Early–mid Miocene erosion rates measured in pre-Dead Sea rift Hazeva River using cosmogenic <sup>21</sup>Ne in fluvial chert pebbles

Abstract

Abstract. The Miocene Hazeva River was a large fluvial system (estimated catchment size > 100 000 km2) that drained the Arabian Plateau and Sinai Peninsula into the Mediterranean Sea during the Early–Mid Miocene. It was established after rifting of the Red Sea uplifted the Arabian Plateau during the Oligocene. Following late Miocene to early Pliocene subsidence along the Dead Sea Rift, the Hazeva drainage system was abandoned and dissected, resulting in new drainage divides on either side of the rift. We utilized a novel application of cosmogenic 21Ne measurements in chert to compare modern erosion rates with Miocene erosion rates that operated when the Hazeva River was active. We find that modern erosion rates derived from cosmogenic 21Ne, 26Al, and 10Be in exposed in situ chert nodules to be extremely slow, between 2–4 mm/kyr. Comparison between modern and paleo erosion rates, measured in chert pebbles, is not straightforward, as cosmogenic 21Ne was acquired partly during bedrock exhumation and partly during transport of these pebbles in the Hazeva River. However, even with bedrock erosion and maintained transport along this big river, 21Ne concentrations measured in Miocene cherts are lower (range between 3.66 ± 1.9 × 106 and 8.97 ± 1.39 × 106 atoms/g SiO2) compared to 21Ne concentrations measured in the currently eroding chert nodules (8.08 ± 1.48 × 106 and 12.10 ± 2.43 × 106 atoms/g SiO2). 21Ne concentrations in Miocene cherts correspond to minimum erosion rates that are at least twice as fast as rates calculated today. We attribute these faster erosion rates to a combination of continuous uplift and significantly wetter climatic conditions during the Miocene.