Page 301 - Carbonate Platforms Facies, Sequences, and Evolution

&
by
280
oped
there
The
mixed
portant
faulting,
breccias,
(Fig. 34).
of
(Fig.
troughs
transported
northwestern
with
of the region.
During the
clastic
Ramales
Urgonian reefs
24).
a
(Arija-Nograro
directly into the
(Fig.
these
In the western
adjacent
regression towards
and
interval is presented
Garcia-Mondejar,
34).
rigenous materials of
and
to
platform
the
acquired
sector),
platform
troughs
Its
the
sand
in Fig.
higher rate
Urgonian reefs of the
1983).
was
carbonate
(Fig.
their
southern
margins
and
which
linear
deposition of the
sea forming fan
the
34)
Slope
margins,
region,
most
basinal Soba-Bilbao deposits in the
by strong fluvial currents
sition, at least in the west of the basin.
areas,
coastal
was
suggest
are
deltas,
sequence
apron
east.
separated
of subsidence
the
J.
plain
indicate
northeastern
in
Synclinorium­
early-middle Albian tran­
along high­
Limestone megabreccias were de­
spread over both the platform and the basin areas.
destruction of these margins. An aspect of the west­
appeared on their margins (Fig. 33). The most im­
been formed in the late Aptian deepened consider­
coarse ter­
mega­
2000 m of thickness, which includes the best devel­
the strong differential subsidence of the basin in u3
fluvial
the
basement
Huici (Fig. 34), which had several troughs of smaller
size converging into it, and was probably linked with
the Bay of Biscay proto-oceanic rift to the northwest
gravel sizes were
them of the Gilbert type (Garcia-Mondejar, 1979).
Oscillations of the shoreline gave rise with time to a
belt
The Gorbea sedimentary sector was also limited
gradient slopes (Ebro sector). Braided rivers flowed
and
the
characteristic
configuration. A palaeogeographic synthesis of this
ern platform margin with development of clinoforms
formation of high-gradient foreslopes and the partial
U3 the
34, showing the eight
in Fig. 35 (Duranguesado area; Fernandez-Mendiola
northern 'corner' of this carbonate buildup is shown
troughs. A palaeogeographical reconstruction of the
times, the incipient intra-platform troughs that had
ably; as a consequence, thick carbonate build ups,
composed of stacked mud mounds-reef mounds,
from carbonate platform sedimentary environments
and Santa Gadea troughs in the west, and with the
with the terrigenous deposits of the Santillana, Sili6
major
reef belt, and a variety of terrigenous materials were
posited intermittently as slope aprons in front of the
main sedimentary sectors distinguished. Because of
'carbonate factory' of the region. It was transitional
many of
About
recorded
is
gin,
(Fig.
delta
being
metry
height
The
similar
Garcia-Monde jar
towards
shown
SW-NE
of
34),
to
clinoforms
one
limestones
calculated.
interpreted
the
in
clastics
the
to
250 m
show
Fig.
sequence
interval is shown
of the
Bilbao
for
ones
the Guernica sector
come
36,
subjected to erosion,
directions,
U4
clear
the
in Fig.
(Fig.
of northern
largest.
Basin
from
(late
38.
34).
described
downlap
(Fig.
basinal
of the escarpment in Fig.
(Fernandez-Mendiola,
respectively.
uplifted
corresponding
foreslope give a minimum relief of =
34).
provenance
above.
In
the other hand, a minimum slope of 1 o
to
An example
The most
halokinetic synsedimentary dome in the
The
1986).
Middle-early
of
sediments
blocks
the
They
a
relationships
36 is 328 m
in
to
(Fig. 37) (Garcfa-Mondejar & Robador, 1989).
indicate
relation
could be added. That gives a minimum palaeobathy­
deposited sediment derived from the platform mar­
and in the north, coarse fan­
feature of it is the Black Flysch trough, which ap­
presence of an uplifted northern Palaeozoic massif.
These
present
respect to the underlying sediments and prograde
formation of the sequence, megabreccias and a clas­
ltxina
with
100 m of supplementary relief for the seafloor
the
calculations relative to the height of the primitive
150 m. If, on
is accepted
and
local
for the adjacent basin talus containing gravitational
(Soba trough), since a relief of more than lOOm for
were
the La Gandara original foreslope (Fig. 13) has been
the
and dimensions of both the troughs and the highs,
carbonate platform conditions prevailed
and by a carbonate escarpment margin in the north
It was limited by a
source areas, most of the terrigenous materials are
In the Aralar and Guernica sedimentary sectors
limited by several troughs, the Synclinorium-Huici
trough with important development of slope apron
to
Bilbao area. This agrees well with results obtained
and Ebro Palaeozoic Massifs (Fig. 34). In the west,
megabreccias is in Bermeo, in the western part of
Basement structural trends controlled the shape
the
from the opposite margin of the same local basin
southeast
indicating extensional patterns in the NW-SE and
the Asturian Massif continued as an emergent area
carbonate facies by the terrigenous Supra-Urgonian
facies (Fig. 23). A palaeogeographic synthesis of this
tic wedge of prodeltaic to proximal turbidite channel
Upper
peared with the late Albian. At the beginning of the
recorded the complete replacement of the Urgonian
important
southeast of the region, perhaps from La Demanda
Albian) was built through successive pulses, which