Abstract
ABSTRACT Exhumed Paleozoic glacial deposits and landforms of the North Gondwana are reported here for the first time from the South Eastern Desert (SED) of Egypt. Using field observations and remote sensing datasets (Advanced Land Observing Satellite [ALOS], Phased Array L-band Synthetic Aperture Radar [PALSAR] radar, multispectral Landsat TM datasets, and digital elevation models [DEMs]), we mapped the distribution of Paleozoic glacial features (i.e. deposits and landforms) in the SED. Two main glaciogenic facies were identified in three locations in the SED: (1) massive, poorly sorted, matrix supported, boulder-rich diamictites in Wadi El-Naam and Korbiai, and (2) moderately-sorted, occasionally bedded outwash deposits in Betan area. Inspection of radar, DEMs, and Landsat Operational Land Imager (OLI) images revealed previously unrecognized ENE-WSW trending glacial megalineations (MLs) over the peneplained Neoproterozoic basement rocks in the central sections of the SED, whose trends align along their projected extension with those of glacial features (tunnel valleys and striation trends) reported from Saudi Arabia. The glaciogenic features in the SED are believed to be largely eroded during the uplift associated with the Red Sea opening, except for those preserved as basal units beneath the Nubia Sandstone Formation or as remnant isolated deposits within paleo-depressions within the basement complex. The apparent spatial correlation of the SED glacial features with well-defined Late Ordovician deposits in North Africa and in Saudi Arabia, and the reported thermochronometric analyses and fossil records are consistent with a Late Ordovician age for the SED glaciogenic features and support models that call on the continuation of the Late Ordovician (Hirnantian) ice sheet from the Sahara into Arabia through the SED of Egypt.
Highlights
Introduction and backgroundTwo main glaciation events of Paleozoic age have been reported from many locations within the Gondwana continent (Eyles 2008; Le Heron et al 2009; Torsvik and Cocks 2013; Lewin et al 2018)
The term ‘Nubia Sandstone Formation’ has been used for the past two centuries (Russegger 1837) and continues to be used today. We speculate that this is one of the main reasons that a number of regional studies concluded that the Late Ordovician glaciation event in North Africa and Arabia is absent in Egypt (Sutcliffe et al 2000; Le Heron et al 2005; Ghienne et al 2007), a conclusion that is at odds with early field-based studies that documented Late Ordovician glacial tillite in the Western Desert and fluvioglacial deposits in the North Eastern Desert and Sinai (Beall and Squyres 1979; Issawi and Jux 1982)
Evidences include: (1) the MLs trends in the South Eastern Desert (SED) align along their strike and projected extension with the Late Ordovician tunnel valleys and striation trends in northwest Saudi Arabia (Vaslet 1990; Clark-Lowes 2005) (Figure 8); (2) zircon and sphene fission track data from the SED indicate that the temperatures predating the onset of cooling and erosion reached approximately 300°C and that the Neoproterozoic rocks were covered by 5–15 km of overburden between the Late Devonian and the Oligocene (Bojar et al 2002)
Summary
Two main glaciation events of Paleozoic age have been reported from many locations within the Gondwana continent (Eyles 2008; Le Heron et al 2009; Torsvik and Cocks 2013; Lewin et al 2018). The term ‘Nubia Sandstone Formation’ has been used for the past two centuries (Russegger 1837) and continues to be used today We speculate that this is one of the main reasons that a number of regional studies concluded that the Late Ordovician glaciation event in North Africa and Arabia is absent in Egypt (Sutcliffe et al 2000; Le Heron et al 2005; Ghienne et al 2007), a conclusion that is at odds with early field-based studies that documented Late Ordovician glacial tillite in the Western Desert and fluvioglacial deposits in the North Eastern Desert and Sinai (Beall and Squyres 1979; Issawi and Jux 1982). The SED MLs are well preserved over peneplained Neoproterozoic outcrops in the central SED, gradually fading towards the Red Sea Hills, and none are recognized within the PG-NSF outcrops This observation together with the reported glacial diamictites in this study at the contact between the Neoproterozoic basement and Paleozoic Nubia Formation (Devonian-Carboniferous) favour a glacial origin for these linear features during the Late Ordovician (Hirnantian) glaciation period. The MLs trends in combination with the suggested ice margin between Wadi El-Naam and Betan are consistent with west-to-east ice sheet movement and can account for the observed change of glaciogenic deposits from subglacial facies in Wadi El-Naam in the west to meltwater deposits in Betan to the east
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