provedor de dados: 83
Autores: 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

Early Eocene 40Ar/39Ar age for the Pampa de Jones plant, frog, and insect biota (Huitrera Formation, Neuquén Province, Patagonia, Argentina)
Provedor de dados: 41
Autores: 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

High spatial resolution analysis of Pb and U isotopes for geochronology by laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS)
Provedor de dados: 42
Autores: 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

SHRIMP U-Pb zircon dating of Pedras Grandes Suite, southern Santa Catarina State, Brazil
Provedor de dados: 42
Autores: Jelinek,Andréa R.; Bastos-Neto,Artur C.; Leite,Jayme A.D.; Hartmann,Léo A.; McNaughton,Neal J.
Two major magmatic pulses of the granitic Florianópolis Batholith in Santa Catarina State, southern Brazil, occurred between 613±5Ma and 595±5 Ma, during the Neoproterozoic Brasiliano Cycle. These ages were obtained by U-Pb isotopic determinations with the sensitive high mass-resolution ion microprobe on igneous zircons from Pedras Grandes Suite in Santa Catarina State. Euhedral zircons remained unaltered close to a fluorite vein deposited at 180?C or more. These ages suggest a northern limit for the Pedras Grandes Suite, explaining the spatial relationship between the fluorite veins and the source rock.
Tipo: Info:eu-repo/semantics/article
Palavras-chave: SHRIMP; Pedras Grandes Suite; Zircon; Geochronology; Fluorite.
Ano: 2005
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652005000100010

40Ar/39Ar geochronology at the Instituto de Geociências, USP: instrumentation, analytical procedures, and calibration
Provedor de dados: 42
Autores: 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

Geochronology and heavy metal flux to Guanabara bay, Rio de Janeiro state: a preliminary study
Provedor de dados: 42
Autores: Baptista Neto,José A.; Peixoto,Tomás C.S.; Smith,Bernard J.; Mcalister,John J.; Patchineelam,Soraya M.; Patchineelam,Sambasiva R.; Fonseca,Estefan M.
Guanabara Bay, located in Rio de Janeiro state. It is surrounded by the second most important metropolitan area of the country. Over recent decades, land disturbance and urbanization in the surrounding area has significantly increased sediment input to the bay and had a negative effect on its overall environmental. This is especially related to high volumes of untreated sewage and industrial effluents. This study evaluates the history of this human impact through detailed examination of a sediment core taken from the northern portion of Guanabara Bay. A geochronology is established using 210Pb dating and related to organic carbon and heavy metal fluxes to the sediments. This gave a calculated net average sedimentation rate for the core of 0.67 cm.year-1....
Tipo: Info:eu-repo/semantics/article
Palavras-chave: 210Pb; Geochronology; Flux of heavy metal; Guanabara Bay.
Ano: 2013
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652013000401317