Page 229 - Carbonate Platforms Facies, Sequences, and Evolution

a
a
in
in
214
Bi6.
stand
widely
Astieri
relative
sea-level
highly
detail
and APl)
bioclastic
change
sequences
boundary,
substantial
Barremian,
and
a highstand
at
the
wedge;
environments,
from
towards
(BA2
the
facies).
sea-level
a
(3)
subsident
the
deposit
at
level (Arnaud, 1988).
including
=
variations
Colchidites
progradation
After
sequences and by marls
displayed
area
the
north
in
in
lowstand
sp.
and APl),
because
detail (Arnaud-Vanneau,
early-late
(Figs 8
by
the
(up
800 m
&
the
of
the
above
to
towards
of
1980;
9).
wedge
zones,
sea-level
sudden
this
highstand deposits are presented here.
to
Barremian
a
for
Only
2000 m
Late Barremian-early Aptian depositional
bioclastic facies of parasequences Bi5 (Fig.
drop
Arnaud,
temporary
hemipelagic
of
the
the
wedge.
in
the basin of
sedimentation
sequences: the Urgonian platform (sequences BA2
1976). Within this high sea-level context, it is con­
retro­
rapid subsidence and the probable variations in sea­
gradation of bioclastic facies of the Bi2 to Bi4 para­
highstand
The
sedimentation rates compensated for both the very
In this rapidly subsiding area, it is difficult to list
early
the
in
early
shallow-subtidal
Barremian. Nevertheless, it does appear that there
series
(Fontaine Graillere marls, Arnaud-Vannheau et al.,
ceivable that at a given time, there could have been
Zones). The former corresponds to a deepening of
was a rise in the early Barremian (Hugii pro parte
boundary
(Moutoniceras, Barremense and Feraudi pro parte
1981),
upper part of the late Barremian (Feraudi pro parte,
The Urgonian limestone consists of two depositional
the early Aptian (parasequences Ail and Ai2). These
relative drop of sea-level of the early-late Barremian
slope of the previous Hauterivian wedge, but spread
Hauterivian-Barremian
wedge then a shelf-margin wedge since parasequence
parasequences
Bi5 and Bi6 were no longer confined to the outer
and Compressissima Zones) and a drop in relative
the
depositional sequences, which have been described
boundary would then have resulted in the rapid and
main
sedimentary productivity and very high
features of the transgressive systems tracts and the
Bs2, Bs3 and BsAi), the second to the lower part of
the first dating to the
begin by a transgressive systems tract and end with
9) and
or
be
(2)
(3)
the
the
top
ites,
edge
which
1987).
sponds
is
contian
of
The
contains
The
resented
is
'facies
sequence).
at
the
Hauterivian
very
basin,
of the Bsl
located
A. Arnaud- Vanneau and H. Arnaud
packstone (Fig.
the
sequence BA2).
distinguished
change laterally,
flooding surface,
transgressive
transgression
In the
at
beds;
maximum
extremely
high
this
11).
glauconite,
lithologically
fine bioclastic facies,
base
( M
(Fig�
Haq
the
Urgonian
to
et
d'installation',
of
systems
Trangressive systems tracts
11):
rich in
southern
base
the
available
al.,
sea-level
the
deepening
of
probably
tract
top
atheronites
platform,
transgressive
the
of
1987).
(1) The
lies
parasequence and to
Vercors,
represented by the Heteroceras marls.
period
ammonites
To the southeast,
three
the
first
Urgonian
by the appearance
systems
This Bs1 parasequence is
ends
limentinus
corresponds
Arnaud-Vanneau
and
ified only in the southern Vercors where it
of
corresponds
on the
directly
palaeontological
in
stages
et
to
deepening
to
tract
(Fig. 8), dated by Feraudi and Astieri Zone ammon­
corre­
charac­
environments begins in the Bsl parasequence, ident­
in the Vo­
several hundreds of metres, into rudist wackestone­
Jura), the transgressive systems tract is always rep­
by the existence of marls and, at the top, by hemi­
transgressive facies (Arnaud-Vanneau et al., 1987).
To the northwest (northern Vercors, Chartreuse,
This horizon,
marls at the base of the Bs2 parasequence (maximum
al.,
locally
The transgressive systems tract of the late Barremian
discontinuity surface covered with ammonites at the
the overlying
level).
outer
can
terized by a clear retrogradation of bioclastic facies
These thin sequences are characterized, at the base,
limestone depositional sequence (BA2 depositional
of
Glandasse
bioclastic limestone formation (for this reason, this
BA1 while it is really at the base of the depositional
thin parasequence is put in the depositional sequence
the
the
Urgonian
From the north of the Vercors to the Jura,
with large rudists and corals and by the presence of
facies
at the top of the early Barremian lowstand wedge,
deposition of Bs2 parasequence and the base of Bs3.
by the presence of small coral reefs surrounded by
(Figs 19 & 20), by thin transgressive facies overlain
a
dara
by coarse bioclastic or oolitic facies (initiation facies
synchronous over the region or whether there is an
is
condensed section highlighting the ultimate stage of
limestone
pelagic marly limestone or fine bioclastic facies which
do not make it clear whether the transgression was
over a distance of several tens to
upon