EXAMINING THE ORIGIN OF MEGA-LINEAR FEATURES IN NORTHERN ARABIA: AEOLIAN, GLACIOGENIC OR TECTONIC FORCINGS

In this study, we delineate the distribution of ENE-oriented mega-linear features in NW Saudi Arabia and investigate their origin using observations extracted from satellite images (e.g. ALOS PALSAR, Landsat, and SRTM) geologic maps, and field observations. These features extend, north of latitude 24°N, over the peneplained Neoproterozoic Arabian Shield (NAS) and the Cambro-Ordovician Saq sandstone. They form sub-parallel valleys/grooves (10s km long and 10s to 100s m wide) over a wide range of NAS lithologic units. Over the Saq sandstone, these features are expressed as elongated ENE hills (a few km long; 100s m wide) and are dissected by N to NNW polished pavements. A tectonic origin for these features is unlikely given their intersections at high angle with major NW and NS-trending structural elements in the area. A wind deflation origin (i.e. yardangs) was proposed for the mega-linear features based on their elongated morphology and their termination along an ancient barchans dune field. However, the proposed aeolian origin cannot account for the restriction of mega-lineations to pre-Late Ordovician rocks. We propose a subglacial erosional mega-lineation origin for these features in response to the transgression of the Hirnantian ice sheet over North Gondawana. This hypothesis is supported by the following observations: (1) the mega-linear features are overlain by the glacial Sarah Formation; (2) their ENE-trend over the NAS is consistent with those of the tunnel valleys and striations to the east; (3) the morphometric parameters of the mega-linear features are consistent with those reported from the recent glacial erosional landforms associated with paleo-ice streams; (4) the association of small-scale glacial landforms (e.g., whalebacks, roche moutonnees and flutes ) with the investigated mega-linear features; (5) the spatial correlation (in paleogeographic reconstructions of the Late Ordovician) between the mega-linear features and the recently reported ENE-trending glacial megagrooves in the South Eastern Desert of Egypt. Findings from this study emphasize the role of glacial forcings processes in shaping the landscape of northern Arabia and suggest that wind erosion and deflation exposed and widened many of the earlier glacial mega-lineations.