Geology Reference
In-Depth Information
Fig. 4 a
Lithostratigraphic
subdivision of the Palaeozoic and
Mesozoic formations in the Sidi
said M
รข
achou basin.
b
Middle
Cambrian shales and sandstones.
c
Triassic sandstone-dominated
red-beds
.
d
Plio-Quaternary
conglomerates rich in marine
fossils (
Photo e
)
(Fig.
7
a); from the base of the escarpment to the top these
are:
(1) A basal unit of white-coloured gypsiferous evaporites
displaying salt tectonic structures, overlain by alter-
nating dolomite, marl and gypsum layers showing a
variety of sedimentary features (laminations, tepee
structure, breccia and bioturbation). These rocks are
overlain by massive and azoic yellowish dolomites.
The basal unit was deposited during the Late Jurassic in
a con
ground
), which is also rich in marine fossils (bra-
chiopods, bryozoa, cnidaria, and echinoids). An
extensive marine depositional environment, possibly
associated with rapid sea-level rise, and accompanying
low sedimentation rates,
'
is
invoked (Fig.
7
a, b,
ni et al.
1998
), however the hard ground could
be an indicative of oxidation in a subaerial tropical
environment.
(3) The uppermost rocks exposed in the escarpment are
mainly brown clay stones with a few intercalated
limestone layers deposited in an open marine environ-
ment such as platform type (Ettach
Ettach
ned hot, arid environment.
(2) The Lower Limestones is a unit formed principally of
limestones preserving a rich marine fauna (ammonites,
brachiopods, gastropods and echinoids). They are
capped by a red oxidized ferruginous surface (
ni et al.
1998
).
In summary, the sedimentary and palaeontological
information preserved in the rocks, that form the escarpment,
'
hard
