Abstract
Abstract. In this work, we utilize a novel application of cosmogenic 21Ne measurements in chert to compare exposure times measured in eroding surfaces in the central Jordanian Plateau with exposure times from chert pebbles transported by the Miocene Hazeva River. 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-to-mid Miocene. It was established after the 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 find 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−1). Comparison between modern and paleo-erosion rates, measured in chert pebbles, is not straightforward, as cosmogenic 21Ne was acquired partly during bedrock erosion and partly during transport of these pebbles in the Hazeva River. However, 21Ne exposure times calculated in Miocene cherts are generally shorter (ranging between 0-0+59 and 242±113 kyr) compared to exposure times calculated in the currently eroding chert nodules presented here (269±49 and 378±76 kyr) and other chert surfaces currently eroding in hyperarid environments. Miocene exposure times are shorter even when considering that they account for bedrock erosion in addition to maintained transport along this large river. Shorter exposure times in Miocene cherts correspond to faster paleo-erosion rates, which we attribute to a combination of continuous surface uplift and significantly wetter climatic conditions during the early-to-mid Miocene.
Highlights
Tectonic and climatic conditions control geomorphological processes through surface uplift, rock weathering, and sediment generation and transport (e.g., Allen, 2008; Whipple, 2009; Whittaker, 2012)
We compared the cosmogenic 21Ne measured in chert pebbles and quartz sand eroded and transported during the midMiocene (∼ 18 Myr) by the Hazeva River with the chert source rock (Eocene chert nodules) currently eroding in the central Jordanian Plateau
We successfully established a novel application for measuring cosmogenic 21Ne in modern and Miocene chert samples, expanding the opportunities and settings in which stable cosmogenic nuclides analysis could be used as a tool to quantify geomorphic processes and ascertaining chert as a viable www.earth-surf-dynam.net/8/289/2020/
Summary
Tectonic and climatic conditions control geomorphological processes through surface uplift, rock weathering, and sediment generation and transport (e.g., Allen, 2008; Whipple, 2009; Whittaker, 2012). Even when geological circumstances do allow for the preservation of older sediments, rates prior to the Pliocene cannot be quantified with the more commonly used cosmogenic radionuclides (10Be and 26Al) due to their half-lives (1.38 Myr and 716 kyr, ; Ivy-Ochs and Kober, 2008) Unlike their radioactive counterparts, stable cosmogenic nuclides have the potential to quantify rates of surface processes as far back as the Lower Cretaceous (Balco et al, 2019; Ben-Israel et al, 2018; Dunai et al, 2005; Libarkin et al, 2002; Sinclair et al, 2019). We quantify differences between erosion rates during the early-to-mid Miocene and rates of hyperarid environments eroding today, and we examine the possible influence of the tectonic and climatic conditions that operated in the region during this time
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