Analysis of geological hiatus surfaces across Africa in the Cenozoic and implications for the timescales of convectively-maintained topography

Abstract

Geological maps are a powerful but underutilized tool for constraining geodynamic processes and models. Unraveling the Cenozoic elevation history of Africa and distinguishing between competing uplift and subsidence scenarios is of considerable interest to constrain the dynamic processes in the mantle beneath the continent. Here, we explore continental-scale geological maps, and map temporal and spatial patterns of geological contacts, assuming that interregional-scale unconformable contacts (hiatus surfaces) on geological maps yield proxy records of paleotopography and vertical motion. We found that significant differences in the spatial extents of interregional-scale hiatus surfaces exist across Africa at the timescale of geologic series. A significant expansion of total unconformable area at the base of the Miocene strongly suggests that the Oligocene was a period of uplift in most of Africa. In southern Africa there is a complete absence of marine sediments in both the Oligocene and Pleistocene. This pattern suggests that southernmost Africa reached a high elevation in the Oligocene, subsided in the Miocene–Pliocene, and has been high again since the latest Pliocene or Pleistocene. Our hiatus mapping results support a dynamic origin of Africa’s topography. In particular, they point to elevation changes at the timescale of geologic series (ten to a few tens of millions of years), which is considerably smaller than the mantle transit time. The timescale for elevation changes in Africa is, thus, comparable with the rapid spreading in the South Atlantic, which have been geodynamically linked to African elevation changes through pressure-driven upper mantle flow.

Ali Mehmet Celâl Şengör: A geologist who unravels the histories of continents and oceans

“…The absence of marine sediments in both the Oligocene and Pleistocene in southern Africa suggests that southernmost Africa uplifted in the Oligocene, subsided in the Miocene-Pliocene, and has been high again since the latest Pliocene or Pleistocene. Carena et al (2019) show that Cenozoic unconformities in Africa are a product of geodynamic processes. The authors conclude that topographic changes on the African continent are coeval with spreading rate variations in the South Atlantic Ocean, indicating a geodynamic link between African elevation changes and pressure-driven upper mantle flow beneath the continent.…”

“…50 and 40 Ma. Carena et al (2019) analyze the geological significance of Cenozoic unconformities in Africa and discuss the relationship between topographic structures and mantle flows beneath the continent. They propose that large expansion of a total unconformable area at the base of Miocene rocks strongly indicates that the Oligocene was a period of uplifting in most of Africa.…”

The Cenozoic evolution of the Intrarif (Rif, Morocco)

“…The origin of these relative sea-level changes is thought to have been controlled primarily by tectonics, although climate cannot be discarded (see below). Works in the Saharan area (Swezey, 2009) and in other African sectors (Carena et al, 2019) studied the hiatus during the Cenozoic in the African continent. In the case of the Cretaceous-Cenozoic boundary, a global warming event (Paleocene-Eocene thermal maximum) is suggested (Carena et al, 2019).…”

“…Works in the Saharan area (Swezey, 2009) and in other African sectors (Carena et al, 2019) studied the hiatus during the Cenozoic in the African continent. In the case of the Cretaceous-Cenozoic boundary, a global warming event (Paleocene-Eocene thermal maximum) is suggested (Carena et al, 2019). This warming should be reflected in sedimentation in a deepening with an absence of unconformities.…”

“…Only an extreme warming such as the Messinian desiccation could provoke an erosive unconformity that is climatically controlled, but this is not the case during the Paleogene. In the case of the Oligocene period, the generalized absence or reduction of strata is also asserted (Swezey, 2009;Carena et al, 2019). This period belongs to a generalized sea-level fall due to global cooling during the build-up of the Antarctica ice sheet (Carena et al, 2019) but also results from an uplifting of part of the African continent caused by rapid seafloor spreading in the South Atlantic that led to the rotation and northward movement of Africa (Carena et al, 2019).…”