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| Small, David; Rinterknecht, Vincent; Austin, William E. N.; Bates, Richard; Benn, Douglas I.; Scourse, James D.; Bourles, Didier L.; Hibbert, Fiona D.. |
| Geochronological constraints on the deglaciation of former marine based ice streams provide information on the rates and modes by which marine based ice sheets have responded to external forcing factors such as climate change. This paper presents new 36Cl cosmic ray exposure dating from boulders located on two moraines (Glen Brittle and Loch Scavaig) in southern Skye, northwest Scotland. Ages from the Glen Brittle moraines constrain deglaciation of a major marine terminating ice stream, the Barra-Donegal Ice Stream that drained the former British-Irish Ice Sheet, depending on choice of production method and scaling model this occurred 19.9 ± 1.5–17.6 ± 1.3 ka ago. We compare this timing of deglaciation to existing geochronological data and changes in a... |
| Tipo: Text |
Palavras-chave: Deglaciation; Scotland; Cosmogenic exposure ages; Chlorine-36. |
| Ano: 2016 |
URL: https://archimer.ifremer.fr/doc/00349/46010/83047.pdf |
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| Simon, Quentin; Thouveny, Nicolas; Bourles, Didier L.; Valet, Jean-pierre; Bassinot, Franck; Menabreaz, Lucie; Guillou, Valery; Choy, Sandrine; Beaufort, Luc. |
| Geomagnetic dipole moment variations associated with polarity reversals and excursions are expressed by large changes of the cosmogenic nuclide beryllium-10 (10Be) production rates. Authigenic 10Be/9Be ratios (proxy of atmospheric 10Be production) from oceanic cores therefore complete the classical information derived from relative paleointensity (RPI) records. This study presents new authigenic 10Be/9Be ratio results obtained from cores MD05-2920 and MD05-2930 collected in the west equatorial Pacific Ocean. Be ratios from cores MD05-2920, MD05-2930 and MD90-0961 have been stacked and averaged. Variations of the authigenic 10Be/9Be ratio are analyzed and compared with the geomagnetic dipole low series reported from global RPI stacks. The largest 10Be... |
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| Ano: 2016 |
URL: https://archimer.ifremer.fr/doc/00358/46910/46811.pdf |
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| Simon, Quentin; Thouveny, Nicolas; Bourles, Didier L.; Bassinot, Franck; Savranskaia, Tatiana; Valet, Jean-pierre. |
| New high-resolution authigenic 10Be/9Be ratio (Be-ratio) records covering the last geomagnetic reversal, i.e. the Matuyama–Brunhes transition (MBT), have been obtained and set on a time scale using benthic δ18 O (Cibicides wuellerstorfi) records. The geographic distribution of the four studied sites allows global comparison between the North Atlantic, Indian and Pacific Oceans. All Be-ratio records contain a two-fold increase triggered by the geomagnetic dipole moment (GDM) collapse associated with the MBT. The stratigraphic position of the Be-ratio spike, relative to marine isotope stages, allows establishment of a robust astrochronological framework for the MBT, anchoring its age between 778 and 766 ka (average mid-peaks at 772 ka), which is consistent... |
| Tipo: Text |
Palavras-chave: Authigenic Be-10/Be-9 ratio; Geomagnetic dipole moment minimum; Matuyama-Brunhes transition (MBT); Geomagnetic polarity reversal; Marine isotope stage 19; Atmospheric Be-10 production rates. |
| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00430/54150/55510.pdf |
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| Molliex, Stephane; Siame, Lionel L.; Bourles, Didier L.; Bellier, Olivier; Braucher, Regis; Clauzon, Georges. |
| Located in the foreland of the Western Alps, the Crau Plain was the outlet of the Durance River in the Pleistocene. In order to constrain its geodynamic evolution in terms of chronology and denudation rates, the two main Quaternary deposits of this plain have been studied based on cosmogenic nuclide Be-10 concentration measurements along depth profiles. The abandonment of the Miramas and Luquier alluvial surfaces occurred at the beginning of glacial periods, Wurm (isotopic stage 4) and Riss (isotopic stage 6), respectively. Discrepancy in denudation rates under similar geomorphological and lithological conditions suggests different denudation processes during glacial and interglacial periods. The denudation rate has been estimated at about 25 mm ka(-1) for... |
| Tipo: Text |
Palavras-chave: Quaternary; Denudation rate; Cosmic ray exposure (CRE) dating; Be-10 depth profile; Provence; Periglacial setting. |
| Ano: 2013 |
URL: http://archimer.ifremer.fr/doc/00149/26040/24740.pdf |
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| Mariotti, Apolline; Blard, Pierre-henri; Charreau, Julien; Petit, Carole; Molliex, Stephane; Aumaitre, Georges; Bourles, Didier L.; Keddadouche, Karim. |
| Marine sedimentary archives are well dated and often span several glacial cycles; cosmogenic Be-10 concentrations in their detrital quartz grains could thus offer the opportunity to reconstruct a wealth of past denudation rates. However, these archives often comprise sediments much finer (< 250 mu m) than typically analyzed in Be-10 studies, and few studies have measured Be-10 concentrations in quartz grains smaller than 100 mu m or assessed the impacts of mixing, grain size, and interannual variability on the Be-10 concentrations of such fine-grained sediments. Here, we analyzed the in situ cosmogenic Be-10 concentrations of quartz grains in the 50-100 and 100-250 mu m size fractions of sediments from the Var basin (southern French Alps) to test the... |
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| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00637/74894/76066.pdf |
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| Simon, Quentin; Bourles, Didier L.; Bassinot, Franck; Nomade, Sebastien; Marino, Maria; Ciaranfi, Neri; Girone, Angela; Maiorano, Patrizia; Thouveny, Nicolas; Choy, Sandrine; Dewilde, Fabien; Scao, Vincent; Isguder, Gulay; Blamart, Dominique; Aster Team,. |
| Geomagnetic dipole moment (GDM) lows associated with polarity reversals or geomagnetic excursions induce significant modulation of the cosmogenic nuclide Beryllium-10 (Be-10) production. Hence, the reconstruction of atmospheric Be-10 production rates from natural archives such as marine sedimentary sequences or ice cores constitutes a complementary approach, independent from paleomagnetic measurements, to decipher past GDM fluctuations. This is particularly important in the Montalbano Jonico succession (South Italy) since it is candidate to host the Global Stratotype Section and Point of the Middle Pleistocene Stage but where the magnetostratigraphic positioning of the Matuyama-Brunhes boundary (MBB) has not been available up to now. This study presents... |
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Palavras-chave: Be-10 cosmogenic nuclide; Authigenic Be-10/Be-9 ratio; Matuyama Brunhes Boundary (MBB); High-resolution oxygen isotope stratigraphy; MIS 19; GSSP stratotype. |
| Ano: 2017 |
URL: https://archimer.ifremer.fr/doc/00420/53183/55042.pdf |
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| Simon, Quentin; Bourles, Didier L.; Thouveny, Nicolas; Horng, Chorng-shern; Valet, Jean-pierre; Bassinot, Franck; Choy, Sandrine. |
| Long-term variations of the geomagnetic dipole moment (GDM) during periods of stable polarity and in transitional states (reversals and excursions) provide key information for understanding the geodynamo regime. Following several studies dealing with the Brunhes chron and the Matuyama–Brunhes transition, this study presents a new authigenic 10Be/9Be ratio (Be-ratio) record obtained from the MD97-2143 core (western Pacific Ocean). This new Be-ratio series yields a record of GDM variations covering the early Brunhes and mid to late Matuyama time period (i.e. 700–2140ka), independently from the relative paleointensity (RPI) record obtained from the same core, that can be compared with available RPI records and stacks. Stratigraphic offsets measured between... |
| Tipo: Text |
Palavras-chave: Authigenic Be-10/Be-9 ratios; Matuyama-Brunhes transition; Jaramillo and Olduvai subchrons; Cobb Mountain and Reunion events; Matuyama geomagnetic excursions; Lock-in depth. |
| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00414/52553/53381.pdf |
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