Page 127 - Carbonate Platforms Facies, Sequences, and Evolution

ive
116
ution
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-o - o
SE
Lower
quence
depend
There
common
changing
f
S 1 Bres
from
COURRY
sub-basins.
radiolarians
are
lowing beds.
but
ESCARPMENT
limestones
lumpy series' =
no
strongly
and
upward
NW
Jumpy facies
Oxfordian
les Ave las
their
ted by black shales
on
nodular
(Elmi, 1971, 1985a).
poor
to
slumping sliding
the persistent shoals
SW
les Vans
in
the down-warped areas.
their
passing into massive beds.
marls
deposits
From the early
continuous
changes are less spectacular.
M.Oxf.
more monotonous upper one
'
and
alternating
is
communities
some .coccoliths.
along
Upper
PAiOLIVE
erosion
. obliquely cut. Adapted from Elmi (1984).
cephalopods.
and
ESCARPMENT
the
'
The
limestones
marls and limestones ('lower lumpy series'
well seen.
palaeogeographic
UZER
=
slope.
�
SWELL
Callovian
Ammonites
ULS), rich in ammonites, to mass­
completely eroded before the deposition of the fol­
Callovian-Lower Oxfordian deposits are represen­
The S9 sequence (Kimmeridgian) shows the evol­
Hettangian to Middle Oxfordian terranes. The dif­
S10 se­
The
are
('Terres Noires') developed in
and to limestones. The missing levels appear sharply
along the course of some major faults. The Upper
and
origin
SSa)
The SS sequence is made of nodular
associations
level made of pelagic micrite which is more or less
marls-limestones
early Oxfordian is only represented by a centimetric
S.
Facies
and thicknesses change rapidly and strongly inside
(Tithonian) is made of nodular limestones
Figure 6 illustrates the changes presented by the
ference between a highly variable lower part and a
the sequences SO to S7, documenting the position of
('upper
Callovian upward, the
with regard to the subsiding
"Terres Noires" (Black Shales)
Elmi
of
to
swell
clear
sandy
the
vertical
shallow
F!
fault, mobile zone
and
sea
Rubino, 1987,
logical
Palaeotectonics
high-energy
are
Privas
calcareous
sequence
\\\\
palaeotectonic
of
platform to the basin.
lateral
evident
Palinspastic profiles (Fig.
platform
facies
sequences
Sub-basin).
influences
during
A
and
traced along the present outcrop.
Triassic basement
is
Transitional facies (U. Callov.-
development
to
ranging
limestones;
of
their
method
some palaeostructures are tangetially cut
this
deposition
be related to con-temporaneous movement
to
from
M. Oxford.)
facies
compare
of
of
Fig. 6. Diagrammatic cross-section of the Hettangian-Oxfordian terranes along the Ardeche Margin of the Subalpine
Basin. The present outcrops are transverse to the Jurassic main trend ('Cevenol' trend) and some of the structures are
LA VOULTE
geometry. The standard succession ranges from low­
shallowing-upward cycles (parasequences). Accord­
corre­
ESCARPMENT
7) have been selected in
Sinemurian to early Bathonian (greatest extent; Fig.
order to give a coherent summary. They have been
(Paiolive
make
the
In consequence,
can
horizontal
ing to Walther's law (Lombard, 1956; see Ferry &
from basin to platform margin. In the Ardeche area,
the horizontal development is commonly different
sponds to large-scale basin filling or to small-scale
the
faults, which altered the gradual transition from the
energy marls and carbonates (basin or distal shelf)
horizontal off-sets of a few 100 m. Such interruptions
furrows or swells, and rapid changes from a deep to
the
breaks occurring across strike-slip faults with minor
evolution is similar to the horizontal facies change
early
for a modern review), this vertical
A varied physiography with steep slopes, narrow
from the vertical succession. There are hiatuses or
2). Influx of coarse-grained quartz and feldspar sand