Éditeur(s) : Gauthier-Villars
Résumé : Calcareous nannofossil assemblages of the family Noelaerhabdaceae have been studied in sediments of seventeen Quaternary cores raised from various climatic areas of the Atlantic and Pacific oceans. These sections display a regular, hiatus-free sedimentation for the last 500000 years. They have been dated using oxygen-isotopic measurements, variations of calcium carbonate content, variations of total nannofossil abundance, thorium measurements and volcanic ash horizons. Coccoliths of the genus Gephyrocapsa have been placed in three distinct taxonomic groups, based on morphological criteria inferred from light-microscope observations. Their acmes, as well as the acme of Emiliania huxleyi, are considered as stratigraphic markers. These markers characterize most of the last thirteen glacial-interglacial climatic stages, as well as some climatic events of lower magnitude (8.5 and 6.5). Most of these markers have global stratigraphic significance: acme of ''closed'' Gephyrocapsa during stages 13,11 and 9, and during event 8.5; acme of ''small'' Gephyrocapsa during stage 7 and event 6.5; acme of ''open'' Gephyrocapsa at top of event 6.5, and during stages 5 and 3; acme of E. huxleyi during stages 3 and 1. Others are only valid south of the southernmost latitude reached by the North-Atlantic polar front during the Quaternary: acme of ''closed'' Gephyrocapsa during stage 12; acme of ''small'' Gepkyrocapsa in early and middle stage 5; acme of E. huxleyi during stage 2. Others are only valid south of 20-degrees-S: acme of ''small'' Gephyrocapsa at the 10/9 stage boundary; acme of ''open'' Gephyrocapsa during stage 6.
Oceanologica Acta (0399-1784) (Gauthier-Villars), 1993 , Vol. 16 , N. 4 , P. 349-362

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00099/21061/18687.pdf
http://archimer.ifremer.fr/doc/00099/21061/

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
The structure and dynamic evolution of a mountain belt piedmont are controlled by strong interactions between tectonics, surface processes (erosion, sedimentation), and climate. Studying these couplings relies on detailed geometric and kinematic analysis of morphostructural markers (folds, faults, terraces, alluvial surfaces) and analysis of syntectonic sedimentation. To study quantitatively how these markers form, evolve and record deformation, we developed a new analogue modelling approach using a specific composite granular material. The originality stands in the simultaneous modelling of orogenic deformation mechanisms and erosion-transport-sedimentation processes, but also in the use of techniques allowing quantitative measurement of morphostructural evolution. This methodology opens new perspectives in the fields of geomorphology (relief dynamics), seismotectonics (study of active faults), and sedimentology (including sequential stratigraphy).
ISSN: 0010-7999

hal-00411972
https://hal.archives-ouvertes.fr/hal-00411972
DOI : 10.1016/j.crte.2008.01.005

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We present reconstructions of late Holocene changes in the source of organic matter and siliceous export production in the Relocanví Fjord (41°S, 72°W), Northern Chilean Patagonia, based on organic carbon content, δ13Corg, N/C ratio, diatom assemblages and biogenic silica contents from three sediment cores. The age models are based on a combination of 210Pb profiles, AMS 14C dating, and on the first occurrence of the diatom Rhizosolenia setigera f. pungens, as a stratigraphic marker in the fjords. The cores span the last 300 to 700 yr. Diatoms dominate the siliceous assemblages in the three cores (98% on average). Our results suggest that precipitation seasonality in the region of Reloncaví was high in CE 1300–1400 and CE 1700–1850, with a clear decreasing trend since CE 1850. The latter trend is in agreement with instrumental records and tree-ring reconstructions. These fluctuations seem to be associated with the Southern Annular Mode (SAM).
ISSN: 0033-5894

hal-01217176
https://hal.archives-ouvertes.fr/hal-01217176
DOI : 10.1016/j.yqres.2015.05.006

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Tarim and Junggar basins in central Asia are capped by a thick pile of conglomerates, called the Xiyu Formation, that are commonly linked to a change in climate and/or accelerated uplift near the Plio-Pleistocene boundary. In order to better understand their origin and significance, we carried out a combined structural and magnetostratigraphic study in the Quilitage syncline (southern Tianshan), where the base of the Xiyu conglomerates is observed at both sides of the syncline. A balanced cross-section shows that, even at a local-scale, the base of the Xiyu conglomerates cannot be regarded as a single continuous stratigraphic layer. On the southern flank of the Quilitage syncline, we collected 172 samples collected for magnetostratigraphic dating identify 17 polarity chrons that date the new section from 5.2 to ~ 1.7 Ma and constrain the base of the Xiyu conglomerate here at ~ 1.7 Ma. This is 4.2 Ma younger than the age of the Xiyu previously found on the northern limb of the same syncline. Together with other magnetostratigraphic studies carried out around the Tianshan, our study unambiguously demonstrates that the onset of deposition of the Xiyu conglomerates is diachronous, and that the conglomerates are systematically younger toward the basin. Consequently, the Xiyu Formation should not be considered as a chronostratigraphic marker related to any particular tectonic or climatic event, but is instead a prograding gravel wedge that has prograded over the underthrusting forelands. A synthesis of chronologic and structural results yields progradation rates over the last 10 Ma on the order of ~ 2.0 mm/yr and ~ 3.9 mm/yr south and north of the Tianshan Mountains respectively. These rates are comparable to the shortening rate across the Tianshan range, suggesting that underthrusting is the main factor governing the progradation rate of the Xiyu Formation.
ISSN: 0012-821X

insu-00414151
https://hal-insu.archives-ouvertes.fr/insu-00414151
https://hal-insu.archives-ouvertes.fr/insu-00414151/document
https://hal-insu.archives-ouvertes.fr/insu-00414151/file/Charreau-EPSL-2009.pdf
DOI : 10.1016/j.epsl.2009.07.035