The Experts below are selected from a list of 807 Experts worldwide ranked by ideXlab platform
Catherine Chaguegoff - One of the best experts on this subject based on the ideXlab platform.
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extreme wave deposits on the pacific coast of mexico tsunamis or storms a multi proxy approach
2012Co-Authors: Maria Teresa Ramirezherrera, Marcelo Lagos, Ian Hutchinson, Vladimir Kostoglodov, Maria Luisa Machain, Margarita Caballero, Avto Goguitchaichvili, Bertha Aguilar, Catherine ChaguegoffAbstract:Abstract Historical and instrumental data show that the Pacific coast of Mexico has been exposed to destructive tsunamis over at least the past 500 years. This coast is also affected by hurricanes generated in the eastern Pacific. The great 1985 Mexico earthquake and its aftershock generated tsunamis that affected the Ixtapa–Zihuatanejo and Michoacan coast. The purpose of our study was two-fold — a) to determine whether storm and tsunami deposits could be distinguished, and b) whether tsunami deposits from historical events are preserved in the tropical environments of the Ixtapa–Zihuatanejo coast. Two anomalous sand units in the Ixtapa estuary are interpreted to be the result of high-energy marine inundation events that occurred in the last century. Several lines of evidence using a multi-proxy approach (historical studies, interviews with local witnesses, geomorphological and geological surveys, coring and trenching, laboratory analyses including grain size, Micropaleontology, geochemistry, magnetic susceptibility and radiometric dating, and numerical modeling) indicate the occurrence of two tsunamis that we link to local events: the 21st September 1985 Mexico and possibly the 14th March 1979 Petatlan earthquakes. We thereby provide the first onshore geological evidence of historical tsunamis on the Pacific coast of Mexico.
Melanie J Leng - One of the best experts on this subject based on the ideXlab platform.
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tephrochronology of marine sediments around the island of montserrat lesser antilles volcanic arc
2008Co-Authors: Jodie K Fisher, Malcolm B Hart, Melanie J Leng, Christopher W Smart, Stephen Sparks, Peter J Talling, Jessica TrofimovsAbstract:The recent history of the Soufriere Hills Volcano, Montserrat, Lesser Antilles volcanic arc, is reconstructed using data obtained from recently drilled submarine cores.Tephra layers in these cores preserve a record of the volcanic history of Montserrat back to ~250 ka on the basis of Micropaleontology and stable isotope stratigraphy. Stratigraphic relationships identified in the cores collected in 2002 and 2005 document the fate of both pyroclastic flows entering the ocean to the east of Montserrat and carbonate-rich turbidites sourced from the carbonate platforms surrounding the islands of the Lesser Antilles. Using oxygen isotope stratigraphy, micropalaeontological analysis and Carbon-14 dating, it can be shown that three significant volcanic events, including the on-going eruption, have occurred over the last 12 ka. Preceding this was a time of volcanic quiescence, with three carbonate-rich turbidite events being documented in many of the cores. Our data suggest that these events occurred during Marine Isotope Stage 2, following the Last Glacial Maximum (LGM) and onset of post-glacial sea level rise.
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late pleistocene tephrochronology of marine sediments adjacent to montserrat lesser antilles volcanic arc
2008Co-Authors: Le A Friant, E J Lock, Malcolm B Hart, Georges Boudon, R S J Sparks, Melanie J Leng, Christopher W Smart, Jeanchristophe Komorowski, Christine Deplus, Jodie K FisherAbstract:The recent history of the Soufriere Hills volcano, Montserrat, Lesser Antilles volcanic arc, is deduced using data obtained from a submarine core collected in 2002. The core contains concentrations of ash and several tephra layers, which are identified by the abundance of glass shards, dense and poorly vesiculated particles, and scoria. The tephra layers have been dated using micropalaeontology and stable isotope stratigraphy. Tephra layers in a marine sediment core off the coast of Montserrat record the volcanic history of South Soufriere Hills–Soufriere Hills volcano back to 250 ka. Eight layers are composed of dense juvenile ash related to dome eruptions, five of which can be directly correlated to dated domes or related pyroclastic flow sequences on land. Six layers are composed of pumiceous glassy ash and relate to significant explosive eruptions. A marker sequence of basalt tephra layers is dated at 124–147 ka and is correlated with construction of the South Soufriere Hills basaltic stratocone. Pelagic sediments between the main tephra layers have low abundances of volcanogenic components ( c . 10 4 years) of dormancy or low activity.
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circulation changes and nutrient concentrations in the late quaternary aegean sea a nonsteady state concept for sapropel formation
2002Co-Authors: J S L Casford, Melanie J Leng, Eelco J Rohling, Ramadan H Abuzied, S Cooke, Christophe Fontanier, V LykousisAbstract:sapropel-forming conditions, we identify the start of ‘‘seasonal’’ stratification and highlight a lag in d 18 O response of the planktonic foraminifer N. pachyderma to termination T1b as identified in the d 18 O record of G. ruber. By use of a simple model we determine that this offset cannot be a function of bioturbation effects. The lag is of the order of 1 kyr and suggests that isolation of intermediate/deep water preceded the start of sapropel formation by up to 1.5 kyr. Using this discovery, we propose an explanation for the major unresolved problem in sapropel studies, namely, the source of nutrient supply required for export productivity to reach levels needed for sustained sapropel deposition. We suggest that nutrients had been accumulating in astagnant basin for 1–1.5 kyr and that these accumulated resources wereutilized duringthe deposition of S1. In addition, we provide a first quantitative estimate of the diffusive (1/e) mixing timescale for the eastern Mediterranean in its ‘‘stratified’’sapropel mode, which is of the order of 450 years. INDEX TERMS: 1050 Geochemistry: Marine geochemistry (4835, 4850); 3030 Marine Geology and Geophysics: Micropaleontology; 3339 Meteorology and Atmospheric Dynamics: Ocean/atmosphere interactions (0312, 4504); 4267 Oceanography: General: Paleoceanography; 4870 Oceanography: Biological and Chemical: Stable isotopes; KEYWORDS: sapropel, Mediterranean, Holocene, foraminifera, climate variability
Frances Westall - One of the best experts on this subject based on the ideXlab platform.
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revealing the biotic origin of silicified precambrian carbonaceous microstructures using raman spectroscopic mapping a potential method for the detection of microfossils on mars
2015Co-Authors: Frederic Foucher, M R Ammar, Frances WestallAbstract:Demonstrating the biogenicity of carbonaceous microfossils can be relatively difficult because of their small size and simple shape, and to the degradation of the associated organic molecules with time. For Precambrian fossils, it generally requires the use of several techniques to study the shape and the composition of the structure itself, as well as its mineral environment. The ability to identify both organic matter and minerals using Raman spectroscopy makes it a key technique in the field of Micropaleontology. Raman instruments are also being developed for the upcoming missions to Mars, ExoMars and Mars 2020, both dedicated to the search for past or present traces of life. However, demonstrating the biotic origin of carbonaceous matter in geological materials using this technique is controversial. Here, we show that Raman mapping instead of single spot analysis can detect variations in the composition of carbonaceous matter associated with fossilized microbes in the 800-Ma-old microfossils from the Draken Formation, Svalbard. This discovery is of great interest because it permits assessment of the biotic origin of a fossilized carbonaceous structure. Raman mapping could thus be of crucial importance in the near future for detecting potential fossilized microbial remains in Martian rocks.
Jodie K Fisher - One of the best experts on this subject based on the ideXlab platform.
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tephrochronology of marine sediments around the island of montserrat lesser antilles volcanic arc
2008Co-Authors: Jodie K Fisher, Malcolm B Hart, Melanie J Leng, Christopher W Smart, Stephen Sparks, Peter J Talling, Jessica TrofimovsAbstract:The recent history of the Soufriere Hills Volcano, Montserrat, Lesser Antilles volcanic arc, is reconstructed using data obtained from recently drilled submarine cores.Tephra layers in these cores preserve a record of the volcanic history of Montserrat back to ~250 ka on the basis of Micropaleontology and stable isotope stratigraphy. Stratigraphic relationships identified in the cores collected in 2002 and 2005 document the fate of both pyroclastic flows entering the ocean to the east of Montserrat and carbonate-rich turbidites sourced from the carbonate platforms surrounding the islands of the Lesser Antilles. Using oxygen isotope stratigraphy, micropalaeontological analysis and Carbon-14 dating, it can be shown that three significant volcanic events, including the on-going eruption, have occurred over the last 12 ka. Preceding this was a time of volcanic quiescence, with three carbonate-rich turbidite events being documented in many of the cores. Our data suggest that these events occurred during Marine Isotope Stage 2, following the Last Glacial Maximum (LGM) and onset of post-glacial sea level rise.
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late pleistocene tephrochronology of marine sediments adjacent to montserrat lesser antilles volcanic arc
2008Co-Authors: Le A Friant, E J Lock, Malcolm B Hart, Georges Boudon, R S J Sparks, Melanie J Leng, Christopher W Smart, Jeanchristophe Komorowski, Christine Deplus, Jodie K FisherAbstract:The recent history of the Soufriere Hills volcano, Montserrat, Lesser Antilles volcanic arc, is deduced using data obtained from a submarine core collected in 2002. The core contains concentrations of ash and several tephra layers, which are identified by the abundance of glass shards, dense and poorly vesiculated particles, and scoria. The tephra layers have been dated using micropalaeontology and stable isotope stratigraphy. Tephra layers in a marine sediment core off the coast of Montserrat record the volcanic history of South Soufriere Hills–Soufriere Hills volcano back to 250 ka. Eight layers are composed of dense juvenile ash related to dome eruptions, five of which can be directly correlated to dated domes or related pyroclastic flow sequences on land. Six layers are composed of pumiceous glassy ash and relate to significant explosive eruptions. A marker sequence of basalt tephra layers is dated at 124–147 ka and is correlated with construction of the South Soufriere Hills basaltic stratocone. Pelagic sediments between the main tephra layers have low abundances of volcanogenic components ( c . 10 4 years) of dormancy or low activity.
Frederic Foucher - One of the best experts on this subject based on the ideXlab platform.
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revealing the biotic origin of silicified precambrian carbonaceous microstructures using raman spectroscopic mapping a potential method for the detection of microfossils on mars
2015Co-Authors: Frederic Foucher, M R Ammar, Frances WestallAbstract:Demonstrating the biogenicity of carbonaceous microfossils can be relatively difficult because of their small size and simple shape, and to the degradation of the associated organic molecules with time. For Precambrian fossils, it generally requires the use of several techniques to study the shape and the composition of the structure itself, as well as its mineral environment. The ability to identify both organic matter and minerals using Raman spectroscopy makes it a key technique in the field of Micropaleontology. Raman instruments are also being developed for the upcoming missions to Mars, ExoMars and Mars 2020, both dedicated to the search for past or present traces of life. However, demonstrating the biotic origin of carbonaceous matter in geological materials using this technique is controversial. Here, we show that Raman mapping instead of single spot analysis can detect variations in the composition of carbonaceous matter associated with fossilized microbes in the 800-Ma-old microfossils from the Draken Formation, Svalbard. This discovery is of great interest because it permits assessment of the biotic origin of a fossilized carbonaceous structure. Raman mapping could thus be of crucial importance in the near future for detecting potential fossilized microbial remains in Martian rocks.