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SOURCE TO SINK STUDY OF THE CONGO SYSTEM SINCE 40 MYR : A MEASUREMENT OF THE RATIO BETWEN MECHANICAL AND CHEMICAL EROSION.

Abstract : The erosional processes are of two types; mechanical and chemical. If the first one are extensively studied, the chemical ones are less known whether it is for the coupling between geomorphological processes and chemical alteration or two the knowledge of the ratio between mechanical and chemical erosion. In 1995 Gaillardet and coauthors proposed based on global geochemical mass budget of the modern Congo River, a ratio between physical and chemical weathering of 1.5. To test this ratio, we here performed a source to sink study of the Congo System (catchment and depositional system up to the abyssal plain) since 40 Myr, time interval during which the Congo catchment did not experience major climate changes. The continental denudation was measured by subtracting the present-day topography from the so-called African Surface, etchplain (weathering surface) shaped between 70 and 40 Ma. This etchplain is today preserved as remnant planation surfaces from the eastern limb of the East-African Dome to the high plateaus of Cameroon and Angola. The deposited volumes were measured from seismic line and petroleum wells. Dated time-lines were drawn based on the principles of the seismic stratigraphy. The measured volumes from the coastal to the abyssal plains were compacted for a better comparison with the eroded volumes. From 40 Ma to today, 799 000 km3 of rocks were denudated over the Congo River catchment and 488 000 km3 of (compacted) sediments were deposited along the delta and the deep-sea-fan. The ratio between eroded and deposited volumes is around 1,64 (1,3 – 2,1 including uncertainties). In the absence of any type of buffer effect with temporary sediments storage along the Congo Basin, we interpret this difference of volume between erosion and sedimentation as the amount of chemical erosion. The value is quite similar to this measured by Gaillardet et al. (1995).
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Submitted on : Thursday, December 1, 2016 - 11:27:16 AM
Last modification on : Friday, April 5, 2019 - 8:17:51 PM

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François Guillocheau, Valentin Galmier, Cécile Robin. SOURCE TO SINK STUDY OF THE CONGO SYSTEM SINCE 40 MYR : A MEASUREMENT OF THE RATIO BETWEN MECHANICAL AND CHEMICAL EROSION.. Source to Sink: a long term perspective of sediment budgets and sources characterization, Géosciences-Rennes, Nov 2016, Rennes, France. pp.62. ⟨insu-01406482⟩

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