Geology Reference
In-Depth Information
Fig. 13
Interpreted seismic prole with location of the onshore and offshore wells drilled in the northern part of the Tarfaya Basin (Had et al.
2008
)
deposits at depth, which represent the oldest deposits of the
Atlantic passive margin formed through the Pangaea rifting
(250
deposits represent a new sedimentary cycle, well developed
in the Atlantic Coastal basins (Figs.
12
and
13
) but much
thinner inland. Let us recall (see above,
geosite A4
) that the
Eocene formations from the internal platform contain
the phosphate layers exploited at Boukraa, southeast of
Laayoune, which are the local equivalent of the renowned
phosphate deposits of
195 Ma) and the subsequent opening of the Central
Atlantic Ocean starting at 195
-
175 Ma. These early sedi-
ments are unconformably overlain by the Lower Cretaceous
clastic deposits, relatively thick in the external platform (Tan-
Tan delta, shown at
geosite B2
). These major geological
events and concepts will be explained on the geosite panel
based on a seismic pro
-
the Meseta domain (Khouribga
plateau).
le (Fig.
13
).
The
geosite B2
is situated half-way between El Ouatia
(Tan-Tan beach) and Tan-Tan city. It exposes coarse, pink
continental sands that illustrate a palaeo-delta environment
developed during the Early Cretaceous (Fig.
14
). The
continental sands are red bed formations that encroached
onto the Sahara, the Anti-Atlas, the Atlas and the Meseta
domains at that time, and began to accumulate as early as
the Middle Jurassic in the Central High Atlas (Frizon de
Lamotte et al.
2008
, with references therein). This sedi-
mentation occurred after a long interval of erosion of the
Sahara and Anti-Atlas domains, in such a way that the red
beds unconformably overlie the deepest parts of the folded
Palaeozoic units and, in places, Precambrian rocks (e.g.,
Ifni inlier, Fig.
2
). The overlying Upper Cretaceous-Tertiary
3.2.2 The Variscan Basement from Tan-Tan
to Mseied
This part of the geotrail, about 60 km-long, passes through a
folded and mountainous area which is the south-western part
of the Anti-Atlas Palaeozoic fold belt (Fig.
15
). Although
narrow with respect to the Anti-Atlas transects farther in the
northeast (e.g., Kerdous-Assa transect, Fig.
2
), the present
transect is much wider than the narrow strip of Palaeozoic
formations observed at Awsard (Fig.
10
). The Laayoune-
Smara transect, half-way between the Awsard and Tan-Tan
transects, offers an interesting cross-section of the fold-thrust
structures of the Dhlou Arc (Rjimati et al.
2011a
).
Geosite B3
, located by the secondary road east of
Tan-Tan allows the visitors to observe the border of the
Fig. 14 a
Lower Cretaceous
uvial sandstones (
Tan-Tan
sands
”
) beneath the Hamada
Plateau west of Tan-Tan,
b
Detail
of cross-bedding in the
uvial
sandstones
“
