Numerous studies on active mountain ranges have demonstrated the interaction between tectonics and climate in shaping topography. Here we explore how variations in rock types have affected the topographic development of the Pyrenees since cessation of orogenesis ca. 20 Ma. Our study is based on a multidisciplinary approach and integrates topographic analyses, rock strength measurements and thermal modelling of low-temperature thermochronological data published across the Central Pyrenees. Results indicate a strong influence of rock strength in determining the post-orogenic morphology of the Pyrenees. We observe a correlation between rock strength and the normalized channel steepness index (ksn) of the different lithologies. Moreover, the highest topography is dominated by the Variscan plutonic massifs which have highest rock strength. Consequently, the drainage divide appears to track the position of these massifs. Abrupt deceleration of exhumation recorded in inverse modelling of low-temperature thermochronologic data suggests that the exhumation of the Variscan massifs also played role in lowering in erosion rates over the massifs during orogenesis.
International audienceAssessing the onset and extent of Northern Hemisphere glaciation is required to understandCenozoic climate change and its impact on topography. While the onset of accelerated Cenozoicerosion is generally associated with the Quaternary at mid-latitudes, some high-latitudepassive margins may have undergone earlier glaciation starting at 38–30 Ma or even 45 Ma.Here we document a rapid phase of exhumation in the East Greenland margin between 68°Nand 76°N starting at 30 ± 5 Ma. The timing is coincident with the dramatic worldwide fall ofsurface temperature at the Eocene-Oligocene transition. Our inference is based on apatitefission track and apatite helium data. We suggest that a transition from an Eocene fluvial toan Oligocene glacial-dominated landscape triggered a period of enhanced erosion. This studyprovides the first onshore potential evidence of the onset of continental ice in East Greenlandmargin at the Eocene-Oligocene transition (ca. 34 Ma), contemporaneously with the onset ofAntarctica glaciation and erosion. Our interpretation is consistent with that based on the oldestice-rafted debris found in the sedimentary records offshore East Greenland and impliesthat East Greenland exhibits the oldest onshore record of Cenozoic glacial erosion on Earth
The transition to a post‐orogenic state in mountain ranges has been identified by a change from active subsidence to isostatic rebound of the foreland basin. However, the nature of the interplay between isostatic rebound and sediment supply, and their impact on the topographic evolution of a range and foreland basin during this transition, has not been fully investigated. Here, we use a box model to explore the syn‐ to post‐orogenic evolution of foreland basin/thrust wedge systems. Using a set of parameter values that approximate the northern Pyrenees and the neighbouring Aquitaine foreland basin, we evaluate the controls on sediment drape over the frontal parts of the retro‐wedge following cessation of crustal thickening. Conglomerates preserved at approximately 600‐m elevation, which is ~ 300 m above the present mountain front in the northern Pyrenees are ca. 12 Ma, approximately 10 Myrs younger than the last evidence of crustal thickening in the wedge. Using the model, this post‐orogenic sediment drape is explained by the combination of a sustained, high sediment influx from the range into the basin relative to the efflux out of the basin, combined with cessation of the generation of accommodation space through basin subsidence. Post‐orogenic sediment drape is considered a generic process that is likely to be responsible for elevated low‐gradient surfaces and preserved remnants of continental sedimentation draping the outer margins of the northern Pyrenean thrust wedge.
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