Evidence of buried paleodrainage in the Wahiba Sands, Oman: New perspective in understanding paleorecharge in the Southern Arabian Peninsula

The dynamic of the monsoon and position of its Intertropical Convergence Zone, as well as global sea level fluctuation are associated and have controlled the paleoclimate of the Wahiba Sands in Oman (Radies et al., 2004). Today the climate of the area is considered as hyper-arid but has also known wetter periods in the past, e.g. Early Holocene, and the paleodrainage mapped in the highland areas around the desert of Wahiba Sands by Robinson et al. 2007, using Radarsat-1 C-band SAR images, are supporting evidences of substantial surficial flows events. However, no drainage networks were detected under the Wahiba desert itself, which motivated our study to explore the area with a lower radar frequency to penetrate deeper into the desiccated dunes. Using ALOS PALSAR L-band radar SAR images, we observe NW-SE and NE-SW oriented paleochannels, under meters to few tens of meters of the linear dunes forming the Wahiba Sands area. The paleochannels are detectable with the loss of radar backscatter that we attribute to different sedimentary materials and their permittivity, porosity and scattering properties. To validate their detection, we perform a 500 MHz ground radar (GPR) survey in the interdunal area and observe them to be few tens of meters wide and about 1m deep. The scattering observed on the radargrams suggests these paleochannels to be filled with centimetric size gravels, which we believe cause the signal attenuation observed on the SAR images. Dunes are found to be highly favorable for the L-band penetration, with power loss of 0.2 dB/m derived from dielectric characterizations of field collected samples. The discovery of these buried paleochannels under the linear dunes brings new insights to construct the paleoclimatic evolution of the southern area of the Arabian peninsula and better understand the indeterminate tropical climate changes during the Late Pleistocene and Holocene.