Fission-track (FT) analysis of detrital zircon from synorogenic sediment is a well established tool to examine the cooling and exhumation history of convergent mountain belts, but has so far not been used to determine the long-term evolution of the central Himalaya. This study presents FT analysis of detrital zircon from 22 sandstone and modern sediment samples that were collected along three stratigraphic sections within the Miocene to Pliocene Siwalik Group, and from modern rivers, in western and central Nepal
The potential link between erosion rates at the Earth's surface and changes in global climate has intrigued geoscientists for decades because such a coupling has implications for the influence of silicate weathering and organic-carbon burial on climate and for the role of Quaternary glaciations in landscape evolution. A global increase in late-Cenozoic erosion rates in response to a cooling, more variable climate has been proposed on the basis of worldwide sedimentation rates. Other studies have indicated, however, that global erosion rates may have remained steady, suggesting that the reported increases in sediment-accumulation rates are due to preservation biases, depositional hiatuses and varying measurement intervals. More recently, a global compilation of thermochronology data has been used to infer a nearly twofold increase in the erosion rate in mountainous landscapes over late-Cenozoic times. It has been contended that this result is free of the biases that affect sedimentary records, although others have argued that it contains biases related to how thermochronological data are averaged and to erosion hiatuses in glaciated landscapes. Here we investigate the 30 locations with reported accelerated erosion during the late Cenozoic. Our analysis shows that in 23 of these locations, the reported increases are a result of a spatial correlation bias-that is, combining data with disparate exhumation histories, thereby converting spatial erosion-rate variations into temporal increases. In four locations, the increases can be explained by changes in tectonic boundary conditions. In three cases, climatically induced accelerations are recorded, driven by localized glacial valley incision. Our findings suggest that thermochronology data currently have insufficient resolution to assess whether late-Cenozoic climate change affected erosion rates on a global scale. We suggest that a synthesis of local findings that include location-specific information may help to further investigate drivers of global erosion rates.
International audienceSome of Earth's greatest relief occurs where glacial processes act on mountain topography1, 2. This dramatic landscape is thought to be an imprint of Pleistocene glaciations3, 4. However, whether the net effect of glacial erosion on mountains is to increase5, 6, 7 or decrease8, 9, 10 relief remains disputed. It has been suggested that in the European Alps, the onset of widespread glaciation since the mid-Pleistocene climate transition11 led to the growth of large, long-lived and strongly erosive alpine glaciers12, 13 that profoundly influenced topography14. Here we use 4He/3He thermochronometry15 and thermal-kinematic models to show that the Rhône Valley in Switzerland deepened by about 1-1.5 km over the past one million years. Our results indicate that while the valley was incised and back-cut, high-altitude areas were preserved from erosion. We find an approximately two-fold increase in both local topographic relief and valley concavity, which occurred around the time of the mid-Pleistocene transition. Our results support the proposed link12, 13, 14 between the onset of efficient glacial erosion in the European Alps and the transition to longer, colder glacial periods at the middle of the Pleistocene epoch
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