Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
The Tian Shan Mountains constitute central Asia's longest and highest mountain range. Understanding their Cenozoic uplift history thus bears on mountain building processes in general, and on how deformation has occurred under the influence of the India-Asia collision in particular. In order to help decipher the uplift history of the Tian Shan, we collected 970 samples for magnetostratigraphic analysis along a 4571-m-thick section at the Jingou River (Xinjiang Province, China). Stepwise alternating field and thermal demagnetization isolate a linear magnetization component that is interpreted as primary. From this component, a magnetostratigraphic column composed of 67 polarity chrons are correlated with the reference geomagnetic polarity timescale between ~1 Ma and ~23.6 Ma, with some uncertainty below ~21 Ma. This correlation places precise temporal control on the Neogene stratigraphy of the southern Junggar Basin and provides evidence for two significant stepwise increases in sediment accumulation rate at ~16–15 Ma and ~11–10 Ma. Rock magnetic parameters also undergo important changes at ~16–15 Ma and ~11–10 Ma that correlate with changes in sedimentary depositional environments. Together with previous work, we conclude that growth history of the modern Tian Shan Mountains includes two pulses of uplift and erosion at ~16–15 Ma and ~11–10 Ma. Middle to upper Tertiary rocks around the Tian Shan record very young (<~5 Ma) counterclockwise paleomagnetic rotations, on the order of 15° to 20°, which are interpreted as because of strain partitioning with a component of sinistral shear that localized rotations in the piedmont.
ISSN: 0278-7407

insu-00376345
https://hal-insu.archives-ouvertes.fr/insu-00376345
https://hal-insu.archives-ouvertes.fr/insu-00376345/document
https://hal-insu.archives-ouvertes.fr/insu-00376345/file/2007TC002137.pdf
DOI : 10.1029/2007TC002137

Éditeur(s) : HAL CCSD
Résumé : The evolution of mountain belt piedmont is controlled by interactions between tectonics, erosion and sedimentation. To study coupling between these processes, we analyze morphometric data collected in the eastern Tian Shan piedmont (NW China) and develop a new analogue modelling technique. The modeling approach uses an experimental set-up and analog material specifically designed to study simultaneously tectonic structures (faults, folds), detailed morphology (drainage basins, channels, alluvial fans, etc.) and stratified sedimentation. Measurement techniques based on laser interferometry and image correlation are also developed to quantify the topographic and kinematic evolution of models.
Our experiments allow a new approach for the study of piedmont morphotectonic evolution. Our results indicate that tectonics mainly controls this evolution. The propagation of deformation and the formation of relief both significantly influence the development of drainage networks, the evolution of drainage basins and the formation of morphotectonic markers. Particularly, a study of alluvial fans and watershed metrics suggests that there is a dynamical equilibrium between uplift, erosion and morphology. In addition, our results show that terrace nucleation is controlled by thrust activity and hydrography adjustments. Folding of terraces responds to a homothetic deformation pattern.
This new methodology brings promising perspectives in the fields of geomorphology, seismotectonics and sedimentology.
L'évolution d'un piémont de chaîne de montagnes est contrôlée par les interactions entre la tectonique, l'érosion et la sédimentation. Pour étudier ces processus, nous avons analysé des données morphométriques issues des piémonts orientaux du Tian Shan (NW Chine) et développé un nouveau type de modélisation analogique. Cette approche utilise un dispositif et un matériau expérimental spécialement conçus pour modéliser simultanément des structures tectoniques (failles, plis), une morphologie détaillée (bassins versants, rivières, cônes alluviaux, etc.) et une sédimentation stratifiée. Des techniques de mesure optique ont été également mises en oeuvre afin de quantifier l'évolution topographique et cinématique des modèles.
Les expériences réalisées offrent une opportunité inédite d'étudier l'évolution morphotectonique d'un piémont. Nos résultats montrent que la tectonique exerce un contrôle de premier ordre sur cette évolution. La propagation de la déformation et la formation des reliefs influencent en effet significativement le développement du réseau de drainage, l'évolution des bassins versants et la formation des marqueurs morphotectoniques. En particulier, l'analyse de la morphométrie des cônes alluviaux et de leurs bassins versants suggère qu'un équilibre dynamique s'installe entre la surrection, l'érosion et la morphologie. Nos résultats montrent également que l'apparition des terrasses est guidée par l'activité des chevauchements et les adaptations de l'hydrographie. Leur modèle de plissement répond à une déformation homothétique.
Cette nouvelle approche ouvre des perspectives d'étude prometteuses en géomorphologie, sismotectonique et stratigraphie.
https://tel.archives-ouvertes.fr/tel-00339145

tel-00339145
https://tel.archives-ouvertes.fr/tel-00339145
https://tel.archives-ouvertes.fr/tel-00339145v2/document
https://tel.archives-ouvertes.fr/tel-00339145/file/These_Graveleau08.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Mass balances are often used to calculate sediment fluxes in foreland basins and denudation rates in adjacent mountain ranges on intermediate to long timescales (from a few tens of thousand to a million years). Here, we study the simple Quaternary catchment-alluvial fan system of the Kuitun River, in northern Tian Shan, to discuss some ideas about sediment storage, release, and bypass in relatively short (100 km long) sediment routing systems. This study shows that the Kuitun catchment and piedmont areas clearly present evidence of a significant and temporary storage of sediments during the Pleistocene. These sediments were then excavated and delivered farther into the foreland basin during the Holocene. The difference between the volumes of materials released from the catchment and piedmont areas (5.5 ± 1.7 km3) and the volume stored in a contemporaneous fan downstream (2.6 ± 0.6 km3) indicates that the latter did not trap the whole sediment load transported by the river. The alluvial fan was bypassed by 27 to 78% of this load toward its distal alluvial plain. If this value is well estimated, it implies a major volumetric partitioning of the deposits between the fan and the alluvial plain, with a very high sedimentation rate in the fan (1.97 ± 0.52 mm*y− 1) and a much lower one downstream (0.11 ± 0.11 mm*y− 1). However, this volumetric partitioning might only occur during periods with a very specific hydrological regime such as the Holocene deglaciation. Eventually, the peculiar sediment storage and release pattern within the Kuitun catchment and piedmont areas during the Pleistocene and Holocene complicates the calculation of mean paleodenudation rates using either sediment budgets or in situ produced cosmogenic nuclides.
ISSN: 0169-555X

insu-00985283
https://hal-insu.archives-ouvertes.fr/insu-00985283
https://hal-insu.archives-ouvertes.fr/insu-00985283/document
https://hal-insu.archives-ouvertes.fr/insu-00985283/file/jolivet-et_al-2014_HAL.pdf
DOI : 10.1016/j.geomorph.2014.01.024

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
The present-day topography of the Tian Shan range is considered to result from crustal shortening related to the ongoing India-Asia collision that started in the early Tertiary. In this study we report evidence for several episodes of localized tectonic activity which occurred prior to that major orogenic event. Apatite fission track analysis and (U-Th)/He dating on apatite and zircon indicate that inherited Paleozoic structures were reactivated in the late Paleozoic-early Mesozoic during a Cimmerian orogenic episode and also in the Late Cretaceous-Paleogene (around 65-60 Ma). These reactivations could have resulted from the accretion of the Kohistan-Dras arc or lithospheric extension in the Siberia-Mongolia zone. Activity resumed in the late Mesozoic prior to the major Tertiary orogenic phase. Finally, the ongoing deformation, which again reactivates inherited tectonic structures, tends to propagate inside the endoreic basins that were preserved in the range, leading to their progressive closure. This study demonstrates the importance of inherited structures in localizing the first increments of the deformation before it propagates into yet undeformed areas.
ISSN: 0278-7407

Droits : info:eu-repo/semantics/OpenAccess
hal-00551323
https://hal.archives-ouvertes.fr/hal-00551323
https://hal.archives-ouvertes.fr/hal-00551323/document
https://hal.archives-ouvertes.fr/hal-00551323/file/2010TC002712.pdf
DOI : 10.1029/2010TC002712

Éditeur(s) : HAL CCSD
Résumé : National audience
Mass balances are often used to calculate sediment fluxes in sedimentary basins and denudationrates in adjacent topographies on intermediate to long timescales (from a few tens ofthousand to a million years). In this study, we focus on simple Quaternary catchment–alluvial fansystems in the northern Tian Shan Range and its foreland basin to discuss some ideas about sedimentproduction, storage, release, and bypass in relatively short (100 km long) sediment routing systems.Based on a geometrical reconstruction of the fans, we estimated the volumes of sediments exportedout of the range and deposited in its alluvial piedmont during the Middle- Late Pleistocene andthe Holocene. This work shows that the two areas clearly present evidence of a temporary butsignificant storage of sediments during the Pleistocene. These sediments were then excavated anddelivered farther into the foreland basin during the Holocene. The difference between the volumesof materials released from the range and piedmont areas and the volume stored in thecontemporaneous fans downstream indicates that the latter did not trap the whole sediment loadtransported by the rivers. The alluvial fans were bypassed by 27 to 78% of this load toward thedownstream alluvial plain. It implies a major volumetric partitioning of the deposits between thefans and the alluvial plain, with a sedimentation rate about twenty times higher in the fans thanin the plain. However, this volumetric partitioning might only occur during periods with a veryspecific hydrological regime such as the Holocene deglaciation. Eventually, the peculiar sedimentstorage and release pattern within the range and piedmont areas during the Pleistocene and Holocenecomplicates the calculation of mean paleodenudation rates using either sediment budgets or in situproduced cosmogenic nuclides.
Association des Sédimentologistes Français. 15ème congrès français de sédimentologie
Chambéry, France

hal-01252100
https://hal.archives-ouvertes.fr/hal-01252100

Éditeur(s) : HAL CCSD
Résumé : International audience
Mass balances are often used to calculate sediment fluxes in sedimentary basins and denudationrates in adjacent topographies on intermediate to long timescales (from a few tens ofthousand to a million years). In this study, we focus on simple Quaternary catchment–alluvialfan systems in the northern Tian Shan Range and its foreland basin to discuss some ideasabout sediment production, storage, release, and bypass in relatively short (100 km long) sedimentrouting systems. Based on a geometrical reconstruction of the fans, we estimated thevolumes of sediments exported out of the range and deposited in its alluvial piedmont duringthe Middle-Late Pleistocene and the Holocene. This work shows that the two areas clearlypresent evidence of a temporary but significant storage of sediments during the Pleistocene.These sediments were then excavated and delivered farther into the foreland basin during theHolocene. The difference between the volumes of materials released from the range and piedmontareas and the volume stored in the contemporaneous fans downstream indicates thatthe latter did not trap the whole sediment load transported by the rivers. The alluvial fans werebypassed by 27 to 78% of this load toward the downstream alluvial plain. It implies a majorvolumetric partitioning of the deposits between the fans and the alluvial plain, with a sedimentationrate about twenty times higher in the fans than in the plain. However, this volumetricpartitioning might only occur during periods with a very specific hydrological regime suchas the Holocene deglaciation. Eventually, the peculiar sediment storage and release patternwithin the range and piedmont areas during the Pleistocene and Holocene complicates thecalculation of mean paleodenudation rates using either sediment budgets or in situ producedcosmogenic nuclides.
Source to Sink: a long term perspective of sediment budgets and sources characterization, Abstracts
Rennes, France

insu-01406440
https://hal-insu.archives-ouvertes.fr/insu-01406440