Le Siderolithique du Tertiaire ouest-africain et le concept de continental terminal

Geochem Geophys Geosyst

Grimaud

Rouby

et al. 2016

Reconstructing the evolving geometry of large river catchments over geological time scales is crucial to constraining yields to sedimentary basins. In the case of Africa, it should further help deciphering the response of large cratonic sediment routing systems to Cenozoic growth of the basin-and-swell topography of the continent. Mapping of dated and regionally correlated lateritic paleolandscape remnants complemented by onshore sedimentological archives allows the reconstruction of two physiographic configurations of West Africa in the Paleogene. Those reconstructions show that the geometry of the drainage is stabilized by the late early Oligocene (29 Ma) and probably by the end of the Eocene (34 Ma), allowing to effectively link the inland morphoclimatic record to offshore sedimentation since that time, particularly in the case of the Niger catchment-delta system. Mid-Eocene paleogeography reveals the antiquity of the Senegambia catchment back to at least 45 Ma and suggests that a marginal upwarp forming a continental divide preexisted early Oligocene connection of the Niger and Volta catchments to the Equatorial Atlantic Ocean. Such a drainage rearrangement was primarily enhanced by the topographic growth of the Hoggar hot spot swell and caused a stratigraphic turnover along the Equatorial margin of West Africa.

Section: 1002/2015gc006169mentioning

confidence: 95%

Stabilization of large drainage basins over geological time scales: Cenozoic West Africa, hot spot swell growth, and the Niger River

Geochem Geophys Geosyst

Grimaud

Rouby

et al. 2016

“…Marine sedimentation is recorded repeatedly until the Late Paleo ceneEarly Eocene, particularly in the Iullemmeden and Chad basins (e.g., Radier, 1959;Greigert, 1966;Kogbe, 1980;Reyment, 1980;Moody and Sutcliffe, 1991). Those series are overlain by fluvial sediments of the Late Eocene-Early Oligocene "Continental Terminal" (Lang et al, 1986(Lang et al, , 1990Chardon et al, 2016;Fig. 2).…”

Section: Geological Outline and Earlier Workmentioning

confidence: 99%

Paleogeographic and structural evolution of northwestern Africa and its Atlantic margins since the early Mesozoic

Rouby

et al. 2017

Geosphere

The geological evolution of northwestern Africa and its continental margins is investigated in the light of nine Meso-Cenozoic paleogeological maps, which integrate original minimal extent of sedimentary deposits beyond their present-day erosional limits. Mapping is based on a compilation of published original data on the stratigraphy and depositional environments of sediments, structures, magmatism, and low-temperature thermochonology, as well as on the interpretation of industrial seismic and borehole data.We show that rifting of the equatorial domain propagated eastward from the Central Atlantic between the Valanginian (ca. 140 Ma) and the Aptian (ca. 112 Ma) as an en echelon strike-slip and rift system connected to an inland rift network. This network defines a six-microplate synrift kinematic model for the African continental domain. We document persistent, long-wavelength eroding marginal upwarps that supplied clastic sediments to the offshore margin basins and a large intracratonic basin. The latter acted as a transient sediment reservoir because the products of its erosion were transferred both to the Tethys (to the north) and the Atlantic Ocean. This paired marginal upwarpintra cratonic basin source-to-sink system was perturbed by the growth of the late Paleogene Hoggar hotspot swell that fragmented the intracratonic basins into five residual depocenters. By linking the evolution of the continental margins to that of their African hinterland, this study bears important implications for the interplay of long-wavelength deformation and sediment transfers over paired shield-continental margin systems.

“…S 1 weathering profile formed on any type of pre‐Eocene rock in West Africa and did not develop on early to mid‐Eocene marine sediments marking the last intracratonic transgression. Post mid‐Eocene fluvial sediments of the Continental Terminal overlie S 1 laterites in the intracratonic basins [ Lang et al ., ]. The S 2 surface and the subsequent glacis developed on the Continental Terminal and on any rock type of its substrate [e.g., Beaudet et al ., ].…”

Section: Denudation Chronology Of West Africamentioning

confidence: 99%

Modes, tempo, and spatial variability of Cenozoic cratonic denudation: The West African example

Beauvais

Geochem Geophys Geosyst

2013

102

[1] Quantifying long-term erosion of tropical shields is crucial to constraining the role of lateritic regolith covers as prominent sinks and sources of CO 2 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 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 three subcontinental-scale lateritic paleolandsurfaces whose age is bracketed by 39 Ar/ 40 Ar dating of lateritic K-Mn oxides. Denudation depths and rates compiled from 380 field stations show that despite heterogeneities confined to early-inherited reliefs, the subregion 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 (10 0 -10 7 yr). These results allow defining a steady state cratonic denudation regime that is weatheringlimited, 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 expression of steady state cratonic denudation regimes in clastic sedimentary fluxes remains to be investigated.