Page 121 - Carbonate Platforms Facies, Sequences, and Evolution

due
and
The
The
kept
Ucel
value
areas
The
nellids.
to
for
subtidal.
zonation
next
processes)
major
with
(Les
Tithonian).
sandstones,
Sequence
the
developed at
or
associated
SO
erosion
boundary
Formation.
Vans).
or
Correlations
rapid
black
variations
to
quartzose
a protected lagoon to
continuous
(Hettangian,
Microfaunas
They
the exception
illustrated in Figs 3 and 4.
beds
are
in the
are
vertical
lithostratigraphic
siltstones.
of
of the
are
Oodolosparites
coincides with the
Callovian,
lower
filled
dolosparites,
are particularly
between sequences
The
poor
(Gracilis Zone of the early Callovian).
non-deposition
changes
and
up
Sl
sandstones and conglomerates reworked
largely
or
many reference sections for the standard
a more open shelf.
in
Tithonian
black
by
SO and
to
nomenclature.
sequences
The
Sl
The environment ranged from intertidal to sh;wllow­
here used as a lithostratigraphic designation for re­
have been placed to highlight significant lithostrati­
from North American usage as a major time strati­
word 'couches' (beds) is used for lithologically het­
calpio­
lated groups of formations depending on their thick­
prevailed on the ridges. In the basins, the sedimen­
into Middle and Upper Liassic limestones). In con­
consists of three facies: basal micrites, median cross­
Kimmeridgian,
ness (Fig. 2), and thus the term differs in meaning
are
greatest distance from the shoreline.
both
the Ucel Variegated Formation (Carnian-Norian).
facies.
graphic subdivision. Boundaries between sequences
graphic changes: unconformities (stratigraphic gaps
siltites
erogeneous formations or members, e.g., alternating
the largest extent of the early Jurassic transgression.
monite successions. The Ardeche area has furnished
and clays. Some channels are known near the positive
sequence has been recognized all along the Ardeche
Sl
The
coquina. This evolution documents the change from
younger
coarse
sequence, it is established that the Sl corresponds to
the Sinemurian-Carixian. French names have been
Tethyan
it has been subsequently eroded (pebbles reworked
Blanche Formation which rests uncomformably on
Rhaetian Croix
drawn following the disappearance of the sandstones
SO begins with the first appearance of thin laminated
is
uncertain for
margin with the exception of the Arenier Pass where
sequence
bedded and rippled oosparites and an Upper Mytilid
stratigraphic
oosparites
marl and limestone sequences. The term 'Series' is
tation was probably continuous but changed abruptly
After the end of Sl, erosion and non-deposition
from the
of
to
the
ites
ous
and
with
more
de Ia
rarely
below
The
the
several
the
basinal
monites
pebbles
S3a
member
ash-grey
member
Variscan
beds
(late
S3
Vaumalle
reworked
immature.
but
limestones.
of
near
are
Late Triassic and Jurassic platforms,
cephalopods.
small
highly
quartzose
the
rocks
the
Garenne'
from
Calcaires
valves ( Cardinia,
nodular
consists
commonly,
ranging
reef
wavy-bedded
made
sequence
France
the
environment.
were
of
in
by
Formation
Domerian,
the base.
subsequence.
of
variable
( Psiloceratinae)
Calcaires
age
limestones.
patches
noduleux
Formation
sandstones
Only
The
early
South
Triassic
and
limestones,
limestones
illustrates
were
Mactromya ).
nodular
exhumed
The
are
from
consisting
bioclastic
have
micrites with a mudstone texture.
(S3c),
S2).
the
Hettangian
of
of Les
cendres
the
noduleux
following
Spinatum
similar
lower
been
coarser
mainly
commonly
to
associated
dolomites
Vans,
siimilar
part
conglomerates
at that time.
and
crinoidal
Triassic
evolution
cendres,
to
Zone).
Abundant
limestones
the
with
Formation
as
those
bi­
am­
abundant in the lower part but become scarce up­
In the Privas area, the top of the equi­
The facies becomes
dolomites. The Vaumalle Formation rests on vari­
crinoidal,
stones rich in brachiopods, belemnites and ammon­
recognized.
pack­
The top can be marked by a bored hard-ground or,
more calcareous towards the top of the member and
Hettangian to the Lower Pliensbachian ( = Carixian).
with cherts and sandstones. Gryphaea coquinas occur
'Couches du
to alternating marls and limestones (lower member
ward. They document a relatively deep platform to
a few ammonites have
without
from
been collected; they are more common in the Privas
In the Aubenas sub-basin, the overlying 'Couches
S3a)
of
or
(upper
S3a
micrites with few bioclasts rhythmically alternating
du Bose' Formation (lower part of S3b) consists of
Ammonites are
hemipelagic marls and limestones to biocalcarenites
consists of grey marls alternating with wavy-bedded
Chateau d'Aubenas' Formation (upper part of S3b)
is made up of crinoidal packstones and grainstones
In subsiding zones, the Domerian is represented by
Formation) to the Carixian (Couches de Ia Garenne).
(Ucel
Domerian. The S3 sequence ranges from the Middle
Along the outcrop, the S4 sequence corresponds
lenticular
beds
sub-basin. The S3 sequence ends with the 'Couches
valent formation was strongly eroded before the late
This
no
Other
and
more
formation is commonly coarsely detrital. Decimetric
pebbles of metamorphic quartzites must have been
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