Aging Africa: Cosmogenic view of erosion, relief generation, and the age of faulting in southernmost Africa

Date:

August 29, 2014

Source:

Geological Society of America

Summary:

A cosmogenic view of erosion, relief generation, and the age of faulting in southernmost Africa has been presented by researchers. By measuring beryllium-10 in river sediment samples, they show that south-central South Africa is eroding at the slow rate of about five meters per million years, consistent with rates in other non-tectonically active regions.

September 2014 GSA Today cover image: Iron-rich silcrete mantles beveled quartzite in south-central South Africa. Deep valleys dissect the landscape and steep hillslopes separate the valley bottoms from the flat, gently sloping pediments.

Credit: Image courtesy Paul Bierman

In the September issue of GSA Today, Paul Bierman of the University of Vermont-Burlington and colleagues present a cosmogenic view of erosion, relief generation, and the age of faulting in southernmost Africa. By measuring beryllium-10 (10Be) in river sediment samples, they show that south-central South Africa is eroding at the slow rate of about five meters per million years, consistent with rates in other non-tectonically active regions.

By measuring 10Be and aluminum-26 (26Al) in exposed quartzites, Bierman and colleagues find that undeformed upland surfaces have changed little since the Pliocene, with minimum exposure ages averaging 1.3 million years and maximum erosion rates averaging 0.34 meters per million years, and no Quaternary movement on faults that displace the quartzite but not the silcrete-mantled pediment surfaces.

10Be measurements in exposed fault scarp samples from the only recognized Quaternary-active fault are consistent with 1.5 m of displacement occurring at 25,000 years ago. They conclude that rates of landscape change on the upland pediment surfaces are an order of magnitude lower than basin-average erosion rates and that, as isostatic response to regional denudation uplifts the entire landscape at several meters per million years, valleys deepen, isolating stable upland surfaces and creating the spectacular relief for which the region is famous.

Story Source:

The above story is based on materials provided by Geological Society of America. Note: Materials may be edited for content and length.

Journal Reference:

Paul R. Bierman, Ryan Coppersmith, Kathryn Hanson, Johann Neveling, Eric W. Portenga, Dylan H. Rood. A cosmogenic view of erosion, relief generation, and the age of faulting in southern Africa. GSA Today, 2014; 24 (9): 4 DOI: 10.1130/GSATG206A.1

Geological Society of America. "Aging Africa: Cosmogenic view of erosion, relief generation, and the age of faulting in southernmost Africa." ScienceDaily. ScienceDaily, 29 August 2014. <www.sciencedaily.com/releases/2014/08/140829135404.htm>.