Geology Reference
In-Depth Information
constituted the northern border of the WAC (Errami and
Olivier
2012
).
rocks, dolomite and limestone, in the MacDonnell Ranges in
central Australia, comprising Proterozoic rocks such as
shale, dolomite and chert, in the Capricorn Ranges in the
southern Pilbara region of Western Australia, comprising
Proterozoic rocks such as shale, dolomite and chert, in the
King Leopold Ranges in the south-western Kimberley of
Western Australia, comprising Proterozoic rocks such as
quartzite, other metasediment, shale, and ironstone, along
the eastern margin of the Andes Mountains, and in the
northern Sahara to southern Algeria region, comprising
Proterozoic rocks. Not all Appalachian-type folding is
comparable because, in the different regions, there are dif-
ferences in rock types, ages, and styles of metamorphism.
The limited range of Appalachian-type folding worldwide
means that those of the Anti-Atlas are globally signi
5.1.9 Imider Geosite: Contacts Between Three
Pan-African Groups: The Saghro Group,
Mgouna Group and Ouarzazate Group
This site, occurring in the eastern Saghro inlier, shows
spectacular contacts between the three main Pan-African
formations (Saghro Group, Mgouna Group and Ouarzazate
Group). The Mgouna Group, which discordantly covers the
volcano-sedimentary Saghro Group and the associated
HKCA granodiorite, consists of a volcano-sedimentary
sequence formed mainly by arkose, micro-conglomerates,
sandstones, tuffs and pyroclastites (Chakir et al.
2007
; Ot-
mane et al.
2007
). The conglomerates occupying the summit
of hills in the area of outcrop marks the limit between
Mgouna and Ouarzazate Groups. The Mgouna Group is
covered discordantly by the Ouarzazate Group which con-
sists mainly, in this part of the Anti-Atlas, of ignimbrite and
rhyolite. The emplacement of these volcanic rocks and the
basic dykes, which cross-cut all the Neoproterozoic forma-
tions, has occurred along sinistral faults during the late Pan-
African Orogeny (Azizi et al.
1990
; Otmane et al.
2007
).
This site gives an overview about the geological evolution of
this part of the AA during the Neoproterozoic time (Errami
et al.
2011
).
cant.
Additionally, each region of Appalachian-type folding
worldwide, though broadly similar, have details of smaller
scale effects and lithological response that renders each
region globally distinct and, as such, in this context, the
Appalachian-type folding of the Anti-Atlas become further
globally signi
cant.
5.1.11 Large Cambrian Trilobite Paradoxides
Large
Paradoxides
occur in the middle Cambrian rippled
sandstone such as in the Bardou Mountain area (Eastern
AA). The trilobites are in various degrees of taphonomic
preservation (from complete to disarticulated fossils). The
local population considered, until the beginning of the
1970s, that collecting trilobites brought bad luck which
actually resulted in their preservation and protection, until
foreign tourists
5.1.10 Appalachian-Type Folding in the Western
Anti-Atlas
The south-west of the AA manifests large-scale folding of
the Appalachian style, best exposed in the southwest region
in the vicinity of Guelmim-Es Smara (Fig.
5
c). The Appa-
lachian-type folding in this region extends over an area of
500 km long by 50 km wide. The rocks involved in the
folding are Palaeozoic sequences, with the limbs of the folds
moderately inclined, and fold axes generally oriented NE-
SW. In the arid, vegetation-sparse setting of Morocco, the
folds are well exposed. Helg et al. (
2004
) consider that this
folding represents a special type of foreland fold belt with a
striking absence of observable thrusts. In terms of folding
and deformation style, they recognize four structural units
with different wave lengths and amplitudes, corresponding
to four distinct stratigraphic levels, separated by the thick
incompetent units of the Middle Cambrian, Silurian, and
Upper Devonian respectively. Helg et al. (
2004
) consider
that the Anti-Atlas folded Palaeozoic rocks are similar in
tectonic style to the Appalachian Valley and Ridge province.
Appalachian-type folding is not common globally. There
are a limited number of locations where it is best developed,
for instance, in the Appalachian Mountains of the USA,
comprising Palaeozoic rocks such as clastic sedimentary
collecting these
fossils
changed this
tradition.
5.1.12 Ordovician Outcrop at Jbel Kissane
The eastward view from Agdz on the Jbel Kissane is famous
as it shows an impressive Ordovician sedimentary rock pile
which consists of shale and sandstone of Arenig and Lian-
virn age, sandstones of the 1st Bani (Llandeilian age) fol-
lowed by the mudstone, shale and siltstone of the Ktaoua
Formation (Caradocian age), and the sandstone of the 2nd
Bani (Ashgillian age) in the summit (Fig.
11
). Jbel Kissane
forms the perched syncline core of the east-trending sync-
linorium which extends between Bou-Azzer and Saghro
Precambrian antiforms.
5.1.13 Silurian and Lowermost Devonian
Orthoceras-Rich and Ammonite-Rich
Limestones
Upper Silurian black limestones containing current-oriented
Orthoceras
occur in the Eastern AA in the Serdrar Mountain
locality (Fig.
8
d, e). Locally, the limestones are linked to
