Page 133 - Carbonate Platforms Facies, Sequences, and Evolution

for
122
and
The
varied
bound
largely
Privas,
taining
depths.
Jurassic
that
Valley),
parts of
Other
to
Callovian
as
a
calculation
Main facies
dolomitized
umbilic-like
Application
high-energy
construction
a
the
crinoids
be abundant.
distinguished.
time
of
differentiated.
deep
interpreted to
of
of
and
foraminifera
ammonite
Aubenas
result
planktonic bivalves
lithologies
marly
deposits
are
Seven
of
because
and
of
fauna
devoid
Bositra-coquinas,
Royden's
theoretical
the
physiography,
the
of
the
the profiles
Bathonian 'Couches de Plat
pseudonodular
(Balanocrinus)
scarce.
are
groups
deposits,
'Couches de Naves',
has
(skeletal
model
A
of
'bathyal' environments.
beds
associated
seem
such
at the top of pelagic lenticular beds.
changing
Ardeche
this facies (200-400 m; Elmi, 1985a).
been
Saint-Ambroix
to
as
range
are
contain
(1982)
facies
with
physiography
cephalopods;
interpreted
given in Fig.
have been deposited in the
the
limestones,
is
subsidence curves
have
as
margin
types
within
they
accepted
allows
The palaeobathymetric estimations used for
limited or protected shelf. Medium-
Alternating marls and fine-grained micrites, con­
are widespread and give indications of shallow outer­
Ammonites can
and basin) as documented by the ammonite fauna.
especially during Liassic and middle Jurassic times.
been
deeper shelf or the proximal basin, commonly in an
are
deep
highly
Upper
The use of the classic nomenclature is inappropriate
Sub-basins.
marls and limestones of the Hettangian (outer shelf
been tested by Brunet (1985) who has established a
model of the amount of distension sustained by the
environments can be accepted for the nodular-like
10 have
However, in the south of the study area (La Ceze
outer-shelf deposits. Similar palaeobathymetry and
commonly
limestones, ferruginous or phosphatic oolitic beds)
(Bositra) but benthic molluscs
vary
outer platform setting, gaps are biostratigraphically
Redon' or the Lower
sandy
environments
a rich and
highs or at the margin of shoals, in neritic sequences
abundant
shelf environments. Stratigraphic gaps occurred on
S.
the
deeper
documented within pelagic or hemipelagic suites or
for
are
the
to
are consistent with those obtained from evaluated
which
reflecting high-to-moderate energy. In the basinal or
the
Elmi
to
The
into
aerial
1985;
stones
mixed
bedded
Les Vans.
Rhaetian
developed
Shallow
controlled
fiat
and
cyclic
sandstones in
abandoned
Avocat,
along
(mud
Continental facies
weathering
terrigenous input.
environment
clays
dolomite developed
is
pers.
sandstones,
the
and
inner-shelf
subsidence
'Couches de
(Fig.
Shallow carbonate shelf
meanders
sandstones,
Ia
oomicrites and oosparites).
during
of
was
11).
sand),
contact
comm.):
('Formation
the lower part of
Croix
interpreted
carbonate
sand
rivers
largely
to
environments
variegated
or
fiat
emergence
fiat
between
marginal
to
Bariolee
Blanche'
Dolomicritic
have
magnesium-rich water (Spy-Anderson, 1980,
with
Fig. 11. Pedogenetic dolocretes and pillars (roots?)
clays
existed
under
clays
mud
balanced
developed through replacement of clay and quartz by
been
dolomite. Ucel Formation, late Triassic. Terraube near
the south (La Ceze Valley) and east (Villeneuve-de­
sub­
Carnian-Norian deposits consist of sandstones, silt­
d'Ucel'.
fiaser­
Four groups of facies have been recognized in the
evaporites of a sabkha environment. The tectonically
by
fiat,
(Martin,
horizons
and
a phreatic lens of
Variegated clays and siltstones were related either
probably seasonal, flooding. Caliche dolocretes and
crusts, dolomitic pillars and replacement of silica by
episodic,
bifurcating deltaic braided stream system. Towards
Berg borehole), the sequence changes progressively
and
a
1981).
(micrites,
also
during the early Hettangian and are represented by