Page 138 - Carbonate Platforms Facies, Sequences, and Evolution

TA,
Two
(TE,
along
these
swales
mosaic
outcrop
dropped
platform
TE).
developed
main
the
TV),
bordered by
and
sedimentation
on
Main divisions
adjacent areas.
The
the
studies
transverse
network.
Rapid thickening
the
an
undergoing
Longitudinal trends
was
and
sub-basins
compartment
The
old
Transverse trends (TO,
basin
by
influence
NW-SE
highly
and
TB,
or
were
trends was
mobile
Escrinet-Arenier
prevailed on
data
the
TV,
considerable
constituent
of these
Orcieres
TA,
zone.
deep
from
an escarpment following
called Ligurian Ocean). The influence
Swells
important
developed
and
differentiated
TV,
These are numbered from I to IX in Fig.
(Rosieres, Saint-Andre-de-Cruzieres) (Fig.
ridges
the eastern,
bore
outer
bilic may have been a small pull-apart basin.
(Fig.
During
throughout
along
sub-basins
19).
of escarpments or slopes which dipped eastward.
These cut the longitudinal framework producing
Fig. 21)
down­
During that time, the Charray um­
shelf.
oceanic crust farther east in the Piemont Zone (so­
Triassic and Jurassic (gaps, reduced thickness, Fig.
the modern
Escrinet and Charray Faults (VI) are recent faults
Ardeche margin. The northern Privas Sub-basin was
4). In the southern area, the Pai"olive (Fig. 8, II) and
jtmction with southern Aubenas Sub-basin is located
Triassic and Hettangian times, they had bordered a
on the
also Fig. 7) sustaining a stronger subsidence than the
late
small weak zone (Charray umbilic; Figs 3 & 21; see
21. The
the
the
Courry (IV) mobile zones controlled the behaviour
La Voulte Fault (Fig. 1A, No. 7; Fig. 21, TV). The
is well documented by
marked the true boundary between a narrow western
holes
1979; Elrni, 1984). The Pai"olive axis (II) commonly
antithetic movement of the La Rousse axis (I) is well
during the early-middle Jurassic rifting stages. The
during the
Bordezac
of some of
evolution
lineaments (TO) and the N-S Uzer Swell (TU) have
as postrifting conditions succeeded the formation of
are
a
21,
a major importance in the distribution of sediments.
late structural trends which had not been modified
transverse network faded out during the late Jurassic
by the rifting. The WSW-ENE Escrinet-La Voulte
late Triassic because of the inherited influence of the
documented during the early tilting (Colongo et al.,
in
by
the
and
The
The
beds
block
After
These
vailed,
During
Figs
bonates
benthos
platform
Lachkar,
bordered
lithologic
noduleux
clays
4
regression
fauna
the
late
Late Triassic and Jurassic platforms,
HISTORY
and
was
by
Triassic
&
of
led
around
and
Subalpine
features
were
9.
tectonics
units:
to
1985),
OF
the
The variations of
palynological
cendres'
France
Carbonate de Base'
Early differentiation
An
the
missing
area
Prerift (pre-Rhaetian)
Ladinian
and
since
sequence
The inception of the
Lower
lower
THE
data
accumulation
continental
is
arid
deposited
restriction
document
the Massif
and
then
the
(CCB,
of
except
a
indicate
in
of
a
became
a
a
Upper Sandstones
S1)
deposition
made
for
early
the
alluvial
member
the
an
which prograded to the southeast.
deep
cating a stronger marine influence.
Central,
of
up
of
the general late Triassic denudation.
the
Sandstones,
General deepening (Hettangian event)
continental
change
(Ucel
VIVARAIS
rapid
calculated
of
Rhaetian to earliest
carbonate progradation competed with
the
shallow
plains
basins
sidence curves reflect extension (Brunet,
the
outer
to
Carnian
a
and
sea.
evaporitic
three
Middle
climate
(Taugourdeau-Lantz
shelf,
1985).
burrowing
times,
Synrift stages with strong tectonics (Rhaetian event)
pre­
Car­
(SO, S1) were largely controlled by local tilt­
Calculated sub­
127
re-
occurred.
The S1 sequence ends with mytilid-coquinas, indi­
containing a wide­
Formation):
bi­
valves (Mactromya) which caused much bioturbation.
main
deltas
1985). The tilting of the Les Eynesses fault is shown
MARGIN
curves show only slight overall extension (Brunet,
Hettangian
subsidence
Next,
deepening:
general transgression flooded the area. Carbonates
a
basin
Hettangian transgression. This could have facilitated
climate coincided with the extensive humidity of the
&
as documented
humid
ammonites, bivalves and sponges became common
and no evidence of algal activity has been recorded;
mytilid-coquina,
spread oolitic level. The ini�ial flooding was probably
deepening.
related to a general sea-level rise. On the borders,
Hettangian shallow marine
the cessation of coarse terrigenous influx related to
'Calcaires
'Complexe