Rimaal: A Sand Buried Structure of Possible Impact Origin in the Sahara: Optical and Radar Remote Sensing Investigation

Eman Ghoneim

doi:10.3390/rs10060880

Abstract

This work communicates the discovery of a sandy buried 10.5 km diameter near-circular structure in the eastern part of the Great Sahara in North Africa. Rimaal, meaning “sand” in Arabic, is given as the name for this structure since it is largely concealed beneath the Sahara Aeolian sand. Remote sensing image fusion and transformation of multispectral data (from Landsat-8) and synthetic aperture radar (from Sentinel-1 and ALOS PALSAR), of dual wavelengths (C and L-bands) and multi-polarization (HV, VV, HH, and HV), were adopted in this work. The optical and microwave hybrid imagery enabled the combining of surface spectral properties and subsurface roughness information for better understanding of the Rimaal structure. The long wavelength of the radar, in particular, enabled the penetration of desert sands and the revealing of the proposed structure. The structure exhibits a clear outer rim with traces of concentric faults, an annular flat basin and an inner ring surrounding remnants of a highly eroded central peak. Radar imagery clearly shows the interior wall of the structure is incised with radial pattern gullies that originate at or near the crater periphery, implying a much steeper rim wall in the past. In addition, data reveals a circumferential of a paleoriver course that flows along a curved path parallel to the crater’s western margin indicating the plausible presence of a concentric ring graben related to the inferred structure. The defined crater boundary is coincident with a shallow semi-circular-like basin in the SRTM elevation data. The structure portrays considerable modifications by extensive long-term Aeolian and fluvial erosion. Residing in the Cretaceous Nubian Sandstone formation suggests an old age of ≤65 Ma for the structure. If proven to be of an impact origin, the Rimaal structure could help in understanding the early evolution of the landscape of the Eastern Sahara and holds promise for hosting economically valuable ore deposits and hydrocarbon resources in the region.

Highlights

Bombardment by meteorites was a major geological process during the early history of Earth [1]
Both Sentinel-2 and LS8 optical satellite images faintly show the Rimaal structure consists of a single circular wrinkle ridge surrounding a basin that is completely infilled by smooth sandy material (Figure 3)
The topography of the area in Sentinel-2 and LS8 is relatively subdued with no obvious expression of a topographic rim to the Rimaal structure

Summary

Introduction

Bombardment by meteorites was a major geological process during the early history of Earth [1]. Unlike the Earth, the lack of the geological and atmospheric process on the Moon and other planets have prevented erosion of their impact craters. Scars of these geologic forces and the past cratered Earth’s surfaces have been deeply erased by erosion and plate tectonic processes [2]. The discovery of new impact structures is of high importance to gain an understanding of the Earth’s early history, and has economic significance as possible hosts of valuable ore deposits (e.g., gold and uranium) and hydrocarbon resources (e.g., oil and natural gas) [3,4]. It is worthwhile to search for new unknown terrestrial impact structures

Methods

Results

Conclusion