Sediment Yield During Late Glacial and Holocene periods in the Lac Chambon Watershed, Massif Central, France

Numerical models have not yet systematically been used to predict properties of fluvial terrace records in order to guide fieldwork and sampling. This paper explores the potential of the longitudinal profile model FLUVER2 to predict testable field properties of the relatively well‐studied, Late Quaternary Allier system in France. For the Allier terraces an overlapping 14C and U‐series chronology as well as a record of 10Be erosion rates exist. The FLUVER2 modelling exercise is focused on the last 50 ka of the upper Allier reach because for this location and period the constraints of the available dating techniques are tightest. A systematic calibration based on terrace occurrence and thicknesses was done using three internal parameters related to (1) the sediment erodibility; (2) the sediment transport distance; and (3) the sediment supply derived from the surrounding landscape. As external model inputs, the best available, reconstructed, tectonic, climatic and base‐level data were used. Calibrated model outputs demonstrate a plausible match with the existing fluvial record. Validation of model output was done by comparing the modelled and measured timing of aggradation and incision phases for the three locations. The modelled range of landscape erosion rates showed a reasonably good match with existing erosion rate estimates derived from 10Be measurements of fluvial sands. The quasi‐validated model simulation was subsequently used to make new testable predictions about the timing and location of aggradation and erosion phases for three locations along the Allier river. The validated simulations predict that along the Allier, reach‐specific dynamics of incision and aggradation, related to the variations in sediment supply by major tributaries, cause relevant differences in the local fluvial terrace stratigraphy. Copyright © 2016 John Wiley & Sons, Ltd.

Section: Landscape Erosion Ratesmentioning

confidence: 99%

Predicting reach‐specific properties of fluvial terraces to guide future fieldwork. A case study for the Late Quaternary River Allier (France) with the FLUVER2 model

Veldkamp

Schoorl

Viveen

2016

Sediment yield and storage variations in the Négron River catchment (south western Parisian Basin, France) during the Holocene period

Macaire

Bellemlih

Di-Giovanni

et al. 2002

Self Cite

In the Négron River catchment area (162 km 2 ), surface-sediment stores are composed of periglacial calcareous 'grèze' (5 ð 10 6 t) and loess (21 ð 10 6 t), and Holocene alluvium (12Ð6 ð 10 6 t), peat (0Ð6 ð 10 6 t) and colluvium (18Ð5 ð 10 6 t). Seventy-five per cent of the Holocene sediments is stored along the thalwegs. Present net sediment yield, calculated from solid discharge at the Négron outlet, is low (0Ð6 t km 2 a 1 ) due to the dominance of carbonate rocks in the catchment. Mean sediment yield during the Holocene period is 7Ð0 t km 2 a 1 from alluvium stores and 7Ð6 t km 2 a 1 from colluvium stores. Thus, the gross sediment yield during the Holocene period is about 18Ð7 t km 2 a 1 and the sediment delivery ratio 3 per cent. The yield considerably varies from one sub-basin to another (3Ð9 to 24Ð5 t km 2 a 1 ) according to lithology: about 25 per cent and 50 per cent of initial stores of periglacial grèze and loess respectively were reworked during the Holocene period. Sediment yield has increased by a factor of 6 in the last 1000 years, due to the development of agriculture. The very high rate of sediment storage on the slope during that period (88 per cent of the yield) can be accounted for by the formation of cultivation steps ('rideaux'). It is predicted that the current destruction of these steps will result in a sediment wave reaching the valley floors in the coming decades. Subboreal and Subatlantic sediments and pollen assemblages in the Taligny marsh, where one-third of the alluvium is stored, show the predominant influence of human activity during these periods in the Négron catchment.

Preservation of the last aggradation phase in climate‐driven terraces: Evidence from Late Quaternary reach‐specific fluvial dynamics of the Allier River (France)

Veldkamp

Schoorl

Claessens

et al. 2020

There is limited knowledge about the preservation of aggradation phases in Quaternary fluvial records. Previous numerical modelling of erosion and deposition in Late Quaternary Allier River (France) generated the prediction that this river has reach-specific fluvial dynamics related to climate-driven tributary sediment-flux dynamics. To test this prediction, new optically stimulated luminescence (OSL) samples were collected of the Late Quaternary Fx terrace at five locations along a stretch of 60km. OSL dates of both quartz and feldspar sand grains indicate that all relatively basalt-poor sediments display significantly different ages for each reach (ranging from 36.3 ± 2.0 to 21.1 ± 2.3ka). The more basalt-rich terrace body consistently yields ages in the range 21.1 ± 1.7 to 16.1 ± 1.5ka, suggesting contemporaneous aggradation along the whole studied Allier reach during this interval. Our own new OSL date of a Tartaret eruption around 16.8 ± 2.5ka also fits this time window, suggesting a direct link with volcanic activity. However, there are many more dated volcanic events that coincide with the older basalt-poor units, making it less likely that a direct link between terrace-sediment basalt content and volcanic activity exists. The timings of the dated depositional events in MIS 3 and 2 all match with simulated climate drivers and published landscape erosion rates. Counterintuitively, the volcanic Chaîne des Puys area supplied more sediment during the cold and dry Last Glacial Maximum. Basalt content in the Allier terrace sediments reflects climate-related sediment-flux dynamics upstream. The scarcity of older basalt-poor sediment bodies from MIS 4 and 3 in the Fx terrace suggests that less sediment was supplied and/or the intermittent erosional phases in the Allier were very effective at removing them. We hypothesize that this observation of predominant preservation of the last aggradation phase could be a common phenomenon in most climate-driven terraces.