|Quartz grain imaged by a scanning electron microscope|
This quartz grain, like many others within the Continental Intercalaire in central Algeria, is interesting because the corners have been well rounded, leaving distinctive broad, bulbous grain edges. Such rounding of quartz grains is nearly always associated with aeolian transport, where sand grains bounce along in the wind and many high-energy impacts polish and round the grain edges. However, the Continental Intercalaire of North Africa is normally considered to have been deposited by rivers, deltas, and lagoons in a marginal marine setting.
|Geologists at work in the Sahara desert of central Algeria|
|Map of the study area, Krechba (In Salah) in central Algeria|
|3D seismic images showing the sinuous river channels|
(indicated by yellow arrows)
However, in an overlying unit we call the Krechba Formation (see the borehole correlation below) the channels disappear and the deposit is dominated by weakly-consolidated sands (shown by the yellow colour) that show convincing microscopic evidence for wind-blown transport.
|Borehole information showing the correlation of the sandstones (shown in yellow) across the study area|
Further details on the work are available in the journal 'Palaeogeography, Palaeoclimatology, Palaeoecology'. 'The Cretaceous Continental Intercalaire in central Algeria: subsurface evidence for a fluvial to aeolian transition and implications for the onset of aridity on the Saharan Platform' by Andrew Newell, Gary Kirby, James Sorensen and Antoni Milodowski found at http://dx.doi.org/10.1016/j.palaeo.2015.07.023.