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See detailMorphometric age estimate of the last phase of accelerated uplift in the Kazdag area (Biga Peninsula, NW Turkey)
Demoulin, Alain ULg; Altin, T. Bayer; Beckers, Arnaud ULg

in Tectonophysics (2013), 608

While the Plio-Quaternary uplift of the Kazdag mountain range (Biga Peninsula, NW Turkey) is generally acknowledged, little is known about its detailed timing. Partly because of this lack of data, the ... [more ▼]

While the Plio-Quaternary uplift of the Kazdag mountain range (Biga Peninsula, NW Turkey) is generally acknowledged, little is known about its detailed timing. Partly because of this lack of data, the cause of this uplift phase is also debated, being associated either to back-arc extension in the rear of the Hellenic subduction zone, to transpression along the northern edge of the west-moving Anatolian microplate, or to extension driven by gravitational collapse. Here, we perform a morphometric study of the fluvial landscape at the scale of the Biga Peninsula, coupling the recently developed R/SR analysis of the drainage network with concavity and steepness measures of a set of 29 rivers of all sizes. While the dependence of profile concavity on basin size confirms that the landscape of the peninsula is still in a transient state, the spatial distribution of profile steepness values characterized by higher values for streams flowing down from the Kazdag massif shows that the latter undergoes higher uplift rates than the rest of the peninsula. We obtain a SR value of 0.324 ± 0.035 that, according to the relation established by Demoulin (2012), yields an age range of 0.5–1.3 Ma and a most probable value of 0.8 Ma for the time of the last tectonic perturbation in the region. In agreement with the analysis of knickpoint migration in a subset of rivers, this suggests that a pulse of uplift occurred at that time and, corroborated by sparse published observations in the Bayramiç and Çanakkale depressions, that the peninsula was uplifted as a whole from that time. This uplift pulse might have been caused by transient compressive conditions in the Anatolian plate when the Eratosthenes seamount came to subduct beneath the Cyprus arc around the early-to-mid Pleistocene transition (Schattner, 2010). [less ▲]

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See detailFactors of knickpoint migration on the moderately uplifted Ardennes Plateau, Western Europe
Beckers, Arnaud ULg; Bovy, Benoît ULg; Demoulin, Alain ULg

Poster (2012, April 27)

In the last two decades, much research has been devoted to the development and refinement of numerical models of river incision. In settings of prevailing bedrock channel erosion, numerous studies used ... [more ▼]

In the last two decades, much research has been devoted to the development and refinement of numerical models of river incision. In settings of prevailing bedrock channel erosion, numerous studies used field data, notably knickpoint data, to calibrate the widely acknowledged stream power model of incision and to discuss the specific impact of various variables (e.g., sediment load, channel width) not appearing explicitly in the model’s simplest form. However, most of these studies were conducted in areas of very active tectonics and high relief, thus displaying an exacerbated geomorphic response to the tectonic signal. Here, we analyze the traces left in the drainage network 0.7 My after the NE Ardennes region (western Europe) underwent a moderate 100-150 m uplift. We identify a set of knickpoints that have travelled far upstream in the Ourthe catchment. Because time becomes a more sensitive variable than distance near the headwaters, we fit the stream power model to the data by minimizing time residuals (i.e., the differences between 0.7 My and the modelled times for the knickpoints to reach their actual location) rather than distance residuals. Our best fit of the stream power model parameters yields m/n = 0.75 and K = 4.63 10-8 m-0.5y-1. We suggest that the discrepancy with the m/n value of 0.5 obtained from field and long profile data of the currently graded downstream part of the catchment’s streams points to a narrowing of the bedrock channel at the passage of a knickpoint. Then, the time residuals of the model fit are regressed against quantitative expressions of bedrock resistance to erosion and junction crossing, showing that both variables significantly affect knickpoint migration. In particular, most of the small tributaries with highly delayed knickpoints display all features characteristic of hanging valleys. However, not all such small streams have developed hanging valleys, and further research is needed to unravel how other controls, e.g., amount and size of the tributary bed load, are determining for the creation of such valleys. [less ▲]

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See detailOn different types of adjustment usable to calculate the parameters of the stream power law
Demoulin, Alain ULg; Beckers, Arnaud ULg; Bovy, Benoît ULg

in Geomorphology (2012), 138(1), 203-208

Model parameterization through adjustment to field data is a crucial step in the modeling and the understanding of the drainage network response to tectonic or climatic perturbations. Using as a test case ... [more ▼]

Model parameterization through adjustment to field data is a crucial step in the modeling and the understanding of the drainage network response to tectonic or climatic perturbations. Using as a test case a data set of 18 knickpoints that materialize the migration of a 0.7-Ma-old erosion wave in the Ourthe catchment of northern Ardennes (western Europe), we explore the impact of various data fitting on the calibration of the stream power model of river incision, from which a simple knickpoint celerity equation is derived. Our results show that statistical least squares adjustments (or misfit functions) based either on the streamwise distances between observed and modeled knickpoint positions at time t or on differences between observed and modeled time at the actual knickpoint locations yield significantly different values for the m and K parameters of the model. As there is no physical reason to prefer one of these approaches, an intermediate least-rectangles adjustment might at first glance appear as the best compromise. However, the statistics of the analysis of 200 sets of synthetic knickpoints generated in the Ourthe catchment indicate that the timebased adjustment is the most capable of getting close to the true parameter values. Moreover, this fitting method leads in all cases to an m value lower than that obtained from the classical distance adjustment (for example, 0.75 against 0.86 for the real case of the Ourthe catchment), corresponding to an increase in the non-linear character of the dependence of knickpoint celerity on discharge [less ▲]

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See detailDating uplift events by a composite metric of fluvial landscapes
Demoulin, Alain ULg

Conference (2012)

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See detailDating uplift events by a composite metric of fluvial landscapes
Demoulin, Alain ULg

Conference (2012)

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See detailRole of land use change in landslide-related sediment fluxes in tropical mountain regions
Guns, Marie; Vanacker, Veerle; Demoulin, Alain ULg

in Geophysical Research Abstracts (2012), 14

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See detailValley downcutting in the Ardennes (W Europe): Interplay between tectonically triggered regressive erosion and climatic cyclicity
Demoulin, Alain ULg; Beckers, Arnaud ULg; Rixhon, Gilles ULg et al

in Netherlands Journal of Geosciences - Geologie en Mijnbouw (2012), 91(1-2), 79-90

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See detailMorphometric dating of the fluvial landscape response to a tectonic perturbation
Demoulin, Alain ULg

in Geophysical Research Letters (2012), 39

Despite constant progress in numerical and field studies of landscape evolution, time evolution is still poorly constrained in many uplifted areas where low denudation rates prevent the use of low ... [more ▼]

Despite constant progress in numerical and field studies of landscape evolution, time evolution is still poorly constrained in many uplifted areas where low denudation rates prevent the use of low temperature thermochronology, especially outside high relief mountainous areas. Here, I show that regional statistics of the landscape metric R involving hypsometric integrals at three nested levels of a catchment are able to isolate the time effect on landscape geometry during the latter’s transient response to a tectonic perturbation. Analysis of 210 catchments from 9 regions of known uplift age worldwide shows that the regionally characteristic, R-derived SR index is in inverse power law relation with the time elapsed since a base level lowering. Suggesting a response time of 5 My, this finding has important implications for quantifying the rate of landform evolution and determining whether a landscape has reached steady-state form. [less ▲]

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See detailModelling the migration of a mid-Pleistocene erosion wave in the Ardennes (western Europe) drainage network: approach and first implications
Beckers, Arnaud ULg; Bovy, Benoît ULg; Demoulin, Alain ULg

Poster (2011, April)

Model parameterization through adjustment to field data is a crucial step in the modelling and the understanding of the drainage network response to tectonic or climatic perturbations. Using a data set of ... [more ▼]

Model parameterization through adjustment to field data is a crucial step in the modelling and the understanding of the drainage network response to tectonic or climatic perturbations. Using a data set of 18 knickpoints that materialize the migration of a 0.7-Ma-old erosion wave in the Ourthe catchment of northern Ardennes (western Europe) as a test case, we explore the impact of various data fitting on the calibration of the detachment-limited stream power model of river incision, from which a simple knickpoint celerity equation is derived. Our results show that statistical least squares adjustments (or misfit functions) based either on the stream-wise distances between observed and modelled knickpoint positions at time t = 0.7 Ma or on differences between observed (0.7 Ma) and modelled time at the actual knickpoint locations yield significantly different values for the m (more exactly, m/n) and K parameters of the model. As there is no physical reason to prefer one or the other approach, we suggest that an intermediate least rectangles adjustment might be the best compromise. In the Ourthe case, this leads to a m/n value lower than that obtained from the classical distance adjustment (0.79 against 0.86), leading to an increase in the non linear character of the dependence of knickpoint celerity on discharge. If we now recall that m/n = c(1-b) (Whipple & Tucker, 1999, JGR 104B: 17661-17674), where c and b are the exponents of the power law relations respectively linking discharge to drainage area and channel width to discharge, we can compare the calculated m/n value with that derived from field measurements of channel width, discharge and drainage area in the presently graded sections of the rivers. Such data taken from Petit et al. (2005, BSGLg 46: 37-50) allow us to derive m/n = 0.48 at equilibrium. As c may be considered constant, the higher m=n value obtained from the knickpoint retreat modelling must be ascribed to a lower b, i.e., to a channel narrowing associated with the transient phase of knickpoint migration. [less ▲]

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See detailQuaternary river incision in NE Ardennes (Belgium). Insights from 10Be-26Al dating of river terraces
Rixhon, Gilles; Braucher, Régis; Bourlès, Didier et al

in Quaternary Geochronology (2011), 6

Although it constitutes a main tool to unravel the regional recent tectonics, the chronology of the Pleistocene river incision is still poorly constrained within the uplifted Ardennes massif (Western ... [more ▼]

Although it constitutes a main tool to unravel the regional recent tectonics, the chronology of the Pleistocene river incision is still poorly constrained within the uplifted Ardennes massif (Western Europe). Here, we use in situ produced cosmogenic 10Be and 26Al concentrations from depth profiles in terrace sediments of several Ardennian rivers (Meuse, Ourthe and Amblève) in order to date the so-called Younger Main Terrace (YMT), a key-level in the drainage network evolution.We present the first absolute dating of the YMT in the lower Meuse valley, where we obtained an age of 725 +/- 120 ka for a terrace deposit buried beneath 3 m of Weichselian loess at Romont. This age is consistent with some previously published estimates based on paleomagnetic data and MIS correlations. However, the ages we obtain for the same terrace level in Ardennian tributaries of the Meuse are significantly younger: 390 +/- 35 ka in the lower Ourthe, and only 220 +/- 31 ka still farther upstream, in the lower Amblève. We thus demonstrate that the post-YMT incision occurred diachronically in NE Ardennes. The ~0.5 Ma timespan needed by the erosion wave to propagate from the lower Meuse towards the Ardennian headwaters contradicts the long-held statement of a climatically driven incision that would have been synchronous throughout the catchments. Finally, we interpret the strong 10Be enrichment displayed by the lower half of the Belle eRoche (lower Amblève) profile as betraying the long-lasting, slow accumulation of the ∼8 m thick terrace deposit in that place. [less ▲]

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See detailUnraveling the Quaternary river incision in the Meuse catchment (NE Ardennes massif, Belgium): insights from 10Be/26Al dating of fluvial terraces
Rixhon, Gilles; Braucher, Régis; Bourlès, Didier et al

Conference (2011)

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See detailThe presence of Homo erectus in NW Europe (Belle-Roche site, eastern Belgium) at ~600 ka attested by Terrestrial Cosmogenic Nuclide dating (10Be)
Rixhon, Gilles; Braucher, Régis; Bourlès, Didier et al

Conference (2011)

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See detailHuman presence at Belle-Roche, in the Ardenne massif (western Europe) : Terrestrial Cosmogenic Nuclides (10Be) dating of fluvial sediments confirms an age of ∼580 ka
Rixhon, Gilles; Braucher, Régis; Bourlès, Didier et al

in Geophysical Research Abstracts (2011), 13

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See detailContexte chronostratigraphique et paléoenvironnemental de la séquence de la grotte Walou : synthèse et perspectives
Pirson, Stéphane ULg; Draily, Christelle; Bovy, Benoît ULg et al

in Pirson, Stéphane; Draily, Christelle; Toussaint, Michel (Eds.) La grotte de Walou à Trooz (2011)

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