Page 245 - Carbonate Platforms Facies, Sequences, and Evolution

in
of
of
for
230
two
high
north
lected
the
linked
period
the
region
the
the
towards
Atlantic
deposits
These
platform
at
Urgonian
to
Barremian
Barremian
cumulated,
late
of
the
two reasons:
the southern
the
(Funk,
in
sea-level
major low
southern
Sedimentological
crisis
(Vercors)
the
(Arnaud,
between
in the Jura
north.
both
limestone
substantial variations
1985),
unconformity
Vercors
stands.
the
and
observations
and
beginning
1988)
of
(2)
Hauterivian
where
sea-level
the
early
Vercors,
has
(Fig.
of
beginning
Hauterivian to early
can
are
little tectonism,
shows
and,
The
in
Jura
eastern Alps (Tollmann, 1987) .
3).
(1) The
the
stands
in
northern
been
be
the
CONC LUSION
the
bioclastic
Aptian
and
Pierre Jaune
Barremian
very
absent
lower
disappear
A.
Barremian
transition between platform and basin.
de
palaeontological
on
the
dated
low
Three major observations can be made.
in relative sea-level,
part
very
separated
strata
vicinity
subduction
Subalpine
and outcrops
particular,
existence
the
as
data
explained
by
of
sediments
cance of this Barremian crisis is questionable,
of
on
of
in
platforms.
of
Formation and the Urgonian limestone formation.
ac­
forming a lowstand wedge. The signifi­
col­
(Glandasse
chains
rapidly
the
late
by the probable effect of NE-SW basement faults.
the
by
characterized by the emergence and erosion of at
allow a large-scale interpretation of the development
Of
two
sea-level
a
the beginning of the early Barremian is
namely
the
these regions, the Vercors is the most interesting for
Neuchatel
bioclastic limestone formation), which are very thick
to the
(2) The very high
northern
but
the
sea-level stand in the late Barremian (Feraudi and
conceivably it is related to the opening of the North
Of the latter, vertical movements on the lsere fault
events which, on the Galicia margin are responsible
are shown by the emergence of the northern region
Neocomian (Boillot et al., 1986) and for the intrusion
Jura
of peridotites (Feraud et al., 1988). It could also be
by wide regional variations in subsidence rates and
the
Subalpine chains. (3) The early Barremian and part
Jura and by the development of a lowstand wedge in
Hauterivian-Barremian boundary which is marked
(Jura domain) and the rapid sinking of the southern
least part of the late Hauterivian sequence in the
(1) The
is
the
not
are
Four
from
coral
small
oolitic
quences
first
laterally
flat,
platform
presence
limestone
limestone
tinguished.
reefs,
reefs.
of
outer slope.
is composed
major
slope of the
but
shoals
environments.
(1)
Arnaud- Vanneau and H. Arnaud
usually
margin
platform margin,
The
late
on
towards
types
palaeogeographical
deep-subtidal
mainly
formation
characterized by
end
the
the
transgressive
of
to
glauconite
on
in
parasequence,
the
Lowstand
corresponded
preponderance of bioclastic
outer
and
position
characterized by its width
sequences,
the
of marly
Hauterivian,
development
valleys (upper Orbitolina beds).
ment of coarse bioclastic facies.
to a
lower
sequences
on
northwest
sequence
part
of
i.e.
wedge
facies,
of
oosparites
of
to
detrital
The
the
shoal
have
and
these
previously
the
layers that
shallow-subtidal.
preponderance
the
below
less
characterized
that
latter,
Orbitolina
and/or
overall thickness reaches 800 m, displays all
of
been
reefs
by
The
minerals.
se­
and by the outstanding develop­
dis­
deposited in shallow-subtidal to supratidal environ­
The sequence stratigraphy is relatively complex.
the early Barremian and the sequence stratigraphy.
emergent
localized towards the middle of the early Aptian is
Astieri Zones) is responsible for the deposition of
Jura platform (Fig. 7). (3) The low sea-level stand
Urgonian
marked in the northern Vercors by the cutting of a
lowstand
wedge indicates that the wedge's upper surface was
sloped
facies
small
and
steeply towards the basin in the southeast and passed
(2) Drowned platform sequences that
were well developed on the Jura platform during the
rudist
agitated
the
the presence of
whose
is characterized by the final drowning of the Urgonian
platform. The corresponding depositional sequence
filled the
and locally up to 30m in depth (Fig. 8). (4) The high
sea-level stand towards the end of the early Aptian
system of incised valleys, tens of kilometres in length
From a sedimentological point of view, emphasis
(up to 10 km), by its
hemipelagic
the Jura
out in the southern Vercors (Glandasse plateau). It
has been placed on the lowstand wedge features of
The lowstand wedge of the early Barremian crops
Sequences of the inner part of the Urgonian platform
(3)
beds)
ments. (4) High sea-level sequences (first Urgonian
facies and the existence of various restricted facies
and the presence of storm beds, locally gullying the
the abundance of benthic foraminifera
Urgonian
facies, by the local abundance of oolites and by the
bryozoan and crinoid facies overlying the spantangid
Hauterivian, characterized by the preponderance of