Geology Reference
In-Depth Information
Fig. 16 a
Transgression of the Lower Cretaceous redbeds on the Bas
Draa Precambrian Massif (Geosite
C1
),
b
Upper Precambrian (Ediac-
aran) metaconglomerates at the south-western tip of the Bas Draa inlier,
showing a Variscan foliation S
2
superimposed onto the Pan-African
fabric
S
0
)
with shallow dipping joints crosscut by a directional fault (
F
), west of
Tilemsoun village
-
S
1
,
c
Vertical Cambrian quartzites (
“
Barre de Goulimine
”
Fig. 17
NE-trending, SW-
plunging fold train in the J. Zini
Cambrian-Ordovician massif
south of the Bas Draa massif
(Landsat scene). The folds are
marked by the competent
quartzite beds interbedded with
incompetent metapelites.
Dashed
road to Mseied. See Fig.
15
for
location
a hiatus occurs beneath the periglacial deposits. Here in the
Jbel Zini, several hundred metres of Middle Ordovician
shales and sandstones are lacking beneath the Upper Ordo-
vician disconformable deposits.
Leaving the pass area, the road goes down into lowlands
underlain by the Silurian and Lower Devonian silts and
clays. The sebkha Liemhagen that extends in these lowlands
is a favorite stop-over for many species of migratory birds,
especially the pink
of the sebkha (Fig.
18
b). Although seen from the distance at
geosite B7, this succession clearly shows in a dark rusty
color the Lower Ordovician (Llanvirn) oolithic iron bed
(Fig.
18
c) that occurs extensively in the Anti-Atlas domain,
and is locally exploited (Imi n
Tourza, north of Alnif in the
Eastern Anti-Atlas; Raddi et al.
2011
). The geometry of the
large, almost cylindrical anticlines formed by the competent
Ordovician quartzites intercalated between the incompetent
Cambrian and Silurian shales is shown strikingly in the
desert landscape. This is a
'
amingo. The best stratigraphic cross-
section of the Ordovician sequence of the Jbel Zini area is
exposed within a breached anticline along the western border
ne example of Appalachian-type
relief derived from the Variscan fold belt,
rst eroded and
