Early-to-mid Miocene erosion rates inferred from pre-Dead Sea rift Hazeva River fluvial chert pebbles using cosmogenic 21Ne

Earth Surf. Dynam., 8, 289–301, 2020 https://doi.org/10.5194/esurf-8-289-2020 © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License. Early-to-mid Miocene erosion rates inferred from pre-Dead Sea rift Hazeva River fluvial chert pebbles using cosmogenic 21 Ne Michal Ben-Israel1 , Ari Matmon1 , Alan J. Hidy2 , Yoav Avni3 , and Greg Balco4 1 The Fredy & Nadine Herrmann Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem, 91904, Israel 2 Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA 3 Geological Survey of Israel, Yesha’yahu Leibowitz 32, Jerusalem, 96921, Israel 4 Berkeley Geochronology Center, Berkeley, CA 94709, USA Correspondence: Michal Ben-Israel () Received: 25 September 2019 – Discussion started: 1 October 2019 Revised: 9 March 2020 – Accepted: 2 April 2020 – Published: 27 April 2020 Abstract. In this work, we utilize a novel application of cosmogenic 21 Ne 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 21 Ne, 26 Al, and 10 Be 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 21 Ne was acquired partly during bedrock erosion and partly during transport of these pebbles in the Hazeva River. However, 21 Ne exposure times calculated in Miocene cherts are generally shorter (ranging between 0+59 −0 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. 1 Introduction 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). Changes in rates of continental uplift and climatic conditions control rates of erosion controlled sediment production, transport, and storage, and they influence fluvial systems and their associated sediment archives (e.g., DiBiase and Whipple, 2011; Ferrier et al., 2013; Vance et al., 2003). Cosmogenic nuclides, mostly radiogenic 26 Al and 10 Be, have been used extensively to study weathering and erosion rates in fluvial systems across different scales and geological settings (e.g., Bierman, 1994; von Blanckenburg, 2005). The decreased preservation of older sediments in fluvial systems, due to burial or recycling, adds difficulty to the reconstruction of past tectonic or climatic conditions with increased sediment age (e.g., Anderson et al., 1996; Gu- Published by Copernicus Publications on behalf of the European Geosciences Union. 290 M. Ben-Israel et al.: Early-to-mid Miocene erosion rates inferred from pre-Dead Sea rift ralnik et al., 2011; Schaller et al., 2002). Furthermore, 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 (10 Be and 26 Al) due to their half-lives (1.38 Myr and 716 kyr, accordingly; 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). Here, we apply stable cosmogenic 21 Ne to sediments deposited during the early-to-mid Miocene (∼ 18 Ma) by the Hazeva River. This massive fluvial system drained parts of the Arabian Peninsula and Sinai into the Mediterranean prior to the subsidence of the Arava Valley along the Dead Sea transform (Garfunkel and Horowitz, 1966; Zilberman and Calvo, 2013). We quantify the time of exposure during erosion and transport of Miocene chert pebbles deposited by the Hazeva River and compare it to exposure times of chert that has been eroding over the recent past (∼ 105 yr). Through this comparison, 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. 2 Geological setting Following an extended period of transgression that ended in the late Eocene, the Mediterranean Sea retreated to its current location (Garfunkel and Horowitz, 1966). This period of relative tectonic tranquility was followed by a series of tectonic and magmatic events that resulted in the rifting of the Red Sea and the Gulf of Aden in the late Eocene to early Oligocene (∼ 35–30 Ma; e.g., Bohannon et al., 1989; Bosworth et al., 2005; Omar and Steckler, 1995). During the last 20–30 Myr, regional doming associated with the emergence of the Afar plume uplifted the Arabian Peninsula from near sea level to its present elevation of ∼ 1 km (e.g., Feinstein et al., 2013; Morag et al., 2019; Wilson et al., 2014). As a result of this uplift, widespread denudation followed, and a regional truncation surface developed in the northern Red Sea and the southern Levant, exposing older strata down to Precambrian formations depending on the preexisting structure (Avni et al., 2012). Following these events, during the early-to-mid Miocene, the uplifted region was drained by a newly established fluvial system, termed the Hazeva River, which flowed northwestward from the eroded terrains towards the Mediterranean Sea, and drained an estimated area > 100 000 km2 (Garfunkel and Horowitz, 1966; Zilberman and Calvo, 2013; Fig. 1). The Hazeva fluvial system operated until the subsidence of the Dead Sea rift, during the late Miocene to early Pliocene, and brought on a dramatic change in morphology, which led to the disruption of Earth Surf. Dynam., 8, 289–301, 2020 F (...truncated)