Page 297 - Carbonate Platforms Facies, Sequences, and Evolution

in
On
al. ,
low
very
time.
areas
(Ebro
The
the
fluvial
second
both
sequence
Mondejar
1979)
Guernica.
low,
dominated
now
sandstones.
transitional
and
one
&
south
U1
gradients
sides
normal marine
In
influence
and
marls
and Synclinorium
(Fig.
the
buried.
Pujalte,
deposits
of the
realm.
for that
from
axis
west
and
30).
In
presumably
Ganecogorta
the
former one slopes towards
the seafloor and
the
which
estuary,
(Ebro)
at the confluence of the Santa
subaerial
nodular
southeastern
are laterally equivalent
south.
towards
west,
and open-marine fauna (ammonites).
1975), and are
of subsidence
part
They suggest
the
part,
originally
lime;;
sandstones
the
of
mudflats, skeletal grainstones) constitute
sedimentary
Finally,
(Fig.
of
tones
in
indicative
extension
30).
was feeding into
In the north­
facies filled the Sili6 trough (Pujalte, 1974; Garcia­
western part of the basin (Fig. 30), relatively deep­
high proportion of mudstones with respect to sand­
received open-marine influence from the northwest.
higher gradients. A possible source area in the south
northerly shallow-marine shelf (Ganecogorta). The
A large sandy delta-estuary
fluvial from marine domains. Farther north was the
stream
to the estuarine
separated
Outcrops of tidal facies (tidal-channel sandstones,
Palaeozoic massif was probably being eroded at that
of
mouth bar were also present, the latter indicating a
with
the
Asturian
(Garcia-Mondejar, 1979). In the west, braided river
stones in the southern part of the fluvial belt suggests
(Fig. 30), among other possible emergent Palaeozoic
Santa Gadea-Mercadillo and Synclinorium
the basin
sectors,
large extent the site of mainly terrigenous deposition
Fig. 23, Fig. 30). A wide belt of fluvial sediments
a
northwest.
and sandstones with local distributary mouth bars
(Ub Lower Aptian), the sedimentary basin was to a
Gadea-Mercadillo
rates of subsidence, were deposited shelf mudstones
was formed in the centre of the basin, approximately
the basin during the formation of the lower part of
in
It
might have been the La Demanda Palaeozoic massif
orbitolinas, ostreids and some corals were deposited,
and a carbonate bank was developed to the north of
in areas with lower
part of the region (Sili6) and shows a clear polarity
axes of subsidence are the main tectonic features of
northeastern part, where the rate of subsidence was
a belt of
the northeast, and the
NW-SE and SW-NE directions, respectively; the
Another though smaller axis is in the central western
water marls with abundant ammonites (Collignon et
mudstones
=
map
stone
sition
rivers
The
The
of u2.
nearly
erosive
previous
deduced
of
subsidence
areas and =
towards the
of Fig.
lower,
Low-energy
1000 m
from
red,
second
constituent facies.
section
processes
east.
30),
Aptian-Albian carbonate episode, Spain
zones,
Aptian-lowermost
thick
so
fluvial
to a
that
in
shows
terrigenous
Urgonian
a
that flowed through
flood-basin
Albian)
the
have
relative
is
characterized the sequence ul.
part
It disappears
sedimentological
deposition
of
been
at
straight
centre
sequence
maximum
that it expanded
the
200 m in the eastern part.
sea-level
mudstones
of
extensive movements in a N -S direction.
U2
analysis,
represented
continued
fall.
sequence
the
Fig. 31. Field aspect of the Lower Aptian rudistid
and
from
Tabular micritic biostromes of rudists are the main
attributed
so
in
limestones in Galdames (upper part of sequence U1).
thickness
U1
in
channels, were close to the continental base level.
southern part of the basin (Ebro sector), with depo­
Lime­
light­
with the Santa Gadea-Mercadillo axis and suggests
sedimentary sector in Fig. 23, not represented in the
(Ortega, 1983), < lOO m in the carbonate northern
The upper
confluence
significant testimony of the long transgression that
carbonate part of the sequence (Fig. 31) (Galdames
200 m in the centre of the basin; it is the more
basin
a
the
of its formation, sandstones, black shales and sandy
of
into some of the adjacent areas during the time span
by carbonate sediments (Fig. 32). At the beginning
The transition zone between the continental and
(Upper
that
sedimentation was never interrupted in low
them
is
marls were deposited in many areas, following the
277
mainly
coloured channel sandstones. No high gradients are
to meandering