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Table of contents
I. Introduction
I.1. Early work
I.2. Discoveries from the ocean floor exploration
I.3. The « tectonics, climate and denudation » debate
I.4. This thesis
II. Context
II.1. The Himalaya
II.1.1. Physiographic and geological units
II.1.2. Precipitations and hydrography
II.1.3. Glaciations
II.2. Tectonics viewed by thermochronometry
II.2.1. Tectonic drivers and elevation change
II.2.2. Evolution of tectonics in the Himalaya
II.3. Climate
II.3.1. Greenhouse gases
II.3.2. Heat redistribution, geography and tectonics
II.3.3. Orbital cycles
II.3.4. Global sea-level
II.3.5. Cenozoic climate change
II.4. Denudation
II.4.1. Mechanical and chemical processes
II.4.2. Erosion, transport and deposition
II.4.2.1. Slope processes
II.4.2.2. Fluvial incision
II.4.2.3. Glacial erosion
II.4.2.4. Complementary erosive processes
II.4.3. Sedimentary flux at modern times
II.5. The sedimentary record
II.5.1. The stochastic nature of sediments
II.5.2. The provenance topic
II.5.2.1. Recycling
II.5.2.2. Drainage evolution
II.5.3. Accumulation rates and sedimentary budgets
II.6. Late Cenozoic evolution of the denudation records
II.6.1. Accumulation rates and sedimentary budgets
II.6.1.1. The deep sea basins
II.6.1.2. Turbiditic fans, continental margins and foreland basins
II.6.2. The seawater continental silicate chemical weathering record
II.6.2.1. The seawater 87Sr/86Sr
II.6.2.2. The seawater 10Be/9Be and δ7Li
II.6.2.3. Consequences for the causes of the CO2 fluctuations in the late Cenozoic
II.6.3. The 10Be/9Be detrital record
II.6.4. The detrital thermochronometric record
II.6.4.1. A few words about thermochronometry
II.6.4.2. Detrital thermochronometric data
II.6.5. The in situ thermochronometric record
II.7. Possible causes for an acceleration of denudation rates
II.7.1. Have sea-level fluctuations altered export of sediments to the deep sea?
II.7.2. Active tectonics
II.7.3. A shift to dry and stormy climate?
II.7.4. A shift to variable climate?
II.7.5. Enhanced glacial erosion?
II.8. Tables
III. Aim of the thesis
III.1. Synthesis of the topic
III.1.1. Tectonics
III.1.2. Climate
III.1.3. Chemical denudation
III.1.4. Physical denudation
III.1.4.1. Sediment accumulation rates
III.1.4.2. Detrital thermochronometry
III.1.4.3. Detrital cosmogenic nuclides
III.1.4.4. In situ thermochronometry
III.2. Aim of the thesis
III.2.1. A record of erosion at an orogenic scale
III.2.2. A new erosion record for South Asia
III.2.3. A check on erosion patterns and increased variability at low latitudes
III.3. Developed approach
III.3.1. Sedimentary archives
III.3.1.1. Bengal Fan Exp. 353 – 354
III.3.1.2. Siwalik sections in the Valmiki Wildlife Sanctuary, Bihar, India
III.3.2. Methodology
IV. Methodologic overview
IV.1. The cosmic flux and its quantification
IV.1.1. The neutron cosmic flux
IV.1.2. The muon cosmic flux
IV.1.3. Quantification of the cosmic flux
IV.2. Computation of denudation rates
IV.2.1. Determination of production rates
IV.2.2. Scaling models
IV.2.3. Analytical computation of quartz in situ 10Be denudation rates
IV.2.4. Topographic and glacial shielding
IV.3. Limits of the 10Be method
IV.3.1. Analytic measurements
IV.3.2. Reproducibility 1
IV.3.3. 10Be production rates, geography of the catchment, provenance and recycling
IV.3.4. Steady-state landscape
IV.3.5. Impact of stochastic events
IV.3.6. Exposure during transport to sink or recent exposure
IV.3.7. Dating
V. Data report: calcareous nannofossils and lithologic constraints on the age model of IODP Site U1450
V.1. Abstract
V.2. Introduction
V.3. Material and methods
V.3.1. Calcareous Nannofossils
V.3.2. Age model
V.4. Results
V.4.1. Calcareous Nannofossils identifications
V.4.2. Age Model
V.5. Tables
VI. Steady erosion of the Himalaya during the late Cenozoic climate change
VI.1. Introduction
VI.2. Approach for erosion rate quantification
VI.3. 10Be concentrations
VI.4. Apparent erosion rates
VI.5. Sr-Nd isotopes
VI.6. Test of the climate forcing hypothesis
VI.7. Implications
VI.8. Methods
VI.9. Extended Methods
VI.9.1. Material
VI.9.2. 10Be/9Be preparation and measurements
VI.9.3. 10Be paleoconcentrations
VI.9.4. Production rates and erosion rates
VI.9.5. Sr-Nd isotopic measurements on bulk silicate samples
VI.9.6. Computation of the fraction fG
VI.9.7. Modern geochemical and granulometric budgets in the Ganga
VI.9.8. Test of the climate forcing hypothesis
VI.9.9. Temporal variability of cosmogenic nuclide production rates
VI.10. Tables
VII. The Valmiki Sections: a new sedimentary record of the Central Himalaya (Draft)
VII.1. Introduction
VII.1.1. The South Asian Monsoon during the late Cenozoic
VII.1.2. Approach
VII.2. Context
VII.2.1. Geology, physiography and precipitation distribution
VII.2.2. The Siwalik molasses
VII.2.3. The Narayani-Gandak drainage basin
VII.3. Material and methods
VII.3.1. Description of the Valmiki Sections
VII.3.2. Material
VII.3.3. Magnetostratigraphy and stochastic correlation dating
VII.3.4. Major and trace element measurements
VII.3.5. Stable isotope measurements
VII.4. Results
VII.4.1. Description of the Valmiki Sections
VII.4.2. The frontal Churia (CR) fold
VII.4.3. The Valmiki Nagar (VR) fold
VII.4.4. Paleomagnetic dating
VII.4.5. Sedimentology
VII.4.6. Age estimate of the frontal Churia (CR) fold
VII.4.7. Age estimate of the Valmiki Nagar (VR) fold
VII.4.8. Major and trace elements
VII.4.9. C and O isotopes
VII.5. Discussion
VII.5.1. Fluvial style evolution
VII.5.2. Recycling
VII.5.3. Detection of a shift of provenance?
VII.5.4. Evolution of precipitations
VII.5.5. Late Miocene shift to C4-dominated vegetation
VII.5.6. Late Pliocene shift back to mixed vegetation
VII.6. Conclusion
VII.7. Tables
VIII. Late Cenozoic evolution of erosion rates in the Narayani-Gandak basin, Central Himalaya (Draft)
VIII.1. Introduction
VIII.1.1. Has climate forced erosion rates in the late Cenozoic?
VIII.1.2. Approach
VIII.2. Geological context of the Central Himalaya
VIII.2.1. Structure and lithology
VIII.2.2. Long-term structural evolution
VIII.2.3. The Narayani-Gandak drainage basin
VIII.2.4. The Valmiki Sections
VIII.3. Material and methods
VIII.3.1. Material
VIII.3.2. Sr-Nd isotopic composition measurements
VIII.3.3. Lithological fraction computing
VIII.3.4. 10Be/9Be measurements
VIII.3.5. 10Be concentration determination
VIII.3.6. 36Cl measurements and 10Be recent exposure contribution
VIII.3.7. 10Be floodplain exposure contribution
VIII.3.8. Determination of paleoerosion rates
VIII.4. Results
VIII.4.1. Sr-Nd isotopes and lithologic fractions
VIII.4.2. 36Cl measurements and recent exposure contribution
VIII.4.3. 10Be paleoconcentrations
VIII.4.4. Evolution of the drainage basin
VIII.4.5. Erosion rates
VIII.5. Discussion
VIII.5.1. Biased 10Be concentrations for old samples?
VIII.5.2. Variability of apparent erosion rates
VIII.5.3. Comparison with other 10Be datasets
VIII.5.4. Comparison with detrital thermochronometry
VIII.5.5. Comparison with in situ thermochronometry
VIII.5.6. Possible causes of the difference between 10Be and in situ thermochronometry
VIII.6. Implications
VIII.6.1. The late Cenozoic climate change in Central Himalaya
VIII.6.2. The late Cenozoic climate change and erosion rates
VIII.7. Conclusion
VIII.8. Tables
IX. Synthesis
IX.1. Context
IX.1.1. Climate change and erosion rate estimates
IX.1.2. Assumptions associated to the use of terretrial cosmogenic nuclides
IX.2. Results
IX.2.1. The Bengal Fan record
IX.2.2. The Valmiki Section record
IX.3. Conclusion
X. Synthèse
X.1. Contexte
X.1.1. Changement climate et estimation des taux d’érosion
X.1.2. Hypothèses associées à l’utilisation des isotopes cosmogéniques terrestres
X.2. Résultats
X.2.1. L’enregistrement du cône du Bengale
X.2.2. L’enregistrement des sections Valmiki
X.3. Conclusion
Bibliography
