Page 151 - Carbonate Platforms Facies, Sequences, and Evolution

1
to
2
4
3
the
Haq
ance
initial
The
lowing
et
of
Aalenian
There
(Angulata
structures.
al.
mentologic
regional
interrupted
recognized.
continuities
Afterwards,
were
is
(S4
by
amount
(or
no
the
data
to
(Fig.
micrites
of tilt-blocks led
Zone)
equal importance
very
of
(1987).
transgression
Cevenol lineaments.
Margaritatus Zone).
to
29)
S6):
and
gives
The
onlap
general)
the
(SO,
evidence
an
occasional
precise
in
thick
allows
marls
important
S1,
of
physiographic
an
occurred during the late Callovian
reduced sedimentation occurring
S2)
the
slumps
sea-level
marly
graphical data are poor at this level.
during
Ardeche
fitted exactly to the Haq et al. curves:
of the subsidence rate (Brunet, 1985).
was
late
opportunity
stratigraphic
the
along
on the
but
to a resumption of the
to
(Villeneuve,
differences
estimation
deposits
the
and
late Carixian event
bound
variations.
test
of
major supercycles can
influx
to
noticeable along the margin itself (see Figs 4 & 9).
sedi­
Sedimentary perturbations and associated shal­
a marginal western bank and an eastern basin con­
major lineaments and it is highlighted by the appear­
general sea-level rise as differences were slight be­
biostrati­
(pre­
and the table of local stratigraphical gaps and dis­
dimin­
coarse terrigenous material into the small subsiding
umbilics. The transition to the basin occurred along
-early Oxfordian.
corresponding variation of the curves of Haq et al.
in the
platform.
tinued to increase from the middle Liassic until the
last important revival of the transitional slope
Vallon,
the
However, some boundaries cannot be
Valvigneres boreholes). This differentiation between
from NNE to SSW owing to the role of the transverse
The early Hettangian deepening was rapid and
Zone (middle Toarcian), but there is no noticeable
the
general models and curves recently summarized by
basin differed strongly from the discontinuous and
A comparison between the cross-section (Fig. 28)
Variabilis
be
The
tween the basin and the margin. Changes were more
respective importance of local tectonics with respect
(1987). Since widespread discontinuities occurred at
The late Domerian-earliest Toarcian shallowing
a
(late Spinatum and Tenuicostatum zones) seems of
Hettangian
widespread; it resulted mainly from an acceleration
At the end of the Sinemurian a narrow platform
existed along the margin and exposure of the edges
of
main
ished and the monotonous sedimentation was only
The differences lessened during the Callovian and
in
9
5
at
6
10
7
8
that
event
A
North
At
the
(1985)
time
Breaks
the
During
Tithonian.
Calloviense
Algeria,
end
Late Triassic and Jurassic platforms,
in
cannot
Africa
in the
in the Tethys.
in
general
of
the
for
end
a
Tethyan Realm.
the
Zone) or slightly
be
have been abrupt.
of
the
France
Zone),
early
Jurassic
later
the
with the eustatic curves.
the
Tethys
of
instance);
instability
shallowing
separated
early
sedimentation
and
Callovian
has
these
Gracilis
on
from
Kimmeridgian
its
prevailed
been
data
their scales are good for discontinuities
the
Aalenian
and
(erosion
namic phase in the evolution of Tethys.
Zone
western France.
(early Murchisonae
Retrocostatum Zone) rather that at its end.
(equivalent
and
during
does
borders,
support
to
during
general
The
Variabilis event seems to be related more to a dy­
in­
Bathonian; consequently, the biostratigraphic corre­
appear to be a significant time on the curves pub­
non­
139
the
not
'Aspidoides Zone' of northwestern Europe (Tethyan
areas (for instance, see Elmi, 1972, 1978). It seems
that a major event (shallowing, regression) occurred
at the beginning of the equivalent of the so-called
( Opalinum
A comparison has also been established with the
scale of discontinuities recognized by Gabilly et al.
the
consistent with the general subsidence then occurring
lished by Haq et al. (1987). In Ardeche, it coincides
with the end of the movement of the tilt-blocks. This
led to a widening of the basin; the local evolution is
and the Tethys; in Ardeche and in other Tethyan
with a deepening which is also well known in much
of southern France; it is not recognized as a general
event and it must be stressed that in many parts of
The Subfurcatum Zone (late Bajocian) coincided
the general shallowing attained a climax in harmony
stability; the transitional slope to the basin seems to
the early Bajocian and the results of a pre-Sauzei
documented
lations lack certainty between northwestern Europe
deposition) were important on the platform during
Zone),
idea that strong tectonics were then dominating the
with deepening in other areas (Tlemcen Mountains
(Moroccan Middle-Atlas, for example) contrasting
the
between the events recognized in Ardeche as well as
in Ardeche perhaps because the stratigraphic data
and 13. Discontinuity no. 2 has not been recognized
1, 3, 4, 8, 10
with the eustatic curves; changes are documented at
The subsequent local evolution seems to fit well
the
fits
the
the end of the early Oxfordian, at the beginning and