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| Titel |
Cenozoic denudation rates of the West African marginal upwarp recorded by lateritic paleotopographies |
| VerfasserIn |
Anicet Beauvais, Dominique Chardon |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250078023
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| Zusammenfassung |
| Quantifying long-term erosion of tropical shields is crucial to constraining the role of
lateritic regolith covers as prominent sinks and sources of CO2 and sediments in the
context of long-term Cenozoic climate change. It is also a key to understanding
long-term landform evolution processes operating over most of the continental surface,
particularly passive margins, and their control onto the sediment routing system. We
study the surface evolution of West Africa over three erosion periods (~ 45-24,
~ 24-11 and ~ 11-0 Ma) recorded by relicts of 3 sub-continental scale lateritic
paleolandsurfaces whose age is bracketed by 39Ar/40Ar dating of lateritic K-Mn oxides [1].
Denudation depths and rates compiled from 380 field stations show that despite
heterogeneities confined to early-inherited reliefs, the sub-region underwent low and
homogeneous denudation (~ 2-20 m Ma-1) over most of its surface whatever the
considered time interval. This homogeneity is further documented by a worldwide
compilation of cratonic denudation rates, over long-term, intermediate and modern
Cenozoic time scales (100 - 107 yr). These results allow defining a steady-state cratonic
denudation regime that is weathering-limited i.e. controlled by the thickness of the
(lateritic) regolith available for stripping. Steady-state cratonic denudation regimes are
enabled by maintained compartmentalization of the base levels between river knick
points controlled by relief inheritance. Under such regimes, lowering of base levels
and their fossilization are primarily imposed by long-term eustatic sea level fall
and climate rather than by epeirogeny. The results suggest that Cenozoic post-rift
vertical mobility of marginal upwarps in the tropical belt was unable to modify slow,
weathering-controlled, steady state denudation regimes. The potentially complex expression
of steady-state cratonic denudation regimes in clastic sedimentary fluxes remains to be
investigated.
[1] Beauvais et al., Journal of Geophysical Research, 113, F04007, 2008. |
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