Date:11/27/2012

rise to a narrow intramontane basin extending 110 km, with a north-south trend. In the northern sector of the basin, streams initially were competent to carve their channels across the rising barrier, but most were later defeated and deflected. However, the deflected water courses collected their discharges into a trunk stream which, thus reinforced, was able to maintain open a water gap that incised 800 m into basement rocks underlying the barrier. In contrast, in the southern reach of the basin, streams were fully contained by the barrier, and their discharges gave rise to a lake that grew in extent until water level reached a spillover point across the barrier; backward erosion followed and the lake waters were drained. The disparate fluvial behavior is attributed to a combination of areally varying rainfall depth, rain shadowing by the rising barrier, and the indirect influence of inherited basement structures in the basin geometry and river channel gradients. A relative time scale for these events is constructed employing techniques and concepts of geomorphology.

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Oligocene regional denudation of the northern Afar dome: Pre- and syn-breakup stages of the Afro-Arabian plate
Y. Anvi et al., Geological Survey of Israel, 30 Malkhe Israel Street, Jerusalem 95501, Israel. Posted online 2 October 2012; http://dx.doi.org/10.1130/B30634.1.

This paper by Y. Anvi and colleagues highlights the critical role played by a regional truncation (erosive) surface (RTS) developed during the Oligocene (between about 31 and 26 million years ago) in the northeastern Afro-Arabian continent. This vast and flat erosional surface developed during the formation of a ~3000 by 1500-km crustal doming above the Afar mantle plume and widespread fluvial erosion that truncated this dome. The RTS separates two principal clastic units that, together with the reconstructed geological features
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Contact: Kea Giles kgiles@geosociety.org Geological Society of America Source:Eurekalert

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