Page 276 - Carbonate Platforms Facies, Sequences, and Evolution

type
lack
region
The
during
cement
of
of
Toucasia
including
included.
Urgonian
discussion
the
age
was
mudstones,
glomerates.
and
foraminifera,
of
of
and
facies:
first
fossils
Albian onwards,
caprotinid-types,
Garcfa-Mondejar
the
Complex is based
the
which characterize
Aptian
Toucasia
Fernandez-Mendiola
terrigenous
are
Rudists
mainly
URGONIAN
and
'massive
defined
sandstones,
are
ern part of the basin (Fig.
controls
(1979),
reef-building
by
Polyconites.
corals,
Urgonian
(1986).
on several
of
elements,
limestones'.
Albian
Rat
the
mostly
monopleurid and radiolitid rudists.
FACIES
orbitolinids.
Pascal
Some
limestones
ENVIRONMENTS
The
breccias
chronology of the
org�nisms,
Complex
times.
(1959)
biofacies, mainly of the Toucasia genus'.
with
orbitolinids,
AND
According
From
as
other
important
and particularly from the
was
and
Urgonian
(1984)
Urgonian is then possible (Wiedmann, 1965).
to
requienid
an
strong
discovery
sequences
Finally,
re­
'ex­
Recent major works specifically devoted to the car­
and Upper Albian (Duvernois et al., 1972; Garcfa­
deter­
Mondejar & Pascal, 1978; Pascal, 1984; Fernandez­
con­
The Urgonian crops out extensively in the north­
several unconformities within the unit permitted the
recognition of megacycles (Garcfa-Mondejar, 1979).
the broad patterns of sedimentation that prevailed
calcite
facies
a
tremely thick sedimentary complex of the Cretaceous
is
sedimentation is presented. An appendix with fossils
1), and consists of thick
Middle
Rat
and
bonate episode are the dissertations of Rat (1959),
and later studies have extended it up to the Middle
that a more precise biozonation of the uppermost
mined by Rat (1959) to be Aptian-Lower Albian,
different
external aspect and microfacies, but with a common
(1959) the term Urgonian refers to a characteristic
and
The Urgonian Complex is > 4000 m thick and is
genera
assemblage zones of
typical
of
made up of a succession of rudistid limestones, marls,
the oyster-like Chondrodonta, calcareous algae and
or planktonic foraminifera are scarce, dating of the
different taxa and on range zones of different benthic
Mendiola, 1986). As useful specimens of ammonites
The Urgonian Complex of the Basque-Cantabrian
crystallization, and rudists as the most characteristic
ammonites are more common so
ostreids,
In
are
units
have
main
those
chert)
which
monly
Fluvial
of Fig.
the
bodies,
red
surfaces
all
of
common
the basin.
3.
sediments
mudstones
and
sandstones
Mudstones
are
description
in
or
Terrigenous
stratigraphic
show
intraplatform
from
environments.
of
basin,
of
fining-upwards
quartz-arenites
occurring
the
Urgonian
have
occur
matrix-supported,
Aptian--Albian carbonate episode, Spain
grey,
the
limestone
on
and
gravel bars (Fig. 4).
formed
trough.
fill
fluvial
interbedded
sediments
in
been identified
migrating
with
floodplain
between
lowermost
without
sedimentary
lithologies
margins
Urgonian Complex are mud-
with
cross-stratified
particular
or
braided
little
sandy matrix.
carbonate platforms and banks.
subarkoses.
cross-sections from
and
Carbonate
the
of fluvial
parts
braided
sequences
sets
thin-bedded limestone or sandstone.
point-bars
evidence
They
sandstone
are
lateral
in
Urgonian
ongm
from
channels,
of the
of
abandoned
are
environments
bioherms
particularly those of braided channel origin.
(Garcia-Mondejar,
are
channels.
limestones
They have
and
bodies,
are the only fossils present. Thinning-
of braided and meandering rivers,
sedimentary
facies
of
clast-
abun­
com­
en­
were
continuity,
The tectonic setting of the Urgonian Complex was
from continental to that of a relatively deep-marine
resting on palaeogeographic highs. The terrigenous
exten­
Megabreccias and
an epicratonic basin bordering a proto-oceanic rift.
ranged
ubiquitous,
Reference to it will be made during the
meanders.
are shown on the map in Fig. 2. A synthesis of the
vironments is shown in the schematic cross-section
Conglomerates are siliceous (quartzites, quartz and
259
commonly, the sandstones contain lateral accretion
1979).
the region. The geographic locations of these sections
and reef-mounds like
of other Albian-aged
derived from Palaeozoic highlands on the margins of
the
black marls and mudstones with variable amounts of
The descriptions that follow are mostly based on
other resedimented deposits are found adjacent to
the bank margins; and they pass laterally into basinal
region. Conglomerates of distal alluvial fan, channel
and
dant cross-stratified sets from migrating megaripples
sively represented in the southern outcrops of the
migrating
Sandstones are predominantly
channels
or
exposure. Transported wood fragments, which are
subaerial
and
sandstone
and
Less
different parts of
and