Page 292 - Carbonate Platforms Facies, Sequences, and Evolution

Its
50m
except
®
base
L___C_
u4 sequence
is the
in some
100m
top
� Shallow marine
SW-NE
� Reef talus limestones
localized
� sandstones & mudstones
of the
areas,
r10m
NW
l2.......2om
previous
®
Fig. 27. Extensive dolomitization (dark areas) in
limestones from the second Urgonian sequence U2.
sequence
thickness of the section shown in the picture is= 400m.
The last sequence, U4, is of middle-late Albian age.
this is in the Escudo area (Fig. 24), where an angular
Ramales sedimentary sector in the area of Matienzo. The
unconformity separating two fluvial units is clearly
U3,
sequence erosion was very intense and left behind
where the pre-U4
no deposits from the sequence U3. An example of
the
the
the
The
An
1979).
evident
western
western
includes
Guernica
correlated
central
sedimentary
part
overlying
thickness
and
corresponding
some
from
with
of
important
to
In basinal
Aptian-Albian carbonate episode, Spain
sectors
western
this
the
the
increases
of
break
areas,
limestone
part
Northern
in
northeastern
(Garcfa-Mondejar,
region
of
Cotero
buted to the same upper limit.
is
boundary
in that
Supra- Urgonian
�:
Gorbea
upper limit of the sequence
the
�
parts
an
like those
Platform
1979).
sandstones from the sequence U3 filled the dissolution cavities. After Garcia-Mondejar & Pujalte (1983).
section
from
of
megabreccias,
region
in
Complex
direction
sedimentation
(Fig.
This
angular
[-: --�:J Black flysch
fault breccia
the
� Sinsedimentary
has
Fig.
may
Aralar,
(Fig.
separating
Fig. 26. Paleokarst structures on top of limestones of the sequence U2 in the area of Gorliz (north of Bilbao). Marine
uncon­
U4 in the south­
uncon­
lithological change at the top of some of the carbon­
rep­
in the Gorbea sedimentary sector, Fig. 23), is attri­
formity disappears very quickly towards the north as
28,
Garcfa-Mondejar, 1979). A regression from marine
23), the
(Garcfa-Mondejar,
region
during the formation of sequence u4 in the central,
(Fig. 28). In some areas of the Ramales sedimentary
sector, fluvial or fluvio-deltaic terrigenous materials
succeeded the marine carbonates. In the northeast
the
and
been
resent the upper limit of the sequence U4. The sharp
base of an interval of resedimented deposits which
(Fig. 24).
ate remnants of the Urgonian Complex (for instance
occurred
22;
carbonates to fluvio-deltaic terrigenous sediment in
formity, which separates the marine carbonates of
the top of the sequence from fluvial sandstones of
273